JP2017227360A - Boiler scale removing method for boiler facility and washing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform an efficient removal of sulfur oxide scale and non-water soluble scale such as rust adhered to an outer surface of a heat transmission pipe of a waste heat recovery boiler, a water wall pipe to which boiler combustion gas is contacted, a superheater tube, a coal saving pipe, an air heater and an electric dust collector and the like.SOLUTION: A boiler plant is washed with water to remove scale of sulfur oxide. A circulation washing is carried out under application of the washing water used for removing scale of sulfur oxide to peel off and remove non-water soluble scale such as rust with circulating washing water of pH acid. Not only sulfur oxide scale adhered to the boiler plant but also non-water soluble scale such as rust can be efficiently removed only through circulation of the washing water without using any chemical solution, without requiring any complex cleaning device and without being restricted by a cleaning location.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a scale removal method for boiler equipment. Specifically, the present invention is a method for efficiently cleaning and removing fuel-derived sulfur oxide scales attached to the boiler heat transfer tube outer surface and the boiler equipment in contact with combustion gas, and water-insoluble scales such as rust. And a cleaning apparatus therefor.

In boiler equipment, the scale of the fuel-derived sulfur oxides comes into contact with the flue gas discharged by burning fuel containing sulfur components in the equipment and piping arranged between the combustion furnace and the chimney. Furthermore, this sulfur oxide scale corrodes the pipe material itself, and rust (iron oxide) adheres as a scale, reducing efficiency due to heat transfer inhibition and increasing differential pressure due to gas flow inhibition. Cause trouble. In particular, in the fin tube, the adhesion of the scale between the fins leads to an increase in the operating differential pressure.
For this reason, it is necessary to remove this scale at the regular inspection so that it does not hinder driving. Conventionally, as the scale removal method, the following method has been proposed.

  Patent Document 1: When cleaning the outer surface of the heat transfer tube of the heat transfer tube group in which the heat transfer tubes having fins are provided side by side, a chemical cleaning process for cleaning the heat transfer tube group with a chemical solution containing a cleaning chemical, and high-pressure water as the heat transfer tube A pre-washing process in which water is sprayed from the upper part of the heat transfer tube group and the falling water is collected under the heat transfer tube group prior to the chemical solution washing and the high pressure water washing process. How to do. In this method, it is possible to check and confirm the presence or absence of water leakage, the operation status of the water supply system, and the water collection system prior to the main cleaning process in the preliminary water cleaning process.

  Patent Document 2: A method of removing an acidic deposit containing a sulfur compound attached to a combustion apparatus of a boiler by contacting with an alkali metal carbonate solution and / or an alkali metal bicarbonate aqueous solution. In this method, acidic deposits can be removed efficiently, simply and safely in a short time without corroding the equipment.

  Patent Document 3: A beam disposed along a tube group of a heat exchanger, a carriage movable along the beam, and a lance supported by the carriage, and water is discharged from jets provided on both sides of the lance. Cleaning device that spouts out. According to this apparatus, the tube group of the heat exchanger can be efficiently cleaned.

  Patent Document 4: Washing method for washing and removing sulfate (especially ammonium salt) compounds and dust deposited between fins of finned heat transfer tubes in a heat recovery system of a plurality of finned heat transfer tubes arranged vertically . A cleaning water spray pipe is horizontally arranged above the finned heat transfer tube group arranged vertically to form a surface flow in which the cleaning water flows down along the fin surface and toward the gap between the fins. By doing so, the deposit deposited between the fins of the finned heat transfer tube is removed.

JP 2011-7360 A JP 2001-348689 A JP 2001-12894 A JP-A-7-77304

  The methods of Patent Documents 1 to 4 have the following problems.

  In patent document 1, the water washing by watering is implemented before chemical washing, and the amount of water washing increases. Further, the use of chemicals is expensive and causes wastewater treatment problems.

  In the cleaning using the alkali metal carbonate or bicarbonate of Patent Document 2, the water is washed in a state where corrosion is suppressed by raising the pH. This method is effective for water-soluble scales, but removal effects cannot be expected for water-insoluble scales such as rust.

  In the method of removing scale with high-pressure jet water disclosed in Patent Document 3, a cleaning effect can be expected in the vicinity of the place where the apparatus can be installed, but the cleaning effect is expected in other portions or where the power of high-pressure jet water does not reach. Can not.

  In the method for removing the scale of the vertical finned heat transfer tube of Patent Document 4, it is considered that water-soluble sulfates (particularly ammonium salts) and dusts included therein can be washed away, but the water-insoluble water attached to the pipe material There is almost no effect in removing rust.

  The present invention solves the above-mentioned conventional problems, and adheres to the outer surface of the heat transfer tube of the exhaust heat recovery boiler, the water wall tube in contact with the boiler combustion gas, the superheater tube, the economizer tube, the air heater, the electric dust collector, etc. It is an object of the present invention to provide a boiler facility scale removing method capable of efficiently removing a sulfur oxide scale and a water-insoluble scale such as rust, and a cleaning device therefor.

As a result of intensive studies to solve the above problems, the present inventors have obtained the following knowledge.
(1) The main component of the sulfur oxide scale that adheres to the boiler equipment is sulfate (particularly ammonium salt), which is water-soluble. Accordingly, the sulfur oxide scale can be removed by washing with water, but the water-insoluble scale attached to the pipe material such as rust cannot be removed by washing with water.
(2) However, when the sulfur oxide scale is washed with water, it dissolves and the pH of the washing water becomes acidic.
(3) By carrying out circulation washing treatment using the washed water that has become acidic, water-insoluble scales such as rust can be dissolved in the acid washed water, or can be removed by accelerating the peeling and dropping off. .

  The present invention has been achieved based on such findings, and the gist thereof is as follows.

[1] A method for removing sulfur oxide scale and water-insoluble scale attached to a boiler facility, wherein the boiler facility is washed with water to form a sulfur oxide scale, and the first step. And a second step of circulating and washing the used washing water as circulating washing water.

[2] The scale removal method for boiler equipment according to [1], wherein the pH of the circulating flush water in the second step is 4 or less.

[3] In the boiler facility according to [1] or [2], the washing water used in the first step is subjected to solid-liquid separation in the second step, and the separated water is used as the circulating washing water. Scale removal method.

[4] The boiler equipment according to any one of [1] to [3], wherein after the second step, a third step is performed in which the boiler equipment is washed in a transient manner using new flush water. Scale removal method.

[5] The scale removal method for boiler equipment according to any one of [1] to [4], wherein the pH of the circulating flush water is measured, and the scale removal status is grasped based on the measured value. .

[6] A cleaning device for removing sulfur oxide scale and water-insoluble scale attached to the boiler equipment, and spraying flush water on the boiler equipment provided at an upper part and / or a side part of the boiler equipment. Or the flushing means to inject, the receiving tank which is provided in the lower part of the boiler equipment and receives the flushing water flowing down or falling from the boiler equipment, and the circulating means for circulating the water in the receiving tank as the circulating flushing water to the flushing means And a boiler equipment cleaning device.

[7] In [6], the circulation means includes a circulation tank into which water in the receiving tank is introduced, a first circulation pipe for introducing water in the receiving tank into the circulation tank, and the circulation tank. A boiler equipment cleaning apparatus, comprising: a second circulation pipe having a circulation pump for supplying water in the tank to the washing means.

[8] The boiler equipment cleaning apparatus according to [7], wherein a scale separator is provided in the first circulation pipe or the second circulation pipe.

[9] In any one of [6] to [8], an introduction unit that introduces new flush water from outside the system into the flush unit, and a discharge unit that drains the water in the receiving tank to the outside of the system are provided. A boiler equipment cleaning apparatus characterized by that.

[10] In any one of [1] to [5], the boiler equipment cleaning device according to any of [6] to [9] is attached to the boiler equipment, and the first step and the second step are performed. A boiler equipment scale removal method characterized by the above.

  According to the present invention, not only sulfur oxide scales attached to boiler equipment, but also water-insoluble scales such as rust, without using a chemical solution, without requiring a complicated cleaning device, and cleaning It can be efficiently removed by only circulating the washing water without being restricted by the site.

  According to the present invention, the sulfur oxide scale attached to the outer surface of the heat transfer tube of the exhaust heat recovery boiler of the boiler equipment, the water wall tube, the superheater tube, the economizer tube, the air heater, the electric dust collector, etc. that are in contact with the boiler combustion gas. It is possible to effectively remove non-water-soluble scales such as rust, effectively recovering the operation differential pressure, thermal efficiency, etc., so that stable operation of boiler equipment can be continued for a long time. become.

It is a schematic diagram of the boiler installation which attached the washing | cleaning apparatus of the boiler installation of this invention.

  Hereinafter, embodiments of the present invention will be described in detail.

[Boiler equipment scale removal method]
In the boiler facility scale removing method of the present invention, the first step of removing the sulfur oxide scale by rinsing the boiler facility to which the sulfur oxide scale and the water-insoluble scale such as rust are attached, and the first step. And a second step of circulating and washing the washing water used in the circulation as circulating washing water, and preferably, after the second step, a third step of washing the boiler equipment in a transient manner using new washing water. However, since the initial washing water in the first step may be very dirty due to the scale, it is effective to discharge a small amount and then shift to the circulation washing in the second step.

  As described above, since the sulfur oxide scale is mainly composed of a sulfate (especially ammonium salt), is water-soluble, and is acidic, water containing sulfur oxide dissolved by washing with water becomes pH acidic. When the washing water used for washing is collected and circulated and washed, the sulfur oxide scale is eluted in the rinsing water, so that the pH of the circulated washing water becomes about pH 1 to 4. Further circulation washing with pH acidic circulation water of pH 4 or less, preferably pH 2 to 3, so that non-water-soluble scales such as rust are dissolved and removed, or peeling and dropping are promoted and removed. Become.

  In this 1st process and 2nd process, since it wash | cleans with acidic circulating water washing water, in order to suppress corrosion of the constituent material of washing | cleaning object, you may add a corrosion inhibitor to circulating water washing water. .

  In the present invention, the progress of scale removal, for example, the transition time from the first step of removing the sulfur oxide scale to the second step of removing water-insoluble scale such as rust in the subsequent circulation cleaning is cyclic. This can be determined by measuring the pH of the rinsing water. That is, when the pH of the circulating flush water is lowered, this is the first step in which the sulfur oxide scale is dissolved and removed, and the pH is lowered according to the amount of sulfur oxide scale eluted. When the pH stops decreasing and the pH becomes constant or shows a rising tendency, the second step is the dissolution of the sulfur oxide scale is completed, and the water-insoluble scale is dissolved or peeled / dropped off. The second step may be completed when the pH of the circulating flush water stops decreasing, but is preferably further performed for about 1 to 2 hours thereafter.

  The progress of descaling can also be grasped by analyzing the suspended solids in the circulating water (for example, deposits in a receiving tank in the cleaning device of the present invention described later) and the sulfate ion concentration of the circulating water.

  Thus, after performing the 1st process and the 2nd process, the inside of the system is washed with water in a transient manner, and the water in the system that has become acidic by circulating and washing with the acidic circulating flush water is used as the system. It is preferable to perform the 3rd process discharged | emitted outside. In this third step, the scale peeled off by the acidic rinsing water and the scale that has floated are discharged out of the system, and the inside of the system is returned to neutral to prevent corrosion of the object to be cleaned.

  This third step is preferably performed until the pH of the wastewater becomes neutral (for example, about pH 5.0 to 7.0). The end time of the third step can be grasped from the measured value by measuring the pH of the waste water.

Further, in this third step or after the third step, a rust inhibitor, a neutralizing agent, or the like may be further sprayed on the object to be cleaned to suppress rusting, corrosion, or the like.
Further, prior to the treatment for rust prevention or corrosion inhibition, it is also preferable to perform brush cleaning or high-pressure water cleaning in order to further clean the object to be cleaned.

  In the present invention, washing with water to be washed may be performed by spraying washing water on the object to be washed, or may be carried out by spraying washing water at a high pressure. In addition, when the washing water is circulated, it is preferable to circulate the SS after removing the peeled water-insoluble scale or the like by sedimentation separation, a scale removing device or a filter.

  The boiler facility scale removal method of the present invention is preferably implemented using the boiler facility cleaning facility of the present invention described below.

  The boiler equipment to be cleaned (scale removal target) in the present invention is not particularly limited as long as it is a boiler equipment to which a water-insoluble scale such as a sulfur oxide scale and rust adheres. Examples include the outer surface of the heat transfer tube, a water wall tube in contact with the boiler combustion gas, a superheater tube, a economizer tube, an air heater, and an electric dust collector.

  As washing water, pure water, industrial water, city water and the like can be mentioned, but normal industrial water is used.

When adding a corrosion inhibitor to washing water, any conventionally known corrosion inhibitor can be used, and specifically, IBIT 2S or IBIT 30AR manufactured by Asahi Chemical Industry Co., Ltd. is applied. Select the type according to the properties of the water to be washed. Only one type of corrosion inhibitor may be used, or two or more types may be used.
The concentration of the corrosion inhibitor in the washing water is 0.03 to 0.5% by weight from the viewpoint of suppressing obstacles due to foaming and wastewater treatment costs after sufficiently obtaining the corrosion inhibition effect of the base material by the corrosion inhibitor. It is preferable to do.

[Boiler equipment cleaning equipment]
Below, the washing | cleaning apparatus of the boiler equipment of this invention is demonstrated with reference to FIG. FIG. 1 is a schematic diagram of boiler equipment equipped with the cleaning device of the present invention.

The boiler equipment cleaning apparatus shown in FIG. 1 has a spray header 2 which is a washing means for spraying or spraying flush water on a cleaning target 1 such as a heat transfer tube of the boiler equipment, and water is sprayed from the spray header 2 to the cleaning target 1. A receiving tank 3 that receives washing water flowing down or falling after washing the object 1 to be washed, and a circulation means for circulating the water in the receiving tank 3 as circulating washing water to the spray header 2 are shown in FIG. The circulation means of the cleaning device shown includes a transfer pump P ₁ for sending out water in the receiving tank 3, pipes 11 and 12 (first circulation pipe) for transferring water from the transfer pump P ₁ to the circulation tank 4, and It consists of a circulation pump P ₂ for circulating the water in the circulation tank 4 to the spray header 2 and pipes 13, 14, 15 (second circulation pipes), and the scale separator 5 between the pipes 13 and 14. Is provided
A pipe 17 for discharging the water in the receiving tank 3 out of the system is provided at the connection between the pipes 11 and 12.
In addition, a pipe 16 for introducing fresh water from outside the system is provided at a connection portion between the pipes 14 and 15.
Instead of the drainage discharge pipe 17 or together with the pipe 17, the drainage discharge pipe 17 </ _b > A may be provided on the discharge side of the circulation pump P < _b > ₂ of the circulation pipe 13. It is also possible to provide a Shinmizu introduction pipe 16A into or the suction side of the circulating pump P ₂ of the circulating pipe 13 with the pipe 16 instead of the fresh water inlet conduit 16.

  When cleaning the boiler equipment, the spray header 2 is installed above the boiler equipment to be cleaned 1 as shown in FIG. 1, and the receiving tank 3 is installed below, and these are the circulation means such as pipes, tanks, and circulation pumps. The washing water is sprinkled from the spray header 2 to the washing target 1, and the circulation washing is performed as described later.

FIG. 1 shows an example of an embodiment of a boiler equipment cleaning apparatus of the present invention, and the cleaning apparatus of the present invention is not limited to that shown in FIG.
For example, in FIG. 1, the spray header 2 is provided above the object 1 to be cleaned, but the spray header 2 is provided on the side of the object 1 to be cleaned and sprayed or spouted with water on the side of the object 1 to be cleaned. The spray header 2 may be provided both above and to the side of the cleaning target 1.
Further, if the water-insoluble scale has good sedimentation, the circulation tank 4 and the receiving tank 3 also serve as a scale separator, and therefore the scale separator 5 is not necessarily required. That is, when the sludge sufficiently settles in the receiving tank 3 and the circulation tank 4 and is subjected to solid-liquid separation, the scale separation device 5 can be omitted.

In FIG. 1, the flush water sprayed from the spray header 2 to the cleaning target 1 is collected in the receiving tank 3 after the cleaning target 1 is washed. After the water-receiving tub 3 is that is transferred to the circulation tank 4 through a pipe 11 and 12 by transfer pump P _1, the circulation pump P ₂ through a pipe 13, as the circulating washing water, scale is separated and removed scale separator 5 After that, it is circulated to the spray header 2 through the pipes 14 and 15 and sprayed again to the object 1 to be cleaned. In the receiving tank 3, SS such as the scale in the washing water is settled and separated during the stay.

To implement the descaling method of the boiler facility of this invention is to introduce a new washing water from a given amount out of the system through the circulation pump P ₂ from the pipe 16, 15 or the pipe 16A, after watering from the spray header 2 above After the first step of dissolving and removing the sulfur oxide scale by circulating and washing in the circulation path, the circulating washing water is further circulated and washed after the pH of the circulating washing water becomes 4 or less, preferably 3 or less. This can be carried out by performing the second step of removing the water-insoluble scale. Note that as described above, the initial flush water in the first step may be very dirty due to the scale, so it is effective to discharge a small amount and then shift to the cyclic wash in the second step.

  At that time, by visually confirming the amount of sludge of the washing water flowing into the receiving tank 3 and the circulation tank 4, and further measuring the pH of the washing water in the circulation tank 4, the circulation pipes 12-14, etc. I can grasp it.

After completing the circulation cleaning of the second step, preferably from the pipe 16, 15 or the pipe 16A through the circulation pump P ₂ by introducing a new washing water is sprinkled from the spray header 2 to be cleaned. 1, the receiving vessel 3 performing a third step of performing transient cleaning to discharge out of the system through a pipe 11, 17 or 17A of collecting water by the pump P ₁ in.
Also at the time of the transition from the second step to the third step and the end of the third step, it is possible to determine the transition and the end based on the measurement results of the pH of the water in the receiving tank 3 and the pipes 11 and 17.

When a pH meter is installed in the system of the boiler equipment with the cleaning device, the introduction of new water, the circulation and discharge of the washing water are determined based on the measured values of the pH meter, the opening and closing of the valves provided in the pipes and the pumps P ₁ , by the control means for controlling the operation of the P _2, it can be performed by automatically without requiring human intervention.

  Hereinafter, the present invention will be described more specifically with reference to examples.

[Example 1]
The scale on the outer surface of the heat transfer tube of the exhaust heat recovery boiler was cleaned and removed in accordance with the present invention in the boiler equipment with the cleaning device of FIG.
Specifically, washing was performed according to the following procedures (1) to (3).
(1) The object to be cleaned is divided into 5 parts, and the washing water per place is dispersed at a flow rate of 110 m ³ / h from the upper part of the heat transfer tube group 1 from the spray header 2 and the sulfur oxide scale is dissolved and removed by washing. Then, the initial flush water was continuously discharged out of the system, and then circulated and washed with the circulation pump P ₂ through the receiving tank 3 and the circulation tank 4.
(2) The pH after the start of circulating washing was 2.2 to 2.5, but after 1.5 hours, the pH of the circulating water rose to 2.7 to 3.5. In addition, the amount of sludge in the liquid at the start of the circulating cleaning was about 5,000 mg / L, but it decreased to about 2,000 mg / L just before the end, so the removal of the water-insoluble scale progressed, just before the end. It was confirmed that the amount of water-insoluble scale was reduced.
(3) After the end of the circulation cleaning, the system was switched to the transient water cleaning, and the water cleaning was carried out for 1 hour.

  Changes in the tube differential pressure (operation differential pressure) and exhaust gas temperature (exhaust temperature) of the exhaust heat recovery boiler when such scale removal processing is carried out once a year are examined, and the results are shown. It was shown in 1.

[Comparative Example 1]
In Example 1, the object to be cleaned was divided into 5 parts, and the cleaning water was sprayed from the top of the heat transfer tube group 1 at a flow rate of 110 m ³ / h for 1.5 hours.
Changes in the tube differential pressure (operation differential pressure) and exhaust gas temperature (exhaust temperature) of the exhaust heat recovery boiler when such scale removal processing is carried out once a year are examined, and the results are shown. It was shown in 1.

As apparent from Table 1, the tube differential pressure showed an increasing tendency in the conventional method (Comparative Example 1), but in Example 1 employing the method of the present invention, the tube differential pressure tended to decrease, Can be operated without problems. In addition, the differential pressure of the tube was rather lowered in Example 1 until now, but the differential pressure has tended to increase year by year. This is probably because the differential pressure showed a decreasing trend because the scale was removed.
In addition, the exhaust gas temperature is less increased in Example 1 than in Comparative Example 1, and the scale is more effectively removed, thereby reducing heat transfer inhibition and improving exhaust heat recovery efficiency. I understand that.

1 Cleaning target part (heat transfer tube group)
2 Spray header 3 Receiving tank 4 Circulation tank

Claims (10)

A method for removing sulfur oxide scale and water-insoluble scale attached to boiler equipment,
A boiler equipment scale comprising: a first step of washing the boiler equipment with water to form a sulfur oxide scale; and a second step of circulating and washing the washing water used in the first step as circulating washing water. Removal method.   The boiler facility scale removal method according to claim 1, wherein the pH of the circulating flush water in the second step is 4 or less.   3. The boiler facility scale removal method according to claim 1 or 2, wherein in the second step, the washing water used in the first step is subjected to solid-liquid separation, and the separated water is used as the circulating washing water.   The scale removal of boiler equipment according to any one of claims 1 to 3, wherein after the second step, a third step of washing the boiler equipment in a transient manner using new flush water is performed. Method.   5. The boiler facility scale removal method according to claim 1, wherein a pH of the circulating flush water is measured, and a scale removal state is grasped based on the measured value. 6. A cleaning device that removes sulfur oxide scale and water-insoluble scale attached to boiler equipment,
Flushing means for spraying or spraying flush water on the boiler equipment, provided on the top and / or side of the boiler equipment,
A receiving tank that is provided at a lower portion of the boiler equipment and receives flush water that flows down or falls from the boiler equipment;
A boiler apparatus cleaning apparatus comprising: circulating means for circulating water in the receiving tank as circulating flush water to the flush means.   7. The circulation means according to claim 6, wherein the circulation means includes a circulation tank into which water in the receiving tank is introduced, a first circulation pipe for introducing water in the receiving tank into the circulation tank, and water in the circulation tank. And a second circulation pipe having a circulation pump for feeding the water to the water washing means.   The boiler equipment cleaning apparatus according to claim 7, wherein a scale separator is provided in the first circulation pipe or the second circulation pipe.   In any 1 item | term of the Claims 6 thru | or 8, It equips with the introduction means which introduces new flush water from the outside to the said washing means, and the discharge means which drains the water in the said receiving tank outside the system. Boiler equipment cleaning equipment.   In any one of Claims 1 thru | or 5, attaching the washing | cleaning apparatus of the boiler equipment of any one of Claims 6 thru | or 9 to a boiler equipment, The said 1st process and a 2nd process are performed. Descale method for boiler equipment.

Images