JP3339130B2 - Chemical cleaning method - Google Patents

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 removing scale adhering to a boiler, a chemical plant, etc., and more particularly to a method for performing chemical cleaning while circulating a cleaning liquid to a portion to be cleaned.

[0002]

2. Description of the Related Art In a boiler, a chemical plant, or the like, scale such as iron oxide adheres to a wall surface or the like during operation, causing a decrease in thermal efficiency or a flow rate inhibition. Chemical cleaning and scale removal.
In such a chemical cleaning, when a part of the scale is dissolved in the cleaning liquid, the other part is peeled off and dispersed in the circulating cleaning liquid in a solid state. If the exfoliated solid is left as it is, it may be circulated again and deposited on the portion to be cleaned, and may be dissolved in the circulating fluid to wastefully consume the cleaning fluid or increase the corrosiveness. For this reason, solids in the circulating cleaning liquid are separated, and cleaning is performed by circulating only the cleaning liquid.

[0003] As a method of removing such solid matter,
A device using a centrifugal separator is known (for example, JP-A-59-157496). In this method, a cyclone separator having a conical lower portion is used as a centrifugal separator. In such a method, the solid separated by the centrifugal separator is obtained as a concentrated solution containing a large amount of the washing solution, but if this is discharged out of the system as it is, the washing solution will be wasted. In addition to the necessity of processing such as neutralization, it is necessary to supply a new cleaning solution. Therefore, if the discharge amount of the concentrated liquid is reduced, the amount of solids leaking into the circulation path increases, and problems such as the accumulation of sludge at the lower part of the centrifuge occur.

[0004] In order to improve this point, a method of separating the concentrated liquid into solid and liquid by sedimentation and circulating the separated liquid is conceivable. However, since the sedimentation requires a long time, the apparatus is increased in size. There is a problem that the amount of the cleaning liquid increases accordingly.
Further, since the cyclone separator is rotated at a high speed, the cone portion is severely worn, the pressure loss is large, and when there is a fluctuation in the flow rate, there is a problem that the separability is greatly reduced.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems by efficiently concentrating and discharging solids with a simple apparatus, and circulating a washing liquid containing less solids for cleaning. It is an object of the present invention to propose a chemical cleaning method in which the amount of corrosion can be reduced in a short period of time with a small amount of a cleaning liquid and cleaning can be efficiently performed.

[0006]

According to the present invention, there is provided a method for performing chemical cleaning while circulating a cleaning liquid to a portion to be cleaned, by introducing the circulating cleaning liquid into a first centrifuge installed in a circulation path of the cleaning liquid. After separating into a first concentrated liquid containing a solid substance therein and a first clarified liquid, the first concentrated liquid is introduced into a second centrifuge, and the second concentrated liquid and the second clarified liquid are separated from each other. Wherein the second concentrated liquid is further solid-liquid separated, the solid is discharged out of the system, and the separated liquid is returned to the circulation path together with the first and second clarified liquids. This is a cleaning method.

In the present invention, the object to be cleaned is
It is an object to be cleaned, such as a boiler or a chemical plant, in which a cleaning liquid is circulated to dissolve a part of the scale and a part is peeled off to perform chemical cleaning.

In the present invention, the centrifugal separator used for separating solids from the circulating washing liquid may be of any structure. For example, as described in JP-A-5-31404, an upper chamber is used. A liquid is introduced in a tangential direction to form a swirling flow, passes through a rectifying hole or slit, forms a rectified low-velocity swirling flow, and descends along the inner wall of the separation cylinder, and the velocity difference between solid and liquid A low-speed centrifugal separator is preferred, in which primary separation is carried out by means of, and the speed is decelerated and changed instantaneously by a lower baffle and a guide, and secondary separation is carried out by a difference in shape and a difference in specific gravity.

In the present invention, a plurality of such centrifugal separators are used, and the circulating cleaning liquid is introduced into a first centrifugal separator provided in the circulation path of the cleaning liquid, and the first concentrated liquid containing solids in the liquid is introduced. And a first clarified liquid containing less solid matter, and the first concentrated liquid is introduced into a second centrifugal separator to be separated into a second concentrated liquid and a second clarified liquid.

Generally, when using a plurality of centrifuges,
The first clarified liquid obtained from the first centrifuge is passed through a second centrifugal separator to be separated into a second concentrated liquid and a second clarified liquid. In this method, Since a large amount of liquid is processed using a plurality of large centrifuges, the efficiency is low and a large amount of concentrated liquid is generated. On the other hand, when the first concentrated liquid is processed by the second centrifuge as in the present invention,
The centrifuge can be small, and the amount of concentrated liquid drawn out from the first centrifuge can be increased to prevent leakage of solids or accumulation of sludge in the first centrifuge.

In the present invention, the second concentrated liquid is further separated into solid and liquid, and the solid is discharged out of the system.
The amount of the concentrate extracted from the centrifuge of the second centrifuge can be increased to prevent the leakage of solids and the accumulation of sludge in the second centrifuge. Even if the amount of the second concentrated liquid withdrawn is large, the amount of liquid itself flowing into the second centrifuge is small, so that the amount withdrawn as the concentrated liquid is small, and the solid-liquid separation device may be small. Thus, the amount of the cleaning liquid staying there is also reduced.

As a solid-liquid separation device, a sedimentation separation device, a filtration device and the like are used. The solid content separated by the solid-liquid separation is discharged as it is or concentrated to the outside of the system, and the separated solution is circulated together with the first and second clarified solutions to the circulation system of the washing solution to be used for washing the object to be washed. .

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. FIG. 1 is a system diagram showing a chemical cleaning method according to an embodiment. In FIG. 1, reference numeral 1 denotes an object to be washed, 2 denotes a circulation path, 3 denotes a circulation pump, 4 denotes a circulation tank, 5 denotes a first centrifuge, 6 denotes a second centrifuge, and 7 denotes a solid-liquid separation tank. is there. Solid-liquid separation tank 7
Is a sedimentation separation tank, but a filtration tank or other solid-liquid separation means may be used.

FIGS. 2 and 3 show the first and the second, respectively.
FIG. 9 is a partially cutaway perspective view showing another low-speed centrifuge used as the centrifuges 5 and 6 of FIG. The centrifugal separators 5 and 6 each have a slowly rotating portion 12 formed by a cylindrical separation tube 11, and an upper chamber 13 above the separation tube 11.
Is provided, and the liquid supply pipe 14 is opened in a tangential direction to form a swirling flow. The upper chamber 13 and the slow swirling section 12 are communicated with each other through a straightening hole 15 in FIG. 2 and a straightening slit 16 in FIG. 3, and are configured to form a rectified low-speed swirling flow of about 7 G and descend. I have. A lower chamber 17 is provided at a lower portion of the separation cylinder 11, and a baffle 18 for decelerating a swirling flow and a guide 19 for turning a downward flow into an upward flow are provided therein. A clarified liquid outlet pipe 20 is provided at the center of the upper part of the separation tube 11 and communicates with a clarified liquid outlet 21 at the upper part of the apparatus, and a concentrated liquid outlet 22 is provided at the center of the lower part of the apparatus.

In the above-described structure, in the chemical cleaning method, first, a cleaning liquid such as an acid solution is introduced into the circulation tank 4, and the cleaning liquid is fed to the article 1 to be cleaned by the circulation pump 3 and circulated through the circulation path 2. The cleaning liquid sent to the object to be cleaned 1 comes into contact with the inner wall of the object to be cleaned 1 and a part of the scale is dissolved in the cleaning liquid. As a result, a part of the scale is peeled off in a solid state and dispersed in the cleaning liquid.

The circulating washing liquid in which the solids are dispersed is supplied to circulation circuit 2
Into a first centrifugal separator 5 provided in the middle of the above, and separated into a first concentrated liquid 5a and a first clarified liquid 5b, and the first concentrated liquid 5a is transferred to a second centrifugal separator 6. It is introduced and separated into a second concentrated liquid 6a and a second clarified liquid 6b. Second concentrate 6a
Enters the solid-liquid separation tank 7 and undergoes sedimentation separation, and the solid content 7a is discharged as it is or concentrated out of the system, and the separated liquid 7b is circulated from the circulation path 2 together with the first and second clarified liquids 5b and 6b. Return to tank 4 and continue washing.

When the low-speed centrifuge shown in FIG. 2 or FIG. 3 is used as the first and second centrifuges 5 and 6, the circulating washing liquid or the first concentrated liquid is supplied from the supply pipe 14 to the upper chamber 13. , Enters the tangential direction at a flow velocity of 1.5 to 2.5 m / sec to form a swirling flow, enters the slow turning portion 12 through the rectifying hole 15 or the rectifying slit 16, and rectifies a low-speed swirling flow of about 7 G. And descend. During this time, the primary separation of the solid and liquid is performed by centrifugal force, and the solids descend while rotating along the inner wall, and settle in the lower chamber 17.
The liquid that has descended while rotating is instantaneously decelerated by the baffle 18 near the lower chamber 17, changes direction to the center side along the guide 19, and rapidly rises in the negative pressure area near the center. As a result, the solid-liquid is subjected to secondary separation, and the solid is separated and settles due to a difference in shape and a difference in specific gravity.

The concentrated liquid containing the separated solids is discharged from a concentrated liquid outlet 22, and the clarified liquid is discharged from a clarified liquid outlet 21 through a clarified liquid outlet pipe 20. At this time, if the amount of the concentrate taken out from the concentrate outlet 22 is reduced, the amount of solids leaking into the clarified liquid increases, and sludge deposits in the lower chamber 17. After the centrifugal separator 5, a second centrifuge 6 is provided.
Since the solid-liquid separation tank 7 is provided after the centrifugal separator 6 described above, the amount of concentrated liquid to be taken out can be increased. For this reason, leakage and accumulation of solids are prevented, and the clarified liquids 5b and 6b having low solids concentration are circulated to prevent solids from accumulating on the object to be cleaned 1 and wasteful consumption of the cleaning liquid, thereby efficiently performing chemical cleaning. be able to.

Even when the amount of the concentrated solution 5a, 6a to be taken out is increased, the amount of the concentrated solution 5a, 6a is gradually reduced, so that the second centrifuge 6 and the solid-liquid separation tank 7 are small. Well, the amount of liquid retained here is also reduced. For this reason, compared to the case where the clarified liquid is processed by multiple centrifuges,
The amount of cleaning liquid retained in the circulation is reduced. In addition, in the above-mentioned washing, undissolved solids are concentrated and separated, so that a washing solution and time required for dissolving them are saved, and an increase in corrosiveness due to the dissolution is prevented. Therefore, chemical cleaning can be performed efficiently in a short period of time and with reduced corrosiveness using a simple apparatus and a small amount of cleaning liquid.

When the low-speed centrifuge shown in FIG. 2 or 3 is used as the first and second centrifuges 5 and 6,
Compared to a cyclone separator that separates with a force of 00 to 6000G, the vessel wall is less worn and the pressure loss is small, so it can be processed with a small pump. It has the advantage that separation is possible even if it is not perpendicular to

The above chemical cleaning is performed by circulating the cleaning solution until the concentration of the eluted iron ions in the circulating cleaning solution becomes constant.
The circulating tank 4 is provided with a heater for heating the cleaning liquid, and also provided with a pump for sending the first concentrated liquid 5a and the separated liquid 7b, but is not shown. After the completion of the circulating cleaning with the cleaning liquid, the circulating cleaning liquid is discharged, and post-treatments such as rinsing, neutralization, and surface treatment are performed with rinsing water, a neutralizing liquid, a surface treatment liquid, and the like to complete the chemical cleaning.

Example 1 A tube to be removed from a once-through boiler of a power plant was used as a treatment object 1, and a low-speed centrifuge shown in FIG. 2 was used as first and second centrifuges. Was done. Citric acid 3 containing corrosion inhibitor and reducing agent as cleaning solution
A 3% by weight aqueous solution of 3% by weight of glycolic acid was maintained at a temperature of 80 to 90 ° C., circulated at a flow rate of 2 m ³ / h, and subjected to chemical cleaning until the eluted iron ion concentration became substantially constant. At this time, the circulating liquid is centrifuged by the first centrifuge 5, the first concentrated liquid 5 a is withdrawn at 0.2 m ³ / h, supplied to the second centrifuge 6, The concentrated solution 6a from 6 was withdrawn at 0.01 m ³ / h and settled and separated in a settling tank of 0.02 m ³ volume.

As a result, the iron ion concentration in the washing solution was constant at 4050 mg / l in 6 hours, and the scale was completely removed. The amount of solids in the washing liquid at the end of washing is 12m
g / l and the recovered solids were 6.7 g. The corrosion amount of the test piece suspended in the object to be cleaned for the corrosion test was STBA20.
1.13 mg / cm ² , STB52 0.65 mg / cm ²
cm ² . After chemical cleaning, introduce washing water and adjust the pH.
When water washing was performed until the iron ion concentration became 5 or more and the iron ion concentration became 20 mg / l or less, the washing water amount was 17 liter. Table 1 shows the above results.

[0024]

[Table 1]

Comparative Example 1 For comparison, the same test as in the example was performed in FIG. 1 except that the second centrifuge 6 was omitted. At this time,
From the first centrifuge 5, the concentrated liquid 5a is supplied at 0.043 m ³ /
h, and sedimented in a sedimentation tank having a capacity of 0.08 m ³ . As a result, the iron ion concentration in the cleaning solution was 4 in 8 hours.
At 240 mg / l, the scale was completely dissolved. The results of the above washing are shown in Table 2. The washing time was longer than in the examples, the amount of collected solids was smaller, the amount of corrosion was larger, and the amount of washing water was larger.

[0026]

[Table 2]

[0027]

According to the chemical cleaning method of the present invention, the concentrated liquid of the first centrifuge for centrifuging the circulating cleaning liquid is centrifuged by the second centrifuge, and the concentrated liquid is further separated into solid and liquid. Since the separated liquid is returned to the circulation system together with the clarified liquid of the first and second centrifuges for chemical cleaning, the solids in the cleaning liquid are efficiently concentrated and discharged by a simple device, and the solids are discharged. The washing can be continued by circulating the washing liquid with a small amount of material, whereby the washing can be efficiently performed by reducing the amount of corrosion in a short time with a small amount of washing liquid, and the amount of washing water for washing after washing. Thus, the effect that the number of images can be reduced can be obtained.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a chemical cleaning method according to an embodiment.

FIG. 2 is a partially cutaway perspective view of a centrifuge used in the embodiment.

FIG. 3 is a partially cutaway perspective view of another centrifuge.

[Description of Signs] 1 Object to be cleaned 2 Circulation path 3 Circulation pump 4 Circulation tank 5 First centrifuge 6 Second centrifuge 7 Solid-liquid separation tank 11 Separation cylinder 12 Slow turning section 13 Upper chamber 14 Supply Liquid tube 15 Rectifying hole 16 Rectifying slit 17 Lower chamber 18 Baffle 19 Guide 20 Clarified liquid outlet 21 Clarified liquid outlet 22 Concentrated liquid outlet

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideo Tsuchida 1-1-1 Higashiko, Seiro-cho, Kitakanbara-gun, Niigata Prefecture 155 Tohoku Electric Power Co., Inc. 1-1-1 155 Tohoku Electric Power Co., Inc.Higashi-Niigata Thermal Power Station (72) Inventor Naomi Nazawa 1-1-1, Higashi-Niigata Thermal Power Station, Tohoku Electric Power Co., Inc. Masanori 3-17-17 Otsugaoka, Numana-cho, Higashi-Katsushika-gun, Chiba Prefecture (72) Inventor Kazuo Fukaya 3-15-12, Minamicho, Chuo-ku, Chiba-shi, Chiba 102 Yamazaki Heights 102 (58) Fields studied (Int.Cl . ^7, DB name) B08B 9/06 B04C 9/00 C23G 1/36

Claims (1)

(57) [Claims] 1. A method for performing chemical cleaning while circulating a cleaning liquid to a portion to be cleaned, comprising: introducing a circulating cleaning liquid into a first centrifuge provided in a circulation path of the cleaning liquid to include a first substance containing solid matter in the liquid; Concentrate and 1st
After the first concentrated liquid is separated into the second concentrated liquid and the second concentrated liquid, the first concentrated liquid is introduced into a second centrifuge to separate the second concentrated liquid and the second concentrated liquid. A chemical cleaning method comprising: discharging solids out of the system; and returning the separated liquid to the circulation path together with the first and second clarified liquids.