JP3202605B2 - Plant chemical cleaning method and equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to chemical cleaning of a plant, and more particularly, to a method and an apparatus for chemically cleaning scale generated by operation of a thermal power plant or a chemical plant.

[0002]

2. Description of the Related Art In chemical cleaning of a boiler or the like, acid cleaning using mainly hydrochloric acid or an organic acid is often performed. In this chemical cleaning, by injecting these chemicals into the system to be cleaned and circulating them, sufficient chemical solution is contacted to dissolve or peel off scales (deposits and deposits) in the system. . It is also common practice to increase the temperature as necessary to promote dissolution. Usually, washing with hydrochloric acid is performed by heating to about 60 ° C., and washing with organic acid is performed by heating to 80 to 90 ° C. When the acid cleaning is completed, it is necessary to completely discharge the chemical component from the system, and water washing (water washing) is performed as a method therefor.

[0003] As a method of water washing, after all the liquid is discharged, water washing water is poured in, and the whole amount is discharged as full water. By repeating this, the chemical component is discharged. Another typical method is to extrude a chemical solution by pouring water washing water into the system with a large capacity pump,
There is a method of extrusion and washing with water. In each case, three to four times the capacity of the system's full water capacity (hereinafter referred to as the retained water volume) is required. After the washing water quality reaches a certain level, a rust prevention treatment step is performed, and the chemical washing is completed. The amount of used water (pure water) used for these chemical cleanings is generally 6 to 7 times the volume of the retained water. For example, 250
m ³ , the total water usage is 1,500 to 1,8
Most of this amount is about 00m ³ , which is all wastewater. In addition, in the above-mentioned acid washing, there is no problem as long as the scale is completely dissolved, but the attached form of the scale is in a state where granular crystals of iron oxide of about 10 to 50 μm are aggregated, The porosity of the scale is also about 3
0%, in a situation where peeling is likely to occur.

[0004] The peeled scale (called sludge)
It may circulate in the system or, depending on the case, accumulate in parts where the flow velocity is low, such as inside the plant (steam-water separator). In order to prevent the deposition, it is necessary to make the circulation flow rate as large as possible. For this purpose, a measure is taken to circulate using a large-capacity pump. However, in the conventional method, since it is sent from the temporary pipe to the pump and circulated to the plant, it is pushed into the plant again. Then, the probability of sludge depositing in the plant increases, and the water quality in the subsequent washing and cleanup during operation of the boiler deteriorates, thereby increasing the amount of water used. As a countermeasure against this sludge, a method of removing the sludge by using an electromagnetic filter in the circulation system (Japanese Patent Publication No. 51-40532) or a method of removing the sludge by centrifugation in the system (Japanese Patent Publication No. 59-15749)
No. 6) has been proposed.

According to the method described above, ferromagnetic sludge can be removed, but other ferrous sludge cannot be removed. Further, the magnetic field of the electromagnet needs to be increased to some extent, so that the apparatus is expensive and the implementation is inferior in cost. I have. about,
Since the solids are centrifuged using a centrifuge or a cyclone, they are not related to the magnetism of the scale, but their classification efficiency is low, and is limited to about 30 μm. And there are many difficult points such as expensive and large equipment arrangement. Furthermore, since the important and most abundant particle size is 5 to 20 μm, it is not suitable for separation of necessary sludge, and sludge actually caught is limited to about ten and several kilograms. Did not.

[0006] As described above, the problems in the chemical cleaning include the deposition of sludge in the apparatus and the use of a large amount of water as a whole.
That is, it is necessary to use as much as 0 to 2,500 m ³ of pure water. Eliminating this enormous use of water is an urgent necessity in recent times where the importance of water resources is often mentioned.
Also, in order to generate such a large amount of wastewater, it is necessary to prepare a tank for receiving the wastewater even temporarily, but few plants have sufficient tanks. For that purpose, it is often necessary to prepare a temporary aquarium, and it has been necessary to solve many problems, such as the problem of the location, safety and cost. In addition, due to such restrictions, drainage cannot be accepted, and sometimes water washing cannot be performed sufficiently, and as a result, there may be cases where termination is performed in an insufficient condition. was there.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, reduces the amount of washing water used, reduces the amount of washing wastewater associated therewith, and further reduces sludge in the circulation system. By completely capturing, it is possible to completely prevent re-infiltration into the object to be cleaned, and to further clean the inside of the system of the object to be cleaned, and to purify and reuse the washing water in the circulation system. It is therefore an object of the present invention to provide a method and an apparatus for chemical cleaning of a plant with simple equipment, which can greatly reduce water used.

[0008]

In order to solve the above-mentioned problems, the present invention provides a chemical cleaning method for a plant combining chemical cleaning and water cleaning, wherein the plant is provided with a cleaning liquid circulation system capable of circulating cleaning. the cleaning solution of the system path, chemical cleaning
Purify by filtration in case of
Ru der those decided to recycling and purifying by-exchange treatment and / or adsorption process. Further, according to the present invention, in a chemical cleaning apparatus for a plant that combines chemical cleaning and water cleaning, a cleaning liquid circulation system capable of circulating cleaning is provided in the plant, and the system includes a filter for chemical cleaning. Tajo
, A filter for water washing and an ion exchanger and / or
It is obtained by the provision of a purification device that consists in adsorber. In the chemical cleaning device, as the filtration body a membrane filter, better to use a large structure of the filtration area, such as a pleated or hollow fiber filter,
This makes it possible to reliably capture sludge in the chemical solution.

[0009]

Next, the present invention will be described in detail.
In general, taking chemical cleaning of a boiler as an example, the overall process is generally as follows. That is, [acid washing] → [water washing] →
[Rust prevention treatment] → [Final rinsing], and the amount of water used for each becomes 1, 3, 1, 3 volumes in order, and when restarting operation, [Boiler cold cleanup] → [ Boiler hot cleanup) → [Boiler operation]
Becomes Of these, what is circulated and washed in the present invention is the acid washing solution, most of the three-volume washing steps, and the water in the final washing step. In the case of the circulation treatment of the acid washing liquid, it is preferable to carry out the filtration treatment. The generation of sludge is often seen during acid cleaning and by the first three hours. This sludge partially dissolves in the acid and partially deposits inside the plant, so that after 3 hours, the amount of sludge in the cleaning liquid gradually decreases. If you capture this sludge with a filter,
Deposition in the plant can be prevented, and subsequent boiler cleanup time and water volume can be significantly reduced.

After washing with hydrochloric acid, the pH of the boiler water does not readily rise and the concentration of chlorine ions does not readily decrease after cold start-up. This is because the chemical liquid remaining in the sludge deposited in the system, which could not be removed by washing with water, exudes little by little. Therefore, if the accumulation of the sludge can be eliminated, such a phenomenon can be stopped. Since the composition of the washing water mainly contains an acid for chemical washing and dissolved iron ions, and is also a suspension (fine iron oxide), these are filtered, ion-exchanged or adsorbed in the present invention. Pure water is regenerated by continuously performing one or more treatments in combination and reused as washing water.

A specific cleaning method will be described with reference to the system diagram shown in FIG. In FIG. 1, the boiler is conceptually shown as an object to be cleaned 1, but there are actually various types. Representative examples include a once-through type, a natural circulation type, and a forced circulation type. Among the once-through type, there are those with a circulation pump and those without. Generally, a circulation line is provided from the boiler main body by a temporary circulation pipe 2, and a circulation process is performed by the pump 3 using the valves 5 and 6 and the pipe 2. Injection of chemicals and heating (injection of steam) are incorporated into this circulation pipe. The end of the washing is a point where the effective concentration of the circulating drug solution and the change in the concentration of iron ions mainly eluted are not observed (saturation point). Usually, the circulation treatment is performed for 6 to 8 hours in the acid washing step.

The circulation flow rate varies depending on the object to be cleaned, but is generally 300 to 600 m ³ / h in a normal once-through boiler. In order to maintain this flow rate, it is necessary to prepare a temporary pipe having a nominal diameter of 150 mm to 250 mm. In the present invention, a pressurized filtration filter is provided as a purification device 4 at the outlet side of the circulation pump 3 to treat the whole amount.
As a result, sludge generated from the object to be cleaned is captured by the filter 4. There are various filters,
At present there is a diameter of 0.1 μm to 100 μm, and a diameter of 0.05 μm is required when more precise filtration is required.
In addition, recently, a filter having a large filtration area and a compact size has been provided to the market. In the present invention, the form of the sludge is mostly around 10 μm, so that any sludge having a filtration capacity of 2.5 μm or less is sufficient as a filtration device for acid washing. The size of the pressure vessel (housing) of the filter varies depending on the processing flow rate.
Recently, very large ones are also commercially available (compacting is possible), but the filtration speed is still basically 1 m / h, and therefore a filtration area of 200 to 300 m ² will be necessary.

[0013] It is preferable that the filtration speed at the water-passing surface can sufficiently maintain 1 m / h. However, in acid cleaning, a colloidal substance (mainly a metal hydroxide or the like) which causes clogging of the filter.
Is not contained at all, so that there is almost no increase in filtration resistance, and thus the filtration speed can take a value of 2-3 m / h. Therefore, the filtration area of the filter is 150 to 200.
If it is m ² , it can sufficiently serve as a filtration device for chemical cleaning. In the above description, in the chemical liquid cleaning, the processing of filtering sludge using a filter has been described. Next, water cleaning will be described. After chemical cleaning, the chemicals in the system are drained by water washing.However, in the most effective method, in the case of natural circulation, the entire amount is drained, the washing water is poured in, and the draining is repeated, In a once-through boiler, there are roughly two methods, for example, by pushing out with a permanent water supply pump or a temporary circulation pump and replacing the water in the system.

These methods will be described with reference to the system diagram shown in FIG. In the above filling and discharging method (feel-and-drain), in FIG. 2, washing water is filled from the valve 8 through the pump 3 to the pipe 1 through the pipe 2. When the article to be cleaned 1 is full, the valve 16 is opened and blown into the drainage tank 12. This must be repeated at least three times. Also, in the above-mentioned extrusion method, it is general that about 2 to 3 times the volume of water is required. However, according to FIG. 2, the valve 5 is closed, and the pipe 2 is connected to the valve 8 via the pump 3 via the pump 3. Then, the end point is determined by monitoring the water quality at the outlet. Two to three times the volume of water is required before washing is completed, but when it is necessary to discharge sludge or the like, it is important to use a flow rate as large as possible.

In any of the methods of the present invention, a temporary circulation line is laid. Therefore, the purifying device 4 is incorporated in the circulation line, and a part of the washing water of the temporary circulation line is provided.
Alternatively, the quality of the washing water is temporarily reformed by circulating the whole water and purifying the water. Since the main components of water quality are acid and metal ions and turbid matter (sludge), purification can be achieved by using a filter body and an ion exchanger for removing these substances. Circulation is carried out by a temporary pump or a main pump, and a line of the purification device 4 is operated in parallel.
By doing so, the water circulating through the object to be cleaned (wash water) is purified, and the water quality in the system is improved. If this pump is operated, the circulation flow velocity in the system is high, and the deposits on the inner surface of the pipe are almost carried out and captured by the purification system.

FIG. 3 is a partially enlarged view of a line of a cleaning water purifying apparatus. In FIG. 3, the ion exchangers 14a and 14a
4b and a purification device 4 having a filter 13. The purifying device 4 is not limited to FIG.
It is also useful to provide a bypass pipe for each ion exchanger or adsorber. It is also possible to separately prepare a pump in the purification system, and a temporary circulation pump may be used together. When an adsorbent is used, it is better in front of the filter 13,
Depending on the nature of the substance, after the ion exchanger 14a, 14
It can be installed instead of or in combination with b. Which one to use may be determined according to the composition of the cleaning agent. In chemical cleaning, a rinsing step is often incorporated after the water cleaning step. This rinsing step dissolves and removes rust generated in the water washing step, but often uses citric acid. In this method, if the circulating water is treated with the cation exchange resin that accompanies the washing process, part of the washing solution remains in the washing water, and in the case of organic acid washing, citric acid is regenerated. Therefore, this can be used as a rinsing liquid.

[0017]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto. Example 1 An example in which the method of the present invention is applied to chemical cleaning of a once-through boiler having a cleaning water amount of 200 m ³ will be described. The specifications of the cleaning liquid are as follows. Citric acid: 2.0% Glycolic acid: 2.0% Inhibitor: 0.3% Reducing agent: 0.1% Treatment temperature: 80-90 ° C

The filter 4 of the purifying apparatus according to the present invention was installed by using this cleaning liquid (organic acid) in a temporary circulation system shown in FIG. The outline of the circulation process is as follows. Circulation flow rate: 400 m ³ / h Circulation time: 8 hours Filtration area: 150 m ² Filtration speed: 400 m ³ / h Filter diameter: φ0.9 μm Filter specifications: Hollow fiber type Filtration linear speed: 2.7 m / h

During that time, the SS content in the circulating fluid before and after the filter was measured using a 0.45 μm membrane filter. The result was as shown in FIG. As shown in the figure, the peak of SS was observed at 2 to 3 hours, then decreased, and at 4 hours, the SS at the inlet of the filter was 3 ppm or less and almost completely filtered. The differential pressure across the filter is
Initially, the pressure difference was 0.5 bar and the filter itself, but then increased by 0.3 bar, increased to 0.8 bar and maintained as it was. The amount of SS (sludge) captured from the graph of FIG. 6 is calculated to be 60 kg, but the actual measured value is 45 kg.
kg. The difference of 15 kg of this value is a result of being dissolved by the passage of the acid solution after being captured by the filter.

Comparative Example 1 A comparative example at the time of substantially similar boiler chemical cleaning is shown. The specifications of the cleaning liquid are as follows. Citric acid: 2.5% Glycolic acid: 2.5% Inhibitor: 0.3% Reducing agent: 0.2% Treatment temperature: 80-90 ° C Washing liquid: 180 m ³ The temporary circulation system at this time is shown in FIG. , But only the filter has been removed from FIG. The outline of the circulation is as follows. Circulating flow rate: 500 m ³ / h Circulating time: 7 hours During that time, the SS content was measured regularly. The result is shown in FIG. One hour after the start of washing, the peak of SS was shown,
After that, it decreased sharply, but SS stabilized at about 30 ppm, and thereafter showed a similar value until the end point.

Comparative Example 2 This is a process using a conventional apparatus for removing SS components by centrifugation. FIG. 5 shows the flow at that time. FIG.
Is an example in which a centrifugal cyclone separator 17 is attached to the suction side of the pump to remove SS. The flow rate of the cyclone is maintained by adjusting the valve 9 to maintain the flow meter at a predetermined value. The specifications of the cleaning liquid are as follows. Hydrochloric acid: 5% Inhibitor: 0.3% Reducing agent: 0.2% Treatment temperature: 55-60 ° C Treatment time: 6h Washing liquid volume: 230m ³

The temporary circulation system at this time is shown in FIG. In the method, a cyclone separator 17 was installed, and a part of the circulating liquid was separated by a temporary pipe 11. The outline of the circulation at this time is as follows. Circulating flow rate: 500 m ³ / h Separator flow rate: 150 m ³ / h The measurement results for SS during that time are shown in FIG. The SS at the inlet of the separator recorded 88 ppm at the second hour of the cleaning,
Thereafter, although decreasing, the SS content of 30 to 40 ppm was present until the end. SS at the outlet side was 41 ppm after one hour as shown in FIG. 8, and thereafter, the difference between the inlet and the outlet hardly occurred. This is a small sludge that exceeds the separation limit of the cyclone, and appears to have floated or settled in the system.

Example 2 An example in which the method of the present invention is applied to chemical cleaning of a once-through boiler having a cleaning water amount of 230 m ³ will be described. The cleaning specifications are organic acid cleaning based on citric acid: 3.0% glycolic acid: 3.0%. The acid washing was completed in 8 hours, and the eluted Fe ion was 8,700 ppm. After the washing was completed, the water was extruded at 800 m ³ / h using a temporary circulation pump to start washing with water. The water quality at the outlet is monitored by electrical conductivity. At the point of 240 μS / cm from the initial stage of the water washing, the extrusion water washing was stopped, the system was converted into a circulation system, and the circulation washing was started through the purification line.

The water quality at that time was as follows. Fe: 800 ppm, SS: 45 ppm, conductivity: 254 μS / cm, turbidity: 50 ppm, pH: 5.4, The main configuration of the purification process in the purification line is as follows. Filter: cartridge filter, 0.2 μm diameter, 150 m ³ , ion exchanger 14a: cation exchange resin 2 m ³ , 14b: anion exchange resin 2 m ³ ,

[0025] In circulation purification flow rate of 800m ³ / h, but was circulating water cleaning, processing the flow rate of the clean-up system at that time 150m ³
/ H. The water quality at the outlet after the purification treatment was as follows. Fe: 0.01 ppm or less, SS: 0.3 ppm or less, conductivity: 0.3 μS / cm, turbidity: 1.0 ppm or less, pH: 6.8, and the progress of the water quality of the circulated purified water during that time is shown in FIG. Show. The water quality is checked, and the electrical conductivity--, Fe ion--, and turbidity--are measured. As shown in FIG. 9, at the third hour, electric conductivity: 5.0 μS / cm, Fe:
2 ppm, turbidity: 100 ppm, Fe is 4% of raw water
Purification was reduced to 1/000 or less, the turbidity also reached the target value, and after 4 hours, the turbidity was sufficiently purified to be 0.7 ppm of Fe and 3 ppm or less. No water injection was performed during this time, and the amount of water saved during the 4-hour circulating extrusion flush corresponds to 600 to 700 m ³ .

Thereafter, the hydrazine concentration was adjusted to 500
ppm and the temperature was increased to 80 ° C. to perform rust prevention treatment. The amount of water used in the process from acid washing to blowing of the rust preventive solution was as follows. Chemical injection blow: 50 m ³ , heated steam: 15 m ³ , extrusion: 290 m ³ , branch pipe flushing: 50 m ³ , superheater ：: 50 m ³ , branch pipe 〃: 28 m ³ , rust preventive liquid blow: 230 m ³ , non Cleaning part flushing blow: 360 m ³ , total: 1,073 m ³ ,

Comparative Example 3 An example is shown in which a once-through boiler of a similar scale is treated by a conventional method. The cleaning method was almost the same as in Example 1, but the composition of the cleaning liquid was 5%. The breakdown is as follows. 2.5% citric acid 2.5% glycolic acid, 7 hours after acid washing, and 9,500 ppm of Fe ions. After the completion of the acid cleaning, the valve 5 is closed and the valves 7 and 8 are opened using the temporary circulation pump 3, and the pipe is pushed into the object to be cleaned from the pipe 2 and is passed through the pipe 2 to the drainage tank 12 at 600 m ³ / h. Start extrusion water washing, 1 hour later, 10 ppm Fe, turbidity 15 pp
m, 1 hour and 10 minutes later, the content of Fe reached 5 ppm, and the extrusion water washing was temporarily stopped. During this time, the flush water is about 700m
^{Was 3} .

Thereafter, the circulation is switched to the piping 2 → the valve 5 → the pump 3 → the valve 6 → the piping 2 → the circulation to the object 1 to be cleaned.
The ion became 18 ppm and the turbidity became 20 ppm. Therefore, water injection was started at a rate of 300 m ³ / h from the valve 8, and the system was switched to circulating water washing for discharging a considerable amount from the valve 7 to the drainage tank 12. One hour later, the content of Fe was 3 ppm, and two hours later, the content was 1 ppm or less, and the turbidity was also 5 ppm or less. The washing water during this time is 600 m ³ . Then add hydrazine,
Rust prevention treatment was performed at 500 ppm. The amount of water used in the process from acid washing to blowing of the rust preventive solution was as follows.

[0029] As described above, the amount of water retained for washing has a difference between 230 m ³ and 250 m ³ , but in chemical washing of a boiler of substantially the same type (through-flow boiler), the use of the present invention can save about 700 m ³ . In addition, about three times the amount of water held was saved.

[0030]

In chemical cleaning of a boiler or the like that temporarily discharges wastewater exceeding 1,500 m ³ in a short time (one day), saving the washing water requires preparing only the water.
And it is necessary to prepare to receive this water that will be drained,
In the present invention, as much as 700 m ^{3 of} water can be saved, and a great effect is produced in this respect as well. This is particularly advantageous when water, which is a resource, is insufficient. In the conventional method of water injection, that is, a method of purifying circulating water by operating the pump 3 to inject water from the valve 8 and discharge a corresponding amount from the valve 7 (circulating water washing), As described above, the amount becomes about two volumes outside the extrusion water. In the present invention, by purifying the dilute washing water, it is used as a water quality that can be sufficiently washed, and it is possible to prevent acid solution or sludge from remaining in the system. Of 1
It is possible to reduce to the extent. Also,
Deterioration of water quality caused by sludge can be eliminated,
This is effective in shortening the time for water cleaning related to the start-up of the entire plant and water cleaning in cleanup.

[Brief description of the drawings]

FIG. 1 is a system diagram for carrying out a chemical cleaning method of the present invention.

FIG. 2 is a system diagram for carrying out another chemical cleaning method of the present invention.

FIG. 3 is a partially enlarged view of a line of the purification device in FIG. 2;

FIG. 4 is a system diagram showing an example of a conventional chemical cleaning device.

FIG. 5 is a system diagram showing another example of a conventional chemical cleaning device.

FIG. 6 is a graph showing the relationship between the cleaning time and SS according to the method of the present invention.

FIG. 7 is a graph showing a relationship between a cleaning time and SS according to a conventional method.

FIG. 8 is a graph showing the relationship between the cleaning time and SS according to another conventional method.

FIG. 9 is a graph showing a change over time of circulating purified water.

[Explanation of symbols]

1: object to be cleaned, 2: temporary circulation pipe, 3: circulation pump,
4: Purification device, 5 to 10, 16: Valve, 11: Purification piping, 12: Drain tank, 13: Filter, 14a, 14b:
Ion exchanger, 15: instrument, 17: cyclone,

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI C02F 9/00 503 C02F 9/00 503Z 504 504B F22B 37/52 F22B 37 / 52B (56) References JP-A-7-90651 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23G 3/00 B08B 3/14 C02F 9/00 F22B 37/52

Claims (3)

(57) [Claims] In a chemical cleaning method for a plant, in which chemical cleaning and water cleaning are combined, a cleaning liquid circulation system capable of circulating cleaning is provided in the plant, and the cleaning liquid in the system is used for chemical cleaning.
Purify by filtration in the case, and filter and ion in the case of water washing
A chemical cleaning method for a plant, wherein the chemical cleaning is carried out by purifying by means of an exchange treatment and / or an adsorption treatment . 2. A chemical cleaning apparatus for a plant which combines chemical cleaning and water cleaning, wherein a cleaning liquid circulating system capable of circulating cleaning is provided in the plant, and a chemical cleaning system is provided in the system .
Purification device with a filter, and a filter and an
Emissions exchangers and / or plants of a chemical cleaning apparatus is characterized by providing a purification apparatus Ru consists of adsorbent. Wherein the filtering body, according to claim 2, which is a large structure of the filtration area of the filter such as a pleated or hollow fiber type I Oh <br/> a membrane filter Cleaning equipment in a modern plant.