JP3242012B2 - How to clean the diffuser washer screen - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a washing method for washing and removing scale adhering to a screen of a diffuser washer installed at the top of a bleaching tower as an apparatus for washing pulp that has been bleached in the preceding stage. is there.

[0002]

2. Description of the Related Art Before explaining a conventional cleaning method, first,
The diffuser washer will be schematically described with reference to FIGS.

FIG. 1 is a longitudinal sectional view showing the entire diffuser. In this figure, reference numeral 1 denotes a bleaching tower, which has a funnel 1a at a lower portion. The finished pulp is to be introduced. Reference numeral 2 denotes a diffuser washer installed on the top of the bleaching tower 1. The washer 2 is disposed so as to be immersed in an upper scraper unit 3 and an upper end of the bleaching tower 1 at a lower side of the unit 3. A screen unit 4, a vertical drive unit 5 for vertically moving the screen unit 4 by a predetermined stroke, and a rotary drive unit 6 for rotating the scraper unit 3.

FIG. 3 shows an example of the screen unit 4. The screen unit 4 comprises a plurality (four to five) of screen rings 7 having a height of about 1300 mm and arranged concentrically. Each screen ring 7 has a thickness of about 50 mm, and a screen plate 7a is stretched on both inner and outer surfaces with an inner center plate interposed therebetween.
It is fixed to, for example, six arms 8 extending radially from the center. The liquid flows through the inside of each arm 8, and the liquid extracted by the screen enters the inside of the arm 8 through the inside of each screen ring 7, further enters the drain box 9 at the tip of the arm 8, It is extracted from the extraction hole 9a. Each extraction hole 9a is connected to a ring pipe 10 provided around the outer periphery of the bleaching tower 1, and this ring pipe 1
The extract is transferred to the outside through 0. Each of the arms 8
A hydraulic cylinder as an up-down driving means 5 is interlockedly connected to the end of the column, and this hydraulic cylinder is fixed to the outer peripheral portion of the bleaching tower 1. Each hydraulic cylinder has about 1 screen unit 4
It is designed to move up and down with a stroke of 50 mm.

The pulp introduced into the lower part of the bleaching tower 1 is
After moving upward in the bleaching tower 1 and reaching the outlet at the upper end through the space between the screen rings 7, it is pushed by the rotating scraper unit 3, and the rounder ring 11 disposed on the outer periphery of the upper end of the bleaching tower 1. And fall by a pipe 12 to a standpipe. Screen unit 4
Rises about 10% faster than pulp and stands still at the upper end for 5-8 seconds, then falls rapidly in about 0.5 seconds. The extraction by the screen ring 7 takes place only during the lifting of the screen unit 4. Screen unit 4
During the extraction, the mat-like pulp formed on the surface of the screen plate 7a of the screen ring 7 during the extraction is cut off, and the surface of the screen plate 7a is kept clean.

As shown in FIG. 2, the scraper unit 3 has four arms 13 connected in a cross shape, two of which are provided with a plurality of washing water dispersion nozzles 14 vertically. The scraper blade 15 is attached to these two. The washing water is rotated by the rotating washing water dispersion nozzle 14.
From the pulp at the intermediate position of each screen ring 7. The washing water replaces the liquid that has entered the bleaching tower 1 together with the pulp, is extracted by the screen ring 7, and is sent to a filtrate tank (not shown). In the figure, reference numeral 16 denotes a hollow rotary shaft which penetrates vertically through the center of the fixed frame 17 and is connected to the base end of each arm 13.
A swivel 18 is interposed between the upper end of the shaft and the fixed frame 17, and a washing water supply pipe 19 is connected to the swivel 18, and the washing water from the supply pipe 19 passes through the hollow portion of the rotating shaft 16. The water is supplied to the washing water dispersion nozzle 14 of the arm 13.

During the liquid extraction process using the screen ring 7 as described above, pulp slag (hereinafter referred to as scale) generally containing calcium oxalate as a main component is generally placed on a screen plate 7a of the screen ring 7. ) Adheres, and if the amount of the scale attached increases, clogging occurs and the screen ring 7
Therefore, it is necessary to periodically stop the operation of the machine and perform the scale removing operation.

However, in order to wash and remove the scale adhering to the screen ring of the screen unit, conventionally,. Jet cleaning with high pressure water,
. A method in which a bleaching tower is filled with a pulp suspension, and washing is performed by circulating fresh water containing a scale dissolving agent in a region covering the screen portion; A method is used in which the bleaching tower is filled with fresh water up to the upper part of the screen unit, a sheet is stretched under the screen unit, and washing is performed by circulating fresh water containing a scale dissolving agent in a region covering the screen part.

[0009]

However, in the above-described cleaning method, the scale on the surface of the screen plate 7a is removed, but the scale attached to the inner surface cannot be removed. Further, in the above-described cleaning method, the circulating water flowing through the screen portion and the pulp suspension are mixed to dilute the scale dissolving agent, so that the cleaning efficiency is poor. Furthermore, in the above-mentioned cleaning method, it is very difficult to attach the sheet to the lower part of the screen unit, for example, the sheet soars, and if there is any gap, the circulating water on the upper side of the sheet and the clean water on the lower side of the sheet are separated. As a result, the circulating water and the fresh water could not be actually distinguished.

[0010] The scale dissolving agent used in the above and the above-mentioned washing methods can be used by keeping it at a predetermined concentration.
Although the scale can be effectively removed, the scale dissolving agent is very expensive, so that it must be used in a minimum amount so as to minimize waste. However, in the above method and the above method, the scale dissolving agent concentration in the circulating water decreases due to the diffusion of the scale dissolving agent into the fresh water below the circulating water level, and the washing effect is deteriorated, and the scale cannot be sufficiently removed. To improve the cleaning effect, a very large amount of scale dissolving agent is required.

Therefore, the present invention can maintain the concentration of the circulating washing water containing the scale dissolving agent at a predetermined concentration,
An object of the present invention is to provide a cleaning method capable of effectively removing scale with a minimum amount of scale dissolving agent used.

[0012]

According to the first aspect of the present invention, as shown in FIG. 4, the scale attached to the screen ring 7 of the screen unit 4 in the diffuser washer 2 installed at the top of the bleaching tower 1 is cleaned. This is a washing method for removing water CW from the warm water HW in which the scale dissolving agent is added and mixed and has a high temperature difference with respect to the water CW. The washing water is filled so as to cover the upper part of the screen ring 7 to form a washing water zone HZ at the upper end in the bleaching tower 1, and the washing water in the hot water zone HZ is discharged to the outside of the bleaching tower 1. Then, the hot water is returned to the hot water area HZ again through the circulation path 20 and used for circulation.

According to a second aspect of the present invention, in the method for cleaning a screen portion of a diffuser washer according to the first aspect,
The temperature difference between the warm water HW, which is the flush water in the warm water area HZ for flush water, and the water CW below the warm water HW is about 40 ° C. or more.

According to a third aspect of the present invention, in the method for cleaning a screen portion of a diffuser washer according to the first or second aspect, the washing water in the hot water area for washing water HZ is circulated outside the bleaching tower through the drain box 9 of the screen unit 4. It is characterized in that it is discharged to the path 20.

According to a fourth aspect of the present invention, in the method for cleaning a screen portion of a diffuser washer according to any one of the first to third aspects, 6 to 10% by weight of a carboxylic acid containing a nitrogen atom as a scale dissolving agent in circulating washing water and a pH of 12 to 12 are used. 1
The method is characterized in that caustic soda is added so as to maintain a value of 3.

According to a fifth aspect of the present invention, in the method for cleaning a screen portion of a diffuser washer according to any one of the first to fourth aspects, the circulation flow rate of the circulating cleaning water is increased with time.

According to a sixth aspect of the present invention, in the method for cleaning a screen portion of a diffuser washer according to any one of the first to fifth aspects, a heating means is provided in the circulation path 20 so that the temperature of the cleaning water flowing through the path 20 is controlled. It is characterized in that it is raised.

According to a seventh aspect of the present invention, in the method for cleaning a screen portion of a diffuser washer according to the sixth aspect,
The heating means comprises a steam heater 23.

[0019]

FIG. 4 schematically shows an apparatus for cleaning a screen portion of a diffuser washer 2 shown in FIGS. 1 to 3, wherein a pipe 20 is connected to the outside of the bleaching tower 1. This circulation path 20
Is connected directly to the washing water introduction part of the scraper unit 3, that is, the hollow part of the rotating shaft 16, or is connected to the washing water supply pipe 19 (see FIG. 2), and the circulation path 2
The other end of 0 is connected to a ring pipe 10 (see FIGS. 1 and 4) connected to each extraction hole 9a (see FIG. 3) of the drain box 9 in the screen unit 4. The circulation path 20 is provided with a washing water tank 21 for storing washing water, and the washing water in the tank 21 is sent to the scraper unit 3 by a pump 22 under pressure. A steam heater 23 is provided between the pump 22 and the scraper unit 3 as heating means for raising the temperature of the circulating washing water.

When the screen ring 7 of the screen unit 4 is washed using the above-described apparatus, the pulp in the bleaching tower 1 is discharged, and then the bleaching tower 1 is filled with the pulp immediately below the screen ring 7, for example. Water CW up to 10-20cm below the lower end of screen ring 7
Put up. The temperature of the water CW is, for example, 30 ° C. Then, the washing water in the washing water tank 21 is pumped by the pump 22 and the hot water HW heated by the steam heater 23 is supplied from the washing water dispersion nozzle 14 of the scraper unit 3 to the bleaching tower 1.
And the hot water HW is filled until it covers the screen ring 7 of the screen unit 4, thereby forming a hot water area HZ for washing water at the upper end in the bleaching tower 1. The temperature of the hot water HW is set to, for example, 70 ° C., and a temperature difference of about 40 ° C. is provided between the hot water HW and the water CW. In FIG. 1, the boundary between the hot water area HZ for washing water and the water area thereunder is indicated by a dashed line.

The hot water HW contains 6 to 10% by weight of a nitrogen atom-containing carboxylic acid as a scale dissolving agent (trade name: Deponax P-140). In this case, add caustic soda and adjust the pH to 10 or more, preferably 12 to 13
Adjust to In other words, the scale dissolving agent Deponax P
This pH range is necessary because the scale dissolution efficiency of -140 is maximum near pH = 12-13. The reason is that the pH of the scale washing solution decreases as the dissolution of the scale progresses, so that pH = 12 to 1 at the start of washing.
It is known that the pH decreases with time even when the value of 3 is set. Therefore, in order to maintain the optimum pH (12 to 13), it is necessary to appropriately add caustic soda. Further, the effect can be obtained when the concentration of Deponax P-140 (scale dissolving agent) used is 2% or more. However,
The upper limit of the concentration is usually 1 in consideration of economy.
Use at 0% by weight or less. Further, in consideration of a more efficient use method of the drug, unnecessary dilution in the middle, and the like, the drug is used in a preferable concentration range of 6 to 10% by weight.
The addition of the scale dissolving agent and the caustic soda is performed in the washing water tank 21.

With the hot water zone HZ for the washing water filling the screen ring 7 formed at the upper end in the bleaching tower 1 as described above, the hot water HW in the hot water zone HZ, that is, the washing water, is supplied to the drain box 9. While discharging from the ring pipe 10 connected to each extraction hole 9a to the return side of the circulation path 20, it is returned to the hot water area HZ for washing water at the upper end portion of the bleaching tower 1 through this circulation path 20, and the circulation is repeated. Water. Then, the scale adhering to the screen ring 7 is washed and removed by the hot water HW in the hot water area HZ, that is, the circulating water. In this washing process, the warm water area H for washing water is used.
The temperature of the circulating water is increased by the steam heater 23 as necessary so that the temperature difference between the hot water HW of Z and the water CW below the hot water H is maintained at 40 ° C. or more as needed.

According to this washing method, the warm water area H for washing water is used.
Since a temperature difference of about 40 ° C. is provided between the warm water HW of Z, that is, the circulating water and the water CW therebelow, for example, circulating water of 70 ° C. (density: 0.978) and water CW of 30 ° C. (density: 0) .9
96), the mixing of the two is prevented, and the concentration of the scale dissolver in the circulating water can be maintained at a predetermined concentration by preventing the decrease in the concentration of the scale dissolver due to diffusion as in the conventional method. In addition, the scale removing effect can be greatly improved, and the amount of the scale dissolving agent used can be minimized.

Further, since the scale dissolving agent concentration in the circulating water can be maintained at a predetermined concentration as described above, the scale of the screen ring 7 is removed with the passage of time by the circulation of the scale dissolving agent. By increasing the flow rate over time, the scale removal effect can be further improved.

In this embodiment, the temperature difference between the hot water HW and the water CW is about 40 ° C., but the temperature difference is about 40 ° C.
By doing so, the density difference between the hot water HW and the water CW becomes larger, and the mixing of the two can be more reliably prevented. This temperature difference may be 40 ° C. or less. Also, as in this embodiment, the warm water area HZ for washing water is used.
The washing water in the drain box 9 of the screen unit 4
The screen ring 7 can be completely washed and the entire screen unit 4 can be effectively washed by discharging the bleaching tower 1 to the circulation path 20 outside. If the steam heater 23 is used as the heating means, the equipment can be simplified and the circulating water can be effectively heated.

[0026]

Next, the change in the amount of scale removed by washing will be described by comparing an example implemented by the conventional method with two examples implemented by the method of the present invention. In addition,% in an example shall show a weight% unless there is particular notice.

[Conventional Example] The bleaching tower 1 is filled with a pulp suspension, and fresh water containing a scale dissolving agent is circulated in an area covering the screen ring 7 of the screen unit 4.
Washing was performed for 14 hours. The temperature of the pulp suspension and fresh water is 35 ° C., and the fresh water contains a scale dissolving agent (trade name Deponax P-140) and p
Caustic soda (20%, 30%)
0 liters). The amount of scale dissolver used is 3
It was 300 kg. As a result, the amount of scale removed was 53 kg.

Example 1 A water CW of about 30 ° C. was spread in the bleaching tower 1 to just below the screen ring 7, and a hot water HW of about 70 ° C. was filled from above to cover the screen ring 7 of the screen unit 4. Thus, a warm water zone HZ for washing water was formed at the upper end of the bleaching tower 1. In this hot water HW,
As a scale dissolving agent, 6 to 10% by weight of a carboxylic acid containing nitrogen atom (trade name: Deponax P-140) was added, and caustic soda (20%, 300 liters) was added so as to maintain pH 12 to 13. With the hot water zone HZ for washing water formed at the upper end in the bleaching tower 1 in this way, the hot water HW in the hot water zone HZ, that is, the washing water, is discharged to the return side of the circulation route 20 while passing through the circulation route 20. Return to the hot water area HZ for washing water at the upper end of the bleaching tower 1 again,
While repeating this, washing was performed for 14 hours. At this time, the amount of the scale dissolving agent used was 3,300 kg. As a result, the amount of scale removed was 155 kg.
Thus, it was about three times that of the conventional method.

Example 2 The cleaning was performed under the same conditions as in Example 1 except that the circulating flow rate of the circulating water (washing water) in the warm water zone HZ for washing water was increased with time. In this case, the change in the circulating water flow rate during the cleaning time is shown by curves A and B in the graph of FIG. 5, where curve A is the first test and curve B is the second test. As a result of performing the washing by increasing the circulation flow rate over time as described above, the scale amount removed is 259 kg,
This is about 4.9 times that of the conventional method and about 1.5 times that of the first embodiment.

As is clear from Examples 1 and 2 above, the scale adhering to the screen ring 7 was effectively removed, so that the amount of pulp washing water passing through the screen during operation was increased, and the pulp concentration was increased. Was reduced from 7% to 9%, and the amount of steam used in the cleaning heater was reduced from 50 tons per day to zero.

[0031]

According to the cleaning method of the first aspect of the present invention, since a high temperature difference is provided between the hot water in the hot water area for cleaning water and the water below the hot water area, the difference in density between the hot water and the water is obtained. The mixing of the two is prevented, and the decrease in the concentration of the scale solubilizer due to diffusion as in the conventional method is eliminated, whereby the concentration of the scale solubilizer in the circulating water can be maintained at a predetermined concentration,
The effect of removing scale can be significantly improved, and the amount of scale dissolving agent used can be minimized.

According to the second aspect, by setting the temperature difference between the hot water and the water to about 40 ° C. or more, the density difference between the hot water HW and the water CW is increased, and the mixing of the two is more reliably prevented. And the descaling effect is further improved.

According to the third aspect of the present invention, the washing water in the washing hot water area is discharged to the circulation path outside the bleaching tower through the drain box of the screen unit, so that the screen ring can be completely washed and the entire screen unit can be effectively used. Can be washed.

According to claim 4, 6 to 10% by weight of a nitrogen-containing carboxylic acid as a scale dissolving agent in the circulating washing water.
By adding caustic soda so as to maintain the pH and the pH 12 to 13, the scale can be more effectively removed.

According to the fifth aspect, the scale removing effect can be further improved by increasing the circulation flow rate of the circulating water with time.

According to the sixth aspect, by providing the heating means in the circulation path, the temperature of the circulating water can be raised as required, whereby the temperature difference between the hot water and the water is always kept high. Can be.

According to the seventh aspect, if a steam heater is used as the heating means, the equipment can be simplified and the circulating water can be efficiently heated.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an entire diffuser used for carrying out the method of the present invention.

FIG. 2 is a perspective view showing a scraper unit of the diffuser washer.

FIG. 3 is a perspective view showing a screen unit of the diffuser washer.

FIG. 4 is an explanatory view showing an apparatus for carrying out the method of the present invention.

FIG. 5 is a graph showing a change in a circulating water flow rate during a cleaning time in an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bleaching tower 2 Diffuser washer 3 Scraper unit 4 Screen unit 5 Vertical drive means of a screen unit 6 Rotation drive means of a scraper unit 7 Screen plate of a screen unit 8 Arm of a screen unit 9 Drain box of a screen unit 9a Extraction hole of a drain box 10 Ring pipe 20 Circulation path 21 Wash water tank 22 Pump 23 Steam heater (heating means) HW Hot water CW Water HZ Hot water area for wash water

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiyuki Miyagi 1 Tomioka-cho, Tonansu-cho, Anan-shi, Tokushima Oji Paper Co., Ltd. Tomioka Mill (72) Inventor Masa-shi Nagao 1-yoshida, Toyocho-cho, Anan-shi, Tokushima Oji Paper Co., Ltd., Tomioka Mill (72) Inventor Hiroyoshi Nagamura 1st Yoshida, Toyoshima-cho, Anan City, Tokushima Prefecture Oji Paper Co., Ltd., Tomioka Mill (72) Inventor, Masafumi Tanaka 1727- Nakasone-cho, Iyo Mishima City, Ehime Prefecture 1 Hakuto Co., Ltd. (56) References JP-A-1-250486 (JP, A) JP-A-4-18184 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) D21C 1/00-11/14

Claims (7)

(57) [Claims] 1. A washing method for washing and removing scale adhering to a screen ring of a screen unit in a diffuser washer installed at the top of a bleaching tower, wherein water is filled in the bleaching tower just below the screen ring, On top of this, a scale dissolving agent is added and mixed, and washing water consisting of warm water having a high temperature difference with respect to the water is filled so as to cover the upper part of the screen ring, and a washing hot water area is provided at the upper end of the bleaching tower. A method for cleaning a screen portion of a diffuser washer, wherein the screen water of the diffuser washer is formed, and the washing water in the hot water area is discharged to the outside of the bleaching tower, returned to the hot water area again through a circulation path, and used for circulation. 2. The method for cleaning a screen portion of a diffuser washer according to claim 1, wherein the temperature difference between the hot water as the wash water in the hot water area for washing and the water below the hot water area is about 40 ° C. or more. . 3. The method for cleaning a screen portion of a diffuser washer according to claim 1, wherein the cleaning water in the cleaning hot water area is discharged to a circulation path outside the bleaching tower through a drain box of the screen unit. 4. A carboxylic acid containing nitrogen atom at 6 to 10% by weight and a pH of 12 to 1 as a scale dissolving agent in circulating washing water.
The method for cleaning a screen portion of a diffuser washer according to any one of claims 1 to 3, wherein caustic soda is added so as to maintain the value of (3). 5. The method for cleaning a screen portion of a diffuser washer according to claim 1, wherein the circulation flow rate of the circulation cleaning water is increased with time. 6. The diffuser washer according to claim 1, wherein a heating means is provided in the circulation path to increase the temperature of the washing water flowing through the circulation path. Cleaning method. 7. The method for cleaning a screen portion of a diffuser washer according to claim 6, wherein the heating means comprises a steam heater.