JP3635816B2 - White water recovery device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a white water recovery apparatus for processing white water generated in a papermaking process so that it can be reused. Specifically, the present invention relates to a white water recovery device that can stably perform a white water recovery operation.
[0002]
[Prior art]
Wastewater such as washing, dilution, dehydration, etc. in the pulp manufacturing process and drainage from the paper machine's wire mesh is called white water. In addition to fibers, this white water contains various chemicals, fillers and other solid substances or various soluble substances.
[0003]
Conventionally, white water is subjected to pressure levitation treatment, coagulation sedimentation treatment, and disk filter treatment to recover white water. Further, after such a primary treatment, a secondary treatment by filtration such as sand filtration, fiber filtration, two-layer filtration, filter medium filtration and the like is also performed.
[0004]
Moreover, adding a slime control agent to such primary treatment or secondary treatment water is also performed. As an inorganic slime control agent, sodium hypochlorite or the like is used. Various organic slime control agents (antibacterial agents) such as dibromonitrilopropionamide are used.
[0005]
[Problems to be solved by the invention]
The conventional example has the following problems.
[0006]
(1) When white water is subjected to primary treatment and then subjected to secondary treatment and highly purified treatment, if the quality of the primary treatment water fluctuates, sufficient secondary treatment water quality cannot be obtained. In general, in the paper manufacturing process, white water of high SS may be suddenly generated due to, for example, a piece of paper in a paper machine, and primary treated water may also suddenly become high SS. When the quality of the primary treatment water deteriorates, the secondary treatment (filtration process) device is clogged, and the filtration status changes (volume filtration becomes surface filtration, resulting in a decrease in filtration capacity. Etc.) and the stable filtration operation is hindered. In addition, backwashing is performed when the filtration device is clogged. However, if the frequency of backwashing increases, not only the operation efficiency of the device decreases but also the amount of backwashing water increases.
[0007]
(2) White water has high BOD and COD, and slime is easily generated. For this reason, a slime control agent is added, but if a large amount of the slime control agent is added, it will remain in the recovered water, causing discoloration and other effects on products made with this recovered water. Conversely, if the amount of slime control agent added is too small, the generation of slime cannot be sufficiently suppressed. In this way, since the amount of addition must be controlled so as not to affect the papermaking system while preventing slime generation, the amount of addition of the conventional slime control agent should be controlled to an appropriate amount. Was difficult.
[0008]
An object of the present invention is to solve the above-mentioned conventional problems and to provide a white water recovery apparatus capable of stably performing white water treatment at a low cost.
[0009]
[Means for Solving the Problems]
The white water recovery apparatus of the present invention performs the solid-liquid separation after adding the flocculant to the white water, followed by solid-liquid separation, and adding the slime control agent to the effluent water of the first processing means. A white water recovery device comprising a second processing means, wherein the effluent water of the second processing means is recovered water, and further comprises a turbidity detection means for detecting the turbidity of the effluent water of the first processing means; And a means for controlling the addition amount of the flocculant in the first processing means based on the detected value of the turbidity detecting means .
[0010]
In such a white water recovery apparatus of the present invention, the flocculant is added to the white water in the first processing means, followed by solid-liquid separation, and then the slime control agent is further added in the second processing means, followed by solid-liquid separation. Thus, SS can be sufficiently removed. In addition, since the slime control agent is added to the effluent of the 1st processing means, the slime generation | occurrence | production in the solid-liquid separation apparatus of a 2nd processing means can be suppressed.
[0011]
In this invention, you may provide the 3rd process means which adds a slime control agent to the outflow water of a 2nd process means, and uses it as recovery water.
[0012]
In the present invention, further provided with a slime detection means for detecting a slime occurrence before Symbol recovered water, slime control in at least one of the second and third processing means based on a detection result of the slime detecting means It is preferable to provide a means for controlling the additive amount.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a system diagram of the white water recovery apparatus according to the embodiment.
[0014]
The white water is added with a flocculant from the flocculant addition device 1 and, if necessary, a zeta potential adjusting agent is added from the addition device 2 and then introduced into the solid-liquid separation device 3 for solid-liquid separation treatment. . The separated solid is returned to the papermaking system. The liquid component is introduced into the first water tank 4 where the slime control agent is added by the addition device 5. Further, turbidity is detected by a turbidimeter 6 provided in the first water tank 4.
[0015]
This turbidity detection signal is input to the controller 20, and the controller 20 controls the flocculant adding device 1 and the zeta potential adjusting agent adding device 2 so that the detected turbidity is equal to or lower than a predetermined value.
[0016]
The outflow water from the first water tank 4 is filtered by the filtering device 7. The solid content filtered by the filtering device 7 is discarded or recovered.
[0017]
The filtered water from the filtering device 7 is introduced into the second water tank 8 where an organic slime control agent is added from the slime control agent adding device 9 as necessary. The outflow water from the second water tank 8 is sent to a papermaking system or a raw material system by an outflow line 10. A slime monitor 11 is provided in a bypass line 12 provided alongside the line 10, and a detection signal of the slime monitor 11 is input to the controller 21. And the slime control agent addition amount from the addition apparatuses 5 and 9 is controlled so that the slime amount detected with the slime monitor 11 may be below a predetermined value.
[0018]
The flocculant added by the flocculant adding apparatus 1 is preferably a polymer flocculant. The addition amount of the polymer flocculant is controlled by the controller 20, but is usually in the range of about 0.5 to 20 mg / L.
[0019]
The coagulation effect is improved by adding a zeta potential adjusting agent together with the coagulant. As this zeta potential adjusting agent, polystyrene sulfonic acid or a salt thereof, dimethylamine-epichlorohydrin condensate, diisobutylene maleate or a salt thereof can be used. The addition amount of the zeta potential adjusting agent is also controlled by the controller 20, but is usually in the range of about 0.5 to 50 mg / L.
[0020]
As the solid-liquid separation device 3, a pressure flotation separation device is suitable, but a coagulation precipitation device, a disk filter, or the like can also be used. The SS concentration in the water flowing into the first water tank 4 from the solid-liquid separator 3 is preferably 150 ppm or less, particularly 50 ppm or less. If the SS concentration is 150 ppm or less, particularly 50 ppm or less, the formation of a mat-like SS layer in the filtration device 7 is small, stable operation is possible, and the frequency of backwashing is low.
[0021]
Since the SS concentration is proportional to the turbidity, the relationship between the turbidity and the SS concentration is obtained in advance, and the value of the turbidimeter 6 provided in the first water tank 4 is converted into the SS concentration. The turbidimeter 6 is preferably provided with a mechanism for periodically cleaning so that dirt on the sensor portion can be removed. The turbidimeter 6 is preferably one that can continuously measure turbidity. Instead of providing the turbidimeter 6 in the first water tank 4, it may be provided in a pipeline before or after the turbidimeter 6.
[0022]
In addition, when the turbidity detected by the turbidimeter 6 is extremely increased (for example, exceeding 200 ppm) due to a sudden increase in SS of white water, the water in the water tank 4 is not supplied to the filtration device 7 as it is but provided separately. It is preferable that the filter device 7 is supplied to the filtration device 7 after being detoured to the filter device. Further, such high SS water may be sent from the water tank 4 to another wastewater treatment system and not supplied to the filtration device 7.
[0023]
Examples of the slime control agent added to the first water tank 4 from the addition device 5 include inorganic and organic slime control agents. Examples of inorganic slime control agents include sodium hypochlorite, chlorine, chlorine dioxide, and hydrogen peroxide.
[0024]
On the other hand, examples of the organic slime control agent include 2,2-dibromonitrilobropionamide (DBNPA), 5-chloro-2,4,6-trifluoroisophthalonitrile, 4,5-dichloro-1,2- Dithiol-3-one, 2,2-dibromo-2-nitroethanol, bis (1,4-bromoacetoxy) -2-butene, methylenebisthiocyanate (MBTC), 5-chloro-2-methyl-4-isothiazoline- 3-one or a metal salt thereof, dimethoxycarbamate, benzyl bromoacetate and the like can be mentioned. These can be used alone or in combination of two or more, and from the standpoint of preventing the generation of resistant bacteria, for example, they can be used alternately every 1 to 3 months.
[0025]
Of the inorganic slime control agent, the addition amount of the chlorine-based slime control agent is controlled by the controller 21 described later, but the concentration in water after addition is 0.05 to 1 mg / L, particularly 0.1 to 0.1 chlorine concentration. It is preferable to control to be 0.5 mg / L. On the other hand, although the addition amount of the organic slime control agent is also controlled by the controller 21, it is generally 0.5 to 300 mg / L, preferably about 1 to 50 mg / L.
[0026]
By adding a slime control agent to the first water tank 4, slime generation in the water tank 4 and the filtration device 7 can be suppressed.
[0027]
When a high concentration slime control agent is added from the addition device 5, most of it is consumed by the filtration device 7. Therefore, in order to maintain the effect up to the treated water side, the addition amount from the addition devices 5 and 9 is remarkably large. There is a need to. The addition amount of the slime control agent from the addition device 5 is only the amount necessary to prevent clogging of the filter medium, and it is added separately from the addition device 9 to prevent the slime in the recovery system, thereby reducing the consumption of the slime control agent. Therefore, it is preferable.
[0028]
As the filtering device 6, in addition to a filter medium filtering device (sand filtering device, two-layer filtering device) and a fiber filtering device, a membrane filtering device such as MF or UF can also be used.
[0029]
As the slime control agent added from the addition device 9 in the second water tank 8, the organic slime control agent (antibacterial agent) as described above is suitable.
[0030]
This organic slime control agent may be added continuously or intermittently.
[0031]
In addition, when an inexpensive inorganic chlorine-based slime control agent is used, it is preferably added from the addition device 5 and the organic slime control agent is added by the addition device 9. If it does in this way, the residual chlorine concentration in the effluent from line 10 can be reduced, and the trouble by chlorine in a papermaking process can be prevented. In addition, the amount of organic slime added from the addition devices 5 and 9 can be reduced to about 1/2 to 1/6, for example, compared to when the organic slime control agent is used alone, and there is no influence on the paper.
[0032]
As the slime monitor 11, as shown in FIG. 2, a slime adhesion tester comprising a stationary outer cylinder 31 and a rotating inner cylinder 32 is suitable.
[0033]
When sample water is continuously supplied between the outer cylinder 31 and the inner cylinder 32, a biofilm (slime) grows and adheres to the surface of the inner cylinder. A torque meter is attached to the rotating shaft 33 of the inner cylinder 32, and a torque that increases in accordance with the amount of biofilm attached is recorded through a torque transducer, thereby continuously recording the amount of biofilm growth.
[0034]
When slime adheres to the surface of the internal cylinder 32, the torque for rotating the internal cylinder 32 increases. Therefore, the internal cylinder 32 is measured by measuring this torque (or a physical quantity corresponding thereto, for example, a motor energization current value). It is possible to detect the amount of slime adhering to the water and to detect the occurrence of water-based slime.
[0035]
In addition to such a torque meter type slime monitor, a known differential pressure type slime monitor can also be used.
[0036]
As shown in FIG. 1, the slime monitor 11 is installed in the bypass line 12, and the inside of the white water treatment apparatus can be predicted during operation by continuously monitoring the occurrence of slime, and the use point at the end of the treated water line 10 It is possible to predict dirt (such as a shower line). Further, when the monitor detects subtle stains, the signal can be input to the controller 21 and used to adjust the amount of the slime control agent added, thereby preventing slime troubles.
[0037]
【Example】
Example 1
White water (pH 7.8, 25-29 ° C.) from a neutral papermaking machine was treated according to the flow of FIG. The average SS concentration of white water is 10 to 30 ppm, about 50% of the SS component is pulp fiber, and the remaining about 50% is inorganic SS.
[0038]
A diallylammonium cationic polymer was used as the polymer flocculant. The added amount is 1 ppm when the SS concentration obtained from the turbidity detected by the turbidimeter 6 is 50 ppm or less, 2 ppm when the SS concentration is 50 ppm or more, 2 ppm is maintained until it drops to 30 ppm, and then becomes 30 ppm or less. It was supposed to return to 1 ppm.
[0039]
As the solid-liquid separator 3, a pressure levitation separator was used.
[0040]
As the turbidimeter 6, Tx Pro-T, WP-302 manufactured by Spectox Co., Ltd. was used.
[0041]
As the filtration device 7, a high-speed two-layer filter (LV = 40 m / Hr, filter medium: anthracite with a particle size of 3 mm and sand with a particle size of 1.7 mm) is used, and the differential pressure between the filter tower outlet and the inlet is 1800 mmAq or more. When it became, it was backwashed. As the slime monitor 11, the one shown in FIG. 2 comprising a rotating inner cylinder 32 (SUS304 rotor) having a diameter of 65 mm and a stationary outer cylinder 31 having an inner diameter of 160 mm (3 L of retained water) is used, and the inflow water amount is 9 L / Hr. It was. A Brookfield torque meter (using a rotational viscometer RE500H manufactured by Toki Sangyo Co., Ltd.) was attached to the rotating shaft of the internal cylinder 32, and the torque during the operation period was automatically recorded every hour via the controller. The number of revolutions was 100 rpm, and the entire cylinder part was immersed in a constant temperature water bath to keep the temperature at 30 ° C.
[0042]
Sodium hypochlorite was added from the addition device 5, and an organic slime control agent formed by blending DBNPA and MBTC at a ratio of 4: 1 was added from the addition device 9. The amount added was controlled as follows. Normal addition amount (when slime monitor detection torque is 300 μN · m or less)
Adder 5: ₂ ppm asCl ₂ continuous addition (residual chlorine concentration in water tank 4 at this time was 0.2 to 0.5 ppm)
Adder 9: 3 times a day, when the detected torque of the added slime monitor exceeds 15 μm per 15 ppm for 15 minutes Adder 5: Increase the continuous addition amount to 3 ppm asCl ₂ Adder 9: Add the amount per addition Increase to 30ppm [0043]
As a result, treated water having an average SS concentration of 2 to 4 ppm was stably obtained from the line 10, and no slime was generated over 30 days. The residual chlorine in this treated water was about 0.1 ppm, and no chlorine trouble occurred in the paper machine.
[0044]
The frequency of backwashing of the filtration device 7 was extremely small, once every 5 hours on average.
[0045]
In addition, the turbidimeter 6 cleaned the sensor part with the wiper once every 30 minutes. Thereby, turbidity could always be detected with high accuracy.
[0046]
Comparative Example 1
The white water was treated in the same manner as in Example 1 except that the flocculant addition amount control based on the detected value of the turbidimeter 6 was not performed and the flocculant was added at a constant rate of 1 ppm from the addition device 1. The frequency was once every 30 minutes and was extremely high. Further, when the SS concentration in white water became 200 ppm or more, SS was generated in a mat shape on the surface of the filter medium of the filtration device 7. This mat-like SS could not be removed by backwashing, and operation was impossible .
[0047]
Real施例2
In Example 1, an alarm is set so that the turbidimeter 6 operates at 200 ppm or more, and when the detected turbidity becomes 200 ppm or more, the water supply to the filtration device 7 is stopped, and the water in the water tank 4 is separated. It was sent to the wastewater treatment facility. Thereafter, when the turbidity returned to less than 200 ppm, the same operation as in Example 1 was performed. As a result, the filtration device 7 could be operated more stably.
[0048]
Example 3
In Example 1, when the turbidity detected by the turbidimeter 6 was 200 ppm or more, the water in the water tank 4 was passed through a screen filter and then supplied to the filtration device 7. Thereby, the filtration device 7 could be operated extremely stably.
[0049]
【The invention's effect】
As described above, according to the present invention, white water can be stably recovered. According to the present invention, troubles due to SS and slime of the solid-liquid separation means can be surely prevented, and a recovery processing operation can be performed stably over a long period of time. Further, according to the present invention, it is possible to prevent generation of slime of recovered water and to prevent chlorine trouble when the recovered water is reused in the papermaking process.
[Brief description of the drawings]
FIG. 1 is a system diagram of a white water recovery apparatus according to an embodiment.
FIG. 2 is a cross-sectional view of a slime monitor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Flocculant addition apparatus 2 Zeta potential regulator addition apparatus 3 Solid-liquid separation apparatus 5,9 Slime control agent addition apparatus 6 Turbidimeter 7 Filtration apparatus 11 Slime monitor

Claims (3)

A first treatment means for solid-liquid separation after adding a flocculant to white water;
A white water recovery device comprising a second processing means for solid-liquid separation after adding a slime control agent to the effluent water of the first processing means, and using the effluent water of the second processing means as recovered water. ,
Further, a turbidity detecting means for detecting the turbidity of the effluent water of the first processing means, and a means for controlling the addition amount of the flocculant in the first processing means based on the detection value of the turbidity detecting means. A white water recovery device comprising:   The white water recovery apparatus according to claim 1, further comprising a third processing means for adding a slime control agent to the effluent water of the second processing means to obtain recovered water. 3. The slime detection means according to claim 1 or 2 , further comprising a slime detection means for detecting a slime generation status in the recovered water, and means for controlling the amount of slime control agent added based on the detection result of the slime detection means. White water recovery device.

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