JPH0679646B2 - Dehydration method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a dehydration treatment method for efficiently dehydrating a slurry containing a large amount of water such as sludge and industrial waste.

[Prior Art] Conventionally, when discarding a slurry such as sludge, it is necessary to sufficiently remove water contained in the slurry. Therefore, in the past, most of them have been processed by mechanical dehydration such as pressing.

However, in mechanical dewatering such as squeezing, with water drainage from the filtration surface during dewatering, compaction blockage due to concentration and deformation of slurry particles on the filtration surface occurs earlier than inside the cake, and the outflow of the filtrate occurs. Remarkably disturbed. As a result, even if the pressure such as squeezing was increased, only the compaction blockage on the filtration surface was further advanced, and the entire slurry could not be dehydrated efficiently.

Therefore, in recent years, electroosmotic dehydration has also been carried out utilizing the fact that negative charges are generated on the surface of slurry particles when the slurry particles come into contact with a liquid containing ions such as water. In this method, a negative electrode is provided in the vicinity of the filtration surface to repel the negatively charged slurry particles on the filtration surface, thereby reducing the consolidation phenomenon of the slurry on the filtration surface and facilitating the filtration of water. is there. Further, a composite dehydration method has also been proposed in which, after the mechanical dehydration described above, the water collected on the surface of the slurry particles by electric attraction is further electrically dehydrated by electroosmosis.

[Problems to be Solved by the Invention] A conventional treatment method by electroosmotic dehydration has a greater dehydration effect than mechanical dehydration methods such as squeezing and centrifugation. There has been a big problem in terms of energy efficiency such as a large amount of power being consumed.

In addition, even in a complex recent method of performing electroosmotic dehydration after mechanical dehydration, since mechanical dehydration is performed first, it is not possible to prevent the occurrence of the slurry consolidation phenomenon on the filtration surface, and it is possible to significantly improve the dehydration efficiency. could not.

Therefore, an object of the present invention is to significantly improve the dehydration efficiency and save energy by a novel combination of electroosmotic dehydration and mechanical dehydration.

[Means for Solving the Problems] In the dehydration treatment method of the present invention, a dehydration accelerator composed of a powdery foaming agent that generates gas by reaction with components of a charged slurry or self-decomposition is mixed with the slurry to be dehydrated. First
A second step of dehydrating the slurry containing a large number of bubbles formed by the use of the promoter by an electroosmosis method in which a direct current electric field is applied between a pair of electrodes sandwiching a filter; and a preliminary step by the electroosmosis method. And a third step of mechanically dehydrating the dehydrated slurry.

In a preferred aspect, the third step comprises a step of dehydrating through the filter in the same treatment tank as the second step.

Here, as the dehydration accelerator, a powder foaming agent such as aluminum powder having a foaming action can be used.

The powder foaming agent is referred to as a dehydration accelerator in the present specification, as will be described later, when the slurry in which bubbles are generated by the addition of the powder foaming agent (foaming slurry) is subjected to subsequent electroosmotic dehydration and mechanical treatment. This is because a great effect of promoting dehydration is exhibited in dehydration.

In addition, the dehydration accelerator is a foam mixed slurry (foaming slurry).
The mixing ratio is preferably 0.6 wt% of aluminum powder as shown in the examples for a slurry containing bentonite of 3.9 wt%, but the mixing ratio is not limited to this. Not something.

It is widely known that hydrogen gas is generated when aluminum powder is mixed with such an alkaline aqueous solution. That is, aluminum, which has a high ionization tendency, is dissolved as ions, and hydrogen ions are generated as gas correspondingly. It is well known that lightweight foam concrete and the like are manufactured from a foam slurry of aluminum powder. Further, in addition to the dehydration accelerator having a foaming action, a dehydration accelerator such as a water-absorbent polymer may be added. As a method of mixing the dehydration accelerator, stirring and mixing are desirable, but the mixing method is not particularly limited to this and other mixing methods are also possible.

Compressing is generally used as mechanical dehydration, but it is not particularly limited to compressing, and mechanical dehydration of various methods such as utilizing centrifugal force, vacuum, or pressurization can be used.

[Operation] The dehydration treatment method of the present invention is a dehydration treatment method having a series of steps in which a dehydration accelerator having a foaming action is mixed with a slurry, electroosmotic dehydration is performed, and then mechanical dehydration such as squeezing is performed. is there.

Depending on the dehydration accelerator, a large number of bubbles are generated in the slurry containing a large amount of water, and these bubbles enter between the slurry particles and transform the slurry into a sponge-like shape. It is considered that the water outflow rate increases with the increase. in this way,
Bubbles generated by the dehydration accelerator having a foaming action,
It has the effect of increasing the amount of dehydration compared to the outflow rate and reducing the amount of power consumption.

FIG. 3 shows the experimental result showing the effectiveness of this method. In this experiment, a bentonite slurry having a concentration of 3.9 WT% obtained by stirring and mixing bentonite with pure water was used as the slurry,
Aluminum powder is used as a dehydration accelerator having a foaming action.
0.6 wt% was used. According to the experimental results, in the case of a bentonite-only slurry that does not contain aluminum powder (indicated by · in the figure), a current of about 0.2 A continues to flow until the dehydration amount reaches about 70 ml, and the power consumption also sharply increases. ing.
On the other hand, in the case of a slurry in which aluminum powder is mixed with bentonite (indicated by ∘ in the figure), the current flowing immediately becomes about 0.03 A, which is about 1/7 of that when not mixed. The power consumption also rises slowly in proportion to the amount of dehydration. This means that if aluminum powder is not mixed, the amount of dehydration does not increase significantly even if a large amount of power is consumed, but by mixing aluminum powder, a large amount of water can be dehydrated with low power consumption. It is clearly shown.

It is thought that this reduction in power consumption is to increase the resistivity of water and reduce the DC power consumption unrelated to electroosmotic dehydration without significantly adversely affecting the electrostatic field due to the generation of a large number of small bubbles. . The reason for the improvement of the dehydration performance in the electroosmotic dehydration of the slurry mixed with air bubbles will be further described.

It is known that the amount of dehydration (fluid amount) Q in electroosmotic dehydration is proportional to the product of the resistivity of the slurry and the amount of current, that is, the applied voltage (for example, interface electric phenomenon: Kitahara, Watanabe, P107, Kyoritsu Shuppan). See KK). On the other hand, the power consumption is proportional to the product of the resistivity and the square of the amount of current, that is, the square of the applied voltage / resistivity. After all, it is understood that the dehydration performance can be improved while the power consumption is reduced due to the increase in the resistivity.

However, it has been difficult to increase the resistivity with an alkaline aqueous solution such as bentonite slurry. However, according to the present invention, it is not difficult to imagine that the inclusion of a large number of bubbles will increase the resistivity by increasing the length of the current path and reducing the cross-sectional area of the current path. And this was verified by the experiments described below.

Therefore, in carrying out the present embodiment, not only the aluminum powder but also a so-called powder foaming agent for generating a large number of bubbles may be mixed in the slurry as the dehydration accelerator. However,
As a matter of course, the alumina powder used as a flocculant or the like does not have a foaming action as a matter of course, so that it is obvious that the action of the present invention cannot be achieved.

In the method of the present invention, electroosmotic dehydration is performed before mechanical dehydration such as pressing. Therefore, during mechanical dehydration, the slurry has already separated into a cake layer and a water layer by electroosmosis. As a result, clogging of the filter and the like is prevented, and the dehydration efficiency in mechanical dehydration is further improved.

[Embodiment] A dehydration treatment method according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a process diagram showing the outline of this embodiment. FIG. 2 is a schematic configuration diagram of a dehydrating apparatus that performs the dehydrating treatment by the dehydrating treatment method of this embodiment.

The present example is a method for dehydrating a slurry, such as a sludge liquid, in which aluminum powder is used as a dehydration accelerator, and dehydration is performed by compression as mechanical dehydration.

As shown in FIG. 1, the steps of the present embodiment are performed by a pretreatment step of filtering the slurry to be treated to an appropriate concentration, a first step of mixing aluminum powder having a foaming action with the slurry, and a first step. The second step of electroosmotic dehydration of the obtained slurry, the third step of further dehydrating the cake-shaped slurry dehydrated by the second step by pressing, and the slurry cake obtained by the third step were discharged. Afterwards, it comprises a post-treatment step for cleaning the device.

As shown in FIG. 2, the dehydration treatment apparatus for dehydrating the slurry by the dehydration treatment method of the present embodiment is a pretreatment step of filtering the slurry and a first step of mixing the dehydration accelerator with the slurry. 1 treatment tank 1, a second treatment tank 2 for performing an electroosmotic dehydration step which is a second step, a mechanical dehydration step which is a third step, and a step which is a post-treatment step of discharging a cake and washing the apparatus. It consists of

The first processing tank 1 has an injection port 11 into which an undiluted solution of a slurry such as sludge is injected at the upper end, and has a substantially rectangular tank shape as a whole. And, it is connected to the second processing tank 2 at the connecting surface 1a which is one of the side surfaces. The bottom surface 16 has a slope that gradually decreases toward the connecting surface 1a. A communication hole 18 communicating with the processing space of the second processing tank 2 is formed at the lower end of the connecting surface 1a. Then, the slide-type shutter 17 opens and closes the communication hole 18.

Further, the first filter 15 is mounted on the side surface facing the connecting surface 1a in a state of being inclined inward from the vertical direction. The roughness of the mesh of the first filter 15 is set according to the filtering condition. An accelerator feeder 12 for charging aluminum powder, which is a dehydration accelerator having a foaming action, is installed on the upper surface. An agitator 14 for agitating and mixing and a drive motor 13 which is the power thereof are installed. The stirrer 14 has a spiral fin 141 and rotates to move the lower slurry upward. Further, a first drain 19 for draining the filtered water filtered by the first filter 15 is provided.

The second processing tank 2 has a tubular shape with a robust side wall. An actuator 24 is provided in an upper portion inside thereof and drives a compression plate 23 connected to the actuator 24. The second filter 22 held on the bottom by a solid holding member
Is provided. A pair of electrodes 21a and 21b are arranged on the lower surface of the compression plate 23 and the lower surface of the second filter 22. Below the second filter 22, a second drain 25 having a predetermined angle and integrally connected to the second filter 22 is provided.
It is rotatably supported by a pivot 26a. The second drain 25 includes a large number of cleaning nozzles 27a and a cleaning liquid injection part 27b.
And has a tip portion 251 formed of an elastic member such as rubber. Further, a releasable lock device 26b is provided at the opposite portion of the pivot portion 26a, and holds the end portion of the second filter 22. Further, a rotating device 28 for rotating its end portion with a wire or the like and holding it at a predetermined position.
Is installed.

A drainage section 29 that collects and drains the water discharged from the first drain 19 and the second drain 25 is arranged at the lowermost portion of the dehydrator.

(Pretreatment Step) A slurry such as sludge liquid for dehydration treatment is injected into the dehydrator through the inlet 11 of the first treatment tank 1. At this time, the communication hole 18 with the second processing tank 2 is closed by the shutter 17.

Once the slurry is infused, it is held for a predetermined time. The first filter 15 filters a certain amount of water.
It is possible to control the concentration of the slurry after being filtered to some extent by appropriately setting the eyes of the first filter 15. Further, since the first filter 15 is formed on the side surface and is inclined inward, even if there is an adhering substance, it easily falls due to its own weight, so clogging is less likely to occur. Even if clogging occurs, the clogging is likely to be removed by the spray or turbulent flow each time the slurry is injected.

By performing this pretreatment process, waste in the subsequent dehydration process can be reduced.

(First Step) In the first step, an aluminum powder as a dehydration accelerator is charged into the first treatment section 1 by the accelerator charging device 12. Then, the aluminum powder and the slurry are sufficiently stirred and mixed by the stirrer 14 rotated by the drive motor 13. The stirrer 14 has a spiral fin 141, and the lower part can be moved upward by rotation, so that the aluminum powder and the slurry are efficiently mixed. By doing so, the bubbles generated by the aluminum powder are evenly mixed in the slurry. In this embodiment, the amount of aluminum powder mixed in the slurry is, for example, 94% water content.
About 0.6% by weight of the slurry is about 0.6%. At this time, the volume of the slurry apparently increases by about 30% due to the generated bubbles.

(Second Step) The slurry in which the bubbles are sufficiently mixed in the first step is
When the shutter 17 slides upward, it flows into the second processing tank 2 through the communication hole 18 that connects the first processing tank 1 and the second processing tank 2. At this time, since the bottom surface 16 of the first processing tank 1 is inclined, the slurry can be easily moved. After the slurry has finished flowing into the processing space below the communication hole 18 of the second processing tank 2, the actuator 24 is brought into a free state and the compression plate is pressed.
23 is lowered by its own weight and brought into close contact with the upper surface of the slurry. The actuator 24 is set to be slidable in a free state in which the power source is stopped. For this reason, the pressing plate 22 can be lowered by its own weight, and can always be kept in close contact with the upper surface of the slurry while having an appropriate pressing force.

Then, a predetermined voltage is applied between the pair of electrodes 21a, 21b disposed below the second filter 22 on the lower surface and the bottom surface of the compression plate 23. At this time, the electrode 21a arranged on the lower surface of the compression plate 23
Is the positive electrode and the electrode 21 disposed below the second filter 22.
b is a negative electrode. In the slurry to which the voltage is applied in this way, the water attracted around the slurry particles is separated from the slurry particles by the electroosmotic action, and separated into the slurry particles and the water layer. Further, on the surface of the second filter 22, the slurry particles whose surface is negatively charged repel the negative voltage of the electrode 21b.
The compaction phenomenon of slurry particles on the surface hardly occurs.

In particular, the bubbles generated by the aluminum powder mixed in the slurry greatly accelerate the dehydration action by electroosmosis, so that the dehydration is efficiently performed.

The dehydrated water passes through the second drain 25 and is drained to the outside of the device by the drainage section 29.

(Third Step) The third step is a step of further dehydrating the electroosmotic dehydrated slurry of the second step by pressing.

The slurry is squeezed by driving the actuator 24 to push down the pressing plate 23 and applying an appropriate pressing force to the slurry. The water remaining in the slurry is squeezed and discharged from the second filter 22. At this time, since the slurry is separated into the slurry particles and the water layer during the electroosmotic dehydration in the second step, the water layer is pushed away from the slurry particles even in the mechanical dehydration by the pressing in this step. It becomes easy to be drained and dehydration is efficiently performed.

When performing this compression, since the compression plate 23 is already located below the communication hole 18, the slurry does not flow back through the communication hole 18 and the shutter 17 is not damaged.

The dehydrated water is drained to the outside of the apparatus by the drainage section 29 through the second drain 25.

All dehydration treatments are completed by the third step.

(Post-Processing Step) After the pressing plate 23 is slightly raised, the lock device 26b supporting the second filter 22 and the like is released. And the turning device 2
By operating 8, the second filter 22 and the like rotate downward about the pivotal portion 26a as a rotation center, and the cake formed by the dewatered residue of the slurry is discharged to the outside by its own weight. When the cake is not completely discharged, the pressing plate 23 is lowered to forcibly discharge the cake.

After discharging the cake, the rotating device 28 is operated to pull up the end portion of the second filter 22, and when the tip end 251 of the second drain 25 is positioned slightly above the discharging portion 29, the rotating device 28
To stop. At this time, the end of the second filter 22 is completely exposed to the outside from the lower end of the side wall of the second processing tank 2. In this state, the cleaning liquid injected from the cleaning liquid injecting section 27b is supplied with a large number of cleaning nozzles 27 arranged on the upper surface of the second drain 24.
It is sprayed from below the second filter 22 and the electrode 21b by a. As a result, the second filter 22 and the like are washed. Since the end portion of the second filter 22 is completely exposed to the outside from the lower end of the side wall of the second processing tank 2, the dirt and deposits remaining on the upper surface of the second filter 22 also flow out and are discharged. It is discharged to the outside by the part 29.

After the cleaning is completed, the rotating device 28 is driven again, the second filter 22 and the like are arranged at the initial position, and the locking device 26
b operates and holds the second filter 22 and the like.

[Effects of the Invention] As is clear from the above description, in the dehydration treatment method of the present invention, electroosmotic dehydration is carried out after mixing a dehydration accelerator, which is a powder foaming agent having a foaming action, into a slurry to be dehydrated. As a result, a higher dehydration effect can be realized as compared with the conventional electroosmotic dehydration, and moreover, power consumption can be reduced.

Further, since the dehydration treatment method of the present invention is a method of performing electroosmotic dehydration before mechanical dehydration, during mechanical dehydration, the slurry is separated into a cake layer and a water layer, and also the filter is clogged. Since this can be prevented, the dehydration efficiency can be further improved.

The configuration and operational effects of the dehydration method of the present invention described above are summarized below.

First, the dehydration method of the present invention is characterized in that it mechanically dehydrates after electroosmotic dehydration of a bubble slurry containing a large number of bubbles formed by mixing a dehydration accelerator composed of a powder foaming agent. .

In this way, the following effects can be obtained.

First, it is possible to improve the dehydration efficiency while reducing the waste of DC power consumption, which was a drawback of the conventional electroosmotic dehydration, in each stage.

Also, the cake layer deposited above the filter by electroosmotic dehydration naturally contains a large number of bubbles. These bubbles in this cake layer are easy to move, crush, or deform due to the urging force such as squeezing in the subsequent mechanical dewatering process, and the cavities in the cake layer where these bubbles were present move water. The water can be smoothly transported to the filter side as a road.

Further, in a preferred aspect of the present invention, further dehydration is carried out by squeezing through the filter used in the electroosmotic dehydration in the treatment tank which has been subjected to the electroosmotic dehydration.

By doing so, the filter is not clogged by the bias of the slurry particles in the anti-dehydration direction due to the action of the electrostatic field in electroosmotic dehydration (the cake layer is separated from the filter and is close to the electrode on the slurry side). Because it is formed),
The mechanical filtration efficiency of the subsequent filter can be increased.

This is the point that the conventional electro-osmotic dehydration / mechanical dehydration method is fundamentally different from the method of first performing preliminary dehydration of the slurry by mechanical dehydration and then performing electro-osmotic dehydration. When mechanical dewatering is first performed in this way, the filter is clogged with slurry particles, which also reduces the filtration efficiency of the subsequent electroosmotic dewatering.

However, when such electroosmotic dehydration of the present invention is performed first and then mechanical dehydration is performed, the amount of water (the amount of treatment) that is different from that of electroosmotic dehydration is large, and power consumption increases. This problem is solved by the increase in resistivity due to the above-mentioned bubble dispersion.

[Brief description of drawings]

FIG. 1 is a schematic process diagram of a dehydration treatment method according to an embodiment of the present invention, and FIG. 2 is a schematic configuration diagram of a dehydrator used in this embodiment. FIG. 3 is an experimental result showing the effectiveness of the dehydration accelerator having a foaming action in the present invention. 1 ... First treatment tank, 2 ... Second treatment tank 12 ... Accelerator injector, 14 ... Stirrer 21a, 21b ... Electrode 22 ... Second filter, 23 ... Squeeze plate

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Claims (2)

[Claims] 1. A first step of mixing a dehydration accelerating agent, which is a powdery foaming agent, which generates a gas by reaction with components of a charged slurry or self-decomposition with a slurry to be dehydrated, and a case where the accelerating agent is formed. A second step of dehydrating the slurry containing a large number of air bubbles by an electroosmosis method in which a direct current electric field is applied between a pair of electrodes sandwiching a filter; and a mechanical step of mechanically treating the slurry preliminarily dehydrated by the electroosmosis method. And a third step of dehydrating. 2. The dehydration treatment method according to claim 1, wherein the third step comprises a step of dehydrating through the filter in the same treatment tank as the second step.