JP2001198569A - Pressurized floating separation method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressurized flotation separation method which enables the separation and removal of agglomerated suspended substances in a raw liquid by forming a descending flow of the raw liquid to be treated and an ascending flow of fine bubbles, uniformly and countercurrently bringing the liquid into contact with the bubbles, and effectively floating and separation the suspended substances without breaking a flocculated material being easily broken. SOLUTION: In the pressurized flotation separation method comprising supplying the raw liquid to be treated from the upper part of a pressurized flotation separation tank, simultaneously forming fine bubbles from the lower part by introducing pressurized water containing dissolved gas and countercurrently bringing the raw liquid into contact with the fine bubbles, at least one nozzle having a hollow frustum shape, in which the bottom part is used as an ejecting part and which has a form defined by following formula: 8<=A/a<=14 and 12 deg.<=θ<=35 deg. (wherein, A is the cross-sectional area of the pressurized flotation separation tank, a is the cross-sectional area of ejecting part of the nozzle, and θ is the opening degree of the nozzle), is arranged per 10 m2 of the cross-sectional area of the pressurized flotation separation tank, and the raw liquid is supplied while setting the discharging part of the nozzle in the upward direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure flotation method and an apparatus therefor, and more particularly, to a method of supplying a stock solution to be treated in a predetermined manner, thereby improving the rate of flotation separation of suspended substances and the like contained in the stock solution. The present invention relates to a pressure flotation separation method and an apparatus therefor.

[0002]

2. Description of the Related Art In the treatment of clean water, sewage, medium water, industrial water and waste water, etc., centrifugal separation using centrifugal force and sedimentation using gravity are used to separate and remove oil and suspended substances in the liquid. The technique of flotation separation is also widely applied because the operation is simple and the economy is high. Sedimentation is a method in which suspended substances in a liquid to be treated (in most cases, water) are separated by sedimentation and sedimentation. Flotation is a method in which suspended substances contained in a liquid to be treated are placed on the liquid surface. It is a method of removing by floating. A suspended substance having a specific gravity larger than that of the stock solution can be separated by sedimentation, and a suspended substance having a specific gravity smaller than that of the stock solution can be naturally floated and floated and separated. However, floc-like flocculated suspended substances such as algae and activated sludge are not easy to settle and separate by flotation.For this reason, fine bubbles are attached or included to reduce the apparent specific gravity and forcedly float. To separate. In this case, the fine bubbles usually have an average particle size of 30 to 150 μm so that the fine bubbles easily adhere to the suspended substance or the like and the disturbance due to the rising of the bubbles does not destroy the floc.
m.

[0003] As a method for generating fine bubbles having a small particle diameter as described above, various methods have conventionally been adopted. For example, there is a method of making finer by mechanical shearing force, or ejecting from a sparger such as a fine perforated plate. However, the most preferred method is a method in which fine bubbles are released by introducing air-dissolved pressurized water in which air is dissolved in pressurized water (liquid) into a treatment system under the atmosphere, which is well known as a pressurized flotation method. Have been. In addition, for suspended substances that are to be separated and removed, by adding a flocculant and flocculating to grow into larger flocs,
The treatment is performed so as to improve the contact efficiency with the fine bubbles and to facilitate the adhesion and the like of the fine bubbles. There are various methods for contacting the stock solution to be treated with the air-dissolved pressurized water.

[0004] As a conventional general method, for example, FIG.
As shown in the schematic cross-sectional view, a pressurized flotation tank 40 of a cylindrical tank is used to apply air-dissolved pressurized water 42
There is a method in which the water is mixed and jetted upward from the bottom of the central liquid supply tube 43 of the pressurized floating separation tank 40 to float the liquid. In this case, the fine bubbles released from the air-dissolved pressurized liquid and the stock solution to be processed come into contact in parallel while rising together in the central liquid supply cylinder 43, and the suspended substance in the stock solution to be processed adheres or contains bubbles. And unite. In addition, the suspended matter combined with the fine bubbles and the bubbles flowing out from the top of the central liquid supply tube 43 further rises and is separated from the processing solution, reaches the surface of the liquid surface, is scraped by the skimmer 44, and is lifted by the floating material discharge portion 45. And is discharged from the processing system through the discharge port 46. On the other hand, the processing liquid flows downward as indicated by the arrow in the figure, and flows out of the processing system from the processing water outlet 47 through an outflow plate such as a perforated plate disposed below the pressurized flotation tank 40.

[0005] As shown in FIG. 5, a pressurized flotation tank 50 is divided into a contact area 51 and a separation area 52. And air is introduced by circulating and pressurizing a part of the treated water, and is introduced into the lower part of the contact area 51 by using it as an air-dissolving pressurized liquid in the air dissolving tower 54. In this method, as shown by the broken line in FIG.
When the air-dissolved pressurized liquid is mixed and introduced into the upper part of the contact area 51, the raw liquid 53 to be processed and the microbubbles supplied in the same manner as in the method of FIG. When the pressurized air-dissolved liquid is introduced into the lower part, the contact efficiency is improved by the counter-current mixing contact as compared with the co-current flow. Regardless of the introduction of any air-dissolved pressurized liquid, the separated suspended substance and the processing liquid that have reached the liquid surface flow into the adjacent separation area 52 and are held for a predetermined time, so that the separated suspended substance on the liquid surface is removed. At the same time, the wastewater is collected by a schema or the like and discharged out of the processing system, and at the same time, the treated water 55 flowing downward in the separation area is collected outside the separation tank 50.

[0006]

The processing time in the above-mentioned pressure flotation method is mainly the moving time of the suspended substance and the time required to reach the liquid surface of the floc combined with the bubbles, and generally about 10 to 10 minutes. 30 minutes. It is necessary to efficiently contact the stock solution to be treated and the fine bubbles, and to maintain the adhered state for the required time. However, in particular,
In the above-described parallel flow contact method, since the liquid flows in the same direction as the undiluted solution to be treated, the contact efficiency is lower than in the countercurrent contact, and there is a possibility that the coalescing with the fine bubbles may not be performed smoothly. In addition, the liquid flow in the processing system may be disturbed, and the bubbles once coalesced may be separated. Many of the suspended substances contained in the undiluted solution to be processed generally have a higher specific gravity than the liquid and are suspended. The substance cannot reach the liquid surface. In general, the flocculated flocculated large suspended substance has an increased contact ratio with fine bubbles and is easily integrated with bubbles such as adhesion. It is also assumed that the flocculated flocs are usually much larger than the microbubbles, so that they are not easily separated.

However, even if the contact efficiency between the microbubbles and the flocculated floc suspended material is improved by adopting the countercurrent contact system shown in FIG. 4 or changing the flow state such as stirring, floc destruction does not occur. To be limited.
In addition, the coalesced state of the microbubbles and the floc-like suspended substance is merely adhesion, and since the specific gravity of both is larger than the specific gravity of the stock solution to be processed, the suspended substance is heavier and the microbubbles are lighter. Suspended substances are easily released, and easily separated due to turbulence of the liquid flow in the flotation tank or shearing force with the fluid. Further, in the above-mentioned method in which the flotation / separation tank is divided into a contact area and a separation area, a time for moving to the separation area is required. There is also. Even if the untreated solution and the microbubbles are brought into contact with each other by any of the conventional methods, the discharge of the pollutants may not be performed smoothly from the system as described above. However, there was a problem that the suspended matter removal rate was reduced. In particular, in the parallel flow contact method shown in FIGS. 4 and 5, the amount of suspended solids flowing out of the treated water is generally larger than the amount of suspended solids in the treated water by the coagulation sedimentation method.

Various devices have already been devised to solve the above problems. For example, a method of adding a surfactant to air-dissolved pressurized water to modify the properties of the air bubble surface so that the generated fine air bubbles easily adhere to the suspended substance floc, and a method for quickly discharging the floating floc out of the system. Mechanical or structural improvements. However, the nature of the suspension, the form and behavior of the suspended substance are complicated, and their application requires an agglutination test using the target stock solution to be treated and a separation test using a small pilot plant. Improvements cannot be a fundamental solution. Therefore, even for a dilute suspension containing a suspended substance that is difficult to precipitate and separate, a coagulation sedimentation method is often used despite the fact that the treatment is not simple without using a coagulation pressure flotation method. .

Generally, the rising speed of the flocculated floc combined with the microbubbles is several times faster than the sedimentation speed of the flocculated floc alone. While it is industrially preferable that the removal of suspended substances is possible in 2 to 1/5, it is pointed out that the removal rate of suspended substances is low, and it has been widely applied to clarification of suspended substance-containing liquids. It has not been. According to the counter-current flotation method as described above, it was expected that the same suspended solids removal rate as that of the sedimentation method could be achieved.However, the counter-current flotation tank was used for test equipment and small-scale equipment. Only had been adopted. As described above, at present, the pressurized flotation method is widely used as a sludge concentration technique without widespread use as a purpose of clarifying a suspension containing a suspended substance as compared with the coagulation sedimentation method. It's just The present invention, in view of the current state of the pressure flotation method, using a simple operation and industrially excellent pressure flotation for the clarification treatment of the suspension, to improve the flotation removal rate of suspended substances, In order to obtain a treated water having a desired turbidity, the conventional pressure flotation method was studied diligently.

As a result, for example, a commercially available flotation tester, and in a small-scale water treatment, a batch-type and continuous flotation separation employs a countercurrent contact system to obtain a high removal rate of suspended solids. Nevertheless, in an industrial large-scale flotation method, a horizontal flow method in which the contact area and the separation area are divided as shown in FIG. 5 or a co-current flow as shown in FIG. A flotation device of the type is employed. As a result of further study on the reason why the countercurrent flotation device is not used in large-scale industrial equipment, it was found that the amount of suspended solids obtained by a small countercurrent contact flotation device for testing such as pilot plants was high. In order to maintain the removal rate, we learned that there was no sufficient study, research, and consideration to perform scale-up properly so far, and from a small pressurized flotation separator to a large-scale pressurized flotation The present inventors have found a design method capable of clarifying a suspended substance at a high removal rate by a countercurrent contact method up to a separation device, and completed the present invention.

[0011]

According to the present invention, a raw solution to be treated containing a coagulant is supplied from an upper part of a pressurized flotation tank, and gas-dissolved pressurized water is introduced from a lower part to generate fine bubbles. A pressurized flotation method in which the stock solution and the microbubbles are brought into countercurrent contact with each other, wherein the nozzle having a frustum with a bottom as a discharge section and having a form represented by the following formulas (1) and (2) is provided. A pressure flotation method is provided, wherein at least one unit is provided per 10 m ^{2 in} cross section of the pressure flotation / separation tank, and the undiluted solution is supplied with the discharge part facing upward. However, in the following equations (1) and (2), A is the cross-sectional area of the pressurized flotation tank, a is the cross-sectional area of the nozzle discharge section, and θ is the opening of the nozzle. 8 ≦ A / a ≦ 14 (1) 12 ° ≦ θ ≦ 35 ° (2)

According to the present invention, there is provided a pressure-flotation / separation apparatus having a frustum at the center of the cross section of a separation tank, a bottom having a discharge section, and having a form represented by the following formulas (1) and (2). At least one processing stock solution supply nozzle is provided per 10 m ^{2 of the} sectional area of the pressurized flotation tank with the discharge section facing upward, and a gas-dissolved pressurized water inlet and a baffle plate are provided vertically below the nozzle. In addition, there is provided a pressure flotation / separation apparatus, wherein the gas-dissolved pressurized water inlet is an orifice nozzle and is disposed so as to be able to jet toward the baffle plate. However, in the following equations (1) and (2), A is the cross-sectional area of the pressurized flotation tank, a is the cross-sectional area of the nozzle discharge section, and θ is the opening of the nozzle. 8 ≦ A / a ≦ 14 (1) 12 ° ≦ θ ≦ 35 ° (2)

The pressure flotation method of the present invention is constituted as described above, and a suspended substance, in particular, a stock solution containing flocculated floc which is flocculated and fragile, is discharged into a flotation tank by discharging a predetermined bottom of a frustum. And then supply it by injecting it upward by means of a nozzle, and then convert it into a downward flow due to the specific gravity of the stock solution to be processed, and simultaneously release the air pressurized solution from below in the flotation separation tank to produce fine bubbles. And raise it. Since the stock solution to be treated and the fine bubbles are brought into countercurrent contact with each other, the contact efficiency is large and the fine bubbles can be easily attached to and contained in the flocculated floc-like suspended solid to be combined.

Further, the nozzle configuration for supplying the stock solution to be treated is set in accordance with the sectional area of the flotation tank, and the air pressurized solution is brought into contact with a baffle plate disposed below to form fine bubbles. The rising flow of the undiluted solution to be treated and the rising flow of fine bubbles in the flotation tank are uniformly maintained without any drift or turbulence, and the contact between the undiluted solution to be treated and the fine bubbles is always smooth. Done. In addition, since the stock solution to be processed and the fine bubbles flow through the flotation tank as described above,
Until the bubble-attached flocculated floc-like suspended substance reaches the liquid surface, and even after floating on the liquid surface, the flocculated floc-like suspended substance and the fine bubbles are always in effective contact with each other, and the suspended substance It is possible to obtain treated water whose removal rate is significantly improved.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. First, how the inventors studied from a small pilot plant for scale-up and reached the present invention will be described. That is, the present inventors first studied the contact between the fine bubbles and the flocculated flocs and the floating distance in the pressure flotation separation method. FIG. 1 is a vertical sectional conceptual view of the pressure flotation apparatus of the present invention, which was proposed by the inventors. In the pressure flotation, the horizontal movement of the suspended suspended material is performed as a single tank without dividing the flotation tank. The design was not accompanied. in this case,
Obviously, the more the fine bubbles and the flocculated floc are in contact with each other, that is, the longer the contact time, and the shorter the distance over which the flocculated flocs combined with the fine bubbles move to the liquid surface, the better.

Therefore, as shown in FIG.
By supplying the stock solution 1 containing the flocculent floc to the upper part of 0 to generate a descending stock solution flow, and simultaneously introducing air-dissolved pressurized water 2 below to generate fine bubbles 3 and generate an ascending flow. The downward flow 4 of the stock solution 1 to be processed and the upward flow 5 of the fine bubbles 3 are always in contact with each other in almost the entire area of the separation tank, and the coalesced flocs and the fine bubbles are easily combined with each other to smoothly float on the liquid surface. Can be done. Also,
Even when the flocculated floc combined with the fine bubbles 3 is separated from the bubbles during the ascent, the flocculated floc in which the suspended substance contained in the undiluted solution to be treated is coarsened because the floc is always in contact with the rising fine bubbles 3. Can be floated to the liquid surface. Furthermore, the scum layer of the flocculated floc suspended substance floating on the liquid surface is constantly supported and pushed up by the fine bubbles continuously rising from below and the floating flocs, and there is almost no danger of re-sedimentation. For this reason, even when the scum layer on the liquid surface is left for several hours or more, the floating state can be maintained, and even in a state where it is difficult to quickly discharge the scum layer, the turbidity of the processing liquid increases and the removal rate of suspended substances may decrease. There is no.

The inventors then investigated the reasons why the pressure flotation method is not widely used as a clarification treatment of the suspension by the conventional method as described above, and at the same time, scaled up to a large industrial device. In order to find a method for improving the pressure, a supply nozzle of the undiluted solution to be treated to be employed in the pressurized flotation tank having a suitable structure based on the above consideration was examined. That is,
It is necessary for the stock solution supply nozzle to consider that the stock solution supplied from the central part of the pressurized flotation tank flows down radially evenly in the circumferential direction of the inner wall while generating a downward flow. Therefore, in place of the simple cylindrical supply nozzle in the conventional method shown in FIG. 4, the outer shape shown in the cross-sectional explanatory view in FIG. It was decided to use a frustum-shaped nozzle having a truncated cone-shaped truncated base as a stock solution inlet. That is, the stock solution to be processed supplied from the stock solution supply pipe to the frustum-shaped nozzle rises along an inclined portion that expands in the upward direction of the frustum-shaped nozzle that is set in a predetermined manner, and from the circumferential portion of the circular discharge port. As a result, the water flows out uniformly and radially and evenly spreads toward the inner surface of the flotation / separation tank, so that it flows down.

The hollow frustum-shaped nozzle as described above is known as an overflow nozzle of a water tank, but has not been employed in the introduction of raw water such as a pressurized flotation device or the like and was first employed in the present invention. Things. In the present invention, the hollow frustum shape of the untreated solution supply nozzle refers to a frustum shape in which the outer shape is a truncated cone at the top, and the smaller the outer surface area having a predetermined opening degree, preferable. This is because fine bubbles rising from the lower part may adhere to the outer surface of the nozzle, and other air bubbles may come into contact with the attached bubbles and become coalesced and become coarse. This is because when these coarse bubbles rise from the nozzle to the liquid surface, the floating scum layer may be broken. Therefore, a hollow frustum shape is preferably used, but a hollow frustum shape such as a regular polygon approximating a frustum shape may be used. In the hollow frustum-shaped nozzle of the present invention, the top is connected to the supply pipe of the stock solution to be treated, and the bottom is directed upward to serve as a discharge port. When the discharge port is directed downward, the downward flow of the supplied untreated liquid does not spread in the peripheral wall direction, so that contact with the rising fine bubbles does not occur.

In the pressure flotation method of the present invention,
Equation (1) is A / a = 12, and equation (2) is 1
It is preferable that 5 ° ≦ θ ≦ 30 ° and A ≦ 4.0 m ² , and the nozzle is arranged at the center of the cross section of the pressurized flotation tank, and the gas-dissolved pressurized water is used. Is preferably injected downward toward a baffle plate disposed vertically below the nozzle. Furthermore, the cross-sectional area of the upper floatation separation tank is not more 5.0 m ² or more, the unit ratio of the sectional area 2.0～5.0M ² per 1 of the separation tank, of claim 1 or 2, wherein It is preferable that two or more nozzles, each of which has A having the unit cross-sectional area (that is, A = 2.0 to 5.0 m ² ), are arranged to supply the undiluted solution, and the nozzle is arranged. it is more preferred unit sectional area is 3.0~4.0m ^2.

In the present invention, the stock solution supply nozzle for supplying the stock solution to be processed into the pressurized flotation tank is designed based on the following conditions. That is, (1) at least one flotation / separation tank with a cross-sectional area of 10 m ² per unit is disposed, (2) the bottom of the hollow frustum body is disposed upward with a discharge port, and (3) the flotation / separation tank cross-sectional area (A) Ratio (A / a) of the cross-sectional area (a) of the stock solution supply nozzle discharge port = 8 to 14, preferably 11 to 12, (4)
The opening degree θ of the frustum portion of the stock solution supply nozzle is 12 to 35 °, preferably 14 to 25 °. If the nozzle shape is not a hollow frustum shape but a conventional circular nozzle, etc., a jet flows onto the liquid surface, disturbing the floating scum layer on the surface, and uneven distribution due to the inability to uniformly distribute raw water There are inconveniences such as doing. Further, the downward direction of the discharge port is not preferable because the contact with the fine bubbles is not effectively performed as described above. A / a = 8 to 1
Outside of the range 4, the flow of the fine bubbles on the inner peripheral surface of the separation tank is disturbed, and a mixed circulation flow or a short-pass flow is generated, so that the downward flow of the raw liquid to be treated and the upward flow of the fine bubbles can be smoothly countercurrently contacted. The water quality such as the turbidity of the treated water decreases. θ = 12-35 °
If θ is too small, it will be the same as a conventional circular straight tube.On the other hand, if θ is too large, it may hinder the rise of microbubbles rising from the lower part as described above and disturb the scum layer. Therefore, it is not preferable.

Further, A> When it is 5 m ² is placing two or more treated solution feed nozzle at a rate of separation tank unit of cross-sectional area the cross-sectional area 2.0～5.0M ² per 1 above design conditions Can perform the same water treatment. In this case, the discharge pressure of the undiluted solution from the undiluted solution supply pipe to the frustum portion inlet of the hollow frustum-shaped nozzle is adjusted in accordance with the undiluted solution supply amount so that the flocculated floc is not destroyed. In the present invention, the design conditions of the preferred form of the frustum-shaped nozzle have been found as a result of various trials and errors as described in the examples below. By using the stock solution supply nozzle formed in accordance with the design conditions of the present invention in a predetermined manner in the pressurized flotation tank, a uniform downward flow of the stock solution to be processed can be generated, and the rise of fine bubbles from below It is possible to improve the contact efficiency of the countercurrent contact with the stream and to prevent sedimentation of flocculated flocs and to prevent water quality deterioration such as turbidity of treated water. By making the distance from the stock solution supply nozzle discharge port to the liquid surface larger than the stock solution discharge port diameter, the discharge flow of the stock solution to be processed does not adversely affect the floating scum.

[0022]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited by the following examples. Example 1 and Comparative Example 1 First, in planning a treatment facility for kitchen wastewater that may contain oil, the oil and suspended matter are coagulated as pretreatment facilities, and then levitation separated under pressure to clarify. In order to perform the treatment, a pilot plant having a cross-sectional structural explanatory view shown in FIG. 3 was manufactured along the structural conceptual explanatory view of the pressurized flotation tank shown in FIG. In FIG. 3, a pressurized flotation tank 20 has a scum discharge unit 21 for discharging a scum floatingly accumulated and held on the water surface by overflowing to the upper outer peripheral surface in a hollow cylindrical shape of transparent plastic having an inner diameter of 30 cmφ and a height of 3 m. It was arranged. The stock solution to be treated is subjected to a flocculation treatment by adding a flocculant or the like in advance in a flocculation tank 22 to coagulate and coarsen the contained suspended substance to form a floc. About 50 below the liquid level at the center of
The liquid was supplied into the separation tank 20 from the discharge port 23 arranged upward at 0 mm. The supply of the stock solution to be processed was performed using the head difference between the liquid level of the flocculation tank 22 and the liquid level of the separation tank 20.

On the other hand, about 500 m above the bottom of the separation tank 20
The baffle plate 25 was disposed at a position m, and the discharge port 27 of the air-dissolving pressurized water introduction nozzle 26 was disposed approximately 50 mm above the baffle plate 25. The discharge port 27 has its tip portion squeezed into an orifice shape so that the pressurized liquid is ejected. The discharge port 27 of the air-dissolving pressurized water introduction nozzle 26 is not particularly limited. For example, a discharge plate having a large number of ejection holes may be used. Further, the processing liquid flowing down and stored in the lower bottom portion of the separation tank 20 is extracted by the pump P, pressurized and sent to the gas dissolving tank 28, and at the same time, air is sent to the gas dissolving tank 28 by the compressor C to be an air pressurized dissolved liquid. . Gas dissolving tank 2
The air pressurized solution No. 8 was supplied from the line L2 to the air-dissolved pressurized water introduction nozzle 26, was discharged from the discharge port 27 toward the baffle plate 25, and generated fine bubbles in the separation tank 20. The processing liquid at the lower bottom of the separation tank 20 was discharged out of the system from the line L3 through the liquid level regulating weir 29.

[0024]

[Table 1]

As the undiluted solution supply nozzle 24 of the pilot plant, the undiluted solution supplied from the center of the flotation tank 20 is designed to flow down while spreading radially evenly in the inner circumferential direction. The nozzle whose outer shape is a hollow frustoconical shape of a truncated cone with a truncated cone at the top is shown in FIG. It was joined with the supply pipe. The shape and shape were formed under the design conditions shown in Table 1 at a flow rate (for example, about 0.5 m / sec) at which the flow rate of the stock solution flowing from the stock solution supply pipe into the nozzle inlet portion did not cause the flocculation floc to break and settle. On the other hand, as Comparative Example 1, a circular tube-shaped nozzle similar to the conventional method shown in FIG. 4 was used in place of the frustum-shaped stock solution supply nozzle 24, and the discharge port diameter was the same as that of the stock solution supply line.
mφ, and a baffle was installed on the upper part to generate a downward flow and not to affect the floating scum. Also,
The operating conditions of the pilot plant configured as described above were as shown in Table 1 below. As a result of clarifying the kitchen wastewater having a suspension degree of 50 degrees, it was 1.5 degrees in Example 1 using the hollow frustum-shaped nozzle, and 2.8 in Comparative Example 1 using the conventional cylindrical nozzle. Degree. From this result, it is understood that the method of supplying the stock solution to be treated into the separation tank using the truncated conical nozzle is excellent in the clarification of the suspension water by the pressure flotation method.

Verification Experiment 1 Next, based on the results of the pilot plant described above, in order to accurately grasp problems related to scale-up, etc., the floatation / separation tank 20 was made of a transparent plastic having the same structure, A test plant equivalent to the actual device with 1.2 mφ, 3 mH in height, and 4 times in diameter (16 times in cross-sectional area) was constructed. Using this test plant, the state of generation of fine bubbles due to the release of air-dissolved pressurized water and the behavior of two fluids, ie, the untreated solution and the fine bubbles, were mainly observed. The operating conditions were adjusted to be the same as in the pilot plant. First, the method of supplying air-dissolved pressurized water was studied. Since the tank diameter became large and the set pressure of the pressurized water was a pressure that could be distributed to a plurality of sections of the tank, the distribution of air-dissolved pressurized water was also studied. At the time of distribution, the ratio of the total amount of pressurized water introduced to the amount of the stock solution to be supplied and the pressurized water pressure are set to 10% by weight and 3 to 7 kg / cm ² , respectively, as in the pilot plant, so that two and three air-dissolved pressurized water introduction nozzles are used. The occurrence and rising state of fine bubbles were observed for the two cases in which the liquid was distributed. Each introduction nozzle has two points at two points that divide a straight line passing through the center of the circular cross section of the separation tank into three equal parts.
Alternatively, three pieces are arranged at three intersections of each side of the equilateral triangle inscribed in the circular cross section of the separation tank and a perpendicular line from the vertex. In addition, the same observation was performed on the arrangement of one nozzle. As a result, in any case, there was no significant change in the generation and rising state of the fine bubbles, and it became clear that the method of introducing pressurized air-dissolved water did not need to be particularly problematic with the scale-up.

Verification Experiment 2 Next, using the same test plant, the fluid behavior of the descending flow of the feed stock solution and the rising flow of fine bubbles was observed. From the observation of the introduction of pressurized water dissolved in air, one introduction nozzle was installed at the lower central part of the separation tank as in the pilot plant. Also, as the stock solution supply nozzle, the flow rate of the stock solution flowing into the nozzle inlet portion does not cause the flocculation floc to be destroyed and settled according to the conventional empirical rule in accordance with the amount of the stock solution to be treated in the scale-up of the separation tank 20 as described above. Under the form conditions shown in Table 2 so as to be about 0.5 m / sec, a frustoconical supply nozzle suitable for a pilot plant was formed, installed and used similarly. The operating conditions were adjusted such that the stock solution was supplied so as to be the same as the pilot plant shown in Table 1. First, the supply of the stock solution was stopped and only the air-dissolved pressurized water was discharged. By the release of the pressurized water in the air, a stable cloudy layer of fine bubbles having a substantially uniform concentration was formed over the entire area of the separation tank from the position of the baffle plate 25 to the surface of the water. In the cloudy layer, a situation in which fine bubbles ascended slowly as a whole was observed.
At this stage, the stock solution to be treated was supplied. Initially, it was expected that the rising speed of the bubbles would be slower because the supply of the undiluted solution would cause a downward flow. However, on the contrary, it was observed that the rising speed of the fine bubbles was increased at the inner wall peripheral surface of the separation tank, and it became clear that an unusual rising flow was generated.

[0028]

[Table 2]

Verification Experiment 3 Next, the supply of the stock solution was stopped again, and only the air-dissolved pressurized water was introduced to form a stable cloudy white layer. Then, the stock solution colored with ink was supplied. It was observed that a part of the coloring stock solution rapidly descended along with peripheral fine bubbles in the center of the separation tank, and the bubbles on the peripheral surface of the inner wall of the separation tank accelerated rising.
Further, it was considered that the coloring gradually moved downward from the upper part and diffused as the stock solution descended, but it was observed that the coloring diffused not only from the upper part but also from the middle part of the separation tank. As a result, it has been found that the flow of the fluid in the separation tank is not only a downward flow of the undiluted solution and an upward flow of the fine bubbles in contact with each other, but also a partial circulating mixed flow and a short path flow. For this reason, in the large-scale counter-current pressure flotation method of the real device class, even if a frustum shape such as a truncated cone is simply adopted as the stock solution supply nozzle, the counter-current contact efficiency cannot always be improved, It became clear that the stock solution supply method should be considered in consideration of other factors.

Using the pilot plant, similar observations were made with the above coloring stock solution. As a result, phenomena such as the mixed circulation flow and the short path flow as described above were not observed. Therefore, the difference in the supply of undiluted solution between the pilot plant and the test plant was examined in detail. First, the feed rate of the undiluted solution is adjusted by increasing the capacity of the separation tank so that the operating conditions shown in Table 1 such as the flow rate and the residence time in the flotation tank become the same. However, the discharge speed of the undiluted solution flowing out of the undiluted solution supply nozzle into the separation tank was examined. That is,
When the stock solution discharge speed from the stock solution supply nozzle discharge port in the pilot plant is neglecting the amount of floating fine bubbles and flocculated floc, the stock solution descending flow rate in the separation tank is equal to the stock solution supply amount (Q). The area (A) and the stock solution supply nozzle discharge port area (a) can be represented by Lvi (stock solution discharge speed) / Lvc (superficial tower speed) = Q / a / Q / A. Therefore, Lvi = Lvc × A / a, and the downstream linear velocity of the pilot plant is 15 m / h = L
As vc, Lvi = 15 m / hour × π (0.3 / 2) ²
/Π(0.088/2) ² = 15 m / hr × 11.6 = 1
It is 74 m / hour. On the other hand, the undiluted solution discharge speed Lvi in the test plant obtained in the same manner was 960 m / hour, and it was clarified that it was significantly different.

Verification experiment 4 Based on the above examination results, the increase in the supply amount of the stock solution accompanying the enlargement of the separation tank should be divided into a plurality of supply nozzles so as not to greatly change the stock solution discharge speed in the pilot plant. And a stock solution was supplied by dividing into two, three, and four pieces. Each stock solution supply nozzle for divided supply was formed in the same shape under the form conditions shown in Table 3 in the shape of a truncated cone. The arrangement of the divided supply nozzles was such that two were arranged in a straight line, three were arranged in a regular triangle, and four were arranged in a square with respect to the cross section of the pressurized flotation tank 20. As in the verification experiment 1, the observation of the microbubbles and the observation of the descending flow of the coloring stock solution were repeatedly performed. As a result, even in the two-part arrangement, the short-pass flow is greatly improved from the color diffusion, the turbulence of the fine bubbles on the inner peripheral surface of the separation tank is small, and when the three-part and four-part arrangements are made, the circulating mixed flow is almost also short-path. It was found that no flow occurred.

[0032]

[Table 3]

However, in order to divide and supply a predetermined amount of stock solution to be processed into a plurality of stock solutions without greatly changing from a set discharge speed value, a pressure loss is added to evenly distribute the stock solution to be processed. Therefore, it is not preferable to divide and supply the stock solution containing the flocculable floc which is easily broken to a plurality of supply nozzles. In practice, the smaller the number of divided stock solutions, the better. For this reason, in order to carry out a single supply nozzle in the same manner as in the pilot plant as in the above-mentioned pilot plant, the undiluted solution supply nozzle used in the pilot plant has the nozzle form as shown in the following example for the actual plant with a separation tank diameter of 1.2 mφ. Various trial and error tests were conducted with reference to the form.

Example 2 An oil-containing suspended water which is the same kitchen wastewater treated in a pilot plant by setting a stock solution supply nozzle manufactured under the form conditions shown in Table 4 below in the same separation tank as the test separation tank. Was processed. Table 2 shows the turbidity of the treated water obtained using each supply nozzle. In addition, the nozzle formed under the form condition of the stock solution supply nozzle used in the pilot plant is shown as nozzle number 1 in Table 4. Further, the configuration conditions of the stock solution supply nozzle shown in Table 2 used in the verification experiments 2 and 3 of the test plant are also shown in Table 4 as the nozzle number 12. From these results, when the stock solution supply nozzles having nozzle numbers of 1 (the same configuration conditions as the pilot plant), 2, 4 and 5 were used, the turbidity of the treated water was low, the scum layer was stable, and the countercurrent pressurization was used. It is clear that the suspension water was clarified effectively by the flotation method. With the nozzles of Nos. 3 and 7, the turbidity of the treated water was low and good, and the scum layer was slightly disturbed, but there was no particular problem in application.
For the nozzles with nozzle numbers 8 to 10, the turbidity of the treated water slightly increased and the scum layer was disturbed, but it can be determined that the turbidity is within the applicable range. On the other hand, when the nozzles of Nos. 6, 11, and 12 are used, the turbidity of the treated water is increased, the scum layer is disturbed, and the fining treatment by the pressure flotation treatment cannot be sufficiently performed. If the frustum opening (θ) is less than 12 °, the height of the frustum becomes extremely large compared to the depth of the separation tank due to the balance between the nozzle discharge port diameter and the diameter of the stock solution supply part, so that it is not practical. It was revealed.

[0035]

[Table 4]

Example 3 The cylindrical pressurized flotation tank of the above test plant was a hollow frustum with a 2.0-m2 square shape and an outer shape of a frustum shape. A countercurrent contact pressure flotation plant was designed and manufactured in exactly the same manner except that a stock solution supply nozzle formed at A / a = 9.8 was installed under the conditions. This plant was treated under the operating conditions shown in Table 5 below with the same kitchen wastewater that was treated in the test plant. As a result, the turbidity of the obtained treated water was 1.0 to 1.5 degrees, and the expected performance was obtained.

[0037]

[Table 5]

[0038]

According to the pressure flotation method and the apparatus of the present invention, a stock solution supply nozzle having a truncated cone shape is used, the degree of opening of the frustum shape, and the area of the top of the cone connected to the stock solution supply pipe. And the height of the frustum portion, and the relationship between the bottom area serving as the nozzle outlet and the cross-sectional area of the separation tank and the like are specified in a predetermined manner. Enables uniform radial outflow, dispersion spreading and downflow. In addition, the moving distance of the flocculated floc combined with the microbubbles to the liquid surface is shortened without disturbing the scum layer floating on the liquid surface and by supplying the untreated liquid to a short distance below the scum layer. And assured levitation. Furthermore, the contact efficiency between the raw solution to be supplied and the rising microbubbles is improved by preventing the rising microbubbles from generating an irregular irregular downflow such as rat hole flow or drift. The contact frictional resistance between the accompanying ascending flow and the descending undiluted liquid flow caused by the ascending flow can be minimized. Furthermore, the scum layer floating on the liquid surface can be stably held for a long time without being disturbed.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of a pressure flotation device of the present invention.

FIG. 2 is an explanatory sectional view of a pressure flotation device pilot plant of the present invention.

FIG. 3 is a diagram illustrating a hollow frustum of a truncated cone shape used as a pressure flotation separator of the present invention, with a frustum bottom serving as a discharge port, and a truncated cone top serving as a stock solution inlet. Sectional explanatory view of a frustum-shaped nozzle

FIG. 4 is a cross-sectional explanatory view of a conventional parallel-flow contact pressure flotation device.

FIG. 5 is an explanatory cross-sectional view of a conventional horizontally movable pressure flotation device.

[Explanation of symbols]

 10, 20, 40, 50 Pressure flotation / separation tank 53 Untreated liquid 2, 42 Air-dissolved pressurized liquid 24 Untreated liquid supply nozzle 23 Discharge port 25 Baffle plate 26 Air-dissolved pressurized liquid introduction nozzle 27 Discharge port

Claims (2)

[Claims] 1. A pressurization for supplying a stock solution to be processed from an upper portion of a pressurized flotation tank and introducing gas-dissolved pressurized water from a lower portion to generate fine bubbles, and to bring the stock solution and the fine bubbles into countercurrent contact. In the flotation method, at least one nozzle having a hollow frustum shape and having a bottom as a discharge part and having a form represented by the following formulas (1) and (2) per 10 m ^{2 of the} cross-sectional area of the pressurized flotation tank. A pressurized flotation separation method, comprising disposing the undiluted solution with the discharge unit facing upward. However, in the following equations (1) and (2), A is the cross-sectional area of the pressurized flotation tank, a is the cross-sectional area of the nozzle discharge section, and θ is the opening of the nozzle. 8 ≦ A / a ≦ 14 (1) 12 ° ≦ θ ≦ 35 ° (2) 2. A pressurized flotation separation apparatus, comprising a hollow frustum-shaped body at the center of the cross section of the separation tank, a bottom having a discharge section, and having the form shown by the following formulas (1) and (2). At least one undiluted solution supply nozzle is provided per 10 m ^{2 of the} cross-sectional area of the pressurized flotation tank with the discharge section facing upward, and a gas-dissolved pressurized water inlet and a baffle plate are arranged vertically below the nozzle. The pressure flotation / separation apparatus, wherein the gas-dissolved pressurized water inlet is an orifice nozzle and is arranged so as to be able to jet toward the baffle plate. However, in the following formulas (1) and (2), A is the cross-sectional area of the pressurized flotation tank, a is the cross-sectional area of the nozzle discharge section,
θ is the opening of the nozzle. 8 ≦ A / a ≦ 14 (1) 12 ° ≦ θ ≦ 35 ° (2)