JP2892604B2 - Method and apparatus for dissolved air flotation and similar gas-liquid contact operations - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates generally to dissolved air floatation (DAF), and more particularly to:
An improved new device for DAF systems and other gas-liquid contact systems for separating and reacting liquid and contact gases.

[0002]

BACKGROUND OF THE INVENTION Many industrial activities involve the separation of oils, fats, greases that must be separated or treated before discharge to the environment or before use in any subsequent step. It is a source of gaseous, liquid and gaseous liquid waste containing emulsified or non-emulsified suspended solids, such as metals, organic and inorganic solids, and condensable organic vapors. These activities include petroleum and vegetable oil refining, iron and steel, food and beverage processing, metalworking, chemical and paint manufacturing, pulp, paper and textile manufacturing, aircraft maintenance, coke oven gas processing, and water conditioning and water conditioning. Includes water treatment. The concentrations of suspended solids and other components can vary widely depending on the source and processing conditions.

[0003] The treatment of liquids and liquid waste as described above is usually carried out in at least two stages. First, the easily settling solids are separated from the liquid medium by gravity, and the floating oily components are scooped. The stable emulsified liquid is then phase separated to separate the remaining oily components from the water. Any remaining dissolved material can be removed if necessary by extraction, adsorption, absorption, distillation, crystallization, membrane separation and chemical separation.

Currently, three widely used methods for separating suspended solids from liquids are gravity separation or sedimentation for solids heavier than liquids, filtration for small particles, and feasibility of floating. Air flotation for suspended material. Of course, air flotation has the greatest applicability and is widely practiced industrially. Air is blown into the liquid, causing the suspended material to float on the surface and allow the surface to scoop the suspended material. However, very small suspended solids are not effectively separated in this way. A more effective method is dissolved air flotation (DAF). High pressure air is dissolved in the liquid to be treated and introduced into the flotation tank at a lower pressure. Microbubbles of air, sized 10 to 40 microns, are released and rise gently through the liquid, pushing up the suspended suspended material to the surface.

[0005] Conventional DAF systems charge untreated stock solution and liquid with dissolved air into a flotation tank through separate inlets located near the bottom. The processing liquid containing the reduced concentration of suspended solids is discharged near the bottom of the tank, while the suspended suspended solids are scooped and removed at the top. Since the suspension of suspended matter by rising (air) bubbles occurs vertically, there is a vertical concentration gradient of liquid suspended matter in the flotation zone. Untreated liquid in contact with the bubbles due to the buoyancy of the rising bubbles moves upwards, while the treated liquid moves downwards. The vertical opposing flows of the two liquids cause turbulence, and the mixing of the two liquids occurs, thereby reducing the separation efficiency.

This turbulence and mixing can be reduced somewhat by reducing the inflow rate and by adding baffles to direct the flocs (agglomerates of suspended solids) / foam to the surface. . Baffles, which are generally cylindrical for cylindrical tanks and flat for rectangular tanks, are placed at an angle of approximately 60 degrees from the horizontal to reduce the speed and coalescence of rising bubbles. I will Liquid rising under suspended material must turn around 180 degrees at the top of the baffle and flow downward to the outlet at the bottom of the tank. Turbulence caused by rising bubbles and suspended matter flowing above the baffle will cause mixing near the liquid level. Therefore, baffles are not very effective. Baffles also greatly reduce the surface area of the tank available for flotation, and require relatively high tanks to allow enough space above the baffles to allow suspended material to flow above the surface of the baffles. In need of. Also, unavoidable turbulence in the contact zone within the baffle may result in poor adhesion of the air bubbles to the suspended solids particles and may cause destruction of the floc-bubble aggregates.

Separation of very dilute concentrations (less than 10 ppm) or very small (less than 10 μm) from liquid media
Separating suspended particles is not generally feasible with conventional DAF systems. Chemicals such as polyelectrolytes and long-chain polymers are used to agglomerate small particles and form agglomerates so that the bubbles form larger aggregates that can be easily contacted and attached. Larger agglomerates are more buoyant and less susceptible to disruption, thus making flotation easier and increasing separation efficiency. Efficiency is 10-40% without such chemicals and 40-90% with chemicals
It is. However, ironically, there are more problems that arise than those that the added chemicals solve. Chemicals not only increase the cost of separation, but also increase the processing time. Agglomeration can occur very quickly in high speed mixing tanks, but floc formation is time consuming and usually takes about 20-3
It takes 0 minutes and requires a slower mixing tank. Only a very small percentage of the chemical dissolved in the liquid is removed along with the actual suspended material. The remaining chemicals must be removed later if their concentrations are unacceptable for recycling or release to the environment.

[0008] More recent DAF systems for reducing mixing between the untreated liquid and the treatment liquid divide the flotation tank into several communicating sections and direct the liquid continuously to each section. The separation is somewhat improved for large tanks, but only slightly for small tanks. In a limited number of smaller sections, for a given flow rate, the mixing will be stronger.

Another system uses a long flotation tank with a liquid inlet at one end and a liquid outlet at the other end. Liquid backmixing (backmixing) can be reduced, but few DAF locations have enough room to accommodate such long tanks.

One of the most popular DAF systems recycles the treated liquid to a flotation tank, which also has advantages and disadvantages. The throughput is reduced, the backmixing of the liquid to be processed is more, and the operating costs are higher. This system is often combined with other techniques to compensate for these shortcomings. In particular, filtration is often selected to produce portable drinking water. However, combining such a technique with dissolved air flotation necessarily adds complexity and increases equipment costs.

[0011] Separation and removal of large heavy solids that tend to settle to the bottom of the tank is another problem. One solution is
Combining low speed agitation with the installation of a separate solids outlet at the bottom of the tank results in undesirable liquid turbulence and mixing.

From all of the above, it is clear that liquid turbulence and backmixing in conventional DAF tanks is a problem that has long been a problem that affects separation efficiency. Baffles and low flow rates reduce turbulence and backmixing, but at the expense of throughput. Chemicals promote separation of liquids, but they also increase processing time, increase costs, and manifest many undesirable side effects. Recirculating the treated liquid itself improves the separation efficiency, but also increases costs and backmixing. Suspended material and / or
Methods and apparatus for removing settled solids also cause turbulence and backmixing. None of these can prevent backmixing of the liquid being processed without sacrificing processing power. High separation efficiencies were achieved only with chemicals and by time-consuming floc formation. Simultaneous removal of suspended solids and settled solids can be achieved, but with the undesirable effect of liquid turbulence.

[0013]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a new and improved DAF method and apparatus that more completely and quickly separates suspended matter from liquid media without turbulence and backmixing. .

It is another object to provide an improved DAF method and apparatus that can separate dilute concentrations of fine suspended solids from a liquid medium.

Yet another object is to provide an improved DAF method and apparatus that facilitates the simultaneous removal of suspended sludge and settled solids without substantial loss in separation efficiency.

Yet another object is to add small amounts of chemicals,
It is another object of the present invention to provide an improved DAF method and apparatus that separates a stable emulsified liquid from a liquid medium and promotes flocculation of suspended solids contained in the liquid medium without addition.

Another object of the present invention is to provide an improved DAF method and apparatus suitable for gas-liquid contact methods.

Briefly, these and other objects are achieved in a DAF system having an upright cylindrical tank having at least one vertical partition forming a spiral flow path. Achieved. A mixture of untreated liquid and liquid saturated with dissolved air under pressure is introduced continuously from one end of the flow path near the bottom of the tank and swirls under plug flow (extruded or piston flow) flow conditions. It flows along a shaped (inner or expanded) path and is discharged at the other end near the bottom. Microbubbles of air released from the liquid rise through the liquid mixture and create buoyancy, which carries all particles of suspended matter with which it comes into contact in a spiral path to the liquid surface.
Centrifugal force and gravity gradually settle large heavy solids to the bottom, which are separately discharged from the liquid. The suspended material on the surface is continuously discharged.

As the mixture of liquids flows through the flow path inwardly at an increasing angular velocity and a radial velocity toward the inner end, or unfolding at a decreasing angular velocity and the radial velocity toward the outer end, The mixture becomes progressively clearer, but the suspended solids increase from the bottom towards the liquid surface. Under steady state conditions, a concentration gradient is created in the depth direction and the length of the passage. Centrifugal forces acting on the liquid also create a radially inward water pressure, which helps the particles to clump without turbulence.

There is no counterflow or backmixing of liquid in the flow path. This is because liquid enters at one end and exits at the other end. The absence of liquid turbulence in the DAF tank is necessary for the particles to stably attach to the bubbles and to separate very dilute concentrations of the particles. The entire internal surface area of the flotation tank is available for flotation. The design and scale-up of flotation tanks is simple and straightforward and plug flow
(Extrusion or piston flow) Follow reactor design principles.

For a better understanding of the nature and objects of the present invention, the following detailed description is set forth in conjunction with the accompanying drawings.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the present invention, turbulence and backmixing of a liquid flowing through a dissolved air flotation (DAF) tank causes the liquid to be treated to pass through an inner or expanded channel. This can be prevented. The liquid inlet at one end of the flow path and the liquid outlet at the other end create a plug flow (extrusion or piston flow) that can achieve maximum separation of all suspended solids in the liquid. Under plug flow conditions, the residence time of the liquid is inversely proportional to its average linear velocity,
It is also equal to the ratio of channel length to velocity, and equal to the ratio of channel volume to liquid flow rate. This condition can be maintained over the entire length of the channel for a wide range of flow rates. This is because, according to the conservation of angular momentum, the radial and tangential components of the flow pressure in the liquid are almost always balanced.

DAF tanks are designed to process liquids at a particular inflow rate. The liquid flow rate and the residence time required for the separation depend on the dimensions (length,
Width and height). For maximum efficiency, the residence time of the liquid should be such that all liquid contacts the air bubbles and that all air bubbles reach the liquid surface before the processing liquid reaches the outlet of the channel. To assure, it should be equal to or slightly greater than the average residence time of the bubbles released from the liquid (ideally less than 130μ). In this way, the supplied air is not wasted at all.

The stand to have an average terminal velocity (terminal velocity) of the rising gas bubbles without aggregate formation through the liquid V _t and the average residence time t of the given depth z, as hydrodynamically follows Can be evaluated. V _t = dz / dt (1) or dt = dz / V _t (2)

(Equation 1) The initial bubble volume is v ₀ = v _Z (P ₀ / P _Z ) (4) where v _Z = volume at depth z, P ₀ = bottom pressure, and P _Z = pressure at depth z, this pressure is It can be related to the density ρ _{l of the} liquid as follows: P ₀ = P _a + (g / g _C ) ρ _l Z (5) and P _Z = P _a + (g / g _C ) ρ _l (Z−z) (6)

[0025] The capacity of the bubble v, and bubbles of diameter d _{p, P a}
= Atmospheric pressure, and Z = total liquid height, has the following relationship: v = (π / 6) d p 3 = v 0 P 0 / [P a + (g / g C) ρ l (Zz)], (7) d p = d p0 {[P a + (g / g _C ) ρ _l z] / [P _a + (g / g _C ) ρ _l (Zz)]} ^1/3 (8)

The strike - the average terminal velocity V _t of bubbles according to the law of the box may be related to its diameter d _{p. ^{V t = gd p 2 △ ρ}} l / 18μ l density difference here △ [rho _l = air and liquid and mu _l = viscosity of the liquid, is.

T _b is obtained by replacing equations (8) and (9) in equation (3) and integrating the following relationship for the rising bubble residence time T _b = (= t):

(Equation 2) For maximum flotation efficiency, the residence time T _l of the liquid, determined equal to the average residence time of the rising bubble T _b. That is, _Tb = _Tl = channel capacity / volume flow rate (11) Since the weight of the particles bound to each bubble is very small compared to the buoyancy of each bubble, the density and volume of the bubble are reduced. It remains substantially constant during the election. This means that for certain solid and liquid loads, the amount of air supplied is sufficient,
Bubble aggregate formation due to turbulence is a valid assumption for normal DAF operation, negligible.

[0028] By equalizing the residence time T _b of bubbles rising versus residence time T _l of the liquid flowing through the channel, the length or height of the flow path can be determined from the other.
The residence times _Tl and _Tb are typically set between 5 and 15 minutes, depending on the properties of the liquid to be treated and the ratio of feed air to liquid load.

A mixture of untreated liquid and air dissolved in the liquid is introduced from either end of the flow path, with a view to preserving angular momentum and the ease of removing settled solids from the bottom of the tank. In view of the above, the inner winding flow is more preferable than the developing flow. To maintain plug flow conditions for high separation efficiency, throughput can also be increased by using several inwardly or expanded channels in a single tank.

Given D with a fixed channel height
The maximum liquid flow rate for the AF tank can be determined by connecting the liquid residence time _Tl and the bubble residence time _Tb with an equation for a predetermined flow path height. Assuming a plug flow for a particular liquid and flow rate, the tank diameter, number of channels, liquid height in the tank, and channel dimensions (length, width and height) are determined hydrodynamically. The liquid height in the tank (typically 1.2-2.0 m) is usually maintained approximately a few inches above the top of the flow path partition to facilitate removal of suspended sludge. Suitable devices are provided for discharging air dissolved in the liquid under pressure into the liquid to be treated and mixing with the liquid to be treated. For large tanks or long flow paths, several air discharge and mixing devices are considered.

Referring now to the accompanying drawings, like reference characters and numerals designate like or corresponding parts throughout the several views. Referring to FIG. 1, a DAF apparatus having a flotation tank 10 for embodying the rights of the present invention is shown. As shown in FIGS. 2 and 3, the tank 10 includes a cylindrical upright outer wall 12, the outer wall 12 being radially partitioned by a spiral wall 14 about its vertical cylindrical axis.
A spiral flow path 16 is formed. The outer end 14a of the spiral partition is fixed to the outer wall 12, and the inner end 14b of the spiral partition terminates near the cylindrical axis.

[0032] Both the untreated liquid L _u and dissolved air containing liquid L _a are mixed in a mixer -18, together liquid is continuously flowed through channel 16, through the outlet 24 with the exception of any suspended solids It is discharged to the sediment trap 26 located at the center of the bottom of the tank 10. The combined liquids pass through a strainer 28, except for sediment collected in trap 26 and any suspended solids, which removes any remaining particles. But stress for a small fraction - processing liquid L _t from Na -28 is sent to the liquid reservoir 30, liquid reservoir 30 is O - bar - flow - determining the liquid level LL in the tank 10 by the rise of the outlet 32 . This method of adjusting the liquid level sometimes produces sludge with a low solids content. Accordingly, the liquid level is controlled by a liquid level sensor (not shown) which generates a signal indicative of the liquid level in a responsive regulator and controls a liquid pump for controlling the liquid inflow rate. It might be desirable.

Processing liquid L saturated with dissolved air under pressure
a small amount of _t is recycled to the inlet 20 of the tank 10 as a liquid L _a. Compressed air from a source 44 is introduced into the liquid L _t input of the pump 46, and all of undissolved air in the liquid L _t is accumulated in dissolution separation tank 48 At a its output, and Lili -Escaped by the device 47. Of course, other means for introducing dissolved air into the untreated liquid _Lu are conceivable. For example, an aspirator or ejector that uses a part of the processing liquid as a working fluid may be used to mix air with the liquid.

Suspended matter or scum floating on the liquid level in the tank 10 due to the contacting microbubbles is removed through a tangential overflow trough 34 at the top of the outer wall 12. A skimmer 36 having a curved blade is mounted on a support 38 so as to be rotatable above the liquid surface, and a low speed motor is provided.
Driven continuously by a tar 40, which discharges suspended matter or scum through the trough 30 for proper disposal. If desired, suspended matter can be removed directly from the liquid surface using a suction head.

The arrows shown in FIGS. 2 and 3 indicate that the liquid flow
Figure 16 illustrates an upwardly winding path for microbubbles of air and suspended suspended matter as it passes through 16. The released air bubbles attach to the free-floating particles of the suspended substance, causing them to rise and float on the surface. Under centrifugal force and gravity, heavier solids continue to flow with the liquid and gradually settle to the bottom of tank 10. A concentration gradient with a maximum at the top for suspended matter and a maximum at the bottom for sediment can thus be created. Heavier solids or sediments are collected in trap 26, which is removed through gate valve 42 and suspended material is forced out by skimmer 36 and exits to overflow trough 34. Any small non-floating suspended material remaining in the liquid is discharged from tank 10 through central outlet 24 and removed by strainer 28. Due to the internal flow of liquid, suspended suspended matter may sometimes show a tendency to accumulate near the center of the tank. In that case, the suspended matter can be easily removed by suction means (not shown) instead of the skimmer 36.

Referring now to the DAF system of FIG.
An upright cylindrical tank 50 is provided for deployment flow. This embodiment is particularly suitable for separating suspended solids in liquids that do not contain precipitated solids. A spiral internal wall 52 forms an evolving flow path 54, which has an inlet 56 in the center of the tank bottom and a peripheral outlet on the side near the bottom of the tank.
And has a flow 58 to provide a developed flow. Untreated liquid L _u is mixed in the liquid L _a and the fixed mixer -60 saturated with dissolved air under pressure is introduced into the tank 50 through Deyufuyuza -62. The liquid mixture expands through the flow path 54 and through the outlet 58 as indicated by the arrow in FIG.
Overflow reservoir through 26 and strainer 28
Go to 30, where the overflow outlet 32 maintains the liquid level LL in the tank 50 in the same manner as described for the system of FIG. Solids collected at the bottom of the tank 50 are removed at a peripheral outlet 59.

The liquid L _a is saturated with dissolved air under pressure in the same way. The compressed air from the air supply source 44 is used as a strainer.
Is dissolved in a small amount of the treatment liquid L _t from 28, and the pump 4
It is led through a tank 48 with 6 and a relief valve 47 to a mixer 60. Other methods and devices for dissolving air under pressure into a liquid include high speed mixing pumps, tanks with or without packing, and stationary mixers.

In a long tank with a spiral channel,
Several discharge devices are provided near the liquid inlet to supply enough bubbles to be evenly dispersed in the liquid to be treated, or along the length of the flow path to distribute the bubbles. Provide along. 7 to 11 show the partition wall 94 of the inner winding.
1 shows an upright cylindrical flotation tank 90 having an outer wall 92 partitioned by
In the manner described for 10, the liquid _Lu is introduced through the peripheral inlet 98 on the side near the bottom of the tank 90 and the outlet 100 at the center of the bottom.
, An inner winding channel 96 is formed.

[0039] Liquid L _a containing dissolved air, diffuser fluidly contacted spiral header -104 at a certain distance - by The -102, and in the stationary mixer -106 and inlet 98 diffuser - The -108, tank 9
Bottom of 0 is mixed with the untreated liquid L _u At a. The diffuser 102 preferably has a nozzle 103 which directs the liquid La in _a downward flow and imparts additional pressure on the liquid to enhance the internal flow. Obviously, for a developing flow, this nozzle is discharged in another direction. This design configuration thereby provides for the continuous introduction of bubbles along the entire flow path of the liquid and increases the capacity of the tank for flotation.
Settled and suspended material is removed in the same manner as described for tank 10.

It is conceivable to provide more than one flow path (channel) in the DAF tank. For example, FIG. 12 shows a flotation tank 110 having three flow paths. This tank is delimited by three spiral walls 112A, 112B, 112C at an angle of 120 °, each having a separate surrounding liquid inlet 114 but having a common central liquid outlet 11 at the center of the bottom of the tank.
6 and has three internal winding channels having one overflow outlet 118 for suspended solids. Fixed mixer -12 for the respective liquid inlet 114 which together liquid L _a and untreated liquid L _u saturated with dissolved air
0 is provided. Of course, this configuration is also suitable for developing flows and the number of spiral walls can be varied according to the specific requirements.

It is clear from the foregoing discussion that several important points must be considered in order to facilitate the practice of the present invention. For a given liquid load, the dimensions (length, height and width) of the flow path in the DAF tank should provide a liquid residence time in the flow path equal to or slightly greater than the residence time of the bubbles in the liquid. It is. This allows sufficient time for bubbles and suspended matter to rise to the surface of the liquid before the liquid reaches the outlet of the flow path. The average linear velocity of the liquid in the flow path must be kept slightly below the value determined from the required residence time. Providing either a longer flow path or a slower flow rate allows the residence time of the liquid to be easily changed. The amount of air supplied should be sufficient for the specified solid and liquid loads.
The volume concentration of bubbles in the liquid to be treated is a very important factor for good flotation. Generally, the higher the bubble volume concentration, the faster the removal of suspended matter. The air required for this reason should be determined by the liquid load, i.e. the liquid flow rate, preferably at least 8-10 g
Air / m ³ water. The average particle size of the released bubbles should be controlled within the range of about 10 to 40 μ by controlling the pressure difference and flow rate across the discharge device. The size of the bubbles is preferably limited to approximately 130μ by limiting the channel height and the liquid level. The solubility of saturated air in a liquid is a function of air pressure and liquid temperature. The actual concentration of dissolved air in the liquid without saturation also depends on the contact time and the mixing effect of the two fluids. Therefore, dissolution of air is also important.

The DAF tank can be placed under a protective cover to protect the suspended sludge layer on the liquid surface from wind and rain. If the recovery of used air or the recovery of treated gas is desired, the top of the tank can be provided with a gas outlet leading to another container, which can be sealed.

The absence of liquid turbulence and backmixing in the DAF tank provided by the present invention allows very high separation efficiencies to be achieved in most industrial applications without flocculants or flocculants. And This includes the separation of very stable dilute emulsions and the separation of liquids at very high speeds. Chemical contamination of the processing liquid can be prevented, thereby eliminating the need for secondary processing of many industrial liquid wastes.

The DAF tank provided by the present invention is simple in design and operation. It can separate difficult emulsions with little or no use of chemicals,
Treat liquids with high speed and high separation efficiency. Many conventional DAF tanks can be easily modified or modified in accordance with the present invention by replacing the existing internal structure with a spiral divider and changing the location of the liquid inlet and outlet.

Other applications of the invention than those described above are possible. It can be used, for example, with little or no modification, alone or mixed with air, using oxidizing gases such as oxygen, ozone and chlorine to treat suspended and dissolved organic-containing liquids, Suspended substances can be removed and dissolved organic substances can be digested at the same time. When applied to the activated sludge process to convert dissolved organic matter in wastewater using microorganisms, a part of the suspended or settled sludge containing microorganisms is mainly recycled and recycled. A portion of the treated wastewater is recycled to dissolve the air or oxygen required for microorganisms and then mixed into the raw wastewater in the DAF tank. To produce drinking water, the raw water must be chlorine, chlorine dioxide,
Biocides such as chlorine donors or non-oxidizing biocides can be treated alone or mixed with air. Gases and gaseous wastes can also be separated or treated according to the invention by physical or chemical absorption using a suitable liquid. On the other hand, the gas dissolved in the liquid can be escaped by desorption by bubbles of the dissolved air. An example is stripping ammonia dissolved in water with air. Obviously, the present invention can be used to treat both liquids and gases, and can be used to react gases with liquids. The present invention can be used for gravity separation of liquids containing many forms of suspended matter, since both the floatable substance and the sedimentable suspension can be removed simultaneously. It can also promote the hydraulic agglomeration of the suspension contained in the liquid to be treated, thus serving as a floc former, with or without separating the flocs formed.

Various details and modifications of the arrangement of parts are set forth to illustrate the principles of the present invention, and various modifications of the individually exemplified details and arrangement of parts are claimed to those skilled in the art. It is understood that this can be done within the spirit and scope of the defined invention.

[Brief description of the drawings]

FIG. 1 is a block diagram of one preferred embodiment of a DAF system according to the present invention.

FIG. 2 represents a plan sectional view of the tank of FIG. 1 along the line 2-2.

3 represents a sectional elevational view of the tank of FIG. 1 along the line 3-3 in FIG. 2;

FIG. 4 is a block diagram of another embodiment of a DAF system according to the present invention using a single flow path deployed flow tank.

FIG. 5 represents a plan sectional view of the tank of FIG. 4 along the line 5-5.

FIG. 6 represents a sectional elevation view of the tank of FIG. 4 along the line 6-6 in FIG. 5;

FIG. 7 is a side view of another embodiment of the present invention of a single channel internal flow having a plurality of dissolved air diffusers.

FIG. 8 illustrates a plan cross-sectional view of the tank of FIG. 7 along line 8-8.

9 is a side cross-sectional view of the tank of FIG. 7 taken along line 9-9 of FIG.

FIG. 10 is a dissolved air diffuser illustrated in FIG.
3 is an enlarged plan view of a partial cross section of FIG.

FIG. 11 is an enlarged elevation view of a partial cross section of the dissolved air diffuser of FIG.

FIG. 12 is a plan cross-sectional view of a multiple flow path internal winding tank of the present invention for use in a DAF system.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B03D 1/04 B03D 1/14-1/26 C02F 1/24 C02F 1/40

Claims (40)

(57) [Claims] 1. A dissolved air flotation device for separating suspended matter from a liquid, comprising a bottom wall and an upright cylindrical outer wall for retaining the liquid, and an equal height below the top of the outer wall from the bottom wall. Extending to a certain height,
At least one upright spiral, having an outer end connected to the outer wall and an inner end upstanding as a free end terminating near the center of the container, forming a spiral-shaped channel. And an inlet means communicating with one end of the flow passage below the top of the partition for discharging the liquid having the suspended substance into the container, and discharging the liquid separated from the suspended substance. A container having an outlet means in communication with the other end of the flow path below the top of the partition for dissolving compressed air in the separated portion of the separated liquid; Means for mixing at least a portion of the provided portion with the liquid and suspended matter introduced through the inlet means ; for adjusting the liquid level in the container above the constant height Means connected to the container; and released from the separate part Device includes; means for removing suspended solids floating on the liquid surface by the microbubbles of air. 2. An inlet means is located near the bottom of the container at the outer end of the partition to provide an inward flow through the flow passage, and the outlet is provided at the outlet of the container. The device of claim 1, wherein the device is centered near the bottom. 3. The liquid inlet means is common to all of the flow paths, is located at the bottom center of the vessel at one end of the flow path, and the outlet means is provided at the other end of the flow path. 2. The method of claim 1, wherein the partition is located near the outer wall at the periphery thereof, wherein each partition is connected to the outer wall to provide a developing flow of liquid through the flow path. apparatus. 4. The means for removing suspended material is located near the outer wall of the container at the level of the liquid level in the container to cause suspended suspended material to overflow from the container. 2. The apparatus of claim 1, including an overflow trough. 5. The apparatus of claim 1 wherein said level adjustment means includes an overflow outlet located at a liquid level in fluid communication with said outlet means. 6. The means for removing suspended material further comprises a curving blade driven by a motor centered above the container and positioned to scoop the liquid level. The device of claim 1, wherein 7. The apparatus according to claim 1, wherein the partition forms a spiral and an adjacent spiral flow path is formed around the center of the container. 8. The apparatus according to claim 2, further comprising diffuser means spaced along the bottom of said flow path for introducing another part of said separate part in the direction of flow. An apparatus according to claim 1. 9. The apparatus according to claim 4, wherein said overflow trough is tangential to said vessel outer wall to facilitate drainage of suspended suspended matter. 10. The apparatus according to claim 6, wherein said motor is a variable speed motor. 11. The apparatus according to claim 3, wherein said liquid outlet means corresponds to the number of flow paths. 12. The container has at least two of said partitions, defines a plurality of said channels, said outlet means being in communication with all of said channels, and a center of said container. The device of claim 1, wherein the device is located at 13. A tank having a flow path, an inlet at one end of the flow path for receiving a liquid and a suspended substance, and the other end of the flow path for discharging a liquid separated from the suspended substance. Dissolved air flotation for removing suspended solids from a liquid, comprising an outlet at an upper surface and an extractor above the flow path for removing suspended substances floating on the surface of the liquid. An apparatus extending from the tank bottom to a height below the tank top, forming an outer end connected to a side of the tank and an upright free end terminating at a radial distance from the center of the tank. At least one upright spiral partition having an inner end and forming a spiral flow path, for dissolving the compressed air in a portion of the liquid discharged from the outlet Means, and liquid and suspended matter taken in at the inlet, and a portion of the liquid Means for mixing at least a portion, and comprise are device. 14. The apparatus of claim 13, wherein said mixing means includes a dissolution tank for evacuating undissolved air in a portion of said liquid. 15. The apparatus according to claim 13, wherein said mixing means includes an air aspirator using said recirculated liquid as a working fluid. 16. A dissolved air flotation device for separating suspended matter from a liquid, wherein the device extends from the bottom to a certain height below the tank top, one end is connected to the tank side, and the other end is connected to the tank center. An inlet for introducing liquid and suspended matter at one end, comprising an upright spiral-shaped partition, terminating at a radial distance and forming a substantially spiral-shaped channel; An upright cylindrical tank communicating with an outlet in the lower section of the tank to discharge liquid separated from suspended matter at the other end, dissolving compressed air in a portion of the discharged liquid Means for communicating with the inlet to introduce at least a portion of the effluent liquid into the inlet for mixing the liquid and the suspended substance; and discharging and suspending the liquid from the liquid. Carried to the surface by microbubbles of air adhering to suspended matter Means arranged in the upper area of the tank to scoop suspended substances in the liquid,
And means in communication with the outlet for discharging liquid at the other end of the flow path. 17. The method according to claim 16, wherein said inlet is located peripherally and directs liquid and suspended matter into the tank, and said outlet is in the center of said tank and the flow through said flow path is internal winding. The described device. 18. The tank according to claim 18, wherein the inlet is at the center of the bottom of the tank and the outlet is located at the periphery to direct the effluent from the tank, so that the flow through the flow path is developed. 17. The device of claim 16, wherein: 19. An inner free end terminating near the center of the tank and having at least one partition forming an inward winding passage extending from near the bottom to a height below the top of the tank. In an upright tank having an inlet and an outlet proximate to either end of the flow path,
A purification method by separating suspended substances from unpurified liquid by dissolved gas flotation, wherein the unpurified liquid is mixed with a purified liquid containing dissolved gas to form a mixture, and the mixture is passed through the inlet. Introducing into the inner flow path, separating the suspended matter from the mixture by gas microbubbles released from the mixture, thereby producing the purifying liquid, and simultaneously discharging the purifying liquid from the outlet Removing the separated material from the surface of the mixture, dissolving gas in the discharged portion of the purified liquid for mixing with the unpurified liquid, and the residence time T of the mixture in the flow path. _{how 1} consists of maintaining a flow rate through the tank of the mixture so that at least equal to the residence time T _b of microbubbles in the mixture, in the mixture at a level near the top of the partition Setsutai. 20. Adding a chemical suitable for separating the unpurified liquid to the unpurified liquid prior to mixing the unpurified liquid with the purified liquid containing the dissolved gas. 20. The method of claim 19, comprising: 21. The method of claim 19, comprising the step of settling and removing sedimentable components of the suspended material through an outlet of the flow path. 22. The method according to claim 19, wherein said gas contains an oxidizing agent. 23. The method according to claim 19, wherein the gas contains a biocide. 24. The method of claim 19, wherein at least a portion of said gas is absorbable by said liquid. 25. The unpurified liquid contains a gas in which contaminants are dissolved, and the gas dissolved in the purified liquid strips at least a part of the gas in which the contaminants are dissolved from the unpurified liquid. 20. The method according to claim 19, which can be performed. 26. The method of claim 19, wherein said gas is a gas that is chemically reactive with said liquid. 27. The method of claim 21, comprising recirculating and adding a portion of said settleable component of suspended material to said unpurified liquid. 28. The method of claim 19 including the step of settling and removing sedimentable components of the suspended material from an outlet at the bottom center of the tank. 29. The method of claim 19, further comprising the step of recirculating and adding a portion of the suspended material removed to said unpurified liquid. 30. The micro-bubble residence time T _b is, z = depth of the mixture Z = total height of the mixture, μ ₁ = viscosity of the mixture Δρ = difference in density between the mixture and the gas d _Po = initial diameter of the foam Pa = atmospheric pressure, ρ ₁ = of the mixture 20. The method of claim 19, wherein the density is: 31. A purification method for separating substances suspended in an untreated liquid, wherein the free inner end terminates near the center of the tank and extends from near the bottom to a level below the top of the tank. Providing an upright tank having at least one partition forming an inner winding flow path and having an inlet and an outlet near the bottom in communication with either end of the flow path; Dissolving the gas in a portion of the processing liquid discharged from the outlet to form a first mixture, mixing the first mixture with the untreated liquid to form a second mixture, and Introducing a second mixture into the channel, removing suspended substances floating on the surface by microbubbles released from the second mixture as the second mixture flows through the channel; Draining the liquid through the outlet, the residence time of the second mixture in the flow path _{How 1} consists of maintaining a flow rate through the tank and the residence time T _b of microbubbles in the mixture of the second to at least equal, a mixture of at said second to the level near the top of the partition Setsutai . 32. The method according to claim 31, wherein the gas is an oxidizing agent for decomposing organic components in the substance. 33. The method of claim 32, wherein said gas is selected from the group consisting essentially of oxygen, ozone, and chlorine. 34. The method of claim 33, further comprising mixing the oxidizing agent with air. 35. The method of claim 31, further comprising adding a portion of the material removed in the untreated liquid to convert organics dissolved in the liquid. 36. The method of claim 31, comprising adding a biocide to the untreated liquid to produce potable water. 37. The method of claim 36, wherein said biocide is selected from the group consisting essentially of chlorine, chlorinated oxides, chlorine donors, and non-oxidizing biocides. 38. The method of claim 37, further comprising mixing the biocide with air. 39. The method according to claim 31, wherein said gas is capable of directly reacting with said liquid. 40. The micro-bubble residence time T _b is, z = depth of the mixture Z = total height of the mixture, μ ₁ = viscosity of the mixture Δρ = difference in density between the mixture and the gas d _Po = initial diameter of the foam Pa = atmospheric pressure, ρ ₁ = of the mixture The method of claim 31, wherein the density is: