JPH08196941A - Method and apparatus for floatation with dissolved air and similar gas-liquid contacting operation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To more perfectly and rapidly separate a suspended substance from a liquid medium by allowing a mixture of an untreated liquid and a liquid saturated with dissolved air under pressure to flow through a vortex passage and carrying the suspended substance to the surface of the liquid within the vortex passage while raising fine air bubbles generated from the liquid through the liquid mixture. SOLUTION: Both of an untreated liquid and a dissolved air-containing liquid are mixed by a mixer 18 and the mixed liquid flows through the passage of a flotation tank 10 and the suspended substance in the mixed liquid is removed to be discharged to a sediment trap 26 and all of residual particles are removed by a strainer 28. The treated liquid from the strainer 28 is sent to a liquid sump 30. A small amt. of the treated liquid saturated with dissolved air under pressure is recirculated to the inlet 20 of the tank 10 as a liquid. Compressed air is introduced into the liquid from a supply source 44 by a pump 46 and the dissolved air in the liquid is accumulated in a dissolved air separation tank 48 to be let escape by a relief device 47. The suspended substance or scum floated to the surface of the liquid in the tank 10 is removed through an overflow trough 34.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates generally to dissolved air floatation (DAF), and more particularly to
It relates to an improved and novel apparatus for DAF systems and other gas-liquid contact systems for separating and reacting liquids with contact gases.

[0002]

BACKGROUND OF THE INVENTION Many industrial activities are oils, fats, greases that must be separated or treated before discharge into the environment or use in any subsequent step. , A source of gases, liquids, and gaseous liquid wastes containing emulsifying or non-emulsifying suspended solids such as metals, organic and inorganic solids, and condensable organic vapors. These activities include petroleum and vegetable oil refining, steelmaking, food and beverage processing, metalworking, chemical and paint manufacturing, pulp, paper and textile manufacturing, aircraft maintenance, coke oven gas treatment, and water conditioning and water conditioning. Includes water treatment. The concentration of suspended solids and other components can vary widely depending on the source and processing conditions.

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

Currently, three widely used methods for separating suspended solids from liquids are gravity separation or settling for solids heavier than liquids, filtration for small particles, and floatability. Air flotation for suspended matter. Of course, the air flotation has the greatest application and is widely used industrially. Air can be blown into the liquid to float suspended matter on the surface and scoop suspended matter at the surface. However, this method does not effectively separate very small suspended solids. A more effective method is dissolved air flotation (DAF). High pressure air is dissolved in the liquid being treated and introduced at a lower pressure into the flotation tank. Microbubbles of air with dimensions of 10-40 microns are released and gently rise through the liquid, pushing suspended solids to the surface.

The conventional DAF system charges an untreated stock solution and a liquid with dissolved air into a flotation tank through separate inlets located near the bottom. Treated liquids containing reduced concentrations of suspended solids are discharged near the bottom of the tank, while suspended suspended solids are skimmed and removed at the top. Since the suspension of suspended solids by the rising (air) bubbles occurs vertically, there is a vertical concentration gradient of the suspended solids in the liquid in the flotation zone. Due to the buoyancy of the rising bubbles, the untreated liquid in contact with the bubbles moves upward, while the treated liquid moves downward. The vertical counterflow of the two liquids creates turbulence and mixing of the two liquids, which reduces the separation efficiency.

This turbulence and mixing can be made somewhat less by reducing the inflow velocity and by adding baffles to direct the flocs (agglomerates of suspended matter) and foam aggregates 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 velocity and coalescence of rising bubbles. Get burned. The liquid rising under the suspended matter must turn approximately 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 floating material flowing above the baffle causes mixing near the liquid surface. Therefore, the baffle is not very effective. The baffle also significantly reduces the surface area of the tank available for flotation and allows for a relatively high tank to ensure sufficient space above the baffle surface to allow suspended material to flow above the baffle surface. In need of. Also, unavoidable turbulence in the contact zone within the baffle can result in poor adherence of air bubbles to the suspended material particles and destruction of floc / air bubble aggregates.

Separation of very dilute concentrations (less than 10 ppm) or very small (less than 10 μ) from liquid media
Separation of suspended particles cannot generally be performed in conventional DAF systems. Chemicals such as polyelectrolytes and long chain polymers are used to agglomerate and build up small particles so that bubbles form larger aggregates that can easily contact and attach. Larger agglomerates are more buoyant and less susceptible to disruption by turbulence, thus making flotation easier and separation efficiency higher. Efficiency is 10-40% without such chemicals and 40-90% with chemicals
Is. However, ironically, there are more problems that occur than the problems that the added chemicals solve. Chemicals not only increase the cost of separation, but also increase the process time. Agglomeration can occur very quickly in high speed mixing tanks, but floc formation is time consuming, typically about 20-3.
It takes 0 minutes and requires a slower mixing tank. Only a very small proportion of the chemical dissolved in the liquid is removed with the actually suspended material. Residual chemicals must be removed later if their concentrations are unacceptable for recycling or release to the environment.

More recent DAF systems for reducing mixing between untreated and treated liquids divide the flotation tank into several communicating sections and direct the liquid to each section. There is some improvement in separation for large tanks, but little for smaller tanks. With a limited number of small sections, for a given flow rate, the mixing is stronger.

Another system uses a long flotation tank having a liquid inlet at one end and a liquid outlet at the other end. Liquid backmixing can be reduced, but there are few DAF locations with sufficient space to accommodate such long tanks.

One of the most popular DAF systems recycles the treated liquid to a flotation tank, which also has its advantages and disadvantages. Throughput is reduced, more backmixing of the liquid is processed, and operating costs are higher. This system is often combined with other techniques to compensate for these drawbacks. Filtration is often selected, especially for making portable drinking water. However, combining such a technique with dissolved air flotation is always more complicated and increases the cost of the device.

Another problem is the separation and removal of large heavy solids that tend to settle at the bottom of tanks. One solution is
In combination with slow stirring and the installation of another solids outlet at the bottom of the tank, undesired turbulence and mixing of the liquid occurs.

From all 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 back mixing, but at the expense of throughput. Although chemicals facilitate liquid separation, they also increase process time, increase cost, and expose many unwanted side effects. Recirculating the treated liquid itself improves separation efficiency, but this also increases cost and backmixing. Suspended matter and /
Methods and equipment for removing settled solids also cause turbulence and backmixing. Neither of these can prevent backmixing of the liquid being processed without sacrificing throughput. 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 undesired effect of liquid turbulence.

[0013]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a new and improved DAF method and apparatus for more completely and faster separation of suspended solids from a liquid medium without turbulence and backmixing. .

Another object is to provide an improved DAF method and apparatus capable of separating dilute concentrations of fine suspended matter from a liquid medium.

Yet another object is to provide an improved DAF process and apparatus that facilitates the simultaneous removal of suspended sludge and settled solids with substantially no loss of separation efficiency.

Yet another object is the addition of small amounts of chemicals,
Or to provide an improved DAF method and apparatus that separates stable emulsified liquids from liquid media and facilitates floc formation of suspended matter contained in the liquid media, with or without addition.

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

Briefly, the above and other objects are in a DAF device having an upright cylindrical tank having at least one vertical partition forming a spiral flow path. To be achieved. The mixture of untreated liquid and liquid saturated with dissolved air under pressure is continuously introduced from one end of the flow path near the bottom of the tank and swirled under plug flow (extrusion or piston flow) flow conditions. It flows along a shaped (inwardly or unfolded) passage and is discharged at the other end near the bottom. Air microbubbles released from the liquid rise through the liquid mixture and create buoyancy, which carries all the particles of suspended matter it contacts to the liquid surface in a spiral path.
Centrifugal and gravitational forces gradually settle large heavy solids to the bottom, which are separately drained from the liquid. Surface suspended matter is discharged continuously.

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

In the channel, there is no counter flow or back mixing of liquid. This is because the liquid enters from one end and goes out from the other end. The absence of liquid turbulence in the DAF tank is necessary for the particles to attach to the bubbles stably and to separate very dilute concentrations of particles. The entire internal surface area of the flotation tank is available for flotation. The design and scale-up of the flotation tank is easy and simple, with a plug flow
(Extrusion flow or piston flow) Follow reactor design principles.

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

[0022]

DETAILED DESCRIPTION OF THE INVENTION 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 inwardly wound or unfolded channel. It can be prevented. The liquid inlet at one end and the liquid outlet at the other end of the flow path create a plug flow (extruded or piston flow) capable of achieving maximum separation of all suspended solids in the liquid. Under plug flow conditions, the residence time of a liquid is inversely proportional to its average linear velocity,
It is also equal to the ratio of flow path length to velocity and to the ratio of flow path volume to liquid flow velocity. This condition can be maintained over the entire length of the channel for a wide range of flow rates. This is because the radial and tangential components of the flow pressure in the liquid are almost always balanced as the angular momentum is preserved.

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

The average final velocity (terminal velocity) V _t and the average residence time t of rising bubbles without aggregate formation through a stationary liquid of a given depth z are hydrodynamically determined as follows. Can be evaluated. V _t = dz / dt (1) or dt = dz / V _t (2) Therefore

[Equation 1] The initial bubble volume is v ₀ = v _Z (P ₀ / P _Z ) (4) where v _Z = capacity at depth z, P ₀ = bottom pressure, and P _Z = pressure at depth z, which is It may be related to the liquid density ρ _l 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)

Bubble volume v, and bubble diameter d _p , P _a
= Atmospheric pressure, and Z = total height of liquid, the following relationship holds. 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)

According to Stokes' law, the average final velocity V _t of a bubble can 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 substituting equations (8) and (9) in equation (3) and integrating the following relationship to the rising bubble residence time T _b = (= t).

[Equation 2] For maximum flotation efficiency, the liquid residence time T ₁ is determined to be equal to the rising bubble average residence time T _b . That is, T _b = T _l = flow path volume / 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 bubble density and volume are It remains virtually constant during the election. This means that for certain solid and liquid loads, the amount of air supplied is sufficient,
Bubble assembly formation due to turbulence is a negligible and valid assumption for normal DAF operation.

By making the residence time T _b of the rising bubbles equal to the residence time T _l of the liquid flowing through the channel, the length or height in the channel can be determined from the other.
Residence times T ₁ and T _b are typically set between 5 and 15 minutes, depending on the characteristics of the liquid being 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, in terms of conservation of angular momentum, and ease of removal of settled solids from the bottom of the tank. From the viewpoint, the inward winding flow is preferable to the expanding flow. Throughput can also be increased by using several flow paths, either wound or unrolled, in a single tank to maintain plug flow conditions for high separation efficiency.

Given D with fixed channel height
The maximum liquid flow rate for the AF tank can be determined by connecting the liquid retention time T ₁ and the bubble retention time T _b with an equation for a predetermined channel 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. A suitable device is provided for releasing the air dissolved in the liquid under pressure into the liquid to be treated and for mixing with the liquid to be treated. For large tanks or long channels, 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 device 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 which is radially bounded 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 ends 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 strainer 28, except for sediment and any suspended solids collected in trap 26, which removes all residual particles. However, for a small portion, the treated liquid L _t from the strainer 28 is sent to the sump 30, which determines the liquid level LL in the tank 10 by raising the overflow outlet 32. . This method of adjusting liquor levels sometimes results in sludge with low solids content. Therefore, the liquid level is controlled by a liquid height sensor (not shown), which generates a signal indicating the liquid level in a controller responsive thereto and controls a liquid pump for controlling the liquid inflow rate. May be desirable.

Treated liquid L saturated with dissolved air under pressure
A small amount of _t is recirculated to the inlet 20 of the tank 10 as liquid L _a . Compressed air from source 44 is introduced into liquid L _t at the input of pump 46, and all undissolved air in liquid L _t is accumulated at its output in melt separation tank 48 and released. -Failed by device 47. Of course, other means for introducing dissolved air into the untreated liquid L _u are conceivable. For example, an aspirator or ejector can be used to mix air with the liquid, with a portion of the processing liquid as the working fluid.

Suspended material or scum that has floated to the liquid level in tank 10 by the contacting microbubbles is removed through a tangential overflow trough 34 at the top of outer wall 12. A skimmer 36 having a curved blade is mounted on a support 38 so as to be rotatable on the liquid surface, and a low speed mode.
It is continuously driven by a turret 40 which discharges suspended solids or scum through 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 is in the flow path.
Figure 16 illustrates an upward inward passage of air bubbles and suspended matter as it passes through 16. The released bubbles attach to the floatable particles of suspended matter causing them to rise and float to the surface. Under centrifugal force and gravity, heavier solids continue to flow with the liquid and gradually settle towards the bottom of tank 10. A concentration gradient with a maximum at the top for suspended solids and a maximum at the bottom for sediments is thus created. Heavier solids or sediment is collected in the trap 26, these are removed through the gate valve 42, and suspended solids are extruded by the skimmer 36 and discharged to the overflow trough 34. Any small non-floating suspended matter that remains in the liquid is discharged from tank 10 through central outlet 24 and removed by strainer 28. Due to the inward flow of liquid, suspended suspended matter can sometimes show a tendency to accumulate near the center of the tank. In that case, the suspended matter can be easily removed by a suction means (not shown) instead of the skimmer 36.

The DAF system shown in FIG. 4 will be described below.
An upright cylindrical tank 50 is provided for the deployment flow. This embodiment is particularly suitable for separating suspended substances in liquids which do not contain precipitated solids. A spiral inner wall 52 forms an unfolded flow path 54 having an inlet 56 in the center of the tank bottom and a peripheral outlet on a side surface near the bottom of the tank.
58, which provides a spreading flow through the channel 54. 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 passes through the flow path 54, the outlet 58, and the trap as shown in FIG.
Overflow reservoir through 26 and strainer-28
At 30, the overflow flow outlet 32 maintains the liquid level height LL in the tank 50 in the same manner as described for the system of FIG. Solids collected at the bottom of tank 50 are removed at ambient outlet 59.

Liquid L _a is saturated with dissolved air under pressure in the same manner. Compressed air from air source 44 is strainer
Dissolved in a small amount of process liquid L _t from 28 and pump 4
6 and a tank 48 equipped with a relief valve 47 leading to a mixer 60. Other methods and devices for dissolving air in a liquid under pressure include high speed mixing pumps, tanks with or without packing, and fixed mixers.

In a long tank with a spiral flow path,
Several discharge devices are provided near the liquid inlet in order to provide an even distribution of sufficient bubbles in the liquid to be treated, or in the longitudinal direction of the flow path to distribute the bubbles. Serve along. 7 to 11 show the inner partition wall 94.
Figure 1 shows an upright cylindrical flotation tank 90 having an outer wall 92 whose interior is partitioned by
In the manner described for 10, the liquid L _u is introduced through a peripheral inlet 98 on the side near the bottom of the tank 90 and the outlet 100 at the bottom center 100
An inwardly wound flow path 96 is formed so as to go out.

[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. Diffuser - The -102 preferably has a nozzle 103, the nozzle 103 toward the liquid L _a downward flow, giving an additional push liquid to enhance inner winding stream. Obviously, because of the spreading flow, this nozzle is ejected in another direction. This design configuration thereby provides for the continuous introduction of bubbles along the entire liquid flow path and increases tank capacity for flotation.
Settled and floating material is removed in the same manner as described in tank 10.

It is conceivable to provide more than one flow channel (channel) in the DAF tank. For example, FIG. 12 shows a flotation tank 110 having three flow paths. The tank is separated by three spiral walls 112A, 112B, 112C at an angle of 120 ° and each has a separate peripheral liquid inlet 114, but a common central liquid outlet 11 at the center of the bottom of the tank.
6 to form three inner-wound flow channels having one overflow outlet 118 for suspended matter. 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 unfolding flow and the number of spiral walls can be changed according to the particular requirements.

From the foregoing discussion, it is apparent that several important points should be considered in order to implement the present invention smoothly. For a given liquid load, the dimensions (length, height and width) of the flow passage in the DAF tank should provide a liquid residence time in the passage equal to or slightly greater than the residence time of the bubbles in the liquid. Is. This allows sufficient time for the bubbles and suspended solids to rise to the surface of the liquid before the liquid reaches the outlet of the channel. The average linear velocity of the liquid in the channel should 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 varied. The amount of air supplied should be sufficient for the specified solid and liquid loads.
The volume concentration of air 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 rate of suspended solids. 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
Should be air / m ³ water. The average particle size of the discharged bubbles should be controlled within the range of about 10-40μ by controlling the pressure difference and the flow rate across the discharging device. The bubble size is preferably limited to approximately 130μ by limiting channel height and liquid level height. 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 unsaturated liquid also depends on the contact time and the mixing effect of the two fluids. Therefore, the 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 it is desired to recover the used air or the processed gas, 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 floc formers. And This includes the separation of very stable, dilute emulsions and the separation of liquids, which takes place at very high rates. Chemical contamination of the treatment liquid can be prevented, thereby obviating the need for secondary treatment 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,
Process liquids with high speed and high separation efficiency. Many conventional DAF tanks can be easily modified or retrofitted in accordance with the present invention by replacing the existing internal structure with spiral-shaped partitions and changing the location of the liquid inlet and outlet.

Applications of the invention other than those described above are also possible. For example, with little or no modification, it can be used for the treatment of suspended and dissolved organic-containing liquids using oxidizing gases such as oxygen, ozone and chlorine, alone or mixed with air, It is possible to remove suspended matter and simultaneously digest dissolved organic matter. When applied to the activated sludge process for converting dissolved organic matter in wastewater using microorganisms, some of the suspended or settled sludge, which mainly contains microorganisms, is recycled and untreated wastewater. A portion of the effluent that has been added to and treated is recycled to dissolve the air or oxygen needed for the microorganisms and then mixed into the untreated effluent in the DAF tank. To produce drinking water, the raw water is chlorine, chlorine dioxide,
Biocides such as chlorine donors or non-oxidizing biocides can be treated alone or in admixture with air. Gases and gaseous wastes can also be separated or treated according to the invention by physical or chemical absorption using suitable liquids. On the other hand, the gas dissolved in the liquid can be released by desorption due to the dissolved air bubbles. An example is the stripping of ammonia dissolved in water by air. It will be apparent that the present invention can be used to treat both liquids and gases and can be used to react gas with liquids. The present invention allows for the simultaneous removal of both suspendable and sedimentable suspensions and can therefore be used in the gravity separation of liquids containing many forms of suspended matter. It can also promote hydraulic agglomeration of the suspension contained in the liquid to be treated and thus serve as a floc former, with or without separating the flocs that form.

Various details and variations in the arrangement of components are set forth to illustrate the principles of the invention, and each individually exemplified detail and variations in the arrangement of components are claimed in the art. It is understood that it can be made within the spirit and scope of the defined invention.

[Brief description of drawings]

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

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

3 represents a vertical cross-section of the tank of FIG. 1 along the line 3-3 of FIG.

FIG. 4 is a block diagram of another embodiment of a DAF system in accordance with the present invention that uses a single flow expansion flow tank.

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

6 represents an elevational sectional view of the tank of FIG. 4 taken along line 6-6 of FIG.

FIG. 7 is a side view of another embodiment of the present invention for a single flow passage with multiple melted air diffusers.

FIG. 8 represents a plan sectional view of the tank of FIG. 7 along the 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.

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

FIG. 12 is a cross-sectional plan view of a multi-passage, internally wound tank of the present invention for use in a DAF system.

Claims (41)

[Claims] 1. A dissolved air flotation device for separating suspended solids from a liquid, comprising a bottom wall and an upright cylindrical outer wall for holding the liquid, and a constant from the bottom wall to below the top of the outer wall. At least one that extends to a height and has an outer end that is in communication with the outer wall and an inner end that is upright as a free end that terminates near the center of the container to form a spiral channel. Separated from suspended material by two upright spiral-shaped partitions, an inlet communicating with one end of the flow path below the partition to contain liquid with suspended material in the container A container having an outlet in communication with the other end of the flow path below the top of the partition for discharging liquid; means for dissolving compressed air into separate portions of the separated liquid; At least a portion of the separated portion was introduced through the inlet Means for mixing with body and suspended matter; means connected to the container for adjusting the liquid level in the container above the height; and discharged from the separate part Means for removing suspended solids suspended on the liquid surface by air microbubbles. 2. The inlet is located near the bottom of the container at the outer end of the partition and the outlet is the bottom of the container to provide inward flow through the flow path. The device of claim 1, wherein the device is centrally located nearby. 3. The liquid inlet is common to all of the flow paths,
The outlet is located at the center of the bottom of the container at one end of the flow path, the outlet is located at the other end of the flow path near the outer wall of the periphery, and each partition is The device of claim 1 in communication with the outer wall to provide a spreading flow of liquid through the flow path. 4. A means for removing suspended solids suspended on the surface of the liquid in the container, the means for removing suspended suspended solids from the container. An overflow located near the outer wall of the container at the height of the liquid level.
The apparatus of claim 1 including a trough. 5. The apparatus of claim 1 wherein said liquid level adjusting means includes an overflow outlet located at a liquid level in fluid communication with said outlet. 6. The removal means further comprises a curvilinear blade positioned to scoop the liquid level, driven by a motor centrally located above the vessel. The device according to claim 1. 7. A device according to claim 1, wherein each of the walls of the partition forms a helix and adjacent spiral flow channels are formed around the center of the vessel. 8. The apparatus of claim 1, wherein the outer wall is generally cylindrical and the container is generally upright. 9. An overflow trough located at the liquid level is positioned tangential to the outer wall of the container to facilitate overflow of suspended suspended material. The device of claim 4, wherein 10. The apparatus according to claim 2, wherein the number of liquid inlets corresponds to the number of flow paths. 11. The apparatus according to claim 3, wherein the liquid outlet corresponds to the number of flow paths. 12. The container has at least two of the partition bodies to form a plurality of the flow paths, and the outlet communicates with all of the flow paths, and the center of the container is provided. The device of claim 1, wherein the device is located. 13. The apparatus of claim 6 wherein said motor is a variable speed motor. 14. A tank having a flow path, an inlet at one end of the flow path for receiving liquid and suspended matter, and the other end of the flow path for discharging the liquid separated from the suspended matter. A dissolved air float for removing suspended solids from the liquid, including an outlet at and an extractor above the flow path to remove suspended solids on the surface of the liquid. A selection device that extends from the bottom of the tank to a height below the top of the tank and forms an outer end that is connected to the side of the tank and an upright free end that ends at a radial distance from the center of the tank. At least one upright spiral-shaped partition having an inner end that forms a spiral-shaped flow path, for dissolving compressed air in a part of the liquid discharged from the outlet. Of the liquid and suspended matter and a portion of the liquid taken up at the inlet. Means for mixing the least part,
A device that contains. 15. The apparatus of claim 14 wherein said mixing means comprises a dissolution tank for venting undissolved air in a portion of said liquid. 16. The apparatus of claim 14 wherein said mixing means comprises an air aspirator using said recirculated liquid as a working fluid. 17. A method for separating suspended solids from a liquid by dissolved gas flotation, wherein a portion of the liquid is mixed with air to form a mixture, the mixture being a spiral form of the liquid. It is released at one end of the channel, blended with the liquid in a predetermined proportion, separating the suspended solids from the liquid by microbubbles of the gas released from the mixture, and at the same time other Draining the separated liquid at the end and removing suspended suspended material from the surface of the liquid on the flow path. 18. The method of claim 17 including the step of adding to the liquid a chemical suitable for separation of the liquid prior to mixing the liquid with a gas. 19. The method of claim 17, comprising the step of settling and removing settling components of the suspended material through the outlet of the flow path. 20. A method of treating a liquid containing suspended and dissolved organic matter according to claim 17, wherein said gas contains an oxidant. 21. The liquid treatment method according to claim 17, wherein the gas contains a biocide. 22. The method of claim 17, wherein at least some of the gas is absorbable by the liquid. 23. The method of claim 17, wherein the liquid contains a dissolved gas and the gas is capable of stripping at least a portion of the dissolved gas from the liquid. 24. The method of claim 17, wherein the gas is a gas that is chemically reactive with the liquid. 25. The method of claim 19 including the step of recycling and adding to said liquid a portion of said sedimentable component of suspended matter. 26. A dissolved air flotation device for separating suspended solids from a liquid, which extends from the bottom to a certain height below the top of the tank, with one end connected to the side of the tank and the other end from the center of the tank An upright spiral-shaped partition that ends in a radial distance and forms a substantially spiral-shaped flow path, the flow path being at one end for the introduction of liquid and suspended matter And an upright cylindrical tank in communication with the outlet in the lower area of the tank for discharging the liquid separated from the suspended matter at the other end, dissolving compressed air in a part of the discharged liquid Means for communicating with the inlet for introducing at least a portion of a portion of the effluent liquid into the inlet for mixing the liquid and suspended matter. Carried to the surface by air microbubbles attached to suspended matter Means located in the upper area of the tank for skimming the suspended solids in a liquid,
And a means in communication with the outlet for discharging liquid at the other end of the flow path. 27. The method of claim 26, wherein the inlet is circumferentially oriented to direct liquids and suspended matter into the tank and the outlet is in the center of the tank and the flow through the channel is inward. The described device. 28. In order to direct the effluent from the tank, the inlet is centrally located at the bottom of the tank and the outlet is located at the periphery such that the flow through the flow path is in a deployed manner. 27. The apparatus of claim 26. 29. The diffuser means of claim 2, further comprising spaced diffuser means along the bottom of said channel for introducing another portion of said portion in the direction of flow. The described device. 30. A method for separating substances suspended in an untreated liquid, the spiral flow extending in an upright tank from the bottom of the tank to a position below the top of the tank. A channel is provided, and an inlet and an outlet are provided in the flow channel at a position lower than the position and communicate with the flow channel at either end, and one of the processing liquids discharged from the outlet is provided. Gas in the part to form a first mixture, the first mixture with the untreated liquid to form a second mixture, and the second mixture through the inlet at a rate that produces a plug flow. A method comprising introducing a mixture into the channel, removing substances floating on the surface when the second mixture flows through the channel, and discharging the treatment liquid through the outlet. 31. The method of claim 30, wherein the gas is an oxidant for decomposing organic components in the material. 32. The method of claim 30, wherein the gas is selected from the group consisting essentially of oxygen, ozone, and chlorine. 33. The method of claim 32, further comprising mixing the oxidant with air. 34. The method of claim 30, further comprising adding a portion of the removed material in the untreated liquid to convert organic matter dissolved in the liquid. 35. The method of claim 30, comprising adding a biocide to the untreated liquid to yield potable water. 36. The method of claim 35, wherein the biocide is selected from the group consisting essentially of chlorine, chlorine oxides, chlorine donors, and non-oxidizing biocides. 37. The method of claim 36, further comprising mixing the biocide with air. 38. The method of claim 30, wherein the gas is capable of direct chemical reaction with the liquid and the reaction mixture is discharged from the channel with the reacted liquid. 39. The method of claim 30, wherein the gas is capable of direct chemical reaction with the liquid and the reaction mixture is discharged from the surface of the liquid along with the reacted gas. 40. The method of claim 17 including the step of settling out the settling components of the suspended material from the central outlet. 41. Recycling and adding a portion of the suspended material removed to the liquid.
The method described in. .