Dissolved Air Float Frc - Toro

© Toro Equipment 2009

ANACONDA FLOTATOR FRC 1

DISSOLVED AIR FLOAT FRC

Dissolved air flotation is a process used to

separate solid (solids in suspension) and liquid (oils and

grease) particles, and to separate and concentrate

sludge.

The process unites the particles that enter the

float with small air bubbles that together form a whole

whose density is less than that of the water, where by

they float. In this way it is possible to separate particles

from the water that initially have a greater density.

When the dissolved air flotation is preceded by

a coagulation-flocculation treatment the results of

separating the solid material in suspension are much

better, reaching an elimination rate of 95% without any

problems at all. This also implies a reduction in the BOD5

of at least 40%, depending on the type of waste.

The dissolved air flotation equipment

developed and manufactured by TORO EQUIPMENT,

S.L. is designed to favour greatly the formation of

compact air/solid or air/oil particles, thus enabling the

rapid elimination of load and grease.



In the treatment of waste water, flotation is used to

eliminate material in suspension and to concentrate the

biological sludge.

The main advantage of the flotation process as opposed

to that of sedimentation is that small or light particles which are

slow to settle can be eliminated better in a shorter time span.

Once the particles are on the surface, they can be collected by

using a surface scraper.

At present, the practical application in waste water

treatment installations is limited to the use of air as the agent

responsible for the phenomenon known as flotation. The

bubbles are added, or their formation is introduced, by one of

the following methods:

• Injection of air into the liquid under pressure followed

by the releasing of the liquid from this pressure

(dissolved air flotation).

• Aeration at atmospheric pressure (flotation by

aeration).

• Saturation with air at atmospheric pressure, followed

by the application of a vacuum to the liquid (flotation

by vacuum).

With all these systems, it is possible to improve the

degree of elimination and the results by the introduction of

Chemical additives.

DISSOLVED AIR FLOTATION

In the DAF systems (Dissolved Air Flotation), the air is

dissolved in the waste water at a pressure of several

atmospheres. The pressure is then released until it returns to

normal. In small installations the total capacity to be treated is

compressed by means of a pump, the compressed air in the

pump's suction tube being added.

It is kept under pressure in a boiler for some minutes to

give the air time to dissolve. Then the liquid under

pressure is fed to the flotation tank through a pressure

control valve, and this means that the air will no longer

remain dissolved, forming minute bubbles distributed

throughout the entire volume of the liquid.

In larger installations, part of the effluent from the DAF

process is recycled, and this is compressed and

semisaturated with air. The recycled flow mixes with the

main uncompressed current before entering the flotation

tank, and this means the air is no longer dissolved and

enters into contact with the solid particles at the inlet of

the tank. The principal applications of dissolved air

flotation are centered on the treatment of industrial

waste water and the thickening of sludge.

FLOTATION BY AERATION

In the flotation by aeration systems, the air bubbles are

directly introduced in the liquid phase by means of

diffusers or submerged turbines. Direct aeration over

short periods of time is not especially effective when

trying to make solids float. The installation of aeration

tanks is not usually recommended for the flotation of

grease, oils or solids present in normal waste water, but

it has been successful in the case of waste water that

has a tendency to form surface foam.

ADVANTAGES OF FLOTATION



FLOTATION BY VACUUM

Flotation by vacuum consists of saturating the waste

water directly with air in the aeration tank, or of allowing the air

to enter the suction pipe of the pump. The application of a

partial vacuum causes the dissolved air to leave the solution in

the form of minute bubbles. The bubbles and the solid particles

they adhere to, rise to the surface to form a layer of foam that is

eliminated by a surface scraping mechanism. Sand and other

heavy solids, which are deposited on the bottom, are

transported to a central sludge collector and extracted from

there by a pump. If the installation has to eliminate the sand

and the sludge must be digested, it would be necessary to

separate the sand from the sludge in a sand classifier before

the latter is pumped into the kiers.

The installation is made up of a covered cylindrical tank,

where a partial vacuum is maintained, and which includes

mechanisms to extract the sludge and the foam. The floating

material is continually swept towards the periphery of the tub,

where it is automatically discharged into a foam channel from

where it is extracted by a pump, also under conditions of a

partial vacuum.

The auxiliary equipment includes a boiler for saturating

the waste water with air, a tank that provides a short interval of

time for the elimination of the large bubbles, the vacuum and

foam pumps.



The waste water is mixed with a flow of recycled air

that has already been treated from the outlet compartment.

Applying Henry's Law, when this flow almost reaches

atmospheric pressure, the saturated water dissipates the

excess air. A well studied system of injectors distributes this

flow throughout the float, causing a jump in pressure so that the

size and quantity of the microbubbles is adequate for achieving

the maximum adhesion-absorption of the impurities.

The bonded air and particles rise to the surface of the

float forming floating sludge, separate from the effluent. This

sludge remains in a thickening area to be evacuated later by

means of a scraper.

Heavy particles, such as sand, remain in the

decantation compartment, situated in the bottom. A

pneumatically activated valve in the small series (FRC-2 up to

FRC-20) and a perpetual screw in the large series (FRC-40 up

to FRC-80) remove the sludge formed. It is then evacuated by

means of a sand container.

In the process designed by TORO EQUIPMENT,

S.L., the flotation takes place in four stages:

FORMATION OF DISSOLVED AIR BUBBLES:

For a correct flotation, the maximum quantity of air

must be introduced into the float. In addition, it must be

distributed in bubbles of the smallest possible size (without

being influenced by electrostatic charges) and this implies:

• The greatest number of bubbles.

• The greatest adherence capacity (especially for

small particles).

In the FRC floats, this is achieved by introducing the

mixture of waste water, recycled water and air into an

antechamber or into the polyelectrolyte injection point (if a

prior chemical treatment is available).

By the application of Henry's Law, the greater the

pressure of the recycled water, the greater the amount of

air transported will be. Also, the passage from the pressure

zone to the antechamber must be immediate and through

pipes as short as possible to avoid the coalescence of

microbubbles of air, giving rise to larger ones.

This is achieved in the FRC by an exclusive

compression system at 4-5 Kg/cm2 and an injection that

generates a pressure jump of up to 0.1 Kg/cm2 inside the

float. To achieve this, the fluid is passed through some

(variable) fine pass pneumatic valves which can be cleaned

automatically from time to time. The result is millions of

bubbles of around 40-60 µm capable of trapping all the

solids in the waste water.

The waste water is mixed with a current of already

treated water recycled from the outlet compartment. This

recycled water is sent through a special compressor to an

air saturation system at a pressure of 5-6 Kg/cm2. Applying

Henry's Law, when this current returns to atmospheric

pressure, the saturated water dissipates the excess air. A

well studied system of injectors distributes this flow

throughout the float causing a jump in pressure so that the

size and quantity of the microbubbles is adequate for

achieving the maximum adhesion-absorption of the

impurities.

DESCRIPTION OF THE FLOTATION PROCESS

1. FORMATION OF DISSOLVED AIR BUBBLES

2. ADHERENCE OF BUBBLES TO THE PARTICLES TO

FORM SOLID/AIR PARTICLES.

3. FORMATION OF THE AIR/SOLID PARTICLES AND

FLOTATION OF THE CONGLOMERATE FORMED.

4. SEPARATION OF THE SLUDGE FORMED.



ADHERENCE OF THE BUBBLES TO THE PARTICLES TO FORM SOLID/AIR PARTICLES:

In the carefully designed antechamber, close contact

between the waste water and the microbubbles is

achieved. The small and homogeneous size of the bubbles

encourages their adherence to the floccules of the effluent.

Once the solid/air particle has been formed it is then

capable of rising to the surface by itself.

The distribution method of the bubbles greatly

influences the microflotation. A series of small valves, that

work automatically and are guaranteed free from

blockages, is used.

FORMATION OF THE AIR/SOLID PARTICLES:

The following is necessary for the good formation of

air/solid particles:

• Laminar conditions.

• Gradients of velocity.

• Composition of the mixture.

The water flows through the laminar package

perpendicular to the ascending flow of the floated particles

and descending flow of the heavy solids. The flow in the

laminar package is completely laminar except on the crest

of the corrugations, where controlled microturbulence is

generated.

This turbulence causes the air/solid particles to collide,

forming larger particles with a diameter of between 250 and

300µm, which, in the form of bunches, make up a kind of

stable floccule of air and solids. This is the ideal size.

The system has a surface load equivalent to half that of

its developed useful surface, that is: it can treat double the

capacity of the rest with the same performance.

The mixture is guaranteed by the system of injection

which gives a perfect waste water recycled water mixture,

thus facilitating the adhesion and formation of

conglomerates of particles.



SEPARATION OF SLUDGE FORMED:

After flotation, the sludge must be concentrated and

separated. There are two kinds of sludge to be separated.

Floated sludge and decanted sludge. The floated sludge is

separated and remains in a thickening zone. It is important to

avoid the deaeration and fall of the sludge as this would allow it

to escape with the effluent. The first sludge to be scraped from

the surface is that which is retained for the longest time. This

allows high degrees of dryness to be obtained (between 6-

10%) without losing efficiency in the separation results.

In the high series of floats (FRC-40 up to FRC-80) the

decanted sludge is concentrated on the bottom and is

evacuated by means of a perpetual screw.

In the small series (FRC-2 up to FRC-20) the heavy sludge

is eliminated by means of a pneumatic valve activated at a

certain time interval, thus making cleaning automatic.



FLOAT

The float is an open rectangular tank made of

polyester reinforced with fibreglass and divided in three

principal chambers:

• Flotation and sludge dragging chamber.

• Treated water spillway.

• Sludge spillway.

The air and water mixture is injected into the chamber

under pressure and the chain of surface scrapers worked

by a pressure regulator (which determines the speed of

the drag) evacuates the sludge through the outlet spillway

by means of gravity along a pipe.

The clean water falls through a spillway into the

collection chamber from where it is evacuated through

pipes.

The degree of sludge thickening will depend, to a

great extent, on the characteristics of the water being

treated, so changes in the water at the inlet will inevitably

bring about changes in the characteristics of the sludge

produced, including the degree of thickening.

In the same way, the results obtained in the

elimination of solids in suspension, and therefore in the

reduction of the contaminating load, will depend largely

on the type of effluent.

As we are dealing here with a physical system of

separation, the most that can be eliminated is the

undissolved load.

COMPRESSION CIRCUIT

This consists of the compressed air supply circuit, the

compressed air-water mixture pump and the INJECTION

CHAMBER for injection to the float. The compressed air is

supplied by a COMPRESSOR, it then passes through an air

filter and a pressure controler, before being mixed with the

recycled water. The working of this compressor is controlled by

a pressurestat situated inside it. The PNEUMATIC PANEL

BOARD includes all the elements needed for the correct

working of the pneumatic circuit which is made up of:

-AIR FILTER: this separates the impurities present

in the air, as well as eliminating the water that forms

due to condensation. To do so, it has a manual

escape valve to avoid the precipitate container from

filling up.

-LUBRICATOR: this lubricates all the air circuits

that need it for their correct functioning.

-PRESSURE CONTROLER: this supplies the ideal

pressure for the inlet circuit of air to the pump.

-PRESSURESTAT: this protects the system from

possible pressure overloads.

-FLOATMETER: this fixes the amount of air injected

into the pump to produce the compression

phenomenon.

-MANOMETERS: through these the following can

be seen:

• The air pressure needed for injection into

the pump.

• The working pressure of the compression

circuit.

DESCRIPTION OF THE EQUIPMENT



COMPRESSION PUMP

The recycling pump produces the impulse and mixes

the compressed air with the recycled water which is sent to

the boiler for injection into the float at a later stage. The

pressure of the mixture is measured with the manometer on

the outside of the panel.

The injection is carried out by means of pneumatic

valves activated by electrovalves. These valves are

periodically automatically cleaned by rapidly opening and

closing.

Bottom drainage: The drainage of the float is carried out

automatically by means of a butterfly valve with a simple

pneumatic switch activated by means of an electrovalve

which opens and closes with a time delay.



• Solid and compact construction. It can be integrated

in complete plants, forming a totally compact set. It

can also be built on portable structures, thus

facilitating transportation and making changes in

ubication possible.

• Chemical treatment with product dosification in the

flocculator can be included as a piece of equipment

that can be coupled directly to the flotation

equipment, thus saving a lot of space.

• Additional hydraulic flexibility (depending on the input

contaminating load) of up to 30%.

• Compression system with a performance of up to

nearly 100%.

• Air injection system.

• Reflocculation.

• Increased dryness of separated sludge when

compared with conventional equipment (depending

on the type of waste water, it will be between 6-10%).

• Purging of decanted sludge.

• Minimum maintenance costs.

• Ease of operation.

• Formation, under controlled conditions, of the air-

solid particles in the package of laminar plates,

resulting in a rapid removal of the solids from the

liquid. Because of the incorporation of the plate

technology, the speed of flotation is extremely low,

1.5 m3/m2xh, as compared with conventional

systems.

• The careful design of the distributing system means

that the distribution is uniform in the upper part of the

transversal section of the F.R.C. system.

• The surface scraping system does not allow the

sludge to remain too long in the floats, in which case

(due to the formation of free fatty acids) fermentation

would begin. In addition, this system is totally exterior

and none of the parts comes into contact with the

water.

• The dry solids are transported and dehydrated by the

surface scraper which is 100% blockage free.

• The speed of the surface scraper can be varied to

bring it into line with any variation of the load at the

inlet.

• The retention time (12 to 14 minutes) eliminates

turbulence caused by temperature gradients.

ADVANTAGES OF FRC EQUIPMENT



The dissolved air flotation equipment FRC has many

applications in the purification of waste water for practically any

type of industry:

• In the food industry to eliminate solids in suspension,

as well as the separation of oils and grease which is

an important problem in the dairy industry,

slaughterhouses, the production of meat and fish

products, etc.

• Following a biological treatment, the FRC float

eliminates 30% of the BOD5 and over 70% if a

coagulation-flocculation treatment has been done

beforehand.

• In industries with emulsified oil problems, a correct

emulsion breaking treatment will prepare the

floccules for separation in the float, thus achieving

excellent results in the elimination of oils.

• In the paper industry for separating the pulp within

the waste water recycling process.

• Purification of typical industrial water; after

coagulation-flocculation, the sludge is floated,

thickened between 6-10%.

Physical-Chemical wastewater treatment.

Paper industry. Fibre recovery.

Separation processes in food.

APLICATIONS



Toro Equipment, S.L, reserves the right to modify, without prior notice, the data and characteristics that appear in this catalog.

TECHNICAL SPECIFICATIONS

Model FRC-2 FRC-5 FRC-10 FRC-15 FRC-20 FRC-40 FRC-80Nominal capacity (m3/h) 2 5 10 15 20 40 80

DimensionsMaximum width A (mm) 795 1.885 1.805 1.885 1.845 2.546 3.295Max height B (mm) 1.300 2.525 2.525 2.525 2.525 2.525 2.525Length L (mm) 2.120 2.330 3.360 4.670 5.900 7.200 9.200Necessary space (m) 3,5x2 3,7x3 4,7x3 6x3 7x3 8,5x4 10,5x4,6Total installed power, Kw 2,7 4,1 4,1 4,1 4,1 7,5 13,75

Material P.R.F.V. P.R.F.V. P.R.F.V. P.R.F.V. P.R.F.V. P.R.F.V. P.R.F.V.Exterior structure Galv steel Galv steel Galv steel Galv steel Galv steel Galv steel Galv steel

TubingWater inlet (mm) 63 110 110 125 160 200 2x200Water outlet (mm) 63 110 110 125 160 200 2x200Sludge outlet (mm) 110 125 125 125 160 200 200Bottom drainage (mm) 63 75 75 90 93 2x110 200Recycling 40 63 63 63 63 63 63

Sludge dischargeAutomatic valves 1 1 1 1 1 1 1Discharge of floating material surface scraper surface scraper surface scraper surface scraper surface scraper surface scraper surface scraper

Scraping mechanismsMaterial AISI 304/PRFV AISI 304/PRFV AISI 304/PRFV AISI 304/PRFV AISI 304/PRFV AISI 304/PRFV AISI 304/PRFV

Installed power (Kw) 0,122 0,37 0,37 0,37 0,37 0,37 0,37

CompressorNº Units 1 1 1 1 1 1 1Model C-2/50 C-2/50 C-2/50 C-2/50 C-2/100 C-2/100 C-2/200Tank capacity (l) 50 60 50 50 200 200 200Power (Kw) 1,5 1,5 1,5 1,5 1,5 1,5 2,2Pressure (Kg/cm2) 6-8 6-8 6-8 6-8 6-8 6-8 6-8



CONSIDERATIONS

The equipment has a gangway to facilitate inspection and maintenance.

When conditions require it and UNDER ORDER the float's structure can

be made in AISI 316 and AISI 304.

The equipment needed to complete the flotation by means of a prior

chemical treatment (FLH, DPR, PAP, dosage pumps and pH controller).

Standard construction of polyester reinforced with fiberglass. For

applications with very high aggressiveness is built with special resins and

polypropylene pipes and thermal circuits.

Optional electrical panel with integrated PLC.

Optional lids in models FRC-2 to FRC-20.

Optional srew sludge extraction.



The flotation process is normally helped by adding

certain chemical compounds. Most of these chemical

reagents function by creating a surface or structure

that allows the air bubbles to be easily absorbed or

trapped. The inorganic chemical reagents, such as

iron or aluminium salts and live silica, are added to

solid particles in such a way as to create a structure

that facilitates the absorption of the air bubbles.

Several organic polymers can also be used to modify

the nature of the air-liquid, solid-liquid interfaces, or

both of them at the same time. In general, these

compounds act by placing themselves on the interface

to produce the desired changes.

The degree of purification obtained when reagents

are added to the waste water depends on the quantity of

reagents used and on the care taken over their control

and operation. Using chemical precipitation, it is possible

to eliminate between 80 and 90% of the solids in

suspension, between 70 and 80% of the BOD5 and

between 80 and 90% of the bacteria. The comparable

elimination values for primary sedimentation tanks,

correctly designed and operated, without the addition of

reagents is between 50 and 70% for solids in

suspension, between 25 and 40% for the BOD5 and

between 25 and 75% for bacteria. Given that the

characteristics of the waste water are variable, the

necessary dosage of reagents should be determined by

laboratory tests (jar test) or with a pilot plant.

CHEMICAL ADDITIVES



MODEL F-Q2 F-Q5 F-Q10 F-Q15 F-G20 F-Q40 F-Q80Caudal nominal 2 5 10 15 20 40 80

Flocculator tube FLH2 FLH5 FLH10 FLH15 FLH20 FLH40 FLH80Length, mm 2.200 2.280 2.390 4.640 6.240 7.200 9.200Height, mm 800 1060 1050 1120 1140 1.440 1490Width, mm 475 550 650 650 780 900 900Nominal diameter 75 110 110 110-125 110-160 160-200 160-250Injection points 3 3 3 3 3 3 3Material PVC/steel PVC/steel PVC/steel PVC/steel PVC/steel PVC/steel PVC/steel

Coagulating pumpType Doser Doser Doser Doser Doser Doser DoserCapacity (l/h) 5 14 27 35 50 75 115Nominal diameter DN4 DN8 DN8 DN8 DN8 DN20 DN20Membrane Teflón Teflón Teflón Teflón Teflón Teflón Teflón

Soda pumpType Doser Doser Doser Doser Doser Doser DoserCapacity (l/h) 10 35 50 75 75 115 160Nominal diameter DN8 DN8 DN8 DN20 DN20 DN20 DN20Membrane Teflon Teflon Teflon Teflon Teflon Teflon Teflon

pH controllerElectrode carrier probe 1 1 1 1 1 1 1pH transmitter 1 1 1 1 1 1 1Converter Digital Digital Digital Digital Digital Digital Digital

Polyelectrolyte pumpType Doser Doser Doser Doser Doser Doser DoserCapacity (l/h) 27 35 75 115 115 160 210Pressure (bar) DN8 DN8 DN20 DN20 DN20 DN20 DN20

Toro Equipment, S.L, reserves the right to modify, without prior notice, the data and characteristics that are shown in this catalog.

Dissolved Air Float Frc - Toro

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