PT85241B - DEVICE FOR COMBINING TRANSFER AND GAS RISE IN WATER TREATMENT TO DEPURATE - Google Patents

Abstract

A gas-liquid contactor for pretreating water to be purified after flocculation and before filtration has a vessel partitioned into two communicating compartments, a water inlet in the upper end of one compartment, a pressurised gas diffuser producing bubbles less than 2 mm in diameter in the same compartment, and an aperture in the base of the partition sized so that liquid flow through it can be faster than the speed of ascent of the bubbles.

Description

The invention belongs to the technical domain of the transfer of gas between a gas phase and a liquid phase, with application to water treatment, namely by ozonation - rise of gas bubbles.

According to the device of the invention, it operates in a single reactor subdivided into several compartments, of which at least one (a) serves to carry out the transfer of the gas with a gas diffuser under pressure (c) traversed by a liquid stream (d) and in which the water to be treated is introduced from top to bottom (e); o or the other compartments designated as ascending compartments (b) communicate with the first (a) through an orifice whose section (s) and orientation are judiciously defined.

The present invention has its application in the technical domain of transfers between gas phase and liquid phase and relates in a particular way to a device

which allows to increase the yields of the transfer and to improve the solubilization of a gas in a liquid by formation of bubbles through a porous material within a contact capacity. It also refers, but not exclusively, to the use of such a device for the treatment of water purification and the purification of used and industrial water by a combined system of ozonation and rise of gas bubbles.

In the most diverse technical fields, there are numerous cases in which problems of diffusion and solubilization of a gas phase in a liquid phase arise. For example, when the liquid is water, the injection of carbon dioxide in a water to be remineralized with the addition of calcium carbonate can be mentioned without limitation; the injection of ozone in a water to be disinfected; the introduction of air in activated sludge according to the biological water treatment processes; the introduction into a water to be purified, according to the flotation technique of a gas that has a mechanical role in the practical realization of this technique, etc.

In all these cases, the problem arises of obtaining gas bubbles capable of providing an acceptable transfer coefficient, as well as the rate of rise of the bubbles in the liquid, for example, in a contact capacity (or reactor) constituted by a column of bubbles.

Several techniques have been proposed or used to obtain gas microbubbles designed to saturate an ambient liquid. For example, in the case of water, one of them is to saturate the water with gas (air, oxygen, ozone) in a room kept under pressure and then expand the water before it enters the contact reactor; This results in very fine gas bubbles with an average diameter of 40 to 100 microns. However, this process requires significant energy consumption and, in addition, microbubbles have a

very slow rise in liquid, which can be a serious obstacle in certain applications.

According to other known processes, an attempt is made to obtain homogeneous series of microbubbles by diffusing the slightly compressed gas through an element of porous material, for example, based on ceramic material or fried metal, the porosity of which is chosen depending on the different desired application parameters. However, according to a general phenomenon observed in such systems, microbubbles tend not to detach themselves from the porous element from which they come out only after reaching the size of a few millimeters, sufficient for Archimedes' impulse to overcome the forces surface tension. They then form a stream of large bubbles that rise very quickly in the contact column at speeds of at least 20 to 25 cm / s. The dispersion obtained is therefore very often insufficient and the loss of gas is important.

In order to improve the yields of gaseous / liquid phase transfer, within the framework of this technique of diffusion through porous material, it is advantageous, during the injection of gas under pressure under the porous device, to sweep the surface of the latter with a stream of liquid (see for example US Patent No. 5,545,731 and French Patent Publication No. 2.

421 671).

In water treatment facilities, the gaseous fluid is generally made up of oxygenated air, or rather, ozonated air. It is known that ozone is a good bactericidal and viricidal agent, which improves the organoleptic qualities of water and that, in addition to its oxidation properties, namely iron and manganese, it is a good flocculation aid. With obtaining the quality of decanting water

of the same, allows a saving of coagulant agent and, with an equal amount of coagulant agent, allows to better eliminate the dissolved organic matter. However, ozonation has a disturbing influence when it is followed by a classic decantation due to the appearance of spontaneous fluctuation phenomena in the flocculators and decanters.

However, _in the current practice known today, in water treatment installations, the two stages of ozonation are carried out successively after flotation.

One of the fundamental objectives pursued by the present invention was to try to combine the transfer of gas (namely by ozonation) and a flotation in a set of pre-treatment of water to be purified, after flocculation and before the filtration of the latter, by means of a system like the one above that is based on the diffusion of gas through a porous material and on the segregation of gas bubbles by the water entrainment speed.

Another objective was to reduce, due to the use of a single reactor, the investment and operating costs and to make the treatment facilities more reliable, obtaining notably improved purification results through this judicious combination of flotation and ozonation,

Another objective was to be able to turn the disturbing phenomenon of spontaneous fluctuation produced during ozonization carried out in decanters and / or flocculators into an advantage and to advantageously associate the spontaneous effect due to pre-ozonation and the effect of rising gas bubbles, avoiding the stagnation of gas bubbles. foam in the contact vats and flocculators. Among other advantages, such a combined process makes it possible to considerably increase the elimination of algae as well as iron and manganese.

To achieve these objectives, the invention proposes a device for transferring gas and rising gas bubbles with ozonation through a porous disc (or equivalent) and washing the surface of the latter by a stream of liquid, according to which it operates in a single reactor separated in at least two compartments in communication with each other; at least one first compartment, called the gas transfer compartment, with at least one pressure gas diffuser whose surface is traversed by a liquid stream with a liquid flow: gas ratio greater than 0.5 and in which the water to be treated is introduced from top to bottom; and at least one second adjacent compartment called the float compartment, said communication being carried out by means of at least one orifice located at the bottom of the compartment separator (s) and whose section a and orientation are such that the velocity Vs of passage the water flow between the gas transfer compartments and the rise of the gas bubbles is greater than the rate of rise Va of these bubbles in the transfer compartment.

As explained further in detail in the present specification, said compartments I are created in the reactor by dividing walls, each of which consists of two fixed or movable walls and can have different positions and orientations but which are always calculated so that when the passage in the free space adapted between them, the speed conditions mentioned above are respected.

One of the objectives pursued when the device according to the present invention was perfected and put into practice was to bring together in this combination of flocculation and water flotation to purify the optimum agitation conditions

and homogenization for the formation of flakes. These conditions can be summarized as follows:

The gas bubbles produced by the diffuser or diffusers and with average diameters of less than 2 mm are formed in an important number and with a more homogeneous size, this with a good dispersion in the water mass, thanks to the passage of the transverse liquid stream over the porous disc surface (which may be raw water, flocculated water or treated water). The stream of water to be treated, sent upwards over the bubble bundle into the gas transfer compartment, selects and transports the finer bubbles - for example, 50 to 500 microns - into the compartment or compartments fluctuation by passing through the spaces or holes mentioned above at a speed Vs which, in practice, must be greater than 100 m / h. The acceleration caused by the speed of the water, during this passage, facilitates the collisions between the microflocs and, for this reason, improves its agglomeration. Note in this regard that the ascending velocity Vf of the bubbles in the flotation room must be greater than the velocity V of the treated water at the outlet of the reactor, in order not to drag gas bubbles and / or charged flakes to the aforementioned outlet. This water outlet speed is advantageously between 10 and 30 m / h.

The larger gas bubbles coming out of the diffuser - for example, with diameters between 500 microns and 2 mm - and whose speed Va is greater than Vs (in practice, greater than 400 m / h) rise in the transfer compartment of gas or diffusion and transfer the gas containing, for example, ozone over the entire height of the reactor.

Such a system for selecting gas bubbles, thanks to

According to the parameters defined above, it is possible to separate the bubbles sufficiently thin to fix onto the flakes of polluting material bubbles of important size that could not play any role in the flotation but would be likely to disturb the formation of floating matter on the reactor surface, which does not it must rise too quickly.

In practice, according to an advantageous application of the present invention, the gas generated by the diffusers, under an average pressure of 0.05 to 0.1 megapascals and with a flow rate generally set at a rate of less than 20 m ^ per hour and per m of porous surface, consists of air or ozonized oxygen, the ozone concentration being generally maintained between 10 and 30 g per np of ozonated air or between 40 and 100 g per m ^ of oxygen. In the process targeted by the invention, ozone behaves as a good flocculation adjuvant according to mechanisms that are still poorly known, but which intervenes in particular phenomena of increased carboxylic functional groups in the medium (which improve the absorption of organic matter over oxides of aluminum and iron), polymerization phenomena of organic compounds with formation of varied biopolymers (nucleic acids, proteins, polysaccharides) that make the action of ozone very effective on waters loaded with algae.

Such pre-treatment of ozonation-flotation upstream of filtration with a sand filter or other type allows an increase in the durations of the filtration cycle that can reach 60%, in particular due to the fact that the filter's colmative power has decreased by at least 70% . Part of the clogging matter was eliminated by flotation while the other part was destroyed by ozone. On the other hand, as the flake formed in the reactor's float compartment is better retained by the filters, the water quality

filtration is clearly improved. For example, it was found, when experimenting with the technique according to the present invention, that an unfiltered water that has not undergone prior ozonation-flotation treatment had turbidity rates of 0.4 to 0.5 NTU while, using the process according to the present invention, the degree of turbidity generally dropped to 0.1 NTU.

The technique described above is particularly well adapted, although not exclusively, for the treatment of colored waters, loaded with algae but not very cloudy and not requiring the use of a decanter. In general, these waters are weakly mineralized. According to an improvement of the present invention, it is possible to remineralize these waters by taking advantage of the good homogenization conditions that exist in the reactor. For this purpose, the water used for washing the surface of porous materials (or diffusers) can be saturated with CO2, for example, by injecting Seltz water, or use for this purpose bicarbonated water by adding lime milk to water. loaded with CO2 · Increased complexation with calcium leads to improved absorption of organic compounds on the flake.

The invention is best understood by means of the following detailed description of non-limiting embodiments and examples shown in the accompanying drawings in which

Figure 1 represents a type of reactor according to the principle of the present invention;

Figure 2 represents a sectional view of the same type of reactor;

Figure 3 represents a variant of the reactor in Figure 2;

Figures 4 to 12 represent various embodiments and positions of two dividers that separate each reactor compartment;

- Figures 13 and 14 represent different types of holes that define the communication or opening between two partitions; and

Figures 15 to 17 represent several variants of the positioning of the gas diffuser systems in a reactor according to the invention.

As shown in Figures 1 to 3, the single gas transfer (or diffusion) and flotation reactor is divided into three compartments, one of which is the central compartment which serves as the diffusion compartment and two designated side b compartments as floating compartments. The compartment a has at least one porous plate or gas diffuser ç which is traversed by a stream of liquid (in this case, water) carried by the pipeline d. The water to be treated reaches the pipeline and the upper part of the reactor that flows according to a downward current and the gas under pressure (for example, ozonated gas) arrives through the pipeline f, the excess ozonated gas being evacuated by the pipe

k. The water to be treated passes, as shown by the arrows shown in Figures 1 to 3, from the central compartment a towards the flotation compartments b, passing through an opening (or hole) of section s located at the bottom of each partition m which separates the compartments and consists of an upper wall and a lower wall n which is inclined in relation to Figures 1 to 3 while the upper wall is in the vertical position.

The treated water leaves the floating compartments b through the pipes h while the floating matter (or

flakes) is evacuated by lowering the water level i and later exiting through the pipes j_. According to a variant shown in Figure 2, the free surface of the water i is irrigated by means of a sprinkler device g which facilitates the evacuation of the floating matter through the pipes 2 after the free level of the water i has been lowered.

According to the variant shown in Figure 3 (in all other points identical to the variant in Figure 2), a bed 1 of filter material can be placed on the bottom of the reactor.

As shown in Figures 4 to 12, the walls o. and n of each separation partition m between the compartments can have different positions and orientations. For example, they can be arranged in vertical alignment (Figure 4) or be out of line with each other (Figure 5) with the possibility that the wall will not rise, in height, the lower end of the wall o (Figure 6). According to the variants of Figures 7 to 9, the walls o and n can be, one inclined and the other vertical, or both inclined. In figure 10, the walls are arranged in order to obtain, in the part above the section (or passage) s., A zone of less turbulence that facilitates the fluctuation in the compartments b.

In the variant shown in Figure 11, the wall n is inclined and goes far beyond the lower end of the upper wall o. In addition, it is envisaged that the two walls will be movable as indicated by the arrows and the dashed line and, consequently, section s can be adjusted so as to be the most appropriate for the passage of the fine bubbles of gas and liquid (water ) from compartment a to compartments b.

In Figure 12, the two walls o. and n are endowed,

I

in their respective extensions, of moving parts ¹ and ^1, which also allow the proper adjustment of the cross section between the two walls.

Figures 13 and 14 represent non-limiting embodiments, in which the passage section s. it consists of either two holes s ¹ or a series s of four holes (for example).

Finally, Figures 15 to 17 represent variant embodiments related to the placement and / or the number of gas diffusion systems c. Contrary to the case of Figures 1 to 3, this diffuser c, installed in the central compartment a, can be arranged either above (Figure 15) or below (Figure 16) of the appropriate passage section s. According to the embodiment shown in Figure 17, the flotation zone according to the invention consists of a central compartment b while the diffusion (or gas transfer) compartments a are located on each side of compartment b. Furthermore, it is important to note, as indicated by the corresponding arrows, that the diffusion systems c and c 'are height adjustable according to the user's wishes.

Numerous studies and experiences have been carried out by the Applicant in the field of water treatment by ozonation-flotation according to the principles set out above. The results obtained are summarized, for illustrative purposes, in a pilot reactor of rectangular shape arranged downstream of a rapid mixing system of classic coagulant reagents and upstream of filtration in a sand and / or anthracite filter.

reactor was of the type shown in Figure 1 (or Figure 2) with the following main parameters:

- bubble diffuser (c) with 150 microns and 1.8 mm in diameter;

- ascending velocity of bubbles in compartment a): 0.01 to 0.18 m / s;

- 0.0102 m passage section (s) which results in a 0.048 m / s Vs velocity for a water flow of x 10 ⁴ np / s provided by the pipeline (e);

- section of each float compartment (b):

”7

0.0748 m which gives a floating water velocity V equal to 6.6 x 10 m / s for a water flow equal to 5 x 10 ~ ⁴ m ^ / s, this speed being such that the gas bubbles and the flake charged to the reactor outlet (j_).

It should be noted that, in the diffusion zone (compartment a), gas bubbles larger than 400 -

- 500 microns and whose speed Va is greater than Vs (0.048 m / s) are not dragged by the water stream through the passage section s_ between compartments a and b. These bubbles guarantee, with their countercurrent movement with the descending water, the transfer of the ozone they contain, throughout the height of the reactor. Thus, they participate in a beneficial hydraulic agitation for the development of the flocculation that begins in the diffusion compartment.

For example, this was treated as a water that was intended to be potable and that had a turbidity of 5 NTU (Nephelometric Turbidity Unit) and a Hazen color of 20 degrees. For comparison, tests were carried out -

- keeping all other conditions the same - in the same type of reactor but diffusing only oxygen (without ozone) on the one hand and, on the other hand, in the absence of the reactor according to the present invention and simply carrying out successive flocculation and filtration operations according to the conventional method.

The water had previously been flocculated with an amount of ferric chloride equal to 3 g / nr and, after treatment, was filtered through a two-layer filter, one of

which with 60 cm of sand of 0.60 mm size and the other with 60 cm of anthracite with a size of 1.4 to 2.5 mm.

In the case of ozonation treatment according to the present invention, an ozonation rate of 0.6 g / m ^ of water was used, with the gas leaving the diffuser (type c in the figures) ozonated oxygen with 40 to 50 g ozone per m of ozone.

The diffuser surface was swept by a flow of liquid that represents about 10% of the amount of raw water to be treated.

The results obtained are summarized in Table I below.

α> CXJ φ 3Ρ Ο + ³ The ρ) Φ Φ Ο φ φ Λ ο ο g <η γ4 ο φ g Λ EH • Η 1—1 Ρί ο ΓΟ t = 5 Ρ <Η 'φ m <Φ ο Γ— Ο Μ «Μ ο m • Μ Ρ Ο Ο Φ Β C \ l ο ο Ρ V Ρ Φ η ITIC • Η Φ φ φ ο β s -Ρ X—> ΡΜ ο Φ C \ J I φ ο Φ Λ -Ρ Β Ρί φ ο d ο φ Ζ- * Ν ο Λ ο ο g R <-Η ο φ g ο Λ ΕΗ • Η <Η Ρί I (XJ Ο Ρ «Η 'φ m ο OJ 32 Ο Μ Φ ρ ^ ί- Γ— Ρ ο Ο Ρ • Η CXJ Ο Ο Ρ V φ Ν • ι »Φ • r-f φ Ρ < Ο ο Ρί 5¾ -Ρ ο Φ

TABLE

Μ

ο Φ Tj Φ γ — 1 φ ΌΙ '__- Ν Ρ m -Η Φ φ Ο Ρί s Ρ2 φ Ρ Ο ο Εη + ³ Lt0 Φ Β φ ο \ Ζ> Ρ! Ρί ζ — s ο ο m Φ φ 'φ g ο xj- Λ ο bfl α ο Λ I — I Γ ~ < Ο ο ο Ή • Η Ο Β CXJ ΙΦ Ρί ι — 1 ο Ρ γΗ ο ο 'φ ΙΓ> 32 Λ d

Fi bfi Ρ Ή φ Μ PM ο Ο

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φ τ3 Φ Ρ -Ρ r — 1 Ο φ φ Ρ Ο Ο ΙΦ θ 'φ φ Φ Ή Ρί -Ρ τ3 «Ρ φ φ φ rH ο Φ φ ο IH ι — 1 Φ Μ) η ο b6 'Φ Φ Ο • Ρ 'Φ > ίΦ ο Φ Ρ Φ Φ τφ φ Φ ο όΙ φ «Η Χ5 Ο Φ 32 Ή Ιφ Ο • Η Ο ο ο ίφ ϋ ! Φ φ θ ' Ρί Φ Φ Ο Ρ φ <Φ Ο Ό φ -Ρ > Ρ Ο f-J rd Ρ φ ο Ρ Γ5 • Η 3 ΡΜ <- ( ο R <Ρ Εη • Ρ

It should also be noted that, in the treatment according to the present invention (operation with 02) »there was an immediate stabilization of the turbidity level of the treated water from the beginning of the filtration cycle, that is, for NTU values from 0.10 to 0.15, during the cycle. The wash duration between two filtration cycles has been advantageously increased from 20 to 35% on average and, in addition, a considerable saving of flocculant product has been noted upstream of the treatment according to the invention.

In other series of experiments with more clogging waters, namely with Baudrey PCB clogging power between 25 and 58, these indexes were reduced at the exit of the reactor, respectively to 6 and 15.

Λ / i

Claims (11)

15. - Device to combine the transfer and rise of gas in a pre-treatment set of water to be purified, after flocculation and before filtration, of the type that uses the diffusion of gas through a porous material and the segregation of bubbles of gas by the water entrainment speed, characterized by the fact that it essentially comprises a single reactor subdivided into at least two communicating compartments, of which at least one first compartment, called the gas transfer compartment, has a gas diffuser under pressure that generates bubbles with a diameter less than 2 mm, the surface of which is run by a liquid stream in a liquid / gas flow ratio greater than 0.5 and in which the water to be treated is introduced from top to bottom, and at least one second adjacent compartment, called the ascent, the said communication being carried out through at least one hole located in the lower part of the partition or the partitions that separate the compartments and whose section is oriented towards opening are such that the speed Vs the passage of the water stream between the transfer and rise compartments of the gas bubbles is higher than the Va rise speed of the gas bubbles in the transfer compartment. 25. The device of claim 1, characterized in that each partition separating the compartments is constituted by two vertical walls aligned between which said section S hole is opened. 3 ^ã . - Device according to claim 1, characterized by the fact that each partition for separating the 17 compartments be constituted by two walls separated from each other in order to be able to make the mentioned orifice of section s. 4 ^â . Device according to claim 1, characterized in that each partition separating the compartments consists of two walls, at least one of which is in an inclined position in relation to the other, with the communication between them made through said hole section s_. 5-. Device according to any of claims 2 to 4, characterized in that said walls are fixed or movable. 6 ?. Device according to any of claims 2 to 5, characterized in that at least two holes are provided between the two walls. 7 ^ê . Device according to one of Claims 1 to 6, characterized in that the gas diffuser is located at a level above the level of the through-hole between said compartments. 8 ^. Device according to any one of claims 1 to 6, characterized in that the gas diffuser is located below the level of the through hole between said compartments. 9-. Device according to one of claims 1 to 8, characterized in that the velocity V is greater than 100 m / h and the ascending velocity Vf of the gas bubbles in the compartment or in the rising compartments is greater than the velocity V of the water. ζ · treated at the outlet of the reactor which is between 10 and 30 m / h. 10 ^. Device according to any one of claims 1 to 9, characterized in that the gas consists of air or ozonated oxygen, in the latter case containing 40 to 100 g of 0 ^ per m ^ of 0 ₂ · 11§. Device according to any of claims 1 to 10, characterized in that the water used to contact the gas diffuser surface is bicarbonated water or water saturated in C0 ₂ 12§. Device according to one of Claims 1 to 11, characterized in that a bed of filter material is installed at the bottom of the reactor. Lisbon, July 2, 1987 Industrial Américo da Silva Carvalho Agçnl. Otical dl Picpiledidi IndaíHI.I Rua Castilho, 201-3. ° Left Telef. 65 13 39 - 1000 LISEOA η. by Ttóítemenfe give VâloHwttóri j ^ .A 0Τ \! muçum (I) e'6euHc> s 3-u ° 2, I I n 3/3 \ ^ 11 i o n