IL45908A - Flotation process and apparatus - Google Patents

Abstract

1471165 Wet separation of solids ERPAC SA 22 Oct 1974 [22 Oct 1973] 45630/74 Reading B2H [Also in Division Cl] Flotation apparatus Fig. 3 for extracting non-colloidal and colloidal materials in suspension from aqueous effluents, comprises a reservoir 1 having first and second treatment zones, a first inlet 3 in said first zone for effluent and facilitating the distribution of the effluent into the reservoir, a second inlet 12 in said first zone for flocculating and coagulating reagents disposed near the bottom of the reservoir close to said first inlet, an injection opening 12 in said first zone for water saturated with compressed air combined with or in proximity to said second inlet, and a battery 16 of rapid separation cells in said second zone for the flocculated material disposed in the reservoir opposite said second inlet and said injection opening, in the direction of circulation of the effluent to be treated. The non- colloidal material e.g. fibres, is recovered from the surface between the partitions 19 in the first zone, and the flocculated colloidal material is recovered from the surface above the battery 16 of lamellar cells.

Description

FLOTATION PROCESS AND APPARATUS This invention relates to a flotation process and to a compact apparatus for carrying out this process.

The field of application of the invention relates to the separation ( i. e. non- colloidal) of ordinary/and/or colloidal materials in suspension from a liquid, and more especially to the treatment of effluents from various types of industry, such as for example paper-making. Non- colloidal mater ial s will be r eferred to here inafter a s "or dinary "; The hitherto known conventional treatment for effluents comprising ordinary and colloidal materials consists of carrying out a succession of operations which comprise principally a simultaneous or non-simultaneous coagulation and flocculation in one or more reactors, in order to bring the two types of electrically neutral materials in suspension into the form of floc!fs, and then of carrying out the separation of the two types of material simultaneously by settling or by flotation in a final reactor.

This method, which is broken down into a number of phases, possesses numerous disadvantages. Quite apart from the multiplicity of equipment used, it requires relatively long treatment times to produce an almost complete reaction between the flocculant or coagulant products and the colloids.

A first objective of the method according to this invention is therefore to reduce the treatment times, by carrying out the coagulation-flocculation in the flotation vessel while the micro-bubbles of flotation air are being produced. The reduction in the treatment time also possesses the advantage of considerably reducing the volume of the equipment required for treating a given flow rate.

It has also frequently appeared to be of advantage in certain industries, such as for example in the manufacture of paper, to be able to separate the non- c olloidal ordinar /materials in suspension from the colloidal materials. It was not possible to effect this separation in the known methods, due to the fact that whole amount the totality of the materials in suspension was separated by settling or flotation after the treatment of the colloids by coagulating and flocculating agents. A second objective of the process according to this invention is to segregate the separated materials so as to recover them at distinct points in the reactor and, if necessary, to enable them to be recycled into the manufacturing sequence. As an example, this would be the case for the fibres in paper-making, which constitute ordinary solid materials in the effluents.

Another objective of the invention is to reduce the quantities of coagulating and flocculating agents used, since they are applied only to that volume of effluent which is charged with colloids, from which the ordinary materials in suspension have been removed.

The process according to this invention is characterised by the fact that, in a first zone of the reactor close to the feed, the effluent is treated by coagulating and flocculating reagents and by water saturated with pressurised air, injected across the flow of effluent, in order to recover from the surface of this zone the ordinary materials in suspension, and that, in a second zone of the equipment close to the discharge for the clean water, separation is carried out of the colloidal materials flocculated in suspension in the first zone and brought into,this second zone, by rapid -separation- -sells--- means of c e ll s for r apid s eparation.

The flotation apparatus according to the invention, for carrying out the process, is characterised by the fact that it comprises a reservoir, a feed for effluent enabling this effluent to be distributed in the reservoir, a feed for flocculating and coagulating reagents disposed in the bottom of the reservoir close to the feed for effluent, an injection opening for water saturated with compressed air close to the reagents feed, and a battery of cell s rapid separation cells for the flocculated materials, disposed in the reservoir opposite to the inlets for reagents and air.

/The invention The invention will be better understood by reference to a non-limiting form of embodiment, illustrated by the attached drawing, in which: - figure 1 shows a diagrammatic view of the installation, illustrating the method and showing the flotation apparatus according to this invention, in a section along a vertical longitudinal plane, - figure 2 is a view of the apparatus from above showing the segregated extraction of the materials in suspension. - figure 2 shows a view analogous to that of figure 1, showing an example cells for of embodiment of the/ rapid separation cell, - figure shows a view of this same installation in section along the plane IV-IV of figure 3.

Referring to figure 1, it will be seen that the apparatus is constituted of an elongated reservoir 1, which possesses on one of its lateral walls 2 an inlet 3 for effluent. In order to facilitate an improved distribution of the effluent to be treated entering the reservoir among the waters and reagents already present there, a partition 4 is provided, which is perforated solely at its lower part 5 to permit the liquid to pass in the direction of the arrow 6. The clean waters are recovered from the overflow or weir 7 provided on the wall 8 of the reservoir opposite to the wall 2. The bottom of the reservoir possesses an upwardly inclined face 9 to give to the liquid and to the reagents an ascending path in the direction of the arrow 10.

A first feed pipe 11 discharges at 12 into the reservoir close to the perforated wall 5 which guides the liquid to be treated. This pipe 11 supplies into the reservoir through the orifice 12 a mixture of flocculating and coagulating agents contained in tanks 13· Water saturated with pressurised air, prepared in the auxiliary tank l^t, is also supplied into the reservoir through the same orifice 12 close to the perforated plate 5· /A second A second inlet 15 has also been provided for air-saturated water; this may be used depending upon the speed of coagulation-flocculation and upon the ease of flocculating the colloids contained in the waters to be treated.

At the end near the wall 8, at which the clean waters are recovered, lamellar cells for * ' there is disposed a battery 16 of/rapid separation laajella- -cells, for example 2, 063, 821 as described in French Patent No. i39/3- }_+ in the name of the applicant and illustrated in figures 3 and 4, where the same references have been used as in figures 1 and 2.

The battery shown in figures 3 and 4 comprises, disposed parallel to one another across the" width of the reservoir 1, three vertical sets, 22-24, of horizontal and superimposed longitudinal elements such as 25.

In the example shown, the elements such as possess a V-transverse section, so that tv/o superimposed elements such as 25 and 26 define between v them a longitudinal duct such as 27, substantially horizontal but ascending from its central portion towards its longitudinal edges. Each element such as 25 possesses, in addition, at each of its longitudinal edges an upwardly oriented vertical flange such as 28, the height of which is less than the vertical distance separating two superimposed elements.

On either side of the vertical eets such as 22, and ≥ there are formed vertical chimneys 29 to 32, which are in communication, on the one hand with the ducts such as 27 at the longitudinal edges of said ducts and, also, at their upper part with the surface 17 of the liquid contained in the reservoir 1. By contrast, the chimneys such as 29 to 32 are closed at least on^the upstream side by vertical partitions such as 33 to 36, which in the present case a'djoin the bottom 9 of the reservoir 1 at their lower portion and a transverse partition 19 which insulates the battery l6 on the upstream side in the region of its upper elements; thus, the liquid to be /purified purified by flotation, arriving from the upstream side, must of necessity follow the ducts such as 27, within which it is guided notably by the flanges such as 28, which nevertheless permit particles having a density less than that of the liquid to pass towards the chimneys 29 to 32, from which these particles ascend towards the surface 17» where they may be recovered.

At the outlet from the battery 16, downstream of the ducts such as 27, received in the treated liquid is acce.ptad.by the overflow 7, from which it is discharged outside the reservoir 1.

Such a device possesses the advantage of preventing any risk of interference between the circulation zone for the liquid to be treated, defined by the ducts such as 27i an the zone of the extracted materials as defined by the chimneys 29 to 32, which are generally closed also on the downstream side by partitions such as 37 similar to the partitions such as 33 to 36.

It will be seen that by means of this apparatus as described, it will be possible in a single compact installation, without any preliminary coagulation-flocculation chamber, to separate the ordinary materials in suspension from the colloidal materials. To do this, the water to be treated entering the reservoir at 6 is immediately mixed with the coagulants and flocculants which enter through the orifice 12 situated close to the inlet 5· Jrom this instant onwards, the coagulation-flocculation reaction of the colloids commences in this first zone in which the liquid moves generally in the direction of the arrow 10. During this movement, the reaction continiees and the colloidal materials progressively attain, as a result of the reagents which modify their environment, a size of flocjts which will be able to be entrained by the battery 16. Simultaneously with the commencement of this reaction of the flocculants and coagulants with the colloids in this first zone, the ordinary materials in suspension ascend to the surface 17. of the liquid in the reservoir in the direction of the arrows 18, assisted ^ in this by the air injected at 12 which becomes decompressed. Partitions 19 are provided in the whole of this first zone which extends from the wall 2 to the battery 16 in order to constitute at the surface boundaries between the recovered sludges of the ordinary materials and those of the flocculated . colloidal materials, these being periodically removed by transverse surface scrapers 20 and 21 operated by any appropriate means. By operating in this way and by adapting, if necessary, the length of this first zone to suit the fluids to be treated, it is possible to achieve in the first zone an elimination of at least 80$ of the ordinary materials contained in the effluent. When the liquid arrives near to the battery 16, the coagulation-floeculation reaction is almost completed and the separation is carried out rapidly by means of the lamellar cells already referred to. In certain cases, in order to promote the growth of the flocks, it may be desirable to carry out a second injection of water saturated with pressurised air through the orifice 15, situated substantially in the middle of the first zone.

The reduction in time by comparison with the conventional process, consisting in the use of two separate reactors, one for coagulation-flocculation, · the other for flotation, is appreciable since the treatment period which was from 15 to 40 minutes now comes down to a period of from 5 to 10 minutes. This reduction of time is due notably to the elimination of the dead times in the second conrentLcnal flotation reactor. In effect, in the method according to the invention the time required for expansion of the compressed air in order to form bubbles of a sufficient size is also used to commence the coagulation-floccu^tion. This progressive degassing also takes place in the first zone before the colloidal materials have reached a sufficient size to be entrained by the battery 16. The colloidal materials separated by this battery 16 /are subsequently are subsequently extracted from time to time, for example by means of the scraper 21. !I¾ey may if desired be recycled in known manner into the first coagulation centers zone in order to increase the concentration of ge ms and thus to increase the speed of the coagulation reaction.

A description has thus been giyen of a flotation process and apparatus permitting selective separation from the effluent, in the first place of the ordinary materials in suspension and in the second place of the colloidal materials. Although the invention has been described with respect to a particular form of execution, it also covers variations in the form and combination of these various elements, as they are claimed. /

Claims (8)

CLAIMS 45908/ 2 WHAT IS CLAIMED IS: ■ ■

1. . Method intended for extracting ordinary^and colloidal materials in suspension from effluents, preferably but not necessarily in a single . operation, characterised by the fact that, in a first zone of the reactor close to the inlet, the effluent is treated by coagulating and flocculating rea.gents and by water saturated with compressed air injected through the effluent flow, in order to recover from the surface of this zone the ordinary materials in suspension, and in that, in a second zone of the apparatus close to the discharge for the purified effluent, the colloidal materials flocculated in suspension in the first zone and entrained into' this second zone are separated by lamellar cells for rapid separation, as hereinbefore defined.

2. Method intended for extracting materials in suspension according to Claim 1, characterised by the fact that a second auxiliary injection of water saturated with compressed air is carried out in the fir st zone.

3. Method intended for extracting materials in suspension according to any one of the preceding claims, characterised by the fact that the colloidal materials extracted in the second zone are partly recycled into the first zone.

4. Flotation apparatus for carrying characterised by the fact that it comprises a reservoir, a feed for effluent facilitating the distribution of the effluent into the reservoir a feed for flocculating and coagulating reagents disposed in the bottom of the reservoir close to the feed. for effluent to be treated, an injection opening for water saturated with compressed air combined with or in proximity, to the feed of reagents, a battery of cells for rapid separation for the flocculated materials disposed in the reservoir opposite to the feeds for reagents and for air in the direction of circulation of the effluent to be treated. ή 45908/2

5. Flotation , apparatus according to Claim ,3, characterised by the fact that it comprises means for evacuating the ordinary materials floated in the fi st zone. * ' ' · ' : ' ' " "

6. Flotation apparatus according to Claim characterised by the fact that it comprises means for removing the colloidal materials from ihe second zone. · ' ' ' ·

7. Flotation apparatus according to any one of the preceding claims, ^"^ characterised by the fact that the bottom of th reservoir has a shape designed to reduce the crose-section from the effluent inlet to th battery of cells. · ' ■· ' '

8. Flotation apparatus accordihgv to any one of the preceding claims, characterieed by the fact that partitions extending substantially transversely to the flow of effluent to be treated are disposed i the fi st zone close to the upper level of the liquid. COHEN ZEDEK & SPtSB ACH P. O. BOX 33116, TEL AVIV. ATTORNEYS FOR APPLICANT.