FR2493173A1 - PRETREATMENT PROCESS AND WORK FOR SEPARATING FOAM FROM WASTEWATER AND INDUSTRIAL EFFLUENTS - Google Patents

Abstract

THE STRUCTURE SHAPES A TANK 12 OR A BASIN WITH A CONDUIT 22 FOR THE INLET OF LIQUID LOADED WITH FOAM OR SKIMMING AND ANY SLUDGE AT AN END. THE INCOMING LIQUID CURRENT IS DISTRIBUTED, UNIFORMED AND TRANQUILIZED BY A DIFFUSER 36 AT THE ENTRY, FOLLOWED BY A PERFORATED SCREEN 44. THE CURRENT THROUGH THE TANK HORIZONTALLY WHILE THE FOAM CONTAINED MOUNTS ON SURFACE 50 AND THE SLUDGE DEPOSITS ON THE BOTTOM 48. THE SLUDGE 28 IS DRAINED THROUGH A PIPE 32, THE LIQUID CLEARS OF THE FOAM AND SLUDGE LEAVES THROUGH A PIPE 30 AND THE FOAM 26 PASSES OVER A CROWNING DAM 58, 60 IN A COMPARTMENT 62 FROM WHICH IT IS DRAINED BY PUMPING. A SECOND 56 SCREEN AVAILABLE VERTICALLY THROUGH THE TANK STABILIZES THE FLOW IN THE OUTLET AREA.

Description

The present invention relates generally to works and

  processes for separating foam or scum and the

  wastewater sludge and industrial effluents.

  As our industrial society continues to develop, the need for adequate treatment of waste water and industrial effluents from treatment facilities, factories and so

  immediately increase more and more. The need to apply a treatment

  even adequate to effluents and wastewater has even become more

  still critical given the risk of damage or

  destruction of the natural environment by the discharge of effluents and water

untreated waste.

  In many industrial cycles and processes, liquid industrial discharges contain unwanted foam and sludge. As a first step in the treatment and purification of the liquid, it is often desirable to first separate the foam and the sludge from the liquid before subjecting it to a subsequent treatment or before returning it to the factory. We understand that the

  separation of foam and sludge from liquid can be very difficult

  eyelash, if not impossible according to the particular qualities of a given used liquid and according to the foam and sludge dispersed in

  this liquid. It is therefore essential to create books and procedures.

  dice capable of producing optimal separation of foam and

sludge from such liquids.

  A typical example of previous attempts to create suitable means for separating foam and sludge from effluents

  is described in U.S. Patent No. 3,301,779.

  According to this patent, the effluent is brought vertically into a flotation and skimming tank where it is allowed to rise to the surface of the liquid; however, before it reaches the surface of the

  liquid, the direction of the effluent is changed in a hori-

  zontal through the skimming tank. When the foam finally reaches the surface, it is removed and sent as scum to an oil recovery plant. However, the turbulence and the need to change the direction of the effluent stream in the skimming tank mean that the conditions for foam separation are not optimal. It would therefore be desirable to create a foam separation structure in which the effluent stream is introduced into and maintained in a separation tank under conditions which optimize the separation of foam.

and liquid sludge.

  The invention provides a method and a work for its implementation, which are capable of separating the foam from fluids containing foam under optimal conditions. The invention is based on the use of a horizontal foam separation tank, having an upstream end and a downstream end. The separation tank has a liquid inlet device loaded with foam at the upstream end for introducing the liquid containing the foam at a relatively high speed into the separation zone defined by the tank. This also includes an outlet device for the evacuation of the

  liquid stripped of foam at the downstream end of the tank.

  According to a first characteristic of the invention, a diffuser device is provided at the inlet of the liquid loaded with foam to diffuse or distribute this liquid into a certain number of relatively slow dispersed streams. The use of this device avoids unnecessary disturbances of the liquid in the separation zone of the tank and also prevents local preferential flows of relatively high intensity, which cause the foam and create the possibility of foam concentrations in the vortices that would inevitably form on the surface in the corners of the area

of seperation.

  According to another characteristic of the invention, a speed equalizing device in the form of a first vertical screen is provided for transforming the flow, already partially tranquilized, coming from the diffuser device into a horizontal flow.

  symmetrical in the separation tank, flow having a distribution

  uniform speed increase from the surface to the bottom of the tank.

  The foam contained in this symmetrical horizontal current rises to the surface on a regular basis. Since the stream of liquid charged with foam flows horizontally at a known uniform speed or which can be easily determined, the speed of this flow or the residence time of the fluid in the separation zone can be modified as necessary so that the foam have enough

  time to rise to the surface before the liquid reaches the extreme

downstream and the outlet of the tank.

  To further improve uniform speed and symmetrical horizontal flow of the foam-laden liquid, a

  another characteristic of the invention provides that a second vertical screen

  cal is installed closer to the downstream end of the separation zone

  tion but upstream of the outlet for the liquid freed from the foam. This second screen prevents any possible non-uniform flow near the liquid outlet from disturbing the stable uniform flow of the

  liquid loaded with foam in the upstream part of the tank.

  It is advantageous to remove the foam rising to the surface during the horizontal flow of the liquid through the separation zone by allowing it to pass over a dam forming a foam overflow at the downstream end, the accumulated foam

  beyond this dam being evacuated by pumping for its milking-

subsequent.

  According to yet another characteristic of the invention, a sludge evacuation is provided to remove the sludges which may have separated by decantation of the liquid laden with foam while

  the foam separates from the liquid in the separation zone.

  It appears from the above that the invention provides a method and a work making it possible not only to improve and increase the separation of foam from effluents and other fluids.

  but also giving the possibility, due to the hori-

  uniform zontal, to vary the dimensions of the tank and the liquid flow rates in a predictable way and so as to ensure a separation

suitable foam.

  Other characteristics and advantages of the invention

  will emerge more clearly from the following description of a

  nonlimiting exemplary embodiment, as well as of the appended drawing, in which - FIG. 1 is a longitudinal section of a foam separator structure according to the invention; - Figure 2 is a partial cross section, taken along the line II-II of Figure 1 but on a larger scale, showing the preferred embodiment of a diffuser pot according to the invention; and - Figure 3 is a partial cross section, taken along line III-III of Figure 1 but on a larger scale, showing part of the preferred embodiment of a

vertical screen according to the invention.

  The foam separator according to the embodiment

  preferred sation of the invention is shown as a whole in Figure 1 and is designated by 10. It comprises a separation tank 12 defining a separation zone 14. The latter has an upstream end 16, a downstream end 18 and a zone intermediate

decantation 20.

  During normal operation, liquid loaded with foam is introduced into the upstream end 16 of the

  separation by an input device such as an inlet pipe 22.

  The liquid containing the foam flows horizontally through the separation zone 14, as indicated by the arrows 24. During this horizontal flow, the foam rises to the surface 50 of the liquid, see the layer of foam 26, and the sludge possibly contained

  in the incoming liquid is deposited on the bottom 48 of the separation tank

  ration 12, see the deposit of sludge 28. The liquid freed from the foam and the sludge is removed at the downstream end 18 of the separation zone by a liquid outlet device such as a pipe

  outlet 30. The sedimented sludge 28 is removed by an evacuation

  tion of sludge 32 and the separated foam 26 is removed from the tank

  separation 12 by a foam outlet pipe 34.

  According to an important characteristic of the invention, a diffuser device, for example a diffuser pot 36, is provided for dispersing the liquid laden with foam as it enters the separation zone 14 through the upstream end 16. The diffuser pot 36 has a casing 38 and an inlet 40. The casing 38 has a greater or lesser number of diffuser outlet holes 42. The liquid loaded with foam enters the tank, via line 22, in a single current at a speed relatively high. This current enters through the diffuser inlet 40 into the casing 38 of the pot, from where it is distributed through the outlet holes 42. In this way, the relatively fast single stream is dispersed in a relatively large number of streams slower. This dispersion constitutes the first of the various measures provided for by the invention for causing the liquid laden with foam to flow symmetrically and uniformly through the separation zone 14. The diffuser pot 36 can be made of any suitable material, for example of plastic, ceramic, metal or any other material not likely to corrode or be attacked

by the foam-laden liquid.

  The shape of the casing 38 is not more critical but it is preferably cylindrical. The size and number of the outlet holes 42 are not particularly critical, although it is preferable that these holes have the same size and are uniformly distributed over the envelope 38. In addition, it is preferable that the area total of the diffuser outlet holes 42 is equal to twice the cross section of the inlet 40 of the diffuser. The number and size of the holes can be adapted to different needs, in particular depending on the size of the envelope 38 of the diffuser pot, the viscosity, the skimming characteristics and the sludge content of the incoming fluid and still other parameters, such as the temperature of the fluid and its speed of flow in the pipe

of arrival 22.

  According to another important characteristic of the invention, a speed equalizing device, such as a first vertical screen

  44, is installed downstream of the diffuser pot 36 to promote the flow

  uniform horizontal level of the liquid loaded with foam during its passage

  ge through the settling zone 20. The fluid stream, having been dispersed in a greater or lesser number of small streams, is dispersed and further tranquilized when it crosses, for the most part horizontally, the holes 46 of the vertical screen 44. This preferably extends from. the bottom 48 of the separation tank to the surface or near the surface 50 of the liquid. The vertical screen 44 ensures that the horizontal flow is symmetrical and has a uniform speed from the surface 50 of the liquid to the bottom 48 of the tank. The first vertical screen 44 can be made of any suitable material, for example plastic, ceramic or metal. Again, it is only important that the material resists attack and corrosion by the foam-laden liquid and the chemicals dispersed therein. In particularly large separation tanks or basins, the vertical screen 44 can be

  made of reinforced concrete or similar materials.

  No more than the outlet holes 42 of the diffuser, the holes 46 and the vertical screen 44 must not have a particular shape, size or orientation for the implementation of the invention; it is however preferable, to produce an optimal tranquilization and symmetry of the flow, that the holes 46 all have the

  same size and are uniformly distributed on the vertical screen 44.

  FIG. 3 shows a preferred arrangement of the holes 46. It can be seen that these are circular holes uniformly distributed over the surface 52 of the first vertical screen. The ratio between the area of the holes 46 and the closed area of the surface 52 is preferably 1: 1. This ratio optimally ensures tranquilization and the uniform distribution of the speed when the thickness of the first vertical screen 44 is relatively small compared to the diameter of the holes 46. In certain applications, for example when the screens are made of relatively thick concrete, the thickness may be closer to the diameter of the holes 46. In such a case, for example when the ratio between the hole diameter and screen thickness is between 1: 1 and 1: 1.5, it is recommended to lower the hole area /

  closed area from 1: 1 to about 1: 2 or 1: 3. It is possible to insert

  install more than one speed equalizer screen in the separation tank

  tion when desired and / or necessary to ensure listening

  slightly symmetrical of the fluid through the separation zone 14 and

uniform flow velocity.

  As the fluid passes through the settling zone 20 in a symmetrical flow and at a uniform speed, all the sludge which it can contain is deposited in a regular manner. At the same time, bubbles of foam rise to the surface, also regularly, that is to say at a constant rate. It goes without saying that the regular sedimentation of sludge and the regular rise of foam will vary not only according to the nature of the effluents, waste water and other fluids laden with foam but also according to their viscosity, their temperature and other factors. Therefore, once the sludge sedimentation and / or foam rise velocities and / or flow rates have been established, the vessel dimensions and the uniform horizontal flow rate can be fixed or changed to ensure that substantially all of the foam rises on the surface and that all

  sludge is deposited before the horizontal current reaches the extreme

  downstream mite 18 from the separation tank 12.

  The downstream end 18 comprises a liquid outlet device such as an outlet pipe 30 for the evacuation of the liquid freed from the foam and the sludge. The inlet opening 54 of the liquid outlet line 30 can be equipped, if desired, with a strainer or the like to prevent certain constituents of the incoming liquid from being discharged into the surrounding environment or from being sent to the following processing steps via line 30. Upon entering the opening 54, the liquid changes speed and thereby produces local turbulence and disturbances in and around the inlet opening 54. In order to prevent these disturbances from being communicated to the settling zone 20, a second vertical screen 56 is provided closer to the downstream end 58 in the separation zone, upstream from the liquid outlet 30. The second screen 56 has preferably a construction similar to that of the first screen 44 and preferably also extends from the bottom 48 of the separation tank to the surface or to

  proximity to the surface 50 of the liquid.

  The vertical wall 58 which ends the separation zone 14 constitutes a foam weir dam. The foam 26 which has collected on the surface 50 of the liquid in the separation zone is

  directs on this surface towards the vertical wall 58 and passes through

  above a terminal element 60 at the top of this wall in a comparison

  foam collector 62. The foam is evacuated from this comparison

  through a foam outlet line 34 and by means of a foam pump (not shown) or any other transfer device

or appropriate evacuation.

  The invention is not limited to the embodiment described and those skilled in the art may make various modifications thereto,

  without going beyond its framework.

Claims (11)

  1, b Process for separating foam or scum and possible sludge from a liquid, characterized in that liquid, charged with foam and possibly sludge, forms a symmetrical horizontal current of substantially uniform speed, d 'o the sludge separates by sedimentation on the bottom (48) and the foam rises to the surface (50), the sludge (28) is removed from the bottom and the foam is removed (26) from the surface.   2. Method according to claim 1, characterized in that the uniform and symmetrical horizontal current is given a sufficiently low speed and it is made to pass through a tank (12) or -a separation basin sufficiently long so that practically all of the   foam and all the sludge separates from the liquid.   3. Method according to claim 1 or 2, characterized in., That the symmetrical horizontal current is formed by diffusing the liquid loaded with foam and any sludge through the holes of a diffuser (36) and passing the liquid thus dispersed through a vertical screen (44) to increase the uniformity of the   flow velocity and symmetry of the horizontal current.   4. Work for the implementation of the method according to one   any one of claims 1 to 3, characterized in that it forms a   tank (12) or a separation basin which defines a separation zone (14) having an upstream end (16) and a downstream end (18), an inlet device (22) provided at the upstream end for introducing a stream of liquid loaded with foam and any sludge in the separation zone, as well as an outlet device (30) for discharging the liquid freed from the foam and sludge from the downstream end of the separation zone, the work further comprising a diffuser device (36) combined with the inlet device for dispersing the stream of incoming liquid into a number of relatively slow streams, a speed equalizer device (44) placed at a distance between the diffuser device (36) and the liquid outlet device (30) for promoting the uniform and symmetrical horizontal flow of the liquid as the foam separates from it by gravity rising to the surface (50), as well as a device (58, 60, 62, 34) of foam removal combined with the downstream end (18) for removing the foam (26)   mounted on the surface of the separation tank (12).   5. Work according to claim 4, characterized in that the diffuser device is formed of at least one diffuser pot (36) having a casing (38) with an inlet (40) for receiving the incoming liquid and outlet holes ( 42) to disperse it in the separation zone (14) in relatively slow currents. 6. A structure according to claim 5, characterized in that the outlet holes (42) all have the same size and are uniformly distributed over the casing (38) of the diffuser, the total area of the holes preferably corresponding to twice as much. section area from the inlet (40) of the diffuser.   7. Work according to any one of claims 4 to 6,   characterized in that the speed equalizing device comprises a first vertical screen (44) arranged through the separation zone (14) and having holes (46), the area of which represents in particular   half the total screen area.   8. Work according to any one of claims 4 to 7,   characterized in that the foam removal device comprises a foam overflow dam (58, 60) at the downstream end (18) and a pumping device for discharging the foam passed over it barrage.   9. Work according to any one of claims 4 to 8,   characterized in that it further comprises a device (32) for evacuating   cuation of sludge provided in the bottom (48) of the separation tank to remove the sludge (28) which have separated by settling of the liquid in the separation zone (14).   10. Work according to any one of claims 4 to 9,   characterized in that the speed equalizing device comprises a second vertical screen (56) arranged closer to the downstream end (18) but upstream from the liquid outlet device (30) to prevent a non-uniform flow near this outlet device does not disturb the uniform flow upstream of the second screen (56), the area of the holes made in the second screen representing in particular   half the total screen area.   11. A structure according to claim 9, characterized in that the holes in the first (44) and the second vertical screen (56) are   same size and are evenly spaced.