GB2101494A

GB2101494A - Foam and sludge separating

Info

Publication number: GB2101494A
Application number: GB08220359A
Authority: GB
Inventors: Donald Firth
Original assignee: Tosco Corp USA
Current assignee: ConocoPhillips Co
Priority date: 1980-11-04
Filing date: 1981-11-03
Publication date: 1983-01-19
Also published as: MA19323A1; AU7698781A; AU531076B2; FR2493173A1; DE3143548A1; GB2088234A; BR8107119A

Abstract

Foam and sludge are separated from a liquid such as industrial waste water and effluent by flowing the liquid at a uniform velocity and substantially horizontally along a tank wherein said sludge settles to the bottom and said foam rises to the top; removing the sludge from the bottom of the tank at 32 and removing the foam from the top of the tank at 60. The uniform flow is imposed on the liquid by constraining it to pass through perforated baffles 44, 56. <IMAGE>

Description

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GB 2 101 494 A 1

SPECIFICATION

Foam and sludge separating method

Background of the Invention

The present invention relates generally to 5 apparatus and methods for separating foam and sludge from industrial waste waters and effluents.

As our industrial society continues expanding, there is an ever-increasing need for adequate treatment for waste waters and industrial effluents 10 from processing plants, factories and the like. The need for adequate treatment of effluents and waste waters has even become more critical in view of possible damage and destruction of the environment due to discharge of untreated 15 effluents and waste waters.

In many industrial settings and processes, the liquid industrial refuse contains undesirable foam and sludge. As a first step in treating and purifying the liquid, it is many times desirable to first 20 separate the foam and sludge from the liquid prior to further processing or return of the liquid to the factory. As will be realized, depending upon the particular qualities of given waste liquid and the foam and sludge dispersed therein, separation of 25 the foam and sludge from the liquid may be very difficult if not impossible. It is therefore essential that apparatus and methods be provided which optimize foam and sludge separation from such liquids.

30 Typical of prior-art attempts to provide a suitable means for separating foam and sludge from waste effluents is United States Patent 3,301,779 issued to Kovacks on January 22, 1965. In Kovacks, the effluent is flowed vertically 35 into a flotation and skimming tank and allowed to flow towards the liquid surface; however, prior to reaching the liquid surface, the direction of the effluent is changed to horizontal movement across the skimming tank. As the foam finally reaches the 40 surface, it is skimmed away as scum to oil-

recovery plant. The turbulent conditions, and the requirement that the effluent stream change direction in the skimming tank, provide for non-optimum foam-separation conditions. It would be 45 desirable to provide a foam separation apparatus wherein the effluent stream is introduced into the separation tank and maintained there in under conditions which maximize foam and sludge separation from the liquid.

50 Summary of the Invention

In accordance with the present invention, a foam separation apparatus and method is provided which separates foam from foam-containing fluids under optimum conditions to 55 thereby enhance foam separation and removal. The present invention is based on a foam separation tank which is horizontally oriented and includes an upstream end and a downstream end. The separation tank further has foam-fluid inlet 60 means associated with the upstream end for introducing foam-containing fluid at a relatively high velocity into the separation zone defined by the separation tank. The separation tank further includes outlet means for removing the foam-free fluid from the downstream end of the tank after foam separation.

As a first feature of the present invention, diffuser means associated with the foam-fluid inlet is provided for diffusing the foam-containing fluid into a plurality of relatively slow moving dispersed streams. The use of the diffuser means to diffuse the inlet stream avoids undue disturbance of fluid in the separation zone of the tank and also prevents strong local preferential flows which cause entrainment of foam and the possibility of foam concentration in the vortices which would inevitably form at the surface in the corners of the separation zone.

In a further feature of the present invention, velocity distribution means in the form of a first vertical screen is provided to convert the already partially pacified flow exiting from the diffuser means to a symmetrical horizontal flow within the separation tank having uniform velocity distribution from the tank surface to the tank bottom. Foam in the symmetric horizontally moving fluid stream will float towards the surface at a constant rate. Since the fluid stream is flowing horizontally at a known or easily determined uniform velocity, the velocity of fluid flow or separation zone length can be altered to insure adequate time for the foam to rise to the fluid surface prior to the fluid stream reaching the downstream end of the tank and being removed therefrom.

An additional feature in accordance with the present invention to even further ensure uniform velocity and symmetric horizontal flow of the foam-containing fluid is a second vertical screen located towards the downstream end of the separation zone but upstream of the foam-free fluid outlet. The second vertical screen prevents any non-uniform flow near the fluid outlet from disturbing the steady state uniform flow of the upstream foam-containing fluid.

The foam which rises to the surface of the fluid as it moves horizontally through the separation zone is conveniently removed by allowing it to pass over a foam spill weir at the downstream end, with the accumulated foam being pumped to further processing.

In a final feature of the present invention, a sludge drain is provided for removing any sludge which settles out from the foam-containing liquid during separation of foam from the liquid in the separation zone.

As will be realized, the present invention not only provides an apparatus and method for enhancing and increasing foam separation from effluents and other fluids, but it also provides a method and apparatus where, because of the uniform horizontal velocity, tank dimensions and fluid stream flow rates can be varied predictably to insure adequate foam separation.

Brief Description of the Drawings

Fig. 1 is a side cross-sectional view of the preferred foam separation apparatus of the

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present invention.

Fig. 2 is a detailed view of the preferred diffuser pot of the present invention taken through the II—II plane.

5 Fig. 3 is a detailed view of the preferred vertical screen of the present invention taken in the III—III plane.

Detailed Description of a Preferred Exemplary Embodiment

10 The preferred foam separation apparatus of the present invention is shown generally at 10 in Fig. 1. The foam separation apparatus 10 includes a separation tank 12 which defines a separation zone 14. The separation zone 14 may be 15 conveniently viewed as having an upstream end 16, a downstream end 18 and an intermediate settling zone 20.

In basic operation, foam-containing fluid is introduced through fluid foam inlet means, such as 20 inlet line 22, into the separation zone upstream end 16. The foam-containing fluid flows horizontally through the separation zone 14 as shown by arrows 24. As the fluid flows horizontally through the tank, foam rises to the 25 fluid surface 50 as shown at 26 and any sludge present settles out to the bottom 48 of the separation tank 12 as shown at 28. The fluid free of foam and sludge is then removed from the separation zone downstream end 18 by way of 30 fluid outlet means, such as outlet 30. The settled out sludge 28 is removed through sludge drain 32 while the separated foam 26 is removed from the separation tank 12 by way of foam outlet 34.

As particularly contemplated by the present 35 invention, diffuser means, such as diffuser pot 36, is provided for dispersing the foam-containing fluid as it enters the upstream end 16 of the separation zone 14. The diffuser pot 36 has a shell 38 and an inlet 40. The shell 38 has a plurality of 40 diffuser outlet holes 42. The incoming foam-containing fluid flows through inlet 22 in a single relatively fast-moving stream. The fluid stream moves through diffuser pot inlet 40 into the diffuser pot shell 38 and is diffused outwardly 45 through diffuser outlet holes 42. In this way, the single relatively fast-moving foam-containing fluid is dispersed into a plurality of slower-moving dispersed streams. This is the first step or stage designed to achieve symmetrical flow and uniform 50 flow velocity of the foam-containing fluid through the separation zone 14. The diffuser pot 36 may be made from any convenient material, such as plastic, ceramics or metal, or any other material which is not subject to corrosion or attack by the 55 foam-containing fluid.

The particular shape of the shell 38 is also not critical. Preferably, the shell 38 is of cylindrical configuration. The size and number of diffuser outlet holes 42 is also not particularly critical, 60 although it is preferred that the diffuser outlet holes 42 be of uniform size and be uniformly spaced about the diffusion pot shell 38. It is preferred, however, that the total area circumscribed by the diffuser outlet holes 42 be equal to twice the cross-sectional area of the diffuser port inlet 40. The particular number and size of holes may be adjusted to suit various needs depending upon the size of the diffuser pot shell 38, the viscosity, foaming characteristics and sludge content of the incoming fluid, and other parameters, such as fluid temperature and stream velocity through inlet 22.

As particularly contemplated by the present invention, velocity distribution means, such as first vertical screen 44, is provided downstream of diffuser pot 36 for promoting uniform horizontal flow of the foam-containing fluid as it passes through the settling zone 20. The fluid stream which has been dispersed into a plurality of small streams is further dispersed and pacified as it flows for the most part horizontally through the holes 46 in the vertical screen 44. Preferably, the vertical screen 44 extends from the separation tank bottom 48 to or very near the fluid surface 50. The vertical screen 44 insures that the horizontal flow of fluid is symmetrical, with uniform flow velocity from the surface 50 of the fluid down to the tank bottom 48. The first vertical screen 44 can be made of any suitable material, such as plastic, ceramic or metal. Again, it is only important that the material be resistant to attack and corrosion by the foam-containing fluid and the chemicals dispersed therein. Further, the first vertical screen 44 in particularly large separation tanks may be made from reinforced concrete or the like.

As with the diffuser outlet holes 42, the holes 46 and vertical screen 44 do not have to be in any particular shape, size or orientation to allow carrying out of the present invention; however, it is preferred, to provide optimum flow pacification and symmetry, that the holes 46 be of uniform size and uniformly spaced about the vertical screen 44. A preferred hole orientation is shown in Fig. 3. The holes 46 are circular and uniformly spaced within the first vertical screen solid surface 52. Preferably, the ratio of the hole 46 area to the solid surface 52 area is 1 to 1. This ratio provides optimum pacification and uniform velocity distribution when the thickness of the first vertical screen 44 is relatively small when compared with the hole 46 diameter. In situations, such as where relatively thick concrete screens or the like are utilized, the thickness of the first vertical screen 44 may be closer in dimension to the diameter of holes 46. In this case, for example when the ratio of the hole diameter to wall thickness is between 1 to 1 and 1 to 1.5, the ratio of hole area to solid area would be lowered from 1 to 1 to about 2 to 3. More than one velocity distribution screen can be placed within the separation tank, when desired and if necessary to ensure symmetrical fluid flow through separation zone 14 and uniform flow velocity.

As the fluid flows symmetrically and with uniform velocity through settling zone 20, any sludge present in the fluid will settle out at a constant rate. Conversely, individual foam bubbles will float to the surface also at a constant rate. As

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will be realized, the constant rate of sludge settling and foam rising for various different effluents, waste waters and other foam-containing fluids will vary according to fluid viscosity, fluid 5 temperature and other factors. Therefore, once the sludge settling and foam rising rates are established, the tank dimensions and horizontal uniform fluid flow velocity may be varied to ensure that substantially all of the foam rises to the 10 surface and all of the sludge settles out prior to the horizontally moving fluid stream reaching the extreme downstream end 18 of the separation tank 12.

At the downstream end 18 of the separation 15 tank 12, fluid outlet means, such as outlet 30, is provided for removing foam-free and sludge-free fluid. The outlet 30 preferably includes an entry opening 54 for receiving the foam-free and sludge-free fluid. If desired, the entry opening 54 20 may include a filter screen or the like to prevent any stubborn sludge or other unwanted contaminants from passing through outlet 30 to the environment or to further processing stages. As the fluid enters the entry opening 54, it 25 changes velocity and therefore results in local turbulence and eddies in and around the entry opening 54. In order to prevent spread of this nonuniform flow to the settling zone 20, a second vertical screen 56 is provided towards the 30 downstream end 18 but upstream of the fluid outlet 30, to prevent any non-uniform flow from and near the entry opening 54 from disturbing the uniform flow of the fluid in settling zone 20. The second vertical screen 56 is preferably of 35 construction similar to that of the first vertical screen 44 and also preferably extends from the separation tank bottom 48 to or very near the fluid surface 50.

The vertical wall 58 which terminates the

40 separation zone 14 functions as a foam spill weir whereby foam 26 which has accumulated on the fluid surface 50 and is flowing horizontally towards the vertical wall 58 flows over the top 60 of the vertical wall 58 into a foam collection

45 trough 62. The foam 26 is evacuated from the foam collection trough 62 through foam outlet 34 by way of a foam pump (not shown) or other suitable foam transfer or evacuation device.

Claims

50 1. A method for separating foam and sludge from a fluid containing the same, characterized by the steps of:

flowing the fluid symmetrically at a substantially uniform velocity to form a

55 substantially horizontally flowing stream wherein said sludge settles to the bottom of said stream and said foam rises to the top;

removing the sludge from the bottom of the stream; and .

60 removing the foam from the top of the stream.
2. A method according to claim 1,

characterized in that the fluid stream is substantially uniformly and symmetrically flowed horizontally at a sufficiently low velocity and in a

65 separation tank of sufficient length to provide complete separation of the foam and sludge from the fluid.
3. A method according to claim 1,

characterized in that said symmetric stream is

70 provided by diffusing said fluid through a plurality of diffuser holes and passing the diffused fluid through a vertically extending screen to further promote substantially uniform flow velocity and symmetrical flow.

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4. A method according to claim 1, substantially as described with reference to the accompanying drawings.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1983. Published by the Patent Office 25 Southampton Buildings, London, WC2A 1AY, from which copies may be obtained.