This invention relates to a method of and apparatus for separating a liquid medium in different components by means of gravity in a manner that a medium to be separ¬ ated is set in slow rotating motion with the axis of rotation substantially vertical, so that the heavier com¬ ponent concentrates in the bottom section of a slow vor¬ tex and the lighter component concentrates in the top section of a slow vortex.

The term "a liquid medium", as used in this specification, refers to various fluids, mixtures thereof as well as various compositions of liquids and solid particles and also compositions of liquids and bubbles. The term "heavy component" refers to that portion of a compound which, by the action of gravity, has a tendency to de¬ scend with respect to the rest of the composition. Ac¬ cordingly, "light component" has a tendency to rise in the composition as gravity pulls the rest of the compos¬ ition downwards.

Prior known are gravity separators, wherein a liquid medium to be separated is set in slow rotating motion. These are disclosed e.g. in US Patents 2 088 294, 3 965 013 and 3 258 123, DE Patent Specification 2 034 794 as well as in GB Patent Specifications 2 082 941 and 2 148 744. In these prior known gravity-operated separators, a slow rotating motion is produced in a settling basin in order to obtain a so-called tea-cup phenomenon. There, a mater¬ ial settled on the bottom gathers along the bottom near the centre of rotation the same way the tails in a con¬ ventional tea cup concentrate in the centre of the bot¬ tom when tea is swirled in a cup. The only purpose of

such slow rotating motion is to gather the particles in one spot. Separation is achieved by gravity, not at all by the slight centrifugal force of a slow vortex. The rotational flow is kept slow so as not to create turbulence near the bottom, which would disturb the descent down to the bottom achieved by gravity. A high velocity motion would also have a tendency to re-blend the particles that have already been separated onto the bottom.

A drawback in the prior known separators is the ineffic¬ iency of a tea-cup phenomenon in large units, as the heavy component does not concentrate in thebottom centre the way it is desired. On the other hand, if this tea¬ cup phenomenon is intensified in the prior known equip¬ ment by slightly increasing the speed of rotation, the disturbing turbulence is drastically increased. In the prior known equipment, due to the long diameters-of the basins, it is often necessary to employ thick layers of liquid, the settling distance of particles down to the bottom increasing accordingly. This leads to a poorer separation result and the time required for settling becomes unreasonably long. Another drawback of the prior art equipment is bulkiness and a complicated and expen¬ sive construction. Due to their bulkiness, the prior art apparatus cannot often be located in cramped spaces. In the prior art equipment, the separation is effected in a single step and, thus, a portion of the heavy com¬ ponent accidentally entrapped in the light components can no longer be separated and added in the heavy com¬ ponent. Due to the great diameter, inclination of the bottom or the floor in the prior art equipment often re¬ mains slight, since the vertical space demand required by a steep funnel-shaped floor is great. The use of just slightly inclined funnels readily leads to the con¬ centration of heavy component on a basin floor as a

deposit, from which it may be re-blended in the flow as well as cause other trouble.

An object of this invention is to reduce the above draw¬ backs and in a method of the invention this is achieved so that two or more slow-moving vortexes are contacted with each other in horizontal direction.

The equipment intended for carrying out the method of this invention is set out in the accompanying claims.

The invention can be applied to a variety of purposes of separating liquid mediums by utilizing gravity. One important application is the separation of solids par¬ ticles from liquids in various processes. These include e.g. the separation of sand from waste water, recovery of minerals and various utilities as well as sorting out particles according to grain size and shape.

The invention will now be described in more detail with reference made to the accompanying drawings, in which

fig. 1 shows an array of settling basins of the invent¬ ion, the outer sections of successive basins be¬ ing linked to each other.

Fig. 2 is a section along a line II-II in fig. 1.

Fig. 3 shows an alternative section along a line II-II in fig. 1.

Fig. 4 shows a system of settling basins, wherein the outer sections of successive and parallel basins are linked to each other.

Fig. 5 shows a system of settling basins of the invent-

ion with a varying basin size.

Fig. 6 shows an array of settling basins of the invent¬ ion, wherein the bain centres make out a zigzag patter .

Fig. 7 shows an array of settling basins provided with a flow-deflection fin.

The principal object of this invention is to make set¬ tling basins more effective and to simplify their con¬ struction. In small units the tea-cup phenomenon, i.e. a flow at the bottom towards the centre, is more effect¬ ive than in large-diameter units, when the flow rate is equal. With the prior art equipment, designing a plural¬ ity of small units leads to a complicated and expensive construction. Instead, with the solution of this in¬ vention, it is possible to eliminate a number of walls and to avoid pipe connections between various units. Thur the equipment according to the invention is much mor onomical. The use of a plurality of s all- di r settling basins also makes it possible to fu - ^* incline the bottom, so the settling material dot. .ιot stick to it very easily.

In an array of settling basins of the invention, the separation proceeds in several steps, whereby heavy com¬ ponent is removed from light component again and again. This improves possibilities of producing a highly pure light component. By using an array of settling basins, the flowing distance can be made quite long and, thus, even the poorly descending particles have more time to reach contact with the bottom. An underflow, occurring in each settling basin the same way as the tea-cup phenomenon, tends to bring the particles near the bottom at several stages, so the separation probability of even

poorly settling particles becomes quite good. It is just the multiplication of separation probabilities which results in high degrees of separation.

With the solution of the invention, it is possible to control the intensity of a tea-cup phenomenon in vari¬ ous units and to have different materials separated in them. In some units, a turbulence can be adjusted to be quite powerful e.g. for washing coarse matter clean of fine matter.

Settling basins according to the invention can be dis¬ posed in a rectangular formation, so they can be readily located e.g. in a room space unlike the traditional large-diameter circular basins. In addition, it is possible to use a plurality of different arrays, as dictated by the available spaces. An array of settling basins of the invention can, if desired, be disposed as a section of a flow channel in a manner that the channel again proceeds normally downstream of said array. Therefore, neither very much space nor expensive pipe systems are needed.

The accompanying figures depict by way of an example a few embodiments of the invention and illustrate the practical operation of the invention. In reality, a great number of practical embodiments can be found for the invention. The designs and dimensions for the equipment of the invention are selected to suit any given application. The selection can be made on the basis of experimental research and theoretical studies.

Designations of the components shown in the figures are as follows

1. wall of a settling basin

2. general travelling direction of a slow-moving vortex 12. a tangential inlet duct

13. light..component _. outlet. ... .

39. a flow divider for separating different vortexes

40. a gate or flow channel 47. an overflow weir

49. vortex centre axis

50. deflection fin

62. undercurrent towards the centre of a basin or so- called tea-cup phenomenon

64. level of a liquid medium

65. heavy component collection funnel

66. flow barrier plate

68. bottom of a settling basin 70. heavy component outlet 71..horizontal plate

72. trailing edge

73. collision edge

Fig. 1 shows an array of settling basins 1 , wherein the successive basins are connected to each other by way of a gate 40 . Some of the outer fringe of a slow- moving vortex 2 of a preceding basin proceeds into the outer section of the next settling basin, where said slow-moving vortex 2 continues. In this case, the slow-moving vortexes of successive basins bear against each other at gate 40 . in the contact zone, both slow-moving vortexes 2 travel in the same direct¬ ion. The array shown in the figure comprises five suc¬ cessive settling basins. The general flowing direction is in this figure from left to right. The supply is effected through a tangential inlet duct 12 , whose height in this case extends from bottom to top of the apparatus. A high inlet duct facilitates a high capa¬ city. The heaviest particles tend to settle down al¬ ready in the first settling basin on the left in the figure. Lighter particles are carried within the flow

into the next basin, wherein gravity continues to col¬ lect particles in the lower section of the basin. The same action is repeated in the following basins. As the flow proceeds slowly from the first to the last basin in an array, gravity concentrates heavy component in the lower basin sections and light component in the top sections. The discharge of light component occurs in the case of this figure only from the last basin at the surface along an outlet 13 . The light com¬ ponent discharges over an overflow weir 47 . In the preceding basins of this array, heavy component is dis¬ charged from the bottom along outlets 70 in a sufficient amount. Said outlet channels 70 are adjusted by means of the opening size, a valve or by a counter- pressure, so that light component is not unnecessarily entrapped in the heavy component. The first four units of the array are in this case a kind of preseparators with not very much flow discharged, but the amount of heavy component is reduced and settled towards the bottom. In the apparatus shown in fig. 1, the settling basins are circular but, regarding the operation of such apparatus, it is also possible to use basin units of other shapes, e.g. elliptical, polygonal as well as different arched shapes. The collection of heavy and light component can be done from the geometric centre of a basin or from some off-centre spot. Especially in the first settling basins, it preferred to employ an eccentric dispostion, so that eccentricity serves to provide room a main flow by-passing the basin unit. If desired, the trailing edges can be extended with vertical plates for separating the flows on different sides from each other. By means of these deflection fins, said gate 40 can also be reduced into a narrow flow channel between settling basins. The edges can be rounded. Especially collision edges 73 can be design¬ ed as rounded. When using sharp collision edges, it is

possible to create an oscillatory motion in settling basins as the flow periodically passes on different sides of the edge. This reciprocating oscillatory mot¬ ion is preferred for keeping the deposit gathered on the bottom in motion and for carrying it gradually to its point of collection.

Fig. 2 shows one possible section along a line II-II in fig. 1. A high tangential inlet 12 has the effect that the inlet flow rate is low which means that there is only a little need for kinetic energy. As the suc¬ cessive basins 1 are by way of gates 40 in direct contact with each other, there will be no resistances of flow therebetween. The level 64 of a liquid med¬ ium is nearly horizontal in various basin units 1, 1 . The original kinetic energy present in the supply can be utilized in the entire array. Thus, the energy de¬ mand is very little. In each settling basin occurs thin-layered flow 62 along the bottom towards the centre. In this thin layer of flow, the settling dis¬ tance to the bottom is very short and, thus, the heavy component can be readily separated. As the same phe¬ nomenon repeats itself in a plurality of successive basins 1 , the effect is intensified. In the case of fig. 2, the lihgt component discharges as an over¬ flow 47 from the last basin. Below the overflow is a horizontal plate 71 for preventing the formation of a free vortex and its air core. Other ways of dis¬ charging the light component can also be used. Similar light component outlets may be provided inseveral basins and even in all settling basins 1 . Heavy com¬ ponent can be passed via channels 70 to a common heavy component collection tank, if so desired, and the pressure level of this tank can be controlled by means of its own overflow. The proportion of flow rates between heavy component and light component can

thus be controlled e.g. by adjusting the relative heights of the overflows of heavy and light component. If desired, the apparatus can also be made pressurized with a pressurized gas layer above liquid level 64 below a tight cover.

Fig. 3 shows one alternative section along a line II-II. In this case, the basin bottoms are staggered in vertic¬ al direction. The staggered steps prevent a direct flow near the bottom from the forward end of an array towards its trailing end. The bottom layer containing a heavy component tends to remain below the steps. As the liquid layer keeps getting lower towards the trailing end, the separation of a heavy component becomes easier as the settling distance becomes shorter. Staggering can also be provided by using gently sloping designs without sharp- edged steps. Staggering can also be used for increasing the height of inlet duct 12 so as to reduce the inlet rate. Staggering can also be provided so that the thick¬ ness of a liquid layer increases from the forward to the trailing end of an array. This takes the heavy and the light component further and further away from each other. Staggering can also be much more pronounced than that shown in the figure. Fig. 3 shows also on principle a possibility of shutting off a part of gate 40 by means of a barrier plate 66 . A flow barrier plate is in this case positioned in the top section to stop a direct flow to a tangential outlet 13 from the surface. A flow barrier plate can also be positioned to stop the passage of floating objects and particles to said light component outlet 13 . The flow barrier plate 66 may be provided, in addition to the vertical member, also with horizontal members, leading e.g. to an L-shaped cross-section. Such a horizontal member prevents the formation of a turbulence created when by-passing a sharp vertical edge. Below said tangential light component outlet 13 occur-

ing near the surface, there may be provided a horizontal plate for separating the bottom layers of liquid from the discharge flow. An effect similar to that obtained by staggering can be achieved by positioning near the bottom some vertical flow barrier plates 66 , whose height is selected as appropriate. Light component can be discharged at various stages of the array of settling basins by using overflows 47 over the outer shoulder. They can be provided at the middle section of an array as in fig. 3 or at the end of an array. By discharging light component little by little, the verticaJ flows can be made as slow as possible, whereby an upwards- directed flow does not pick up heavy component from the bottom and carry it along.

In fig. 4, parallel and successive settling basins 1 are in contact with each other through gates 40 . The settling basins make up a system of basins or pools with only minor flow dividers 39 between various basins. Thus, The required amount of building mater¬ ial is relatively little as compared to the equal num¬ ber of completely separate basins. Such flow dividers 39 can also be of light construction and even hollow, if desired. If necessary, they can also be used as overflows 47 for the discharge of light component. Flow dividers 39 can, if desired, be mounted as sepa¬ rate units on the common bottom or floor of basins 1, 1 . A hollow flow divider 39 can be allowed to build hydraulic pressure inside, so the structure can be made very light indeed as a result of the counter-pressure. In the case shown in fig. 4, an oscillatory action can be made effective if flow dividers 39 are fitted with sharp collision edges. In fig. 4, the light com¬ ponent outlet is shown the same way as in fig. 2, but from all basin units 1 . By applying the solution of

fig. 4, it is possible to combine the high capacity of a large-sized basin and the effective tea-cup phenomenon 62 found in small-sized basins.

Fig. 5 shows one solution, wherein the size of settling basins 1 is varying. At the outset of array 1, 1 , the smaller diameter produces a stronger underflow 62 than what occurs in the larger basins towards the end. Thus, the heaviest particles, settled on the bottom at the outset of an array, are effectively gathered in their point of collection, but the quiet flow at the trailing end facilitates the separation of even slowly settling particles. In the case shown in fig. 5, the separator is, in a way, part of a flow channel extend¬ ing from inlet 12 to outlet 13 . If desired, a settling separator can be designed without heavy com¬ ponent collection systems 70 , in which case the heavy component just settles on the bottom of basins

1 , wherefrom it is periodically removed e.g. by digging or sucking with separate devices. The size of settling basins in an array can also be gradually di¬ minishing.

Fig. 6 shows a solution in which basins 1 are disposed in a zigzag-pattern. A flow passing through the appa¬ ratus from inlet 12 to outlet 13 is forced to travel a distance as long as possible, which means that there is a long time available for settling. In most basins

1 , the main flow turns more than 180" leading to an intensified tea-cup phenomenon 62 in the turning area.

Fig. 7 depicts a solution in which a gate 40 is provid¬ ed with a deflection fin 50 for increasing the tangent¬ ial direction of flow. In this figure, an inlet 12 is positioned outside the radius of a first basin unit tan-

gentially. Thereafter, because of the outer wall, the inlet flow is forced to work its way closer to the ^" centre of first basin 1 . This intensifies the ef¬ fect of tea-cup phenomenon 62 . This type of arran¬ gement is preferred particularly in the lower section of inlet 12 near the bottom.