Technical Field This invention relates to an apparatus and method for separating solids from a liquid.

Background of the Invention In a known process for removing solids suspended in water the water is first treated with a chemical flocculant,

coagulant, or other chemical reagent to enhance

sedimentation. The suspension is then passed to some kind of settlement tank where the solid are allowed to settle out from the rest of the water. In its simplest form such a settlement tank can just be a rectangular or circular plain tank. Such plain tanks are, however, required to have a very large area to handle a given flow rate of effluent and that can make their use awkward or impossible.

In order to reduce the required tank area, it is known to fit inclined plates in an upper region of a tank.

Such plates increase the effective surface area of the tank enabling a given area of tank to handle a greater flow of effluent than could be handled by a plain tank of the same size. As the suspension is passed slowly up through the spaces between the plates, solids separate out from the suspension and slide down the plates to the bottom of the tank from where they can be removed. Examples of apparatus of this kind are described and shown in GB 2398519A.

We have found that there are times when solids settle out of the suspension onto the inclined plates but then remain on the plates. Thereafter there can be an increased tendency for solids to build up on the plates.

It is an object of the invention to provide an

improved apparatus and method for separating solids from a liquid .

Summary of the Invention

According to the invention there is provided a tank for separating solids from a suspension of the solids in liquid, the tank having an upper region containing a multiplicity of inclined plates and a lower region for collecting solids settling from the upper region, the tank further including one or more vibrators for vibrating the inclined plates in a direction aligned with their

directions of inclination.

By vibrating the inclined plates and, according to the invention, vibrating them in a direction aligned with their directions of inclination, sticking of solids to the plates is inhibited.

Preferably, at least some of the inclined plates are secured together in a common assembly and the assembly is arranged to be vibrated by the one or more vibrators . More preferably all the inclined plates are secured together in one assembly; all the plates can then be vibrated as a single unit.

The common assembly is preferably supported within the tank on a plurality of resilient supports arranged to allow the assembly to be vibrated in a direction substantially aligned with the directions of inclination of the plates in the assembly. Preferably each of the resilient supports is fixed to the tank. At least one of the plurality of

resilient supports may extend from a bottom region of the common assembly.

The plates may be inclined at an angle in the range of 30 degrees to 65 degrees to the horizontal.

The assembly preferably includes a member above the inclined plates. The member may be secured in a fixed relationship to the assembly. The member may extend across the assembly in a direction substantially parallel with the gaps between the plates. The one or more vibrators may be mounted on the member. The member is preferably elongate and preferably of generally tubular form. In an embodiment of the invention described below, two vibrators are mounted on the member.

It is within the scope of the invention for the vibrations to have components in directions not aligned with their directions of inclination, but it is preferred that substantially all the vibrations of the plates are in the planes of the plates and, more preferably, in a

direction aligned with their directions of inclination. Vibrators can take a wide variety of forms and many are suitable for use with the present invention but a particularly suitable vibrator is of a kind that includes an eccentrically weighted rotary member. Preferably at least two vibrators including eccentrically mounted weights are provided and the weights are arranged to be rotated in opposite directions of rotation.

Typically the frequency of vibration is in the range of 10 strokes per second to 100 strokes per second, a stroke being defined as a complete cycle of oscillation.

More preferably the frequency of vibration is in the range of 30 to 70 strokes per second.

The present invention may be applied to a flat- bottomed tank, for example of the kind shown in

GB 2398519A, but it will often be preferred that the lower region of the tank includes sloping bottom walls inclined at angles greater than 30 degrees to the horizontal. The walls may be inclined at an angle of more than 45 degrees to the horizontal. The walls may define one or more hoppers in the lower region of the tank. In the case where the tank is flat-bottomed the lower region below the plates may be of much less depth than the upper region.

The tank is preferably portable, allowing it to be moved from one site to another. It is, however, also possible for the invention to be employed in a permanently sited tank. For example, the walls of the tank may be formed of concrete.

According to the invention there is also provided a method of separating solids from a suspension of the solids in liquid, the method including the following steps:

providing a tank having an upper region containing a multiplicity of inclined plates, and a lower region for collecting solids settling from the upper region,

vibrating the inclined plates in a direction aligned with their directions of inclination, and

feeding the suspension of the solids into the tank, solids from the suspension sliding down the inclined plates into the lower region of the tank.

Preferably an assembly of the plates is vibrated as a unit .

All the vibrations of the plates are preferably in a direction aligned with their directions of inclination.

The frequency of vibration is preferably in the range of 10 strokes per second to 100 strokes per second and more preferably in the range of 30 to 70 strokes per second.

The tank may be mobile and may be used at one site after another. Thus the method preferably further includes the step of subsequently moving the tank to a new site and repeating the vibrating and feeding steps at the new site. It is, however, also possible for the tank to be

permanently sited at one location.

According to the invention there is also provided a tank for separating solids from a suspension of solids in liquid, the tank having an upper region containing a plate assembly comprising a multiplicity of inclined plates secured in a fixed relationship to each other; a member arranged in a fixed relationship to the multiplicity of inclined plates; and one or more vibrators mounted on the member for vibrating the inclined plates in a direction aligned with their directions of inclination; the tank further including a lower region for collecting solids settling from the upper region.

It will be appreciated that the apparatus and method of the invention as described herein are closely related and that therefore essential or preferred features of one may, unless indicated otherwise or clearly inappropriate, be incorporated into the other. For example, the method of the invention may use any form of the tank of the

invention. Similarly, a tank of the invention may be so configured as to be suitable for use in a method according to any form of the invention. Features described above in respect of the apparatus of the invention may be

incorporated into the method of the invention and vice versa . Brief Description of the Drawings

By way of example embodiments of the invention will now be described with reference to the accompanying

schematic drawings, of which:

Fig. 1 is an exploded isometric view of a tank

assembly for separating solids from a liquid; and Fig. 2 is a side view of the tank assembly of Fig. 1 with a side sheet of the assembly removed to reveal the interior of a tank. Detailed Description of Embodiments

The tank assembly shown in the drawings may be used as part of a system for removing dissolved solids from water. The water is first treated to precipitate the solids as floes. A standard way of separating the floes from the water is to use a clarifier tank including inclined plates.

Many designs of such tank are known and one that is similar in some respects to the tank described herein with reference to the drawings is the tank shown and described in GB 2398519A.

The envelope of space encompassing the tank assembly is of approximately cuboidal shape. The assembly has a base frame 1 from which legs 2 extend upwardly to support a tank 3. The tank 3 has opposite side walls 4, an end wall 5 and an opposite end wall 6. The side walls 4 are

approximately vertical as is the end wall 5, but the end wall 6 is inclined upwardly and outwardly apart from a lower portion 7 that is approximately vertical and a top portion 8 that is approximately horizontal. The top portion 8 includes an outlet 9 from which clarified water leaves the tank 3 and the wall 5 includes an inlet 10 near its top, through which water carrying suspended solids is passed into the tank 3. The bottom of the tank 3 may be almost flat as

described in GB 2398519A, but in the illustrated embodiment it is formed with a pair of hoppers 11 of inverted pyramid shape. Each of the hoppers have outlets 12 at their bottoms through which solids separated from the water can be removed from the tank.

The tank is provided with lifting eyes 14 to enable it to be lifted on and off a lorry for transport from one site to another.

An inclined plate unit 20 is mounted inside the tank

3. The unit comprises a multiplicity of inclined parallel plates 21 assembled together in fixed relationship. In the particular example shown there are about 50 plates and the plates are inclined at an angle of about 55 degrees to the horizontal. The assembly of plates is closed at its sides and ends but open along its top and bottom. The assembly fits inside the tank 3 and is supported in the region of each of its four bottom corners on a resilient mounting 26 which in turn is fixed to the tank 3. As can be seen in Fig. 2, when the unit 20 is mounted in the tank 3, there is a space 22 in the tank below the unit 20, referred to herein as the lower region of the tank, whilst the region of the tank accommodating the plates is referred to as the upper region of the tank.

The unit 20 includes top side supports 23 which extend upwardly above the plates 21 on opposite sides of the tank 3. A tubular member 24 extends across the tank from one support 23 to the other in a direction parallel to the gaps between the top edges of the plates 21. A pair of vibrators 25 are mounted on the tubular member 24. The unit 20 has lifting eyes 15 to enable it to be lifted in and out of the tank 3 for maintenance.

In operation of the tank assembly, effluent to be clarified is fed into the tank assembly through the inlet 10, passes down into the lower region 22 of the tank and then up through the channels formed between the plates 21. As the water passes slowly up through those channels, floes settle out of the flow and onto the plates 21. The floes then slide down the plates and settle in the hoppers 11 from which they can be removed at intervals via the outlets 12. The water from which the floes have been removed flows out of the top of the channels and passes out of the tank through the outlet 9.

During operation of the tank, the vibrators 25 are drivenandgenerate an oscillating force in the direction indicated by a double-headed arrow A in Fig. 2. The vibrators may be of any suitable kind, known per se, for producing a directional vibration. In the present example, they are rotary vibrators relying on an eccentrically mounted weight that is rotated to generate the vibrations; in the particular example described, the vibrators are made and sold by Vibratechniques Ltd. More particularly, each vibrator is the MVSI 3/1810 sold by that company. That vibrator rotates at 3,000 rpm and therefore generates a linear vibration at a frequency of about 50 cycles per second. The vibrator is electrically powered. The two vibrators are driven in opposite directions of rotation and together generate the desired linear vibration. As shown in the drawings the vibrators are mounted with their bases perpendicular to the desired direction of vibration. The vibrators 25 therefore cause the unit 20 to oscillate on its mountings in the direction of the arrow A, namely in a direction aligned with the directions of inclination of the plates 21. That vibration inhibits the floes from sticking to the plates 21.

In the description above, one particular example, together with certain variations, has been described, but it should be understood that many other variations and modifications are also possible. For example, although the tank shown in the drawings is mobile and can be moved from one site to another, it may alternatively be a permanently sited tank unable to be moved from one location to another.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or

foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be

appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims.