SE452121B - FLOTATIONSANLEGGNING - Google Patents

Abstract

A floatation tower for paper recovery has a set of cells one above the other, holding the fibrous paper paste, and into which water and compressed air are injected so that the impurities mix. with the bubbles to form a foam which can be removed separately. Water is admitted as a thin layer at the same time as the air to mix. with the liquid paste as it is circulated in a thin layer in a mixing chamber, passing it through and along the flow, controlling the thickness of the layer. Air is then admitted to skin off the foam and drive it into a collector vessel below, for recycling. By a similar process for each cell, ink, kaolin and fibres can be removed separately. The mixing chamber is conical, with a tangential lop entry.

Description

In such a flotation plant, separation of the foams containing the contaminants from the purified liquid is an important function, because if this is not done adequately, the plant will not work efficiently and cause difficulties due to the nature of the foam itself. Tests carried out have suggested that the use of mechanically movable equipment for treating the foam should be avoided.

US-A-3,523,891 (Mehl) discloses a device for removing foam floating at the liquid surface in a rectangular cell chamber which is divided by spaced apart electrode plates which ensure a sinusoidal path for the liquid.

SE-B-7114902-5 (Degremont, Publ. No. 381,410) describes a flotation tank which uses a liquid which is saturated with a gas under pressure to treat another liquid to be purified. The two liquids are introduced into an antechamber arranged at the bottom of the flotation tank, the antechamber being open adjacent to the tank. The treatment liquid is injected into the atrium through a tube and forced into a horizontal flow in order to prevent as far as possible from being brought into contact too early with the liquid being treated, which is introduced in a vertical upward direction. The connection of the atrium to the treatment of the fluid is stated to be "non-tangential". the liquid will then not follow a generally circular flow pattern around the axis of the cell.

An object of the invention is to provide an improved plant which, while avoiding the stated mechanical equipment, allows efficient separation of foams containing contaminants from purified liquid.

The plant according to the invention is of an initially stated type and is characterized essentially in that the inlet is located in the lower part of the cell and is tangentially directed towards its outer wall to form a substantially circular flow pattern of the incoming liquid around the axis of the cell. , and that the foam outlet comprises an axial outlet tube in the cell, which leads through the bottom of the cell and extends to the foam layer.

The invention provides effective treatment of the foam without the use of moving parts for the purpose.

The recirculation means may suitably comprise a pipe arranged axially in the outlet pipe in the cell with an open end exposed to the foam-laden air to said outlet pipe and at its opposite end in connection with the suction means.

The plant further suitably comprises a number of cells which are arranged to be stacked coaxially one on top of the other with communicating outlet pipes.

Further features and further details in connection with the invention will appear from the following description of a plant which refers to the accompanying drawings. These show only by way of example an embodiment of the invention, which is particularly suitable for decolorizing pulp produced from old newspapers.

Fig. 1 is a schematic side view of a multi-storey facility.

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

The plant comprises four flotation cells 1, 2, 3, 4. These cells are annular and axially superimposed on each other, so that they form four steps or levels in a tower with a number of bottoms or floors 5. It is obvious that the tower can have a number of steps that differ from four.

The defibrated, chemically pretreated pulp in the form of a fibrous suspension containing a foaming agent is delivered by means of a pump 6 via a tube 7 to the inlet 11a of the cell 1, whereby it first passes a mixing chamber 8. This chamber has a narrow passage in which it the fibrous suspension circulates in the form of a thin layer, at the same time as air is supplied to the same transverse movement path 452 121 along a part thereof through a tube 9 which is connected to an air pressure source (not shown) via a valve 10.

The mixing chamber 8 communicates with the annular cell 1 through a tube 11 which leads tangentially into the cylindrical wall of the cell near its floor 5, so that the fibrous suspension is caused to circulate around the central tube 12 of the annular cell 12. created in the suspension adheres to the contaminants and causes them to rise to the surface in the form of foam. This is carried out of the cell via the outlet 18 of the tube 12, partly due to the vortex movement of the suspension and partly due to a stream of air generated over them. A vertical plate arranged above the level of the pulp guides the foam to the outlet.

The foam is collected in a vessel 13 surrounding the tube 12 and discharges into a waste tank 37 which is filled with water. The air stream for dispensing the foam is introduced into the upper part of the cell through a tube 14 which is connected to a vacuum suction 15, which is located over a frustoconical axial tube 16 for recirculating the air which causes the foam to escape. This tube is arranged concentrically in the central outlet tube 12 for foam and is common to all superimposed cells. The air discharging the foam enters the cell via the opening 17 and leaves it through the outlet 48 carrying the foam, which under the influence of gravity falls into the vessel 13, while the air exits through the tube 16. The latter extends into the adjacent cell 2 while forming a cone, which tapers upwards and is directed towards the further pipe for recirculation of the air which causes the foam to be delivered to said adjacent cell and to the other cells 3, 4. The parts constituting the pipe 16 form a cyclone, and thus gives the foam a swirling movement, which allows separation of air sucked into the tube under the action of the suction device 15, when it returns to the tube 14 to be used again for dispensing foam.

The mass which is partially purified in cell 1 leaves the latter via a pipe 19 provided with a pump 20 which allows an increase in the pressure. The tube 19 is included in the mixing chamber 452 121 of the subsequent cell 4 located in the last stage of the tower, and the process that takes place is identical to that used in the first cell as is the case in the other cells.

These are successively fed with the pulp or water containing fibers of increasing purity, while the foam collected in the other cells is in turn recycled to the lower cell.

The foam containing the waste from the first cell and other cells can, of course, either be recycled or dispensed at each step for treatment in a separate device depending on the product type of pulp.

The plant also includes a lid 40 that closes the cell in the first stage; an inspection window 41 which allows rapid emptying to effect purification, an emptying valve 42 to each cell, a flap 46 in the air tube for transporting foam, a floor or a bottom 43 in the tube T2 for receiving recycled waste material, a tube 44 for dispensing this waste material into cell 1, and a tube for dispensing accepted pulp into cell 2 which processes the most highly purified pulp.

The described invention relates to a plant for decolorizing pulp. It can be used for other purposes, for example purification of alloys or for purification of fiber-laden water by flotation of fibers.

It is clear that the invention is not limited to the embodiment described above and illustrated in the drawings without many modifications being made to the design, arrangement and composition of certain constituent elements without departing from the spirit of the invention. The invention thus relates to all conceivable modifications - within the scope of its basic idea as defined by the appended claims.

Claims (7)

452 121 Patent claims A plant for eliminating contaminants in the form of solid particles in liquid by flotation, which plant comprises at least one substantially cylindrical flotation cell (1), an inlet (11a) for supplying liquid to the cell, aeration means (9, 10) for providing an air stream to form bubbles in the liquid which adhere to and cause the contaminants to rise upward to form a surface foam on the liquid in the cell and outlets (18, 19) for separately dispensing surface foam on the liquid in the cell and purified liquid from the cell, respectively. , foam ejecting means (14) for directing an air stream into said surface foam for blowing the foam towards and out through its outlet (18), said foam ejecting means further comprising suction means (15) and means (16) for recirculating the air in the air stream, k characterized in that the inlet (11a) is located in the lower part of the cell (1) and is tangentially directed towards its outer wall to form a substantially circular flow pattern of the incoming liquid around the axis of the cell, and that the foam outlet comprises an axial outlet tube (12) in the cell, which leads through the bottom (5) of the cell and extends to the foam layer. Plant according to claim 1, characterized in that the recirculation means comprise a pipe (16) arranged axially in the outlet pipe (12) in the cell with an open end exposed to the foam-laden air to said outlet pipe and at its opposite end in communication with the suction means (15). Plant according to claim 2, characterized in that it comprises a number of cells (1, 2, (3, 4) arranged to be stacked coaxially one on top of the other with communicating outlet pipes (12). Plant according to claim 3, characterized in that said axially arranged tubes (16) are arranged to communicate when the cells (1-4) are stacked one on top of the other, and that the plant comprises a single suction means ( 15) for operating the communicating tubes (16) for forming air currents to the foam metering means of the cells. ii4s2 121 Plant according to claim 4, characterized in that the aeration means (9, 10) of each cell is provided with means for regulating the bubble size produced by the air injection into the liquid and comprises pipes (19) for connecting the outlet for purified liquid to each cell except one with the inlet (1Ta) to another cell to effect a series of treatment steps for the fluid in the cells. Plant according to claim 5, characterized in that it is provided with an axial pipe (16) for recirculating the air for the escape of foam, which pipe is common to all cells. Plant according to any one of claims 3-6, characterized in that the tube (16) which recirculates air for the escape of foam from the lower cell (1) extends into the adjacent cell (2) during formation. of a cone which tapers upwards and is directed towards the pipe (16) with larger diameter for recirculating air for the departure of foam from the adjacent cell (2) and other cells.