Patent Application
20210205769
The invention relates to a device for generating gas bubbles in suspensions for the enrichment of mineral and non-mineral raw materials and the use of such a device. For the purposes of this application, suspensions are mixtures of liquids and raw materials, in particular mineral resources, such as copper, tin, platinum group metals (iridium, rhodium or palladium), phosphates and slag in a finely ground phase, which are contained in tanks of flotation cells. For the purpose of separating desired raw materials from this suspension, said suspension is mixed and swirled with air within the tanks, so that a gas bubble-air mixture is formed. As a result, three zones are formed within the suspension. In the lower third of the tank, the swirling of the suspension and, as a result, the generation of bubbles takes place. In the overlying third of the tank, the so-called calming zone, the bubbles with the adhering hydrophobic raw material particles drive towards the surface of the suspension and deposit in the upper third of the tank as foam. This foam leaves the tank of the flotation cell at its top by an overflow and is available for further processing by means, which are known per se.
In order to generate the swirling of the suspension within the tank, a rotor executes a rotational movement with a speed to be defined within a surrounding stator. As a result of this rotational movement, the suspension is sucked through the gap between the stator and the support device and returned to the surrounding area of the suspension through the casing of the stator. In this case, a portion of the suspension containing hydrophilic raw materials sinks back to the bottom of the tank and is dug from there.
By simultaneously introducing air into the suspension, the suspension is enriched with gas bubbles. As a result of the swirling of this gas bubble suspension mixture, a force acts on the gas bubbles and these break down further into smaller and smaller bubbles.
Category-specific devices for generating gas bubbles are well known from the prior art.
The document U.S. Pat. No. 4,283,357 A describes a rotor-stator mechanism in which the air distributor, which is located in the rotor, directs the air against the stator vanes using tangentially arranged air guidance channels. In this case, the air guidance channels form an angle between 20° and 60° relative to the radial.
The document 9266121 B2 discloses a rotor with vanes, which extend vertically and are arranged radially to the axis of rotation and which are provided with curved vane exterior edges. The air flows through the channel extending inside the drive shaft and the rotor through the air intake openings and into the suspension. The air is directed to the air intake openings of the rotor through a network of inner air guidance channels located at the upper central portion of the rotor. Furthermore, the rotor is designed such that the suspension in the middle part of the rotor is sucked axially along the axis of rotation and is directed through corresponding outlet openings back into the surrounding suspension.
The document US 2015/0251192 A1 describes a stator with a plurality of vertically aligned baffles arranged around the rotor. The rotor is connected to a vertically aligned shaft. The vanes of the rotor extend vertically and are curved at their exterior edges. The baffles of the stator also extend vertically and are provided with a plurality of horizontally arranged slots for better shear effect. Furthermore, the air intake openings required for ventilation of the suspension are arranged so that the air is passed between the vanes of the rotor.
The document U.S. Pat. No. 4,425,232 A discloses a stator-rotor combination in which the inner sides of the stator baffles follow the contour of the exterior edges of the stator vanes and have the same distance.
Possible arrangements and embodiments of air outlet openings are described in the document U.S. Pat. No. 6,805,243 B1. In this case, flat, horizontal slots are a preferred embodiment. Furthermore, the position of the air outlet openings underneath the plate of the rotor is disclosed.
The document U.S. Pat. No. 4,551,285 A describes a rotor which is surrounded by vertically arranged baffles. The vanes of the rotor are radially arranged on a rod and extend from its exterior side to half of the radius. Furthermore, smaller vanes act as air intake vanes in the area of the drive shaft.
The document U.S. Pat. No. 6,772,885 B2 discloses an embodiment of the plate of a rotor, which has an angle of inclination between 5° and 70° in the direction of the bottom side of the rotor.
An embodiment of a stator-rotor arrangement for improving the pumping power of such arrangements is described by EP 0287251 B1. Due to the arrangement of the baffles in relation to the exterior edge of the rotor, precisely the gas bubbles located at the bottom of the tank of the suspension-filled flotation cell are lifted and split.
CN 2 02 490 592 U discloses a powder-liquid mixing device comprising a mixer having a powder inlet, a liquid inlet and a liquid outlet. The mixer comprises a stator and a rotor. The wall of the stator comprises a plurality of holes and the rotor has a claw-shaped metal sheet, which is attached to the rotor by means of screws. The rotor is driven by a motor wherein shear and centrifugal forces are generated to disperse and homogenize the powder in the liquid.
A disadvantage of all above-mentioned rotor-stator combinations is that these devices have a low efficiency in the extraction of raw materials with low-grade occurrence. Especially in this case it is necessary to extract such raw materials from a finely ground mineral phase, which requires the smallest possible gas bubbles with small size differences. Existing plants are able, by extending the residence time of the swirled suspension in the region of the rotor-stator combination, to generate small bubbles, which are suitable for the extraction of these raw materials. However, this leads to a deterioration in the efficiency of such flotation plants.
To overcome these disadvantages of the prior art, the object of the invention is to generate a flow in suspensions, which extends the residence time of the gas bubble suspension mixture in the region of the stator and at the same time sets the flow rates at such a high level that the plants maintain a high efficiency.
This object is achieved by a stator-rotor combination for generating gas bubbles in suspensions, which is disclosed by claim 1. Further developments according to the invention are disclosed in the dependent claims.
According to the invention, the rotation-symmetric rotor is connected to a hollow drive shaft, whose axis of rotation is arranged concentrically with respect to the central axis of a surrounding stator. The rotor is composed of a plate, which represents the upper side of the rotor and a plurality of vanes extending axially and parallel to the axis of rotation away from the plate. Furthermore, the rotor is provided beneath its plate with air intake openings, which allow air to enter the suspension via the hollow drive shaft, the air guidance channels and the air intake openings. Preferably, the rotor is designed as a welded component, an additively manufactured component or a moulded component. The axis of rotation of the rotor is normal to the surface of the suspension.
The stator is designed as a cylindrical hollow body, which encloses the rotor. In this ca, the rotor and stator are arranged to each other so that the stator projects beyond the rotor on its upper side. The lower end of the rotor projects beyond the bottom of the stator and is located at the level of the gap between the stator and a vortex breaker, which is connected to the bottom surface of a support device. The casing of the stator consists of a plurality of strip-shaped, radially oriented baffles, which thereby form a perforated, cage-like shell, which can be flowed through by the suspension.
The stator is positioned on a support device which ensures a defined distance between the stator and the bottom surface and which introduces the forces acting on the stator due to the flow resistance into the bottom of the tank of the flotation cell. On the bottom plate a vortex breaker, known per se, is positioned, which serves to swirl the flowing suspension and the use of which is well known.
According to the invention, the vanes of the rotor extend at different distances from the plate in the axial direction. In this case, the inner edges of the shorter vanes have a radial distance from the drive shaft. The baffles of the stator are inclined relative to the axis of rotation. In this case, a first partial quantity of the baffles has an angle α of 30° to 60° and a second partial quantity of the baffles have an angle α′ of −30° to −60° and thus allow a continuous swirling and thus fragmentation of the bubbles within the suspension. In particular, the values of the angles α and α′ are the same. The baffles are materially interconnected and thereby form the casing of the stator.
In a preferred embodiment of the rotor, the exterior contours of all the vanes taper in a convex-curved manner as the distance from the plate increases. A straight exterior edge of the rotor is used when the production costs should be as low as possible. A higher efficiency of the rotor can be achieved with a curved exterior contour of the vanes.
In a preferred embodiment, a first partial quantity of the rotor vanes has the same length as the overall height of the rotor. A second and third partial quantity is made shorter, wherein the vane lengths of this second and third partial quantity are the same length, or in a preferred embodiment, have different longitudinal extensions, in order to obtain a stronger mixing of the suspension gas bubble mixture.
Preferably, all the vanes of the rotor are connected with the drive shaft in a form-fitting or materially connected manner. In a particularly preferred embodiment of the rotor, the shorter vanes are radially spaced from the drive shaft. This radial distance r is between 30% and 70% of the radius R and leads to an improved air bubble distribution within the suspension.
In a particularly preferred form of the rotor, the inside edges of the shorter vanes are tapered or pointed to a point towards the axis of rotation. This has the advantage that the air entering the suspension is guided with a low resistance on these vanes along these vanes and thus contributes significantly to the high efficiency of flotation systems, which are provided with such a device.
In a further preferred embodiment, the lower edges of the shorter vanes are horizontally oriented or inclined. They form an angle γ between 0° and 60°, relative to the horizontal, which has an advantageous effect on the swirling of the suspension.
In order to supply air to the suspension, the drive shaft of the rotor is made hollow. Thus, air can be blown through this drive shaft into the rotor. Within the rotor, this air is distributed via air guidance channels to the preferably radially arranged air intake openings. The air guidance channels are preferably aligned so that they direct the air towards the bottom of the tank of the flotation cell. Here, the air guidance channels are preferably oriented at an angle ε between 20°-60°, relative to the axis of rotation.
In one embodiment of the invention, the inner and outer circumferential surfaces of the stator are formed in a straight line and spaced from each other. In an alternative embodiment of the stator, the exterior circumferential surface is convexly curved. The inner and exterior circumferential surface in this embodiment always have the same distance from each other and thus have a positive influence on the bubble distribution.
The stator is preferably a welded component or a molded component or an additively manufactured component having a plurality of integrally interconnected metal sheets. On the one hand, the metal sheets represent the total quantity of the baffles, on the other hand, the cover ring, the intermediate rings and the seal ring are formed as metal sheet and are integrally connected to the baffles. The total quantity of baffles is divided in a preferred embodiment evenly on two partial quantities of baffles. The baffles are enclosed by the cover ring and the seal ring and subdivided by the optional intermediate rings. In this way, it is possible to advantageously produce a stiff and firm stator, which, on the one hand, absorbs the loads due to the flow resistance, while on the other hand, it may quickly be replaced, since the stator is subject to wear. In a preferred embodiment, the stator is divisible for the purpose of disassembly and assembly. Preferably, this dividing plane is vertically aligned by vertically aligned metal sheets or is arranged horizontally by divisible intermediate rings. In this preferred embodiment, the vertical divider plates or divisible intermediate rings are releasably connected together. In a particularly preferred embodiment of the rotor, the vertically divided segments can additionally be divided horizontally in order to then remove or insert them through manholes located at the bottom of the tank of the flotation cell. Advantageously, it is possible to disassemble and assemble the stator without having to manipulate the rotor. The segments are designed such that they consist of a part of the baffles, which are enclosed in the vertical direction by the cover ring, the intermediate ring and the cover ring. In the circumferential direction of the stator, a segment is delimited by the vertically arranged baffles.
For the purpose of easy manufacture of the stator, the cover ring is aligned horizontally. However, it has proven to be useful to tilt the ring. The inclination is such that the inner edge of the cover ring is inclined toward the bottom. The particularly preferred inclination angle β is 30° to 60°. By means of this particularly preferred embodiment, the flow resistances for the swirled suspension are reduced, so that a more uniform swirling in the region of the stator can be ensured. The foam which is formed can then be removed from the surface by means of pumps.
The abrasive effect of the suspension on the vanes of the rotor and on the baffles of the stator cause a strong wear of the metallic material. It therefore proves to be advantageous if these components are coated with a low-cost wearable layer of plastic. In an alternative embodiment, the regions of the vanes and baffles that are exposed to the flow of the suspension, are hardened by a local structural change. This reduces the wear of the components. In addition, eliminating the polyurethane coating provides a weight advantage and increases the efficiency of the plant.
According to the invention, such rotor-stator combinations are used within tanks of flotation cells and are positioned in the lower third of the tank.
In order to practice the invention, it is also expedient to combine the above-described designs, embodiments and features of the claims of the invention with each other in a suitable arrangement.
The invention will be described below with reference to several embodiments and is represented graphically in the accompanying figures. The coordinate system used in the figures illustrates the orientation of the device within the suspension. The plane formed by the axes x and y is parallel to the surface of the suspension. The axis z is aligned normal to this plane.
A preferred embodiment of the device for generating gas bubbles is shown in
The embodiment of the rotor (15) shown in
In
In
The vertically divisible stator (16) of
Another alternative embodiment of the stator (16) is disclosed by
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2018 109 952.5 | Apr 2018 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/059437 | 4/12/2019 | WO | 00 |
