Aeroprobe probes used by mining industry
FLSmidth Minerals is constructing and marketing mining equipment. One of the most successful lines of their products are flotation cells. The flotation cells are large tanks, ranging from 6 m3 to 300 m3 equipped with an impeller, a stator and openings to feed the ore. The tank is filled with water, and ground ore is supplied in the form of slurry. Compressed air is then delivered to form very small bubbles. Hydrophobic ore particles like coal or copper particles are then attached to the bubbles, floated to the top and then are collected and thus separated from the raw material removed from the mine.
The flotation process requires that the three-phase flow consisting of water, bubbles and particles is agitated to promote the collision of bubbles and particles and thus the formation of bubble/particle aggregates. This is achieved by allowing the stream generated by the impeller to impinge upon the blades of the stator plates and break up into large and small vortices.
The Aeroprobe probe inserted between the FLS impeller and the stator.
Aeroprobe designed an experimental rig that allowed a five-hole probe to be inserted in a FLS cell, and traversed along planes normal to the radial direction as shown in the figure below. In this figure the impeller and the stator are not shown. Tygon tubing connects the probe ports to the sensor module, and Aeroprobe system components facilitate the traversing of the probe and automated data acquisition.
In the photograph to the left, the probe is shown mounted on a probe holder shaft and situated in between the impeller and the stator. The impeller blades are not shown, because they are covered by a circular disc that separates them from the upper part of the flotation cell.
Measurements were obtained in two domains, first in the space between the impeller and then beyond the stator but close to the stator blades outer edges. Only one quarter of the stator is shown schematically in the following figure, in which we also include a system of coordinates.
The flow emerges from the impeller with a strong circumferential component, namely a component in the z direction. This component is suppressed by the stator plates, but as a result, each plate must generate a region of dead water flow. This was indeed what was discovered using the Aeroprobe system. The pink plane shown in the Figure below indicates the plane of measurements. A grid was defined on this plane and the Aeroprobe traversing system placed the Aeroprobe probe at each grid point and obtained the three velocity components at this point in space. The red lines on this plane are a visual aid and denote the radial projection of one stator plate and the annular horizontal surface that covers the plates.
An example of the obtained data is shown in the next figure. These are contours of the radial component of the velocity. As expected the suction side of the plate, namely the region on the positive side of the z axis indicates very low radial velocity. But the pressure side, i.e. domain of negative z indicates high radial velocities. Of great significance to the manufacturer of this machine is the finding that this flow emerges as a strong radial jet, and that it favors the very top of the impeller/stator domain.
The radial component of the velocity obtained with the Aeroprobe system.
