The present invention is developed in the field of operation, monitoring and control of mining mills, specifically it refers to a system and a process to determine online the characteristics of worn balls and the fragments thereof, which have been ejected. of a semi-autogenous mineral grinding mill (SAG) in a material that includes the ground ore and that are discharged in free fall into a chute from one or more magnets, for example electromagnets, that capture worn balls and the fragments of steel from the same from the ejected material, where said electromagnets are suspended on a conveyor belt on which the ejected material goes.
The semi-autogenous mineral grinding mills (1) are machines, which basically consist of a rotating drum with horizontal axis, which has an inlet (6) of ore (load) to be ground at a first end and an outlet (7) of the ground ore (filler) that has reached the desired size, through a second end. Through the inlet (6) there are also added metal grinding media, generally spherical in shape and preferably made of steel, corresponding to the grinding balls. In the case of wet grinding, water is also added, in this way, the internal load of the semi-autogenous mill is composed of grinding balls, ore and water (8) that are in permanent movement in the grinding chamber (2) while the semi-autogenous mill rotates. In
One of the important elements of a semi-autogenous mineral grinding mill is the internal grate (4), which has a plurality of grooves (5) separated by ribs (35), which have an opening with a predetermined size, so that the ore (10) that has reached this size leaves the semi-autogenous mill (1). The balls (9) used as grinding elements in the semi-autogenous mill (1), when added to the semi-autogenous mill, have a size greater than the opening of the groove (5). As the mineral grinding process occurs, the balls (9) wear out by abrasion and decrease their diameter, becoming smaller balls (11) that reach the size of the groove (5) opening and, therefore, also pass to the discharge chamber (3) and then to the outlet (7), leaving the semi-autogenous mill (1) towards the classifiers (14), or towards a conveyor belt (15). Also, during the grinding process, there are balls (9) that break, and thus, these broken balls (12) also reach a sufficient size to pass through the opening of the groove (5), as shown in
During the operation of the semi-autogenous mill, the grate (4) can also suffer the fracture of one of its ribs (35), as shown in
The kinetic energy provided by the rotary movement of the semi-autogenous mill to the internal load, undergoes several transformations during the process. This is the main energy that has the internal load (8), ore, water and grinding elements. Part of it is transformed into heat energy that is acquired by water, ore (10) and balls (9), and mainly these last two since they are more time inside the grinding chamber (2), until they are reduced in size to leave the semi-autogenous mill (1). Of these two, the grinding elements (9) are in the grinding chamber (2) for a much longer time than the ore (10), reaching periods of 20 to 40 days or more, depending on the process conditions, the refill ball size and grate opening size. For this reason, grinding elements have a greater boost in heat energy.
Likewise, under certain conditions, the energy produced by the impacts of the balls (9) is large enough for them to fracture or break and leave the grinding chamber (2) of the semi-autogenous mill (1) as a broken ball (12), such as explained in
Following the grinding process, ore and steel pieces come out from the semi-autogenous mill, which reaches the external classifier, which allows the separation of the fine ore and the coarse fraction that contains both ore (pebbles) and balls and/or larger ball fragments, which follow the conveyor belts to subsequent processes. In general, the pebbles are reduced in size using cone crushers that are damaged if steel elements are present in the feed, leading, for example, to the fracture of their components, causing them to be stopped for the corresponding repair. This condition forces the worn balls, the larger balls that have come out through a slot with a broken rib, and the broken balls to separate from the ore, because these fragments of steel balls are not desired during the process.
To separate worn steel balls and broken steel balls, there are known methods of separating worn steel balls and fragments of broken balls from the ore using magnets placed on the conveyor belt that transport the coarse fraction of the product from the semi-autogenous mill (called pebbles) that are generally larger than ½ in. (1.27 cm). One of the most used methods includes using electromagnets to capture the steel balls and fragments of broken balls, separating them from the ore that leaves the semi-autogenous mill, to later unload them to be deposited in collection bins and/or tanks located under the conveyor belt.
From the point of view of the efficiency of the grinding process, it is important to keep the mass of steel corresponding to whole balls (9) stable in the grinding chamber (2), so that the uncontrolled output of balls (9) by wear or tear of the same or by the fracture of the grate (13) are events that must be detected in the shortest possible time to take control actions.
That is why the need arises to know in the most exact way possible the amount of grinding elements that come out of the semi-autogenous mill, and the mass of each of these elements, in order to replace the balls necessary to keep constant either their quantity or the sum of the mass of balls in the grinding chamber, in addition to knowing if they come out as spent or broken balls, which will allow action to be taken on the grinding process, and in the longer term on the quality of the balls.
In the state of the art there have been attempts to solve part of this problem. Thus, for example, document WO 2016/000024 discloses a monitoring device in the form of a camera in a protection casing that is fixed to a structure at the outlet of the feed chute and in a particular embodiment to a flange that is extends outwardly over the outlet structure. The flange is also compatible with a light also in a protective housing. The feed chute feeds the ore into a mill. The camera and light housings contain a viewing window that is flushed by water jets and the window is protected by a visor that can be opened when the interior of the mill is to be recorded. The arrangement allows characterizing the load inside the mill to be monitored while the mill is free of vapors and stopped or moving slowly. This solution makes it possible to identify the steel balls only when they are in contact with the surface.
Document WO 2013/067651 discloses a direct visual monitoring system for sensing the interior of a rotary mill, comprising a monitoring unit, a main control unit and an operation and management unit, where the monitoring unit is located inside a feed hopper and is adjusted according to the physical characteristics of said feed hopper and the dimensions of the mill, to allow a direct view of the inside of the mill. The operating method comprises having inside the monitoring unit, a container of sensors to sense its interior temperature; determine the acceleration in the vertical axis, in the lateral horizontal axis and in the frontal horizontal axis, as a function of time; acquire two-dimensional images of the geometric conditions inside the mill; acquire two-dimensional thermal images of the interior of the mill; and executing a distance detection on one or more planes. A problem with this solution is that it does not allow to identify or characterize the worn balls or fragments of the balls that are inside the mill. Another problem with this solution is that it does not allow to determine the damage in the internal grate but only in the mill liners.
Document WO 2007/124528 discloses a method of monitoring a SAG (semi-autogenous) grinding mill or an AG (autogenous) grinding mill. The method of monitoring the mill involves generating an image of the position of the load inside the mill in real time when it is rotating. The method further includes the use of a processor to build an image of the load inside the mill, while the load is falling, in order to determine which phase is in contact with the inner wall of the mill drum in the regions that are detected. This solution allows to identify when the steel balls are in contact with the inner wall, however, it does not allow to identify or characterize the worn balls or fragments of the balls that are inside the mill.
Another solution to be considered is that described in patent application CL 574-2017, in the name of the applicant, which discloses a system for detecting worn balls, broken balls and ore outside the mill on the surface of a screen of a sieve or trommel that retains the larger material coming out of a semi-autogenous mill or a conveyor belt through a system comprising infrared spectrum cameras and visual spectrum cameras, which include their respective transmission media. This solution makes it possible to identify and characterize the worn balls or fragments of the balls that are mixed with the ore expelled from the semi-autogenous mill, however, the disclosed configuration does not allow it to be physically possible to make the detection in any arrangement of the elements used to the exit of the semi-autogenous mill. Another possible problem with this solution is that if the thermal energy acquired by the steel balls and their fragments is not sufficiently greater than that acquired by the ore, then the identification and characterization of the balls, larger ball pieces and mineral could lose precision.
Prior art solutions disclose monitoring devices and methods that allow characterizing the loading conditions both inside and outside the mill, such as on the surface of the external ore classifier or on the conveyor belt that removes the ore particles, and balls of sizes larger than the groove of the external classifier screen. A prior art solution considers the identification and characterization of the worn balls or fragments of the balls leaving the mill. However, none of the disclosed solutions allows to identify the steel balls and their fragments at a stage after the conveyor belt when the steel balls are separated from the rest of the ore. For this, the present invention proposes a receiving element whose surface is a screen, from which emanates the information for the system, which receives the worn balls and broken balls from the free fall when they are discharged from the electromagnet located on the conveyor belt, said receiving element comprising a channel that serves to detect the balls and fragments of balls, being able to characterize them in shape and size using image capture and processing devices.
The present invention refers to a system and process that acts downstream of a separation process between the steel pieces and the fragments of the ore that come out of a semi-autogenous mill for the grinding of minerals and that consists of a system comprising one or a plurality of instruments for capturing images, such as, for example, digital cameras, each sensitive to light of different wavelengths, such as the visual spectrum, which are pointed towards the surface of a receiver element of the steel pieces or chute that receives the steel balls and their pieces from the separation process, such as, for example, a chute through which the steel balls and their fragments move when they are discharged from this process, and with the possibility of orienting each sensor image in a way not parallel to the others. By digitally processing the images obtained with the sensor (s), the dimensions and morphology of the balls and ball fragments that are discharged from the separation process are determined. These image sensors, or digital cameras, capture the image in their operating spectrum, which is recorded in the memory of a data processing means of the system.
With the present invention, it will be possible to identify the fragments of balls that come out from a semi-autogenous mill and that are separated from the ore in a subsequent process, and to characterize by size the fragments of balls that are discharged from this process and that slide or roll on the surface of the receiver element or chute. It will also be possible to quantify the amount of steel that comes out from the inside of the mill, classifying them, in addition, as balls worn by abrasion, that is, those that come out as rounded pieces and, on the other hand, the broken balls, or in general, in any new morphological class that is of interest for the operational evaluation of the mill and for the analysis of the quality of the grinding media.
The present invention will help in the management of the internal ball loading in SAG mills, as well as to manage the steel consumption as grinding media, since it will provide online information to make the decision to reload new balls according to the fragments of balls that are separated from the ore that comes out of the mill. It will also allow to establish corrective actions, since, if excessively worn or broken balls come out, it is possible to evaluate and manage improvements in the quality of the grinding media or in the operating conditions, both factors that can be the cause of accelerated wear or massive breakage of grinding media.
Additionally, the system and process of the present invention will be able to indirectly infer the breakage of one or more grates, by observing that the exit rate of grinding media of size greater than the average of the past few hours increases.
The drawings are included to provide a further understanding of the invention and form part of this description and further illustrate some of the preferred embodiments of this invention.
The present invention refers to a system that works associated with a semi-autogenous mill (1) for ore grinding. The system is installed outside the semi-autogenous mill (1) in an area after the separation process of the steel balls and their fragments from the ore coming out of the semi-autogenous mill (1), which allows observing the surface of a receiving element or chute (19) that receives the discharge from the separation process. From the semi-autogenous mill (1) comes out a material composed of steel balls, fragment of balls and ore after the grinding process, where said material is on a conveyor belt (15) in which acts on the conveyor belt (15) one or more magnets, for example electromagnets (18) suspended on the conveyor belt that capture the balls and fragments of steel that go along with the ore on the conveyor belt (15) from the belt itself. The balls and fragments of steel separated on the conveyor belt (15) by the electromagnets (18) are subsequently discharged in free fall into collection containers and/or bins (25) located below the conveyor belt (15). In the present invention, a receiving element or chute (19) is inserted which receives said balls and fragments of steel captured by the electromagnet(s) on its surfaces before free fall when the electromagnets are discharged, said chute (19) serving as a screen for the detection of balls and fragments of balls, being able to characterize them in shape and size. The chute (19) is necessary in a length that allows the detection of the balls and fragments of balls for an adequate characterization where said length is such that the balls roll on its surface and the fragments of ball can slide and fall without accumulating.
As shown in
The visual spectrum camera (16) has visual spectrum image data transmission means (17), whether wired or wireless. The data transmission means (17) transmits the data to the data processing means (20), being a processor, a PC computer, a PLC programmable logic controller or the like. The data processing means (20) have means for receiving (not shown) the data sent by at least one camera (16).
The surface of the receiving element of the balls and fragments of balls, for example, of a chute (19) constitutes a fundamental element of this invention. This surface is a screen (24) from which the information for the system emanates. At least one visual spectrum camera (16) is installed pointing towards the surface of the screen (24) of said chute (19) to capture and record the image of the balls and fragments of balls that roll or slide on the surface of the screen (24) of the chute (19) and transmit it with the visual spectrum image data transmission means (17), starting the counting of the balls and fragments of balls discharged from the separation process. This count also discriminates between worn (rounded) and broken (irregularly shaped pieces) balls. To do this, the visual spectrum camera (16) is used that captures and records a high resolution image of the balls (9) showing the contour and size of the worn and broken balls.
The data processing means (20) processes the visual spectrum image data and transmits the processed data by control data transmission means (21) as information to a control center (22), which determines the actions to be taken, depending on the information delivered by the data processing means (20). The control center (22) sends corrective instructions (23) to a control means or to the semi-autogenous mill operator (1), to correct the problem reported by the data processing means (20).
As shown in the flow chart in
The load flow (8) conformed by the ore (10) and the balls (9), which passes through the grooves (5) of the internal grates (4) of the semi-autogenous mill (1), reaches the conveyor belt (15), where at least one electromagnet (18) captures the balls and fragments of steel that go on said conveyor belt (15) allowing said balls and fragments of steel to be separated from the ore (10) that is transported as a whole in a separation process. The balls and fragments of steel are discharged from said at least one electromagnet (18) and reach the surface of the screen (24) of the chute (19), where at least one visual spectrum camera (16) takes a set of visual images (26). Said at least one visual spectrum camera (16) sends the visual images (26) captured through visual spectrum transmission means (17) towards the data processing means (20).
The images (26) sent through the transmission means (17) are received in an image conditioning module (27), where said captured images (26) are processed. In the module (27) an image conditioning is carried out, where the geometry of the balls (9, 11) and fragments of balls (12) is subtracted with respect to the background, leaving only the image of the worn balls and the broken balls. In this same module (27) the intensity of the image is adjusted to perform the morphology determination operations of the balls (9, 11) and fragments of balls (12). The information generated in the module (27) is transferred to the module (28) of identification and tracking of the elements on the chute (19), whose images have already been conditioned. The information of the balls identified and tracked on the chute (19) is sent to a module (29) where they are analyzed using morphology and sizing determination techniques. The information from this analysis is sent to a discrimination analysis module (30) where the balls (9, 11) and fragments of balls (12) are differentiated.
The process continues through the characterization module (31) where the worn balls or fragments of balls are counted, characterizing the sizes and shapes of the balls (9, 11) and fragments of balls (12), that is, of the metal that is on the chute (19). From this analysis, the volume of the worn balls and fragments of broken balls is determined, and once the density of the steel is known, the mass of steel that leaves the semi-autogenous mill (1) is determined, and that can be delivered punctually or as mass flow by setting a period of time, such as per hour. Thus, it is possible to know online and in real time the approximate amount of metal that comes out from the semi-autogenous mill (1).
In the size analysis module (32), balls and fragments of balls are analyzed according to the size of the grate groove. This dimensional analysis corresponds to comparing the size of the worn balls and the fragments of broken ball with the size of the grate groove and if the former are larger, it is deduced that a fracture of the internal grate has occurred. The size of the hole produced can be determined by measuring the largest size of worn balls and fragments of broken ball on the chute (19).
For this purpose, in the analysis module (32), an analysis is performed to obtain the groove sizes of the grates from the maximum ball size. The analysis is performed using grate groove size data, reload ball size (new ball added to mill), and process data, conjugated with mill data such as speed, power, weight (obtained from load cells and/or oil pressure in breaks) and noise, previously loaded in a mill data module (34). The reload ball size can be entered by the mill operator and process data can be obtained directly in connection with the semi-autogenous mill operational control system (1).
The module (33) delivers the results of the previously described process, providing information on the output rate of balls and fragments of balls. In the event that the size of the balls is greater than the size of the internal grate groove used, an alarm will be issued for this anomaly. In the same way, if the number of balls in the chute (19) is greater than a preset value or range of values, the system will issue an alarm for this anomaly, so that in the control center (22) a means of control or mill operator take the necessary corrective action for the grinding process. The same happens when there is an excess of broken balls on the chute (19), activating an alarm.
A sharp decrease in the amount of balls and ball fragments on the chute (19) may indicate a malfunction of said at least one electromagnet (18) acting on the conveyor belt (15) which may result in clogging of crushers used to reduce the size of the pebbles preventing them from being returned to the semi-autogenous mill or sent to the ball mills, which corresponds to the subsequent size reduction stage. A sharp increase in the number of balls and ball fragments on the chute (19) can indicate poor ball quality that may result in excessive wear or breakage or indicate an operating condition that results in damage to the ball load.
Number | Date | Country | Kind |
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1231-2019 | May 2019 | CL | national |
Filing Document | Filing Date | Country | Kind |
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PCT/CL2020/050048 | 5/2/2020 | WO |