Patent Application
20210255078
Orebodies are intrinsically variable in composition and physical properties by virtue of their heterogeneous nature. Few orebodies consist of one single lithology or any other geological classification (ore types). This variability is usually evident from orebody characterization programs by showing the spatial distribution of these properties. Orebody complexity is well recognized; However, the design of most processing plants is still performed using fixed or discrete values of the orebody properties as input parameters. Designing a process plant has many conventions, and one of these is that selecting the 80th percentile value of a key measurement; where the 80th percentile is determined based on the availability and representation of the test sample in the LOM.
Mining companies tend to invest more in understanding resources than in understanding metallurgy, of which comminution testing is a key component. If the test work program is not adequately executed and interpreted, there are risks of establishing wrong design criteria and compromising the final design. One consequence of this is that several projects have underperformed (mainly throughput) and have resorted to spending additional capital to mitigate the problem (e.g. secondary crushing, high-intensity blasting and/or barren pebble rejection). Another consequence is that some financiers are expressing less confidence in the engineer's ability to predict the performance of grinding circuits, and this has impacted on the ability of companies to obtain funding.
Comminution tests are a critical element in the proper design of ore beneficiation plants. Traditionally, test work has been conducted with a few representative reference samples. For geometallurgical modelling, the entire ore body is explored based on drill-core samples to understand the variability within the resource and to establish spatial geometallurgical domains that show the differential response to mineral processing. Setting up a geometallurgical program for an ore deposit requires extensive test work. Methods for testing the comminution behaviour must therefore be more efficient in terms of time and cost, but also with respect to sample requirements. The integration of the test method into the geometallurgical modelling framework is also important.
Geometallurgical mapping/modelling is needed for finding out the properties of ore bodies or other rock bodies or particles thereof. For this purpose, rock particles are subjected to breakage characterization test.
Breakage characterization test can give useful information regarding features of the rock bodies for better designing the process equipment such as comminution devices of the mining industry processing plant. Deeper knowledge regarding rock breakage properties would be highly advantageous because more than 50% of the energy consumed in mining is consumed in comminution, compared to only 10% in excavation.
Different techniques have been developed to assess the breakage characteristics of rocks or orebodies and to generate the parameters for modelling. A drop-weight test is an example of a conventional method for assessing the breakage characteristics of a single piece of rock or an orebody. A conventional drop-weight test (DWT) ore breakage device requires laborious manual procedures and fixed energy levels. In such a drop-weight test, either an orebody under examination or a weight arranged to drop on the orebody is raised to a determined height and then allowed to drop, thus causing breakage of the orebody (if the height is sufficient to cause the breakage). The breakage energy level is determined by the height. Use of such fixed energy levels is also inaccurate.
An object of the present invention is to provide a test arrangement to solve or to alleviate the above disadvantages. The purpose of the invention is to enable fast and low-cost single particle breakage testing in a wide range of rock sizes. The characterization intends to measure the compressive strength and the actual total energy absorbed by each particle. The absorbed energy is then related to the progeny produced from the parent particle.
The objects of the invention are achieved by a test arrangement and method which are characterized by what is stated in the independent claim. The preferred embodiments of the invention are disclosed in the dependent claims.
An advantage of the disclosed test arrangement and method is that it is able to accurately produce extensive rock compressive strength and single particle breakage characterization data, while still being able to remain fast and suitable for low-cost online testing.
In the following the invention will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which:
Referring to
The adjustment mechanism 6 or 8 can also been seen as a hinge or a part of the hinge, intended for protection purposes. Relating to that, if the force caused by the crushed particle exceeds the friction produced by pressing the support beam 2 against the support frame 1, then the support beam 2 may rotate around the part 8 (adjustment mechanism/hinge) to allow the second wheel 3′ to escape and relieve the force, as a protection mechanism against excessive loading.
During the operation of the arrangement, the gap adjustment mechanism is locked and the upper and lower ends of the support beam 2 do not move. End of the support beam 2 is pressed/clamped against the support frame 1 so that the friction between the parts prevents the support beam 2 (carrying the second wheel 3′) from moving.
Individual rock particles RP enter the gap G between the parallel counter rotating wheels 3, 3′ one-at-a-time. The arrangement comprises force measurement arrangement 7, 7′ for measuring the breakage force of each rock particle RP. Force is measured from the forceful bending (caused by rock particle RP between the wheels 3, 3′) of the support beam 2, support beam 2 is locked to its place at both ends of the support beam 2.
One or both ends of the beam 2 could be hinged against the frame 1 after the gap adjustment is fixed in place. Both the rotation and the horizontal movement of the end of the support beam 2 in relation to the support frame changes the bending behaviour of the beam 2, this which can be taken into account by software calibration.
In an embodiment, the force measurement arrangement 7, 7′comprises one or more strain gauges, sensing the bending deformation of the vertical support beam 2. The support beam 2 (carrying the second wheel 3′) and the related strain gauges together form a load cell. In an embodiment and as an example only, a suitable strain gauge can be Kyowa KFG-5-120-C1-11L3M3R. Other means of measuring the bending of the support beam 2 are possible, too. The force measurement arrangement 7, 7′is to measure information relating to the rock particle compressive strength, said force measurement arrangement 7, 7′ being coupled via lines 17, 17′ to a processor PR, said processor PR being arranged to calculate the breakage force applied to each rock particle RP over time.
Crushing wheels 3, 3′ i.e. comminution wheels i.e. rotatable crushing elements can be narrow wheels, having narrow axial width of for example 25-50 mm, and diameter of for example 20-80 cm. One possible material for wheels 3, 3′ is metal, such as hardened steel. An example of the weight of each wheel 3, 3′ is 10-100 kg, such as 40-60 kg, this depends on the required maximum available energy.
Additionally, test arrangement TA comprises a drive arrangement M1, M2 for rotating the crushing wheels. Drive arrangement can be integrated gearless electric motors M1, M2. As an example only, suitable power rating for electric motors is 50-100 W.
Crushing wheels 3, 3′ are facing each other and they define therebetween an input gap G for the rock particles RP, said wheels 3, 3′ being arranged to crush/comminute rock particles to smaller daughter particles DP (progeny). Test arrangement is arranged to receive only one rock particle at a time to be inputted to the input gap between the wheels 3, 3′. This may be arranged by controlling a feed mechanism such that only one rock particle enters the input gap at a time. The applied force for breakage and the energy absorbed by each particle is measured by the methods presented below.
Width of the gap G is adjusted to be less than the size (minimum diameter) of the inputted rock particle RP. In an example, width of the gap G is percentage (25 to 75%) of the average particle size (diameter). Particle size can range from 8 mm to 50 mm.
The test arrangement TA further comprises an energy measurement arrangement 5, 5′ for determining of the energy absorbed by each rock particles during breakage, said energy measurement arrangement 5, 5′ being coupled to said processor PR via lines 15, 15′, said processor PR being arranged to calculate energy absorbed by each rock particle RP during the breakage. The energy measurement arrangement may be arranged to measure the energy applied directly to the rock particle during the breakage, thus directly indicating the energy required to break the rock particle. Some embodiments of the arrangement are described below.
Word “processor” is to be understood widely, it can be microprocessor (CPU), computer or some other suitable element, and it can be an integral unit, or it can have several related but possibly detached elements such as discrete components. The processor may be coupled to a memory that may be non-transitory such as a memory chip or a memory circuit. The memory may store at least one computer program product comprising a computer program code of instructions readable by the processor. The computer program code may then configure the processor to execute a computer process for determining the breakage properties of rock particles on the basis of the measurements described herein.
Processor PR includes, or has access to, data which contains the relationship of the measured feature (strain, speed) and the calculation output (compressive strength, breakage energy, and/or a degree of breakage of the rock particle).
Regarding the corresponding method, it is a method for testing breakage properties of rock particles. The method comprises: weighing the rock particles mass, inputting rock particles (one at a time) between two counter-rotating crushing wheels 3, 3′ for crushing rock particles to smaller daughter particles, accomplishing (performing, carrying out) a force measurement for measuring information relating to the breakage force applied to each rock particle RP, accomplishing (performing, carrying out) an energy measurement for measuring information relating to energy absorbed by each rock particle (RP), calculating breakage force applied to each rock particle (RP), and calculating energy absorbed by each rock particle PR. The weight of the rock particles is measured with a suitable weighing device, and the weight value is transferred/inputted to the processor PR. In a case where there is a feeding mechanism for feeding the rock particles to the input gap, a weighing device may be arranged on the feeding mechanism such that the rock particle is weighed before entering the input gap. The measured weight is then electronically input from the weighing device to the processor.
In an embodiment, the energy measurement arrangement 5, 5′ is an arrangement for measuring the energy loss of the rotatable wheels 3, 3′ during the breakage event of each rock particle RP. The crushing of rock particle RP between the wheels 3, 3′ slows down the speed (and rotational moment) of the wheels 3, 3′, and the amount of loss of speed (and loss of rotational moment) refers to the amount of energy loss, which in turn refers to the amount of energy given from counter-rotating wheels to the rock particle RP. Regarding the corresponding method, in an embodiment, the method is such that energy loss of the rotatable wheels 3, 3′ during the breakage event of each rock particle is measured.
In a further embodiment, the energy measurement arrangement 5, 5 comprises a sensor structure, said sensor structure being arranged to measure from the wheels 3, 3′ one or more of the following: speed, angular velocity, rotational position. Sensor structure may comprise optical rotary encoder, having a hoop with a gear-like pattern of teeth, which are measured by an infrared optical gate of the type TCST-1103, mentioned as an example only. The sensor structure may then compute the reduction in the speed and/or angular velocity during the breakage, thus indicating the amount of energy transferred directly from the wheels 3, 3′ to the rock particle during the breakage.
In the embodiment shown in
Regarding breakage events, in a typical breakage event, there is a sharp peak of force when the rock particle enters the gap and touches both wheels, followed by a short sustained plateau of force as the pieces of the rock are reduced further in size, and then a short taper off as the remaining pieces exit the gap. The highest forces measured are typically at the beginning of the breakage event with the initial breakage across the whole cross-section area of the particle. This follows approximately the relationship of Stress=Force/Area, where the stress required to break the particle depends on the material (ideally), so the amount of force required to break a particle or a fragment becomes less when the cross-section area of the particle or fragment of a particle becomes smaller. The smaller the gap is in relation to the original particle size, the more the particle has to break down to fit through it. This means more force must be sustained for a longer time, and more energy is spent.
In order to get more reliable measurement data from the force measurement sensors 7, 7′ and/or from energy measurement sensors 5, 5′, in an embodiment to the test arrangement TA comprises of a controller CNT for controlling the integrated gearless drive arrangement M1, M2, for disabling and/or limiting the drive arrangement M1, M2 regarding rotating the crushing rolls, in order to create interference-free conditions for the measurement operations during breakage events. In an embodiment. the power supply to the motors M1, M2 is stopped to allow free rotation. The motor will keep revolving with the roll (wheel). A non-integrated drive configuration may also be mechanically separated by a mechanism, such as a clutch or a ratchet to remove the influence of the motor from the wheel. In any case, the crushing wheels 3, 3′ will keep on rotating since the wheels 3, 3′ still have rotational kinetic energy. The energy measurement arrangement may then measure the reduction in the rotational kinetic energy of the wheels by measuring the reduction in the angular velocity or speed of the wheels. The reduction is a measure of the energy transferred from the wheels to the rock particle during the breakage.
Regarding the corresponding method, in an embodiment, the method is such that drive arrangement M1, M2 of the wheels is disabled and/or limited regarding rotating the crushing wheels, in order to create interference-free conditions for the measurement operations during breakage events.
Referring to above, in an embodiment, the size analysis system SAS is coupled to said processor PR, and said processor PR is arranged to determine the correlation between the degree of breakage and measured energy absorbed by the rock particles RP. Regarding the corresponding method, in an embodiment the method is such that the method comprises determining correlation between degree of breakage and measured energy the rock particles RP.
Referring to
During the breakage, the energy and force measurement arrangements measure the breakage energy and force, e.g. in the above-described manner. The measured breakage energy absorbed per rock particle is stored in the memory accessible to the processor. Upon measuring the mass and the breakage energy, the processor computes the specific energy per rock particle (block 308). In block 312, the particle size distribution (PSD) or degree of breakage (t10) are measured for the broken rock particles. The degree of breakage may be measured automatically by the SAS, or it may be measured manually, e.g. by using a sieve. The measured degree of breakage may comprise the full PSD and/or a tx parameter such as the t10 parameter. The PSD and/or degree of breakage is measured for a set (i.e. sample) of rock particles and stored in the memory. In summary, the memory may store, for each rock particle, a record comprising the mass, breakage energy and force, as well as the degree of breakage of the population of rock particle. Upon computing the specific energy and the degree of breakage for the rock particles, the correlation between the two parameters may be built in block 314 by the processor. The correlation may include performing a regression analysis or fitting for the sample set where each sample comprises a pair of a degree of breakage and a corresponding specific energy (the samples of
In an embodiment, the procedure of
Mean(Ecs)/%−X
where %−X is the cumulative percentage of particles passing a chosen sieve of aperture size X (measured after the breakage, naturally). The aperture of the sieve (X) may be defined in terms of microns, e.g. 150 microns, 270 microns, or any other size. For example, if the mean specific energy measured from the breakage of multiple rock particles (e.g. 20 particles or 50 particles) is 1 kWh/t and the cum%pass is 10% for a 150 micron sieve (10% of broken rock particles pass the sieve), the size-specific energy is 10 kWh/(t of −150 microns). The size-specific energy may then be mapped to the grindability parameter BBMWi value by using a correlation table stored in the memory. The correlation table may be built via empirical measurements and, in the context of the present embodiment, the mapping table is readily provided.
In an embodiment, the test arrangement TA is arranged to determine the compressive strength of the tested material (rock particles RP). For measuring the compressive strength, the force measurement arrangement may be used. In block 306 of
It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/FI2020/050100 | Feb 2020 | US |
| Child | 17140686 | US |
