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DisciplinaProcessamento de Minerais I198 materiais2.051 seguidores
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impeded by the interaction of the particle stream with the 
This sampling analysis can be performed on essentially any cross belt sampler and potentially on other 
types of samplers as well. It is able to detect small biases and can be used to test alternative sampler designs 
and modes / speeds of operation. DEM simulation is able to show that many sample cutters that satisfy 
existing standards in fact produce significant bias whilst others that do not satisfy the standards have either 
small to undetectable bias. In particular, sampler cutters that are made 4 times the topsize (instead of the 
standard 3 times) and which are moved at twice the speed can have samples that are around 1/3 smaller 
(potentially allowing smaller and therefore cheaper sampling systems to be used) while producing biases that 
are less than the detectable 1% level used here. 
Particle separation using vibrating screens is a common method for dividing mill or crusher output into a 
product stream and a recycle stream. The efficiency of a screen is determined by the size and shape of the 
screen openings, the size and shapes of the particles to be separated and the amplitude and frequency of the 
screen motion. DEM allows screen efficiency to be easily evaluated. Figure 5 shows an 800 mm square 
section of a vibrating screen operating with near vertical motion at around 5 Hz. The bed consists of around 
8000 particles with diameters between 10 and 60 mm. The screen acceleration is enough for the bed to 
separate from the screen deck during the upper part of the screen motion and then to crash back down. Each 
landing of the bed leads to a spurt of finer particles through the screen. The screen motion used here leads to 
a pulsing flow through the deck. The flow of fines is ultimately limited by the percolation/transport rates of 
the fines from the upper to the lower regions of the bed. Poor design of the grate openings for a given 
material can also lead to inefficiencies in the passage of finer particles through the screen. DEM also allows 
wear patterns and relative rates of wear to be assessed. In particular, the evolution of the screen geometry 
according to the calculated wear rates allows predictions of the change in screen open area with the screen 
wear to be made. This is a key to understanding the changes in performance of the screen with time (wear). 
The ability to make such predictions allows designers and end-users to optimize their screens for the 
expected feed size distributions. 
Figure 5. Panel of a vibrating screen. 
Hopper discharge 
Hoppers are an important part of all materials handling operations. DEM simulation can help with 
understanding the flow pattern within complex hopper designs, including segregation effects. Understanding 
these can lead to more uniform mass flow and more uniform composition between the ports and throughout 
the discharge process. The stress distributions on the hopper walls, particularly when different combinations 
of ports are opened and closed (inducing potentially huge and very rapid stress changes) can also be 
evaluated in order to assist with structural design of the hoppers. Figure 6 shows an example of a 4 m high 
and 1.5 m diameter hopper (with a hopper half angle of 30o) and with four symmetric discharge ports. There 
are around 70,000 particles with diameters in the range 25-60 mm. 
Figure 6. Discharge from a four-port hopper. 
Separation in a large conveyor splitting bin 
Large splitting bins are used to fulfil a range of functions. They can: 
! act as an interchange between different conveyor belts, 
! provide a buffer for the downstream processing plants, 
! enable an incoming stream to be divided into a number of outgoing streams. 
It is useful to understand the effect of the bin/conveyor geometry on the material characteristics on 
outgoing conveyors. 
Figure 7 shows a complex splitter bin system modelled using DEM. The particles are coloured by size 
with red/large and blue/small. The incoming conveyor is oriented at 45° to the bin and carries rock at 10 m/s 
with a flow rate of 5000 tph into a bin with a 6 m square top and a 6 m height. This stream separates from the 
head pulley and travels on a parabolic trajectory over the bin where it is deflected downward by a large 
central impact plate. 
The structure of the flow around the impact plate is clear. The upper part of the stream is deflected 
upwards and to the sides forming a dense parabolic concentration of particles above the impact point that in 
turn produces a distinctly separate stream of particles on either side. The left one falls towards the back left 
corner of the bin and the other towards the front right corner. The lower part of the incoming stream is 
deflected immediately downwards into the middle of the bin. 
Figure 7. Splitter bin showing incoming and outgoing conveyors, apron feeders and an impact plate. 
The lower half of the bin is split into two parts by a splitter plate and each side converges to form a long 
slot hopper. Each hopper then discharges onto an apron feeder that moves with speed of 1.5 m/s and which 
draws out material. Each discharge stream then falls around 0.75 m onto a smaller 900 mm conveyor belt. 
The two exit belts are parallel, with gentle but different downhill grades and have speeds of 6 and 7 m/s 
The incoming particle stream is expected to be substantially segregated during its transport along the 
conveyor, with the fines concentrated in the lower region adjacent to the belt. The DEM particles have been 
generated just above the belt with such a vertical size segregation pattern imposed. This is clearly indicated 
by the layer of blue fines visible on the underneath of the stream after it has departed the head pulley in 
Figure 7b. This vertical segregation of the particles is very important since it interacts strongly with the sub-
division of the incoming stream generated by the impact plate into three distinct streams falling into different 
parts of the bin. Since the central downward stream from the impact plate consists predominantly of material 
from the bottom of the incoming stream it then consists of mainly finer particles. Conversely, the two side 
streams (directed into opposite corners of the bin) consist of mostly of coarser particles from the upper parts 
of the incoming stream. The combination of the impact plate and the vertical segregation of the incoming 
stream appears to be an efficient separation mechanism generating multiple streams with different 
compositions into the bin. 
The apron feeders draw their material preferentially from the back of the hoppers with this material 
deposited on the bottom of the belt with smaller amounts of material drawn from the front of the bin 
overlayed on top of this. For the left hopper (as seen in Figure 7c), the coarse material is deposited towards 
the back so this coarse material is removed first and ends up at the bottom of the left outgoing conveyor with 
finer material deposited on top. For the right hopper, the coarse material is deposited towards the front so 
that finer material at the back is removed first and ends up at the bottom of the right outgoing conveyor with 
coarser material deposited on top. This can create an apparent visible surface composition difference 
between the outgoing belt, purely because of the layering of the different sizes produced by the action of the 
apron feeders on oppositely segregated material along the length of the slot hoppers. This is not an overall 
composition difference between the belts, but is a surface difference due to the different layering on the belts. 
This effect is generated by the difference in angle between the incoming and outgoing conveyors. 
A real composition difference can be created though by the choice of location of the impact plate. If the 
impact plate is symmetrically located,