loading and hauling rates. The
investigation, which lasted for 1.5 yr,
involved controlled changes to
blasting parameters. Each blast was
evaluated by measuring the
fragmentation, as well as the single
cycle load times. The theory stated that
if single cycle load times could be kept
constant, while reducing the powder
factor, significant cost savings would
be achieved.
This study collected data from over
70 blasts across a variety of geological
conditions. After measuring a baseline,
powder factors were slowly reduced
by lowering the explosive column
collar, while increasing the blast hole
burden and spacing. The results found
that, although the powder factor was
decreased, the rock fragmentation only
increased by a minimal amount. The
minor variation in fragmentation is a
strong indication that a significant
amount of the energy from the blasts
was unused. Even with a slight
increase to average rock size, the single
cycle loading time remained nearly
constant for the large P&H 4100
shovels and decreased for the smaller
shovels.
Overall, this project lowered the
powder factor by 11%, resulting in a
5.7 million kg reduction in explosives.
While this project achieved significant
cost savings, the author feels that
further powder factor reduction can
still be achieved. As fragmentation
only increased slightly and resulted in
constant single-cycle load times, there
is still room to further optimise
blasting. One key factor in this study is
that the optimisation process was
carried out for the removal of
overburden and, as such, the effect on
crusher efficiency was not a
consideration.
Shovel-based monitoring
A critical part of this study was
measuring blast results consistently. To
achieve this, the operation used
image-based fragmentation technology
from Motion Metrics. This technology
is a component of the company’s field
tested ShovelMetrics
TM
platform,
which has been installed on over
250 shovels at 50 mine sites globally.
The product is available on all mining
shovels, including Joy Global and
Caterpillar rope shovels, as well as
Komatsu, Liebherr, Hitachi and
Caterpillar hydraulic face shovels.
The system consists of a rugged
industrial camera mounted to the
point sheave of a mining shovel,
providing a unique view of the shovel
bucket. Intelligent algorithms running
on an embedded CPU in the operator’s
cab process the camera feed to detect
when the bucket is full. Images of full
buckets are then captured and
processed to determine the material
size distribution. An essential part of
any image-based fragmentation
system is its ability to scale the rocks in
the image. Traditional camera-based
approaches use an object of a known
size, such as a basketball, to indicate to
the software the relative scale of the
rocks. The advantage of the
ShovelMetrics™ system is that it can
use the known size of the shovel
bucket as a scaling factor.
The captured fragmentation images
are sent through the mine network to a
server running the MetricsManager™
system provided by Motion Metrics.
This data integration system
consolidates information from any
number of ShovelMetrics™
installations and the data is made
available to mine engineers and
management through a powerful
web-based application.
This approach provides
fragmentation data captured at a
regular interval, usually one image
every 5 min. during normal daytime
operation. With little to no requirement
for manual input during the data
gathering, this system can provide rich
information as the shovel moves
through the blast. When correlated
with GPS information, the material
size distributions through a blast can
be correlated with the blast simulation,
validating its accuracy.
Portable fragmentation
analysis
Although this shovel-based
fragmentation solution provides rich
information, there are some situations
where it may not be the most
convenient approach. For example, an
operation may want to evaluate rock
size in a stockpile being loaded by
small excavators where the
PortaMetrics
™
rugged fragmentation analysis tablet.
Example image from a PortaMetrics™ device with 3D point cloud.
92
|
World Coal
|
August 2015
