tsv mining: critical density in mining and changes to sustainable low cost production
DESCRIPTION
TSV Mining's presentation on Critical Density in opencut mining operations and its impact on sustainable low cost production. From the mining boom, the increase in production for some operations may have crossed a point where sustainable low cost production may no longer be possible without redesign of how the operation functions.TRANSCRIPT
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TSV Mining Pty Ltd [email protected]
M: +61 438 886 473 www.tsvmining.com.au
Presented by:
Christopher Braund
Director
Background
From Phillip Ball’s book Critical Mass, and his discussion of the
traffic flow modeling work by Nagel Schreckenburg (NaSch Model).
Moving from stable traffic flow, to metastable, to an unstable traffic
jam.
Understanding the effects of the Critical Density Point in traffic flow
modelling and applying it to the open cut mining system.
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Critical Density
Critical Density is where a system passes a density point where
it tends into a metastable and potentially unstable state.
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Metastable State
Metastable literally means to be “next to stable”.
It is a state which is stable but only needs the slightest provocation
in order for it to fall into an unstable state.
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The NaSch Model
Traffic flow has been modelled since the 1960’s. Modelling work
by Nagel and Schreckenburg (NaSch Model) in the mid 1990’s
can give us a better understanding on the effects of traffic
density to flow:
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Stable traffic flow
Flow
Rate
Density (cars / km)Critical
Density
Here traffic flows well. The lower density
of cars means that the traffic is capable
of handling unplanned events such as a
motorist suddenly breaking. However it
will reach a point where the traffic is at a
critical density.
Stable
state
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Metastable traffic flow
Flow
Rate
Density (cars / km)Critical
Density
Metastable
statePast this critical density point, the density
and flow rate of the traffic can still
continue to increase, however it is in a
metastable state, and hence it will not be
able to tolerate any unplanned, disruptive
events.Stable
state
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Traffic jam
Flow
Rate
Density (cars / km)Critical
Density
Metastable
state
Event
occurs
Traffic Jam
In this state a simple reaction by a driver, say
suddenly breaking to avoid an incident, will
cause a chain reaction. The traffic flow rate will
suddenly descend and density will increase
creating a traffic jam.
Stable
state
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Getting out of the traffic jam
Flow
Rate
Density (cars / km)Critical
Density
Metastable
state
Event
occurs
Traffic Jam
In order for the traffic to again increase
its flow rate, it must reduce its density.
The amount of cars coming into the traffic
jam must be reduced in order to bring the
traffic back into its free flowing state. It
must be reduced back down below its
critical density.
Stable
state
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The traffic jam is a one way loop
Flow
Rate
Density (cars / km)Critical
Density
Metastable
state
Event
occurs
Traffic
Jam
The traffic jam cannot be reversed. It
cannot revert back to being in a
metastable state without first going
back to a stable state below the
critical density point.ONE WAY
LOOPStable
state
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Mining in a stable stateT
hro
ughput
Process DensityCritical
Density
In the stable state, the throughput from the
operation is consistent and cost are controlled.
It can handle most events that occur within the
operation. Inventory is healthy and sustained.
Processes have minimal impact on one
another.Stable
state
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Mining in a metastable to
unstable state
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NOTE: the line is curved past the Critical Density Point as the change occurs gradually with the change in inventories. The
traffic inventory is consumed in seconds, and hence has a sharp drop.
Costs and throughput in the
unstable state
The metastable state is where issues can occur in the mining
industry.
Operations will run at their highest throughput with predictable costs
for a time, however it eventually becomes unsustainable.
As the operation trends to the unstable state, throughput drops and
costs rise.
Adding processes into the system makes things worse, with more
interactions, more complexity and higher costs (like adding more
cars into the traffic jam).
Eventually the operation bites the bullet and see that to go forward
they must take a hit on production in order to re-build depleted
inventories and stabilise.
This is done and the loop starts again as the operation tries to go
back into the metastable state.
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Reducing throughput and density
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Is the drop in production required to
bring the system back to a stable
state? As always, this is site dependent, however in most cases it may
not be required. Why?
Unlike a set traffic system, the Critical Density Point and the
steepness of the production line is not fixed in a mining system.
Steepening the production lineT
hro
ughput
Process DensityCritical
Density
Some ways in which to steepen the
production line:
• Increase the operational strike or
area of the operation
• Increase the on bench capacity of
processes by combining like
processes, moving to larger fleets, or
by increasing performance of fleets
Throughput is increased
while maintaining the same
density
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Move the Critical Density Point to
the right
Thro
ughput
Process DensityCritical
Density
The critical density has
been moved to the right
allowing for an increase in
density and throughput.
Moving the Critical Density Point to the
right can be a very cost effective method
of increasing the throughput. The
methods of doing this are around
changing the environment and policies of
the operation:
• Enabling parallel processing
• Remove constraints that restrict
material flow
• Redesign to improve material flow
• Improve task balance in the operation
• Improved mining methodology
• Improved equipment mobility and
flexibility
• And many more…..
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Critical
Density
Moving the Critical Density Point when
already in a metastable or unstable state
Some of the options for moving the Critical Density point to the
right will temporarily increase the density of the processes.
If the area is already in an unstable state, these options have
the potential to temporarily restrict throughput for a period of
time, ie things will get worse before they can improve.
When attempting to shift the Critical Density Point when already
in an unstable state, options that do not temporarily increase
density should be implemented first.
Watching the Critical Density Point
Care must be taken to ensure that the movement of the Critical
Density Point does not shift to the left unnoticed.
There are factors which shift the point to the left which cannot be
avoided (eg increased depth and stripping as a mine progresses).
There can also be changes to an operation that at first do not
appear to have an effect, however they may have shifted the
Critical Density Point left far enough to move the operation into a
unstable state.
Even though a shift may have occurred, it may take years before
the consequences are felt.
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The Critical Density Point influence
on the operation
Depending on what side of the Critical Density Point an operation, or
parts of the operation sits on will have an impact on how it will react
to change.
Changes to the operation can include:
Changing processes
Adding processes
Reducing inventories
Increasing production
Changing operational policies
Implementing projects
A stable operation will react differently to change then one that is
metastable or unstable.
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The Critical Density Point can be
measured
Although this presentation is abstract, TSV Mining has actually
measured the Critical Density Point of operations.
By using customised models including all processes that occur in
the operation, as well as replication of the movement of material, it
can be shown when areas will not produce more, regardless of how
much more equipment is allocated to the area. Due to additional
interactions, the production will deteriorate when adding more
equipment to the area.
Options to change the steepness of the production line, and to the
location of the Critical Density Point can also be measured and
valued
Summary
An operation that moves from a stable to an unstable state, will
pass through a metastable state where production is higher and
costs are managed, however it is not sustainable.
There is a significant delay before the consequences of instability
effect the operation (it can take years for some operations).
Once unstable, operations have three options to get back to a
stable state:
1. Drop production and rebuild inventories and stabilise
2. Steepen the production line
3. Shift the Critical Density Point to the right
Changes to the operation (in particular operational policies) shift
the Critical Density Point significantly.
Operations will react differently to change, depending on where
they sit with respect to the Critical Density Point.
Always customised – no two sites are
the same
Thank you
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