1. T
HE STOCKYARD PLAYS A VITAL ROLE
in the mine-to-ship supply chain.
Operations at a stockyard are unique,
complex, and dynamic – efficiencies or the
lack thereof at this crucial stage can make an
enormousdifferencetoacompany’sbottomline.
Central to this is the challenge of overcoming
what is sometimes called the ‘short term
scheduling problem.’
The overarching goal of stockyard oper-
ations is simple: load ships with the tonnage
requested and at the right quality specification,
anddothisasquicklyaspossible.Butlikemany
things in life this is easier said than done. In
fact, the reality of ensuring efficient usage of
resourcesandspacewithinastockyardtoachieve
this goal can be a logistical nightmare.
To start with, demand and quality
specifications for each outbound product are
unique, and each ship needs to be loaded with
the right products at the right quality. Adding
to the complexity of this is the fact that the
contents of trains coming from a mine differ
in quality, and the content is only known
accurately post-departure and not before. One
option here is to identify trains that will result
in the right quality when stacked together, and
arrangethestackingprocesslikeso.Anotheristo
blend material from different stockpiles during
reclaiming,butthismeansmorereclaimerswith
a lower average throughput. Either way, the
scheduler will want to stack inbound material
in such a way that the difference between the
average quality and target quality is minimised
at any given time.
This challenge is made yet more complex
by the fact that train and ship schedules are
a given, and relatively inflexible. Trains need
to be able to quickly dump their cargo so
that rolling stock of empty trains is available
at mines for the next load. Ships have a very
limited time window during which they can
be loaded.
Of course, the stockyard itself has a
finite capacity, with limited resources. These
input-output gymnastics must be achieved via
a limited number of car-dumpers, shiploaders,
reclaimers, stackers, ship berths, stockpiles
and so on, all within a tight timeframe to
ensure high throughput. Then there are the
REAL-TIME
STOCKYARD
OPTIMISATION:
the short-term scheduling problem,
and how to fix it
The ‘short term scheduling problem’ — a fiendish puzzle that has sapped the efficiency of the
mine-to-ship supply chain for decades, costing millions. Ben Koch, Director of Engineering and
Vinay Mehendiratta, PhD, Director of Research and Analytics at Eka explore the challenge,
and how recent technological breakthroughs have finally provided a solution.
Operations at a stockyard
are unique, complex, and
dynamic – efficiencies
or the lack thereof at this
crucial stage can make an
enormous difference to a
company’s bottom line.

2. wider constraints: for instance, operating
constraints such as the time taken to move
material from stockpile A to stockpile B, or
safe operating limits of equipment all need to
be factored in.
It’s a jigsaw puzzle of the highest order:
but unlike a jigsaw it is dynamic – the state
of affairs on the ground and the objectives
are constantly moving. Ships can be delayed.
Shiploading windows are determined based on
tonnage, ship schedule, and tide forecast and
it is imperative shiploading windows are not
missed.Trainsmayarrivelate,orwiththewrong
quality.Equipmentbreaksdown.Thepotential
variables are too long to list. All these variables
mean that decisions made within any planning
andschedulingframeworkwillfrequentlyneed
toberevisitedatshort-notice,andarrangements
recalibratedtoaccommodatethedisturbancein
such a way that the impact on throughput and
cost is minimised. This is made more difficult
still by the fact that decisions are inter-related
in complex ways. This, in short, is the ‘short
term scheduling problem.’
How to tackle such a fiendish problem?
There is a trilemma here: the ideal aim is to
maximise accuracy and throughput while
minimising cost. But at first glance focusing
on any two factors will hurt the third. You can
minimise cost and maximise throughput, but
you’ll sacrifice accuracy. You can maximise
accuracy while minimising cost, but at the
expense of throughput. And you can simulta-
neously maximise accuracy and throughput by
throwing traditional resources at the problem
(more manpower, more machinery) – but then
your costs balloon. All three are unacceptable
from a business point of view.
The magic sauce for unravelling the
trilemma and squaring the circle lies – as
with many of these sorts of problems – in
technology. This becomes plain when one
The magic sauce for
unravelling the trilemma
and squaring the circle
lies — as with many of
these sorts of problems —
in technology.
Inbound
Train
Arrival
Car
Dumper
Assignment
Stockpile
Location
Assignment
Stacking
Method
Dwell
Stockpile
Reclaiming
Assignment
Reclaiming
Method
Shiploader
Assignment
Berth
Assignment

3. considers the deeply interrelated nature of
decisions in short-term scheduling alongside
the number of decision combinations involved
in planning and optimising tasks. To illustrate,
take a 24 hour period and imagine there are 2
ships, 25 trains a day, 24 stockpiles, 3 stackers,
3 reclaimers, 2 shiploaders, 2 car-dumpers,
and 5 products. That makes for a gargantuan
1,036,800 potential stacking and reclaiming
decisions.Scale-wise,that’sajobforacomputer,
not a human.
More specifically, it’s a job for modern,
sophisticated real-time stockyard optimisation
systems. These use successive linear program-
mingbasedonthe‘MixedIntegerProgramming’
approach. In English, this means that – taking
all of the discussed factors as inputs along with
stockyard layout – they are able to optimise
schedules, resources and stacking/reclaiming
methods to maximise throughput at the same
time as maximising quality on an automated
basis (at a small fraction of the time and cost
thatdoingitmanuallyorthroughlesspowerful
systems would require). A good system will be
able to produce an optimal stacker, reclaimer,
car-dumper and shiploader schedule in under
30seconds,andwillcontinuetodosoathourly
intervals as conditions change.
Once such a system is in place, it can
deliver myriad business benefits. It provides
automated planning for the next 24 hour
period – a godsend given that the quality
of commodities on inbound trains next day
and the rest of the week is an unknown. A
good system will optimise the stacking and
reclaiming approach in such a way that room is
made to accommodate the next day’s trains. It
will also allow for the automatic creation of an
alternativeplanshouldequipmentbreakdown,
and incorporate this possibility into planning
(e.g. stacking product in two stockpiles with
two reclaimers to minimise risk of disruption
in the event of a breakdown). And it will go
a long way to helping keep inventory below
stockyard capacity: high inventory has a major
negative effect on throughput.
Optimisationaside,anothermajorbusiness
benefit is that such systems allow for users to
quickly run ‘what if’ scenarios. Users can select
for different stacking and reclaiming methods,
and change a whole range of variables from
equipment available to ship-loading speed and
so on. They can then compare and contrast the
results. This makes for a powerful tool when
it comes to longer-term planning. A stockyard
operatorwillbeabletoquicklysee,forinstance,
theimpactofaforecastreductioninequipment
available in the yard.
Ultimately, however, the only benefit
that counts at the end of the day is the benefit
to the bottom line. And a good stockyard
optimisation system can deliver this in spades.
Even what appear to be minute improvements
in efficiency and scheduling can translate into
huge savings. Given that a reclaimer reclaims
10,000 tons of iron ore per hour; adding just
5 minutes more productivity per machine
means enhancing throughput by 800 tons per
machineperday.Assuminganironpriceof$50
per ton, which makes for a daily generation of
$40K per machine – a stockyard optimisation
system will very quickly pay for itself.
Even what appear to be
minute improvements
in efficiency and
scheduling can translate
into huge savings.
REAL-TIME
STOCKYARD
OPTIMISATION
SYSTEM
INPUTS
Inbound Trains: Train Schedule,
Train Consist, Train Quality
Stockyard: Stockyard Layout,
Stockyard Inventory, Stockyard Quality
Outbound Ship: Ship Schedule, Ship
Consist, Ship Quality
Equipment Stockpile Mapping
OUTPUTS
• Berth to ship assignment
• Shiploader to berth assignment
• Identify stockpiles to fill the ship
• Blending operations
• Reclaimer job schedule
• Stacker job schedule
• Stockpile location
• Stacking method
• Reclaiming method
• Inward train to car dumper job schedule
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