metso underground crushers.pdf
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Aspects of
Underground Primary Crusher Plant DesignAuthored by Ari Jaakonmäki, M.Sc. Mining, Metso Minerals Inc, Tampere, Finland
Presented by Darcy Flath, Technical Support Engineer, Metso Minerals Industries,
Inc. Waukesha, WI USA
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SIZING A CRUSHING PLANTReal estate in an underground mine is usually at a prime cost;
therefore, the design of primary crushing plants faces more limita-
tions than on surface where you could say the sky is the limit.
However, the primary crushing and transportation of the ore to
surface are often dimensioned so that they define the capacity of
the mine; whatever limits the functionality of the plant may limit
the output of the mine.
Capacity
Required capacity defines the size and type of crushing equipment
and also the number of parallel crushers or plants required to meet
the mine production rate. Most suppliers and EPCM providers
have simulation and calculation tools for the basic equipment and
capacity selection, however, especially underground, the selection
criteria gets wider, usually in the direction of securing production
capacity with a larger safety margin.
Jaw crushers are the most common solution when the throughput
is less than 1000 tonnes per hour, depending a bit on the scalping
solutions, which will be discussed later. Above 1000 tph, primary
gyratory crushers begin to look interesting; there are no exact
boundaries but above 2000 tph, jaw crushers get rare except in a
parallel plant layout. Generally jaw crushers are in the clear majori-
ty in underground crushing.
Capacity depends also on the feed size and material type intro-
duced to the plant and required product curve. In most cases,
the first stage of crushing really has two functions:
• To get the material small enough for transporting
out of the mine
• To get a suitable product curve for the next stage
of comminution
In either case, the top size of the material ends up typically in the
range of 300 – 350 mm, which is good for belt conveyors and fits
into most secondary crushers without causing process risks, to
achieve this top size, the crusher setting is in the range of 200 mm
or below, depending on rock characteristics. The belt may be the
means of transporting the crushed ore out of the mine but even
when it’s not, there is usually a conveyor somewhere in the materi-
als handling process, so the requirements need to be met.
There are mines where more than one stage of crushing takes
place underground but mostly the lower cost and higher flexibility
of surface construction result in only primary crushing being done
underground.
Most underground mining methods produce a feed that is f iner
than in a typical open pit mine, resulting in higher capacity
through-plant; however, surprises do happen and there needs to
be a way to handle oversize feed material when the requirement
occurs.
ABSTRACT To fix a primary crushing plant that has been excavated and built underground is complicated and
costly; therefore, careful planning pays good dividends. This paper looks at different aspects of plant
design including capacity, installation, layout, maintenance and safety.
This paper focuses on hard rock applications, however, some of the findings will apply also to crushing
softer minerals using other than compression crushers, for instance, impact crushers, sizers, etc...
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Figure 1 The Inmet Mining Corporation Pyhäsalmi Mine underground crushing plant. The plant is automated and is operated from
a surface control room 1.4 km above the crusher. Push feeder into the crusher, no scalping.
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Overhead Crane
Ore Pass + Feeder Ore Pass + Feeder
Water Spray
Push Feeder
Feed Chute
Metso C200 Jaw Crusher
LHD Dump
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Scalping is recommended for a jaw crusher because:
• Capacity increases when material below crushersetting bypasses the crusher, also the energy
consumption is lower. In the simulated example
shown in Figure 2, the plant capacity drops over
40% if the scalping is removed; the volumetric load
of the crusher itself remains the same.
• The life of wear parts increases. A jaw crusher usually
wears more manganese steel per crushed ton than a
gyratory crusher, because the kinematics of a
single toggle jaw crusher cause an oval motion and
the fines typically create a grinding action at the
bottom part of the jaw dies.
• Feeding fines into the crusher may increase peak-stress
loads because of packing, i.e. material being
compacted as far as it compacts; this is enhanced by
moisture, which again is highest in the fines and quite
common in underground mines.
The most compact way scalping can be arranged is with a vibrat-
ing grizzly feeder. However, it is usually beneficial for the process
to use a separate feeder and scalper, in this way both components
can be optimized for improved process control and performance.
Points against scalping:
• If a separate scalping grizzly is used, that means
introducing a new piece of equipment into the
process, it is a capital cost and will require
maintenance. The installation also requires chutes and
other bypass arrangements which may become a
space and maintenance access issue depending on
the layout options. A feeder is required anyway for a
jaw crusher but the scalping functions can be
discussed.
• A common reason against installing a scalper is that
typically in an underground mine the feed is not asclean of foreign objects as in a sur face operation.
Underground mine feed often includes debris such as
rock bolts, wire mesh, cable, pieces of pipe, or wood, etc.,
which may get stuck in the scalping grizzly.
• If the crushing plant is planned to be operated
remotely and as automated as possible, the debris can
cause unpredictable clogging of the grizzly. Getting
someone to the plant to clean things up can take a
while and the cleaning itself takes time. This adds up to
production stoppages, lower long term capacity and
process reliability.
• In practice dealing with issues like debris andoccasional slightly oversize feed can be helped by
selecting a crusher size that is clearly above the
theoretical need and thus less sensitive to variations
in the process.
Scalping or not is mainly a jaw crusher issue. A primary gyratory is
not as sensitive to fines, the machines are large, steep and have a
relatively short stroke compared to setting, allowing fines to flow
though easier. The kinematics produce a straight compressive
crushing function without the grinding action found in a single
toggle jaw, therefore the liner wear is not as high per ton of
crushed material.
Figure 2 Simulated capacity difference between scalping
or not scalping in a primary crushing plant.
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To scalp or not to scalp?
Scalping before a jaw crusher is usually recommended. In most cases, gyratory crushers would be
fed with all the excavated ore, because of the different technical construction and behavior
of the two crushers.
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Figure 4 Jaw crusher plant with Apron feeder and scalping with a vibrating grizzly.
Modular bolted construction is a definite advantage from
this point of view. Some jaw crushers are built in this way,
some not, and even if practically all gyratories break intobolt connected modules, the modules can be pretty bulky.
A top shell of a 54 inch machine weighs 60 – 70 tonnes so
lifting capacity is definitely an issue in addition to size. The
heaviest part for maintenance in a Metso C200 jaw crusher
is the pitman assembly which weighs approximately 40
tonnes and requires 5 m of vertical space plus clearances in
lifting.
Ramp access gives some flexibility in the installation phase,
at least comparing to having to sling everything through a
shaft.
Ore transportation is often operating at different hours and
hourly capacity than many other functions in the mine,
therefore it is advisable to consider some buffer capacity.
Often the crusher is built below or on top of an ore pass,
this brings up practical and safety issues in installation and
also in maintenance. For this purpose, there needs to be a
quick and safe way to prevent objects or people falling
through the crusher, especially in a jaw crusher where
changing the wear parts happens quite often.
4
Figure 3 Lifting of the pitman into a jaw crusher.
Installing the Machinery and Plant Layout
The primary crushing plant is most commonly built close to the deepest part of the mine, getting the
machinery to the final location can be quite challenging. The most demanding unit is the crusher
itself; feeders, bins and platework are easier to handle for size and weight.
Ore Pass
Apron Feeder
Grizzly
C140 Jaw Crusher
Ore Pass
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If there is an ore pass underneath the crusher, it
increases the height between the crushing section and
the feeders, belts, etc., below, safe and quick personnel
access needs to be planned to the top and bottom of
the installation, a lift might be a consideration.
Cranes and other lifting equipment need to be suitable
mainly for maintenance but can also be used for the
installation. Overhead bridge cranes are most common
in underground crushing plants as they can efficiently
use the available space and have a constant lifting
capacity throughout the area. In selecting lifting
equipment and reserving space for lifting, it is good to
note that over the years, the demands on capacity and
reliability have a tendency to increase the weight and
sometimes the size of key components. The nextmachine you eventually want to use, when time comes
to replace the current one, may be slightly bigger but
would ideally go into the same plant layout without
excavation work or major modifications.
It is difficult to pick debris out of the primary feed, but
if there is a belt after the crusher, that would be a good
place to locate a magnetic separator and suff icient
space around it to get rid of at least the magnetic parts
of unwanted materials, rather than send it to the next
stage of comminution.
Figure 5 Installation of a jaw crusher plant at Newcrest Mining Ltd Cadia Valley Operations Ridgeway Deeps gold mine.
LHD loading into feed hopper, apron feeder to crusher, no scalping.
Figure 6 Jaw crusher plant with scalping with a
vibrating grizzly feeder.
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C140 Jaw Crusher
Apron Feeder
50 t Overhead Crane
LHD Load Points 2 Sides
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One often neglected question is that if you lift something out of
the crusher, where do you put it? In practice it means floor space
and headroom, one tip to save space is to build a hole in the floor
for the mainshaft, you lay the pitman from the jaw crusher on its
side to work on bearings or place the gyratory mainshaft upright.
When you are not using the hole you need to cover it.
Preventive and predictive maintenance is largely based on good
planning and follow-up, including the discipline to follow visual
inspection and lubrication schedules. There’s a learning curve on
improving plant availability in specific conditions. One key factor
in plant design is that if a service point is not readily accessible,
there is a temptation to neglect it. With today’s 3D CAD tools, it
is quite simple to review service access to various points before
construction.
Figure 7 Access to service points under crusher at Ridgeway Deeps Gold Mine.
Automatic and centralized lubrication are ways to improve the maintenance process with low cost actions. As many of these under-
ground plants will operate unmanned for most of the time, the automation and diagnostic systems should be utilized to their maximum,
this includes well placed cameras to key points.
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Maintenance
Planning the crushing plant for maintenance is an important part of achieving high process reliability
and availability. Lifting requirements for the major components has been discussed above but it
should also be noted that the routine maintenance includes lifting wear and spare parts, well located
jib cranes or monorails may be the answer. In large crushers, even the tools needed for opening or
tightening bolts can get bulky and benefit from having a lifting device handy.
Access to Service
Points Under Crusher
Push Plates to Cover Surge
Bin Maintenance
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Most lifting incidents appear to happen in connection with medi-
um size objects around the plant. The big components seem to
get a higher level of attention and planning and small parts don’t
cause as much reported damage. Routine maintenance proce-
dures may take place under time pressure and are often thought of
as not requiring so much specific attention every time. Typical
issues are not using the proper lifting devices or procedures, result-
ing in hand or foot injuries, sometimes even more serious conse-
quences. Instructions, training, discipline and availability of infor-
mation are key in prevention, as well as availability and condition
of correct lifting devices.
Access to maintenance points has been pointed out earlier; how-
ever, the safety aspect to this is to design as much of the service
procedures to be done from ground level or proper service and
access platforms. Climbing on wet or dusty surfaces should be
avoided whereever possible, this is partly an equipment engineer-
ing issue but has also a strong connection to plant design.
Control of the excavation and ore loading and hauling processes
should remove most of oversize handling or move it to safe loca-
tions. As the world is not perfect, corrective actions are occasional-
ly needed, the most efficient way is to operate a hydraulic boom
and hammer remotely to break up oversize or arching before or in
the crusher. A serious risk of accidents exists when this is done
manually; also if you need to send someone down to clear things
up it cuts production time.
Removing debris is related to the previous topic, except that it can
get even more improvised and require the use of the crane and
other devices in addition to the boom and hammer. An additional
flavor of this problem is that especially steel objects can get stuck
under tension so that when released they jump into unwanted
directions.
Moving parts as flywheels, belts, etc., should be protected with
proper guards. Sometimes the guard designs are clumsy or get
damaged so that there is a temptation not to replace them after
repairs or sometimes they have not been installed at all. Local safe-
ty regulations usually cover this area quite closely and technical
solutions are not overly complicated.
Dust suppression on the feed side of a primary plant is always
demanding, especially if you need to maintain the option to feed
the plant with trucks or LHD’s. In practice, water mist is the only
universal solution. Most underground plants plan to operate
unmanned and when personal presence is required it would most-
ly be in a pressurized and filtered control cabin. When the operator
or service person needs to move in the plant itself personal protec-
tive equipment should be used.
In more confined spaces like transfer points under or after the
crusher, it is easier to install suction and f iltering to keep the air
quality under control.
Eventually dust gathers on horizontal surfaces and needs to be
cleaned away. This means usually washing, in which case floor incli-
nations, drainage and potentially sumps and pumps need to be
thought of. If heavier accumulation of material is expected e.g.
under conveyors, space should be considered for a skid-steered
loader.
Fire suppression and fire safety procedures should be carefully con-
sidered, not so much because fires in crushing plants would be
very common but because any fire underground can have severe
consequences. The fire load normally consists of rubber in convey-
ors or v-belts and lubricants, in some occasions the crushed mate-
rial itself presents a potential hazard, e.g. high sulphur content dust
can be inflammable in certain conditions.
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SAFETY
In our experience, some of the most common types of safety issues
that affect a crushing plant are connected with:
• Lifting wear and spare parts
• Slipping on or off machines
• Clearing blockages in the crushing chamber
• Removing unwanted material from the feeder,grizzly or crusher
• Protection of moving parts
• Dust
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However, there are ore deposits that spread out over large horizon-
tal distances and are mined by, e.g. room-and-pillar methods, withhigh production rates, these mines have a different logistical chal-
lenge. Moving blasted ore with LHD equipment gets increasingly
costly and inefficient after 400 – 500 m and, in most cases the dis-
cussion turns into trucks but also belt conveyors are used success-
fully. Compared to trucks, belt conveyors are less flexible but have
clear advantages in operating and maintenance costs and are envi-
ronmentally more correct than diesel driven equipment. But, as
pointed out earlier, to put material on a belt, it needs to be primary
crushed.
The technical solution is to use rubber tired towable crushing
equipment or a crawler mounted self propelled unit, an example isshown below. Due to space limitations underground, these units
are small to medium in size but to optimize the mining sequence
at different areas, you can have several of them. The same technol-
ogy is used in surface mining, the difference is mostly in making
the size more compact and running on electric power instead of
diesel.
Figure 8 Underground application of a portable primary crushing plant with feed hopper unit and jaw crusher unit.
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MOBILE SOLUTIONS
Most underground mines try to keep their infrastructure as compact as possible and use gravity where
they can. In practice, this means locating the primary crushing plant close to the bottom of the mine
with ore passes coming down towards it and a silo under the crushing plant to buffer capacity
fluctuations. If ore is hoisted through a shaft the crusher is close by to shorten belt conveyors.
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Figure 9 Portable underground primary crushing plant. For transportation the crusher section and feed hopper part are separated
and towed to new location separately with LHD’s.
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