Note: Descriptions are shown in the official language in which they were submitted.
CA 02440311 2003-09-04
1 Title: VARIABLE GAP CRllShIER
2
3 Introduction and Prior Art
4
In the field of mining the technology of Oil-sand recovery and processing is
unique to the
6 deposits found in Northern Alberta, Canada in terms of the evolution of the
process and
7 equipment suitable for mining and processing the oil-sand. In the oil-sand
mine,
8 equipment used to excavate and transport the run-of-mine (ROM) oil-sand ore
is as
9 large in scale as at any world-wide mining operations, typically using
electric-hydraulic
shovels of up to 62 cubic metre capacity buckets loading into haulage trucks
of up to 400
11 tonnes capacity to transport the ROM oil-sand ore to a centralized oil-sand
slurry
12 preparation facility.
13
14 Due to the massive scale of the mining equipment and the characteristics of
the oil-sand
itself, the ore received from the mining operation typically contains a very
large range of
16 lump sizes spanning from 3,500 mm and weighing up to 30 tonnes down to sand
17 particles of a few millimeters. The ROM ore typically contains up to 30%
moisture, 2%
18 to 18% bitumen and 45% to 55% sand content by weight and also contains
amounts of
19 siltstone rock having an unconfined compressive strength of 165 to 221 MPa
as a waste
component.
21
22 The harsh environmental conditions at oil-sand operations encompass an
ambient
23 temperature range from +35 degrees Celsius down to -51 degrees Celsius. All
mining
24 and slurry preparation equipment is required to function with unhindered
effectiveness
and productivity under these ambient conditions. Materials handling properties
of the
26 ROM ore are highly variable over this temperature range. 'The oil-sand ore
comprises
27 frozen, highly abrasive lumps in winter but exhibits sticky, cohesive
behaviour in summer,
28 largely due to the influence of the contained moisture and bitumen
components.
29
A slurry preparation process step is typically required to prepare all ROM ore
to be
31 suitable for long-distance transport as a water-based slurry to a remote
upgrading facility,
32 at single-stream production rates exceeding 10,000 tonnes per hour of ROM
oil-sand.
33 Typical prerequisites for efficient slurry pumping are crushing the oil-
sand ore to minus
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1 100 mm followed by the preparation of a homogeneous water slurry, typically
with a
2 consistency of about 64% solids by weight at a specific gravity of 1.5.
3
4 Current practice for oil-sand slurry preparation in the industry requires
the use of multiple
series-wise equipment processing steps to accomplish controlled ore feeding,
screening
6 and crushing prior to slurry pipelining. Disadvantages of the prior art for
oil-sand slurry
7 preparation include a primary constraint of requiring a screening process
step and oil-
8 sand re-handling steps to ensure control of the maximum size of lumps. The
variable
9 gap crushing innovations disclosed in this specification potentially enable
acceptable oil-
sand lump size reduction to be achieved and controlled by crushing steps
rather than by
11 screening steps.
12
13 It is well known in the prior art to use two crushing steps in series to
handle a large lump
14 size reduction ratio. In the case of oil-sand the crushers would typically
be arranged to
reduce lumps from 2,500 mm down to 100 mm (reduction ratio of 25 to 1 ).
Conventional
16 practice would use a primary crushing step of, for example, from 2,500 mm
down to 600
17 mm (ratio 4.2 to 1 ) by setting the primary crusher roll gap to 600 mm,
followed by a
18 secondary crushing step of, for example, 600 mm down to 100 mm (ratio 6 to
1 ) by
19 setting the secondary crusher roll gap to 100 mm. This is a necessary
practice both to
balance the crushing work load between the two series-wise crushing machines
and to
21 enable the rolls to be able to "grab" the maximum lump size presented to
each crushing
22 step. The geometrical concept of an adequate "pinch angle" between the
rolls to enable
23 the rolls to "grab" a given maximum lump size is a function both of lump
size and gap
24 width between the rolls for given roll diameters.
26 Also well known in the art is the random nature of particle or lump size
distributions
27 arising from the mining process, in which although a very large fraction of
the ore will
28 comprise lump sizes smaller than the expected maximum 2,500 mm, larger lump
sizes
29 wiH occur from time to time. A conventional primary crusher used in oil-
sand with the roll
gap set to 600 mm and roll diameters of 3,000 mm, for example, will be able to
"grab" a
31 2,500 mm Pump (reduction ratio 4.2 to 1 ) with minimal interference
occurring to the
32 overall crushing throughput, but if a 3,500 mm or larger lump presented
itself in the feed
33 to the crusher (reduction ratio > 5.8 to 1 ) there would likely be some
delay and difficulty
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1 for the crusher rolls to be able to "grab" the lump, thus causing
obstruction of flow and
2 potential spillage of feed requiring a shut-down of the ore crushing
operation.
3
4 For prior art crushers a possible option to improve the handling of large
lump sizes
would be to set a large gap width at the primary crusher, thereby achieving a
more
6 favourable "nip angle" for large lumps. This solution is highly limited in
that it not only
7 throws a much higher percentage of the crushing duty onto the secondary
crusher but
8 also negatively impacts the secondary crushing reduction ratio. A second
option is to
9 screen the ore stream feeding one of the crushing stages to control the lump
size
reduction ratio presented to that crushing stage. This known practice requires
additional
11 equipment and structure to be added to the crushing plant and results in
the unwanted
12 accumulation of reject, oversize ore lumps requiring separate handling.
Alternatively it is
13 known to install auxiliary equipment to break the large lumps using
mechanical energy or
14 to employ some type of mechanical grapple to remove the lump from the
throat of the
crusher. Both of these solutions entail the addition of capital-intensive
equipment and
16 steel structure and require semi-continuous operator attention and
intervention . These
17 are known disadvantages of the prior art and also present serious safety
hazards to
18 personnel in the mining industry as well as frequently causing spill and
loss of production.
19
Successfully controlling the maximum lump size in the run-of-mine oil-sand ore
21 preparation process is an essential requirement to facilitate subsequent
oil-sand slurry
22 pipeline transportation. The minimum oil-sand slurry pumping velocity is
dictated by
23 maximum lump size handled and requires effective control to minimize the
operating risk
24 of plugging the final oil-sand slurry delivery pipeline.
26 Also, it will be appreciated by one skilled in the art that whether or not
the crushing
27 service is in oil-sand or in other types of mining ores there is always a
strict requirement
28 to control maximum lump size so as to ensure the success of the subsequent
processing
29 step.
31 With Reference to the Figures:
32
33 Figure 1 is a simplified isometric view of a dual-roll crusher assembly
incorporating
34 preferred embodiments of the invention;
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1
2 Figure 2 is a simplified elevation view of the dual-roll crusher assembly of
Figure 1
3 showing more clearly the relationship of the crusher rolls and a simulated
lump to be
4 crushed.
6 Figure 3 is a simplified elevation view of the dual-roll crusher assembly of
Figure 2
7 shawing an enlarged gap between the crusher rolls.
8
9 Figure 4 is a schematic crushing equipment system process flowsheet using
two, series-
wise crushers in an improved ore preparation plant for the preparation of run-
of mine oil-
11 sand ore for a subsequent processing step.
12
13 In Figure 1, a dual-roll crusher assembly is shown mounted on a structural
base 1
14 comprising a fixed roll 2 and a movable roll 3, with projecting shaft 4 on
the fixed roll for
mounting a drive means (not Shawn) and projecting shaft 5 on the movable roll
for
16 mounting a drive means (not spawn), bath rolls being held by the structural
base 1 in a
17 substantially parallel relationship with each other and in a substantially
horizontal plane
18 and having a nominal gap 6 maintained between them. Fixed crusher roll 2 is
arranged
19 with bearing means 7 in bearing holder means 8 at each end thereof and
movable roll 3
is arranged with bearing means 9 (not shown) in bearing holder means 10 at
each end
21 thereof. Bearing holder means 10 is arranged with slide means 1 ~1 at its
base and
22 coupling means 12 enabling attachment of actuator means 13 which can be
mativated to
23 slide the movable pulley assembly to the left or to the right, effectively
increasing ar
24 decreasing the nominal gap 6 between the rolls. A spherical shape 14 is
illustrated
above the gap between the crusher rolls 2 and 3 to simulate a lump of run-of-
mine ore
26 which can be drawn into the crushing zone above and through the gap by the
teeth on
27 the rolls and forced to pass through the gap. The shape 14 can typically be
significantly
28 larger in diameter than the nominal gap width between the crusher rolls.
29
In Figure 2 the crusher assembly mounted on base 1 having fixed roll 2 and
movable roll
31 3 is shown with a simulated run-of mine ore lump 14 entering the crushing
zone between
32 the two rolls. The nip angle 15 is shown to be a geometrical relationship
between the
33 lump size, the roll diameter and the gap width between the rolls. In the
illustration, teeth
34 on the surface of the rolls are shown as intermeshing in the gap.
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1
2 In Figure 3 the effect of increasing the gap by movement of movable roll 3
to the left is to
3 allow lump 14 to drop further into the crushing zone, thus enabling the
teeth on the rolls
4 to more easily "grab" the lump and force it into the crushing zone and
through the gap.
6 In Figure 4 mine haulage truck 16 dumps run-of-mine ore into receiving
hopper 17 from
7 which reclaim conveyor 18 withdraws run-of-mine ore and feeds it via chute
19 to
8 primary crusher 20 to create primary crushed ore. The primary crushed ore
passes
9 through chute 21 to conveyor 22 feeding via chute 23 to secondary crusher 24
to create
secondary crushed ore. The secondary crushed ore passes through chute 25 to
11 conveyor 26 and chute 27 to subsequent process step 28.
12
13 In Figures 1, 2 and 3 the feed hopper side plates controlling feed to the
crusher have
14 been omitted for clarity, but it will otherwise be clear that the only
possibility of the full
stream of ore passing through the crusher is that all lumps first be reduced
by the rolls to
16 a size equal to or less than the nominal crusher gap width between the
rolls. In tact, the
17 basic presumption of the successful operation of the process flowsheet in
Figure 4 is
18 that the full stream of run-of-mine ore will be reduced sufficiently in
size after passing
19 through the crushing equipment system illustrated in the flowsheet to be
suitable for a
subsequent processing step 28.
21
22 As explained in conjunction with the Figures the preferred embodiments of
the present
23 invention for the dual-roll crusher are the provision of bearing holder
slides and actuation
24 means for adjusting the position of the movable roll so as to obtain an
operable "variable
gap" crusher. For conventional crushers the roll gap can only be changed
manually
26 while the crusher is shut-down. Control of the crusher gap width has never
been
27 available as an operating parameter in the prior art. The corollary
provision of sensing
28 means and logical interpretation means, such as a known industrial
programmable lagic
29 controller with pre-programmed set-points, enables closed loop crushing
control
strategies to be implemented based upon measurement of selected
characteristics of
31 the oil-sand ore in combination with selected operating parameters of the
crushing
32 equipment system itself, thereby to incrementally increase or decrease the
crusher roll
33 gap and thereby to control the crushing operation in a beneficial way.
34
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1 The present invention enables a larger range of lump size reduction ratios
to be handled
2 in a given crushing equipment system using less equipment than the prior
art. It also
3 enables unique and valuable crushing control strategies such as load sharing
between
4 series-mounted crushers. It will be possible to implement anticipatory as
well as reactive
control of oil-sand crushing based upon specific measurable characteristics of
run-of
6 mine ore and primary crushed ore and secondary crushed ore. R possible
associated
7 flow sheet innovation is the elimination of prior art screening and oil-sand
re-handling
8 and accumulation of unwanted rejects due to the improved ability to control
the
9 maximum lump size.
11 For example, since the primary and secondary crushers are installed in
series and are
12 handling the same stream of oil-sand ore it will be possible to distribute
the actual
13 crushing duty load equally between them by measuring the power delivered to
each
14 crusher and adjusting the roll gap at one or both of the primary and
secondary crushers
to balance the power draw, thus enabling control of relative wear rates
between the
16 crushers and extending the operating interval between shut-downs for major
17 refurbishment. Balancing the crushing duty between the primary and
secondary
18 crushers may also enable increasing the crushing plant oil-sand ore
throughput rate or
19 minimizing crushing power consumption as alternate strategies for improving
mining
profitability. Finally, for crushing run-of-mine oil-sand ores which are
highly variable both
21 in composition and in lump size distribution, both seasonally and also
between individual
22 mine haulage truck loads, the capability of balancing the crushing loads as
a continuous
23 operating function is both unique and valuable for optimizing crushing duty
and
24 throughput at each of the primary and secondary crushers and in the process
flowsheet
itself. No such beneficial capabilities or operating strategies are available
in the prior art.
26
27 Known means of measuring crusher load include at least sensing means such
as
28 measuring power delivery to the crusher rolls or' measuring 'the weight of
oil-sand
29 material carried on selected conveyors by means such as belt weigh scales.
31 Variable gap crushing of the present invention could also be controlled by
observation of
32 external factors in the crushing equipment system process flowsheet,
enabling the
33 crusher gap to be adjusted in anticipation of receiving a particularly
large lump of ore into
34 the throat of the primary crusher. In this case the roll gap could be
incrementally
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1 increased, thus improving the "nip-angle" of the rolls to enable the large
lump to be more
2 easily gripped by the teeth on the rolls and to be forced into the crushing
zone above
3 and through the gap. Although oversized large lumps might flow through the
primary
4 crusher for several seconds in this instance, system throughput rates could
then be
temporarily reduced for the time it would take for the secondary crusher to
handle the
6 extra crushing duty, without compromising the required control of maximum
lump size
7 delivered to a subsequent processing step. No such beneficial capabilities
or operating
8 strategies are available in the prior art.
9
Beneficial crushing control strategies could also be based on observation of
lump size in
11 the primary or the secondary crushed ore streams. Any observed increase or
decrease
12 in average lump size in the primary crushed ore, possibly due to wear or
breakage of
13 primary crusher teeth, could provide a control basis for incrementally
closing or opening
14 the primary crusher gap, respectively, both to control crushing system
thoughput rate
and to control crushing duty at the secondary crusher. Similarly, any observed
increase
16 in average lump size in the secondary crushed ore could provide a control
basis for an
17 operator alarm or to incrementally reduce the secondary crusher gap so as
to ensure
18 meeting the maximum lump size specification for the subsequent process
step. No such
19 beneficial capabilities or operating strategies are available in the prior
art.
21 Known means of observing lump size include at least sensing means such as,
for
22 example, optical imaging means and level sensing means in feed hoppers or
on
23 conveyors in the crushing equipment system.
24
Although much of the foregoing discussion refers specifically to the mining
environment
26 and conditions of Canadian oil-sand are it will be readily appreciated by
one practiced in
27 the art that the improvements described for primary and secondary roll
crushers and for
28 crushing equipment system process flowsheets will also be beneficial for
other mining
29 plants handling other types of mining ores. Also, it will be understood
that the quoting of
specific capacity or dimensional data for the crushing equipment system is not
intended
31 to exclude the use of other capacities and dimensions, when such use falls
within the
32 spirit of the invention.
33
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Lt will also be clear to one practiced in the art that means to remove tramp
metal such as
2 a conventional belt magnet must be provided for the process flowsheet.
Although not
3 shown in Figure 4, this tramp metal removal means is understood to be
present and
4 would typically be mounted on at feast one of the conveyors on the
flowsheet.
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