Note: Descriptions are shown in the official language in which they were submitted.
TITLE: HYDRAULIC HOISTING OF POTASH AND OTHER EVAPORITE ORES
FIELD OF TECHNOLOGY
[0001] The present specification relates generally to evaporite ore mining,
and more
particularly, to methods of hydraulic hoisting of potash, polyhalite, trona
and other
similar evaporite ores from underground mines.
BACKGROUND
[0002] In underground potash and comparable evaporite mines, conventional
mining
operations typically engage extensive ore extraction and transportation
equipment,
and highly skilled personnel. Boring machines cut and move the ore away from
the
mining faces. The extracted ore is conveyed to the vicinity of the mine shaft
and then
hoisted to surface in open-topped containers called skips.
[0003] The tonnages and depths from which evaporite ores are hoisted typically
require many years to construct and significant capital investment. In
Saskatchewan,
for example, potash ore hoisting is typically accomplished through concrete
lined
shafts 16 ft or more in diameter and approximating 3,000 ft deep. The shafts
are
fitted with about 200 ft - 300 ft high headframes required to deflect the
hoist ropes
and house ancillary equipment. The hoists or winders utilized to raise and
lower the
skips are approximately 20 ft in diameter and have a hoist motor nominal of
10,000
kW.
[0004] It is a challenging problem to increase, on an incremental basis, the
output
from a mine that has reached or is approaching its maximum
mechanical/electrical
hoisting capacity. In such cases, increasing mine output would normally
require
construction and operation of another mine shaft at a very high cost.
Operators must
pay not only the costs of additional underground equipment and personnel, but
also
the large ultimately sunk capital cost of the hoisting plant. The cost of the
hoisting
plant is often a significant drawback to increasing mine production because it
is both
a large potential capacity increase in the hoisting rate and a prohibitive
capital cost.
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This and other drawbacks associated with conventionally-sought approaches to
increasing the hoisting rate of underground mines are addressed by the methods
disclosed herein.
[0005] Hoisting of potash ore with saturated brine has been conducted to
examine
plugging of the hoist pipe (Shook, CA; Gillies, RG and Schergevitch, PJ.
Concentration Changes in Hydraulic Hoisting of Potash Ore. In: International
Conference on Bulk Materials Storage, Handling and Transportation (4th: 1992:
Wollongong, N.S.W.)).
[0006] Improved methods of hoisting potash, polyhalite and other evaporite
ores from
underground mines are desirable.
[0007] The preceding examples of the related art and limitations related to it
are
intended to be illustrative and not exclusive. Other limitations of the
related art will
become apparent to those of skill in the art upon a reading of the
specification and a
review of the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The described embodiments may be better understood by reference to the
following description and the accompanying drawings. Additionally, advantages
of
the described embodiments may be better understood by reference to the
following
description and accompanying drawings.
[0009] FIG. 1 is a vertical sectional elevation view through a shaft of an ore
hoisting
circuit in accordance with an example;
[00010] FIG. 2 is a vertical sectional elevation view through a shaft of a
hydraulic
hoisting circuit in accordance with an example;
[0010] FIG. 3 is an elevation view of a wet product separation plant in the
hydraulic
hoisting circuit of FIG. 2;
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[0011] FIG. 4 is an elevation view of an underground dry ore screening plant
in the
hydraulic hoisting circuit of FIG. 2;
[0012] FIG. 5 is an elevation view of an underground slurry preparation
circuit in the
hydraulic hoisting circuit of FIG. 2; and
[0013] FIG. 6 is a flowchart illustrating a method of hydraulic hoisting of
potash ore
in accordance with an example.
DETAILED DESCRIPTION
[0014] Representative applications of methods according to the present
application
are described in this section. These examples are being provided solely to add
context and aid in the understanding of the described embodiments. It will
thus be
apparent to one skilled in the art that the described embodiments may be
practiced
without some or all these specific details. In other instances, well-known
process
steps have not been described in detail to avoid unnecessarily obscuring the
described embodiments. Other applications are possible, such that the
following
examples should not be taken as limiting.
[0015] In the following detailed description, references are made to the
accompanying drawings, which form a part of the description and in which are
shown, by way of illustration, specific embodiments in accordance with the
described
embodiments. Although these embodiments are described in sufficient detail to
enable one skilled in the art to practice the described embodiments, it is
understood
that these examples are not limiting; such that other embodiments may be used,
and
changes may be made without departing from the scope of the described
embodiments.
[0016] The following describes an exemplary method for hydraulically hoisting
potash (or other evaporite ore) 'fines' material from an underground mine. The
method includes mining an ore deposit using a boring machine to generate Run-
of-
Mine (ROM) material at a mine face, conveying the generated ROM material to an
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underground dry ore screening plant, screening the ROM material relative to a
threshold size wherein the threshold size is a feed size of one or more
flotation cells
at a surface wet product separation plant, mixing 'fines' material, comprising
ROM
material that is below the threshold size, with a supply of saturated brine to
create a
slurry mixture wherein the saturated brine prevents the 'fines' material from
dissolving
into the slurry mixture, and pumping the slurry mixture to the surface via one
of a
shaft and a borehole to the surface wet product separation plant.
[0017] With reference to FIG. 1, an ore hoisting circuit is shown in
accordance with
one example. According to this example, "Run-of-mine "(ROM) material 102 is
mined
and transported on conveyor belt 120 where it is fed, via flop gate 122, to an
underground dry ore screening plant 108 (shown in FIG. 2) for screening (and
as
discussed below, for hydraulic hoisting of 'fines' material). After screening,
oversize
or 'coarse' material is returned via conveyor belt 120 from the underground
dry ore
screening plant 108 to the existing mining infrastructure 104 for skipping to
the
surface. In this example, conveyor belts 120 are configured with feeders 126,
and
ROM or 'coarse' material can be stored temporarily in storage bins 124 and
surge
bins 128 as necessary to maintain and/or regulate the output of the production
line.
The returned 'coarse' material is loaded on skips at a loading pocket 130 for
mechanical hoisting to the surface through an existing shaft 106. The hoisted
'coarse'
material is conveyed to a (surface) mill input dry circuit for milling.
[0018] Turning to FIG. 2, a hydraulic hoisting circuit is shown according to
one
example. The hydraulic hoisting circuit includes an underground dry ore
screening
plant 108 (described with reference to FIG. 4), an underground slurry
preparation
circuit 110 (described with reference to FIG. 5), and a (surface) wet product
separation plant 114 (described with reference to FIG. 3). Generally speaking,
the
underground dry ore screening plant 108 separates and directs the 'coarse'
material
to the ore hoisting circuit of FIG. 1 and conveys the 'fines' material to the
underground slurry preparation circuit 110 for hydraulic hoisting (as
described below,
what is hoisted is a slurry mixture made up of a saturated brine laden with
the 'fines'
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material) to the surface via a shaft or shafts 202 (which may be the existing
shaft 106
in one example). Alternatively, hydraulic hoisting of the slurry mixture can
be via one
or more boreholes, instead of the existing shaft. The hydraulic hoisting can
be to a
vertical height approximating 3,000 ft. After the slurry mixture has been
hoisted to the
surface, a wet product separation plant 114 separates the potash (or other
ore) from
the slurry mixture. There is no technical limit to the vertical height of the
hoisting,
either above or below the stated 3,000 ft.
[0019] In general, mine output is typically restricted within one or more
constraints.
For example, a typical mechanical/electrical hoisting system uses a drum or
friction
type hoist with a finite maximum hoisting capacity. This finite hoisting
capacity is
determined by factors such as available hours of operation, depth of hoisting
and is
contingent on a power connection to the hoist motor. These factors determine
the
amount of material that can be hoisted in an existing shaft and headframe on
an
hourly and annual basis.
(0020] In accordance with examples of the present specification, mining output
of ore
can be increased within the constraints of the existing mechanical/electrical
hoisting
plant by differentiating the 'fines' material from the 'coarse' material. The
'fines'
material is mixed in a saturated brine solution and hydraulically hoisted by
pumping
while the 'coarse' material is hoisted as part of the existing skip hoisting
system and
up to the full capacity of that existing hoisting system.
[0021] Advantageously, by screening the ROM material 102 via an underground
dry
ore screening plant 108, examples of the present specification enable the
hydraulic
hoisting of 'fines' material in parallel with (or in lieu of, as the case may
be) the
skipping of 'coarse' material, allowing for the increasing of mine output on
an
incremental basis. This is in contrast to some previous approaches in which
all ROM
material is skipped to surface. Advantageously, techniques of the present
specification permit increasing the output from a mine that is producing at or
near
existing hoisting plant infrastructure capacity.
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[0022] The skilled reader will appreciate that one example of the present
specification is directed to a method of hydraulically hoisting potash 'fines'
material
from an underground mine working level to a surface processing plant via an
existing
shaft 106. However, the present specification is not limited to the mining of
potash
.. ores but also extends to polyhalite ores or any evaporite mineral ores,
crushed or
fragmentary rock or other 'fines' material that is capable of being
hydraulically
hoisted. The disclosed techniques can be applied to any evaporite-type
deposits in
addition to potash deposits. For example, the present specification can be
applied to
any deposits that are mined using boring machines that generate ROM material
(including 'fines' material that is generated by virtue of the mining method
at the
face).
[0023] The term potash refers to potassium compounds and potassium-bearing
materials, the most common being potassium chloride (KCl). Potash is most
commonly used as a fertilizer and in some other industrial applications as
well.
[0024] According to one example, the typical potash ore ROM material 102,
produced by a continuous face borer (also known as a continuous mining
machine),
is sized at 76,200 pm x 0 pm (approximately 3 in x 0 in). After comminution at
the
surface crushing/screening plant, a typical feed size to mill is 100% minus
3,360 pm.
The ROM material, as produced by the continuous mining machinery, contains
approximately 50% that falls within the required mill feed size range, and
therefore,
does not require any further size reduction.
[0025] In accordance with one example in the present specification, potash
'fines'
material is material passing under a threshold size of about 3,360 pm and
potash
'coarse' material is material equal to and greater than the threshold size of
about
3,360 pm. The present specification is not limited to these dimensions; other
values
or ranges of values are intended to be covered by the present specification.
The size
can be selected or adjusted using the vibratory screen 412 discussed below
with
reference to FIG. 4. In one example, the threshold size is selected to be no
greater
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than a feed size to the flotation cells in a wet product separation plant 114
or other
surface processing plant. Advantageously, controlled selection of the
threshold size
may reduce the amount of materials handling at the wet product separation
plant 114
or other surface processing plant.
[0026] In accordance with one example, the method of the present specification
separates the ROM material 102 into two (2) size particle size streams
underground
¨ 'coarse' or oversize material (e.g., at 2,830 pm or greater) and 'fines' or
undersize
material (e.g., at 100% minus 2,830 pm). According to one example, the
vibratory
screen 412 can be set at 1/8 in (3,175 pm) to enable the 2,830 pm material to
pass
as 'undersize'. The 'coarse' material is skipped to surface in the existing
mechanical/electrical hoisting plant and the 'fines' material is pumped to
surface
using positive displacement pumps. The term 'undersize' in the present
specification
refers to that size which is suitable for feeding to flotation cells of a
surface mill with
no further size reduction.
[0027] As the screening operation produces the two particle size streams
simultaneously, skipping and pumping also have to occur simultaneously, except
for
short periods that any storage capacity for either material size will allow.
This means
that, after a hoisting plant has reached its maximum capacity; there is still
the ability
to add another increment to the mine output, in the same shaft without
affecting the
existing mechanical/electrical hoisting system. This represents an increase in
mine
output above the current shaft hoisting capacity, with no change to the
mechanical/electrical hoisting plant.
[0028] The maximum potential 'undersize' that can be made available for
hydraulic
hoisting and the quantity of that undersize is a function of the screening
efficiency in
separating the ROM material into the particle streams at the designated split
size. In
one example, the 'undersize' potash ore pumped to the surface can be
introduced
into an existing potash processing circuit after the 'oversize' potash ore is
crushed
and screened (i.e., in an existing plant) and prior to scrubbing.
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[0029] The ratio of the 'fines' material to the `coarse' material in the ROM
material
102 from the mine workings is a function of the nature of the deposit and the
mining
method and equipment.
[0030] FIG. 3 illustrates a (surface) wet product separation plant 114 in
accordance
with an example. After hoisting, the slurry mixture is stored in surface
atmospheric
pressure discharge tanks 302. Centrifugal pumps 304 pump the slurry mixture
through a bank of hydro cyclones 306 ¨ waste is pumped to a brine settling and
recovery circuit (not shown) and product is sent for scrubbing (i.e., to an
existing and
expanded capacity wet scrubbing plant (not shown)).
[0031] FIG. 4 illustrates an underground dry ore screening plant 108 in
accordance
with an example. In this example, ROM material 102 travels along conveyor belt
404
which may be fitted with one or more magnets 402 to move the ROM material 102
throughout the production line. The production line can also include one or
more
trippers 406 and surge bins 408. The ROM material 102 is fed via one or more
feeders 410 to vibratory screens 412. The vibratory screens 412 direct
undersize or
'fines' material to the underground slurry preparation circuit 110, while
oversize or
`coarse' material is directed to the ore hoisting circuit (FIG. 1), using
conveyor belts
404.
[0032] In this specification, a vibratory screen 412 encompasses any screening
machine including a drive that induces vibration, a screen cloth that causes
particle
separation, and a deck which holds the screen cloth and the drive and is the
mode of
transport for the vibration. The vibration can be sinusoidal or gyratory. The
screen
cloth or media is defined by aperture (mesh) size, and can be made of any type
of
material such steel, stainless steel, rubber compounds, polyurethane, brass,
etc.
Though the present specification uses the term "vibratory screen", it will be
appreciated that this term extends to any other technique of mechanical
separation of
ROM material 102 into one or more channels or streams of the ROM material 102.
According to one example, the apertures can be defined by reference to a
flowsheet
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of the (surface) wet product separation plant 114.
[0033] FIG. 5 illustrates an underground slurry preparation circuit 110 in
accordance
with an example. 'Fines' material from the underground dry ore screening plant
108 is
loaded into one or more agitated storage tanks 514, after being conveyed
through
one or more metal detectors 502, magnets 504, flop gates 506, conveyor belts
508,
surge bin 510 and feeders 512, and mixed (using valves 520) with a supply of
saturated brine kept in a surge tank 522 supplied by a line or lines from the
surface.
The mixture or slurry of saturated brine and 'fines' material is pumped using
positive
displacement pumps 516 to the surface via the shaft 202. In accordance with
one
example, the storage tanks 514 will include agitators (not shown) that
maintain the
solids of the slurry mixture in homogeneous suspension. An agitated slurry
holding
tank 518 (also called a dump tank) positioned at the bottom of the shaft 202
(or
boreholes) is configured to hold the slurry mixture in the event of a power
loss and
the need to vacate the vertical lines to the surface.
[0034] Advantageously, the use of a saturated brine, rather than an
unsaturated
brine or water, as the conveyance medium for the hydraulic hoisting prevents
the
'fines' material from dissolving in the slurry mixture. Use of unsaturated
brine will
partly dissolve the potash 'fines' material in the mixture en route to the
surface in the
pipeline, an undesired result. As used in the present specification, the term
"dissolving" refers to the process of mixing or combining a solute and a
solvent to
form into a solution which cannot be separated by a simple process like
filtration. The
skilled reader will appreciate that the extent of solubility can vary and that
expressions such as "prevent a solute from dissolving" mean that a solute is
practically or slightly insoluble in a given solvent.
[0035] According to one example, saturated brine is the required medium to
prevent
the potash ore from dissolving into solution. Clarified saturated brine from
an existing
thickener overflow circuit on the surface (not shown) can be directed to and
then
down the shaft (or boreholes) in one or more steel pipes.
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[0036] More generally, in the present specification, use of the term brine
encompasses a high-concentration solution of salt (e.g., sodium chloride
and/or
potassium chloride) and saturated refers to a solution containing the maximum
(or
substantially maximum) possible amount of a dissolved salt.
[0037] To provide the transport medium for pumping the 'undersize' material
(e.g.
potash ore material) to the surface requires that a steady and reliable supply
of
saturated brine is provided to the pumps 524 which may be positive
displacement
pumps or any other type of pump that is known. In one example, the source of
the
saturated brine can be the surface processing plant (in conventional surface
scrubbing circuits, brine is added to crushed ore in a series of agitated tank
cells to
dislodge impurities from the potash).
[0038] In accordance with the present specification, the slurry mixture is
prepared
through the continuous mixing of the 'fines' material with the saturated brine
from the
surface in storage tanks 514 located adjacent to the pumps 524. FIG. 5 shows
two
storage tanks 514 for the slurry mixing, each sized to serve two pumps 524,
but
variations to such arrangement are possible without departing from the scope
or
intent of the present specification.
[0039] According to one example, the maximum mine design output is potash ore
contained in a slurry mixture at a consistency of up to about 60% solids by
weight.
The slurry mixture can be mixed up to about 60% solids by weight by metering
from a
(dry solids) 'undersize' material surge bin 510 and a saturated brine surge
tank 522,
both ahead of the slurry mixing storage tanks 514.
[0040] According to one example, agitators (not shown) disposed in the storage
tanks 514 work to maintain the solids of the slurry mixture in homogeneous
suspension at all times. The percentage solids in the tanks can be monitored
continuously by using a small pumped sampling loop and gamma gauge. In one
example, the storage tank 514 can be sized to retain sufficient slurry for 30
minutes
of pumping at full capacity. This can then size each tank to hold a measure of
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solids in slurry form at up to about 60% solids by weight. In the event of a
power or
equipment failure, the agitator can be designed to remobilize the fully loaded
slurry
tank after solids settling. The pumps 524 can be arranged in two groups of two
(or
three) pumps per slurry pipeline (not shown).
.. [0041] In the event that power is lost whilst the slurry mixture is in
transit between
the pumps 524 and the surface processing plant, the entire contents of the
slurry
pipeline can be dumped or unloaded into a slurry holding tank 518 near the
shaft
bottom to avoid the solids settling in the pipe. To mitigate this risk, the
pumps 524
cam be connected to an emergency power source, even if the pumps 524 have to
operate at a lower capacity. The aim is to prevent the mean slurry velocity,
in both
the vertical and horizontal sections of the pipeline, from being less than the
critical
settling velocity of the particles. Whilst solids settling in the horizontal
or sub vertical
pipelines can re-mobilize readily upon the pumps 524 restarting, the same may
not
necessarily be said for the vertical pipelines. Solids settlement in the
vertical section
may eventually resemble a 'plug' of material which may be expected to approach
solidification with time. This cannot be allowed to occur. The 'dumped' slurry
can be
held in the slurry holding tank 518 and re-introduced into the slurry circuit
at the
earliest possible time in order to maintain an empty slurry holding tank 518
for
emergencies.
[0042] The pumps 524 can pressurize the slurry lines sufficiently to enable
the slurry
to be transported to two surface atmospheric pressure discharge tanks 302,
each
with an agitator (not shown). The function of the tanks 302 is to prevent any
back
pressure or varying pressure on the pumps 524. Each tank 302 can be sized for
30
minutes retention time, or some other suitable measure, at full mine output
rate. Each
tank 302 can be equipped with centrifugal pumps 304 and a bank of hydro
cyclones
306, to concentrate the solids as suitable feed to a scrubbing section of the
plant (not
shown) and send the clarified overflow to a thickening circuit (not shown).
[0043] A flowchart illustrating an example of a method of hydraulically
hoisting
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potash 'fines' material from an underground mine is shown in FIG. 6. The
method
may be carried out by using the plant described with reference to FIG. 1
through FIG.
5. Implementing such a method is within the scope of a person of ordinary
skill in the
art given the present description. The method may contain additional or fewer
processes than shown and/or described, and may be performed in a different
order.
[0044] At 600 of FIG. 6, the method begins. A saturated brine is prepared at
602
and is transported underground at 604. ROM material is mined. At an
underground
dry ore screening plant 108, the ROM material is screened at 606. The
undersize or
'fines' material, relative to a threshold size (shown at 610), is mixed with a
saturated
brine to prepare a slurry mixture at 612. The slurry mixture is hoisted to the
surface at
614 via a shaft or a borehole. Oversize or 'coarse' material is transferred to
a skip
circuit at 616 and is mechanically hoisted to the surface at 618. The method
ends at
620.
[0045] The present specification discloses a method of hydraulically hoisting
potash
'fines' material from an underground mine including the steps of mining a
potash ore
deposit using a boring machine to generate a ROM material at a mine face,
conveying the generated ROM material to an underground ore screening plant,
screening the ROM material relative to a threshold size wherein the threshold
size is
a feed size of one or more flotation cells at a surface product separation
plant, mixing
'fines' material, comprising the ROM material that is below the threshold
size, with a
saturated brine to create a slurry mixture wherein the saturated brine
prevents the
potash 'fines' material from dissolving into the slurry mixture, and pumping
the slurry
mixture to a surface location via one of a shaft and a borehole to the surface
product
separation plant.
[0046] According to one example, the screening step includes passing the ROM
material through a plurality of sized apertures within a vibrating screen
cloth. The
apertures can be sized based on potash ore flotation characteristics
determined by a
flowsheet of the surface product separation plant. According to one example,
the
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apertures can be sized at about 1/8 in.
[0047] The saturated brine can be a mixture of sodium chloride and potassium
chloride salts, in accordance with one example.
[0048] The mixing can include agitating the slurry mixture in tanks to
maintain solids
of the slurry mixture in homogeneous suspension and to prevent settling. The
pumping can include moving the slurry mixture through pipes using one or more
positive displacement pumps that are pressurized to transport the slurry
mixture
through the pipes to a surface atmospheric pressure discharge tank. in the
event of a
power loss, the method can include dumping the slurry mixture in a slurry
holding
tank near a shaft bottom to prevent settling in the pipes.
[0049] According to an example, the saturated brine can be from an existing
thickener overflow circuit (not shown) at the surface product separation
plant.
[0050] The mixing step can be performed underground. The saturated brine can
descend for underground mixing in one or more pipes.
[0051] According to one example, the coarse material is conveyed to a circuit
for
skip hoisting. According to this example, the hydraulic hoisting (pumping) and
the
skip hoisting can be performed substantially simultaneously in parallel to
increase a
rate of output of mine operations. And, when the skip hoisting is
substantially at
capacity, the hydraulic hoisting augments production to increase an overall
capacity
of the rate of output of mine operations.
[0052] The present specification also discloses the use of a saturated brine
for
hydraulic hoisting by mixing the saturated brine with potash 'fines' material
including
screened ROM material from an underground mine to create a slurry mixture. The
saturated brine prevents the potash 'fines' material from dissolving into the
slurry
mixture. The saturated brine can be a mixture of sodium chloride and potassium
chloride salts.
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[0053] The present specification further discloses a method of hydraulically
hoisting
'fines' material from an underground mine including the steps of mining a
deposit
using a boring machine to generate ROM material at a mine face, conveying the
generated ROM material to an underground (e.g., dry) ore screening plant,
screening
the ROM material relative to a threshold size wherein the threshold size is a
feed size
of one or more flotation cells at a surface wet product separation plant,
mixing 'fines'
material, comprising the ROM material that is below the threshold size, with a
saturated brine to create a slurry mixture wherein the saturated brine
prevents the
'fines' material from dissolving into the slurry mixture, and pumping the
slurry mixture
to the surface via one of a shaft and a borehole to the surface (e.g., wet)
product
separation plant.
[0054] It will be recognized that while certain features are described in
terms of a
specific sequence of steps of a method, these descriptions are only
illustrative of the
broader methods disclosed herein, and may be modified as required by the
particular
application. Certain steps may be rendered unnecessary or optional under
certain
circumstances. Additionally, certain steps or functionality may be added to
the
disclosed embodiments, or the order of performance of two or more steps
permuted.
All such variations are considered to be encompassed within the disclosure and
claimed herein.
[0055] Furthermore, the various aspects, embodiments or features of the
described
embodiments can be used separately or in any combination.
[0056] The foregoing description, for purposes of explanation, used specific
nomenclature to provide a thorough understanding of the described embodiments.
However, it will be apparent to one skilled in the art that the specific
details are not
required in order to practice the described embodiments. Thus, the foregoing
descriptions of specific embodiments are presented for purposes of
illustration and
description. They are not intended to be exhaustive or to limit the described
embodiments to the precise forms disclosed. It will be apparent to one of
ordinary
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skill in the art that many modifications and variations are possible in view
of the
above teachings.
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