Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR CONSOLIDATING MATURE FINES TAILINGS
FIELD OF THE INVENTION
[001] The present invention relates to treatment of tailings including mature
fines tailings.
BACKGROUND OF THE INVENTION
[002] In general, tailings ponds arising from oil sands operations consist of
three layers. The
bottommost layer consists mostly of sand and large particles (>0.5 mm) that
fall to the base of
the pond under the action of gravity. The middle layer consists of mature
fines tailings
("MFT"), a material that has the general consistency of yogurt and which
contains a large
amount of water and some residual oil trapped within the interstitial space of
clays and fine
sand. The topmost layer consists of mostly water with very fine solids
suspended within the
water. MFT is a composite material comprising water, clay, sand, and residual
hydrocarbons.
[003] In oil sands operations, tailings including MFT are produced during the
oil sands
extraction process wherein the clay and solids are separated from the oil sand
to yield bitumen.
[004] The tailings including MFT, in typical practice, are deposited into
large ponds where the
sand component settles to the bottom of the system whereas the next densest
material, the MFT,
accumulates in a middle layer above the sand layer and below the water layer.
The water can
contain fine suspended particles that remain in suspension for considerable
periods of time. The
tailings materials that enter the tailings pond from the oil sands mining
processing plant also
contain oil. In typical practice, up to 1% of the material that is placed in
the tailings pond is oil.
However, this oil remains locked within the tailings material in the pond and
is not produced
from the pond.
[005] The key issue confronted by oil sands mining operations from an
environmental point of
view is the accumulation of tailings ponds ¨ they are massive and have the
potential for leaks of
the water contained in the ponds to the environment.
[006] The intention of all oil sands mines is that the tailings ponds are
eventually returned to
their original state (e.g., boreal forest).
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[007] A primary issue faced when dealing with 1ViFT is that the porosity is
relatively large but
the permeability is very low (and water is bound to the clays through
electrostatic and van der
Waals forces). It is desired that the MFT be consolidated by having the water
removed from the
layer, but this is complicated by the lack of permeability.
[008] Given the nature of MFT with its fine particles and low permeability,
the amount of time
it will take for natural (under gravity) consolidation of 1ViFT is widely
acknowledged to be on
the order of hundreds to thousands of years. This means that practically,
there is no present
commercial solution for these tailings ponds to quickly consolidate them to
enable their return
to their original state.
[009] What is needed, therefore, is a method for more quickly consolidating
the MFT layer in
a tailings pond.
SUMMARY OF THE INVENTION
[010] According to the present invention, consolidation of 1ViFT is achieved
by using injection
of a first fluid directly into the MFT layer, the fluid consisting of
additives that help to achieve
consolidation of the 1ViFT. In some exemplary embodiments of the present
invention, a second
fluid is injected into the 1ViFT to unlock the oil within the 1ViFT. This oil
can then be collected
at the surface of the MFT for sale.
[011] According to a first broad aspect of the present invention, there is
provided a method for
treating a mature fines tailings layer in a tailings deposit, comprising the
steps of:
a. providing an injection system configured for injection of a first fluid,
the first
fluid comprising an additive effective to increase consolidation of the mature
fines tailings layer;
b. positioning the injection system so as to deliver the first fluid directly
into the
mature fines tailings layer;
c. injecting the first fluid directly into the mature fines tailings layer;
d. ceasing injection of the first fluid and allowing the first fluid and
the additive to
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interact with the mature fines tailings layer; and
e. allowing the mature fines tailings to further consolidate.
[012] In some exemplary embodiments of the first broad aspect, the injection
system
comprises a well, which may be vertical, horizontal, deviated or multilateral.
The injection
system may alternatively comprise a distribution plate system, which may be a
perforated plate
system positioned at a base of the mature fines tailings layer or in an
underlying sand layer or
positioned near a top of the mature fines tailings layer.
[013] The additive in the first fluid preferably comprises at least one metal
halide, which is
preferably selected from the group consisting of aluminum chloride and iron
chloride.
[014] In some exemplary methods, a gas is directly injected into the mature
fines tailings layer
before or after the step of injecting the first fluid, and the gas is allowed
to disturb the mature
fines tailings layer and release entrapped hydrocarbon, and allowing the
released hydrocarbon to
rise to surface for collection. The gas is preferably selected from the group
consisting of air,
nitrogen, carbon dioxide, and mixtures thereof. The gas is most preferably
carbon dioxide, and
in such case exemplary methods may further comprise injecting a second fluid
comprising an
alkaline solution, and allowing the alkaline solution to interact with the
carbon dioxide to
produce carbonate to further consolidate and strengthen the mature fines
tailings layer.
[015] In some exemplary methods, a second fluid may be injected which
comprises an
additive selected from the group consisting of polymer and nanocrystals.
Preferably, the
polymer is polyacrylamide and the nanocrystals are a cellulose nanocrystal
suspension.
[016] One key advantage of the present invention is that the solids do not
have to be mobilized
for processing, e.g., transported to a barge, which means that the energy
savings and thus cost
savings for the present invention may be greater than that of conventional
processes where the
MFT is moved for processing.
[017] Given the environmental impact of tailings ponds, there is an ongoing
need for safe and
effective processes to consolidate and strengthen MFT so that the ponds can be
emptied of
water and recovered back to their original form before the mine was installed.
The
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consolidation of 1ViFT as described herein and the subsequent removal of water
may enable a
more rapid conversion of these tailings ponds to their original state. The
requirement to
consolidate the 1ViFT to a particular strength is because after reclamation,
soil and trees and
plants will be placed on top of the reclaimed MFT layer.
[018] One novel aspect of the present invention lies in the use of wells or
distribution systems
to directly inject fluids into the reservoir to consolidate the MFT, and for
the injection of
additional fluids to yield oil from the 1ViFT, and the collection of the oil
from the system for
sale.
[019] In general, the present specification describes methods to consolidate
1ViFT to a fraction
of its present volume by direct injection of a set of water-borne chemicals
into the MFT layer in
the tailings pond. Furthermore, in some embodiments of the present invention a
different set of
fluids are optionally injected into the 1ViFT layer to enhance mixing of the
chemicals but to also
mobilize trapped oil from the 1ViFT to the top surface of the pond.
[020] In a broad aspect of the present invention, mixtures of metal halide
(for example, MX
where M = aluminum, iron, sodium, potassium or copper, and X = fluoride,
chloride, bromide
or iodide) solutions with and without acid and/or base (to adjust pH as
required to make it more
acidic which may aid in consolidation of the MFT) are injected directly into
the MFT layer.
The mixture may be injected through a well (horizontal, vertical, deviated or
multilateral) into
the volume of MFT preferably such that the contact of the solution with the
MFT is maximized.
The well can also take the form of a distribution plate in some embodiments.
The advantage of
injecting the solution directly into the 1ViFT is that the solid mass of the
MFT is not moved (and
thus the energy intensity of the process is far less than that of one where
the 1ViFT is transported
for processing). Thus, this process could be done in an already existing
tailings pond with no
transportation of the MFT.
[021] In an optional mixing step, gas is also injected into the MFT layer,
preferably but not
necessarily using the same well, to cause mixing of the solution and the
1ViFT. The gas rises
through the 1ViFT causing movement and disturbance of the 1ViFT and solution
thus enabling the
two to mix. The mixing, however, could be done in alternate manners where, for
example, the
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original solution is jetted into the 1\,/iFT to achieve the mixing.
[022] After the solution and the MFT mix, the MFT consolidation is enhanced,
and with the
optional gas injection step some of the oil within the MFT is floated to the
top of the water
column above the 1\,/fF T layer. This oil can be collected by skimming the
pond.
[023] In one exemplary embodiment, a cellulose nanocrystal suspension or
polymer can be
injected into the MFT, either before or after the gas injection step, to
further consolidate the
MFT. Polymers and nanocrystals and nanoparticles and microparticles can be
added to either or
both of the initial injected fluid and the gas. The
nanoparticles/microparticles can consist of, for
example, silica or iron oxide particles with or without functional acid/base
groups and salts.
[024] The gas injected can consist of air, carbon dioxide, nitrogen, natural
gas, or mixtures
thereof
[025] According to one exemplary embodiment of the present invention, the
method
comprises:
a. Drilling or placing a well or distribution system into the MFT layer of the
tailings pond. The well is preferably completed using any existing completion
technology that promotes uniform injectivity of the solution into the MFT
layer,
and the preferred embodiment is a horizontal well that sits a few meters above
the base of the MFT layer, depending on the layer thickness.
b. Preparation of the primary solution on surface (the preferred embodiment
being
FeCl3 and A1C13, 10% concentration).
c. Injection of the primary solution through the well into the MFT layer. The
volume of the primary solution injected should be large enough to contact the
desired volume of AfFT (the preferred embodiment is that at least 1 pore
volume
of primary solution is injected into the targeted volume of the 1\,/fF T
layer). The
pore volume is defined as the volume in the 1\,/iFT that is not solid ¨ it is
the
volume of the fluids (water and oil) that is in the MFT .
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d. If needed, there can be an optional soak period where the primary solution
can
mix with the MFT layer.
e. Next, gas (preferably nitrogen, carbon dioxide, air or a mixture of these
components) is injected into the 1ViFT layer. The gas rises through the MFT
and
mixes the solution and 1ViFT by buoyancy forces. The gas injection step does
not
need to be long in duration but should be sufficient to sufficiently mix the
system
(the preferred embodiment is injection of greater than 1 pore volume of the
targeted MFT layer).
f. After gas injection has stopped, the system is left to sit and consolidate.
g. If carbon dioxide is injected into the 1ViFT layer in Step e., then a
secondary
solution containing alkaline materials can be injected into the MFT layer.
This
will react with the injected carbon dioxide to form carbonates which will
further
consolidate and strengthen the MFT layer. The carbon dioxide can be sourced
from flue gas or upgrader process streams. In a preferred embodiment, the
injection of the alkaline solution can be done directly after the primary
solution
or together with the primary solution. In other embodiments, other materials
such as polymers or cellulose nanocrystal can be injected into the MFT layer,
as
described above.
h. Next, the oil that has floated to the top of the topmost water layer is
collected by
standard methods to collect oil slicks from the top of water layers.
[026] In certain embodiments, gas injection is not undertaken so as to only
consolidate the
MFT layer.
[027] In a further embodiment, gas injection may be done prior to the
injection of the primary
solution (Step b. above) to first release oil from the MFT. Thereafter, the
primary solution is
injected into the oil-depleted MFT layer.
[028] The present invention can also be used with non-oil sands tailings ponds
such as mineral
mining tailings ponds.
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[029] Detailed descriptions of exemplary embodiments of the present invention
are given in
the following. It is to be understood, however, that the invention is not to
be construed as being
limited to these embodiments. The exemplary embodiments are directed to
particular
applications of the present invention, while it will be clear to those skilled
in the art that the
present invention has applicability beyond the exemplary embodiments set forth
herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[030] Features and advantages of embodiments of the present application will
become
apparent from the following detailed description and the appended drawings, in
which:
[031] FIG. 1A-H are diagrams exemplifying one implementation of the methods
described
herein for treating a MFT layer.
[032] FIG. 2A-B display results of using the method described here.
[033] FIG. 3 shows an example of the resulting 1ViFT after the method
described here is
applied and the top water is removed.
[034] FIG. 4 shows an additional example of results for mixtures of additives
with MFT.
[035] FIG. 5 shows an additional example of results after an exemplary method
according to
the present invention described herein is applied.
[036] FIG. 6 shows an additional example of results after an exemplary method
according to
the present invention described herein is applied.
[037] Exemplary embodiments of the present invention will now be described
with reference
to the accompanying drawings.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[038] Throughout the following description, specific details are set forth in
order to provide a
more thorough understanding to persons skilled in the art. However, well known
elements may
not have been shown or described in detail to avoid unnecessarily obscuring
the disclosure. The
following description of examples of the invention is not intended to be
exhaustive or to limit
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the invention to the precise forms of any exemplary embodiment. Accordingly,
the description
and drawings are to be regarded in an illustrative, rather than a restrictive,
sense.
[039] The below description relates to treatment of 1ViFT to consolidate the
MFT and
optionally to yield residual oil.
[040] At present, there are no large scale processes that exist to consolidate
MFT and produce
its residual oil.
[041] The present invention takes a new approach, and instead of moving the
1ViFT to a surface
facility for treatment, it is treated in situ within the pond and consolidates
in place to allow
reclamation.
[042] Processes that transport the 1ViFT to a location for processing consume
large amounts of
energy not only for transporting 1ViFT to the processing site but also back to
the pond for final
deposition. In the novel method described herein, none of the solids are
transported but rather
additives are mixed with the MFT in place and water rejection from the 1ViFT
layer occurs
vertically due to the gas moving under buoyancy forces. This means that the
energy required
for this process is much lower than that of other processes. Furthermore,
since the energy
intensity is lower, so too is the greenhouse gas intensity of the process. If
carbon dioxide is
injected with the gas, some fraction of it will be fixed within the tailings
pond, especially if an
alkaline solution is added to the 1ViFT layer.
[043] The reduction of the volume of the tailings material as well as
rejection of clear water
which can be sent back for recycling and further use or treatment and disposal
is a key
advantage of the method described herein. Also, the process does not involve
moving tailings
materials from the pond to a processing site and back which reduces the risk
of spills or
exposure to the environment. If the gas optionally used includes carbon
dioxide, then there is
potential that it can be fixed in the consolidated tailings material thus
reducing greenhouse gas
emissions of other processes if the carbon dioxide is sourced from the other
processes, e.g., an
upgrader.
[044] Since no tailings solids are moved in the process, the energy required
for the process is
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reduced over that of processes where the tailings have to be moved. This
implies that the cost
of the process described herein will be significantly lower than that of
processes that require
tailings transportation.
[045] Throughout this specification, numerous terms and expressions are used
in accordance
with their ordinary meanings.
[046] FIG. 1A-H illustrates an exemplary implementation of the present
invention for
consolidation of 1ViFT with residual oil production. The original state of the
tailings pond is
displayed in FIG. 1A.
[047] In the first step, a well or distribution system is placed within the
tailings layer,
preferably within the base section of the 1ViFT layer as shown in FIG. 1B. The
primary solution
consists of salt solutions or preferably metal halides (MX where M = aluminum,
iron, sodium,
potassium or copper, and X = fluoride, chloride, bromide or iodide) into the
MFT layer.
Although not essential, the pH can be altered to make the injected primary
solution alkaline to
enhance consolidation of the MFT layer. The most preferred materials in the
primary solution
are aluminum chloride and iron chloride.
[048] FIG. 1C displays the preparation of the primary solution on surface.
This can also be
done on a barge floating on the surface of the tailings pond or offsite.
[049] FIG. 1D shows the step of injecting the primary solution into the MFT
layer. The
targeted volume of primary solution is preferably equal to at least one-half
pore volume in the
MFT layer. The preferred volume of primary solution is equal to 1 to 2 pore
volumes of
primary solution injected into the 1ViFT layer. One-half pore volume of
primary solution will be
enough to achieve the desired effect, but it is preferable to have 1 to 2 pore
volumes of primary
solution. The greater the volume of primary solution, the greater the
reduction of electrostatic
charges in the MFT. In this step, the MFT materials will react with the
injectants and reduce the
static electrical charges within the MFT and allow it to consolidate and
release water. Also, in
this step a small amount of oil will be released from the MFT materials. This
oil is released
through the convective mixing of the primary solution and the MFT as well as a
reduction of the
electrostatic charges in the 1ViFT due to the injection of the primary
solution components.
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[050] FIG. 1E displays a 'soak' step where the primary solution is allowed to
mix with the
MFT layer. In this step the MFT will continue to react with the primary
solution and some oil
will be further released from the MFT.
[051] FIG. 1F shows the next step of the process where a gas is injected into
the AfFT layer.
The gas further mixes the AfFT with the primary solution and also adheres to
the released oil
and due to buoyancy forces lifts the oil from the MFT layer to the top of the
water layer above
the MFT layer. The oil that is raised to the top of the water layer may be
collected by skimming
it from the top surface of the water. The preferred gas for this step is
carbon dioxide, nitrogen,
air or mixtures thereof The amount of gas injected is preferably between one-
half and three
pore volumes (of the AfFT layer) of gas. The preferred amount is 1-2 pore
volumes of the MFT
layer of gas. FIG. 1G illustrates another resting period after the gas has
risen out of the AfFT
layer, showing the further-consolidated MFT.
[052] In FIG. 1H, a final step is shown, where if carbon dioxide was injected
into the AfFT
layer in Step f, a secondary solution containing an alkaline base is added to
the AfFT to further
consolidate the layer by having the carbon dioxide react with the alkaline
solution to convert it
to carbonates. This further consolidates the AfFT layer and also strengthens
it for future
reclamation of the tailings pond. The alkaline solution can be, for example,
calcium hydroxide
or magnesium hydroxide with solutions of silicates or metal halides. The
preferred components
are calcium hydroxide and/or magnesium hydroxide.
[053] In another embodiment, polymer or cellulose nanocrystals are added in
the last injection
step to further consolidate and strengthen the MFT.
[054] An example of experimental results is illustrated in FIG. 2A-B and FIG.
3.
[055] FIG. 2A-B shows an example of the results from using the method
described here. FIG.
2A displays an example of the original MFT material. FIG. 2B shows two
examples of the
results of the consolidation and oil extraction procedure described herein.
The results show that
the water is rejected from the AfFT layer and the AfFT solids are
consolidated.
[056] FIG. 3 shows the results of the AfFT after gas injection and top water
removal. In this
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example, the 1ViFT is consolidated to about 50% of its original volume. In
over 200 experiments
conducted by the present inventors, the MFT layer was consolidated to between
15 and 50% of
its original volume depending on the materials used and the gas injection
volume. In the
preferred embodiments, the 1ViFT was consolidated to about 50% of its original
volume and
about 0.6 g of oil were extracted per 100 mL of MFT processed.
[057] When distilled water is injected into the 1Vif T as the primary
solution, the tailings solids
remain in a suspended state. No consolidation was observed.
[058] The injection system can be located either on land or on a barge.
Extended reach wells
can be used if done from land.
[059] FIG. 4 shows the results of tests wherein a mixture of iron(III)
chloride and
polyacrylamide polymer was mixed with MFT (approximately 0.5 gallons) placed
within a 2.5
gallon fish tank. Before the mixture was added to the tank, the MFT was either
mixed with the
iron(III) chloride and polyacrylamide polymer at either 1,000 or 20,000 rpm.
The results
display the amount of water spontaneously released from the MFT. In the case
where water
alone was added to the 1Vif T, no water was released from the tailings
mixture.
[060] The results show that for the mixtures obtained at 1,000 rpm
(Experiments B and C), the
addition of CO2 helps to accelerate the amount of water released from the
tailings mixture. At
the higher mixing speed of 20,000 rpm (Experiments D and E), the difference of
the water
released is more pronounced between the case without and with CO2. Experiment
D (20,000
rpm with no CO2 added) has less water released than that of Experiment B
(1,000 rpm with no
CO2 added); this is likely due to the mixing generating finer clay particles
and causing
reduction of the polyacrylamide polymer chains which would tend to cause more
water
retention. One reason why gas might help to yield greater water release is due
to the mixing it
causes when it bubbles through the tailings mixture layer. As the iron(III)
chloride affects the
electrical double layer between clay particles and helps to mobilize water
within the clay matrix,
the gas provides a vertical upward displacement force, due to buoyancy, that
moves unbound
water to the top of the tailings mixture. The results show that the addition
of the metal halide
and polymer help to reject water from the MFT.
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[061] FIG. 5 compares the final solid content of the Experiments A to E (pre-
mix tests in 2.5
gallon tanks) to Experiment F (in-situ test in 2.5 gallon tank demonstrating
the method
described herein). For Experiment F, measurements of solids content were taken
on the tailings
samples treated by the in-situ method at the side of the tank where treatment
solution and air
were pumped into the tank from the sparger. The samples were taken after 513
hours (21 days)
of time after the treatment solution and air was injected. Further
measurements were taken along
the length of the sparger. Samples were also taken at the opposite side of the
tank where there
was no well. The results demonstrate that the in-situ process yielded a
tailings material with
higher solids content than that of the pre-mixed tests.
[062] The results presented in FIG. 5 demonstrate that the solids content for
the in-situ sample
reached as high as 50 wt.%. The 50 wt.% sample was taken along the side of the
tank with the
sparger, near the middle of the sparger length. The results show that the
highest solids content in
the in-situ experiments were near the bottom of the tailings layer where the
injection well was
located. A high solids content was also measured near the end of the sparger
whereas the
measurement taken near the inlet of the sparger had the lowest solids content.
[063] The results of FIG. 5 demonstrate that the in-situ method (Experiment F)
is capable of
generating higher solids content (and thus, higher water rejection) in the
1ViFT than that of the
pre-mixed samples (Experiments A to E). Thus, the in-situ method yields more
consolidation
than that of pre-mixed samples.
[064] FIG. 6 compares results of consolidation where different amounts of
iron(III) chloride
and polyacrylamide polymer are injected into a layer of MFT in a 2.5 gallon
fish tank by using
the method described here. The rate of height decrease was faster initially
before about Hour
284 than that beyond Hour 294. It is interesting to note that this is the same
time at which the
fractures began to develop in the 1ViFT due to the drying of the 1ViF T. The
opening of fractures
in the deposits still produces a reduction in the volume of the tailings,
however, this manifests
as a shrinkage also in the lateral area of the tailings as the widths of the
fractures extend
laterally as well as vertically into the tailings volume.
[065] The results show that consolidation of the MFT may reach above 50% using
the in situ
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method described here.
[066] Unless the context clearly requires otherwise, throughout the
description and the claims:
[067] = "comprise", "comprising", and the like are to be construed in an
inclusive sense, as
opposed to an exclusive or exhaustive sense; that is to say, in the sense of
"including, but not
limited to".
[068] = "connected", "coupled", or any variant thereof, means any connection
or coupling,
either direct or indirect, between two or more elements; the coupling or
connection between the
elements can be physical, logical, or a combination thereof.
[069] = "herein", "above", "below", and words of similar import, when used to
describe this
specification shall refer to this specification as a whole and not to any
particular portions of this
specification.
[070] = "or", in reference to a list of two or more items, covers all of the
following
interpretations of the word: any of the items in the list, all of the items in
the list, and any
combination of the items in the list.
[071] = the singular forms "a", "an" and "the" also include the meaning of any
appropriate
plural forms.
[072] Words that indicate directions such as "vertical", "transverse",
"horizontal", "upward",
"downward", "forward", "backward", "inward", "outward", "vertical",
"transverse", "left",
"right", "front", "back", "top", "bottom", "below", "above", "under", and the
like, used in this
description and any accompanying claims (where present) depend on the specific
orientation of
the apparatus described and illustrated. The subject matter described herein
may assume
various alternative orientations. Accordingly, these directional terms are not
strictly defined
and should not be interpreted narrowly.
[073] Where a component (e.g., a circuit, module, assembly, device, drill
string component,
drill rig system, etc.) is referred to herein, unless otherwise indicated,
reference to that
component (including a reference to a "means") should be interpreted as
including as
equivalents of that component any component which performs the function of the
described
component (i.e., that is functionally equivalent), including components which
are not
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structurally equivalent to the disclosed structure which performs the function
in the illustrated
exemplary embodiments of the invention.
[074] Specific examples of methods and systems have been described herein for
purposes of
illustration. These are only examples. The technology provided herein can be
applied to
contexts other than the exemplary contexts described above. Many alterations,
modifications,
additions, omissions and permutations are possible within the practice of this
invention. This
invention includes variations on described embodiments that would be apparent
to the skilled
person, including variations obtained by: replacing features, elements and/or
acts with
equivalent features, elements and/or acts; mixing and matching of features,
elements and/or acts
from different embodiments; combining features, elements and/or acts from
embodiments as
described herein with features, elements and/or acts of other technology;
and/or omitting
combining features, elements and/or acts from described embodiments.
[075] The foregoing is considered as illustrative only of the principles of
the invention. The
scope of the claims should not be limited by the exemplary embodiments set
forth in the
foregoing, but should be given the broadest interpretation consistent with the
specification as a
whole.
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