Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR DRYING OIL SAND MATURE FINE TAILINGS
FIELD OF THE INVENTION
The present invention generally relates to the field of treating oil sand fine
tailings.
BACKGROUND
Oil sand fine tailings have become a technical, operational, environmental,
economic
and public policy issue.
Oil sand tailings are generated from hydrocarbon extraction process operations
that
separate the valuable hydrocarbons from oil sand ore. All commercial
hydrocarbon
extraction processes use variations of the Clark Hot Water Process in which
water is
added to the oil sands to enable the separation of the valuable hydrocarbon
fraction from
the oil sand minerals. The process water also acts as a carrier fluid for the
mineral
fraction. Once the hydrocarbon fraction is recovered, the residual water,
unrecovered
hydrocarbons and minerals are generally referred to as "tailings".
The oil sand industry has adopted a convention with respect to mineral
particle sizing.
Mineral fractions with a particle diameter greater than 44 microns are
referred to as
"sand". Mineral fractions with a particle diameter less than 44 microns are
referred to as
"fines". Mineral fractions with a particle diameter less than 2 microns are
generally
referred to as "clay", but in some instances "clay" may refer to the actual
particle
mineralogy. The relationship between sand and fines in tailings reflects the
variation in
the oil sand ore make-up, the chemistry of the process water and the
extraction process.
Conventionally, tailings are transported to a deposition site generally
referred to as a
"tailings pond" located close to the oil sands mining and extraction
facilities to facilitate
pipeline transportation, discharging and management of the tailings. Due to
the scale of
operations, oil sand tailings ponds cover vast tracts of land and must be
constructed and
managed in accordance with regulations. The management of pond location,
filling, level
control and reclamation is a complex undertaking given the geographical,
technical,
regulatory and economic constraints of oil sands operations.
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Each tailings pond is contained within a dyke structure generally constructed
by placing
the sand fraction of the tailings within cells or on beaches. The process
water,
unrecovered hydrocarbons, together with sand and fine minerals not trapped in
the dyke
structure flow into the tailings pond. Tailings streams initially discharged
into the ponds
may have fairly low densities and solids contents, for instance around 0.5-10
wt%.
In the tailings pond, the process water, unrecovered hydrocarbons and minerals
settle
naturally to form different strata. The upper stratum is primarily water that
may be
recycled as process water to the extraction process. The lower stratum
contains settled
residual hydrocarbon and minerals which are predominately fines. This lower
stratum is
often referred to as "mature fine tailings" (MFT). Mature fine tailings have
very slow
consolidation rates and represent a major challenge to tailings management in
the oil
sands industry.
The composition of mature fine tailings is highly variable. Near the top of
the stratum the
mineral content is about 10 wt% and through time consolidates up to 50 wt% at
the
bottom of the stratum. Overall, mature fine tailings have an average mineral
content of
about 30 wt%. While fines are the dominant particle size fraction in the
mineral content,
the sand content may be 15 wt % of the solids and the clay content may be up
to 75 wt%
of the solids, reflecting the oil sand ore and extraction process. Additional
variation may
result from the residual hydrocarbon which may be dispersed in the mineral or
may
segregate into mat layers of hydrocarbon. The mature fine tailings in a pond
not only has
a wide variation of compositions distributed from top to bottom of the pond
but there may
also be pockets of different compositions at random locations throughout the
pond.
Mature fine tailings behave as a fluid-like colloidal material. The fact that
mature fine
tailings behave as a fluid significantly limits options to reclaim tailings
ponds. In addition,
mature fine tailings do not behave as a Newtonian fluid, which makes
continuous
commercial scale treatments for dewatering the tailings all the more
challenging. Without
dewatering or solidifying the mature fine tailings, tailings ponds have
increasing
economic and environmental implications over time.
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There are some methods that have been proposed for disposing of or reclaiming
oil
sand tailings by attempting to solidify or dewater mature fine tailings. If
mature fine
tailings can be sufficiently dewatered so as to convert the waste product into
a reclaimed
firm terrain, then many of the problems associated with this material can be
curtailed or
completely avoided. As a general guideline target, achieving a solids content
of 75 wt%
for mature fine tailings is considered sufficiently "dried" for reclamation.
One known method for dewatering MFT involves a freeze-thaw approach. Several
field
trials were conducted at oil sands sites by depositing MFT into small, shallow
pits that
were allowed to freeze over the winter and undergo thawing and evaporative
dewatering
the following summer. Scale up of such a method would require enormous surface
areas
and would be highly dependent on weather and season. Furthermore, other
restrictions
of this setup were the collection of release water and precipitation on the
surface of the
MFT which discounted the efficacy of the evaporative drying mechanism.
Some other known methods have attempted to treat MFT with the addition of a
chemical
to create a thickened paste that will solidify or eventually dewater.
One such method, referred to as "consolidated tailings" (CT), involves
combining mature
fine tailings with sand and gypsum. A typical consolidated tailings mixture is
about 60
wt% mineral (balance is process water) with a sand to fines ratio of about 4
to 1, and
600 to 1000 ppm of gypsum. This combination can result in a non-segregating
mixture
when deposited into the tailings ponds for consolidation. However, the CT
method has a
number of drawbacks. It relies on continuous extraction operations for a
supply of sand,
gypsum and process water. The blend must be tightly controlled. Also, when
consolidated tailings mixtures are less than 60 wt% mineral, the material
segregates with
a portion of the fines returned to the pond for reprocessing when settled as
mature fine
tailings. Furthermore, the geotechnical strength of the deposited consolidated
tailings
requires containment dykes and, therefore, the sand required in CT competes
with sand
used for dyke construction until extraction operations cease. Without sand,
the CT
method cannot treat mature fine tailings.
Another method conducted at lab-scale sought to dilute MFT preferably to 10
wt% solids
before adding Percol LT27A or 156. Though the more diluted MFT showed faster
settling
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rates and resulted in a thickened paste, this dilution-dependent small batch
method
could not achieve the required dewatering results for reclamation of mature
fine tailings.
Some other methods have attempted to use polymers or other chemicals to help
dewater MFT. However, these methods have encountered various problems and have
been unable to achieve reliable results. When generally considering methods
comprising
chemical addition followed by tailings deposition for dewatering, there are a
number of
important factors that should not be overlooked.
Of course, one factor is the nature, properties and effects of the added
chemicals. The
chemicals that have shown promise up to now have been dependent on oil sand
extraction by-products, effective only at lab-scale or within narrow process
operating
windows, or unable to properly and reliably mix, react or be transported with
tailings.
Some added chemicals have enabled thickening of the tailings with no change in
solids
content by entrapping water within the material, which limits the water
recovery options
from the deposited material. Some chemical additives such as gypsum and
hydrated
lime have generated water runoff that can adversely impact the process water
reused in
the extraction processes or dried tailings with a high salt content that is
unsuitable for
reclamation.
Another factor is the chemical addition technique. Known techniques of adding
sand or
chemicals often involve blending materials in a tank or thickener apparatus.
Such known
techniques have several disadvantages including requiring a controlled,
homogeneous
mixing of the additive in a stream with varying composition and flows which
results in
inefficiency and restricts operational flexibility. Some chemical additives
also have a
certain degree of fragility, changeability or reactivity that requires special
care in their
application.
Another factor is that many chemical additives can be very viscous and may
exhibit non-
Newtonian fluid behaviour. Several known techniques rely on dilution so that
the
combined fluid can be approximated as a Newtonian fluid with respect to mixing
and
hydraulic processes. Mature fine tailings, however, particularly at high
mineral or clay
concentrations, demonstrates non-Newtonian fluid behaviour. Consequently, even
though a chemical additive may show promise as a dewatering agent in the lab
or small
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scale batch trials, it is difficult to repeat performance in an up-scaled or
commercial
facility. This problem was demonstrated when attempting to inject a viscous
polymer
additive into a pipe carrying MFT. The main MFT pipeline was intersected by a
smaller
side branch pipe for injecting the polymer additive. For Newtonian fluids, one
would
expect this arrangement to allow high turbulence to aid mixing. However, for
the two
non-Newtonian fluids, the field performance with this mixing arrangement was
inconsistent and inadequate. There are various reasons why such mixing
arrangements
encounter problems. When the additive is injected in such a way, it may have a
tendency to congregate at the top or bottom of the MFT stream depending on its
density
relative to MFT and the injection direction relative to the flow direction.
For non-
Newtonian fluids, such as Bingham fluids, the fluid essentially flows as a
plug down the
pipe with low internal turbulence in the region of the plug. Also, when the
chemical
additive reacts quickly with the MFT, a thin reacted region may form on the
outside of
the additive plug thus separating unreacted chemical additive and unreacted
MFT.
Inadequate mixing can greatly decrease the efficiency of the chemical additive
and even
short-circuit the entire dewatering process. Inadequate mixing also results in
inefficient
use of the chemical additives, some of which remain unmixed and unreacted and
cannot
be recovered. Known techniques have several disadvantages including the
inability to
achieve a controlled, reliable or adequate mixing of the chemical additive as
well as poor
efficiency and flexibility of the process.
Still another factor is the technique of handling the oil sand tailings after
chemical
addition. If oil sand tailings are not handled properly, dewatering may be
decreased or
altogether prevented. In some past trials, handling was not managed or
controlled and
resulted in unreliable dewatering performance. Some techniques such as in
CIBA's
Canadian patent application No. 2,512,324 (Schaffer et al.) have attempted to
simply
inject the chemical into the pipeline without a methodology to reliably adapt
to changing
oil sand tailings compositions, flow rates, hydraulic properties or the nature
of particular
chemical additive. Relying solely on this ignores the complex nature of mixing
and
treating oil sand tailings and significantly hampers the flexibility and
reliability of the
system. When the chemical addition and subsequent handling have been
approached in
such an uncontrolled, trial-and-error fashion, the dewatering performance has
been
unachievable.
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Yet another factor is the technique of handling or treating the MFT prior to
chemical
addition. MFT is drawn up by pumps or dredging equipment from tailings ponds
and
preferably sent via pipeline to the dewatering treatment area. The tailings
ponds, however,
may contain a variety of materials that could disrupt the MFT dewatering
process. For
instance, in the raw MFT there may be mats of bitumen, particularly in the
cold winter
months. There may also be other extraneous debris such as pieces of wood,
glass, plastic,
metal or natural organic material that can be entrained with the MFT as it is
taken from the
pond. Such unwanted materials can interfere with the MFT process equipment and
chemistry.
Given the significant inventory and ongoing production of MFT at oil sands
operations, there
is a need for techniques and advances that can enable MFT drying for
conversion into
reclaimable landscapes.
SUMMARY OF THE INVENTION
The present invention responds to the above need by providing processes for
drying oil
sand fine tailings.
Accordingly, the invention provides a process for drying oil sand fine
tailings, comprising
providing an in-line flow of the fine tailings; continuously introducing a
flocculant solution
comprising an flocculation reagent into the in-line flow of the fine tailings,
to cause
dispersion of the flocculant solution and commence flocculation of the fine
tailings;
subjecting the fine tailings to flocculation conditioning in-line to cause
formation and
rearrangement of flocs and increasing the yield shear strength to form an in-
line flow
comprising flocculated fine tailings; subjecting the flocculated fine tailings
to water release
conditioning to stimulate release of water while avoiding over-shearing of the
flocs; and
depositing the fine tailings to allow the release of water, formation of a non-
flowing fine
tailings deposit and drying of the non-flowing fine tailings deposit.
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This process enables effective action of the flocculation reagent to occur in-
line by
allowing dispersion, flocculation and water release, resulting in reliable
deposition and
drying of the fine tailings deposit.
The invention also provides a process for drying oil sand fine tailings,
comprising
providing an in-line flow of the fine tailings; continuously introducing a
flocculant solution
comprising a flocculation reagent into the in-line flow of the fine tailings
by rapid mixing,
to cause dispersion of the flocculant solution and commence flocculation of
the fine
tailings to form flocs, the rapid mixing comprising: providing a mixing zone
in the in-line
flow of the fine tailings, the mixing zone comprising turbulence eddies which
flow into a
forward-flow region; continuously introducing the flocculant solution into the
in-line flow
such that the flocculant solution disperses within the turbulence eddies and
into the
forward-flow region while avoiding over-shearing the flocs, to produce a
flocculating
mixture; inputting a sufficient energy to the flocculating mixture to cause
formation and
rearrangement of the flocs while stimulating water release without over-
shearing the
flocs; and allowing the fine tailings to release water and dry.
This rapid mixing enables the flocculant solution to be dispersed throughout
the fine
tailings in-line such that the subsequent input of energy allows improved
water release
and drying.
Various embodiments, features and aspects of oil sand fine tailings drying
process will
be further described and understood in view of the figures and description.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig 1 is a general representative graph of shear yield stress versus time
showing the
process stages for an embodiment of the present invention.
Fig 2 is a general representative graph of shear yield stress versus time
showing the
process stages for another embodiment of the present invention.
Fig 3 is a graph showing the relationship between shear stress and shear rate
for an
MFT sample, illustrating the non-Newtonian nature of MFT at higher solids
contents.
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Fig 4 is a side cross-sectional view of a pipeline reactor for performing
embodiments of
the process of the present invention.
Fig 5 is a partial perspective transparent view of a pipeline reactor for
performing
embodiments of the process of the present invention.
Fig 6 is a partial perspective transparent view of the pipeline reactor of Fig
5 with cross-
sections representing the relative concentration of flocculant solution and
MFT at two
different distances from the injection location.
Fig 7 is a close-up view of section VII of Fig 6.
Fig 8 is a close-up view of section VIII of Fig 6.
Fig 9 is a side cross-sectional view of a variant of a pipeline reactor for
performing
embodiments of the process of the present invention.
Fig 10 is a side cross-sectional view of another variant of a pipeline reactor
for
performing embodiments of the process of the present invention.
Fig 11 is a side cross-sectional view of another variant of a pipeline reactor
for
performing embodiments of the process of the present invention.
Fig 12 is a partial perspective transparent view of yet another variant of a
pipeline
reactor for performing embodiments of the process of the present invention.
Fig 13 is a graph of shear yield stress versus time comparing different mixing
speeds in
a stirred tank for mature fine tailings treated with flocculant solution.
Fig 14 is a bar graph of water release percentage versus mixing speeds for
mature fine
tailings treated with flocculant solution.
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Fig 15 is a graph of yield shear stress versus time in a pipe for different
pipe flow rates
for mature fine tailings treated with flocculant solution.
Fig 16 is a schematic representation of treating mature fine tailings with a
flocculant
solution.
Fig 17 is another schematic representation of treating mature fine tailings
with a
flocculant solution.
Fig 18 is another schematic representation of treating mature fine tailings
with a
flocculant solution.
Figs 19 and 20 are graphs of percent solids as a function of time for
deposited MFT
showing drying times according to trial experimentation.
Fig 21 is a graph of second moment M versus MFT flow rate for different
mixers.
DETAILED DESCRIPTION OF THE INVENTION
Referring to Figs 1 and 2, the general stages of an embodiment of the process
will be
described. The oil sand fine tailings are treated with a flocculant solution
by in-line
dispersion of the flocculant solution into the fine tailings, then
conditioning the fine
tailings by inputting a sufficient energy to cause the formation and
rearrangement of
flocculated fine tailing solids to increase the yield shear strength while
enabling water
release without over-shearing the flocculated solid structure that can then
form a non-
flowing deposit. The flocculated fine tailings are deposited to allow the
water release and
the formation of a non-flowing deposit which is allowed to dry.
The present specification should be read in light of the following
definitions:
"Oil sand fine tailings" means tailings derived from oil sands extraction
operations and
containing a fines fraction. They include mature fine tailings from tailings
ponds and fine
tailings from ongoing extraction operations that may bypass a pond, and
combinations
thereof. In the present description, the abbreviation MFT will be generally
used, but it
CA 02678818 2015-10-29
should be understood that the fine tailings treated according the process of
the present
invention are not necessarily obtained from a tailings pond.
"In-line flow" means a flow contained within a continuous fluid transportation
line such as
a pipe or another fluid transport structure which preferably has an enclosed
tubular
construction.
"Flocculant solution comprising a flocculation reagent" means a solution
comprising a
solvent and at least one flocculation reagent. The flocculant solution may
contain a
combination of different flocculation reagents, and may also include
additional
chemicals. The solvent comprises water but may include other compounds as
well, as
desired. Flocculation reagents are compounds that have structures which form a
bridge
between particles, uniting the particles into random, three-dimensional porous
structures
called "flocs". Thus, the flocculation reagents do not include chemicals that
merely act
electrostatically by reducing the repulsive potential of the electrical double
layer within
the colloid. The flocculation reagents have structures for forming floc
arrangements upon
dispersion within the MFT, the flocs being capable of rearranging and
releasing water
when subjected to a specific window of conditioning. The preferred
flocculation reagents
may be selected according to given process conditions and MFT composition.
"Molecular weight" means the average molecular weight determined by
measurement
means known in the art.
"Dispersion", as relates to the flocculant solution being introduced into the
in-line flow of
MFT, means that upon introduction within the MFT the flocculant solution
transitions
from droplets to a dispersed state sufficient to avoid under-reacting or over-
reacting in a
localized part of the MFT which would impede completion of the flocculation in
the
subsequent conditioning stage to reliably enable dewatering and drying.
"Flocculation conditioning" is performed in-line and involves the flocculation
reagent
reacting with the MFT solids to form flocs and through rearrangement reactions
increase
the strength of the flocculating MFT.
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"Water release conditioning" means that energy is input into the flocculated
MFT so as to
initiate rearrangement and breakdown of the structure to release water from
the
flocculated matrix. The energy input may be performed by in-line shearing or
by other
means. "Release of water" in this context means that water selectively
separates out of
the flocculated MFT matrix while leaving the flocs sufficiently intact for
deposition.
"Over-shearing", which is a stage that defines the limit of the water release
conditioning
stage and is to be avoided, means that additional energy has been input into
the
flocculated MFT resulting in dispersing the structure and resuspending the
fines within
the water. Over-sheared MFT releases and resuspends fines and ultrafines
entrapped
by the flocs back into the water, essentially returning to its original fluid
properties but
containing non-functional reagent.
"Non-flowing fine tailings deposit" means a deposited flocculated MFT that has
not been
over-sheared and has sufficient strength to stand while drying. While the
water release
from the flocs is triggered by conditioning, the MFT deposit may have parts
that continue
to release water after it has been deposited. The drying of the MFT deposit
may then
occur by gravity drainage, evaporation and permeation. The removal of water
from the
flocculated MFT may also occur before deposition, for instance when a stream
of
release water separates from the flocculated MFT upon expelling for
deposition.
"Yield shear strength" means the shear stress or pressure required to cause
the MFT to
flow.
In one embodiment of the process of the present invention, the oil sand fine
tailings are
primarily MFT obtained from tailings ponds given the significant quantities of
such
material to reclaim. The raw MFT may be pre-treated depending on the
downstream
processing conditions. For instance, oversized materials may be removed from
the raw
MFT. In addition, specific components of the raw MFT may be selectively
removed
depending on the flocculation reagent to be used. For instance, when a
cationic
flocculation reagent is used, the raw MFT may be treated to reduce the
residual bitumen
content which could cause flocculant deactivation. The raw MFT may also be pre-
treated
to provide certain solids content or fines content of the MFT for treatment or
hydraulic
properties of the MFT. More regarding possible pre-treatments of the raw MFT
will be
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understood in light of descriptions of the process steps herein below. The
fine tailings
may also be obtained from ongoing oil sand extraction operations. The MFT may
be
supplied from a pipeline or a dedicated pumped supply.
In one embodiment, the process is conducted in a "pipeline reactor" followed
by
deposition onto a deposition area. The pipeline reactor may have various
configurations,
some of which will be described in detail herein below.
The MFT to be treated is provided as an in-line flow in an upstream part of
the pipeline
reactor. The properties of the MFT and its particular flow characteristics
will significantly
depend on its composition. At low mineral concentrations the yield stress to
set the MFT
fluid in motion is small and hydraulic analysis can approximate the fluid
behaviour of a
Newtonian fluid. However, as mineral concentration increases a yield stress
must be
overcome to initiate flow. These types of fluids are a class of non-Newtonian
fluids that
are generally fitted by models such as Bingham fluid, Herschel-Bulkley yield-
power law
or Casson fluid. The rheological relationship presented in Fig 3, illustrating
a yield stress
response to shear rate for various mineral concentrations in a MFT sample,
considers
MFT as a Bingham fluid. MFT may also be modelled in viscometric studies as a
Herschel-Bulkley fluid or a Casson Fluid.
Empirical data and modelling the rheology of in-line MFT have confirmed that
when a
flocculant solution is added by conventional side injection into a Bingham
fluid MFT,
solution dispersion is very sensitive to flow rate and diameter ratios as well
as fluid
properties.
In one aspect of the process, particularly when the flocculant solution is
formulated to
behave as a non-Newtonian fluid, the dispersion stage is performed to cause
rapid
mixing between two non-Newtonian fluids. Rapid non-Newtonian mixing may be
achieved by providing a mixing zone which has turbulence eddies which flow
into a
forward-flow region and introducing the flocculant solution such that the
turbulence
eddies mix it into the forward-flow region. Preferably, the flocculant
solution is introduced
into the turbulence eddies and then mixes into the forward-flow region.
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Figs 4 and 5 illustrate a pipeline reactor design that enables such rapid
mixing of non-
Newtonian fluids. The MFT is supplied from an upstream pipeline 10 into a
mixing zone
12. The mixing zone 12 comprises an injection device 14 for injecting the
flocculant
solution. The injection device may also be referred to as a "mixer". The
injection device
14 may comprise an annular plate 16, injectors 18 distributed around the
annular plate
16 and a central orifice 20 defined within the annular plate 16. The MFT
accelerates
through the central orifice 20 and forms a forward-flow region 24 and an
annular eddy
region 22 made up of turbulence eddies. The injectors 18 introduce the
flocculant
solution directly into the eddy region 22 for mixing with the turbulent MFT.
The
recirculation of the MFT eddies back towards the orifice 20 results in mixing
of the
flocculant solution into the MFT forward-flow. The forward-flow region 24
expands as it
continues along the downstream pipe 26. For some mixer embodiments, the
forward-
flow region may be a vena-contra region of a jet stream created by an orifice
or baffle.
The main flow of the MFT thus draws in and mixes with the flocculant solution,
causing
dispersion of the flocculant solution, and flocculation thus commences in a
short
distance of pipe. The injection device 14 illustrated in Figs 4 and 5 may also
be referred
to as an "orifice mixer". For the mixer of Figs 4 and 5, the preferred range
of orifice
diameter "d" to downstream pipe diameter "D" is 0.25 ¨ 0.75.
Figs 6-8 illustrate the performance of an orifice mixer based on computational
fluid
dynamic (CFD) modeling and empirical data obtained from a test installation on
a MFT
pipeline reactor. The MFT flow rate in a 2 inch diameter pipe was 30 LPM and
flocculant
solution was injected at about 3 LPM. The 2 inch long orifice mixer had an
orifice to
downstream pipe diameter ratio d/D = 0.32 with six 0.052 inch diameter
injectors located
on a 1.032 inch diameter pitch circle. Due to the density difference between
the MFT
and flocculant solution, a useful method of characterizing the degree of
mixing is to
determine the second moment M of the concentration C over the pipe cross
section A in
the following equation where is the
mean concentration for the fully mixed case (thus
directionally M = 0 is desired).
1 (C
M ¨f ¨1 cif"
AAC
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= 14
In Figs 6-8, the dark areas represent MFT that has not mixed with the
flocculant solution
(referred to hereafter as "unmixed MFT"). Just downstream of the mixer, the
unmixed
MFT region is limited to the central core of the pipe and is surrounded by
various
flocculant solution-MFT mixtures indicative of local turbulence in this zone.
As the
flocculant solution is miscible in MFT, the jetting of the flocculant solution
into the
turbulent zone downstream may cause the flocculant solution to first shears
the
continuous phase into drops from which diffusion mixing disperses the
flocculant into the
MFT.
The CFD model was based on a Power-law-fluid for the flocculant solution and a
Bingham-fluid for the MFT without reactions. The Bingham-fluid approximation
takes into
account the non-Newtonian nature of the MFT as requiring a yield stress to
initiate flow.
Bingham-fluids are also time-independent, having a shear stress independent of
time or
duration of shear. Preferably, the CFD model is primarily used to determine
and improve
initial mixing between the flocculant solution and the MFT.
The injection device 14 may have a number of other arrangements within the
pipeline
reactor and may include various elements such as baffles (not shown). In one
optional
aspect of the injection device shown in Fig 9, at least some of the injectors
are oriented
at an inward angle such that the flocculant solution mixes via the turbulence
eddies and
also jet toward the core of the MFT flow. In another aspect shown in Fig 10,
the orifice
has a reduced diameter and the injectors may be located closer to the orifice
than the
pipe walls. The injectors of the mixer may also be located at different radial
distances
from the centre of the pipeline. In another aspect, instead of an annular
plate with a
central orifice, the device may comprise baffles or plates having one or
multiple
openings to allow the MFT to flow through the mixing zone while creating
turbulence
eddies. In another aspect shown in Fig 11, the injectors face against the
direction of
MFT flow for counter-current injection. Fig 12 illustrates another design of
injection
device that may be operated in connection with the process of the present
invention. It
should also be noted that the injection device may comprise more than one
injector
provided in series along the flow direction of the pipeline. For instance,
there may be an
upstream injector and a downstream injector having an arrangement and spacing
sufficient to cause the mixing. In a preferred aspect of the mixing, the
mixing system
allows the break-up of the plug flow behaviour of the Bingham fluid, by means
of an
CA 02678818 2015-10-29
orifice or opposing "T" mixer with MFT and flocculant solution entering each
arm of the
Tee and existing down the trunk. Density differentials (MFT density depends on
concentration ¨ 30 wt% corresponds to a specific gravity of ¨ 1.22 and the
density of the
flocculant solution may be about 1.00) together with orientation of the
injection nozzles
play a role here and are arranged to allow the turbulence eddies to mix in and
disperse
the flocculant solution.
The following table compares the second moment values for the orifice mixer
(Fig 4) and
a quill mixer (Fig 12) at various locations downstream of the injection
location for the
same flows of MFT and flocculant reagent solution.
Downstream Distance
L/D Orifice Mixer (Fig 4) Quill Mixer (Fig 12)
1 11.75 5.75
2 3.17 3.65
3 1.75 2.89
5 1.10 2.24
10 0.65 1.39
Near to the injection point of the orifice mixer as shown on Fig 7, there is a
larger region
of unmixed polymer surrounding a strong MFT jet with a "M" value of 11.75,
However,
the mixing with the MFT jet occurs very rapidly so that by 5 diameters
downstream of the
injection point shown as Fig 8 with a second moment M value of 1.10. In
contrast, for the
quill mixer as shown Fig 12, the initial mixing with a second moment M value
of 5.75 only
improves to 2.24 by 5 diameters downstream of the injection point. Mixing by
the orifice
mixer is preferred to the quill mixer.
Preferably, the mixing is sufficient to achieve an M < 2 at LID = 5, and still
preferably the
mixing is sufficient to achieve an M < 1.5 at L/D = 5, for the pipeline
reactor. Controlling
the mixing at such preferred levels allows improved dispersion, flocculation
and
dewatering performance.
Initial mixing of the flocculant solution into the MFT is important for the
flocculation
reactions. Upon its introduction, the flocculant solution is initially rapidly
mixed with the
CA 02678818 2015-10-29
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fine tailings to enhance and ensure the flocculation reaction throughout the
downstream
pipeline. When the flocculant solution contacts the MFT, it starts to react to
form flocs
made up of many chain structures and MFT minerals. If the flocculant solution
is not
sufficiently mixed upon introduction into the pipe, the flocculation reaction
may only
develop in a small region of the in-line flow of tailings. Consequently, if
the tailings are
subsequently mixed downstream of the polymer injection, mixing will be more
difficult
since the rheology of the tailings will have changed. In addition, the flocs
that formed
initially in the small region can be irreversibly broken down if subsequent
mixing imparts
too much shear to the flocs. Over-shearing the flocs results in resuspending
the fines in
the water, reforming the colloidal mixture, and thus prevents water release
and drying.
Thus, if adequate mixing does not occur upon introduction of the flocculant
solution,
subsequent mixing becomes problematic since one must balance the requirement
of
higher mixing energy for flocculated tailings with the requirement of avoiding
floc
breakdown from over-shearing.
The initial mixing may be achieved and improved by a number of optional
aspects of the
process. In one aspect, the injection device is designed and operated to
provide
turbulence eddies that mix and disperse the flocculant solution into the
forward flow of
MFT. In another aspect, the flocculation reagent is chosen to allow the
flocculant
solution to have decreased viscosity allowing for easier dispersion. The
flocculant
solution may also be formulated and dosed into the MFT to facilitate
dispersion into the
MFT. Preferably, the flocculation reagent is chosen and dosed in conjunction
with the
injection conditions of the mixer, such that the flocculant solution contains
sufficient
quantity of reagent needed to react with the MFT and has hydraulic properties
to
facilitate the dispersion via the mixer design. For instance, when a viscous
flocculant
solution displaying plastic or pseudo-plastic non-Newtonian behaviour is used,
the mixer
may be operated at high shear injection conditions to reduce the viscosity
sufficiently to
allow dispersion into the MFT at the given hydraulic mixing conditions. In yet
another
aspect, the flocculation reagent is chosen to form flocs having increased
shear
resistance. Increased shear resistance enables more aggressive, harsh mixing
and
reduces the chance of premature over-shearing of the resulting flocs. The
increased
shear resistance may be achieved by providing the flocculant with certain
charge
characteristics, chain lengths, functional groups, or inter- or intra-linking
structures. In
another aspect, the flocculation reagent is chosen to comprise functional
groups
CA 02678818 2015-10-29
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facilitating rearrangement and selective water release. In another aspect, the
flocculation
reagent is chosen to form large flocs facilitating rearrangement and partial
breakdown of
the large flocs for water release. In another aspect, the flocculation reagent
may be an
organic polymer flocculant. The polymer flocculant may have a high molecular
weight,
such as above 10,000,000, or a low molecular weight. The high molecular weight
polymers may tend to form more shear resistant flocs yet result in more
viscous
flocculant solutions at the desired dosages. Thus, such flocculant solutions
may be
subjected to higher shear injection to reduce the viscosity and the turbulence
eddies
may be given size and spacing sufficient to disperse the flocculant solution
within the
pipeline mixing zone.
In another aspect, the flocculation reagent may be chosen and dosed in
response to the
clay concentration in the MFT. The flocculation reagent may be anionic,
cationic, non-
ionic, and may have varied molecular weight and structure, depending on the
MFT
composition and the hydraulic parameters.
It should be noted that, contrary to conventional teachings in the field of
MFT
solidification and reclamation, the improvement and predictability of the
drying process
rely more in the process steps than in the specific flocculation reagent
selected. Of
course, some flocculation reagents will be superior to others at commercial
scale,
depending on many factors. However, the process of the present invention
enables a
wide variety of flocculation reagents to be used, by proper mixing and
conditioning in
accordance with the process steps. By way of example, the flocculant reagent
may be
an organic polymer flocculant. They may be polyethylene oxides,
polyacrylamides,
anionic polymers, polyelectrolytes, starch, co-polymers that may be
polyacrylamide-
polyacrylate based, or another type of organic polymer flocculants. The
organic polymer
flocculants may be obtained from a flocculant provider and subjected to
selection to
determine their suitability to the specific commercial application.
Initial mixing was further assessed in a conventional stirred mix tank by
varying the initial
speed of the mixer. Fig 13 presents indicative lab test results comparing
rapid mixing
(230 RPM) and slow mixing (100 RPM). The test results with the mixer at the
higher
initial speed developed flocculated MFT with a higher shear yield strength
significantly
faster than tests with the mixer at a lower speed. For the lower speed, the
time delay
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was attributable to dispersing the flocculant solution into the MFT. Moreover,
Fig 14
indicates that the fast initial mixing also resulted in higher initial water
release rates,
which results in reduced drying times.
While the lab scale stirred tank demonstrated benefits from fast mixing, other
results
also demonstrated the effect of over-mixing or over-shearing, which would
break down
the flocculated MFT such that the MFT would not dewater. The lab scale stirred
tank is
essentially a batch back-flow reactor in which the mixer imparts shear firstly
to mix the
materials and secondly to maintain the flocculating particles in suspension
while the
reactions proceed to completion. As the operational parameters can be easily
adjusted,
the stirred tank provides a valuable tool to assess possible flocculation
reagent
performance. Lab scale stirred tank data may be advantageously coupled with
lab
pipeline reactor tests and CFD modelling for selecting particular operating
parameters
and flocculation reagents for embodiments of the continuous in-line process of
the
present invention.
The MFT supplied to the pipeline reactor may be instrumented with a continuous
flow
meter, a continuous density meter and means to control the MFT flow by any
standard
instrumentation method. An algorithm from the density meter may compute the
mineral
concentration in MFT and as an input to the flow meter determine the mass flow
of
mineral into the pipeline reactor. Comparing this operating data to
performance data for
the pipeline reactor developed from specific flocculation reagent properties,
specific MFT
properties and the specific pipeline reactor configurations, enables the
adjustment of the
flowrate to improve processing conditions for MFT drying. Operations with the
mixer in a
12 inch pipe line processing 2000 USgpm of MFT at 40% solids dewatered MFT
with a
pipe length of 90 meters.
Referring back to Figs 4 and 5, after introduction of the flocculation reagent
in the mixing
zone 12, the flocculating MFT continues into a conditioning zone 28. The
conditioning
stage of the process will be generally described as comprising two main parts:
flocculation conditioning and water release conditioning.
At this juncture, it is also noted that for Newtonian fluid systems, research
into
flocculated systems has developed some tools and relationships to help predict
and
CA 02678818 2015-10-29
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design processes. For instance, one relationship that has been developed that
applies to
some flocculated systems is a dimensionless number called the "Camp number".
The
Camp number relates power input in terms of mass flow and friction to the
volume and
fluid absolute viscosity. In non-Newtonian systems such as MFT-polymer mixing
both
pipe friction and the absolute viscosity terms used in the Camp number depend
on the
specific flow regime. The initial assessment of the pipeline conditioning data
implies the
energy input may be related to modified Camp number. The modified Camp number
would consider the flocculating agent, the rheology of the flocculated MFT in
addition to
the flow and friction factors.
Flocculation conditioning occurs in-line to cause formation and rearrangement
of flocs
and increases the yield shear stress of the MFT. Referring to Figs 4 and 5,
once the
MFT has gone through the mixing zone 12, it passes directly to the
flocculation
conditioning zone 28 of the pipeline reactor. The flocculation conditioning
zone 28 is
generally a downstream pipe 26 with a specific internal diameter that provides
wall shear
to the MFT. In one aspect of the process, the flocculation conditioning
increases the
yield shear stress to an upper limit. The upper limit may be a single maximum
as shown
in Fig 1 or an undulating plateau with multiple local maximums over time as
shown in Fig
2. The shape of the curve may be considered a primary function of the
flocculant
solution with secondary functions due to dispersion and energy input to the
pipeline,
such as via baffles and the like.
Water release conditioning preferably occurs in-line after the flocculation
conditioning.
Referring to Figs 1 and 2, after reaching the yield shear upper limit,
additional energy
input causes the yield stress to decrease which is accompanied by a release of
water
from the flocculated MFT matrix. Preferably, the water release conditioning
occurs in-line
in a continuous manner following the flocculation conditioning and before
deposition. In
this case, the water release may commence in-line resulting in a stream of
water being
expelled from the outlet of the pipe along with depositing flocculated MFT.
The release
water will quickly flow away from the MFT deposit, especially on a sloped
deposition
area, while the MFT deposit has sufficient strength to stand on the deposition
area.
Here, it is preferred to have no high-shear units such as pumps in the
downstream pipe.
The hydraulic pressure at the MFT pipeline reactor inlet is preferably
established so that
no additional pumping which may over-shear the flocs would be required to
overcome
CA 02678818 2015-10-29
both static and differential line head losses prior to deposition. It is also
preferred not to
disturb the deposited MFT with further shearing, but rather to let the MFT
deposit dry after
in place, upon deposition. Alternatively, instead of being performed in-line,
the water
release conditioning may occur in a controlled shearing apparatus (not shown)
comprising
baffles, an agitator, a mixer, or a rotary separator, or a combination
thereof. The water
release conditioning may also occur after the flocculated MFT is deposited,
for instance by
a mechanical mechanism in an ordered fashion. For instance, the water release
conditioning may comprise driving a dozer through the non-flowing fine
tailings deposit. In
such a case, the flocculated MFT would be deposited as a gel-like mass at a
shear yield
strength allowing it to stand but tending not to promote water release until
additional energy
input is applied. By conditioning the flocculated MFT back down from a yield
stress upper
threshold, the process avoids the formation of a gel-like water-retaining
deposit, reliably
enabling water release and accelerated drying of the MFT.
Care should also be taken not to expel the MFT from a height that would
accelerate it to
over shear due to the impact on the deposition area or the previously
deposited MFT.
The flocculation conditioning and the water release conditioning may be
controlled in-line by
varying the flow rate of the MFT. Preferably, the flow rate may be as high as
possible to
increase the yield stress evolution rate of the flocculating MFT, while
avoiding over-shear
based on the hydraulic shear of the pipeline to the deposition area. Tests
were conducted in
a pipeline reactor to determine conditioning response. Fig 15 identifies the
response to
varying the pipeline flow rate. A 34 wt% solids MFT was pumped through a 2
inch diameter
pipe at a flow rate of about 26 LPM for the low flow test and about 100 LPM
for the high
flow test. A 0.45% flocculant solution was injected at about 2.6 LPM for the
low flow test
and at about 10 LPM for the high flow test. At high flows, the maximum yield
shear stress of
the flocculated MFT occurs earlier than at low flows. This observed response
indicates that
the total energy input is an important parameter with input energy being
hydraulic losses
due the fluid interacting with the pipe wall in this case.
Referring to Figs 4 and 5, the conditioning zone 28 may include baffles,
orifice plates, inline
static mixers or reduced pipe diameter (not shown) particularly in situations
where layout
may constrain the length of the pipeline reactor, subject to limiting the
energy input so the
flocculated MFT is not over sheared. If the flocculated MFT is over sheared,
CA 02678818 2015-10-29
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the flocs additionally break down and the mineral solids revert back to the
original
colloidal MFT fluid which will not dewater.
In one preferred embodiment of the process, when the yield stress of the
flocculated
MFT at release is lower than 200 Pa, the strength of the flocculated MFT is
inadequate
for dewatering or reclamation of the deposited MFT. Thus, the yield shear
stress of the
flocculated MFT should be kept above this threshold. It should be understood,
however,
that other flocculation reagents may enable a flocculated MFT to dewater and
be
reclaimed at a lower yield stress. Thus, although Figs 1 and 2 show that a
yield stress
below 200 Pa is in the over-shearing zone, these representative figures do not
limit the
process to this specific value. When an embodiment of the process used 20% -
30%
charge anionic polyacrylamide high molecular weight polymers, the lower
threshold of
the yield shear stress window was about 200 Pa, and the flocculated MFT was
deposited preferably in the range of about 300 Pa and 500 Pa, depending on the
mixing
and MFT solids content. It should also be noted that the yield shear stress
has been
observed to reach upper limits of about 400 - 800 Pa in the pipeline reactor.
It should
also be noted the yield shear stress of the MFT after the initial water is
released when
the MFT is deposited has been observed to exceed 1000 Pa.
In general, the process stage responses for a given flocculation reagent and
MFT are
influenced by flocculant type, flocculant solution hydraulic properties, MFT
properties
including concentration, particle size distribution, mineralogy and rheology,
dosing levels
and energy input.
The process provides the advantageous ability to predict and optimize the
performance
of a given flocculant reagent and solution for dewatering MFT. The mixing zone
ensures
the efficient use of the flocculation reagent and the pipeline conditions of
length, flow
rate and baffles if required provide the shear necessary to maximize water
release and
avoid over-shearing when the MFT is discharged from the pipeline reactor.
In one embodiment of the process, after the in-line water release
conditioning, the
flocculated MFT is deposited to form a non-flowing MFT deposit. The
conditioned MFT is
suitable for direct deposition on a deposition area, where water is released
from the
solids, drained by gravity and further removed by evaporation to the air and
optionally
CA 02678818 2015-10-29
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permeates into the deposition area. The deposition area may comprise sand
surfaces to
facilitate draining and permeation. The MFT deposit dries so as to reach a
stable
concentration of the MFT solids for reclamation purposes. In other alternative
embodiments for dewatering flocculated MFT, solid-liquid separation equipment
may be
used provided the shear imposed does not over-shear the flocculated MFT. The
MFT
pipeline reactor may be used to treat MFT or other tailings or colloidal
fluids having non-
Newtonian fluid behaviour for deposition or for other dewatering devices such
as filters,
thickeners, centrifuges and cyclones.
In one aspect of the process, the MFT is continuously provided from a pond and
has a
solids content over 20 wt%, preferably within 30 - 40 wt%. The MFT is
preferably
undiluted. After the flocculant solution is dispersed into the MFT, the
flocculated MFT
releases water thus allows in-line separation of the water from the
flocculated MFT.
Embodiments and aspects of the present invention will be further understood
and
described in light of the following examples.
EXAMPLES
Example 1:
As mentioned in the above description, lab scale stirred tank tests were
conducted to
assess mixing of a flocculant solution into MFT. The lab mixer was run at
initial speeds
of 100 RPM or 230 RPM. The dosage of 30% charge anionic polyacrylamide-
polyacrylate shear resistant co-polymer was about 1000 g per dry ton. Figs 13
and 14
show that the fast initial mixing shortens the yield stress evolution to
enable dewatering
and also increases the water release from the MFT.
Example 2:
As mentioned in the above description, lab scale stirred tank tests were
conducted to
assess mixing of different dosages of flocculant solution into MFT. The lab
mixer was
run at speeds of 100 RPM or 230 RPM for flocculant solutions containing
different doses
of dissolved flocculation reagent. The dosages of flocculant ranging from 800
to 1200 g
per dry tonne of MFT indicated adequate mixing and flocculation for
dewatering. The
flocculation reagent here was a 30% charge anionic polyacrylamide-polyacrylate
shear
CA 02678818 2015-10-29
= 23
resistant co-polymer with a molecular weight over 10,000,000. A dosage range
of 1000 g
per dry tonne 20% was appropriate for various 30% charge polyacrylamides for
MFT
with clay content of 50 to 75 %.
Example 3:
As mentioned in the above description, continuous flow pipeline reactor tests
were
conducted. Results are shown in Fig 15 comparing high and low flow rates. A 34
wt%
solids MFT was pumped through a 2 inch diameter pipe at a flow rate of 26 LPM
for the
low flow test and 100 LPM for the high flow test. A 0.45% organic polymer
flocculant
solution was injected at 2.6 LPM for the low flow test and at 10 LPM for the
high flow
test. The distance from injection to deposition was 753 inches or 376.5 pipe
diameters.
The 2 inch long orifice mixer had an orifice to downstream pipe diameter ratio
d/D = 0.32
with six 0.052 inch diameter injectors located on a 1.032 inch diameter pitch
circle. For
the high flow test the six injector diameters were increased to 0.100 inch.
Example 4:
As mentioned in the above description, computational fluid dynamic (CFD)
modelling
was conducted. The CFD modeling considered the flocculant solution as a Power-
law-
fluid and the MFT as a Bingham-fluid in the mixing zone and confirmed both the
adequate mixing of the injection device of Figs 4 and 5 and the inadequate
mixing of the
conventional side branch tube as discussed in the Background section under the
same
conditions. The MFT flow rate in a 2 inch diameter pipe was 30 LPM and polymer
solution was injected at 3 LPM. The 2 inch long orifice mixer had an orifice
to
downstream pipe diameter ratio d/D = 0.32 with six 0.052 inch diameter
injectors located
on a 1.032 inch diameter pitch circle. The MFT had a density of 1250 kg/m3 and
a yield
stress of 2 Pa while the polymer solution had a density of 1000 kg/m3, with a
power-law
index n = 0.267 and a consistency index of 2750 kg s2/m.
Furthermore, the visualization shown in Figs 6-8 is only possible by CFD
modelling due
to the opaqueness of actual MFT. For MFT, the CFD model incorporates non-
Newtonian
fluid behaviours into the hydraulic analysis to develop a robust design for a
variety of
possible combinations and permutations between various MFT properties and
flocculation reagent solutions.
CA 02678818 2015-10-29
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Example 5:
As described above, the present invention resides in the process steps rather
than in the
specific flocculation reagent selected. A person skilled in the art may select
a variety of
flocculation reagents that enable in-line dispersion, flocculation, water
release and non-
flowing deposition. One selection guideline method includes taking an MFT
sample
representative of the commercial application and using a fast-slow mixer test
to observe
the water release capability of the flocculant. In the fast-slow mixer test,
the flocculant is
injected into the mixer running at a fast mixing rate and after a delay of 7
seconds the
mixer is switched to slow mixing. Water release may then be assessed. For
instance,
test have been run at 230 RPM (corresponding to a shear rate of 131.5 s-1) for
fast
mixing and 100 RPM (corresponding to a shear rate of 37. s-1) for slow mixing.
A fast-
slow mixer test was conducted on 10%, 20%, 30% and 40% charge anionic
polyacrylamide flocculants and the 30% charge anionic polyacrylamides enabled
superior water release. The use of such 30% charge anionic polyacrylamides in
the
pipeline reactor and CFD modeling validated this approach. In addition, the
fast-slow
mixer test was conducted on high and low molecular weight linear anionic
polyacrylamide flocculants and the high molecular weight polyacrylamides
enabled
superior water release. The fast-slow mixer test may be combined with the CFD
model
to test the mixing of the flocculant solution at the density of the desired
formulation. Such
cross-validation of flocculation reagents and solutions helps improve the
process
operating conditions and validate preferred flocculation reagents and
solutions.
Example 6:
Trials were performed and showed that a flocculation reagent could be injected
into MFT
in-line followed by pipeline conditioning, deposition and drying. Figs 16-18
schematically
illustrate different experimental setups that were used. For Figs 16 and 17,
the
flocculated MFT was deposited onto beaches and for Fig 18 into a deposition
cell.
The MFT was about 36 wt% solids and was pumped from a pond at flow rates
between
300 and 720 gal/min. The flocculant solution was injected in-line at different
locations.
One of the flocculant reagents used was a 30% charge anionic polyacrylamide-
sodium
polyacrylate co-polymer with a molecular weight over 10,000,000. The
flocculated MFT
ws conditioned along a pipeline and then expelled out of spigots arranged in
series.
CA 02678818 2015-10-29
In order to monitor the progress of the drying, samples were taken and
analyzed for
percent solids. The drying times to achieve 75 wt% solids ranged from 5 to 7.5
days
depending on the sample location. Deposition areas having a slope showed
faster
drying. Figs 19 and 20 show some results at two different sample points of the
drying
times of deposited MFT.
Dosages between 0.6 Kg to 1.1 Kg per dry tonne of MFT provided preferred
drainage
results, and much cleaner effluent water than those outside this range. Trials
revealed
that incorrect dosage may reduce dewatering for a number of reasons. If the
dosage is
too low, some of the MFT goes unflocculated and overall there is a lack of
dewatering
performance. Overdosing flocculant applications may also lead to reduced
dewatering
due to allowing water to become bound up in semi-gelled masses with the solids
making
it more difficult to provide conditioning sufficient to allow water release
with the given
pipeline dimensions and hydraulic conditions. Both of these situations were
observed
and dosage adjustments were made to compensate. In addition, water quality
depends
on dosage control. Overdosing or inadequate mixing (resulting in localised
overdosing)
resulted in poor water quality with at times over 1 wt% solids. Increased
dosing control,
the preferred dosage range and rapid initial mixing helped resolve water
quality issues
and improve dewatering and drying of the deposited MFT. Other observations
noted that
the deposited MFT dewatered and dried despite significant precipitation, thus
resisting
re-hydration from precipitation.
Reclamation of the MFT deposits was further observed as vegetation from seeds
tossed
on the deposition area was later noted to be growing well.
Example 7:
One of the challenges to successful treating of MFT is the process variations
encountered in operations. It may be desired to use a side injection nozzle to
for mixing
liquids into MFT. Using the mixing algorithm developed for the MFT pipeline
reactor
model, Fig 21 compares a typical side injection nozzle to the orifice nozzle
of Fig 4 on a
2 inch pipeline for a range of MFT flows based on:
¨ The MFT is 30 wt% solids and modeled as a Herschel-Bulkley fluid with a
yield
stress of 2 Pa and high shear rate viscosity of 10 mPa s. Density was 1250
kg/m3.
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26
¨ The flocculant solution was modeled as Power Law fluid with n = 0.267 and
consistency index (k) of 2750 kg s2/m. Density was 1000 kg/m3 and the flow
rate
was 1/10 the MFT volume flow rate
¨ The orifice mixer had a 0.32 orifice ratio.
¨ The flow area for injecting the polymer solution was the same for both
mixers.
Fig 21 illustrates that the orifice mixer of Fig 4 provides significantly
preferred mixing
than the conventional side injection nozzle over the range of MFT flows.
The process of the present invention, which is a significant advance in the
art of MFT
management and reclamation, has been described with regard to preferred
embodiments and aspects and examples. The description and the drawings are
intended to help the understanding of the invention rather than to limit its
scope. It will be
apparent to one skilled in the art that various modifications may be made to
the invention
without departing from what has actually been invented.
