Note: Descriptions are shown in the official language in which they were submitted.
METHOD OF MEASURING A SLURRY FEED FOR A SOLID-LIQUID
SEPARATION PROCESS
BACKGROUND
Field of Disclosure
[0001] The disclosure relates generally to the field of solid-liquid
separation of slurries,
for instance oil sand streams.
Description of Related Art
[0002] This section is intended to introduce various aspects of the art,
which may be
associated with the present disclosure. This discussion is believed to assist
in providing a
framework to facilitate a better understanding of particular aspects of the
present disclosure.
Accordingly, it should be understood that this section should be read in this
light, and not
necessarily as admissions of prior art.
[0003] Solid-liquid separation of slurries, such as mining slurries, is
often desired. For
instance, it is often desirable to separate solids from liquids in oil sand
streams. Additional
background on oil sand processes will now be provided.
[0004] Modern society is greatly dependent on the use of hydrocarbon
resources for fuels
and chemical feedstocks. Hydrocarbons are generally found in subsurface
formations that can be
termed "reservoirs". Removing hydrocarbons from the reservoirs depends on
numerous physical
properties of the subsurface formations, such as the permeability of the rock
containing the
hydrocarbons, the ability of the hydrocarbons to flow through the subsurface
formations, and the
proportion of hydrocarbons present, among other things. Easily harvested
sources of
hydrocarbons are dwindling, leaving less accessible sources to satisfy future
energy needs. As the
costs of hydrocarbons increase, the less accessible sources become more
economically attractive.
[0005] Recently, the harvesting of oil sand to remove heavy oil has
become more
economical. Hydrocarbon removal from oil sand may be performed by several
techniques. For
example, a well can be drilled to an oil sand reservoir and steam, hot air,
solvents, or a
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combination thereof, can be injected to release the hydrocarbons. The released
hydrocarbons may
be collected by wells and brought to the surface. In another technique, strip
or surface mining
may be performed to access the oil sand, which can be treated with water,
steam or solvents to
extract the heavy oil.
[0006] Oil sand extraction processes are used to liberate and separate
bitumen from oil
sand so that the bitumen can be further processed to produce synthetic crude
oil or mixed with
diluent to form "dilbit" and be transported to a refinery plant. Numerous oil
sand extraction
processes have been developed and commercialized, many of which involve the
use of water as
a processing medium. Where the oil sand is treated with water, the technique
may be referred to
as water-based extraction (WBE). WBE is a commonly used process to extract
bitumen from
mined oil sand. Other processes are non-aqueous solvent-based processes. An
example of a
solvent-based process is described in Canadian Patent Application No.
2,724,806 (Adeyinka et
al, published June 30, 2011 and entitled "Process and Systems for Solvent
Extraction of Bitumen
from Oil Sands"). Solvent may be used in both aqueous and non-aqueous
processes.
[0007] One WBE process is the Clark hot water extraction process (the
"Clark Process").
This process typically requires that mined oil sand be conditioned for
extraction by being crushed
to a desired lump size and then combined with hot water and perhaps other
agents to form a
conditioned slurry of water and crushed oil sand. In the Clark Process, an
amount of sodium
hydroxide (caustic) may be added to the slurry to increase the slurry pH,
which enhances the
liberation and separation of bitumen from the oil sand. Other WBE processes
may use other
temperatures and may include other conditioning agents, which are added to the
oil sand slurry,
or may operate without conditioning agents. This slurry is first processed in
a Primary Separation
Cell (PSC), also known as a Primary Separation Vessel (PSV), to extract the
bitumen from the
slurry.
[0008] In one bitumen extraction process, a water and oil sand slurry is
separated into
three major streams in the PSC: bitumen froth, middlings, and a PSC underflow.
[0009] Regardless of the type of WBE process employed, the process will
typically result
in the production of a bitumen froth that requires treatment with a solvent.
For example, in the
Clark Process, a bitumen froth stream comprises bitumen, solids, and water.
Certain processes
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use naphtha to dilute bitumen froth before separating the product bitumen by
centrifugation.
These processes are called Naphtha Froth Treatment (NFT) processes. Other
processes use a
paraffinic solvent, and are called Paraffinic Froth Treatment (PFT) processes,
to produce
pipelineable bitumen with low levels of solids and water. In the PFT process,
a paraffinic solvent
(for example, a mixture of iso-pentane and n-pentane) is used to dilute the
froth before separating
the product, diluted bitumen, by gravity. A portion of the asphaltenes in the
bitumen is also
rejected by design in the PFT process and this rejection is used to achieve
reduced solids and
water levels. In both the NFT and the PFT processes, the diluted tailings
(comprising water, solids
and some hydrocarbon) are separated from the diluted product bitumen.
[0010] Solvent is typically recovered from the diluted product bitumen
component before
the bitumen is delivered to a refining facility for further processing.
[0011] The PFT process may comprise at least three units: Froth
Separation Unit (FSU),
Solvent Recovery Unit (SRU) and Tailings Solvent Recovery Unit (TSRU). Mixing
of the solvent
with the feed bitumen froth may be carried out counter-currently in two stages
in separate froth
separation units. The bitumen froth comprises bitumen, water, and solids. A
typical composition
of bitumen froth is about 60 wt. % bitumen, 30 wt. % water, and 10 wt. %
solids. The paraffinic
solvent is used to dilute the froth before separating the product bitumen by
gravity. The foregoing
is only an example of a PFT process and the values are provided by way of
example only. An
example of a PFT process is described in Canadian Patent No. 2,587,166 to
Sury.
[0012] From the PSC, the middlings, comprising bitumen and about 10-30
wt. % solids,
or about 20-25 wt. % solids, based on the total wt. % of the middlings, is
withdrawn and sent to
the flotation cells to further recover bitumen. The middlings are processed by
bubbling air through
the slurry and creating a bitumen froth, which is recycled back to the PSC.
Flotation tailings (FT)
from the flotation cells, comprising mostly solids and water, are sent for
further treatment or
disposed in an External Tailings Area (ETA).
[0013] In ETA tailings ponds, a liquid suspension of oil sand fines in
water with a solids
content greater than 2 wt. %, but less than the solids content corresponding
to the Liquid Limit
are called Fluid Fine Tailings (FFT). FFT settle over time to produce Mature
Fine Tailings (MFT),
having above about 30 wt. % solids.
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[0014] As described above, solid-liquid separation of slurries is often
desired. Successful
solid-liquid separation depends heavily on the sluny feed to the solid-
separation process. One or
more additives are typically used to achieve physiochemical change in the
slurry such as
flocculation, agglomeration, or aggregation, to facilitate solid-liquid
separation. One factor of
interest is the amount of additive(s) that is required to achieve good process
performance for a
specific slurry feed. Additive dosage is typically determined offline and
applied to a consistent
slurry feed. However, when slurry feeds change quickly and frequently, such an
approach may
no longer be effective or practical.
SUMMARY
[0015] It is an object of the present disclosure to provide a method of
measuring a slurry,
intended as a feed to a solid-liquid separation process.
[0016] Disclosed is a method comprising:
a) providing a slurry intended as a feed to a solid-liquid separation process;
b) removing a slip stream from the sluiTy; and
c) measuring at least a portion of the slip stream at a plurality of additive
dosage
levels to obtain a characteristic indicative of a degree of flocculation,
agglomeration, or aggregation for each of the plurality of additive dosage
levels.
[0017] The foregoing has broadly outlined the features of the present
disclosure so that
the detailed description that follows may be better understood. Additional
features will also be
described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] These and other features, aspects and advantages of the disclosure
will become
apparent from the following description, appending claims and the accompanying
drawings,
which are briefly described below.
[0019] Fig. 1 is a flow chart of a method of measuring a slurry.
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F0020] Fig. 2 is a graph of median chord length as a function of additive
dosage, as
measured by FBRM.
[0021] Fig. 3 is a graph of average pixel value standard deviation as a
function of additive
dosage, as measured by PVM.
[0022] Fig. 4 is a graph of average pixel value standard deviation as
function of flocculant
dosage.
[0023] Fig. 5 is a graph of additive dosage as a function of slurry SFR.
[0024] Fig. 6 is a flow diagram of a method of measuring a slurry.
[0025] Fig. 7 is a flow diagram of a method of measuring a slurry.
[0026] Fig. 8 is a flow diagram of a method of measuring a slurry.
[0027] It should be noted that the figures are merely examples and no
limitations on the
scope of the present disclosure are intended thereby. Further, the figures are
generally not drawn
to scale, but are drafted for purposes of convenience and clarity in
illustrating various aspects of
the disclosure.
DETAILED DESCRIPTION
[0028] For the purpose of promoting an understanding of the principles of
the disclosure,
reference will now be made to the features illustrated in the drawings and
specific language will
be used to describe the same. It will nevertheless be understood that no
limitation of the scope of
the disclosure is thereby intended. Any alterations and further modifications,
and any further
applications of the principles of the disclosure as described herein are
contemplated as would
normally occur to one skilled in the art to which the disclosure relates. It
will be apparent to those
skilled in the relevant art that some features that are not relevant to the
present disclosure may not
be shown in the drawings for the sake of clarity.
[0029] At the outset, for ease of reference, certain terms used in this
application and their
meaning as used in this context are set forth below. To the extent a term used
herein is not defined
below, it should be given the broadest definition persons in the pertinent art
have given that term
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as reflected in at least one printed publication or issued patent. Further,
the present processes are
not limited by the usage of the terms shown below, as all equivalents,
synonyms, new
developments and terms or processes that serve the same or a similar purpose
are considered to
be within the scope of the present disclosure.
[0030] Throughout this disclosure, where a range is used, any number
between or
inclusive of the range is implied.
[0031] A "hydrocarbon" is an organic compound that primarily includes the
elements of
hydrogen and carbon, although nitrogen, sulfur, oxygen, metals, or any number
of other elements
may be present in small amounts. Hydrocarbons generally refer to components
found in heavy
oil or in oil sand. However, the techniques described are not limited to heavy
oils but may also
be used with any number of other reservoirs to improve gravity drainage of
liquids. Hydrocarbon
compounds may be aliphatic or aromatic, and may be straight chained, branched,
or partially or
fully cyclic.
[0032] "Bitumen" is a naturally occurring heavy oil material. Generally,
it is the
hydrocarbon component found in oil sand. Bitumen can vary in composition
depending upon the
degree of loss of more volatile components. It can vary from a very viscous,
tar-like, semi-solid
material to solid forms. The hydrocarbon types found in bitumen can include
aliphatics,
aromatics, resins, and asphaltenes. A typical bitumen might be composed of:
19 weight (wt.) % aliphatics (which can range from 5 wt. % - 30 wt. %, or
higher);
19 wt. % asphaltenes (which can range from 5 wt. % - 30 wt. %, or higher);
30 wt. % aromatics (which can range from 15 wt. % - 50 wt. %, or higher);
32 wt. % resins (which can range from 15 wt. % - 50 wt. %, or higher); and
some amount of sulfur (which can range in excess of 7 wt. %), the weight %
based upon
total weight of the bitumen.
In addition, bitumen can contain some water and nitrogen compounds ranging
from less than 0.4
wt. % to in excess of 0.7 wt. %. The percentage of the hydrocarbon found in
bitumen can vary.
The term "heavy oil" includes bitumen as well as lighter materials that may be
found in a sand or
carbonate reservoir.
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[0033] "Heavy oil" includes oils which are classified by the American
Petroleum Institute
("API"), as heavy oils, extra heavy oils, or bitumens. The term "heavy oil"
includes bitumen.
Heavy oil may have a viscosity of about 1,000 centipoise (cP) or more, 10,000
cP or more,
100,000 cP or more, or 1,000,000 cP or more. In general, a heavy oil has an
API gravity between
22.3 API (density of 920 kilograms per meter cubed (kg/m3) or 0.920 grams per
centimeter cubed
(g/cm3)) and 10.0 API (density of 1,000 kg/m3 or 1 g/cm3). An extra heavy
oil, in general, has
an API gravity of less than 10.0 API (density greater than 1,000 kg/m3 or 1
g/cm3). For example,
a source of heavy oil includes oil sand or bituminous sand, which is a
combination of clay, sand,
water and bitumen. The recovery of heavy oils is based on the viscosity
decrease of fluids with
increasing temperature or solvent concentration. Once the viscosity is
reduced, the mobilization
of fluid by steam, hot water flooding, or gravity is possible. The reduced
viscosity makes the
drainage or dissolution quicker and therefore directly contributes to the
recovery rate.
[0034] The term "bituminous stream" refers to a stream derived from oil
sand that
requires downstream processing in order to realize valuable bitumen products
or fractions. The
bituminous stream is one that comprises bitumen along with undesirable
components.
Undesirable components may include but are not limited to clay, minerals,
coal, debris and water.
The bituminous stream may be derived directly from oil sand, and may be, for
example, raw oil
sand ore. Further, the bituminous stream may be a stream that has already
realized some initial
processing but nevertheless requires further processing. Also, recycled
streams that comprise
bitumen in combination with other components for removal as described herein
can be included
in the bituminous stream. A bituminous stream need not be derived directly
from oil sand, but
may arise from other processes. For example, a waste product from other
extraction processes
which comprises bitumen that would otherwise not have been recovered may be
used as a
bituminous stream.
[0035] The term "solvent" as used in the present disclosure should be
understood to mean
either a single solvent, or a combination of solvents.
[0036] The terms "approximately," "about," "substantially," and similar
terms are
intended to have a broad meaning in harmony with the common and accepted usage
by those of
ordinary skill in the art to which the subject matter of this disclosure
pertains. It should be
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understood by those of skill in the art who review this disclosure that these
terms are intended to
allow a description of certain features described and claimed without
restricting the scope of these
features to the precise numeral ranges provided. Accordingly, these terms
should be interpreted
as indicating that insubstantial or inconsequential modifications or
alterations of the subject
matter described and are considered to be within the scope of the disclosure.
[0037] The articles "the", "a" and "an" are not necessarily limited to
mean only one, but
rather are inclusive and open ended so as to include, optionally, multiple
such elements.
[0038] The term "paraffinic solvent" (also known as aliphatic) as used
herein means
solvents comprising normal paraffins, isoparaffins or blends thereof in
amounts greater than 50
wt. %. Presence of other components such as olefins, aromatics or naphthenes
may counteract the
function of the paraffinic solvent and hence may be present in an amount of
only 1 to 20 wt. %
combined, for instance no more than 3 wt. %. The paraffinic solvent may be a
C4 to C20 or C4 to
C6 paraffinic hydrocarbon solvent or a combination of iso and normal
components thereof. The
paraffinic solvent may comprise pentane, iso-pentane, or a combination thereof
The paraffinic
solvent may comprise about 60 wt. % pentane and about 40 wt. % iso-pentane,
with none or less
than 20 wt. % of the counteracting components referred above.
[0039] With reference to Figure 1, disclosed is a method comprising:
a) providing (102) a slurry intended as a feed to a solid-liquid separation
process;
b) removing (104) a slip stream from the slurry; and
c) measuring (106) at least a portion of the slip stream at a plurality of
additive
dosage levels to obtain a characteristic indicative of a degree of
flocculation,
agglomeration, or aggregation for each of the plurality of additive dosage
levels.
[0040] SLURRY COMPOSITION AND SOLID-LIQUID SEPARATION
[0041] The slurry is intended as a feed to a solid-liquid separation
process. Any suitable
slurry may be used. For instance, in addition to the oil sand streams
discussed below, other mining
streams may be used. The solid-liquid separation may alternatively be water
clarification. The
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slurry may alternatively be a solid-liquid slurry stream, waste stream, or
drilling mud from a
drilling operation.
[0042] As described above in the background section, it is often
desirable to separate
solids from liquids in oil sand streams.
[0043] An "oil sand stream" is any suitable stream stemming from oil
sand. Examples
include, but are not limited to, oil sand, a bituminous stream, a bitumen
froth, oil sand tailings, a
stream from aqueous based extraction, a stream from solvent based extraction,
a solvent diluted
bitumen froth, a hydrotransport slurry, a solvent-ore slurry, or a combination
thereof.
[0044] The oil sand tailings stream may stem from aqueous based
extraction or solvent
based extraction. The oil sand tailings stream may comprise coarse tailings,
middlings, flotation
tailings, froth separation tailings, tailings solvent recovery unit (TSRU)
tailings, fluid fine tailings
(FFT), mature fine tailings (MFT), thickened tailings, thickener overflow,
centrifuged tailings,
hydrocycloned tailings, or a combination thereof. The oil sand tailings stream
may include at
least one of a feed stream to a thickener, a thickener overflow, and a
thickener underflow. The
oil sand tailings stream may include a feed stream to a centrifuge, filter, or
inline mixer. Oil sands
tailings streams are a subset of what may be called a "slurry", which is a
flowable liquid/solids
mixture.
[0045] An example of a solid-liquid separation process in the oil sands
field involves
introducing an oil sand tailings stream, which in this example is a feed
stream to a thickener (or
"thickener feedstream"), into a thickener along with a flocculant and/or a
coagulant to facilitate
solid-liquid separation and thus water recovery and tailing disposal.
Flocculant dosage may be
adjusted to improve flocculation for a given thickener feedstream. When the
thickener feedstream
being introduced into the thickener is highly variable, flocculant dose
adjustment in real-time
based on changing slurry feed to improve flocculation is important to
thickener operation and
performance. Floc formation can be affected by multiple factors, such as
thickener feedstream
composition, water chemistry, flocculant quality, and impurity content. For
example, a floc size
that is too small may lead to a lower settling rate, higher fines loss,
thickener bed expansion, or
flooding. A floc size that is too large (and therefore too heavy), may lead to
higher bed rheology,
poor dewatering, thickener rake operation difficulty, or rat-holing. Sub-
optimal or poor additive
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dosage may lead to sub-optimal or poor thickener performance or a reduction in
thickener
availability, which may lead to lower fines recovery efficiency, a more
challenging deposition
operation, or decreased process water availability.
[0046] Another suitable solid-liquid separation process is the re-
flocculation of a
thickener underflow (i.e. a slurry). In this process, a flocculant is added to
the sheared underflow
from a thickener such as described in the preceding paragraph. In this way, a
second flocculation
occurs to repair broken or partial flocs due to shearing before discharging to
facilitate solid-liquid
separation of the thickener underflow in a deposition area.
[0047] Some processes have lower feed variability, for instance because
their tailings are
conditioned with hydrocyclones or are processing Mature Fine Tailings (MFT),
which have
matured to a narrow compositional range in a tailings pond. The additive
dosage adjustment
described herein may nonetheless be useful in such processes. In particular,
despite lower feed
variability or narrower fine content variation, the additive dosage also
depends on other
variability, such as clay mineralogy, water chemistry, feed rheology, etc.
Proper and timely
dosage adjustment to account for process variability for desired process
performances is useful.
[0048] The solid liquid separation may involve re-flocculation of shared
thickened
tailings, inline flocculation of MFT, or MFT centrifuging. In solvent-based
extraction and
agglomeration of oil sands, the subject additive may be the bridging liquid
used.
[0049] SLIP STREAM MEASUREMENT
[0050] By using a slip stream for measurement, smaller volumes of slurry
may be
removed from the main process for measurement. Using a slip stream is distinct
from grab
sampling methods where small samples are taken from a slurry and are analyzed.
Grab sampling
can be slow as the lab analysis can take significant time and therefore
adjustments are necessarily
based on dated measurements which can limit their effectiveness. Additionally,
a grab sampling
sample may not be a good representation of the slurry due to its size and
sampling location in
what may be a heterogeneous slurry.
[0051] The slip stream may be returned to the slurry or may be sent for
waste treatment.
Alternatively, an inline mixer may be disposed upstream of the slip stream
exit or the slip stream
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may be taken from an area of turbulent flow, such as after a piping elbow or
flow meter to assist
homogeneous sampling.
[0052] The measurement of the slip stream may be performed by any
suitable instrument
or technique capable of obtaining the characteristic indicative of a degree of
flocculation,
agglomeration, or aggregation, with sufficient accuracy.
[0053] The characteristic indicative of a degree of flocculation,
agglomeration, or
aggregation (also referred to herein simply as "characteristic") may include a
measure of
flocculent, agglomerate, or aggregate size; a measure of flocculent,
agglomerate, or aggregate
settling rate; a measure of supernatant tubidity; a measure of flocculent,
agglomerate, or aggregate
compaction density; or a measure of flocculent, agglomerate, or aggregate
filtration rate.
[0054] The "characteristic" may be obtained by measuring particle size,
for instance
using particle size analyzers, for instance focused beam reflectance
measurement (FBRM) probes
or particle vision measurement (PVM) probes. Both FBRM and PVM probes may be
inserted
directly into the slip stream to measure the degree of flocculation,
agglomeration, or aggregation.
Bench testing has indicated that both FBRM and PVM probes are capable of
determining
underdose for flotation tailings and mature fine tailings flocculation.
However, as shown in
Figures 2 (which is based on measurement obtained from an FBRM probe) and 3
(which is based
on measurement obtained from a PVM probe), these probes cannot distinguish
between an
optimal state and an overdose state.
[0055] The obtained characteristics may be used to determine a
recommended additive
dosage level of the slurry, as illustrated below. Additionally, the obtained
characteristics may be
used with correlation reference data to determine a compositional parameter of
the slurry.
Examples of composition parameters are fines content and clay content. Where
the determined
compositional parameter falls outside of an operation window of the solid-
liquid separation
process, one may bypass the solids-liquid separation process and pass the
slurry to a designated
area as an untreated slurry.
[0056] For Figures 2 to 5, the following setup was used. FBRM and PVM
were mounted
and directly inserted into a one liter slurry pail under agitation with a
stand mixer which provides
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the mixing needed for solid particle suspension and flocculation. Multiple FT
(Floatation
Tailings) and FT/MFT (Floatation Tailing/Mature Fine Tailings) mixtures with
different SFRs
(Sand to Fines Ratios), solid content (SC), and bitumen content (Bit) were
tested with the setup.
For each testing feed, chord length distribution and images were captured,
after the addition of
variant polymer dosages, by FBRM and PVM, respectively.
[0057] FBRM is scanning laser microscopy, developed in the 1990's and
commercially
available from Mettler Toledo. In FBRM, a rotating lens provides a focused
laser beam at an
external surface of a sapphire window in a circular mode at a fixed rate. When
the beam meets a
particle, backscattered light is generated, a time lag between the laser
emission and the reflection
times' scanning velocity is measured, and a chord length is generated. Chord
length is on scanning
path from one endpoint to the other. Thousands of chords are measured during
single duration (2
sec), generated chord length distribution.
[0058] PVM ((Particle Vision and Measurement) is a probe-based video
microscope that
visualizes particles sizes, shapes and concentrations. PVM continuously
generates 1090x820 tm
greyscale images of slurry in real time.
[0059] As flocculation takes places, fine particles were captured and
aggregated into
larger flocs, displaying more longer chords and fewer shorter chords in FBRM
output while
presenting water channels (i.e. dark area) in PVM images. Statistical analysis
of FBRM chord
length distributions and image analysis of PVM can thus be used to quantify
flocculation level.
For example, FBRM square-weighted mean chord length (sq MCL) and average
standard
deviation of the pixel values of PVM images can track the degree of
flocculation. FBRM sq MCL
relates to aggregate size; the higher MCL value, the larger the aggregate
size. A low standard
deviation of PVM image indicates the pixel colors are relatively uniformly
grey, as is typical with
underflocculated fines or a low or no flocculation level. A high standard
deviation indicates that
flocs are present, with bright flocs and darker water channels.
[0060] The gray areas at the left at each of Figures 2 and 3 show the
approximate levels
of underdosing of the additive. As can be seen in Figures 2 and 3, utilizing
either of these
detection methods (FBRM in Figure 2 or PVM in Figure 3) that for a given
slurry stream
condition, there is an optimum dosage amount which for dosages above that
amount either
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1) additional additive dosage is wasted with little or no optimization of the
desired effect, or 2)
additional additive dosage begins to result in a decrease in the optimal
desired effect.
[0061] The "characteristic" is also a function of both slurry sand-to-
fines ratio (SFR) and
solids content. Therefore, placing FBRM or PVM probes into a thickener
feedwell for feedback
control, as opposed to using a slip stream, may be challenging or impractical
when faced with
feed variability.
[0062] On the other hand, as illustrated in Figure 4, for a given slurry,
recommended
additive dosage levels can be determined with measurements at a plurality of
additive dosage
levels. When the measurements at these additive dosage levels are taken off
one or more slip
streams from the slurry, where the slip stream(s) are representative of the
slurry, the information
can be used to inform processing decisions to the slurry in real-time, thereby
realizing feed
forward control. For a wide range of slurry variability, integration of an
operation strategy such
as illustrated in Figure 5, may not only facilitate additive dosage
recommendation against a
changing slurry but may also infer compositional range, providing guidance on
upstream or
downstream operation, such as changing a tailing stream(s) blending ratio,
recycling FFT, or
changing bed residence time. In Figure 5, each of the four dosage levels, e.g.
(n-1) to (n+2), can
be used to operate a corresponding range of feed SFR to maintain sustained
dynamic thickener
operation at design hydraulic rate without incurring bed flooding and rat-
holling, respectively.
Instead of SFR, another compositional characteristic may be used.
[0063] Measurements at a plurality of additive dosage levels off slip
stream(s) may be
taken cyclically, sequentially, simultaneously, or any combination thereof.
Figures 6 to 8
illustrate installation scheme examples that may be used to realize real-time
process control.
Where the plurality of additive dosage levels are termed n-y, n, n+z, and the
obtained
characteristics at the plurality of additive dosage levels are termed signal
(n-y), signal (n), and
signal (n+z), where y and z are predetermined incremental additive dosage
levels, where y and z
are the same or different, one can record the relationship of the three
signals and determine a
dosage level recommendation according to the following rules:
- if signal (n-y) < signal (n) < signal (n+z), then signal for
additive dosage level of
(n+z) to the slurry and increase dosage level in next slip stream dosing;
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- if
signal (n-y) < signal (n) = signal (n+z), then signal for additive dosage
level of
(n) to the slurry; and
- if
signal (n-y) = signal (n) = signal (n+z), then signal for additive dosage of
(n-y)
to the slurry and lower additive dosage level in next slip stream dosing.
[0064]
Figure 6 is an example of a "cyclic" scheme. A slip stream (604) is taken from
a
slurry (602) and may be passed through a flow meter and/or a density meter
(606). The flow
meter may be used to measure and/or regulate flow while the density meter may
be used to
measure slip stream density. An additive (608) is injected into the slip
stream (604) which is then
passed through an inline or dynamic mixer (610). An analyzer (612) measures
the slip stream at
the n-y dosage level to obtain a characteristic indicative of a degree of
flocculation,
agglomeration, or aggregation at the n-y dosage level. The method is repeated
for dosage levels
of n and n+z and the method continues according to the above rules.
[0065]
Figure 7 is an example of an "in series" or sequential scheme. A slip stream
(704)
is taken from a slurry (702) and is passed through a flow meter and/or density
meter (706). An
additive (708a) is injected into the slip stream (704), to achieve an n-y
dosage, and the slip stream
is then passed through an inline or dynamic mixer (710a). An analyzer (712a)
measures the slip
stream at the n-y additive dosage to obtain a characteristic indicative of a
degree of flocculation,
agglomeration, or aggregation for the n-y additive dosage.
The method is repeated with
incrementally more additive (n and n+z) using additional additive (708b and
708c), additional
inline or dynamic mixers (710b and 710c), and additional analyzers (712b and
712c). The method
then continues according to the above rules.
[0066]
Figure 8 is an example of an "in parallel" or simultaneous scheme. One slip
stream (804) is taken from a slurry (802), and separated into three sub slip
streams (804a, 804b,
and 804c) (which may also be referred to as portions of the slip stream) which
are passed through
flow meters and/or density meters (806a, 806b, and 806c), respectively.
Additive (808a, 808b,
and 808c) is added to the sub slip stream to achieve dosage levels of n-y, n,
and n+z, respectively,
followed by inline or dynamic mixers (810a, 810b, and 810c), respectively and
the sub slip
streams are analyzed by analyzers (812a, 812b, and 812c), respectively. The
method then
continues according to the above rules.
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[0067] Figures 6 to 8 merely illustrate three of a myriad of possible
configurations.
Ancillary instrumentation or equipment in the slip stream(s) may be added to
improve
stabilization or accuracy, depending, for instance, on slurry variability.
Ancillary instruments may
include, but are not limited to, a density meter, a buffering tank, and a
dynamic mixer.
[0068] Density meter(s) may be installed in the main slip stream(s) or in
a portion of the
slip stream(s) to measure the density of the slip stream(s) or portions
thereof.
[0069] Static or dynamic mixing unit(s) may be installed in slip
stream(s) to induce the
flocculation, agglomeration, or aggregation at different additive dosage
levels.
[0070] The additive may be injected via one or multiple injection ports.
The additive(s)
may be introduced to the slip stream(s) at pre-determined level(s) and
frequency prior to the
mixing unit(s).
[0071] Flow meter(s) may be installed in the main slip stream or a
portion of the slip
stream(s) to measure and/or regulate the flow rate(s) of the slip stream(s) or
portions thereof.
[0072] A dilution stream may be introduced to slip stream(s) in
conjunction with flow
meter(s) and density meter(s) in slip stream(s) or stream(s) between the
slurry(ies) and the slip
stream(s) to regulate density or solid content of the slip stream(s) prior to
additive injection.
[0073] A buffering unit such as continuous flow stirred-tank reactor
(CSTR) may be
installed between the slurry and slip stream(s) to buffer the flow, that is,
to reduce the fluctuation
of the slurry prior to additive injection.
[0074] The slip stream(s) may be heated prior to being exposed to the
analyzer(s).
[0075] There may be one slip stream off each main feed line to each
analyzer unit.
Alternatively, there may be multiple slip streams off each slurry line to each
solid-liquid
separation unit.
[0076] Certain main slurry lines may have a single slip stream and
certain main slurry
lines have multiple slip streams.
[0077] There may be one online analyzer in each slip stream or there may
be multiple
analyzers in each slip stream.
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[0078] There may be one analyzer in each of some slip stream(s) and
multiple analyzer(s)
in each of other slurry line(s) to a solid-liquid separation unit.
[0079] PROCESS ADJUSTMENT
[0080] Based on the obtained characteristic, the slurry or the solid-
liquid separation
process may be adjusted. For instance, the following may be adjusted: additive
dosage level,
flocculant dosage level, coagulant dosage level, agglomerant dosage level, or
flocculant mixing.
The adjustment may include combining the slurry with another stream in a
proportion to satisfy
operational specifications of the solid-liquid separation process. The
adjustment may be of an
operating parameter of a thickener in the solid-liquid separation process. For
instance, the
operating parameter of the thickener may include a bed height of the
thickener, a feed rate to the
thickener, an underflow rate from the thickener, a residence time in the
thickener, or a rake torque.
The adjustment may include adjusting an operating parameter downstream of a
thickener in the
solid-liquid separation process. For instance, the operating parameter
downstream of the
thickener may include dilution of a thickener underflow or additional additive
addition to the
thickener underflow.
[0081] Adjustments may be performed in real-time. "Real-time" as used
herein may
include some delays such as processing delays but is distinct from, for
example, off line
measurement, analysis, and adjustment.
[0082] Adjustment may also include:
- adjusting the rate at which one or more flocculant(s) are added
to a thickener
feed stream
- adjusting the rate at which one or more flocculant(s) are added
to a thickener
underflow stream during re-flocculation
- adjusting the rate at which other additives (e.g. coagulants)
are added to a
tailings treatment process
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- adjusting whether a tailings stream from an extraction plant (e.g. flotation
tailings (FT) or froth treatment tailings (FTT) (e.g. TSRU tailings)) are fed
to
a tailings treatment process or are by-passed to a designated area
- adjusting the rate at which Fluid Fine Tailings (FFT) are fed
to a mixbox for
mixing the slurry
- adjusting the rate at which an additional tailings streams,
such as coarse sand
tailings (CST), are fed to a mixbox for mixing the slurry
- adjusting the operating parameters of flocculant mixing
equipment during re-
flocculation (e.g. dynamic mixer rotations per minute (rpm))
- adjusting operating parameters of a thickener (e.g. underflow
and overflow
rates, rake speed, and shear thinning loop speed) to control the residence
time
and bed height in the thickener.
[0083] As mentioned briefly above, for a wide range of slurry
variability, integration of
an operation strategy such as illustrated in Figure 5, may not only facilitate
additive dosage
recommendation against a changing slurry but may also infer a compositional
range of the slurry,
providing guidance on upstream or downstream operation, such as changing a
tailing stream(s)
blending ratio, recycling FFT, or changing bed residence time. The correlation
between slurry
composition and additive dosage may be continuous or discrete. The slurry
compositional range
may be compared to an acceptable operating window of a tailings treatment
process to determine
whether the slurry should be fed to the treatment unit or diverted to a
designated area, e.g. a
tailings pond.
[0084] The composition and solid mass flow rates and/or blending rate of
a slurry to a
thickener may be adjusted by varying the feed rates of FFT or another stream
(e.g. CST) to
achieve a target dosage level, thus regulating an overall feed composition
range to a solid-liquid
separation unit to maintain its steady and desired performance and managing
additive supply.
[0085] Operation parameters of a solid-liquid separation unit, e.g. bed
height of a
thickener, may be adjusted to match the compositional range of the slurry to
achieve a desired
product specification.
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[0086] The inferred compositional range variation along with feed rate
and density as a
function of stream time may be integrated to inform compositional range of
thickener underflow,
that may then be used together with additional information for further process
decisions of
downstream operations, for instance dilution, dosage level of flocculation,
agglomeration or
aggregation steps, mixing control, use of additional additives, or diversion
of a stream.
[0087] The method described herein may also be used to screen additive(s)
types and
performances against a live feed stream by using one or multiple slip streams
and comparing them
against base additive(s) in use.
[0088] Compositional online analyzer(s) in the slurry(ies) or slip
streams may be used for
dosage control and to provide guidance to downstream or upstream operations.
[0089] Compositional online analyzer(s) in the slurry(ies) or slip
streams may be
integrated with flocculation monitoring system(s) in the same or separate slip
streams for dosage
control and to provide guidance to downstream or upstream operations.
[0090] A correlation may be developed between an optimal dosage for the
slip stream(s)
and an optimal dosage level for the main stream(s) and used for dosage
recommendation.
[0091] A system for implementing a method described herein may include: a
slurry line
for carrying the slurry; at least one slip stream line for carrying a slip
stream; and at least one
analyzer for measuring at least a portion of the slip stream at the plurality
of additive dosage levels
to obtain the characteristics indicative of the degree of flocculation,
agglomeration, or aggregation
for each of the plurality of additive dosage levels. Consistent with Figure 8,
the at least one slip
stream feeds may have at least three sub slip streams arranged in parallel,
and each sub slip stream
may comprise at least one analyzer for measuring the sub slip stream at at
least one of the plurality
of additive dosage levels to obtain a characteristic indicative of a degree of
flocculation,
agglomeration, or aggregation for each of the plurality of additive dosage
levels corresponding to
each of the sub slip streams.
[0092] It should be understood that numerous changes, modifications, and
alternatives to
the preceding disclosure can be made without departing from the scope of the
disclosure. The
preceding description, therefore, is not meant to limit the scope of the
disclosure. Rather, the
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scope of the disclosure is to be determined only by the appended claims and
their equivalents. It
is also contemplated that structures and features in the present examples can
be altered,
rearranged, substituted, deleted, duplicated, combined, or added to each
other.
[0093] The
scope of the claims should not be limited by particular embodiments set forth
herein, but should be construed in a manner consistent with the specification
as a whole.
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