Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
METHOD OF MEASURING A SLURRY USING A NON-REPRESENTATIVE
SAMPLE
BACKGROUND
Field of Disclosure
[0001] The disclosure relates generally to the field of measurement of
slurries, for
instance measurement of oil sand slurries.
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] Measurement of slurries, such as mining slurries including oil
sand slurries is
often desired. 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
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processes 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).
[00131 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
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are called Fluid Fine Tailings (FFT). FFT settle over time to produce Mature
Fine Tailings
(MFT), having above about 30 wt. % solids.
[0014] As described above, measurement of slurries, such as mining
slurries including
oil sand slurries is often desired. Such measurements may be used for myriad
purposes
including process control. For instance, solid-liquid separation of slurries
is often desired.
Successful solid-liquid separation depends heavily on the slurry 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. Measurement of
slurries may also be
useful to obtain fines flow distribution in a unit or area of a plant, or to
obtain a plant-wide fines
balance, for instance to control an oil sand mining operation or tailings
deposition management.
SUMMARY
[0015] It is an object of the present disclosure to provide a method of
measuring a slurry,
for instance an oil sand slurry.
[0016] Disclosed is a method comprising:
(a) providing a slurry comprising a fluid and solids;
(b) removing a slip stream from the slurry, wherein the slip stream is a
non-
representative sample;
(c) measuring, directly or indirectly, a fluid flow rate in the slip
stream;
(d) measuring, directly or indirectly, a fluid flow rate in the slurry;
(e) measuring, directly or indirectly, a flow rate of a particle of
interest in the slip
stream; and
(f) converting, using (c), (d) and (e), the flow rate of the particle of
interest in the
slip stream to a flow rate of a particle of interest in the slurry.
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[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 diagram showing particle distribution in a slurry
stream with a
slipstream having an analyzer, the slipstream being representative of the
slurry stream (prior
art).
[0020] Fig. 2 is a diagram showing particle distribution in a slurry
stream with a
slipstream having an analyzer, is the slipstream being non-representative of
the slurry stream.
[0021] 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
[0022] 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.
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[0023] 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 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.
[0024] Throughout this disclosure, where a range is used, any number
between or
inclusive of the range is implied.
[0025] 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.
[0026] "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.
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The term "heavy oil" includes bitumen as well as lighter materials that may be
found in a sand or
carbonate reservoir.
[0027] "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 10.00 API (density of 1,000 kg/m3 or 1 g/cm3).
An extra heavy
oil, in general, has an API gravity of less than 10.00 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.
[0028] 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.
[0029] The term "solvent" as used in the present disclosure should be
understood to
mean either a single solvent, or a combination of solvents.
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[0030] 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
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.
[0031] 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.
[0032] 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.
[0033] The term "fines" means mineral solids sized less than 44 microns.
[0034] The term "sand" means mineral solids sized greater than or equal
to 44 microns.
[0035] The term "fines flow rate" means the flow rate of fines and may
be on a volume
or mass basis unless otherwise indicated.
[0036] The term "solid flow rate" means the flow rate of solids and may
be on a volume
or mass basis unless otherwise indicated.
[0037] The term "sand to fines ratio" or "SFR" means the mass ratio of
sand to fines
unless otherwise indicated.
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[0038] The present inventors have found that it is possible to use a non-
representative
slipstream of the slurry to carry out certain valuable measurements and still
obtain accurate an
analysis of the slurry. This is accomplished using a using a "dispersed
particle in fluid"
approach. For the purpose of the analysis, the ratio of particles of interest
(e.g. fine particles) to
water is taken to be the same in a slipstream as in the slurry. Experimental
data supporting this
approach is provided below. The experimental results herein have led to the
discovery that the
fines concentration and fines-to-fluid ratio are relatively consistent over
different mixing
conditions and subsampling locations. This is true even when the sands content
varies in the
sample due to non-homogeneity of the sampling process. This makes the fines
concentration
and fines-to-fluid concentration robust characteristics (i.e., essentially
constants) across the
mixing conditions and subsampling locations. Accordingly, the present
inventors have found
that it is possible to use a non-representative slipstream of the slurry to
carry out certain valuable
measurements and still (with the knowledge of this constant relationship
between the water and
fines content even when a truly representative sample is not taken) to
accurately predict the
composition or certain parameters in the slurry stream wherein it was
previously thought could
only be achieved if the sample stream was an accurate representation of the
slurry stream
composition.
[0039] The present approach enables flexibility in sampling and analyzing
systems and
methods by being able to calculate slurry stream compositions without the need
for ensuring
that the analyzed sample is representative (i.e., has essentially the same
composition) as the
slurry stream. For example, this approach enables the use of online analyzers
with simple, non-
representative sampling systems. The sampling points may be at any position
around a slurry-
carrying pipe that contains slurry, after a pump, or in fully developed flow,
and based on any
suitable sampler design and line size, provided solids settling and plugging
can be controlled,
but with this new knowledge of utilizing a "dispersed particle in fluid"
approach under the
current discovery, full mixing and distribution of the slurry at the point of
sampling (to ensure
homogeneity of the sample) is not necessary as taught in the prior art. The
resultant
measurements may be used for myriad process controls, for instance feed-
forward process
setpoint tuning or feedback process control. Precise measurement of fines,
clays and other
slurry properties may enable improved control of many key process parameters
such as
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flocculent dosage, caustic dosage, throughput, etc. Sampling can be
significant challenge on
slurry streams. Well-designed sampling systems can be expensive and complex,
and still may
not capture fully representative samples. The present approach may enable
accurate online
slurry analysis and parameter optimization with relatively rudimentary
sampling systems.
[0040] The approach may be used with any suitable slurry stream to
measure the
concentration of any class of particle which tends to remain well dispersed in
the slurry. The
approach may also be used with an online analyzer or 'experiment' to measure a
property or
optimum operating parameter that would be expected to follow the water or a
dispersed class
of particle. For example, the experiment could involve dosing an additive in
different
concentrations and monitoring the slurry response to determine the optimal
dose of the additive
fora desired processing outcome.
[0041] Fig. 1 is a diagram showing the particle distribution of a slurry
stream (102) in
a main pipeline (104) with a "representative" slipstream (106) removed from
the main slurry
line for analysis representative of the prior art. Here, the representative
slipstream (106) is
passed through analyzer (108) for analysis. The analyzer may be used to
determine a mass flow
rate, a particle flow rate, or a solids flow rate. As can be seen in the
"representative" slipstream
(106) in Fig. 1 in the prior art, in order to get a true analysis of the
composition of the slurry
stream, or certain key parameters thereof, care must be taken to ensure that
the "representative"
slipstream (106) has essentially the same composition and particle
distribution as the slurry
stream (102). This requires ensuring adequate mixing of the slurry stream and
positioning of
the slipstream sampling system to ensure the slipstream is representative of
the slurry stream.
Additionally, in the prior art, if the slipstream (106) is not representative
of the slurry stream
(102), the results will have an inherent error, or skew, leading to improper
slurry stream
compositional inference. This is further illustrated by comparing the exploded
view (110) of
the slurry stream (102) and the exploded view (112) of the "representative"
slipstream (106),
where, in the prior art, the composition/distribution in both slurry stream
(102) and the
"representative" slipstream (106) must be essentially the same for proper
operation.
[0042] Fig. 2 is a diagram showing the particle distribution of a slurry
stream (202) in
a main pipeline (204) with a "non-representative" slipstream (206) removed
from the main
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slurry line for analysis representative per the present disclosure. Here, the
non-representative
slipstream (206) is passed through analyzer (208) for analysis. The analyzer
may be used to
determine a mass flow rate, a particle flow rate, or a solids flow rate. As
can be seen in the
"non-representative" slipstream (206) in Fig. 2, in order to get a true
analysis of the composition
of the slurry stream, or certain key parameters thereof, it is not necessary
to ensure that the
"non-representative" slipstream (206) has essentially the same composition and
particle
distribution as the slurry stream (202). Therefore, in the present
embodiments, it is no longer
necessary to provide adequate mixing of the slurry stream and positioning of
the slipstream
sampling system to ensure the slipstream is representative of the slurry
stream. Additionally,
errors in the data obtained from the analyzer (208) may be reduced since the
present "dispersed
particle in fluid" approach removes some of the uncertainty in the analyzer
readings. This
concept is further illustrated by comparing the exploded view (210) of the
slurry stream (202)
and the exploded view (212) of the "non-representative" slipstream (206),
where, as can be
seen, the present embodiments can utilize a "non-representative" slipstream
(206) wherein it is
not required that composition/distribution in both slurry stream (202) and the
"representative"
slipstream (206) be essentially the same for proper operation.
[0043] Optional density meters (not shown) may be used to measure the
density of
slurry stream (202) and the "non-representative" slipstream (206). While this
is not required to
obtain all key compositional/parameters values of the slurry stream (202) from
the analysis of
the "non-representative" slipstream (206), the density measurements may be
required to
determine some of the key compositional/parameters values of the slurry stream
(202) based on
the analysis of the "non-representative" slipstream (206).
[0044] Various slurries could be analyzed, for instance hydrotransport
slurries; primary
separation vessel slurries; middlings; extraction tailings such as coarse sand
tailings (CST),
flotation tailings (FT), froth treatment tailings; pond tailings such as fluid
fine tailings (FFT)
and mature fine tailings (MFT); tailings treatment streams such as thickener
feeds, thickener
overflow (0/F), thickener underflow (U/F), cyclone overflow (0/F), centrifuge
inlet and outlet
streams, and flocculant mixer inlet and outlet streams.
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[0045] Various dispersed particles could be measured, for instance fines
less than 44
microns, fines less than 2 microns, clays, and dispersed bitumen.
[0046] Examples of methods of analysis include laser diffraction,
ultrasonic, image
analysis, turbidity, K40 analysis, laser induced breakdown spectroscopy
(LIBS), near infrared
(NIR), prompt gamma neutron activation analysis (PGNAA). For analyzing
dispersed bitumen,
a tailings oil analyzer or NIR may be used.
[0047] Examples of slurry properties or optimum operating parameters may
include
optimum flocculent dosage, carrier fluid viscosity, optimum caustic or other
process additive
dosage, and predicted primary separation cell (PSC) separation performance.
[0048] A "representative sample" is a sample where the fluid and solids
profile is
substantially the same as the fluid and solids profile of the slurry from
which the sample is
obtained. In conventional methods, a representative sample is obtained and
analyzed to provide
an analysis of the slurry.
[0049] A "non-representative sample" is a sample where the fluid and
solids profile
differs substantially from the fluid and solids profile of the slurry from
which the sample is
obtained. A sample is considered "non-representative" when it would not be
deemed as an
appropriate representation of the slurry profile for use in conventional
methods.
[0050] A method may comprise:
(a) providing a slurry comprising a fluid and solids;
(b) removing a slip stream from the slurry, wherein the slip stream is a
non-representative sample;
(c) measuring, directly or indirectly, a fluid flow rate in the slip
stream;
(d) measuring, directly or indirectly, a fluid flow rate in the slurry;
(e) measuring, directly or indirectly, a flow rate of a particle of
interest in the slip
stream; and
(0 converting, using (c), (d) and (e), the flow rate of the particle
of interest in the
slip stream to a flow rate of a particle of interest in the slurry.
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[0051] The slurry is a flowable mixture of fluid and solids. The slurry
may be any
suitable slurry where a non-representative sample may be used to measure
desired properties of
the slurry using the approach described herein. The slurry may be an oil sand
stream intended
as a feed stream to a solid-liquid separation process, tailings treatment
process, bitumen
extraction process, or bitumen recovery process. The oil sand stream may be an
oil sand tailings
stream. The oil sand tailings stream may stem from an aqueous based extraction
process. The
oil sand tailings stream may stem from a solvent-based extraction process. 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 comprise a feed stream
to a thickener,
a thickener overflow, or a thickener underflow. The oil sand tailings stream
may comprise a
feed stream to a centrifuge, filter, or inline mixer. The slurry may comprise
a mining slurry,
for instance a hydrotransport slurry. The slurry may comprise a thickener
underflow. The
slurry may comprise a drilling mud or waste stream from a drilling operation.
[0052] 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 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.
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[0053] 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.
[0054] 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 fines 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.
[0055] 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.
[0056] The fluid is the non-solid portion of the slurry. The fluid may be
water, or water
and bitumen. Water and bitumen have the same density and therefore can be
viewed together
as a fluid for the purposes of the fluid and solid analysis. The solids may
comprise particles of
various sizes and may comprise sand and fines. "Flow rate" as used herein may
be on a volume
or mass basis unless otherwise indicated.
[0057] The "particle of interest" may be, for instance, fines (i.e.
mineral solids sized
less than 44 microns), clay (i.e. mineral solids sized less than 2 microns),
or any other suitable
category of solids. The particle of interest should be a particle that is
readily suspended in a
= stirred fluid.
[0058] Step (e) may comprises:
(el) measuring, directly or indirectly, a solid flow rate in the slip
stream; and
(e2) measuring, directly or indirectly, a concentration, or a concentration
parameter,
of the particle of interest on a dry solid basis in the slip stream.
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[0059] Step (f) may comprise converting, using (c), (d), (el), and (e2),
the measured
concentration, or the measured concentration parameter, of the particle of
interest on a dry solid
basis in the slip stream to a flow rate of the particle of interest on a dry
solid basis in the slurry.
[0060] The method may further comprise measuring, directly or
indirectly, a solid flow
rate of the slurry stream.
[0061] The method may further comprise calculating a concentration of
the particle of
interest on dry solid basis using the measured solid flow rate of the slurry
stream and the flow
rate of the particle of interest in the slurry.
[0062] Where the concentration, the concentration parameter, or the flow
rate of the
particle of interest on the dry solid basis in the slurry falls outside of an
operation window of a
solid-liquid separation process, the method may comprise bypassing a solids-
liquid separation
process and passing the slurry to a designated area as an untreated slurry.
The operation window
can be violated or exceeded by either SFR or flow rate of the particle of
interest. If only the
SFR is too large or too small, the fine stream or sandy stream may be cut back
or added to bring
the SFR back into range. If the flow rate of particle of interest is out of
range, then the flow rate
of slurry may be cut back.
[0063] Based on the concentration, the concentration parameter, or the
flow rate of the
particle of interest on the dry solid basis in the slurry, the method may
comprise adjusting
flocculent mixing in the slurry.
[0064] Based on the concentration, the concentration parameter, or the
flow rate of the
particle of interest on the dry solid basis in the slurry, the method may
comprise adjusting a
downstream solid-liquid separation process.
[0065] The method may further comprise
(h) determining an additive dosage to the slip stream; and
(i) converting, using (c) and (d), the determined additive dosage to a
recommended
additive dosage to the slurry.
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[0066]
The step of determining the recommended additive dosage to the slip stream
may comprise 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 a plurality of additive dosage levels and using the
following logic rules,
wherein the plurality of additive dosage levels are termed (n-y), (n), and
(n+z), characteristics
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:
[0067]
if signal (n-y) < signal (n) < signal (n+z), then signal for additive dosage
(n+z) to the slip stream and increase dosage level in next slip stream dosing;
[0068]
if signal (n-y) < signal (n) = signal (n+z), then signal for additive dosage
(n) to the slip stream; and
[0069]
if signal (n-y) = signal (n) = signal (n+z), then signal for additive dosage
(n-y) to the slip stream and lower additive dosage level in next slip stream
dosing.
[0070]
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. 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. 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, these probes cannot distinguish between an optimal
state and an
overdose state. The obtained characteristics may be used to determine a
recommended additive
dosage level of the slurry, as illustrated below. Additionally, the obtained
characteristics may
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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. The method may further comprise, based on the
recommended
additive dosage to the slurry, adjusting the additive dosage to the slurry.
The adjusting of the
additive dosage may be performed in real time. The additive may comprise a
flocculant, a
coagulant, or an agglomerant. Canadian Patent No. 2,925,223 (Liu et al.)
provides additional
detail on an iterative approach to adjusting additive dosage.
[0071] Step (c) may comprises measuring a flow rate in the slip stream,
measuring a
density of the slip stream, and calculating the fluid flow rate in the slip
stream from the
measured density and known or estimated densities of the fluid and the solids.
Theoretically,
if such an analyzer were available, solid content could be measured directly
as well. Therefore,
if the mass flow rate measured from step (e) is known instead of the
volumetric flow rate, solid
content measurement from step (c), then a density measurement is not needed.
[0072] Step (d) may comprise measuring a flow rate in the slurry,
measuring a density
of the slurry, and calculating the fluid flow rate in the slurry from the
measured density and
known or estimated densities of the fluid and the solids.
[0073] The measurements of steps (c) and (d) may be performed by one or
more online
analyzers. The measurements of steps (c) and (d) are by volumetric flow meter
or mass flow
meter.
[0074] The method may further comprise floating off bitumen in the slip
stream to
reduce bitumen interference in slip stream measurement.
[0075] Density meter(s) may be used to measure density of the slurry or
slip stream.
Flow meter(s) may be used to measure and/or regulate the flow rate(s) of the
slip stream(s) or
portions thereof
[0076] Various process adjustment may be made based on measured or
calculated
parameters. For instance, for solid-liquid separation processes, the following
may be adjusted:
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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, a rake torque, or dilution water addition control to achieve a
desired fines-in-fluid
concentration range for a thickener operation. 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.
[0077] 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.
[0078] 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
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
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adjusting the rate at which an additional tailings stream, 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.
[0079] The measured and calculated parameters may provide guidance on
upstream or
downstream operation, such as changing a tailing stream(s) blending ratio,
recycling FFT, or
changing bed residence time. For example, a 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.
[0080] 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.
Additionally, feed composition range adjustment is important to achieve
downstream deposit
properties in a deposition area.
[0081] 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.
[0082] 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.
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[0083] The approach described herein may be used in hydrostransport
slurry lines
feeding PSCs (primary separation cells) where fines flow and fines
concentration information
is useful. Various PSC operational adjustments may be made based on measured
or calculated
parameters using the approach described herein.
[0084] Table 1 provides examples of slurries, particles of interest, and
process control
which may be used with the approach described herein.
[0085] Table 1. Examples of slurries, particles of interest, and process
control.
Slurry Particle class or particle Process control
property
Thickener feed (FT & FFT Fines or clay content Flocculant dose setpoint,
combined) Optimal flocculant dose (see throughput, dilution
rate,
Canadian Patent No. bed level
2,925,223, Liu et al.)
Flotation tailings Fines or clay content Flocculant dose, blending
ratio with FFT
Coarse tailings Fines or clay content Tailings beaching
operation
for fines capture
Fluid fine tailings Fines or clay content Flocculant dose, blending
ratio with FT
Hydrotransport Fines or clay content Caustic, dilution water,
temperature
Middlings Dispersed bitumen content, Flotation cell rate,
mixing
fines speed, dilution water
addition, air injection rate
[0086] In Table 1, the coarse tailing operation is related to beaching
and fines capture
on the beach. For example, knowing SFR of coarse tailings could help determine
the discharge
rate, discharge location, the need to bring in FFT over for mixing, duration
of beaching, etc.
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=
[0087] For the hydrotransport line, knowing fines flow or fines
concentrations, could
be used to determine ore fine level, which may guide caustic dosage to the
PSC, the need for
adding a secondary additive, adjusting PSC dilution water or operation
temperature. Such
adjustment is described, for instance, in Canadian Patent No. 2,967,868
(Castellanos et al).
[0088] A method for online determination of a concentration of a class
of particles of
interest in a slurry stream may comprise:
flowing a slurry through a primary pipe or in a vessel, the slurry comprising
a
carrier fluid and particles of different classes;
taking a slipstream off the primary pipe or vessel using a sampling line or
other
flow splitting device;
measuring a density of the slipstream;
computing a solids content and a carrier fluid content in the slipstream from
the
measured density and known or estimated densities of the carrier fluid and
solid
particles;
feeding the slipstream into an analyzer to measure a concentration of the
particle
class of interest;
computing a ratio of the particle class of interest to carrier liquid in the
slipstream;
measuring a density of the primary slurry stream;
computing a solids content and a carrier fluid content in the primary slurry
stream from the measured density and known or estimated densities of the
carrier fluid
and solid particles;
computing a flow rate of the particle class of interest in the primary stream
by
assigning the same ratio of particle class of interest to carrier fluid as was
measured in
the slipstream; and
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computing a concentration of the particle class of interest in the primary
stream
on a dry solid basis by dividing the flow rate of the particle of interest to
the flow rate
of the solids in the primary slurry stream.
[0089] Experiment
[0090] A high SFR slurry (15 wt. % solids content, "SC") with a density
of 1.10 kg/L
was mixed in a bucket at different mixing conditions and then subsampled from
different
locations while mixing.
[0091] Table 2. Subsamples Analysis
Mixing Sampling Sample SC Sample SFR Sample Bucket SFR
Location wt. % Fines-to-
Fluid Ratio
Mid RPM Top 5 0.9 0.031 4.7
Mixing
Mid RPM Bottom 19 6.8 0.029 5.0
Mixing
Hand Mixing Top 4 0.2 0.030 4.9
Hand Mixing Bottom 22 8.8 0.029 5.1
[0092] These results demonstrate that the mixing is not sufficient to
fully suspend all
solids to obtain a representative sample. These results also demonstrate that
the fines
concentration and the fines-to-fluid ratio are relatively consistent over
different mixing
conditions and subsampling locations. This makes the fines concentration and
fines-to-fluid
concentration (i.e., a "constant" value in the sampling process, regardless of
the true
representativeness of the sample, that was never before realized) more robust
characteristics of
the sample across the mixing conditions and subsampling locations.
Accordingly, the present
inventors have found that it is actually possible to use a "non-
representative" slipstream of the
slurry to carry out certain valuable measurements. It should be understood
that numerous
changes, modifications, and alternatives to the preceding disclosure can be
made without
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departing from the scope of the disclosure. The preceding description,
therefore, is not meant
to limit the scope of the disclosure. Rather, the 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.
[00931
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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