Note: Descriptions are shown in the official language in which they were submitted.
219522
TREATMENT OF OIL. WATER AND SAND MIXTURES
TECHNICAL FIELD
The present invention relates to a method of and apparatus for the treatment
of
oil, water and sand mixtures and more particularly to the treatment of storage
residues
comprising oil, water and sand.
BACKGROUND ART
Oil storage tanks are used to store the mixture of fluids that is immediately
pumped from oil wells in the field. In such tanks, the oil, water and solid
phases separate and
the solids settle to the bottom of the tank and the oil rises to the top. As
oil is drawn from
the top of the tank, sand and water may accumulate at the bottom of the tank.
Other
particulate matter such as shale or clay may also accumulate. A significant
amount of oil may
remain emulsified in the water and adsorbed on the surface of the solid
particulate matter.
This is especially true for the heavy oils which are produced in certain
regions of Alberta and
Saskatchewan, Canada. The water may have significant concentrations of
chlorides in
solution.
The oily sand is occasionally removed from storage tanks by a process known
as "stinging" where a jet of water is used to stir up the sand at the same
time suction is
applied by a vacuum truck to remove the oily sand and water. The oily sand and
water may
then be disposed of or utilized in applications such as dust control on gravel
roads. An
219652
analysis of a sample taken from a storage tank in Innisfree, Alberta
demonstrates the
following composition of the non-aqueous components:
Table 1 lw:w~
Oil/Paraffin 17.65%
Asphaltene 1.81%
Carbonates 0.34%
Iron Salts 0.68%
Insolubles 79.52%
The insolubles consisted primarily of high silica sand.
Conventional techniques for separating the sand such as settling pits or
centrifuging do not effectively remove and recover all of the non-sand
components. Nor are
such conventional techniques cost-effective or environmentally sound. Of
course it is well
known that certain surfactants will remove the oil from the sand, however,
there is no known
process for doing so and economically recovering both the oil and the sand.
There is a need in the art for a new method and apparatus of recovering clean
sand and refinable oil from such mixtures which is effective in completely
separating these
components in an economical and convenient manner. It would further be
advantageous if
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21~ss2~
such a method were continuous and could be performed by an apparatus that is
self contained.
DISCLOSURE OF INVENTION
The present invention relates to an apparatus for separating solids comprising
sand from oil in a feedstock comprising the solids, the oil, and an aqueous
phase. In one
aspect of the invention, the apparatus comprises:
(a) first, second, third and fourth cells each comprising an agritation
chamber and a
settling chamber, wherein each agitation chamber comprises an inlet, an outlet
and agitation
means and wherein each settling chamber comprises an inlet, a fluid outlet and
a solids outlet
and wherein the solids outlet of the first settling chamber leads to the inlet
of the second
agitation chamber, the solids outlet of the second settling chamber leads to
the inlet of the
third agitation chamber and the solids outlet of the third settling chamber
leads to the fourth
agitation chamber;
(b) means to introduce the solids, the oil and the aqueous phase through the
inlet
of the first agitation chamber;
(c) solid collection means associated with the solids outlet of the fourth
settling
chamber;
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219632
(d) transfer means associated with each of the solids outlet of the settling
chambers
to transfer solids from the settling chamber to the next agitation chamber or
the solid
collection means.
The agitation means may comprise a rotatable paddle having an axis of rotation
and at least one baffle member. In a preferred embodiment, there are two
baffle members
which are elongate and oriented parallel to the axis of rotation of the
paddle.
There may also be first, second, third and fourth transfer tanks associated
with
the fluid outlets of the first, second, third and fourth settling chambers
respectively, wherein
the transfer tanks receives the oil and aqueous phase from the corresponding
settling chamber
and at least one transfer tank comprises skimming means to collect oil which
coalesces and
floats to the top of the fluid within each oil skimmer tank. The first, second
and third
transfer tanks may comprise skimming means to collect oil which coalesces and
floats to the
top of the fluid within each transfer tank.
In a preferred embodiment, a fresh water supply is provided which is
associated
with the fourth agitation chamber along with a disposal tank and aqueous phase
circulation
means for introducing fresh water into the fourth agitation chamber and
circulating the
aqueous phase from the fourth transfer tank to the third agitation chamber,
from the third
transfer tank to the second agitation chamber, from the second transfer tank
to the first
agitation chamber and from the first transfer tank to the disposal tank.
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~ns~2z
In a preferred embodiment, the solid transfer means comprises at least one
pressurized fluid jet. Further, each settling chamber has a bottom end and
defines a bottom
opening and comprises a door associated with the bottom opening and moveable
between a
closed position and an open position and wherein the bottom opening is
positioned above the
inlet of the next agitation chamber in the case of the first, second and third
settling chambers
or the solid collection means in the case of the fourth settling chamber,
whereby solids
passing through the bottom opening enter the next agitation chamber on the
solid collection
means.
The at least one pressurized fluid jet causes solids settled at the bottom of
each
settling chamber to pass through the bottom opening when the door is in the
open position.
There may be a plurality of upper and lower pressurized fluid jets and control
means to
activate the fluid jets sequentially with the opening and closing of the door
in the following
sequence:
(a) once the level of solids settled at the bottom of the settling chamber
exceeds a
predetermined level above the upper fluid jet, the door is opened;
(b) the lower fluid jets are activated;
(c) the door is closed; and
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219~~N~
(d) the upper fluid jets are activated;
whereby the activation of the lower fluid jets causes a portion of the settled
solids to be
displaced and pass through the opening and the activation of the upper fluid
jets causes the
remaining settled solids to take the place of the displaced settled solids.
In a second aspect of the invention, its method form, the invention comprises
a
method for separating solids comprising sand from oil in a feedstock
comprising the solids
and the oil, the method comprising the steps of:
(a) combining the feedstock with an aqueous phase comprising water and an
effective amount of a surfactant to form a first mixture;
(b) agitating the first mixture at a temperature in the range of about 85 to
95°C to
form a first froth-like emulsion;
(c) removing the first emulsion and allowing the first emulsion to settle such
that
the oil coalesces and separates from the aqueous phase and the solid particles
settle;
(d) removing the settled solids from step (c) and combining the settled solids
with
additional aqueous phase to form a second mixture;
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296522
(e) repeating steps (b), (c) and (d) as steps (e. l), (e.2) and (e.3) with the
second
mixture;
(f) removing the settled solids from step (e.3) and combining the settled
solids
with additional aqueous phase to form a third mixture;
(g) repeating steps (b), (c) and (d) as steps (g.1), (g.2) and (g.3) with the
third
mixture;
(h) combining the settled solids from step (g.3) with additional aqueous phase
and
agitating to wash the solids;
(i) collecting the solids.
The additional aqueous phase added to the agitation of step (h) comprises an
effective amount of a demulsifier and may or may not comprise the surfactant
agent. The
agitation steps occur within agitation chambers of the apparatus described
herein. The settling
steps occur within settling chambers of the apparatus described herein. The
settling chambers
comprise transfer means to remove solids accumulated at the bottom of the
settling chamber
and deposit the solids into the next cell.
2196522
~.
The aqueous phase is recirculated by the following additional steps:
(a) recovering the aqueous phase from the fourth settling chamber and
transferring
said aqueous phase to the third agitation chamber;
(b) recovering the aqueous phase from the third settling chamber and
transferring
said aqueous phase to the second agitation chamber;
(c) recovering the aqueous phase from the second settling chamber and
transferring
said aqueous phase to the first agitation chamber; and
(d) recovering the aqueous phase from the first settling chamber and
transferring
said aqueous phase to a disposal tank from where said aqueous phase may be
disposed or
transferred to the first agitation chamber.
As a result of the recirculation of aqueous phase, some demulsifier is present
in
each of the agitation steps. Feedstock is continuously added to the first
agitation chamber and
each step of the method is substantially continuous once the method is
initiated.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic diagram of a preferred embodiment of the invention.
_g_
219622
Figure 2 is a cross-sectional view of a settling chamber of the invention.
Figure 3 is a cross-sectional view of an agitation chamber of the invention.
Figure 4 is a plan view of a treatment cell.
Figure 5 is a cross-sectional view of a skimmer tank of the invention.
BEST MODE OF CARRYING OUT INVENTION
Referring to Figure 1, the invention in its apparatus form is an apparatus for
separating an inert, solid inorganic fraction comprising sand from oil in a
feedstock
comprising the solid fraction, oil and an aqueous phase. The apparatus
comprises four cells
each comprising an agitation chamber and a settling chamber. In the preferred
embodiment of
the apparatus, the four cells are arranged in a cascading fashion to assist in
the flow of
feedstock through the apparatus. Feedstock is received in the first cell and
moves through the
cells in sequential order, as described hereinafter. The preferred embodiment
is hereinafter
described in relation to an apparatus where each agitation chamber is
approximately 3 metres
long, 2.5 metres wide and 2 metres deep, with a capacity of approximately 50
barrels. Each
corresponding settling chamber has an approximate capacity of 10 barrels. Of
course, the
invention described herein is not limited to an apparatus of those dimensions
and may be
practised on a larger or smaller scale.
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CA 02196522 2003-11-03
In a second aspect of the invention, the invention is a method for separating
an
inert, solid inorganic fraction comprising sand from oil in a feedstock
comprising the sand, oil and
an aqueous phase. The invention in its method form will be described
concurrently with the
description of the apparatus and its operation.
Referring to Figures 2, 3 and 4, each cell is comprised of an agitation
chamber and
a settling chamber which are separated by a short transfer pipe. Each cell,
and the apparatus in
general, is constructed using conventional and well-known tank fabrication
techniques. In the
preferred embodiment, the agitation chamber is substantially rectangular in
shape while the
settling chamber is cylindrical. The settling chamber has a conically tapered
bottom section. The
transfer pipe between the agitation chamber and the settling chamber allows
overflow from the
agitation chamber to enter the settling chamber.
The flow of feedstock through the invention is as follows. Oily sand to be
processed is introduced into the first agitation chamber by means of a
conveyor. The feedstock
passes through a shaker screen to separate larger particles. Feedstock is then
mixed with water
which is recycled from the process as described below and a surfactant which
is injected into the
first agitation chamber by means of a chemical pump. The oil, sand and aqueous
phase are
agitated in the agitation chamber by a paddle which is mounted on an axle for
rotation. The
agitation produces a frothy emulsion which overflows into the first settling
chamber through the
transfer pipe. The overflow of feedstock into the first settling chamber is
caused by continuous
addition of feedstock into the first agitation chamber. In the first
219~~2~
settling chamber, the sand settles to the bottom and is transferred to the
next agitation
chamber as described below. The oil and aqueous phase is drawn off and pumped
to a first
skimmer tank where the oil is allowed to coalesce and float to the surface and
is collected.
The aqueous phase from the first skimmer tank is pumped to a disposal tank
where it may
either be pumped down a disposal well or reused in the first agitation
chamber. The process
of agitation with chemical treatment and settling is repeated in the second,
third and fourth
cells. Sand from the fourth settling chamber is transferred to a basket
centrifuge to remove
water. The end product is clean, dry sand.
The paddle is rotated by conventional motor means which produces sufficient
power to effectively agitate the feedstock. In the preferred embodiment, an
electric motor
having a peak capacity of 30 h.p. is effective. The agitation process is aided
by baffles
which run longitudinally across the agitation chamber, parallel to the axle
and paddle. The
baffles are preferably cylindrical and placed on either side of the paddle.
In the preferred embodiment, the paddle is centrally located within the
agitation chamber and rotates about a horizontal axis which is centred in the
horizontal plane,
as shown in Figure 2, and is located just below centre in the vertical plane,
as shown in
Figure 3. The paddle comprises two blades affixed to the axle in a planar
manner. The
blades are shaped to be wider at the two ends of the paddle as illustrated in
Figure 3.
Agitation is also aided by a sloping floor as shown in Figure 3. In the
preferred embodiment,
the floor is sloped in stages to approximate a curve which steepens as it
approaches the lateral
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2I9G~2~
walls of the agitation chamber which are parallel to the rotation axis of the
paddle. The
radius of the curve is perpendicular to the rotation axis of the paddle. The
purpose of the
curve is to eliminate corners in the agitation chamber to ensure that
feedstock does not get
trapped where it might not be effectively agitated.
As shown in Figure 2, each settling chamber has a comically tapered bottom
portion and hydraulically actuated bottom doors. Water jets are provided at
four levels along
the bottom portion to approximately midway up the settling chamber. As the
sand settles to
the bottom, it compacts slightly under its own weight and may not move even
when the
bottom doors open. To displace the sand into the next cell, water is jetted
into the settling
chamber from the lower two rows of jets which dislodges the bottom level of
sand up to the
second row of jets. The dislodged sand falls through the open bottom doors and
into the next
agitation chamber. The doors are then closed. Next, the upper two rows of jets
are activated,
dislodging the sand level with the upper rows and allowing that sand to settle
to the bottom of
the settling chamber. Once enough sand settles to again reach past the
uppermost row of jets,
the process may be repeated. If the settlement rate of sand in the settling
chamber is known,
the sequential operation of the doors and water jetting may be operated by a
timer.
Alternatively, sensors (not shown) may be placed within the settling chamber
to determine the
level of settled sand and sequentially activate the doors and water jets.
As shown in Figure 1, first, second, third and fourth skimmer tanks are
provided to receive the fluid component comprising the oil and aqueous phases
which is
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2191522
recovered from the first, second, third and fourth settling chambers
respectively. The first,
second and third skimmer tanks include means to skim off the oil which
coalesces and floats
to the top and pumps to draw off the aqueous phase for recycling within the
system. The
fourth skimming tank in the preferred embodiment does not require skimming
means to
collect oil as there is insufficient oil in that tank to coalesce and float to
the surface.
As shown in Figure 5, the skimmer tanks are of conventional construction,
having a skimming chamber, a water chamber, a baffle separating the two
chambers, an inlet,
an oil outlet and a water outlet. The baffle is raised approximately 30
centimeters off the
skimming tank floor to allow passage of the aqueous phase into the water
chamber while the
oil remains in the skimming chamber.
The aqueous phase from the first skimmer tank is pumped to a disposal tank
which acts as a reservoir for the system. Excess fluid in the disposal tank
may be pumped
down a disposal well. If additional fluid is required in the first agitation
chamber, it may be
drawn from the disposal tank. Aqueous phase from the second skimmer tank is
pumped into
and reused in the first agitation chamber. Similarly, aqueous phase from the
third skimmer
tank is pumped into the second agitation chamber and aqueous phase from the
fourth skimmer
tank is pumped into the third agitation chamber.
Each agitation chamber is heated by a conventional steam coil to a temperature
of approximately 90° Celsius. It has been found that effective results
are obtained in the
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219u52~
range of 85° to 95° Celsius. In the first agitation chamber, the
paddle is rotated at
approximately 60 rpm which produces a froth-like emulsion of oil, sand and the
aqueous
phase. A surfactant is added to the first agitation chamber to aid in the
separation of the oil
from the sand.
In the second agitation chamber, the agitation step is repeated under
identical
conditions to the first agitation chamber. Aqueous phase containing surfactant
from the third
skimmer tank is added as described above. Additional surfactant is added if
necessary to
bring the concentration of surfactant in the aqueous phase to an effective
level. As in the first
cell, a froth-like emulsion is produced which is drawn off through the
transfer pipe into the
second settling chamber. There again, the sand settles to the bottom. When the
second
settling tank fills to capacity, the step of jetting the sand to the next
(third) agitation chamber
is repeated. From the second settling chamber, the oil and the aqueous phase
are pumped to
the second skimmer tank. After sufficient oil has accumulated in the second
settling tank, it
is skimmed off and collected. The aqueous phase is pumped back to the first
agitation
chamber to be reused in the system.
The agitation step is repeated in the third agitation chamber with sand from
the
second settling chamber and aqueous phase from the fourth skimming tank. It is
unnecessary
to agitate this mixture as vigorously as in the first two agitation chambers
as most of the oil
has been removed from the feedstock by this point in the process. In the
preferred
embodiment agitation in the range of 20 to 40 rpm is sufTicient. Again, the
agitated mixture
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2~9G52~
i
feeds into the third settling chamber where the sand settles to the bottom and
is transferred to
the fourth agitation chamber. The aqueous phase and oil is removed to a third
skimming tank
where the oil skimming step is repeated. The aqueous phase from the third
skimming tank is
reintroduced into the system in the second agitation chamber.
The fourth cycle is primarily a wash cycle to remove all traces of treatment
chemicals and soluble components from the initial feedstock. Sand from the
third settling
chamber is combined with fresh water and agitated in the fourth agitation
chamber. No
surfactant is added because the sand is substantially free of oil. As in the
third agitation
chamber, vigourous agitation is unnecessary: rotation of the paddle in the 20
to 40 rpm range
is sufficient. A demulsifier is added to the fourth agitation chamber to
clarify the aqueous
phase. As in the previous three cycles, the sand mixture enters the fourth
settling chamber
where the sand settles out. The sand is jetted with fresh water to a
centrifuge basket which
removes the water, leaving clean dry sand. Other means to dry the sand may be
used in place
of the centrifuge basket, however, it is preferable that the water recovered
from the drying
means be recycled in the system. The water removed by the centrifuge basket
may be
recycled into the fourth agitation chamber.
As in the previous three cycles, the aqueous phase is collected in the fourth
skimming tank. No oil is recovered from the fourth settling tank because there
is very little
oil associated with the sand entering the fourth cell and also because no
surfactant is used in
the fourth cell.
-15-
219GS2)
1
Because the aqueous phase is recycled from each cell to the previous cell, the
demulsifier added to the fourth cell fords its way back to the first cell, in
diminishing
concentration through the cells. Therefore, in the first cell, the demulsifier
is present,
although significantly more dilute than in the fourth cell, along with the
surfactant which is
added to the first agitation chamber. The demulsifier should not interfere
with the efficacy of
the surfactant in the first agitation chamber. The concentration of the
surfactant is such that
the oil is effectively removed from the sand in the first agitation chamber
but is not so high
as to interfere in any appreciable way with the separation of the oil from the
aqueous phase in
the first skimming tank. The same may be true of the second and third skimming
tanks.
A surfactant which is suitable and effective for this process is X-TOL XT-
85'"'
which is available commercially from Petrolite Canada Inc., Calgary, Alberta.
According to
the manufacturers description, XT-85~ is a water soluble, acidic surfactant
which disperses
and suspends organic and inorganic acids and solubilizes heavy hydrocarbons. A
suitable and
effective demulsifying agent is Reaction 11104'M which is available
commercially from
Edmonton Chemical Distributors Inc., Edmonton, Alberta. According to the
manufacturer's
description, Reaction 11104T"' is a solution of cationic polyamines which
effectively clarifies
water by resolving oil in water emulsions.
The surfactant and the demulsifier are used in accordance with the
manufacturer's specifications. In the preferred embodiment of the present
invention, XT-85T°'
is injected into the first, second and third agitation chambers to achieve a
concentration of 100
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21g~~2z
ppm ( I litre per 100 barrels) continuous. Reaction 11104'M is introduced at a
rate of 25 ppm
continuous into the fourth agitation chamber.
Once the preferred process has been initiated, only small amounts of the
surfactant need be added to the first and second agitation chambers to
maintain an effective
concentration because of the recirculation of the aqueous phase from the third
cell. However,
because the aqueous phase in the third cell is free of surfactant, greater
amounts of the
surfactant should be added to the third agitation chamber to achieve an
effective
concentration.
Testing of the inventive process on a bench scale prototype apparatus was
performed on a variety of samples to determine the oil content remaining on
the sand.
Dichloromethane (DCM) extractions were performed on dried samples of sand
produced by
each wash cycle and the results are shown in the following table:
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219G~22
TABLE 2
DCM EXTRACTION OF COMPARTMENT CONTENTS
Sample No. W1% Oil in Wt% Oil in Wt% of OriginalWt% of Original
Feed Extracted Oil ExtractedOil in Sand
Sand Sand
54.4(R1-C1) 1.89 0.202 89.31 10.69
54.4(R1-C2) 1.89 0.137 92.75 7.25
54.4(Rl-C3) 1.89 0.133 92,96 7.04
54.4(R1-C4) 1.89 0.036 98.10 1.9
54.4(R2-CI) 1.89 0.212 88.78 11.22
54.4(R2-C2) 1.89 0.157 91.69 8.31
54.4(R2-C2) 1.89 0.135 92.86 7.14
54.4(R2-C4) 1.89 0.018 99.05 0.95
54.9(Rl-C2) 11.22 0.201 98.21 1.79
54.9(Rl-C3) 11.22 0.150 98.66 1.34
54.9(Rl-C4) 11.22 0.106 99.06 0.94
Note: Cl, C2, C3, C4 denote compartment numbers
R1 denotes the first run and R2 denotes the second ran.
As may be seen sample, 54.4 was subjected to two runs: Rl and R2. In Rl, the
sample
began at 1.89% oil (w:w). The first wash cycle reduced oil content to 0.202%.
Further wash
cycles reduced oil content to 0.036%. In R2, a reduction to 0.018% was
achieved. Sample
54.9 began at 11.22% oil, which was reduced to 0.106% after four wash cycles.
Another sample (54.11) began with 7.79% oil and was reduced to 1.29% oiI
after four wash cycles. This was an unacceptable result and was found to have
resulted from
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219522
a high level of polar compounds which were resistant to the surfactant action
of XT-85'~"I. In
such a case, it is likely necessary to vary the surfactant to deal with the
chemical composition
and nature of the feedstock.
In the first, second and third settling tanks, very fine solids, less than 5
microns
in diameter such as clay and shale, settle out and must be periodically
removed from the
bottom of the tank. A convenient method of removal is use of a "stinging" and
vacuum
process, which is well known in the art.
The test data was obtained using a process which did not feature the recycling
and recirculation of the aqueous phase, however, the concentrations of the
surfactant and the
demulsifier were such that similar results should be achieved in both
instances.
Those skilled in the art will readily appreciate that modifications can be
made
in the arrangement of the present invention while remaining within the scope
of the present
invention.
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