U.S. patent application number 12/851250 was filed with the patent office on 2011-03-17 for heat and water recovery from oil sands waste streams.
Invention is credited to James A. Dunn, Payman Esmaeili, Brian C. Speirs.
Application Number | 20110061610 12/851250 |
Document ID | / |
Family ID | 41571017 |
Filed Date | 2011-03-17 |
United States Patent
Application |
20110061610 |
Kind Code |
A1 |
Speirs; Brian C. ; et
al. |
March 17, 2011 |
Heat and Water Recovery From Oil Sands Waste Streams
Abstract
Methods and systems for recovering heat and water from waste
streams produced during oil sands extraction to form dry, stackable
tailings. A tailings stream is preheated in a heat exchanger,
thereby reducing the energy required to dry the tailings. The
preheated tailings are then dried, thereby reducing the tailings to
dry stackable tailings or thickened tailings suitable for mine
backfill. Heat and high-quality water are recovered from the drying
operation and re-used in the preheat operation, or in other steps
of oil sands extraction or treatment processes, thereby reducing
the overall heat and water requirements.
Inventors: |
Speirs; Brian C.; (Calgary,
CA) ; Esmaeili; Payman; (Calgary, CA) ; Dunn;
James A.; (Calgary, CA) |
Family ID: |
41571017 |
Appl. No.: |
12/851250 |
Filed: |
August 5, 2010 |
Current U.S.
Class: |
122/32 |
Current CPC
Class: |
Y02P 70/40 20151101;
F26B 23/002 20130101; F26B 2200/14 20130101; C10G 1/047 20130101;
Y02P 70/405 20151101; Y02P 70/10 20151101; C10G 1/045 20130101;
F26B 1/00 20130101 |
Class at
Publication: |
122/32 |
International
Class: |
F22B 1/02 20060101
F22B001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 16, 2009 |
CA |
2,677,479 |
Claims
1. A method for treating a tailings stream produced during
extraction of bitumen from oil sands, comprising: drying the
tailings stream in a dryer using input steam in indirect thermal
contact with the tailings stream to produce a dried tailings
stream, whereby the input steam converts to a condensed water
effluent; and recycling steam produced from the dryer back into the
dryer, wherein the input steam comprises (i) the recycled steam and
make-up steam, or (ii) the recycled steam passed through a
compressor, and optionally make-up steam.
2. The method of claim 1 further comprising, prior to drying the
tailings stream, introducing the tailings stream into a heat
exchanger to preheat the tailings stream and produce a preheated
tailings stream which is then fed into the dryer.
3. The method of claim 2 wherein the preheating in the heat
exchanger is by indirect contact with the condensed water effluent
which is passed from the dryer.
4. The method of claim 2 wherein the heat exchanger is a
self-cleaning heat exchanger.
5. The method of claim 1 wherein the input steam comprises the
recycled steam and the make-up steam.
6. The method of claim 1 wherein the tailings stream comprises at
least one of the following: coarse tailings, fine tailings, froth
separation tailings, and tailings solvent recovery unit
tailings.
7. The method of claim 6 wherein the fine tailings comprise a
middling stream, flotation tailings, or mature fine tailings.
8. The method of claim 1 further comprising increasing a solid
content of the tailings stream fed to the dryer by introducing a
portion of the dried tailings stream into the tailings stream.
9. The method of claim 1 wherein the step of drying the tailings
stream is carried out below atmospheric pressure, such that the
boiling point of water is reduced, leading to a lower temperature
of the dried tailings.
10. The method of claim 9 wherein the dryer pressure is controlled
by an ejector, the ejector also serving to remove produced steam
from the dryer, and to mix the steam produced from the dryer with
make-up steam.
11. The method of claim 1 wherein the input steam comprises a
combination of recycled steam and make-up steam passed through the
compressor.
12. The method of claim 1 further comprising recovering at least
one heavy mineral from the dried tailings stream.
13. The method of claim 12 wherein the at least one heavy mineral
comprises zirconium oxide or titanium oxide.
14. The method of claim 1 further comprising mixing the dried
tailings with a bypass stream of untreated tailings.
15. The method of claim 1 wherein the condensed water effluent from
the dryer is processed in a separation step to recover condensed
hydrocarbons.
16. A system for treating a tailings stream produced during
extraction of bitumen from oil sands, comprising: a dryer for
receiving the tailings stream and input steam, drying the tailings
stream using heat from the input steam, and producing a condensed
water effluent; and a steam recycling unit for recycling steam
produced from the dryer back into the dryer, wherein the input
steam comprises (i) the recycled steam and optionally make-up
steam, or (ii) the recycled steam passed through a compressor, and
optionally make-up steam.
17. The system of claim 16 further comprising a heat exchanger for
receiving the tailings stream and the condensed water effluent from
the dryer in indirect thermal contact with one another, and
preheating the tailings stream using heat from the condensed water
effluent, prior to drying.
18. The system of claim 16 further comprising an ejector for
providing the input steam.
19. The system of claim 18 wherein the ejector is also for
controlling a pressure environment in the dryer.
20. The system of claim 16 wherein the input steam comprises steam
removed from the dryer and passed through a compressor, with
make-up steam as required.
21. The system of claim 20 wherein the make-up steam is combined
with the steam removed from the dryer before the compressor.
22. The system of claim 20 wherein the make-up steam is combined
with the steam removed from the dryer after the compressor.
23. The system of claim 16 wherein the dryer comprises a shell for
receiving the input steam and a cavity for receiving the preheated
tailings stream, the shell and the cavity being distinct
compartments in thermal communication with one another.
24. The system of claim 16 further comprising a mixer for adding a
bypass stream of untreated tailings to dried tailings exiting the
dryer.
25. A method for treating a tailings stream produced during
extraction of bitumen from oil sands, comprising: a) introducing
the tailings stream and a flue gas into a first heat exchanger to
preheat the tailings stream, b) introducing the tailings stream
into a second heat exchanger to preheat the tailing stream, wherein
step a) is performed before step b) or step b) is performed before
step a), to produce a preheated tailings stream, c) drying the
preheated tailings stream in a dryer using input steam in indirect
thermal contact with the preheated tailings stream to produce a
dried tailings stream, whereby the input steam converts to a
condensed water effluent, d) recycling steam produced from the
dryer back into the dryer, wherein the input steam comprises (i)
the recycled steam and optionally make-up steam, or (ii) the
recycled steam passed through a compressor, and optionally make-up
steam; and e) passing the condensed water effluent from the dryer
to the second heat exchanger to preheat the tailings stream.
26. A system for treating a tailings stream produced during
extraction of bitumen from oil sands, comprising: a first heat
exchanger for receiving the tailings stream and a flue gas, and
preheating the tailings stream using heat from the flue gas; a
second heat exchanger for receiving the tailings stream and a
condensed water effluent and preheating the tailings stream using
heat from the condensed water effluent, wherein the first or the
second heat exchanger is placed upstream of the other; a dryer for
receiving the preheated tailings stream and input steam, heating
the preheated tailings stream using heat from the input steam to
produce a dried tailings stream, and producing the condensed water
effluent used in the second heat exchanger; and a steam recycling
unit for recycling steam produced from the dryer back into the
dryer, wherein the input steam comprises (i) the recycled steam and
optionally make-up steam, or (ii) the recycled steam passed through
a compressor, and optionally make-up steam.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from Canadian Patent
Application 2,677,479 filed 16 Sep. 2009 entitled HEAT AND WATER
RECOVERY FROM OIL SANDS WASTE STREAMS, the entirety of which is
incorporated by reference herein.
FIELD OF THE INVENTION
[0002] The present invention relates generally to recovery of heat
and water from waste streams produced during oil sands
extraction.
BACKGROUND OF THE INVENTION
[0003] Oil sands are deposits comprised of bitumen, clay, sand, and
connate water, and make up a significant portion of North America's
naturally-occurring petroleum reserves. To produce a marketable
hydrocarbon product from the oil sands, the bitumen must be
recovered from the oil sands matrix. Depending on geographic
location, bitumen may be recovered by surface mining or in-situ
thermal methods, such as steam assisted gravity drainage (SAGD),
cyclic steam stimulation (CSS), vapor extraction process (VAPEX),
liquid addition to steam for enhancing recovery (LASER) or
derivatives thereof.
[0004] Because the bitumen itself is a highly viscous material,
separating it from the extracted sands poses certain practical
difficulties. The common industry practice for bitumen recovery (or
extraction) from surface mineable oil sands is based on the Clark
Hot Water Extraction (CHWE) process. This process is a water-based
bitumen extraction process, where hot water, air, and process aides
are added to crushed ore. An oil-rich froth "floats" or rises
through the mixture as a hydrocarbon phase. The result is an
extract that typically comprises two parts: a hydrocarbon phase
known as a bitumen froth stream, made up of bitumen, water and fine
solids, and an aqueous phase known as extraction tailings, made up
of coarse solids, fine solids, water and some unrecovered
hydrocarbon. The bitumen froth stream typically comprises bitumen
(approximately 60% by weight), water (approximately 30% by weight)
and solids (approximately 10% by weight), and must undergo a froth
treatment process to separate the organic compounds from the water
and the solid contaminants. Due to the high viscosity of the
bitumen froth, the first step is typically the introduction of a
solvent, usually a hydrocarbon solvent such as a naphtha or a
paraffinic solvent. This step is known as froth separation (FS),
and helps to accelerate the separation of solid particles dispersed
within the froth by both increasing the density differential
between the bitumen, water, and solids and lowering bitumen
viscosity. Separation is carried out by any number of methods, such
as centrifugation or simply allowing solids to settle by gravity.
The result of the froth treatment process is diluted bitumen and a
second tailings stream, known as froth treatment tailings, made up
of water, solids, residual solvent and residual hydrocarbon, that
requires secondary treatment to recover the residual solvent and
prepare the tailings for disposal. The first step in this secondary
treatment process is to recover as much of the residual organic
solvent as possible through any number of processes known
collectively as tailings solvent recovery (TSR). Recovered solvent
can then be reused in the FS process. Tailings from a TSR unit,
known as TSRU tailings, are then disposed of into storage (or
tailings) ponds. The specific properties of the tailings will vary
depending on the extraction method and processing step from which
they originate, but in all cases, the tailings streams are
essentially spent water, process aids, residual hydrocarbon and
waste solids left over once the usable bitumen has been
removed.
[0005] While effective, the extraction treatment processes require
the use of significant quantities of water, and heat to raise the
temperature of the water, which significantly increases the cost
associated with recovery of petroleum from the bitumen-laden oil
sands. Most of the process inputs, including the water and energy
used in the processes end up in the product streams; over 60% of
the enthalpy invested in the extraction process is "lost" to the
tailings stream, along with approximately three barrels of water
per barrel of bitumen extracted.
[0006] One known method of recovering the water is to simply store
the tailings stream in tailings ponds, and allow the solid
components to settle and separate from the water over time. The
heat content of tailings escapes into the atmosphere, while the
tailings water is retained for future use, with some loss due to
evaporation. This tailings storage method is ineffective for at
least three reasons: firstly, it is not very efficient, as a
significant amount of time is required for most of the solid
materials to settle out of the tailings by operation of gravity
alone; secondly, it does not allow for the recovery of any of the
large amount of energy contained within the tailings stream in the
form of heat, which is significant, as tailings are initially sent
to the ponds for storage at temperatures between 20 and 90.degree.
C.; thirdly, the resulting tailings ponds are voluminous, occupying
a large footprint of land that cannot be used for any other
purposes during the settling process.
[0007] Rather than simply storing the tailings in ponds, it is
desirable to recover as much of the invested water and enthalpy
from the tailings stream as possible to reduce the overall cost of
extracting bitumen from the oil sands, to minimize land footprint
and to minimize fresh water withdrawal. The energy and water
recovered can ideally be reused in the extraction process. This has
the advantage of improving the overall energy efficiency of the
extraction process. It is further desirable to minimize the volume
of tailings that must be disposed. By removing as much water as
possible from tailings, the waste streams can be substantially
reduced to the sand, clay and other minerals originally extracted
from the oil sands. In this form, the tailings can be easily
disposed of through, for example, direct mine refill to reduce or
eliminate tailings ponds and minimize land footprint.
[0008] Several attempts to recover heat, water and other reagents
from tailings streams are known. Exemplary methods are disclosed in
U.S. Pat. Nos. 4,343,691, 4,561,965 and 4,240,897, all to
Minkkinen. These patents are directed to heat and water vapor
recovery using a humidification/dehumidification cycle. U.S. Pat.
No. 6,358,403 to Brown et al. described a vacuum flash process used
to recover hydrocarbon solvents from heated tailings streams. There
has been, however, a lack of success in effective water and energy
recovery.
[0009] For both economic and environmental reasons, it is desirable
to provide an alternative method for recovering water and energy
from tailings streams, as well as to reduce the overall volume of
tailings that must be disposed of.
SUMMARY OF THE INVENTION
[0010] It is therefore an object of the present invention to
obviate or mitigate at least one disadvantage of known systems or
methods.
[0011] In one aspect, there is provided methods and systems for
treating tailings produced during oil sands extraction. A tailings
stream is preheated in a heat exchanger, thereby reducing the
energy required to dry the tailings. The preheated tailings are
then dried, thereby changing the tailings to dry stackable tailings
or thickened tailings suitable for mine backfill. Heat and
high-quality water are recovered from the drying operation and
re-used in the preheat operation, or in the oil sands extraction
process, thereby reducing the overall heat and water
requirements.
[0012] In accordance with another aspect, there is provided a
method for treating a tailings stream produced during extraction of
bitumen from oil sands, comprising: drying the tailings stream in a
dryer using input steam in indirect thermal contact with the
tailings stream to produce a dried tailings stream, whereby the
input steam and evaporated water from the tailings evaporated
during drying convert to a condensed water effluent; and recycling
steam produced from the dryer back into the dryer, wherein the
input steam comprises the recycled steam and optionally make-up
steam.
[0013] In accordance with yet another aspect, there is provided a
system for treating a tailings stream produced during extraction of
bitumen from oil sands, comprising: a dryer for receiving the
tailings stream and input steam, drying the tailings stream using
heat from the input steam, and producing a condensed water
effluent; and a steam recycling unit for recycling steam produced
from the dryer back into the dryer, wherein the input steam
comprises the recycled steam and optionally make-up steam.
[0014] In accordance with still another aspect, there is provided a
method for treating a tailings stream produced during extraction of
bitumen from oil sands, comprising: a) introducing the tailings
stream and a flue gas into a first heat exchanger to preheat the
tailings stream, b) introducing the tailings stream into a second
heat exchanger to preheat the tailing stream, wherein step a) is
performed before step b) or step b) is performed before step a), to
produce a preheated tailings stream, c) drying the preheated
tailings stream in a dryer using input steam and evaporated water
from the preheated tailings evaporated during drying produced vapor
in indirect thermal contact with the preheated tailings stream to
produce a dried tailings stream, whereby the input steam and the
evaporated water from the preheated tailings convert to a condensed
water effluent, and d) passing the condensed water effluent from
the dryer to the second heat exchanger to preheat the tailings
stream.
[0015] In accordance with still another aspect, there is provided a
system for treating a tailings stream produced during extraction of
bitumen from oil sands, comprising: a first heat exchanger for
receiving the tailings stream and a flue gas, and preheating the
tailings stream using heat from the flue gas; a second heat
exchanger for receiving the tailings stream and a condensed water
effluent and preheating the tailings stream using heat from the
condensed water effluent, wherein the first or the second heat
exchanged is placed upstream of the other; and a dryer for
receiving the preheated tailings stream and input steam, heating
the preheated tailings stream using heat from the input steam to
produce a dried tailings stream, and producing the condensed water
effluent produced in the second heat exchanger.
[0016] Other aspects and features of the present invention will
become apparent to those ordinarily skilled in the art upon review
of the following description of specific embodiments of the
invention in conjunction with the accompanying Figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Embodiments of the present invention will now be described,
by way of example only, with reference to the attached Figures,
wherein:
[0018] FIG. 1 is a flow diagram illustrating an overview of a
method of tailings treatment according to one disclosed
embodiment;
[0019] FIG. 2 is a schematic of an example of a tailings treatment
system in accordance with one disclosed embodiment; and
[0020] FIG. 3 is a schematic of an example of a tailings treatment
system using a flue gas in accordance with one disclosed
embodiment.
DETAILED DESCRIPTION
[0021] Generally, in one embodiment the present invention provides
a method and system for using drying to recover water and heat
energy from tailings streams in oil sands extraction, such as
mature fine tailings, coarse tailings, TSRU tailings, fine
tailings, and froth separation tailings. Because of the high energy
required by conventional drying, using it in the tailings treatment
process has not previously been considered practical; however, by
recovering heat energy from the evaporated water through drying in
accordance with one aspect of the present invention, drying
processes may now form an integral part of the treatment process.
As will become apparent in view of the following examples and
embodiments, water and heat recovered during drying of a tailings
stream can be used to preheat the rest of the tailings stream,
thereby reducing the amount of energy required to be input for the
drying operation. Preheating is optional. While the following
examples are presented in the context of tailings streams generated
by a bitumen extraction process, one of ordinary skill in the art
will appreciate that embodiments of the present invention may be
implemented in any oil sands extraction process that produces a
stream of tailings comprising solid(s) and liquid(s). The system
and methods described herein are equally applicable to any process
using or generating any aqueous slurry or mine tailings. For the
purposes of this description, the general terms "tailings" and
"tailings stream" will be used to denote any aqueous slurry, mine
tailings or other solid-liquid mixture used or generated in mining
or industrial operations from which heat and/or water can be
recovered. Further, the tailings may be provided directly from the
extract from the oil sands, from any secondary (or subsequent)
recovery or any portion of the process that generates water and/or
solids including tailings ponds. The tailings may or may not also
comprise solvents which were added to the oil sands to assist in
the bitumen extraction process.
[0022] A drying operation generally comprises heating the tailings
stream, thereby providing energy required for the water in the
stream to undergo vaporization. Once the phase change occurs, water
vapor is liberated from the tailings stream and can be collected
through a variety of methods, including, but not limited to, vacuum
or steam sweeping. In a drying operation, a dryer must first add
sufficient heat, referred to here as sensible heat, to raise the
temperature of the tailings stream to the boiling point of water.
The dryer must then add the energy required for the water to
undergo the change from its liquid phase to its vapour phase. This
energy is typically referred to as the heat of vaporization. At all
practicable pressures, however, the drying process requires the
addition of a substantial amount of energy. In fact, the major part
of heating requirement can be captured from the vapour produced
during drying. In accordance with one aspect of the present
invention, the recovered heat can be sent directly to the drying
operation. Any recovered heat can be supplemented by additional
energy added to the drying operation through a heat transfer medium
such as fuel or steam to reach the energy threshold required for
the drying process.
[0023] FIG. 1 shows a general overview of an embodiment of the
invention. Tailings stream 100 from a bitumen separation process
undergoes preheat 110. The preheat step is optional. A heat
exchanger is particularly suitable for the preheat operation, as it
allows for indirect transfer of heat from one substance to another
by conduction through a wall or other barrier separating the two
substances. In this manner, the two substances may exchange heat
between one another without ever coming in direct contact with one
another or being mixed in any way. Because of the nature of
tailings streams in oil sands extraction, the environment within
the heat exchanger may be highly susceptible to fouling, or the
accumulation of solid material along its inner surfaces.
Accordingly, in one embodiment of the invention, the heat exchanger
is a self-cleaning heat exchanger of any self cleaning technology
known in the art. Examples include circulating fluidized bed
exchangers (such as those designed by Klaren B V, Rotterdam, The
Netherlands), turbulence inducing or scraping devices, or heat
exchangers with an on-line cleaning design (using circulating
balls), etc. However, as one of ordinary skill in the art will
appreciate, other heat exchangers capable of indirect transfer of
heat from either a liquid or gaseous substance to a tailings stream
may be used.
[0024] By way of background in respect of circulating fluidized bed
exchangers designed by Klaren, BV, self-cleaning heat exchange
technology can be applied in most vertically oriented shell and
tube exchangers. The fouling prone fluid flows upward inside the
tubes, is charged with solid particles that are swept upward with
the fluid producing a scouring action on the walls of the tubes as
they travel. A unique distribution system in the inlet channel
provides a uniform distribution of liquid and particles into all
the tubes. From the outlet channel, the particles are carried to
the separator where they disengage from the liquid and are returned
through the external downcomer into the control channel and from
there through the connecting line between control channel and inlet
channel into the inlet channel. The flow of particles is activated
by the control liquid flow, which is a fraction of the total liquid
flow supplied to the exchanger. By changing the control liquid
flow, the intensity of the cleaning action can be varied. If
desired, the cleaning can also be applied intermittently.
[0025] Preheated tailings stream 115 flows from preheat operation
110 into the drying operation 120. Make-up steam 150 provides dryer
120 with a part of the enthalpy required by the drying process. As
preheated tailings stream 115 is dried, it is separates into two
distinct portions, namely, water vapor 180 and solid cake 140. The
water content of the solid cake 140 may be adjusted to the desired
end-product composition process requirements, and could range from
a pumpable product to a dry cake. The solid cake may comprise
insufficient water to flow, which is usually below about 60 mass %
water. The water content of the solid cake output could also be
between 40 and 60 mass %, or between 0 and 40 mass %. The water
vapor 180 is removed from the dryer and commingled with make-up
steam 150. The addition of stream 180 to make-up steam 150 provides
the rest of enthalpy requirement for the drying process through
condensation in an indirect fashion. Following heat transfer, input
steam 150 is condensed and removed from drying operation 120 as
condensed water effluent 160. The condensed water effluent 160 is
the result of water vapor 180 released from the tailings 115 and
steam introduced to carry out the drying. Condensed water effluent
160 is then used in preheat operation 110. For example, if the
preheat operation employs a heat exchanger, the enthalpy of the
condensed water effluent 160 is transferred to tailings stream 100
through the indirect heat transfer between the compartments of the
heat exchanger. This has the effect of preheating the tailings
stream 100, raising its temperature and reducing the energy
required to carry out the heating in drying operation 120.
Following the indirect heat transfer, much of the enthalpy from
condensed water effluent 160 has been passed to the tailings
stream, and leaves preheat operation 110 as high purity water 170.
A significant benefit of this approach in addition to the drying of
the tailings, is capturing the originally contaminated water
present in the tailings stream as high quality, distilled water. In
another embodiment of this invention, the recovered water stream is
subsequently used in the extraction process or utilized in an
integrated thermal in-situ and mining and extraction operation to
generate steam.
[0026] FIG. 2 shows an example of the tailings treatment system in
accordance with an embodiment of the invention. Tailings stream 200
flows through heat exchanger 210, for instance at a temperature of
approximately 36.degree. C., where it is preheated by condensed
water vapor effluent 240, as discussed above. Suitable temperatures
include those below the boiling point of water. As discussed below,
a portion of tailings stream 200 may form a bypass stream 295. The
preheated tailings 220 then enter dryer 230. The tailings are dried
with heat energy from input steam 237, provided by ejector 235.
This steam is a mixture of the water evaporated during drying and
make up steam added to the system through ejector 235. The role of
the ejector is to produce slight vacuum inside the dryer 230,
remove the produced water vapor 238, mix the produced water vapor
238 with make-up steam 236, and to provide the combined steam at a
higher pressure and temperature than the released vapor from
tailings. Alternatively, produced steam 238 can be compressed using
a compressor, such that minimal or no make-up steam 236 would be
required. Dryer 230 is optionally and preferably in an indirect
dryer configuration, whereby input steam 237 injected into the
dryer is contained within a shell surrounding the dryer cavity, and
does not come into direct contact with the tailings. The heat
required for drying, therefore, is indirectly transferred from the
steam through the shell to the tailings. Input steam 237 loses heat
to the preheated tailings, and, as input steam 237 condenses, the
tailings will absorb the latent heat of condensation of the water
vapor. Any indirectly heated dryer may be used (for example a
rotary drum or paddle), but may optionally comprise design features
that mix the product and/or scrape the drum walls to minimize
thermal resistance. An example of a commercial dryer is the K-S
biosolids dryer system for biosolids and biological sludge drying
(Komline-Sanderson, Peapack, N.J., U.S.A). An indirect steam dryer
is described in U.S. Pat. No. 5,291,668. Dryer 230 may comprise one
or more dryers, in series or parallel, at least one of which uses
indirect steam heating as discussed herein. Other dryer units could
use electrical heating for example. The steam used in the dryer
could be superheated or at any pressure/temperature required.
[0027] As the preheated tailings 220 are dried, water vapor escapes
as produced steam 238. This steam is substantially free of
minerals, as the salts originally contained in the tailings stream
remain with the dried solids. Produced steam 238 is piped back and
mixed with makeup steam 236, such that the enthalpy released during
the drying operation can be conserved and re-used as the drying
operation continues. Hydrocarbons and solvents originating in the
preheated tailings stream 220 that are volatilized and subsequently
condensed in the condensed water vapor effluent 240, in addition to
the water, can be separated from the recovered water and used at
any point in the process. Water-hydrocarbon separations means known
in the art may be used (for example oil removal filters, membranes,
centrifuges, or separators). For instance, a conventional two-phase
separator in stream 240 or 239 could be used. Decantation could
also be used to remove hydrocarbon solvents. However, since the
condensation of produced steam 238 results in clean, high quality
water, one of ordinary skill in the art will appreciate that any
water collected therefrom may be put to any variety of uses,
including, but not limited to, other phases of the oil sands
extraction process. Non-limiting examples of uses for recovered
water include boiler feed water for SAGD operations, utility steam,
makeup water, etc.
[0028] Streams 239 or 240 may be the equivalent of about 48000
m.sup.3/d of warm or hot water. This water may be used in bitumen
extraction to significantly reduce the fresh water requirements of
a conventional bitumen mining and extraction operation, by about
half, for instance. Alternatively, it may be used in a SAGD
operation to supply more than the necessary boiler feed water (BFW)
in a 20,000 bbl/d to 30,000 bbl/d thermal in-situ operation that
may be adjacent to the mining/extraction operation. The recovery of
this water is an alternative method to make BFW from process
affected water.
[0029] According to one embodiment of the invention, input steam
237 has temperature and pressure from ejector 235 of 103.degree. C.
and 113 KPa, respectively. The input steam should be at a
sufficiently higher temperature than both the inlet tailings
temperature and boiling point of water at the cavity operating
pressure to transfer heat across the dryer wall at the desired
rate. Optionally and preferably, ejector 235 also creates a
low-pressure environment, for instance below atmospheric pressure,
within the cavity of dryer 230, such that the boiling point of
water is reduced, leading to a lower temperature of the dried
tailings. The ejector controls pressure in the dryer cavity and in
the dryer shell using makeup steam 236 as a motive fluid. The
pressure in the dryer cavity may be reduced to any practical limit.
Parameters that set the limit are in part based on make up steam
236 pressure, ejector pressure ratio, mass flow rate ratio between
make-up steam 236 and produced steam 238 This lowers the boiling
point of water within the cavity, and the water contained within
the tailings will consequently undergo a phase change to a gaseous
state at a lower temperature and pressure. In this manner, the
ejector can serve two functions: raise the pressure of produced
steam stream 238 so that it can be introduced to dryer 230 at a
higher temperature, and lower the pressure in the cavity of dryer
230 so that tailings water will evaporate at a lower
temperature.
[0030] As it condenses, input steam 237 leaves dryer 230 as
condensed water effluent 240, at a temperature of approximately
83.degree. C., or higher than the tailings temperature in
accordance with this example. Condensed water vapor effluent 240
then flows through a second compartment of heat exchanger 210 and,
through indirect heat transfer, preheats the tailings stream 200
currently flowing through the first compartment. During normal
operation of this embodiment of the invention, sufficient sensible
heat is transferred from condensed water effluent 240 to the
tailings stream 200, such that the temperature of the tailings
increases from 36.degree. C. to 55.degree. C., thereby greatly
reducing the energy required by dryer 230 to dry the preheated
tailings. Following preheat, the condensed water vapor effluent 240
leaves heat exchanger 210 as liquid water at a temperature of
60.degree. C. The recovered water 239 may then be collected and
used in the extraction process or to make boiler feed water for
steam generation in an integrated thermal in-situ and
mining/extraction operation. Higher throughput may also be achieved
where less than the full amount of steam is condensed in the dryer,
but a portion of the steam is condensed in the heat exchanger 210.
Optionally, the preheat heat exchanger may be eliminated, by
increasing the length or surface area of the dryer such that
condensed water vapor effluent 240 leaves the dryer at about
60.degree. C.
[0031] A further aspect of the present invention provides for
converting a tailings stream to dry, stackable tailings that can be
disposed of through, for example, direct mine refill, water
capping, overburden capping, capping with consolidated tailings, or
sand layering. An output of the drying operation is solid cake 250,
which comprises dried clay, sand, residual hydrocarbons and other
mineral deposits from the tailings. Because solid cake 250 has been
separated from much of the water originally contained in tailings
stream 200, the overall volume of tailings to be disposed is
significantly reduced and thus reduces the footprint of the
tailings pond. Optionally, the solid cake is mixed with bypass
stream 295, which is some portion of untreated tailings stream 200,
for instance 5 to 20%, or about 10% in this example. The bypass
stream assists in processing a larger volume of tailings and
produces a pumpable material so that expensive trucks or conveyors
are not required. To make the tailings particularly suitable to
backfill, the moisture content should range from 0-40%, preferably
between 10-20%. This final mixing step is carried out by mixer 280
and results in thickened tailings 290, which is composed of a
substantial portion of solids tailing material, for instance
approximately 75% solid tailings material. Thickened tailings 290
can then be disposed of in any desired manner, although they are
particularly suitable for "back fill," or refilling the oil sands
mine from which the original unprocessed bitumen was extracted.
[0032] According to one embodiment of the invention, solid cake 250
is divided into two parts: solid cake remainder 270 and recycled
solid stream 260. Solid cake remainder 270 then undergoes the
optional mixing treatment discussed above, followed by disposal.
Recycled solid stream 260, which in this example is approximately
50% of solid cake 250, is piped back and mixed with preheated
tailings 220 as the drying operation continues. This increases the
solid content of the dryer's feed, thereby reducing fouling within
the dryer itself Approximately 50% of solid cake 250, is piped back
and mixed with preheated tailings 220 to increase the solid content
of the dryer feed to an acceptable level (for example over 35%). In
this example, the solid content of the dryer's feed was increased
to approximately 37% by combining with the recycle stream. As the
solid content increases, materials become less sticky in the dryer,
which is an advantage in a high temperature operation.
[0033] FIG. 3 shows another embodiment of the present invention,
whereby a tailings stream undergoes two separate preheat operations
to further improve the efficiency of the treatment process.
Elements common between this embodiment and the exemplary
embodiments previously discussed are marked in FIG. 3 with labels
matching those in previous figures, and function as described
above.
[0034] Tailings stream 300 enters a first heat exchanger 301, which
functions according to the same principles described above with
reference to heat exchanger 210. As discussed above, the heat
exchangers are optionally and preferably self-cleaning heat
exchangers to minimize fouling. First, heat exchanger 301 receives
hot flue gas 305 and uses it as the heat source to initially
preheat tailings stream 300. Flue gas 305 (optionally and
preferably with minimal sulfur content) may be sourced from any
other step in the oil sands extraction process or an integrated
thermal in-situ operation that produces a gas capable of flowing
through first heat exchanger 301 and providing heat energy to
tailings stream 300, such as from a boiler. Optionally and
preferably, flue gas 305 passes through fan 310, which serves to
increase the pressure inside first heat exchanger 301, because flue
gas is at atmospheric pressure, and should be increased to account
for the pressure drop within exchanger 301. Fan 310 may also be a
compressor. In one example of the embodiment shown in FIG. 3,
tailings 300 enter heat exchanger 301 at a temperature of
36.degree. C. Flue gas 305 is at a temperature of approximately
150.degree. C., and provides sufficient heat to the tailings in
first heat exchanger 301 so as to increase the temperature of the
tailings to 60.degree. C. An induced fan could be used to pull the
flue gas through the heat exchanger. This would be positioned on
stream 313 and has the benefit of handling a lower temperature,
higher density gas.
[0035] Following the first preheat operation, the cooled flue gas
and any condensed water vapour 306 from first heat exchanger 301 is
collected and separated in separator 311. This allows the system to
recover additional water, as flue gas 305 may contain significant
water content. The water content of cooled flue gas 306 is
collected from separator 311 as condensed liquid 312, which, if
desired, may be added to water 239 (discussed above with reference
to FIG. 2), thereby becoming part of the total water recovered from
the tailings treatment process, or become feed for another process.
The remaining components of cooled flue gas 306 are released from
separator 311 as separator flue gas 313.
[0036] The tailings preheated during the first preheat operation
leave first heat exchanger 301 as initially preheated tailings 302.
These tailings may then undergo a second preheat operation in heat
exchanger 210, which transfers heat to initially preheated tailings
302 from condensed water vapor effluent 240 as discussed above with
reference to FIG. 2. The remaining elements shown in FIG. 3
function in the same manner as the corresponding elements shown in
FIG. 2, and the elements in FIG. 3 are consequently labeled with
identical identifiers for ease of reference to the discussion
above. In particular, a bypass stream 295 is taken from the
tailings stream 300 and mixed with solid cake remainder 270 by
mixer 280 to form thickened tailings output 290. Preheated tailings
220 are fed to dryer 230 and are at, according to this example,
approximately 90.degree. C. Condensed water vapor effluent 240 from
dryer 230 is fed into heat exchanger 210 at approximately
99.degree. C. in this example. Produced steam 238 released from the
dryer 230 is mixed with makeup steam 236 to form input steam 237
which is introduced into dryer 230 by ejector 235. Solid cake 250
exits the dryer once the drying operation is complete. Optionally
and preferably, a portion of solid cake 250 is separated and sent
as recycled solid stream 260 to mix with preheated tailings 220 to
help reduce fouling inside the dryer.
[0037] The embodiments of the invention that include two distinct
preheat steps may provide even greater efficiency to the overall
tailings treatment process, as enthalpy from flue gas 305 which
might otherwise be lost is instead transferred to the tailings
stream, thereby further reducing the heat energy required by dryer
230. In addition, water contained in the flue gas 305 which might
otherwise be lost is instead at least partially collected by
separator 311, and forms part of the total water collected during
the treatment process. However, as one of ordinary skill in the art
will appreciate, flue gas 305 may be sourced from another
industrial or extraction process and still function in accordance
with embodiments of the invention.
[0038] In accordance with another embodiment of the invention,
valuable heavy minerals can be recovered from oil sand tailings.
Heavy minerals are defined herein as minerals having a specific
gravity greater than about 2.85, and including, without being
limited to, such minerals as rutile, ilmenite, leucoxene, siderite,
anatase, pyrite, zircon, tourmaline, garnet, magnetite, manzite,
kyanite, staurolite, mica, and chlorite. Material extracted from
oil sands often includes deposits of usable heavy minerals such as
titanium and zirconium. In order to recover usable resources from
the material, solid cake 250 may also be subjected to a heavy
minerals recovery step. Several non-limiting examples include
gravity, electrostatic, chemical, and magnetic separation
techniques, although another suitable method for extracting heavy
minerals from a solid cake may be used for this purpose. This step
allows for recovery of additional valuable resources from treated
tailings, further improving the recovery of valuable resources
during oil sands extraction, thereby making the entire process more
economically viable and reducing the amount of waste material that
must be disposed of. It should be noted that heavy metal recovery
or another separation process (such as coarse solid removal using a
separation device) may be employed at any point in the tailings
treatments as additional embodiments of the present invention.
[0039] Several other advantages of treating tailings streams
through drying in accordance with the present invention may
include, but are not limited to: recovering extraction process
water as high-quality warm water; achieving a net gain in sensible
heat by an appropriate heat integration scheme; producing dry,
stackable tailings, thereby reducing dykes in current tailings
treatment and reducing the overall volume of tailings that must be
disposed of; reducing the footprint of oil sands extraction, and
allowing for the potential recovery of valuable heavy metal oxides,
such as titanium and zirconium oxides.
Example
[0040] With reference to FIGS. 2 and 3, Table 1 provides flow rates
and temperatures, according to one embodiment, for certain streams
identified by their reference numbers.
TABLE-US-00001 TABLE 1 Flow rates and Temperatures Reference Flow
rate Temperature number (stream) tons per hour (.degree. C.) FIG. 2
200 2820 36 220 2540 55 236 100 147 240 2055 83 270 580 95 290 865
75 295 280 36 239 2055 60 FIG. 3 220 2540 90 236 12.5 147 239 1950
64 240 1950 99 300 2820 36 302 2540 60 305 1100 150 313 1030 40 239
and 312 2035 63 together
[0041] In the preceding description, for purposes of explanation,
numerous details are set forth in order to provide a thorough
understanding of the embodiments of the invention. However, it will
be apparent to one skilled in the art that these specific details
are not required in order to practice the invention.
[0042] The above-described embodiments of the invention are
intended to be examples only. Alterations, modifications and
variations can be effected to the particular embodiments by those
of skill in the art without departing from the scope of the
invention, which is defined solely by the claims appended
hereto.
* * * * *