Note: Descriptions are shown in the official language in which they were submitted.
CA 02948419 2016-11-10
TREATMENT AND RECYCLE OF LANDFILL LEACHATE INTO EVAPORATORS OF
AN IN SITU HYDROCARBON RECOVERY OPERATION
TECHNICAL FIELD
[0001] The technical field generally relates to in situ hydrocarbon
recovery, and
more particular to the treatment of aqueous waste streams derived from
produced water.
BACKGROUND
[0002] In the context of in situ hydrocarbon recovery operations,
production fluid that
is recovered from a production well is separated into a hydrocarbon stream and
a
produced water stream. The produced water stream contains various
contaminants,
including organic compounds, dissolved salts, and suspended solids. The
produced
water can be subjected to water treatment in order to produce a treated water
stream
suitable for use as boiler feed water that can be supplied to a steam
generator, such as
a once-through steam generator (OTSG).
[0003] The water treatment units as well as the OTSG generate contaminant-
enriched aqueous streams, such as blowdown streams. Blowdown streams can be
further treated or supplied to a disposal site. In some situations, the
blowdown streams
are supplied to a zero liquid discharge (ZLD) system that recovers water and
generates
a solids-enriched sludge that is sent to a landfill. There are various
challenges
associated with the handling, treatment and disposal of aqueous waste streams
derived
from produced water.
SUMMARY
[0004] In some implementations, there is provided an in situ hydrocarbon
production
process, comprising: injecting a mobilizing fluid comprising steam into a
hydrocarbon-
containing formation; recovering a production fluid from the formation, the
production
fluid comprising hydrocarbons and water; separating the production fluid into
a
hydrocarbon stream and a produced water stream; subjecting the produced water
stream to water treatment to produce a treated water; feeding the treated
water into a
steam generation unit comprising at least one once-through steam generator
(OTSG), to
produce steam and blowdown; supplying the steam as at least part of the
mobilizing fluid
for injection into the hydrocarbon-containing formation; supplying the
blowdown to a zero
1
CA 02948419 2016-11-10
or reduced liquid discharge (ZLD/RLD) system to produce recovered water and a
solids-
enriched sludge, the ZLD/RLD system comprising at least one evaporator;
supplying the
solids-enriched sludge to a landfill for disposal; retrieving leachate
produced from the
landfill; pre-treating the leachate to produce a pre-treated leachate stream;
and recycling
the pre-treated leachate stream as part of the feed stream supplied into the
at least one
evaporator of the ZLD/RLD system.
[0005] In some implementations, the pre-treating comprising adding a
chemical
agent to the leachate. In some implementations, the chemical agent comprises a
chelating agent, an anionic dispersant for dispersing inorganic suspended
solids, a scale
inhibitor, a hydrocarbon dispersant, and/or an anti-foam agent.
[0006] In some implementations, the mobilizing fluid is dry steam. In some
implementations, the mobilizing fluid is injected via an injection well and
the production
fluids are recovered from a production well. In some implementations, the
injection well
and the production well each has a vertical section and a horizontal section.
In some
implementations, the injection well and the production well form a vertically
spaced-apart
well pair operable for steam-assisted gravity drainage (SAGD).
[0007] In some implementations, the process also includes supplying the
blowdown
to a first evaporator that produces a first condensate stream and a first
evaporator
blowdown stream; supplying the first evaporator blowdown stream to a second
evaporator that produces a second condensate stream and a second evaporator
blowdown stream; supplying the second evaporator blowdown stream to a
crystallizer
that produces a crystallizer slurry; and supplying the crystallizer slurry to
a dryer that
produces the solids-enriched sludge.
[0008] In some implementations, the ZLD/RLD system comprises the first
evaporator, the second evaporator, the crystallizer, and the dryer. In some
implementations, the at least one evaporator that receives the pre-treated
leachate
stream consists of the first evaporator. In some implementations, the at least
one
evaporator that receives the pre-treated leachate stream comprises the first
evaporator.
In some implementations, the at least one evaporator that receives the pre-
treated
leachate stream further comprises the second evaporator.
2
CA 02948419 2016-11-10
[0009] The at least one evaporator that receives the pre-treated leachate
stream
comprises the second evaporator.
[0010] In some implementations, there process also includes supplying a
first portion
of the leachate to the at one evaporator; and supplying a second portion of
the leachate
to the crystallizer. In some implementations, all of the pre-treated leachate
stream is
supplied to a single evaporator. In some implementations, the single
evaporator is the
first evaporator. In some implementations, the single evaporator is the second
evaporator.
[0011] In some implementations, the process also includes supplying the
leachate
from the landfill to a lagoon; supplying the leachate from the lagoon to a
holding tank
that is proximate to the evaporator; and supplying the leachate from the
holding tank to
the at least one evaporator.
[0012] In some implementations, the process also includes combining the pre-
treated leachate stream with the blowdown to form the feed stream supplied
into the at
least one evaporator.
[0013] In some implementations, there is provided a process for treating
landfill
leachate derived from leaching from a solids-rich sludge by-product of an in
situ
hydrocarbon recovery operation, the process comprising recycling a waste water
stream
comprising the landfill leachate into an evaporator that is part of the in
situ hydrocarbon
recovery operation.
[0014] In some implementations, the evaporator is part of a zero or reduced
liquid
discharge (ZLD/RLD) system. In some implementations, the ZLD/RLD system
comprises
a first evaporator, a second evaporator, a crystallizer, and a dryer arranged
in series;
and the waste water stream is recycled into the first evaporator and/or the
second
evaporator. In some implementations, the process also includes pre-treating
the waste
water stream prior to introduction into the evaporator. In some
implementations, the pre-
treating comprises adding a chemical agent to the leachate. In some
implementations,
the chemical agent comprises a chelating agent, an anionic dispersant for
dispersing
inorganic suspended solids, a scale inhibitor, a hydrocarbon dispersant,
and/or an anti-
foam agent.
3
CA 02948419 2016-11-10
[0015] In some implementations, there is provided a process for treating
waste water
derived from a by-product of a bitumen production operation, the process
comprising:
retrieving a waste water stream from a disposal site comprising the by-product
and the
waste water; pre-treating the waste water stream to produce a pre-treated
waste water
stream; and recycling the pre-treated waste water stream into an evaporator
that is part
of an in situ hydrocarbon recovery operation.
[0016] In some implementations, the bitumen production operation is an oil
sands
extraction operation, and the disposal site is a tailings pond from which the
waste water
stream is retrieved. In some implementations, the waste water stream comprises
leachate and the disposal site is a landfill. In some implementations, the
bitumen
production operation is the in situ hydrocarbon recovery operation. In some
implementations, the in situ hydrocarbon recovery operation comprises steam
assisted
gravity drainage (SAGD).
[0017] In some implementations, the by-product comprises a solids-enriched
sludge
that is derived from a zero or reduced liquid discharge (ZLD/RLD) system of
the in situ
hydrocarbon recovery operation. In some implementations, the ZLD/RLD system
comprises a first evaporator, a second evaporator, a crystallizer, and a dryer
arranged in
series; and the waste water stream is recycled into the first evaporator
and/or the
second evaporator.
[0018] In some implementations, the pre-treating comprises adding a
chemical
agent to the waste water stream. In some implementations, the chemical agent
comprises a chelating agent, an anionic dispersant for dispersing inorganic
suspended
solids, a scale inhibitor, a hydrocarbon dispersant, and/or an anti-foam
agent.
[0019] In some implementations, all of the pre-treated waste water stream
is
supplied to the first evaporator. In some implementations, all of the pre-
treated waste
water stream is supplied to the second evaporator.
[0020] In some implementations, there process also includes adding the pre-
treated
waste water stream to a blowdown stream to form an evaporator feed stream; and
supplying the evaporator feed stream to the evaporator. In some
implementations, the
blowdown stream comprises blowdown from a once-through steam generator (OTSG)
that is part of the in situ hydrocarbon recovery operation.
4
CA 02948419 2016-11-10
[0021] In some implementations, there is provided a method for selecting
and
treating waste water streams derived from a hydrocarbon production operation,
comprising: determining compositional characteristics of each waste water
stream;
determining production rates or volumes of each waste water stream;
determining
disposal capacity characteristics of disposal sites at which respective waste
water
streams are held; determining operational feed quality characteristics and
operational
capacity characteristics of one or more units that are part of a zero or
reduced liquid
discharge (ZLD/RLD) system that is part of an in situ hydrocarbon recovery
operation;
and based on the determined compositional characteristics, production rates or
volumes,
disposal capacity characteristics, operational feed quality characteristics,
and
operational capacity characteristics, performing the following steps:
selecting a waste
water stream for recycling and reprocessing; selecting a unit of the ZLD/RLD
system to
receive the selected waste water stream; blending the selected waste water
stream with
the feed of the selected unit to form a combined feed stream; and supplying
the
combined feed stream into the selected unit.
[0022] In some implementations, the selected waste water stream comprises
landfill
leachate and the selected unit comprises an evaporator. In some
implementations, the
selected unit comprises multiple evaporators. In some implementations, the
units of the
ZLD/RLD system comprise an evaporator, a crystallizer, and a dryer. In some
implementations, determining capacity characteristics of the units comprises
determining
capacity of associated vapor coolers.
[0023] In some implementations, there method also includes determining pre-
treatment requirements for the waste water streams based on at least one of
the
following: the determined compositional characteristics, the production rates
or volumes,
the feed quality characteristics of the units, and the capacity
characteristics of the units;
and subjecting the selected waste water stream and/or the combined feed stream
to a
selected pre-treatment.
[0024] In some implementations, the units comprise a mechanical vapor
recompression (MVR) evaporator, an MVR feed flash tank, a steam-driven
evaporator,
and a crystallizer.
CA 02948419 2016-11-10
[0025] It should be noted that variables/characteristics that are obtained
or
measured and used for selection, blending and recycling steps can be dynamic
variables
and can also include static variables such as specifications for units. It
should also be
noted that a select number of variables/characteristics can be used for
selection,
blending and recycling steps, and such selected variables/characteristics can
be chosen
based on their degree of impact on the given process implementation. For
example,
certain variables/characteristics can be used or prioritized if they have a
high impact on
the given process, whereas others that have little to no impact may be
minimized or
ignored.
[0026] In some implementations, there is provided a method for treating
internal
waste water streams generated by an in situ hydrocarbon recovery operation and
external waste water streams obtained from a disposal site, comprising:
analyzing the
internal and external waste water streams to determine compositional
characteristics
thereof; and distributing the internal and external waste water streams as
multiple
recycled waste water streams into an evaporative waste water treatment system
that is
part of the in situ hydrocarbon recovery operation.
[0027] In some implementations, the internal waste water streams comprise
boiler
blowdown. In some implementations, the boiler blowdown is obtained from a once-
through steam generator (OTSG). In some implementations, the external waste
water
streams comprise landfill leachate.
[0028] In some implementations, the method includes subjecting external
waste
water streams to pre-treatment prior to introduction into the evaporative
waste water
treatment system. In some implementations, the pre-treatment comprises
chemical
addition.
[0029] In some implementations, the evaporative waste water treatment
system
comprises a zero or reduced liquid discharge (ZLD/RLD) system.
[0030] In some implementations, the evaporative waste water treatment
system
comprises an evaporator and a crystallizer. In some implementations, the
evaporative
waste water treatment system comprises multiple units and the distributing of
the
multiple recycled waste water streams comprises: supplying a first recycle
stream into
the evaporator; and supplying a second stream into the crystallizer. In some
6
CA 02948419 2016-11-10
implementations, the first and second recycle stream are selected for
recycling into the
evaporator and the crystallizer, respectively, based on silica content. For
example, a
higher silica waste stream can be recycled to the crystallizer while a lower
silica waste
stream can be recycled to the evaporator.
[0031] The techniques described herein can facilitate various advantages,
such as
facilitating operational advantages in a ZLD/RLD system, reducing fresh water
requirements, enhancing the use of available capacity of unit in a ZLD/RLD
system,
reducing costs of alternative waste water disposal methods, and managing the
risk of
scale formation in reprocessing units.
BRIEF DESCRIPTION OF DRAWINGS
[0032] Fig 1 is a block diagram showing of a hydrocarbon recovery operation
and a
produced water treatment operation.
[0033] Fig 2 is a block diagram of units for treating waste water streams
in an in situ
hydrocarbon recovery operation.
[0034] Fig 3 is another block diagram of units for treating waste water
streams in an
in situ hydrocarbon recovery operation.
[0035] Fig 4 is another block diagram of units for treating aqueous streams
in an in
situ hydrocarbon recovery operation.
[0036] Fig 5 is a further block diagram of units for treating a waste water
stream.
[0037] Fig 6 is a block diagram of an operation for treating waste water
streams.
DETAILED DESCRIPTION
[0038] Waste water streams can be analyzed and recycled back into various
units of
an evaporative waste water treatment system, based on the composition of the
waste
water streams as well as the capacities and operating limits of the units. In
some
implementations, a waste water stream can be retrieved from a waste disposal
site and
recycled into an evaporator that is part of an in situ hydrocarbon recovery
operation,
thereby reducing capacity issues for the waste disposal site, recovering
additional water
from the waste water stream for reuse in the in situ hydrocarbon recovery
operation, and
7
CA 02948419 2016-11-10
r
leveraging existing equipment (i.e., the evaporator). In some implementations,
the waste
water stream includes aqueous leachate that is recovered from a landfill or a
lagoon,
and is derived from the disposal of a solids-enriched sludge, which can be the
end-
product of a zero or reduced liquid discharge (ZLD/RLD) system. The ZLD/RLD
system
can include at least one evaporator, a crystallizer and a dryer. The aqueous
leachate
can be recycled as part of the feed water supplied to the evaporator, which is
part of the
ZLD/RLD system. In some implementations, the aqueous leachate can be pre-
treated
using various pre-treatment methods, including the addition of chemical agents
prior to
introduction into the evaporator.
[0039] Falling film evaporators that are used for in situ hydrocarbon
recovery
operations are not typically designed or identified for recycling waste water
streams
obtained from disposal sites (e.g., landfills) that are external or remote to
the in situ
hydrocarbon recovery facility. The falling film heat exchange that occurs
within such
evaporators can have fouling issues when the feed stream has high levels of
contaminants, which can lead to costly shutdowns. While certain units, such as
crystallizers, are designed to handle solids formation and thus can handle
higher
contaminant levels in their feed streams, evaporators are not. Landfill
leachate and other
waste water streams retrieved from remote disposal sites can have high and
variable
contaminant levels.
[0040] Furthermore, waste water streams derived from hydrocarbon production
operations can be selected based on various factors, including composition and
disposal
site capacity, and recycled into pre-selected units of a ZLD/RLD system based
on unit
capacity and feed quality requirements. By selecting and matching waste water
streams
with particular units of the ZLD/RLD system, additional water can be recovered
for reuse
and capacity issues for the waste water disposal can be overcome.
[0041] A "ZLD" system refers to a system that treats waste water from a
facility and
includes multiple units that leverage evaporative recovery of water for
enabling recycle
of virtually all of the recovered water back into the facility. ZLD systems
include
evaporation of the waste water until the dissolved solids and contaminants
form crystals,
which are removed and dewatered. Water vapor from evaporation can be condensed
and returned into the facility. For the purposes of the present description, a
ZLD system
8
= CA 02948419 2016-11-10
can be defined as one that enables at least 90% of the water entering the ZLD
system to
be recovered and recycled back into the facility.
[0042] An "RLD" system is similar to a ZLD system, but has a recycle
percentage
that is lower than 90% of the water entering the RLD system. RLD systems also
rely on
evaporative water recovery.
[0043] It should be noted that both ZLD and RLD systems can include
units such as
ultrafiltration (UF), ion exchange, reverse osmosis (RO), among others,
depending on
process design.
[0044] "Leachate" is a liquid that has passed through solid material
and has
extracted soluble and/or suspended components from the solid material.
Leachate is
often collected from a lower level where the liquid has accumulated after
draining
through the solid material.
[0045] A "landfill" is a site for the disposal of waste materials. The
waste material is
typically dumped into a confined disposal area, compacted to reduce volume,
and
covered with layers of soil. Covering may be done daily or other frequencies.
Landfills
can include leachate collection systems that capture leachate that has passed
through
the waste material.
[0046] "Blowdown" is a general term that includes waste water streams
generated
by equipment and unit operations, such as steam generators, evaporators, and
other
units. Blowdown from steam generators (e.g., OTSGs) is contaminated water
intentionally wasted from the steam generator to avoid concentration of
impurities during
continuing evaporation of steam. Since boiler feed water includes some
contaminants
and the generated steam includes essentially no contaminants, the blowdown
from
steam generators typically includes much higher contaminant levels compared to
the
feed water. For example, OTSG-type steam generators typically generate
blowdown that
has contaminant levels that are four to five times higher than the feed water.
Blowdown
is generated by OTSGs continuously during operation. Other types of units can
generate
blowdown periodically when the units are evacuated by pressure.
[0047] Referring to Fig 1, in the context of an in situ hydrocarbon
recovery operation
(e.g., SAGD), production fluid 10 is recovered via a production well 12 that
is located in a
9
CA 02948419 2016-11-10
hydrocarbon-containing formation 14. Many in situ hydrocarbon recovery
operations use
a mobilizing fluid, such as steam 16, that is injected via an injection well
18 into the
formation in order to reduce the viscosity of the hydrocarbons. Mobilizing
fluids can be
particularly useful for mobilizing heavy hydrocarbons such as heavy oil or
bitumen. It
should be noted that other hydrocarbon mobilization mechanisms can be used,
e.g.,
electromagnetic heating.
[0048] The production fluid 10 includes hydrocarbons and water as well as
various
other components, such as suspended mineral solids and dissolved salts. The
water in
the production fluid 10 can come from injected aqueous mobilizing fluids
(e.g., steam or
hot water) and/or from native water present in the formation itself.
[0049] Still referring to Fig 1, the production fluid 10 is supplied to a
separator 19
which produces a hydrocarbon stream 20 and a hydrocarbon-depleted produced
water
stream 22. This separation step can be performed with the addition of a
hydrocarbon
diluent or without. The hydrocarbon stream 20 can be further processed to
remove
contaminants and produce a hydrocarbon product that can be stored and/or
pipelined.
The hydrocarbon-depleted produced water stream 22 can be supplied to another
oil-
removal separator 24 which removes residual oil 26 and produces a produced
water
stream 28.
[0050] The produced water stream 28 can then be supplied to a water
treatment
operation, which may include a number of different water treatment units. Fig
1
illustrates the scenario where the water treatment operation includes a warm
lime
softener (VVLS) 30 followed by a weak acid cation (WAC) exchange unit 32,
which
produces a treated water stream suitable for use as boiler feed water 34. It
should be
noted that other water treatment units can also be used (e.g., evaporators)
instead of, in
series with and/or in parallel with WLS and WAC exchange units.
[0051] The boiler feed water 34 can be supplied to a steam generator, such
as an
OTSG 36, which produces wet steam 38 and an OTSG blowdown stream 40. The wet
steam 38 can be separated to produce dry steam which can be fed to the
injection well
18 as part of, or all of, the mobilizing fluid 16.
[0052] Still referring to Fig 1, the OTSG blowdown stream 40 includes
various
contaminants, including organic compounds, dissolved salts, suspended solids,
= CA 02948419 2016-11-10
hardness and silica. Part of the OTSG blowdown stream can be recycled back
upstream
into one or more of the water treatment units. However, continuously recycling
all of the
OTSG blowdown to such unit would lead to upcycling of contaminants in the
system.
Thus, at least a portion of the OTSG blowdown stream 40 can be supplied to a
waste
water treatment system, which may be a ZLD system 42. The ZLD system 42 can
include various units that recover water from the blowdown stream and produce
waste
streams that have increasing solids concentrations.
[0053] Fig 1 illustrates an example of a ZLD system 42 that can be
used. The OTSG
blowdown stream 40 is supplied to a first evaporator 44 that produces a first
condensate
stream 46 and a first evaporator blowdown stream 48. It should be noted that
multiple
OSTG blowdown streams can be combined together and then supplied to the
evaporator. The first evaporator blowdown stream 48 is then supplied to a
second
evaporator 50 that produces a second condensate stream 52 and a second
evaporator
blowdown stream 54. The first and second condensate streams can be recycled
back
into the system as boiler feed water or for other uses. The second evaporator
blowdown
stream 54 can then be fed to a crystallizer 56 which removes additional water
55 and
facilitates crystal formation to produce a crystallizer slurry 58. The
crystallizer slurry 58
can then be supplied to a dryer 60 that produces a solids-enriched sludge 62.
[0054] The solids-enriched sludge 62 can then be supplied to a
landfill 64, which is
located off-site compared to the ZLD system 42 and the overall in situ
hydrocarbon
recovery operation. The landfill 64 can receive various waste streams (e.g.,
sludge 62
from the dryer 60, a portion of the crystallizer slurry 58, etc.) in different
proportions. The
landfill 64 can generate leachate 66, which may be produced at higher levels
depending
on the quantity of precipitation 68.
[0055] Referring still to Fig 1, the leachate 66 can be pumped from
the landfill or
another intermediate holding area back to the ZLD system 42. In some
implementations,
the recycled leachate 66 is added to the blowdown stream 40 to form an
evaporator feed
stream 70 introduced into the first stage evaporator 44. In some scenarios,
the
leachate 66 can be combined with an additive stream 72, which can be a make-up
water
stream or a chemical addition stream, to form a pretreated leachate stream 74
that is
combined with the blowdown stream 40. The combination of the leachate stream
66 with
the additive stream 72 and/or the blowdown stream 40 can be done using various
11
= CA 02948419 2016-11-10
pipeline joints (e.g., T or Y addition joints) or various mixers (e.g.,
static, in-line, stirred
tank, etc.).
[0056] It should be noted that the leachate 66 or portions thereof can
be recycled to
other units that are part of the ZLD system or part of another unit operation.
As will be
explained in further detail below, the leachate 66 can be recycled to one or
more units of
the ZLD system and there may be a recycle system that controls adaptive
recycle
strategies.
[0057] In some scenarios, the leachate 66 can be mixed with OTSG
blowdown
and/or upstream evaporator blowdown (also called evaporator "purge" or
evaporator
"brine"), and the resulting mixture can be fed into the evaporator sump. The
evaporator
recovers water from the leachate, and thus acts as a pre-concentrator so that
the
downstream crystallizer can handle the fluid more efficiently.
[0058] Referring now to Fig 2, there may be multiple waste water
streams VVWA,
VWVB, VVVVC that are retrieved and recycled back into the ZLD system. One or
more of
the waste water streams can be leachate derived from the landfill. A recycle
system 76
can be provided in order to manage and control the recycling of the waste
water streams
into the different ZLD units. The recycle system 76 can include piping and
valves that
are arranged to facilitate adding different waste water streams together,
keeping
different waste water streams separate, and feeding different waste water
streams and
flowrates into different ZLD units. The recycle system 76 can also include
recycle lines
that supply waste water to part of the water treatment system used for the
produced
water (e.g., WLS 30). The recycle system 76 can be configured and controlled
to provide
different waste water streams and pre-determined or continuously modulated
flow rates
into the evaporators 44, 50, the crystallizer 56, the dryer, and other units.
In some
implementations, the only units that receive the waste water streams are the
evaporators 44, 50 and the crystallizer 56. In some implementations, as
illustrated in
Fig 1, the only units that receive the waste water streams are the evaporators
44, 50. A
control unit 78 can be provided to control the recycle system 76 and its
valves and other
flow control apparatuses to provide the desired flows of waste water to the
desired units.
[0059] Referring now to Fig 3, a pre-treatment unit 80 can be used to
pre-treat the
leachate and/or other waste water streams prior to introduction into the
evaporator 44.
12
CA 02948419 2016-11-10
Multiple pre-treatment units (generally indicated as PT and/or 80) can be
provided for
pre-treating different waste water streams and/or for providing different pre-
treatments.
In some implementations, pre-treatment can include the addition of one or more
chemicals. For example, chemical additives can include a chelating agent, an
anionic
dispersant for dispersing inorganic suspended solids, a scale inhibitor, a
hydrocarbon
dispersant, and/or an anti-foam agent. There may therefore be at least one
chemical
addition line 82 for supplying one or more chemicals to the pre-treatment unit
80.
Chemical agents can be delivered as part of one or more aqueous solutions, and
can be
added simultaneously or sequentially to the leachate and/or to the evaporator
feed
stream (i.e., after combining the leachate with the blowdown). Various
formulations of
chemical agents can be provided depending on water chemistry, evaporator
operation
and other process parameters, in order to reduce or avoid fouling in the
evaporator.
[0060] In addition, the pre-treatment unit 80 can be controlled to adapt
the pre-
treatment (e.g., chemical dosages) in accordance with measured contaminant
levels.
Since landfill leachate and other waste water streams can vary in composition,
a
measurement unit can be provided to measure certain contaminants levels (e.g.,
suspended solids, organics, salts, hardness, silica, etc.) in order to adapt
the pre-
treatment to the measured values. For example, if high suspended solids
content is
detected, the pre-treatment can be modified to include a filtering step. If
high organic
content is detected, the chemical dosage of the hydrocarbon dispersant can be
increased.
[0061] Still referring to Fig 3, each of the recycle lines for supplying a
portion of
recycled waste water can be equipped with its own pre-treatment unit 80a, 80b,
80c,
which may be particularly useful when the recycled portions are respectively
supplied to
different units suited to handling different water chemistries. For instance,
an upstream
unit 84 may be designed and operated to facilitate handling of streams having
high
contaminant concentrations, and thus the pre-treatment unit 80a for that waste
water
stream may be able to reduce chemical addition and/or avoid adding certain
chemicals
altogether. Fig 4 illustrates a scenario where two different pre-treatment
units 80x, 80y
are respectively used for two different evaporators 44, 50.
[0062] In some scenarios, as illustrated in Fig 5, the pre-treatment unit
80 may
include a tank that receives the leachate 66 from a lagoon 86, and is coupled
to multiple
13
CA 02948419 2016-11-10
chemical addition lines 80a, 80b for receiving the chemical compounds to pre-
treat the
leachate 66. Pumps 88 can be provided for transporting the leachate 66, and
holding
tanks 90 can be provided as well. Trucking 92 can also be used to remove
leachate from
the lagoon, but the leachate recycle system can reduce or even eliminate as
recourse to
expensive trucking.
[0063] Still referring to Fig 5, the treated leachate stream 74 can be
added to an
evaporator 100, which can be downstream from another evaporator 102 and
upstream
from a crystallizer 56. The upstream evaporator 102 can receive a feed stream
104 that
includes blowdown derived from an OTSG and/or from other units used in an in
situ
hydrocarbon recovery operation. The upstream evaporator can be a Mechanical
Vapor
Recompression (MVR) evaporator, for example.
[0064] Recycling waste water streams, such as landfill leachate, to an
evaporator
can facilitate certain operational advantages in the ZLD system. For example,
in some
scenarios, processing recycled waste water streams into the crystallizer can
be
constrained by limited capacity of the crystallizer equipment, such as the
capacity of the
vapor cooling system and solids handling unit of the crystallizer. By
recycling the waste
water stream (all or in part) to the evaporator of the ZLD, additional
crystallizer capacity
can be obtained.
[0065] In some scenarios, the evaporator that is used to receive and treat
the
recycled waste water stream (e.g., leachate 66) is selected as an evaporator
having
excess capacity. In situ hydrocarbon recovery operations may include a
multitude of
evaporators having different designs, sizes, capacities and purposes. For
example,
some evaporators can be used to treat produced water in order to produce
condensate
for use as boiler feed water, whereas other evaporators can be used as part of
a ZLD
system. Some in situ hydrocarbon recovery operations can have multiple trains
as part
of steam generation system, and some or all of the trains can include one or
more
evaporators in parallel (as a bank of evaporators) and/or in series. Depending
on a
variety of factors (e.g., process design, equipment sizing, operating
parameters, etc.) a
given evaporator may have excess capacity in terms of the flow rate of feed it
can
receive and/or in terms of the contaminant levels it can handle. Thus, an
evaporator
having excess capacity can be selected for receiving the leachate 66. In
addition, when
the evaporator has a certain excess capacity in terms of the contaminants it
can handle,
14
CA 02948419 2016-11-10
the pre-treatment of the leachate 66 can be provided and adapted so that the
evaporator
feed stream 70 comes close to but does not exceed contaminant limits for that
evaporator.
[0066] In some implementations, an existing evaporator that is part of an
existing
facility is identified and used for the recycle strategies disclosed herein.
Alternatively, a
new facility can be designed where at least one evaporator is overdesigned
purposefully
for the possibility of adding a recycle stream from an off-site source of
waste water, such
as landfill leachate. In such a case, the evaporator can be overdesigned
relative to the
anticipated design requirements for handling blowdown, thus leaving excess
capacity for
landfill leachate or another waste water stream. The evaporator can be
overdesigned
based on a maximum potential flow rate of landfill leachate that can be
determined
based on the maximum expected leachate production rates (e.g., according to
variables
including precipitation, lagoon holding capacity, sludge disposal rates,
etc.).
[0067] It should be noted that various waste water streams from outside the
hydrocarbon recovery facility can be retrieved and recycled into the
evaporator. For
example, landfill leachate can be retrieved by collecting the leachate from
the landfill,
supplying the leachate to a holding vessel or lagoon, and then pumping the
leachate
back to the facility as part of the evaporator feed stream. Landfill leachate
that is derived
from waste materials generated by in situ hydrocarbon recovery operations
and/or oil
sands mining operations could be used. In another example, tailings pond water
may be
used as a source of off-site waste water, where the tailings water could be
pre-treated by
filtering and treated to reduce or eliminate emulsifying behaviour (i.e.,
reduce surfactant
content). Thus, in general, the waste water can thus be retrieved from a
disposal site
used to dispose of by-products that come from a bitumen production operation.
The
disposal site is typically located remotely from the evaporator to which the
waste water
stream is recycled. A retrieval system including pumps, pipelines and holding
tanks can
thus be provided.
[0068] The pre-treatments (e.g., chemical addition) can be done at the
remote
disposal site and/or at the in situ hydrocarbon recovery facility. For
example, depending
on the mixing requirements and reactivity of the chemical additives, certain
chemicals
can be added near the disposal site prior to pumping of the waste water stream
to the in
situ hydrocarbon recovery facility, particularly where pipeline mixing can be
beneficial to
CA 02948419 2016-11-10
the chemical addition. Alternatively, chemical addition after pipeline
transportation and
thus proximate to the in situ hydrocarbon recovery facility may be used for
chemicals
that have rapid mixing or reaction.
[0069] In operation, overall volumes of recycled and reprocessed leachate
can be
balanced by storing excess fluid in the lagoon during the high volume season
and
reprocess it during low volume season. For example, excess volumes of leachate
can be
stored in the lagoon during times of high precipitation and leachate
production (e.g.,
spring), and then accumulated leachate can be accessed from the lagoon during
times
of low leachate production (e.g., winter). In some implementations, the flow
rate of the
leachate that is recycled back into the evaporator can vary depending on
various factors.
For example, during the winter, little to no leachate is produced by the
landfill due to
freezing, whereas in the spring time and times of high precipitation a greater
amount of
leachate may be produced. Managing variable flow rates of leachate or other
waste
water streams can be facilitated by recycling such streams back into the
evaporator and,
optionally, into other units in the facility (e.g., crystallizer).
[0070] In some implementations, the waste water stream to be recycled and
processed in the evaporator can be identified and classified from a number of
different
potential waste water streams. In the context of in situ hydrocarbon recovery
operations
and bitumen mining and extraction operations, many different waste water
streams can
be generated, stored, treated, and disposed of as part of waste management.
Waste
waters can be classified based on certain characteristics (e.g., salinity,
hardness, free
oil, silicate, solids content, etc.). Then, based on the feed stream quality
and capacity
limits of one or more units of the ZLD system or a Reduced Liquid Discharge
(RLD)
system, a blending ratio can be determined for blending the input stream of
one more
units with one or more waste water streams. High cost waste water streams,
such as
landfill leachate, can be prioritized for recycling and reprocessing. In
addition, the pre-
treatment can be determined for each waste stream and/or each blend, as
necessary.
[0071] In some implementations, the waste water selection and treatment
method
can include the following steps:
(I) determine compositional characteristics of each waste water stream;
(ii) determine production rates of each waste water stream;
16
CA 02948419 2016-11-10
(iii) determine capacity characteristics of the disposal site at which each
waste water stream is held;
(iv) determine alternative treatment options for the waste water streams
(e.g.,
trucking excess leachate from lagoon) and the cost and challenges
thereof;
(v) determine operational feed quality characteristics of the streams being
fed into one or more units that are part of the ZLD or RLD system (e.g.,
evaporators, crystallizers, dryers, etc.), which may include determining
compositional or physicochemical properties of the feed streams entering
such units;
(vi) determine operational capacity characteristics of one or more of the
operating units (e.g., evaporators, crystallizers, dryers, and associated
equipment such as vapor coolers, etc.), which may include assessing
available capacity of such units based on operational parameters, inlet
and outlet flow rates, and vessel size information; and
(vii) based on (i) to (vi) and, optionally, additional information such as
pre-
determined or known information that may include:
(1) feed quality limits of one or more units that are part of the ZLD or
RLD system (e.g., evaporators, crystallizers, dryers, etc.); and
(2) capacity limits of one or more units that are part of the ZLD or RLD
system (e.g., evaporators, crystallizers, dryers, and associated
equipment such as vapor coolers);
perform the following steps:
(a) recycle one or more of the waste water streams into the ZLD system
and/or RLD system;
(b) blend the recycled waste water streams with one or more of the feed
fluids of the units to form corresponding feed streams; and
17
CA 02948419 2016-11-10
(c) feed the combined streams into the respective units, thereby
reprocessing the waste water streams.
[0072] It should be noted that certain variables including those of (i) to
(vi)
mentioned above can be considered dynamic in that they can change over time
due to
various factors. For example, the compositional characteristics of each waste
water
stream (i) can change due to the source of waste water streams, the
precipitation levels,
the upstream process variations that produced the waste from which the streams
were
derived, and so on. The production rates of each waste water stream (ii) can
also vary
due to factors such as time of year (e.g., high rates in spring when high
amount of
precipitation versus low rates in winter), the rate of waste production, the
composition of
the waste from which the streams were derived, and so on. Similarly, the
capacity
characteristics of the disposal site(s) (iii) can vary due to the rate at
which waste has
been disposed, the rate at which waste streams are being removed, and
precipitation.
The alternative treatment options for the waste water streams (iv) can also be
determined based on costs, equipment availability, and other factors. The
operational
feed quality characteristics (v) can change over time due to the upstream
process, e.g.,
impurity levels of the produced water that relate to the properties of the
formation,
operation of the units upstream of the OTSGs (e.g., upsets), and so on. While
the feed
quality for each unit may be kept within a known operating envelope, there may
be
notable changes to the composition of the feeds over time (e.g.,
concentrations of the
different impurities can change over time). The operational capacity
characteristics (vi) of
the units of the ZLD or RLD system can change due to upstream or downstream
operation. For example, a unit may operate with decreasing excess capacity as
the feed
rate increases, which may be due to ramping up the process or taking a similar
parallel
unit offline for maintenance or repair. In addition, a unit's capacity may be
considered to
decrease due to internal fouling that can reduce the throughput of material
that the unit
can effectively handle. Such dynamic characteristics can be monitored and
analyzed
over time in order to perform steps (a) to (c) mentioned above.
[0073] It should also be noted that certain variables including those of
(1) and (2)
mentioned above can be considered static in that they can be pre-determined or
are
generally known. For example, certain units may have feed quality limits (1)
that are
recommended by manufacturers or pre-determined by the process operator. The
feed
quality limits can include maximum levels of impurities that can be
effectively handled at
18
CA 02948419 2016-11-10
certain operating conditions, for example. In addition, certain units may have
capacity
limits (2) that are recommended by manufacturers or pre-determined by the
process
operator. The capacity limits can be based on unit size, vessel wall
thickness, pressure
and temperature tolerances, piping, instrumentation or other construction
parameters.
Such static characteristics can also be used in combination with various
dynamic
characteristics to perform steps (a) to (c) mentioned above.
[0074] Certain variables that can be considered dynamic may not vary
sufficiently
over the time period of interest to warrant continued monitoring and analysis
in
determining the blending and recycle strategy into the ZLD/RLD system. For
example,
for relatively stable process operations, one may observe relatively constant
feed quality
characteristics (v) and operational capacity characteristics (vi) of the
units. In such
instances, one may consider such variables as being relatively static and they
can
therefore be determined based on pre-determined or known information.
[0075] The method can also include determining pre-treatment requirements
for the
waste water streams in light of one or more characteristics determined in (i)
¨ (vi). For
example, taking the two potential waste water streams of tailings pond water
and landfill
leachate, one can determine that landfill leachate is suitable to be recycled
back into a
ZLD/RLD evaporator having excess capacity. It is also noted that this waste
water
selection and treatment method can be implemented in part by the recycle
system 76
(as shown in Fig 2) where one or more different waste water streams (WVVA,
VWVB,
VVWC) can be blended with one or more feed streams to different units of the
ZLD/RLD
system. The controller 78 can be configured to receive input information
regarding the
various determined characteristics in order to adjust the blend ratios, as
needed. The
recycle system can be adjusted on a continuous basis based on continuous input
of
information, or can be implemented in a relatively consistent manner based on
previously-determined information.
[0076] Referring now to Fig 6, some implementations of the waste water
selection
and treatment method will be described in greater detail. The ZLD/RLD system
42 can
be leveraged to treat multiple waste water streams, which may include internal
waste
water streams 106a, 106b, 106c as well as external waste water streams 108a,
108b,
108c, 108d. The internal waste water streams are produced by the in situ
hydrocarbon
recovery and steam generation facility 107, and may include blowdown streams
19
CA 02948419 2016-11-10
obtained from OTSGs or other units, such as WLS units, evaporator units used
to treat
the produced water, as well as other units used in the system. The internal
waste water
streams 106a, 106b, 106c can be fed into one or more of the units of the
ZLD/RLD
system 42 as individual streams, or they can be combined together and fed as a
single
feed stream into the ZLD/RLD system 42. The internal waste water streams 106a,
106b,
106c can have different compositions including different concentrations of
organic
compounds, dissolved salts, suspended solids, hardness, and silica. The
internal waste
water streams 106a, 106b, 106c or the combined feed stream can be monitored
and/or
analyzed to determine compositional features (e.g., one or more of the above-
mentioned
components) prior to entering the ZLD/RLD system 42.
[0077] The external waste water streams 108a, 108b, 108c, 108d are derived
from
unit, facilities or disposal sites that are outside of the in situ hydrocarbon
recovery and
steam generation facility 107. One example of an external waste water source
110 is a
landfill 64a, 64b, which may receive sludge 62 and/or other solid waste
derived from the
in situ hydrocarbon recovery and steam generation facility 107 and/or the
ZLD/RLD
system 42. The external waste water sources 110 can include other disposal
sites, such
as ponds, lagoons, and the like. The external waste water streams 108a, 108b,
108c,
108d can include leachate, tailings cap water, and other types of waste water
that has
come into contact with the environment. Each of the external waste water
streams 108a,
108b, 108c, 108d can be fed into one or more of the units of the ZLD/RLD
system 42 as
individual streams, or they can be combined together and fed as one or more
combined
feed streams into the ZLD/RLD system 42. For example, two leachate streams
(108a,
108b) can be combined together and fed into the ZLD/RLD system 42 as a single
feed
stream supplied to a single unit (e.g., an evaporator) or the combined stream
can be split
into distinct streams that are fed into different units of the ZLD/RLD system
42.
[0078] In some implementations, waste water streams (e.g., external and
internal)
are first analyzed for compositional features, such as organic compounds,
dissolved
salts, suspended solids, hardness, and/or silica. Then, one or more waste
water streams
are selected for introduction into the ZLD/RLD system 42, based on the
compositional
features. The analyses can be done online, at line and/or in the laboratory
setting. In
addition, in some scenarios, certain waste water streams can be combined
together to
form a combined waste water stream for introduction into a certain unit of the
ZLD/RLD
system 42. For example, waste water streams that are high in silica can be
combined
CA 02948419 2016-11-10
together to form a silica-rich waste water stream which is introduced into a
unit that can
handle high silica contents, such as the crystallizer; while waste water
streams that are
lower in silica can be combined together to form a silica-poor waste water
stream which
is introduced into a unit that may be more sensitive to silica, such as an
evaporator. One
challenge to waste water recycling is the prevention of silica fouling inside
steam-driven
and mechanical-driven evaporators. If these evaporator units become fouled,
they will
first limit production and can lead to plant outages for equipment cleaning
and
maintenance is required. Silica scales are not only difficult to remove, but
are also costly
to do so. Consequently, the recycle points into the plant can advantageously
be provided
in the context of managing the risk of scale formation, chemical interaction
for scale
mitigation, water recovery, and solids formation for land fill disposal.
[0079] In some implementations, waste water streams can be combined in
order to
bring the concentration of a given component below a pre-determined or desired
threshold for the unit into which the combined waste water stream will be
recycled. For
example, a high silica waste water stream can be combined with a low silica
waste water
stream in a proportion such that the silica content of the combined stream is
below the
silica limit for operation of a mechanical- or steam-driven evaporator. Thus,
the high
silica waste water stream can be recycled and treated in the evaporator
despite its high
silica levels. In addition, in some implementations multiple waste water
streams can be
combined together to reduce chemical requirements for a given unit.
[0080] In another example, a waste water stream with high total suspended
solids
(TSS) can be selected for recycling into the crystallizer, which is designed
for high solids
streams. Other waste water streams that have lower TSS can be selected for
recycling
into the evaporators.
[0081] In yet another example, waste water streams can be blended based on
their
compositions in order to obtain a desired blended composition having chemical
requirements below a pre-determined or desired level. For instance, a chemical
treatment formula can be determined in which maximum qualities of various
chemical
additives (e.g., chelating agent, dispersant, anti-foam) are established based
on various
parameters (e.g., cost, impact on process, equipment availability, etc.).
Certain waste
water streams may have chemical treatment requirements that exceed the maximum
qualities of certain chemical additives. In such cases, the waste water
streams can be
21
CA 02948419 2016-11-10
combined with another waste water stream that has lower chemical treatment
requirements (e.g., for a given chemical additive or for several chemical
additives) such
that the combined waste water stream falls within the chemical treatment
requirements
and therefore can be recycled.
[0082] In some implementations, both internal waste water streams and
external
waste water streams can be stored in a common containment structure, such as a
lagoon. Alternatively, external waste streams can be stored in such structures
while
internal streams are held in tanks or supplied directly into ZLD/RLD equipment
via
pipeline.
[0083] The monitoring/analysis of various waste water streams can
facilitate
enhanced blending and treatment of those streams by tailored introduction into
the
ZLD/RLD system. This not only increased utilization of ZLD/RLD equipment
capacity but
also reduces offsite disposal or storage of waste streams.
[0084] In some scenarios, the waste water streams can be selected and
recycled
such that the ZLD/RLD system operates at a recycle percentage of 100%, instead
of
around 90% for ZLD or lower recycle rates for RLD. In some scenarios, more
than 100%
recycle can be achieved if precipitation is taken into consideration, since
leachate can
include precipitation that was not part of the water used at the in situ
hydrocarbon
recovery facility. Achieving 100% or more water recycle can reduce fresh water
requirements, which is another advantage of the methods described herein.
[0085] The methods described herein can be applied to existing ZLD/RLD
systems
through retrofitting (e.g., addicting a recycle system that includes piping,
valves,
monitoring, etc.) or to new ZLD/RLD systems. The methods can also be applied
to other
evaporative water treatment technologies that may not necessarily go by ZLD or
RLD.
[0086] In some implementations, the method can include alternating or
modifying the
recycle between two different units. For example, a waste water stream can be
recycled
into a ZLD/RLD evaporator and then the recycle can be partly or fully switched
to the
ZLD/RLD crystallizer. The switch can be due to various factors, such as an
increase in
contaminants in the waste water stream or an increase in blowdown flow rate
into the
evaporator requiring additional capacity, for example.
22
CA 02948419 2016-11-10
[0087] It is also noted that the external waste water streams can be partly
recycled
back into the in situ hydrocarbon recovery and steam generation facility 107,
via a
recycle line 112. This recycled waste water can be fed to one or more units of
the facility,
some of which are described in relation to Fig 1, for example. In some
implementations,
portions of the waste water can be recycled into different units of the in
situ hydrocarbon
recovery operation, notably units that are part of the produced water
treatment system
and the steam generators. For instance, portions of the waste water can be fed
directly
into OTSGs which can handle higher contaminant content compared to other types
of
boilers, particularly where the boiler feed water stream 34 has a composition
that can
accommodate an increase in contaminants. This recycle approach can have the
benefit
of debottlenecking or increasing the capacity of the water treatment units.
[0088] In some implementations, the recycle control unit 78 (illustrated in
Fig 2) can
be configured and operated to analyze and control the recycling of multiple
waste water
streams, having the same or different compositions, into both the in situ
hydrocarbon
recovery facility 107 and the ZLD/RLD system 42. The control unit 78 can
receive
information regarding the composition and flow rate of the waste water
streams, the
composition and flow rate of the input streams into each of the units, and the
operational
parameters of the units. The control unit 78 can also be configured with
information
regarding upper threshold limits of the units in terms of the contaminant
levels that can
be handled. The control unit 78 can then be configured to distribute the waste
water
streams to appropriate units of the in situ hydrocarbon recovery facility 107
and the
ZLD/RLD system 42, thus allowing feedforward process control of the waste
water
recycling. The control unit 78 can also receive information regarding the
output streams
of the units, in order to monitor the performance of the units and potentially
enable
feedback process control.
[0089] Furthermore, the waste water pre-treatment strategy can be managed
in
order to provide different pre-treatments for different streams. For example,
in some
scenarios, a filtration unit can be provided for filtering only waste water
streams that
have certain solids content characteristics (e.g., solids concentration,
solids particle size
distribution, etc.), and the streams having such solids content
characteristics can be
treated separately or as a blended stream fed to the filtration unit. In
another example,
chemical additives can be provided via separate chemical addition assemblies
such that
the dosing of each chemical additive can be done based on a particular waste
water
23
. CA 02948419 2016-11-10
stream to be recycled. For instance, for a waste water stream having high
silica and low
organics, the chemical addition can be managed by providing a higher dose of a
silica
scale prevention chemical (e.g., polyvalent metal hydroxides) and a lower dose
of a
hydrocarbon dispersant. By pre-treating the waste water streams individually,
overall
chemical dosage requirements can be reduced.
[0090] In addition, in some scenarios, the feed stream into which the
recycled waste
water stream is to be introduced may include residual chemicals from upstream
unit
operations which can be leveraged for the waste water stream. For example, if
the feed
stream already has high levels of hydrocarbon dispersants that would be able
to
disperse the organics contained in the waste water stream to be added to the
feed
stream, then chemical pre-treatment can be adapted by reducing or avoiding
further
addition of hydrocarbon dispersant. The feed streams can thus be analyzed for
such
properties and the chemical pre-treatment can be adjusted accordingly (e.g.,
via the
control unit 78).
[0091] It should be noted that various steps or features described
herein can be
combined with other steps, features, implementations, methods and processes
described herein. In addition, in some cases, process steps can be conducted
in various
orders that may not be explicitly be described herein. Waste streams can be
obtained
from various sources that can be derived from in situ hydrocarbon recovery
operations,
oil sands mining and extraction operations, steam generation operations,
and/or other
mining or industrial process operations. The processes and methods described
herein
can also be used with various in situ hydrocarbon recovery operations besides
SAGD,
including cyclic steam stimulation (CSS), steam drive, in situ combustion,
solvent-
assisted processes, hybrid processes, and so on, including combinations
thereof. The
processes and methods described herein can also be used during various stages
of the
operational life of the in situ hydrocarbon recovery operation, including
start-up, ramp up,
steady state, and wind down.
24
