Note: Descriptions are shown in the official language in which they were submitted.
CA 02435344 2007-07-27
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METHOD OF REMOVING WATER AND CONTAMINANTS FROM
CRUDE OIL CONTAINING SAME
FIELD OF THE INVENTION
The present invention is directed to an enhanced crude
oil dehydration process and apparatus, and more
particularly the present invention is directed to a crude
oil dehydration and decontamination process which can
overcome the instability problems encountered with prior
art for treating high water cut heavy oil streams, provide
enhanced thermal energy input and recovery methods, remove
suspended and dissolved compounds from inlet feed and
recover diluent from oil treatment units in an efficient
manner.
BACKGROUND OF THE INVENTION
Throughout many regions of the world, heavy oil, a
hydrocarbon material having much higher viscosity or lower
API gravity (less than 20 API, typically 7 to 12 API) than
conventional petroleum crude, is being economically
recovered for commercial sale. During the recovery process
and prior to the transport to refineries for upgrading, the
heavy oil receives preliminary treatment for water and
solids removal to generally achieve basic sediment and
water (BS & W) content less than 0.5% by volume and
chloride content less than 30 ppm (wt), more recently, the
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chloride content has been decreased to less than 10 ppm.
Water content of the treated heavy oil typically is
required to be 0.3% by volume or less.
Conventional crude oil treatment methods were proven
to be ineffective with respect to heavy oil until the
advent of the technology set forth in US Patent Reissue No.
33,999, Clare et al., reissued July 21, 1992 and Canadian
Patent 1,302,937, Clare et al., reissued on June 9, 1992.
These patents describe a simple apparatus which can be
located in remote oil producing areas for dehydrating heavy
oil with low risk of foaming and unstable operating, while
continuously achieving dry oil which exceeds requisite
specifications. These dehydrators were found to be
restricted to feed oil water content of less than 5% water
cuts and susceptible to foaming and process instability
during high water feed rates. Throughout the operation of
several of these dehydrators known from practicing the
technology in patents Re33,999 and 1,302,937, areas for
improvement were discovered to overcome the limitations of
feed oil water content and unstable operation caused by
pretreatment upsets.
Further refinements in the crude oil processing were
developed by Kresnyak and Shaw in United States Patent No.
6,372,123, issued April 16, 2002.
In the dehydration of crude, significant fluctuations
in the temperature in the dehydrator can be experienced
since heat enthalpy is continuously removed in order to
vaporize the water in the crude oil. Kresnyak and Shaw
recognized that this heat enthalpy needed to be restored in
order to stabilize the temperature within the dehydrator
and more particularly, the temperature of the heated
dehydrated crude oil within the dehydrator. By
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recirculating at least a portion of the dehydrated crude
and contacting this with the source of crude oil
immediately below the vaporizing surface in the dehydrator,
a substantially uniform temperature of the vaporizing
surface in the dehydrator was realized. Accompanying
advantages were immediately realized in terms of reduced
foaming within the dehydrator and less process impediments
Further, additional problems have been experienced in
dehydration techniques in that although dehydrated heavy
oil is achieved, high concentrations of suspended solids,
such as clay and silica and dissolved compounds such as
chlorides remain in the treated oil. These undesirable
compounds continue to create many problems in pipeline
transportation systems and refinery facilities to the
extent that they depreciate the commercial valve of heavy
oil.
It has been found in field applications that mineral
salts, silica, clay inter alia that remain in the
dehydrated crude promote corrosion cracking in stainless
steel components and induce scale accretion and/or fouling
of surfaces critical to efficient and consistent operation
of the. apparatus in the refiner and pipeline systems.
Generally speaking, the salt crystals mix with the oil and
coalescence results to form larger crystals which can pass
through the refinery desalination equipment.
In view of the fact that the dehydration process is a
water removal system for the crude oil, it then follows
that mineral concentration is a distinct drawback.
Advances have been made in respect of this limitation and
in particular, dehydrators have been modified to include a
demineralization/solid removal unit operation to avoid any
concentration of the latter within the treatment circuit.
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Having set forth the background of the dehydration
technology, one of the remaining process limitations that
was discovered relates to the use of diluent in the system.
Unfortunately, within the processes and particularly the
first generation dehydration technology, a. significant
amount of diluent was required. Typically, 20% to 50% by
volume diluent was required in order to effect the first
generation processes. Clearly, this has significant impact
on the available volume within the pipeline and as a
natural consequence, pipelines either had to :be 50% larger
in order to have the same efficiency in the absence of the
diluent or, the process was inherently 20% to 50% less
efficient. Although a detriment, first generation systems
had inherent advantages such as good separation and
operated at significantly cooler temperatures.
In flash treatment systems subsequently developed, the
process produced dry oil, did not involve the extensive use
of many pieces of equipment to handle different unit
operations and therefore was more affordable and more
importantly, did not require any diluent. Despite the
significant advantages, flash treatment systems were not
equipped to handle chloride problems as indicated above.
It would be advantageous if methodology could be
developed which unifies all of the positive attributes of
first generation processes with flash treatment process
without the disadvantages and in particular, without the
requirement for a diluent make up. The present invention
is directed to a union of all of the positive attributes of
existing systems and conveniently provides for high diluent
recycle.
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Accordingly, one object of the present invention is to
provide advances to overcome the limitations encountered by
the previous art.
SUMMARY OF THE INVENTION
5 One object of the present invention is to provide a
dehydration method for dehydrating crude oil containing
water and recycling diluent used in the method.
A further object of one embodiment of the present
invention is to provide a method of removing water and
solids from crude oil containing water ar.td solids to
provide a clean dry oil, comprising:
a separation phase, a dehydration phase and a diluent
recovery phase, the dehydration phase including:
providing a source of crude oil containing water;
adding a diluent to the source of crude oil;
a separation phase to remove at least a portion
of the water;
dehydrating the crude oil containing water in a
dehydrator having a vaporizing surface of dry crude
oil at a temperature sufficient to vaporize water
contacting the surface;
exposing the source of crude oil to the dry crude
oil to vaporize the water and at least a portion of
diluent in the source;
the diluent recovery phase including:
heating the dehydrated crude to liberate diluent;
stripping the diluent; and
recirculating recovered diluent to the crude oil
containing water in the separation phase.
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One of the attractive benefits of the methodology as
set forth herein relates to the fact that it can be easily
retrofitted on to existing first generation dehydration
systems in order to provide for high diluent recovery.
This is advantageous since the oil processing industry is
experiencing difficulty in obtaining a diluent due to a
shortage of suitable diluent materials.
The method set forth herein is designed to recover and
recycle a high proportion of the diluent (at least 90%) and
in some cases, 99% or greater recovery is achievable. As
an example, for a typical 30,000 BOPD (barrels of oil per
day) commercial SAGD (steam assisted gravity drainage)
operation, this recovery translates to less tlaan one truck
load of diluent makeup within a system on a daily basis.
In the present technologies available, this insignificant
diluent makeup has not been achievable. As those skilled
in the art will appreciate, this sigriificantly adds to the
efficiency of the overall method which, in turn,
immediately translates to a significant increase in
profitability of the overall process.
Conveniently, when at least a portion of the dry crude
oil recycle stream around the dehydrator enters the
dehydrator and is distributed below the surface of the hot
crude oil in the dehydrator a consistent temperature is
maintained at or above the vaporization temperature of
water and at or below the surface of the oil and throughout
the contained oil, thereby providing a means to mitigate
the risk of process upsets and instability due to foamiing.
A further object of the present invention is to
provide a dry crude recycle stream around the dehydrator to
mix with the feed stream, to allow an input of supplemental
heat energy (external or waste heat energy)to remove a
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portion of diluent to result in an energetically efficient
and balanced process.
This process effectively unifies the best aspects of
blend treatment and flash treatment to provide a process
which can remove unwanted solid and salt compounds,
dehydrate the crude oil and maximize the efficiency of the
diluent that is used in the system. Accordingly, in the
methodology of the instant invention a dry clean oil
product is formulated and this is done while providing a
maximum efficiency on the recovery of diluent used in the
process. In terms of the make up diluent, commercially
available diluents may be employed such as synthetic crude
oil (SCO), naphtha and natural gas condensates.
The overall method unifies all of the best attributes
of the existing technologies to provide a cooler process
which operates in a stable manner to produce clean dry oil.
As a further very significant advantage, the pipelines
employed for transportation can be anywhere from 20% to 50%
smaller in capacity in view of the fact that no diluent is
added into the system. This feature alone, presents a
significant savings and when taken into account with the
fact that the operation of the primary treatment plant may
be decoupled and operated independently from the pipeline
and the SAGD well pads independently operated, the overall
methodology clearly has significant ramifications in terms
of efficiency, profitability and utility.
As a further advantage of the present invention, the
process is arranged simultaneously to recover from a source
of crude oil diluent fluids that have been added to a
reservoir with SAGD injection steam. These diluent fluids
can be simultaneously recovered with the method and
returned back to injection steam. This method provides a
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significant reduction in injection steam (20-400); for a
fixed steam injection rate there will be 20-40% more
bitumen produced.
In the prior art, there has always been the
requirement for diluent transportation and concomitant
equipment with the technology set forth herein, there is no
requirement whatsoever for a diluent facility or any
pipeline or other transportation means for handling large
volumes of the diluent.
In respect of the demineralization/solid removal, many
of the standard techniques used to produce clean oil can be
employed in this system which renders the overall process
operationally simplistic relative to existing blend
operations which experience complications such as process
upsets and oil treatment instability.
The dry crude oil surface may be selectively heated by
reintroduction of dry crude oil, auxiliary heat addition,
etc. The important aspect is that the heat used for
vaporization is replaced so that a uniform or substantially
uniform surface temperature is maintained. This is one
important unit operation to maintain.
Enhancements have been developed to eliminate the
limits imposed by water cut of the source crude oil feed
and to provide a very clean and dry heavy oil product
relatively free of water, solids and chlorides.
The present invention relates to process enhancements
to an apparatus used for dehydrating crude oil containing
water, comprising a casing, means for admitting and
distributing the liquid crude oil into the casing and onto
the host surface of the dry crude oil, means for
controlling the level of crude oil and a means to transfer
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heat energy sufficient to maintain the liquid oil at or
above the distillation temperature for evaporating water,
light hydrocarbons and at least a portion of diluent.
A further embodiment of the present invention is to
recycle and blend the condensed light hydrocarbon produced
from the dehydrator, with the raw source crude oil, to
provide a blend treating oil/water separation pretreatment
step. The light hydrocarbons can optionally be combined
with additional diluent solvents to achieve both the volume
and composition of diluent required to treat the emulsions.
The diluent acts as a solvent for the oil, reducing the
viscosity and density of the heavy crude oil and creates
the density difference to separate the heavy oil from the
produced water and solids. The separation step can be
performed at the temperature and pressure conditions of the
raw well effluent or source oil. Any heavy portion of
additional diluent will pass through the dehydrator and be
retained in the sales oil as shipping diluent.
The light hydrocarbons and water exiting the casing
are condensed by any suitable means known in the art, and
collected and separated into water and light hydrocarbon
liquid phases. Any non-condensable vapors are released
from the apparatus for disposition by any safe means. Dry
crude oil meeting pipeline BS & W specifications is pumped
from the dehydrator to the stripper for final diluent
recovery prior to transport for refining and upgrading.
Typically, the dehydrator taught in the current art
performed well to produce dry crude oil, however several
problems have been encountered:
1. The dehydrator was limited to crude oil feed
water cuts (wc) of less than 10 % water to oil, and more
specifically less than 5 % wc to reduce the risk of
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unstable operation with foaming tendencies. This required
the need for a conventional treater means upstream of the
dehydrator to reduce raw crude oil water cuts from 50 to 20
% wc down to less than 5 % wc prior to feeding the
5 dehydrator.
2. The dry crude oil exiting the dehydrator contains
high chloride content, causing metallurgy and corrosion
problems with downstream refineries facilities and
transportation pipelines.
10 3. It was found that by flash evaporating off the
water and by effectively eliminating all emulsions, solids
such as clays and silica compounds, concentrated in the dry
oil phase, had a tendency to buildup, plug and/or cause
heat element damage.
4. It has been further experienced that the
dehydrator is susceptible to unstable operations and
foaming tendencies causing dehydration temperature swings
and wet oil production.
The present invention seeks to address these concerns
by providing methodology and apparatus to exceed the
performance of the dehydrator beyond the prior art.
In one embodiment of the invention, at least a portion
of the dry crude oil exiting the dehydrator is recycled and
mixed with the inlet crude oil feed prior to entering the
dehydrator casing. By increasing recycle flow, a
consistent and stable inlet water cut composition can be
maintained at the entrance to the casing to control the
tendency to foam and create operational complications.
With greater recycle rates, the raw water cut levels can be
increased above the 10 % wc stable level and continuous
stable operation is maintained. This eliminates the need
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for conventional treatment ahead of the dehydrator and can
avoid dehydrator process upset if an upstream treater is
used and a treater upset occurs.
A further embodiment of the invention requires that at
least a portion of the recycled dry crude oil be recycled
and distributed immediately below the dry crude oil
evaporating surface. This method ensures that the
temperature of the surface of the dry oil in the dehydrator
is maintained at or above the flash evaporating temperature
of water. Water and other flashing liquids droplets from
the feed are not permitted to penetrate the surface of the
crude oil, thereby preventing the cooling below the surface
and creating surface breakdown foaming and unstable
dehydrator operation.
Advantageously, external heat transfer means can be
added to the recycle circuit supra to regulate the precise
temperature of the feed stream to the dehydrator casing.
This method enhancement will regulate the precise level of
pre-flashing of water and other flashing liquids vapor in
the feed oil to control the residual water. level contacting
the hot dry oil surface. This step can be used to prevent
the overcooling of the bath and eliminate the foaming
effects caused by excessive evaporation surface breakdown.
As a further feature, a solid/liquid separation
device, examples of which include a filter, hydro cyclone,
centrifugal separators, gravity separators, centrifuge or
any combination thereof, etc., may be employed in the
circuit of the recycle stream continuously or on a batch
basis to remove suspended solids from the hot dry oil.
Additionally, a clean water washing circuit may be
added to the dehydrator feed to reduce undesirable
dissolved compounds, such as chlorides, f:rom the dry crude
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oil. The entire contaminated water stream, or a portion
thereof, is treated by a suitable treatment method to
create a clean water stream and a highly concentrated
brine, slurry or solid product. The recovered clean water
is recycled back to the raw crude oil for oil pretreatment.
Generally water or any aqueous solution containing
compounds for enhancing the extraction of chloride is most
desirable, otherwise any regenerable fluid with a suitable
aggressive solubility for chlorides may be considered.
It is preferable that in add.ition to achieving a
dehydrated oil, having a BS&W content of less than 0.5% wc
by volume and greater than 90o diluent recovery, the
embodiments of the invention in combination, or separately
applied, can produce a dry clean crude oil, substantially
free of solids and diluent, containing less than 10 ppm
(wt) chlorides, in a continuous and istable operation, with
low risk of foaming and process upsets. The oil produced
by the present process is readily vendible and is most
desirable, particularly in the case of heavy crude oils
with gravities in the 7 API to 20 API range.
Having thus described the inventiori, reference will
now be made to the accompanying drawings illustrating
preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic flow diagram which illustrates
the dry oil recycle to the dehydrator feed stream and
dehydrator;
Figure 2 is an additional schematic flow diagram
showing external heat exchange on the recycle for
temperature adjustment of the feed or surface of the
dehydrator or both;
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Figure 3 is a further schematic flow diagram showing a
solid/liquid separator for removal of suspended solids;
Figure 4 is a schematic flow diagram illustrating the
addition of water washing for removal of dissolved
compounds such as chlorides;
Figure 5 is a schematic flow diagram illustrating a
further embodiment of the present invention;
Figure 6 is a section along line 6-6 of Figure 5;
Figure 7 is a schematic flow diagram illustrating a
further embodiment of the present invention;
Figure 8 is a schematic flow diagram illustrating yet
another embodiment of the present invention;
Figure 9 is a schematic flow diagram illustrating a
further embodiment of the present invention;
Figure 10 is a schematic flow diagram illustrating
another embodiment of the present invention;
Figure 11 is a schematic flow diagram illustrating a
still further embodiment of the present invention; and
Figure 12 is a schematic flow diagram illustrating a
diluent recovery circuit.
Similar numerals employed in the Figures denote
similar elements.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to Figure 1, heavy oil with a viscosity
of between 7 API and 20 API denoted by numeral 10,
typically includes a mixture of crude oil, water, oil/water
emulsion, dissolved compounds such as chlorides and solid
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particles such as clay, metals and silicas and may contain
diluent. The crude oil is mixed with diluent of 30-50% by
volume and generally received in a gravity separator,
heated or non heated treater 12, under pressure from
between atmospheric pressure to 100 psig (700 kPag). This
will depend on the quantity of diluent present in the oil.
Heated treaters typically operate from 170 F to 285 F (77 C
to 141 C). In the treaters, solid particles and bulk
brackish water is separated and removed from the raw crude
oil at 14. Water cuts of less than 10%, to more typically
between 5% and 1% by volume can be achieved in the raw
crude/diluent feed 18 exiting the primary treatment through
a valve member 20. The water stream 22 generally contains
dissolved compounds such as sodium chloride, (5,000 to
50,000 ppm (wt)) and silica, and suspended compounds such
as clay and sand.
The raw crude oil/diluent mix at approximately between
5% and 1% water cut in the emulsion form, containing no
free water, enters the dehydrator 24 where the crude oil
and emulsions are evenly distributed onto the hot surface
of dry crude oil (not shown), operating at or above the
evaporation temperatures of the water and other flashing
liquids. Water and other flashing l:iquids are flashed off
the oil or separated by distillation, with water and low
boiling temperature hydrocarbon and diluerit components from
the oil exiting through the column 26 and passing through
line 28. If desired, the water and lower boiling
components may be sent to a condenser 30 and subsequently
to a vapor liquid separator 32. Dehydrated higher boiling
point crude oil is discharged from the dehydrator 24
through line 34.
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In the separator 32, water and light hydrocarbons are
separated by differences in specific gravity. The water is
discharged through line 36 and pump 38. The light
hydrocarbons are transferred from the separator 32 using
5 pump 40 via line 42, and can be removed for disposal at
line 44 or at least a portion recycled and mixed with the
inlet crude oil 10 via line 46, to dilute the incoming
crude oil and thereby facilitate its further treatment.
Non condensable, i.e. light hydrocarbons, inert gases
10 (nitrogen, carbon dioxides, hydrogen sulfide) are vented
from separator 32 and disposed of or recovered by any
suitable safe means at 80.
As shown by Figure 1, dry oil can be recycled from 48
and recycled as stream 50 to mix with the inlet feed 18,
15 prior to being distributed onto the hot oil surface in the
dehydrator 24.
In order to maintain the temperature of the hot oil
surface, at least a portion of the recycle stream 50 can be
recycled directly to the dehydrator 24 and be distributed
at or immediately below the surface of the hot dry crude
oil. It has been found that by recycling the dry crude oil
to inlet stream 18, and separately or in combination with
recycling dry crude oil to the surface of the hot bath by
using stream 52 (dashed lines), the following significant
benefits can be realized:
a) The water cut of the raw crude oil at stream 18
can be increased to greater than 10%, and even greater than
20% by volume. This enhancement means that the requirement
for conventional treatment denoted as 12 can be eliminated,
without risk of process instability and foaming of the
dehydrator.
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b) If a conventional primary treatment 12 is used,
the recycle stream can be used to isolate the dehydrator
from unstable or operational complications if the
pretreatment becomes unstable. This means that the dry
crude oil sales specification is not at risk, and rerun of
off spec sales oil from sales oil storage tanks and
pipelines is avoided.
The ratio of recycle at 50 to inlet feed can vary
depending on the actual temperature and rate of the recycle
52 and the level of feed conditioning and water cut
reduction required at the inlet to the dehydrator.
Similarly, the rat4_o of recycle 52 to recycle 50 will vary
for each application in order to establish a balance
between dehydrator feed conditioning and dehydrator surface
temperature. Depending on the relative size of oil recycle
50 to dry sales oil 34, common pumps or separate pumps may
be used, as known to those skilled in. the art. Recycle 52
can also be provided by separate pumping means.
Referring to Figure 2, shown is an enhancement to the
recycle variation of Figure 1, where a heat exchanger means
54 is added to the recycle circuit t:o condition the
temperature for steams 56 and 52. The streams, 56 and 52
can be heated or cooled to the same temperature or
independently to separate temperatures in order to seek the
thermal balance of the feed stream and hot crude oil bath
surface. Any form of suitable heat source, such as direct
fired heaters, indirect fired heaters, heat exchangers or
heat recovery or cooling apparatus may be selected. A
further consideration for temperature at the streams 56 and
52 is whether the feed is from a heated primary treatment
means at 170 F to 285 F (77 C to 141 C) or from a raw crude
storage tank at 60 F to 100 F (16 C to 38 C)
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Figure 3 illustrates an additional enhancement to
include a solid/liquid separator means 62, used to remove
suspended solids such as clay, sand, and precipitated salts
from the dehydrated crude oil. The solid/liquid separator
62 may be selected from any suitable separator device known
to those skilled in the art, such as gravity separators,
clarifiers, filter, screens, cyclones and centrifuges. The
recycle stream from 50, is sized to satisfy the range of
operation of the solid/liquid separator device 62 and
specifically sized to accommodate a solids removal rate at
64 greater or equal to the solids content entering the
dehydrator 24 at 18 and being produced in the dehydration
process.
The removal of the solids can be performed on a
continuous or batch basis and prirnarily allow for the
ongoing removal of solids from the dehydrator 24 to prevent
buildup and plugging. Buildup of solids on the heating
elements contained in 24 or external to 24 is detrimental
to the elements performance and can become a safety issue.
Turning to Figure 4, shown is a further variation of
the invention showing the addition of a water wash means to
the dehydrator to remove dissolved solids. The raw crude
oil can contain high concentrations of sodium, calcium,
magnesium, chlorides, sulfur, carbonates, silica, etc. All
these compounds, especially the chloride are currently
undesirable in the dry crude sales product and may have
significant commercial impact on the price for the crude
oil, or even restrict sales. Typically, refineries are
currently requiring less than 30 ppm(wt) chlorides in the
sales crude oil.
Using the enhancement shown by Figure 4, clean water
66 is injected and intimately mixed with the raw crude oil
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at 68. The feed mixture 10 is passed through primary
treatment separator at 12. The bulk of the brine contaminated
water is separated from the oil and discharged through line 22
to a water treatment unit 70.
5 The washed crude oil is discharged at 18 and becomes the
feed stream to the dehydrator. The feed can be conditioned
either in the primary treatment 12 or by using the recycle
stream 50 and 52 to ensure stable dehydrator 24 operation.
The washed crude at 18 contains significantly reduced levels
10 of dissolved compounds, meeting or exceeding the sales oil
specification requirements.
The water treatment scheme selected for each application
must ensure that the undesirable compounds in stream 22 are
sufficiently removed to satisfy the process removal
requirements at 18. Typical water treatment practices, are
microfiltration, reverse osmosis, distillation, flocculation,
clarification and coagulation.
Treated water 72 enters the treated water surge vessel 74
and is transferred by pump 76 for reinjection at 68 using line
66.
As an option, condensed water from the separator 32 can
be transferred directly by pump 78 to either the treated water
surge tank 74 via line 79 or to a water treatment unit 70 by
line 82 if water treatment is required. The net water
production would discharge from the separator 32 at stream 84,
or from the water treatment unit 70 by means of stream 88.
Fresh water makeup can be introduced to the treated water
storage tank 74 at 90 if a water balance deficit is
encountered.
Referring now to Figure 5, shown is a further embodiment
of the present invention where the dehydrator 24
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is divided into zones for solids separation. As is
illustrated in Figure 5, there is a solid separation zone,
generally denoted by numeral 100 within the dehydrator 24 and
a clean, dry oil zone denoted by numeral 102. Zones 100 and
102 are separated by a separation baffle 104, which baffle 104
may be composed of any suitable baffle structure known to
those skilled in the art for isolation of a liquid containing
suspended solids such that the baffle facilitates sufficient
residence time to permit gravity settlement of the existing
solid or solids which are in a growth phase. The baffle 104
therefore provides a weir where hot/dry oil may flow into zone
102 substantially free of any solids. A portion of the
hot/dry oil may be reintroduced to dehydrate 24 via line 57.
The solid (not shown) may be collected in a pan structure
denoted by numeral 106 and shown best in Figure 6.
The dry oil recirculation loop, denoted by numeral 108
containing suspended solids from between 0 weight percent and
30 weight percent and more particularly, near 0 (0.5 weight
percent) to 5 weight percent are pumped through line 50 to a
solids/liquid separation means 62. The solids may be removed
by simple purge stream via line 64 (either batch or
continuous) or by a solid/liquid separation device such as a
gravity settling tank or vessel, filter device, filter press,
hydrocyclone, centrifugal separator or centrifuge or any
combination of these components (none of which is shown) A
flushing recycle loop (not shown) is commonly included between
line 50 and pans 106 to assist with flushing of the solids and
prevents solids build up. A washing solvent, such as a
portion of the diluent created by the flash treating process,
denoted by numeral 110 may be used to wash the solids free of
any hydrocarbon compounds.
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The hot dehydrated oil, now substantially free of
suspended solids is recycled from separation device 62 to the
dehydrator bath surface via 52 (just beneath the surface as
shown in the drawing) and/or the source oil inlet, denoted in
5 this Figure by numeral 53. The hot dry oil surface circulates
,internally along the dehydrator and accumulates into the
dehydrated oil zone 102 for further transfer by a line 34.
Further heat energy may be added to the recycle stream 51 to
maintain a level of vaporization in the source oil inlet and
10 the desired temperature of the hot dry oil surface. Where the
temperature of the source oil at 18 is sufficiently high to
meet the energy balance of the dehydrator for a given source
oil water content, then stream 53 may be deleted entirely.
Heat energy may be added in the recycle streams and/or
15 internally of the bath of the dehydrator 24 as discussed
herein previously. Common practices of internal heating, well
known to those skilled, consist of fire tubes or other heating
devices (not shown).
The solids, sludge and other wash diluent as well as
20 hydrocarbon carryover from separation device 62 may be
disposed of directly or redissolved/slurried into the source
water with a mixing device, globally denoted by numeral 112.
Diluent and hydrocarbon fluids can be skimmed from tank 112
through circuit 114 and recycled via line 46 to the source 10.
The recycle rate for a circuit 50 may be set by the
process heating requirements of the streams 52 and 53 or the
minimum rate required by the solid liquid separation device 62
to remove the level of source suspended and produce solids on
a continuous or batch processing basis. The recycle streams
may also be separate with different pumping devices to meet
specific needs. The size of the
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solids and particle distribution of the solids will vary
depending on the solid composition, the level of solid
residence time and the final solids concentration designed
into the dehydrator and the methodology selected for removal.
Referring now to Figure 7, shown is a further variation
of the arrangement shown in Figure 5. In this embodiment, the
baffle 104 is absent from the internal volume of the
dehydrator 24. In this configuration, solids collect in the
entire bottom of the dehydrator 24 and collect at the pans 106
illustrated in Figure 7 and in cross section in Figure 6.
Recycle stream 50 supplies necessary thermal energy as
discussed herein previously and may also be employed for
flushing pans 106.
A separate stream 116 can be drawn from the bottom of
dehydrator 24 and passed through a solid liquid separation
device 118. Dry crude, substantially free of solids can then
be transferred from the separation device 118 via line 34.
Any surplus dry oil can be recycled to provide a defoaming
function to flash gases (not shown), the surplus oil indicated
from separation device 118 via line 120.
With respect to Figure 8, the treater 24, in this
embodiment, is reconfigured from the longitudinally disposed
arrangement shown in the previous Figures to a conical version
as illustrated in Figure 8 having a conical collection section
109. This arrangement is useful for higher solids loading in
the material to be treated, to accommodate space restriction
or alternate distillation configurations.
In the example, the dehydrator 24 is reconfigured to a
vertically disposed cylindrical design with a conical bottom
section. An advantage associated with this arrangement have
been the possibility of introducing the
CA 02435344 2007-07-27
22
recycle oil and or source oil via a centrifugal entry. This
has energy ramifications since it is known that mechanical
agitation, particularly by a centrifuge, will result in solid
particles being disassociated from the liquid within which
they are contained. At the same time gravity settling is
achieved in the bottom conical section of the dehydrator. By
combining the two separation techniques, i.e. the mechanical
agitation and the gravity separation, a dry clean oil zone
develops approximately in the middle region of the dehydrator,
broadly denoted by numeral 122 and solids are prevented from
entering this zone due to the motion of the fluid and the
introduction of a coaxial baffle 124. Dry oil, substantially
devoid of any solids is removed via line 48 and transferred
for subsequent unit operations or sales or further recycled
back to dehydrator 24 for any other suitable purpose
(defoaming, temperature control, etc.). Dry oil with solids
entrained therein is transferred to separation device 62 as
indicated herein previously where a substantial amount of the
solids are removed by simply purging or by suitable separation
as discussed herein previously.
Turning to Figure 9, shown is a further variation on the
conical dehydrator system. In this embodiment, dry oil with
solids entrained therein is collected entirely within the
conical section denoted by numeral 109 of dehydrator 24. Once
within the conical section 109, the fluid is circulated to
provide the necessary energy requirement at loops 52 and 53 as
discussed herein previously. A portion of the collected
material may be collected along line 56 and passed to a
liquid-solid separation device 62.
In Figure 10, further modifications to the dehydrator 24
are illustrated in the process flow diagram depicted. In this
embodiment, a distillation tower extends from the dehydrator
24, with the distillation tower being broadly
CA 02435344 2007-07-27
23
denoted by numeral 126. This is a particularly convenient
feature since the distillation portion 126 can be employed to
selectively separate and distill any hydrocarbon fraction
desired.
Operational parameters for the distillation tower 126
will be appreciated by those skilled in the art. The
distillation apparatus may be attached directly to the unit or
provided separately.
Turning to Figure 11, shown is a dehydration, separation
and upgrading process flow diagram where the dehydration
circuit shown herein previously is joined with an overall
processing scheme for upstream heavy oil production such as
SAGD or CSS. Dehydrated crude leaves the dehydrator at 42'.
In this embodiment, the source is well effluent, sharing
a common numeral with the source from previous flow diagrams.
The effluent 10, which is typically at a temperature of
greater than 285 F and at approximately 350 psig (140 C and
2400 kPa) is introduced for pretreatment at 12 where bulk
water, solids, dissolved compounds, inter alia are removed.
The hot emulsion, generally containing less than 5 weight
percent BS and W is flashed in dehydrator 24 at atmospheric
pressure and temperatures of greater than 220 F (105 C) where
the water and light hydrocarbons are distilled and suspended
solid contaminants are removed. The dry heavy oil exiting the
system at 34 is a particularly useful stream for heavy oil
partial upgrading processes (such as distillation, vacuum
distillation and solvent deasphalting) where the crude oil
product quality is upgraded from approximately 7 to 10 API to
about 21 API with a viscosity of less than 350 CSt at 10 C,
primarily for pipeline transport to refineries.
CA 02435344 2003-07-17
24
As an alternative, the cleansed dry heavy oil is also
suitable as a precursor material for full upgrading
conversion such as visbreaking, hydro processing, and
thermal cracking. In the absence of the upgrading process,
the cleansed dry crude requires blending with about 20% to
30% by volume diluent and subsequently must be shipped as
dilute crude product by pipeline to a refinery capable of
treating the blended heavy oil.
By following the enhancements independently or in
combination, the process methods as described by this
invention, will result with dry clean crude oil meeting or
exceeding new sales specifications for commercial sale.
As a further variation, Figures 9 and 10 illustrate an
optional diluent makeup stream 130 which can be mixed with
the light hydrocarbon stream 46 and blended with the source
crude oil 10 prior to the pretreatment step 12. The
addition of the diluent reduces the density and viscosity
of the heavy oil and creates the density difference and
separation motive force between the heavy oil and the
produced water, thereby breaking down the oi7., emulsion and
producing a lower water cut oil feed to the dehydrator at
18. A further advantage of this embodiment is that the
pretreatment separation step can be performed at the source
crude oil inlet pressures and temperatures, typically less
than 284 F (140 C), thereby requiring no additional heat
energy input. The diluent makeup stream can primarily
contain heavier molecular weight components, such as
pentane and heavier, and perform the separation function
and generally pass through the dehydrator with the sales
oil and form part of the shipping diluent volume required.
A further advantage of the blend treating pretreatment
step is that only the low water cut dehydrator feed 18 is
CA 02435344 2007-07-27
heated to above 212 F (100 C) for flash treating. The
dehydrator operating temperature and pressure are selected, by
those skilled in the art, to match the required diluent 130
and light hydrocarbon 46 volume and composition and perform
5 the basic water distillation function. By carefully selecting
the dehydrator distillation and hydrocarbon recycling
conditions, a specific hydrocarbon distillation cut can be
achieved for the sales oil, thus providing a controlled feed
composition 34 for further downstream full or partial
10 upgrading operations 120.
Turning to the embodiment of the invention shown
schematically Figure 12, a diluent recycle system is shown as
a further unit operation in the dehydration and solid removal
method. Effluent stream 10 undergoes pretreatment 12 as
15 indicated with previous embodiments. The temperature at which
the effluent is contacted for pretreatment is between 284 F
(140 C) and 356 F (180 C). Prior to contacting the
pretreatment phase of the operation, the stream is cooled by a
heat exchanger which may comprise a boiler feed water heat
20 exchanger as an example to less than 212 F (100 C) and more
desirably between 176 F (80 C) and 203 F (95 C) for
atmospheric downstream processing.
Recycled diluent (discussed in greater detail herein
after) is mixed with the effluent material at 142 prior to
25 contact with the pretreatment phase.
As generally described herein previously, pretreatment,
although indicated in Figure 12 as a single unit operation may
comprise several operations globally denoted by numeral 300
including free water knockout, desalination, filtration or any
combination of operations to facilitate reduced water content
and salt content in the effluent stream (bitumen emulsion)
Produced water recovered from the pretreatment
CA 02435344 2003-07-17
26
operation is recovered and recycled through stream 22 to be
used as boiler feed water for, example, a SAGD steam
generation operation.
Once pretreated, the emulsion exiting the pretreatment
operation 12 contains significantly lower concentrations of
salts, solids and water. In particular, the water content
is less than 10% by volume and more desirably less than 2%
by volume. This pretreated emulsion is pumped by pump 144
and passed through heat exchanger 146 prior to entering the
dehydrator 24, the latter having been discussed thoroughly
herein previously. Additional heat is added to the stream
148 from heat exchanger 146 with the quantity of heat being
sufficient to vaporize at least some of the water in the
stream and the light diluent hydrocarbons. Z'ypically, the
temperature of the stream is between 266 F (130 C) and
356 F (180 C). As a further efficient provision, further
heat can be added by heat exchanger 54 from stream 51 to
recover substantially all of the water and a significant
portion of the light hydrocarbon diluent.
Having been exposed to the dehydrator, the emulsion
exits as a dry bitumen via stream 34 and is elevated in
temperature to between 392 F (200 C) and 662 F(350 C) by
heat exchanger 150. This assists in full diluent recover.
Having been exposed to heat exchanger 150, the stream 152
(now elevated in temperature to approximately 392 F
(200 C)) enters a steam stripping tower 154 where steam,
denoted by numeral 153 is used to strip the diluent from
the bitumen. The quantity of steam required and the
temperature of streams 18, 51 and 152 are optimized for the
type of diluent being used. Typical diluents include
synthetic crude oil (SCO), naphtha and natural gas
condensates. In terms of the quantity of recycled diluent,
CA 02435344 2003-07-17
27
this is determined by the bitumen water separation
parameters required in the pretreatment phase 12.
The vapor recovered from dehydrator 24 and stripping
tower 154 may be either independently or commonly collected
and condensed in a cooler 30 and vessel 32. A portion of
the light hydrocarbon diluent may be transferred as reflux
back to the stripper 154, denoted by numeral 156. The
remaining amount and major amount of the condensed diluent
is recycled to the onset of the process at 142. Preheating
may be applied using exchanger 158 to control the inlet
conditions at the pretreatment phase 12. Any water 36 and
non-condensable vapors separated in vessel 32 are disposed
of in an efficient manner.
Dry crude exiting stripper 154, denoted by numeral 155
may be recirculated through heat exchanger 146 for heat
recovery and subsequently discharged. A further heat
exchanger 160 may be provided for temperature reduction.
The solvent to bitumen ratio which establishes the
rate of diluent recycle and injection at 142 is generally
optimized between 0.1 and 1Ø As an example, it is
typical to have a ratio of about 0.3 to 0.6 diluent to
bitumen. Optimization of this parameter avoids the onset
of asphalting precipitation and minimizes overall energy
consumption. Further, optimization of the actual
composition of the diluent recycle stream is important; a
great amount of aromatic as opposed to paraffinic
hydrocarbons in the recycled diluent may be desirable in
order to avoid asphalt precipitation and optimize recycle
rate of the diluent. Composition of the diluent can be
adjusted by changing composition of the diluent make up and
by process parameter adjustment.
CA 02435344 2003-07-17
28
By the methodology followed in Figure 12, it has been
found that extremely high recycle rate (greater than 90%
and in some cases greater than 98%) recovery of the diluent
is possible. This provision eliminates the requirement for
major processing units at the r_efinery/upgrader and
alleviates the burden in the industry currently realized by
a lack of diluent and further avoids unnecessary
expenditure typically associated with resupplying diluent
at a site. This inherently makes the process more
efficient and cost effective.
In terms of the stripping operation, although a
stripping tower has been set forth in Figure 12, it will be
readily appreciated that any separation technique which
achieves the desired result may be employed. Such suitable
techniques include multiple flashing, distillation, vacuum
flashing, super critical separation and any other unit
operation in combination with or without a stripping tower
known to achieve the desired result and apparent to those
skilled in the art.
Although embodiments of the invention have been
described above, it is not limited thereto and it will be
apparent to those skilled in the art that numerous
modifications form part of the present invention insofar as
they do not depart from the spirit, nature and scope of the
claimed and described invention.
