Note: Descriptions are shown in the official language in which they were submitted.
CA 02364831 2001-12-11
METHOD OF REMOVING WATER AND CONTAMINANTS
FROM CRUDE OIL CONTAINING SAME
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 and remove
suspended
and dissolved compounds from inlet feed.
Throughout many regions of the world, heavy oil, a hydrocarbon material
having much higher viscosity or lower API gravity (less than 20 API, typically
70 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). 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,
1
CA 02364831 2001-12-11
areas for improvement were discovered to overcome the limitations of feed oil
water
content and unstable operation caused by pretreatment upsets.
Further, additional problems have been experienced with the prior art 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.
Accordingly, one aspect of the present invention is to provide advances to
overcome the limitations encountered by the previous art.
One aspect of the present invention is to provide for a dry crude oil recycle
stream around the dehydrator to mix with the feed to reduce the ratio of
residual water
to oil contacting the oil surface of the dehydrator and thereby allow for
higher raw
crude oil water cuts, while maintaining a stable dehydration operation.
A further aspect of one embodiment of the present invention is to provide a
method of removing water and solids from crude oil containing water and
solids,
comprising:
a dehydration phase and a separation phase, the dehydration phase including:
providing a source of crude oil containing water;
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CA 02364831 2001-12-11
providing a dehydrator for dehydrating the crude oil containing water,
the dehydrator having an inlet and an outlet and a vaporizing surface of dry
crude oil at temperatures sufficient to vaporize water contacting the surface;
exposing the source of crude oil to the dry crude;
vaporizing the water in the source;
the separation phase including:
isolating within the dehydrator solids present in dehydrated crude from
the dehydrated crude; and
re-circulating at least a portion of dehydrated and solid separated crude for
contact with at least one of the dehydrator or the source of crude oil for
maintaining a
substantially uniform temperature at the vaporizing surface.
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 foaming.
A further aspect 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) or recovery of heat
energy
from the dehydrator to result in an energetically efficient and balanced
process.
A still further aspect of one embodiment of the present invention is to
provide a
method of removing water and solids from a crude oil containing water and
solids,
comprising:
a dehydration phase and a separation phase, the dehydration phase including:
providing a source of crude oil containing water;
3
CA 02364831 2001-12-11
b t
providing a dehydrator for dehydrating the crude oil, the dehydrator
having an inlet and an outlet and a vaporizing surface of dry crude oil at a
temperature sufficient to vaporize water contacting the surface;
contacting the source and the dry crude oil to flash water from the
source to thereby remove the water from the source;
the separation phase including:
isolating within the dehydrator solids present in dehydrated crude from
the dehydrated crude;
re-circulating the dehydrated crude oil for contact immediately below the
vaporizing surface; and
re-circulating the dehydrated crude oil for mixing with the source of
crude oil, whereby the vaporizing surface is selectively heated to return heat
energy lost from flash evaporating water from the source.
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.
A further aspect of the present invention is to provide a means to remove
suspended solids accumulated in the contained dry crude oil introduced with
the
source oil and produced during dehydration.
Suspended solids in the dry crude oil recycle stream, may be removed by a
separator means on a continuous or batch basis to avoid buildup, plugging, and
other
complications.
A further aspect of the present invention is to water wash the raw crude oil
source combined with the treatment in the dehydrator to remove the soluble
dissolved
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CA 02364831 2001-12-11
solids or contaminants introduced by the source crude oil and generate a low
conductivity produced water and clean dry crude oil.
Until the advent of the present invention, prior art methods related to heavy
oil
dehydration had been limited by the stability of operation and risk of
foaming, level of
water cut or emulsion level in the heavy oil feed and the level of chloride,
clay and
silica compounds in the dry sales crude oil.
A still further aspect of one embodiment of the present invention is to
provide a
method of upgrading effluent containing crude oil to dehydrated crude oil,
comprising:
a conditioning phase, a dehydration phase, and a separation phase, the
conditioning phase including:
providing a source of effluent at least containing crude oil with water
entrained therein and solids;
pretreating the effluent to remove at least some of the water and solids
to thereby concentrate the crude oil;
the dehydration phase including:
providing a dehydrator for dehydrating the crude oil, the dehydrator
having an inlet and an outlet and a vaporizing surface of dry crude oil at
temperatures sufficient to vaporize water contacting the surface;
exposing the crude oil to the dry crude;
vaporizing the water in the crude oil to dehydrate the crude oil; and
the separation phase including:
isolating within the dehydrator solids present in dehydrated crude to
form clean dehydrated crude oil.
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.
5
CA 02364831 2001-12-11
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 heat
energy sufficient to maintain the liquid oil at or above the distillation
temperature for
evaporating water and light hydrocarbons.
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 heavier 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. The separation step can be performed at the temperature and
pressure conditions of the raw well effluent or source oil. The heavy portion
of the
diluent will pass through the dehydrator and be retained in the sales oil of
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-condensible 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 for transport to refining and
upgrading
operations.
Typically, the dehydrator taught in the current art performed well to produce
dry
crude oil, however several problems have been encountered:
6
CA 02364831 2001-12-11
1. The dehydrator was limited to crude oil feed water cuts (wc) of less than
% water to oil, and more specifically less than 5 % we to reduce the risk of
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 %
we down to less than 5 % we prior to feeding the 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.
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 % we stable level and continuous
stable
operation is maintained. This eliminates the need for conventional treatment
ahead of
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CA 02364831 2001-12-11
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 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 vapour 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, from the dry
crude 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
8
CA 02364831 2001-12-11
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 addition to achieving a dehydrated oil, having a BS&W
content of less than 0.5% we by volume, the embodiments of the invention in
combination, or separately applied, can produce a dry clean crude oil,
substantially
free of solids, containing less than 30 ppm (wt) chlorides, in a continuous
and stable
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 invention, reference will now be made to the
accompanying drawings illustrating preferred embodiments and in which:
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;
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;
9
CA 02364831 2001-12-11
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; and
Figure 11 is a schematic flow diagram illustrating a still further embodiment
of
the present invention;
Similar numerals employed in the Figures denote similar elements.
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 particles such as
clay,
metals and silicas. The crude oil is generally received in a gravity
separator, heated or
non heated treater 12, under pressure from between atmospheric pressure to 100
psig. 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 5% by volume
can be
achieved in the raw crude feed 18 exiting the primary treatment through a
valve
member 20. The water stream 22 generally contains dissolved compounds such as
CA 02364831 2001-12-11
sodium chloride, (5,000 to 50,000 ppm (wt)) and silica, and suspended
compounds
such as clay and sand.
The raw crude oil at approximately 5% 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. Water is flashed off the oil
or
separated by distillation, with water and low boiling temperature hydrocarbon
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.
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 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 condensible, i.e. light hydrocarbons, inert gases
(nitrogen,
carbon dioxides, hydrogen sulfide) are vented from separator 32 and disposed
of or
recovered by any suitable safe means.
As shown by Figure 1, dry oil can be recycled from 48 and recycled as stream
50 to mix with the inlet feed 18, 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
11
CA 02364831 2006-11-24
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.
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 ratio 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 to
condition
the temperature for streams 53 and 52. The streams, 53 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
12
CA 02364831 2006-11-24
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).
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
primarily 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 10 at 68. The feed mixture 10 is
passed
13
CA 02364831 2001-12-11
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.
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 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 by line 80 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 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
14
CA 02364831 2001-12-11
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.
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 (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.
The hot dehydrated oil, now substantially free of suspended solids is recycled
from separation device 62 to the dehydrator bath surface 52 Oust beneath the
surface
as shown in the drawing) and/or the source oil inlet, denoted in 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 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
CA 02364831 2001-12-11
energy may be added in the recycle streams and/or 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 hydrocarbon carryover
from separation device 62 may be disposed of directly or redissolved/slunied
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 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 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
16
CA 02364831 2006-11-24
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. 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 has been the possibility of introducing the 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 102 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 106 of dehydrator 24. Once
within the
17
CA 02364831 2001-12-11
conical section 106, the fluid is circulated to provide the necessary energy
requirement
at loops 52 and 53 as discussed herein previously.
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 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.
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
18
CA 02364831 2001-12-11
with a viscosity of less than 350 cSt at 10 C, primarily for pipeline
transport to
refineries.
As an alternative, the cleansed dry heavy oil is also suitable as a precursor
material for full upgrading conversion such as visbreaking, hydroprocessing,
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 oil 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 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.
19
CA 02364831 2001-12-11
A further advantage of the blend treating pretreatment step is that only the
low
water cut dehydrator feed 18 is heated to above 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 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 upgrading operations
120.
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.
