Note: Descriptions are shown in the official language in which they were submitted.
~2~ `S
This invention relates to a method and apparatus for
treating crude oil, and in particular heavy hydrocarbon crude
oil.
In the treatment of heavy hydrocarbons at or near
producing wells, it is desirable to remove all or virtually
all of the water entrained in the oil. In general, water can
be removed from the oil simply by heating the mixture to boil
the water. However, such boiling, e.g. in a storage tank
resul-ts in the evolution of steam which creates large
quantities of foam formed of steam bubbles in an oil film.
The foaming is, at best, difficult to control and forms a
spill with a volume many times greater than the volume of the
liquid.
Apparatuses for treating crude oil are disclosed,
for example by Canadian Patent No. 1,122,135, issued to
Koppers Company, Inc. on April 20, 1982, and U.S. Patents
Nos. 3,441,499 and 3,453,205, both issued to A. W. Francis,
Jr. et al on April 26, 1969 and July 1, 1969, respectively.
In general, currently available dehydrators rely on
differences in the specific gravity of oil and water to
effect gravity separation. The gravity separators use a heat
source to raise the temperature of the crude oil which
reduces the viscosity of the oil to promote phase
separation. Such a process is not par-ticularly effective for
heavy crude oils, which have specific gravities close to that
:~25721~
of water. The addition o-f emulsion breakers have often
proven to be of little value.
Other dehydrators utilize vacuum towers combined
with heaters for removing water as steam below atmospheric
pressure. The vacuum is created by vapour compressors which
condense or flare the resulting pressurized steam to the
atmosphere. Such a method requires many separate pieces of
shipment, is expensive and is best suited to large central
plant facilities. Controlled boiling has also been attempted
using tray-type towers or expensive heat exchangers.
An object of the present invention is to provide a
relatively simple, easy to operate apparatus which can be
located in remote oil producing areas for dehydrating crude
oil. Another object of the invention is to provide a method
of dehydrating oil which is relatively easy to carry out,
even in remote areas.
Accordingly, the present invention relates to an
apparatus for dehydrating crude oil containing water
comprising:
(a) treater means for separating water and
entrained solids from the oil;
(b) dehydrator means for receiving oil from the
treater means, said dehydrator means being
adapted to remove residual water from said oil
- to yield dehydrated oil and a mixture of steam
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and light hydrocarbon vapour;
(c) condenser means for condensing said mixture,
(d) separator means for separating water from the
liquid mi~ture received from the condenser
means; and
(e) pipe means for returning at least a portion of
the light hydrocarbon liquid from the separator
to said treater means, whereby the crude oil
subjected to treatment is diluted for more
efficient saparation of oil and water, due to
viscosity reduction and gravity differences.
The invention also relates to a method for
dehydrating crude oil containing water
. comprising:
(a) subjecting said crude oil to pressure
treatment to separate water and entrained
solids from the oil;
(b) dehydrating the thus treated crude oil by
evaporation to yield a dehydrated crude oil,
and a mixture of steam and light hydrocarbon
vapours;
(c) condensing the mixture produced in the
dehydration step;
(d) separating water and light hydrocarbons
from tha mixture, and
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(e) continuously returning at least a portion
of said light hydrocarbons to the crude oil in
said pressure treatment step, whereby the crude
oil subjected to pressure treatment is diluted
for more efficient separation of oil and water.
It is preferable that the dehydrated oil has a water
content of less than 0.5~ by volume and be acceptable for
pipe line transmission to a refinery. Such oil is readily
saleable, particularly in the case of heavy crude oils with
specific gravi-ties near or less than that of the produced and
accompanying water.
The invention will ncw be described in greater
detail with reference to the accompanying drawings, which
illustrate a preferred embodiment of the apparatus of the
present invention, and wherein:
Figure 1 is a schematic flow diagram of an apparatus
in accordance with the present invention:
Figure 2 is a schematic longitudinal sectional view
of a dehydrator used in the apparatus of Fig. 1 taken
generally along line II-II of Fig. 3;
Figure 3 is a cross-section taken along line III-III
of Fig. 2; and
Figure 4 is an end view of the dehydrator of Figs. 2
and 3.
With reference to Fig. 1, the apparatus of the
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present invention includes a treater 1/01 gravity separator
for receiving crude oil from an inlet 2 via line 3. The
fluid entering the treater 1 is a mixture of oil, water and
solid particles such as clays, metals and silicas. The
pressure treater 1 is a commercial available item, which
operates at pressures from zero to 700 kpa or more, and a
temperature of 80 to 140C. The raw crude oil is
discharged from the treater 1 through line 4 and valve 5.
Such oil contains less water, less oil/water emulsion and
less solids, the latter having been separated by gravity and
removed with water through a line 6 and a valve 7. Light,
unstable hydrocarbon components are discharged from the
treater 1 through a vent 8 and a regulating valve 9.
Crude oil from the treater 1 enters a dehydrator
generally indicated at 12 which is described hereinafter in
greater detail. In the dehydrator 12, oil and water are
separated by distillation, water and low boiling temperature
hydrocarbon components of the oil rising through a column 13
and passing through a line 14 to a condenser 15 and then to a
vapour/li~uid separator 16. Dehydrated oil is discharged
from the dehydrator 12 through line 17 and a pump 18. Some
of the dehydrated oil is returned to the dehydrator 1~
through line 19 for stripping additional distillate from the
heavy crude oil in column 13.
In the separator 16, water and hydrocarbon
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distillate are separate by virtue of their different speci~ic
gravities. The separated water is discharged through outlet
line 20, a pump 21 and a valve 22. A rising liquid level in
the separator 16 causes the valve 22 to open, so that the
pump 21 discharges the water to storage (not shown,~. Light,
non-condensable components are aischarged from the separator
16 through vent line 25.
Light hydrocarbon liquid~ which has a specific
boiling point range determined by the operating temperature
of de~lydrator 12 and which is stable at a-tmospheric
temperature and pressure is returned to the p~essure treater
1 through pipe 26 and line 3, via pump 24. E~cess
hydrocarbon liquid can be withdrawn from the system through a
line 30 and a valve 31~
~ eferring to Figs. 2 to 4, the dehydrator 12 of the
present invention includes a casing 35 for receiving fluids
from the pressure treater 1 through the line 4. mhe fluid
entering the dehydrator 12 flows into a spray tube 36 and is
sprayed onto liquid 37 already in the casing 35. In this
manner, the liquid being introduced is ev~nly distributed on
the hot crude oil liquid 37 in the dehydrator 12.
The liquid 37 in the dehydrator 12 is heated by a
generally U-shaped firetube 40, which is immersed in the
liquid. Fuel is introduced into the tube 40 via inlet end asl
and burned. Exhaust from the tube 40 is discharged to the
atmosphere through a vertical discharge tube 42.
The liquid 37 is normally at 110 to 150C and a
pressure of close to atmospheric, i.e. less than 20 kpa.
Boiling occurs at the surface 43 of the liquid 37. The
surface 43 acts as a heat sink, liberating water in the form
of steam in a direction countercurrent to the incoming crude
oil. Virtually all of the water in the crude oil is removed
in the dehydrator 12. Light hydrocarbons are liberated with
the water, because of the temperature and pressure
conditions, and because of steam distillation above the
surface 42. Heavy or higher boiling components are stripped
from the distillate by dehydrated oil sprayed into the
dehydrator 12 through a spray head 45 at the bottom of the
column 13. The head 45 receives dehydrated oil from the line
19. The dehydrated oil spray also acts as a foam suppressant
by collapsing bubbles 46 at the surface 43 of the liquid 37.
The discharge of foam with the distillate is further
inhibited by baffles 47 extending transversely in the casing
35 on each side of the entrance to the column 13.
In operation, crude oil including oil, water and
solids enters the treater 1. In the treater 1, the crude oil
is treated to reduce the water, emulsion and solids content
of the oil. The crude oil and emulsions flow into the
dehydrator 12 where the liquid is evenly distributed on the
surface 43 of the oil bath 37. Water is liberated as steam,
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and is discharged from the dehydrator 12 with light or low
boiling hydrocarbons through the line 14 to the condenser
15. The vapours are converted to liquid water and
hydrocarbons which are fed into the separator. In the
separator, the water and hydrocarbons condensate (both low
liquid) are separated.
The light hydrocarbon liquid is returned to the
treater 1 through the line 26. The liquid is, in effect, a
synthetic, tailor-made diluent or solvent, which is readily
soluble in the raw crude oil. The composition of the liquid
can be altered by controlling the temperature and pressure in
the dehydrator 12, and the temperature in the condenser 15.
For example, higher temperatures and/or lower pressures in
the dehydrator 12 will encourage separation of heavier or
high boiling point components of the crude oil.
The above described process is repeated continuously
until the diluent recycled through the line 26 is stabilized,
i.e. of consistently the same composition. As more and more
diluent is recycled, the specific gravity of the crude oil in
the treater 1 is reduced. For example, a 14 API crude oil
is reduced to a 23 API crude oil. Such artifici~l
lowering of the crude oil specific gravity creates a
reduction of the overall crude oil viscosity in the pressure
treater 1. At selected optimum temperature and pressure,
such reduced viscosity encourages the breakup and separation
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of water/oil emulsions. Water is removed through the valve
7. Solids in the emulsion leave with the water. Initially,
the oil flowing into the de~ydrator 12 from the treater 1 has
a high water content, but as -the specific gravity of the oil
in -the treater 1 decreases, the water content in the line 4
also decreases.
What has been done is to permit the commonly used
gravity vessel, namely the pressure treater, to perform the
oil and water separa-tion process using an artificial solvent
or diluent. ~ 3 to 18 API oil is changed to an artificial
18 - 25 API synthetic crude, which encourages p~ase
separation of oil/water emulsion into separate oil and water
steams. This eliminates solids and salt (from salt water)
contamination which remains if the crude oil is delivered
directly to the evaporative dehydrator. Once the synthetic
diluent has been created, the pressure treater is as
effective as with light conventional crude oils. ~ny water
remaining in the crude oil (usually 0.5 to 1.5% by volume)
can be evaporated in the dehydrator to yield a substantially
water-free, low solids crude oil. The process can be
expedited if an outside source o diluent is added to the
system initially. Once entered and stabili7ed, the diluent
remains in the closed process loop. In effect, the
dehydrator causes upstream conventional equipment to be more
effective, so that less energy is required to boil off
~%s7~s
entrained water.
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