U.S. patent application number 16/353352 was filed with the patent office on 2019-07-11 for desalter operation.
The applicant listed for this patent is ExxonMobil Research and Engineering Company. Invention is credited to Magaly C. Barroeta, Gregory M. Mason, Jose X. Simonetty, Ashok Uppal, Mohsen S. Yeganeh.
Application Number | 20190211273 16/353352 |
Document ID | / |
Family ID | 56407351 |
Filed Date | 2019-07-11 |
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United States Patent
Application |
20190211273 |
Kind Code |
A1 |
Barroeta; Magaly C. ; et
al. |
July 11, 2019 |
DESALTER OPERATION
Abstract
Improved separation of oil and water as well as suspended solids
from the emulsion layer formed in a petroleum desalter is achieved
by injection of demulsifier into the desalter vessel to achieve a
higher localized concentration of demulsifier in the emulsion layer
so as to promote improved oil/water separation from the emulsion
layer. The demulsifier may be injected into the water layer or the
oil layer in the region of the emulsion layer or directly into the
stabilized emulsion layer.
Inventors: |
Barroeta; Magaly C.;
(Tomball, TX) ; Mason; Gregory M.; (Baton Rouge,
LA) ; Uppal; Ashok; (Sarnia, CA) ; Yeganeh;
Mohsen S.; (Hillsborough, NJ) ; Simonetty; Jose
X.; (Kingwood, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ExxonMobil Research and Engineering Company |
Annandale |
NJ |
US |
|
|
Family ID: |
56407351 |
Appl. No.: |
16/353352 |
Filed: |
March 14, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14994623 |
Jan 13, 2016 |
10260007 |
|
|
16353352 |
|
|
|
|
62104234 |
Jan 16, 2015 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10G 31/08 20130101;
C10G 33/02 20130101; C10G 33/04 20130101; C10G 53/02 20130101 |
International
Class: |
C10G 31/08 20060101
C10G031/08; C10G 53/02 20060101 C10G053/02; C10G 33/04 20060101
C10G033/04; C10G 33/02 20060101 C10G033/02 |
Claims
1. A petroleum desalter unit having a desalter vessel having: an
inlet for an oil/water mixture, electrical grids within the vessel
for imposing an electric field on the oil/water mixture in the
vessel to cause separation of the mixture into a denser water layer
containing dissolved salts and a supernatant oil layer with the
formation of a stabilized emulsion layer between the oil layer and
the separated water layer, a water outlet for removing water from
the denser water layer, an oil outlet for removing oil from the
supernatant oil layer demulsifier injectors for injecting
demulsifier into the vessel in the region of the emulsion
layer.
2. A petroleum desalter unit according to claim 1 which comprises
demulsifier injectors for injecting demulsifier directly into the
emulsion layer.
3. A petroleum desalter unit according to claim 1 which comprises
demulsifier injectors for injecting demulsifier directly into the
denser water layer.
4. A petroleum desalter unit according to claim 1 which comprises
demulsifier injectors for injecting demulsifier directly into the
denser water layer towards the emulsion layer at a distance of not
more than 20 cm from the interface between the oil and water
layers.
5. A petroleum desalter unit according to claim 1 which comprises
demulsifier injectors for injecting demulsifier directly into the
supernatant oil layer.
6. A petroleum desalter unit according to claim 1 which comprises
demulsifier injectors for injecting demulsifier directly into the
supernatant oil layer towards the emulsion layer at a distance of
not more than 20 cm from the interface between the oil and water
layers.
7. A petroleum desalter unit according to claim 1 in which the oil
and water layers flow from the region of the inlet to the
respective oil and water outlets in a general flow direction and
the vessel comprises demulsifier injectors for angularly injecting
demulsifier towards the general flow direction.
8. A petroleum desalter unit according to claim 3 which comprises
demulsifier injectors for injecting demulsifier directed towards
the bottom of the vessel.
9. A petroleum desalter unit according to claim 8 in which the
injectors for injecting demulsifier directed towards the bottom of
the vessel are located not more than 46 cm from the bottom of the
vessel.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 14/994,623, filed on Jan. 13, 2016, which
claims priority to U.S. Provisional Application Ser. No. 62/104,234
filed Jan. 16, 2015, herein incorporated by reference in its
entirety.
FIELD OF THE INVENTION
[0002] This invention relates to crude petroleum desalting and to
the desalter unit.
BACKGROUND OF THE INVENTION
[0003] Crude petroleum normally contains mineral salts that may
corrode refinery units; the salt is removed from the crude oil by a
process known as "desalting", in which hot crude oil is mixed with
water and a suitable demulsifying agent to form a water-in-oil
emulsion which provides intimate contact between the oil and water,
transferring salt into the water. The salty emulsion is then passed
into a high voltage electric field inside a closed separator
vessel. The electric field forces water droplets to coalesce,
forming larger water droplets. As the water droplet volumes
increase, they settle to the bottom of the tank under gravitation.
The desalted oil forms at the upper layer in the desalter from
where it is continuously drawn off for distillation. The salty
water is withdrawn from the bottom of the desalter.
[0004] During operation of desalter units, a stable emulsion phase
(also known as a "rag layer") of variable composition and thickness
forms above the interface between the oil and the separated bulk
water phase at the bottom of the desalter. This interface will be
referred to here as "oil/bulk-resolved water interface". The
formation of a rag layer is mostly due to stability of the
oil/bulk-resolved-water interface caused by natural surfactants
(e.g. asphaltenes, naphthenic acid) and/or solids. Solids,
particularly, can reside at the interface generating a physical
barrier against the immersion of water droplets into the bulk water
phase at the bottom of the desalter. The formation of the rag layer
is especially problematic for crude with high amounts of natural
surfactants and/or solids. The growth of the rag layer reduces
workable volume and may cause shorting within the electric circuit
and force unplanned and costly desalter shut down. Additionally,
processing crudes with high rag layer formation tendencies in
current desalter configurations may cause poor desalting (salt
removal) efficiency as a result of the accumulation of solids at
the bottom of the vessel, and/or a solids-stabilized rag layer
leading to erratic level control and insufficient residence time
for proper water/oil separation. Formation of the rag layers has
become a major desalter operating concern, generating desalter
upsets, increased preheat train fouling, and deteriorating quality
of the brine effluent and disruption of the operation of the
downstream wastewater treatment facilities.
[0005] The water content of the rag layer may range from 20 to 95%
water with the balance being hydrocarbon (normally full range crude
oil) and up to 5 weight percent inorganic solids. Precipitated
asphaltenes, waxes, and paraffins may also be found at elevated
levels in the rag layer (compared to the incoming crude oil) which
combine with particulates (solids), to bind the mixture together to
form a complex structure that is highly stable. Intractable
emulsions of this kind comprising of oil, water and solids make
adequate separation and oil recovery difficult. Often, these stable
emulsions arising from the desalter are periodically discarded as
slop streams. This results in expensive treating or handling
procedures or pollution problems as well as the fact that crude oil
is also lost with these emulsions and slop streams.
[0006] Refinery sites which process high solids-content crudes have
the most pervasive problems with emulsion formation. Heavy crude
oils and bitumens from Western Canada, which contain elevated
levels of small clay fines and other small solids, are particularly
prone to forming large volumes of highly stable emulsions. With
such feeds, growth of the rag layer is more prevalent. These feeds
are, however, being introduced to refineries in greater quantities
despite two main disadvantages related to the efficacy of
desalting. First, the viscosity of these crudes can be quite high,
so transport of water through the feed is slower than in high API
gravity crude. Second, the density mismatch between water and oil
is lower, so the gravitational energy gradient is reduced compared
to higher API gravity crudes. Growth of the rag layer in the
desalter requires either the amount of crude passed through the
desalter to be reduced or removal of the rag layer from the
desalting vessel for external treatment.
[0007] Attempts to mitigate the effects of rag layer formation are
normally carried out by withdrawal of the emulsion from the unit or
by the addition of chemical demulsifiers upstream of a desalter.
The use of demulsifiers has proven to be effective in reducing
emulsion stability between electrodes in a desalter, but may not be
effective in reducing the rag layer build-up which is mainly due to
stability of the oil/bulk-resolved-water interface. The common
practice for application of demulsifiers has been to add the
chemical demulsifiers to the water, oil, or the emulsion before
introducing the oil/water mixture to the electric field, as shown
by the following references:
[0008] U.S. Pat. No. 5,746,908 (Mitchell/Phillips Petroleum),
discloses the use of steam to form an emulsion and then adding
demulsifier to the mixture.
[0009] U.S. Pat. No. 7,867,382 (Droughton) discloses the use of
demulsifier and mesoporous materials for reducing water-in-oil
emulsion stability.
[0010] U.S. Pat. No. 7,923,418 (Becker/Baker Hughes) discloses the
use of acrylate polymer emulsion breakers for reducing stability of
a water-in-oil emulsion.
[0011] U.S. Pat. No. 7,981,979 (Flatt/Nalco) discloses the use of
siloxane cross-linked demulsifiers for reducing water-in-oil
emulsion stability.
[0012] A shortcoming of the current practice is due, in part, to
the inability of chemical demulsifiers to reach high enough
concentrations at the oil/bulk-resolved-water interface,
particularly at the beginning of the desalter operation.
Accordingly, the need persists for more effective techniques for
mitigating the effects of rag layer formation.
SUMMARY OF THE INVENTION
[0013] We have now found that injection of the demulsifier into the
desalter vessel can result in higher concentrations of the
demulsifier in the emulsion layer which forms above the interface
between the denser water layer and the supernatant oil layer. By
achieving this higher, localized concentration of demulsifier in
the region where it is needed, namely, in the emulsion layer
itself, a consequent improvement in separation of the oil and water
phases from the emulsion layer is achieved.
[0014] The demulsifier may be injected directly into the emulsion
layer or onto it with injectors located either in the water layer
or the oil layer, facing in the appropriate direction, i.e. upwards
from the water layer and downwards from the oil layer. When the
demulsifier is injected from either the oil or water layers, it is
preferably injected in the region of the emulsion layer in order to
secure the desired higher concentration of demulsifier in the
emulsion layer. Provision may be made in the desalter vessel for
locating the injection points at multiple locations in the vessel,
spaced either vertically or horizontally from each other or both
vertically and horizontally. In this way, the thickness of the rag
layer may be controlled more readily within predetermined limits so
that operation of the desalter is materially improved.
[0015] The desalting process entails mixing a crude oil with water
and exposing a mixture of oil and water in the form of an
emulsified oil/water mixture to an electric field to cause
separation of the mixture into a denser water layer containing
dissolved salts and a supernatant oil layer with the formation of a
stabilized emulsion layer between the oil layer and the separated
water layer, typically being located above the interface between
the denser water layer and the supernatant oil layer. This layer
often contains emulsion-stabilizing solids which normally inhibit
separation of the oil and water into separate phases. According to
the present invention, demulsifier is added to the water layer or
the oil layer or directly into the stabilized emulsion layer to
destabilize the emulsion so as to promote separation of the oil and
water which can then be removed as separate phases. Optionally,
demulsifier may also be added to the oil/water mixture upstream of
the desalter.
[0016] A petroleum desalter unit according to the invention
comprises a desalter vessel having an inlet for an oil/water
mixture and electrical grids within the vessel for imposing an
electric field on the oil/water mixture in the vessel to cause
separation of the mixture into a denser water layer containing
dissolved salts and a supernatant oil layer with the formation of a
stabilized emulsion layer between the oil layer and the separated
water layer; a water outlet for removing water and an oil outlet
for removing oil are also provided. Demulsifier injectors are
located for injecting demulsifier into the vessel at in the region
of the emulsion layer.
DRAWINGS
[0017] FIG. 1 shows a much simplified schematic of a crude
petroleum desalter unit utilizing the option of direct injection of
the demulsifier into the emulsion layer or into the water
layer.
[0018] FIG. 2 shows a much simplified schematic of a crude
petroleum desalter unit utilizing the option of injection from the
oil layer downwards into the emulsion layer.
[0019] FIG. 3 shows a much simplified schematic of a crude
petroleum desalter unit utilizing the option of injection from the
oil layer at varying angles towards the emulsion layer.
[0020] FIG. 4 shows a much simplified schematic of a crude
petroleum desalter unit utilizing the option of injection downwards
into the water layer using an existing mudwash system.
[0021] FIG. 5 shows a much simplified schematic of a crude
petroleum desalter unit utilizing the option of injection from the
water using radial distributors.
[0022] FIG. 6 shows a much simplified schematic of an injection
gage for injecting demulsifier at multiple locations and
angles.
DETAILED DESCRIPTION
[0023] Desalting is one of the first steps in crude refining. It is
done to remove salts and particulates to reduce corrosion, fouling
and catalyst poisoning. In a typical desalting process, fresh water
(also referred to as wash water) is mixed with oil to produce a
water-in-oil emulsion, which in turn extracts salt, brine and some
particulates from the oil. The salty emulsion is then sent to a
desalter unit where the application of an electric field forces
water droplets to coalesce. Large electrocoalesced water droplets
settle under gravity and penetrate through the
oil/bulk-resolved-water interface to immerse into the resolved bulk
water phase at the bottom of the desalter. The desalted oil and the
resolved bulk water are then removed at the top and the bottom of a
desalter, respectively.
[0024] The wash water used to treat the crude oil may be derived
from various sources and the water itself may be, for example,
recycled refinery water, recirculated wastewater, clarified water,
purified wastewater, sour water stripper bottoms, overhead
condensate, boiler feed water, clarified river water or from other
water sources or combinations of water sources. Salts in water are
measured in parts per thousand by weight (ppt) and typically range
from fresh water (<0.5 ppt), brackish water (0.5-30 ppt), saline
water (30-50 ppt) to brine (over 50 ppt). Although deionized water
may be used to favor exchange of salt from the crude into the
aqueous solution, de-ionized water is not normally required to
desalt crude oil feedstocks although it may be mixed with
recirculated water from the desalter to achieve a specific ionic
content in either the water before emulsification or to achieve a
specific ionic strength in the final emulsified product. Wash water
rates may be between approximately 5% and approximately 7% by
volume of the total crude charge, but may be higher or lower
dependent upon the crude oil source and quality. Frequently, a
variety of water sources are mixed as determined by cost
requirements, supply, salt content of the water, salt content of
the crude, and other factors specific to the desalting conditions
such as the size of the separator and the degree of desalting
required.
[0025] Conventional types of demulsifier commonly used in the
processing of crude oil are useful in the present process although
the process is not reliant on the particular selection of
demulsifier. Among the demulsifiers which may be used are those
typically based on the following chemistries: polyethyleneimines,
polyamines, polyols, ethoxylated alcohol sulfates, long chain
alcohol ethoxylates, long chain alkyl sulfate salts, e.g. sodium
salts of lauryl sulfates, epoxies, di-epoxides (which may be
ethoxylated and/or propoxylated). A useful class of polyamines
comprises the succinated polyamines prepared by the succination of
polyamines/polyamine/imines with a long chain alkyl substituted
maleic anhydride.
[0026] Challenged crudes (i.e. crude with a high amount of
particulates and/or natural emulsifiers) have been shown to produce
a substantial amount of stable emulsion layers (a.k.a. rag layer),
accumulating above the interface between the oil and resolved bulk
water. The existence of a rag layer is mostly due to the inability
of electrocoalesced droplets to break the oil/bulk-resolved-water
interface. The rag layer in the desalter typically contains a high
concentration of oil, residual water, suspended solids and salts
which, in a typical example, might be approximately 70% v/v water,
30% v/v oil, with 5000-8000 pounds per thousand barrels (PTB)
(about 14 to 23 g/l.) solids, and 200-400 PTB (about 570 to 1100
mg/l.) salts. The aqueous phase contains salts from the crude oil.
Crudes with high solids contents present a particularly intractable
problem since the presence of the solids, often with particle sizes
under 5 microns, may act to stabilize the emulsion and the
oil/bulk-resolved-water interface, leading to a progressive
increase in the depth of the rag layer.
[0027] The present invention is especially useful in its
application to challenged crudes containing high levels of solids
and it may also be applied to benefit the desalting of high
asphaltene content crudes which also tend to stabilize the emulsion
layer and the oil/bulk-resolved-water interface in a desalter. The
conventional mitigation strategies carried out by enhancing the
electrocoalescence in the desalter by, for example, the upstream
addition of chemical demulsifiers tend to be less than totally
effective in reducing the stability of the oil/bulk-resolved-water
interface. This is likely due to the inability of the additive to
fully reach the oil/bulk-resolved-water interface at the beginning
of the desalting operation. Thinning of the oil film between
electrocoalesced water droplets and the resolved bulk water phase
is mainly due to the gravitational force. A slow rate of film
thinning reduces the ability of electrocoalesced water droplets to
immerse into the resolved bulk water phase, causing the growth of a
rag layer. The rate of film thinning strongly depends on the
particulates and the chemistry of the oil at that interface and it
may depend on physical parameters different from those of the
electrocoalescence mechanism. The mechanism of emulsion stability
within the electrodes, therefore, may not be the same as that of
the stability of the oil/bulk-resolved-water interface. This in
turn demands the different additive treatment for the
oil/bulk-resolved-water interface which is provided in the present
desalting process.
[0028] To accommodate growth and movement of the emulsion layer in
the vessel, the emulsifier inlet line may be provided with a
manifold with inlet ports at different vertically spaced levels
permitting the emulsifier to be injected into the emulsion at one
or more of the ports as required. The ports may be provided with
manually or, more preferably, automatic, operated valves to control
the injection of the demulsifier. Addition of to demulsifier into
the resolved bulk water phase and/or rag layer can also be combined
with addition of other demulsifiers upstream of the desalter.
[0029] FIG. 1 shows a vertical cross-section of a desalter vessel
in in which injection of the demulsifier takes place at rag layer
level and optionally into the water layer using a straight pipe
design as a header system. The incoming crude oil feed to be
desalted enters by way of line 1 and is mixed with fresh wash water
feed from line 2 in mixing valve 3 to emulsify the water into the
oil before the mixture is introduced into the desalter vessel (5).
Under the high voltage electric field induced by means of electrode
grids (4), the separation of the oil phase (6) and the water phase
(8) takes place with the emulsion phase (rag layer) (7) forming at
the interface between the oil and water phases. Demulsifier is
injected directly into the emulsion layer or the water phase by way
of line (9) with discharge outlets located along the length of the
line to promote the desired distribution into the emulsion or into
the water layer in the region of the emulsion layer. When injected
into the water layer, the injection is preferably effected not more
than 20 cm from the lower level of the emulsion layer and even more
preferably within 10 cm of the lower edge of the emulsion layer in
order to promote the high demulsifier concentration in or at the
emulsion layer. The feed rate to the injector line is controlled by
means of valves (10) and (11). Desalted oil is withdrawn from an
outlet in the upper portion of the vessel and passes to refinery
processing in line 12; salty water (brine) containing salts washed
out of the crude is withdrawn from an outlet at the bottom of the
vessel through line 13 and sent to waste water recovery.
[0030] With this improved control of the emulsion layer position
and thickness, the injection line (9) may be positioned at a
suitable fixed level in the vessel but if different crude feeds
generating emulsion layers of different thicknesses are liable to
be encountered, a plurality of separately valved injection lines
may be located within the vessel with control of demulsifier to the
line at the appropriate level for optimal demulsification.
[0031] FIG. 2 shows a vertical cross-section of a desalter vessel
in which injection of demulsifier takes place into the rag layer
using a downward facing header in the oil phase. A header system
(9) is positioned above the rag layer (7), with nozzles or slots
facing downwards to deliver demulsifier chemical above the
interface from the emulsion/oil phase (6).
[0032] FIG. 3 shows a horizontal cross-section of a desalter vessel
in which injection of demulsifier into desalter using injection
quills varying location, angle, and velocity. Injection quills (9)
positioned around the perimeter of the desalting vessel can be used
to deliver demulsifier chemical into the rag layer (7) or onto it
from above or below from a variety of angles with varying
velocities and flowrates controlled by suitable valving and control
devices. Depending upon the locations of the mixture inlet and the
oil and water outlets, and the general flow direction of the oil,
water and emulsion layers in the vessel, the injectors may be
angled concurrent with relative to the general flow axis so as to
promote flow or to promote mixing by countercurrent injection.
[0033] Combinations of injector configurations may be used, for
example, injection into bother the water and oil layers by use of
an injection line below the emulsion layer and above it in the oil
layer.
[0034] FIG. 4 shows a vertical cross-section of a desalter vessel
in which injection of demulsifier into desalter is effected using
the current mudwash system. The mudwash system (9) which is
important for the removal of solids that accumulate on the bottom
of the desalting vessel. A header, located approximately 18 inches
(46 cm) from the bottom of the vessel and running the length of the
desalter, has a number of downward facing water spray nozzles
designed to disturb solids and prevent accumulation on the vessel
bottom. This system can be used to deliver the demulsifier chemical
to the water phase (8) within the desalting vessel with limited
modification to the existing unit.
[0035] FIG. 5 shows a vertical cross-section of a desalter vessel
in which injection of demulsifier into the rag layer is effected
using a radial distributor design. Radial distributors (8) fed with
demulsifier from manifold (9) can be used to deliver demulsifier
chemical to the rag layer (7) with a minimum vertical component of
velocity. The distributors may simply have a flat plate over the
vertically oriented outlet conduit or have a domed or downturned
cap similar to the "bubble cap" of a distillation column.
[0036] FIG. 6 is an isometric schematic of an injection system in
which demulsifier is injected both above and below the rag layer
using a cage distributor. A cage distributor can be positioned with
the rag layer "inside the cage, allowing for delivery of the
demulsifier chemical from both above and below the rag layer. The
cage injection system itself may have multiple lines extending
above and below the emulsion layer and these may inject demulsifier
into various angles at or into the emulsion layer. Using a
cage-type injector, the demulsifier can be directed upwards,
downwards as well as in any angular direction in or around the
cage.
* * * * *