U.S. patent application number 17/616858 was filed with the patent office on 2022-09-29 for desalter configuration integrated with steam cracker.
The applicant listed for this patent is ExxonMobil Chemical Patents Inc.. Invention is credited to John E. Asplin, Magaly C. Barroeta, Chee-Kong Leong, Asit K. Mondal, Mark A. Nierode.
Application Number | 20220306949 17/616858 |
Document ID | / |
Family ID | 1000006448655 |
Filed Date | 2022-09-29 |
United States Patent
Application |
20220306949 |
Kind Code |
A1 |
Nierode; Mark A. ; et
al. |
September 29, 2022 |
Desalter Configuration Integrated with Steam Cracker
Abstract
The present disclosure provides for processes for producing
light hydrocarbons. In an embodiment, a process includes
pressurizing the hydrocarbon feed in one or more pumps producing a
pressurized hydrocarbon feed and heating the pressurized
hydrocarbon feed in one or more heat exchangers to produce a heated
hydrocarbon feed. The process includes mixing the heated
hydrocarbon feed with water and separating an inter-stage
hydrocarbon feed from interstage water. The process includes mixing
the inter-stage hydrocarbon feed with water and separating a
desalted hydrocarbon feed from outlet water. The process includes
pyrolysing the desalted hydrocarbon feed in a steam cracker.
Inventors: |
Nierode; Mark A.; (Kingwood,
TX) ; Barroeta; Magaly C.; (Tomball, TX) ;
Leong; Chee-Kong; (Singapore, SG) ; Asplin; John
E.; (Khlong-Hok, TH) ; Mondal; Asit K.; (Yanbu
Al Bahar, SA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ExxonMobil Chemical Patents Inc. |
Baytown |
TX |
US |
|
|
Family ID: |
1000006448655 |
Appl. No.: |
17/616858 |
Filed: |
June 17, 2020 |
PCT Filed: |
June 17, 2020 |
PCT NO: |
PCT/US2020/038102 |
371 Date: |
December 6, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62865732 |
Jun 24, 2019 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10G 2300/4081 20130101;
C10G 55/04 20130101; C10G 2300/201 20130101 |
International
Class: |
C10G 55/04 20060101
C10G055/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 31, 2019 |
EP |
19206399.8 |
Claims
1. A desalting process, the process comprising: providing a
hydrocarbon feed comprising heavy hydrocarbon; pressurizing the
hydrocarbon feed to produce a pressurized hydrocarbon feed; heating
the pressurized hydrocarbon feed in one or more heat exchangers
producing a heated hydrocarbon feed; mixing the heated hydrocarbon
feed with water and separating an inter-stage hydrocarbon feed from
inter-stage water; mixing the inter-stage hydrocarbon feed with
water and separating a desalted hydrocarbon feed from outlet water;
dividing the desalted hydrocarbon stream into at least first and
second portions, at least one hydrocarbon-recycle stream away from
the desalted hydrocarbon feed; pyrolysing at least part of the
first portion of the desalted hydrocarbon feed in a steam cracker;
and combining at least part of the second portion of the desalted
hydrocarbon feed with at least a portion of the hydrocarbon
feed.
2. The process of claim 1, wherein the pressurization includes
pressurizing the hydrocarbon feed in at least one pump to a
pressure of from about 101 kPa (abs) to about 2000 kPa (abs).
3. The process of claim 1, wherein heating comprises heating the
pressurized hydrocarbon feed to a temperature from about
100.degree. C. to about 150.degree. C.
4. The process of claim 1, further comprising storing at least a
portion of the desalted hydrocarbon feed in a surge drum.
5. The process of claim 1, wherein 1 wt. % to 50 wt. % of the
desalted hydrocarbon feed resides in the second portion, and
wherein the second portion is combined with the hydrocarbon feed in
at least one storage tank.
6. The process of claim 1, wherein the pyrolysis is performed at a
temperature from about 760.degree. C. to about 1100.degree. C., and
wherein the first portion contains .ltoreq.4 wppm of salt.
7. The process of claim 1, further comprising a pyrolysis pressure
from about 60 kPa (gauge) to about 500 kPa (gauge).
8. An apparatus for removing contaminants from a hydrocarbon feed
containing heavy hydrocarbons, the apparatus comprising: a first
desalter; a second desalter in fluid connection with the first
desalter; a steam cracker in fluid connection with the second
desalter, a storage tank in fluid connection with the first
desalter, and a hydrocarbon recycle line in fluid connection with
the second desalter and the storage tank.
9. The apparatus of claim 8, further comprising, a vapor-liquid
separator fluidically and thermally integrated with the steam
cracker, and wherein the first and/or second desalters utilize
water injection for the desalting.
10. The apparatus of claim 8, further comprising a surge drum in
fluid connection with the second desalter and the steam
cracker.
11. The apparatus of claim 9, further comprising a third desalter
situated between the second desalter and the steam cracker and in
fluidic communication with the second desalter and the steam
cracker.
12. The apparatus of claim 8, further comprising a recycle line in
fluid connection with the steam cracker and the first desalter.
13. The apparatus claim 12, further comprising a recycle line in
fluid connection with the steam cracker and the storage tank.
14. The apparatus of claim 11, further comprising a recycle line in
fluid connection with the steam cracker and the hydrocarbon recycle
line.
15. An apparatus for removing contaminants from a hydrocarbon feed
containing heavy hydrocarbons, the apparatus comprising: a desalter
having an established electric field; a storage tank in fluid
connection with the desalter; a hydrocarbon recycle line in fluid
connection with the desalter and the storage tank; and a steam
cracker in fluid connection with the desalter.
16. The apparatus of claim 15, further comprising a surge drum in
fluid connection with the desalter and the steam cracker.
17. The apparatus of claim 15, further comprising a recycle line in
fluid connection with the steam cracker and the storage tank.
18. The apparatus of claim 15, further comprising a recycle line in
fluid connection with the steam cracker and the desalter.
19. The apparatus of claim 15, further comprising a recycle line in
fluid connection with the steam cracker and the hydrocarbon recycle
line.
20.-26. (canceled)
27. A process for producing light hydrocarbons from a hydrocarbon
feed containing heavy hydrocarbons, the process comprising:
pressurizing the hydrocarbon feed to produce a pressurized
hydrocarbon feed; heating the pressurized hydrocarbon feed in one
or more heat exchangers producing a heated hydrocarbon feed; mixing
the heated hydrocarbon feed with water to produce an emulsion,
separating from the emulsion at least a desalted hydrocarbon feed;
storing at least a portion of the desalted hydrocarbon feed in one
or more surge drums, and pyrolysing in at least one steam cracking
furnace at least a portion of the desalted hydrocarbon feed and/or
at least a portion of the stored desalted hydrocarbon feed.
28. (canceled)
Description
PRIORITY
[0001] This application claims priority to and the benefit of U.S.
Provisional Application No. 62/865,732, filed Jun. 24, 2019, and
European Patent Application No. 19206399.8 which was filed Oct. 31,
2019, the disclosures of which are incorporated herein by reference
in their entireties.
FIELD
[0002] The present disclosure relates to processes for upgrading
hydrocarbons by removing salts; to apparatus, systems, and
equipment useful for such upgrading; to the use of such upgraded
hydrocarbons as feed for steam cracking, to the steam cracking of
such feeds, and to the products of such steam cracking
BACKGROUND
[0003] Historically steam cracker feedstocks to produce olefins
have come from refinery process streams and the refining process
has removed many of the contaminants that were present in the
feedstocks making them more compatible for steam cracking in a
steam cracker furnace. However, growth in the demand for olefins
has exceeded the growth in demand for refined fuels. Therefore, it
has become increasingly desirable to utilize raw feedstocks (e.g.
various crudes) as feed to steam crackers to produce olefins. The
use of crude oil in steam cracking would remove dependency on the
limited supply and relatively high costs of the various refinery
fuel cuts.
[0004] Salts, metals, particulates and asphaltenes are contaminants
found in or produced from the raw resin containing feeds such as
crude should be managed in order to meet the stringent product
specifications and operating requirements in a steam cracker.
Processing hydrocarbons, e.g., crude oil or other raw feedstocks,
with contaminants in a steam cracker involves management of: (i)
furnace coking resulting from salts, metal, particulates and
asphaltenes; (ii) corrosion associated with salts; (iii) product
specification for by-product streams; and (iv) operational
management due to the contaminants or their by-products in the
steam cracker processing unit.
[0005] Although acceptable limits on salts and/or particulate
matter concentrations in a steam cracker feed comprising
hydrocarbons ("hydrocarbon feed") can vary with steam cracker
furnace design and operating conditions, the salt removal may be
desired when salt content (e.g., sodium chloride content) exceeds a
fraction of a ppm or few ppm by weight ("wppm") of the hydrocarbon
feed. Desalting removes salts and particulates to reduce corrosion,
erosion, fouling and catalyst poisoning. In certain conventional
desalting processes, water is mixed with a hydrocarbon feed and
subsequent separation of the oil and water phases, e.g., in one or
more desalters. The separation of the phases may be improved at
elevated temperatures where the viscosity of the crude oil is
lessened. In order to avoid vaporization of the crude oil and/or
water at the higher temperature, a desalter may also run at an
elevated pressure. One conventional process for hydrocarbon feed
desalting is disclosed in U.S. Pat. No. 5,271,841. According to
that process two desalters are operated in series, with the first
desalter operated at a lesser temperature than the second deslater.
A more recent conventional process for steam cracking hydrocarbon
feeds containing salt is disclosed in U.S. Patent Application
Publication No. 2006/0094918. According to that process, a
hydrocarbon feed is heated in a convection section of a steam
cracking furnace. Vapor and liquid streams are separated from the
heated feed, with at least a portion of the salt contained the
hydrocarbon feed being conducted away with the separated liquid
phase. The separated vapor phase, which has a lesser salt content
than the hydrocarbon feed, is steam cracked in a radiant section of
the steam cracker. Sill more recently, U.S. Patent Application
Publication No. 2007/0004952 discloses desalting hydrocarbon feed
in a first desalter, heating the hydrocarbon feed in a convection
section of a steam cracking furnace, and then carrying out a second
desalting on the heated hydrocarbon feed. A vapor-liquid separator
is then used to separate a vapor-phase stream (lean in salt) and a
liquid-phase steam (rich in salt) from the desalted feed. The
vapor-phase stream in steam cracked in a radiant section of the
steam cracking furnace. Now, however, even more stringent
limitations on hydrocarbon feed salt content are needed to achieve
desired steam cracking product quality and run length goals. See,
e.g., Sundaram, K. M. et al. in (32D) How Much Is Too Much?--Feed
Contaminants and Their Consequences AIChE 2018 Spring Meeting and
Global Congress on Process Safety Apr. 23, 2018, Orlando, Fla. for
a discussion of limitations on feed contaminants.
[0006] Crude tanks (typically external floating-roof tanks) being
large (e.g. 500,000 bbl) are not generally designed to store crude
above ambient pressure or temperature. Therefore, before entering a
desalter, the hydrocarbon feed may be pressurized with one or more
pumps and pre-heated through one or more heat exchangers. The
desalted hydrocarbon feed can be conducted to a steam cracking
furnace, where a steam cracking process can be carried out to
produce products such as light olefin.
[0007] Steam cracker furnaces are sensitive to disruption in feed
because they are typically supply fired duty at elevated
temperatures for an endothermic reaction (as opposed to simple
distillation in a CDU/pipe still), meaning that loss of hydrocarbon
feed includes a loss of an endothermic heat sink which can lead to
a heat imbalance exceeding the design temperatures of the furnace.
The sensitivity to feed disruption means that reliable desalter
performance (e.g. controls, interface, removal-efficiency, etc.)
may ensure hydrocarbon feed reaches the steam cracking furnace at
uninterrupted acceptable rates. Therefore, for steam crackers, the
level of contaminants and reliable feed flow should each be
managed, even during fast rate changes as furnaces are brought
online or offline. A reliable flow of hydrocarbon feed to the
furnace prevents wear on furnace parts due to heat imbalances and
thermal stress reducing or eliminating the frequency of plant
shutdowns for furnace repair and refurbishment. Robust contaminant
management (e.g. removal-efficiency of various salts) may allow for
flexibility in hydrocarbon feed flow especially during start-up and
shutdown of individual steam crackers, including during normal
decoking procedures.
[0008] There is a need for improved processes to remove
contaminants from unrefined steam cracker feedstocks despite
anticipated and/or unexpected increases or decreases in flow to the
steam cracker(s) (due to regular furnace decoke cycles) in order to
produce high value light olefins.
SUMMARY
[0009] This disclosure provides processes for producing light
hydrocarbons, including high value light olefin, from a hydrocarbon
feed containing heavy hydrocarbons, where there may be fluctuations
in the feed flow rate.
[0010] In at least one embodiment, a process includes pressurizing
the hydrocarbon feed in one or more pumps to produce a pressurized
hydrocarbon feed. The process includes heating the pressurized
hydrocarbon feed in one or more heat exchangers to produce a heated
hydrocarbon feed. The process also includes mixing the heated
hydrocarbon feed with the water, and separating an inter-stage
hydrocarbon feed from inter-stage water. The process further
includes mixing the inter-stage hydrocarbon feed with water and
separating a desalted hydrocarbon feed from outlet water. An
upgraded hydrocarbon feed which comprises, consists essentially of,
or even consists of the desalted hydrocarbon feed can be pyrolysed
(e.g., in one or more steam cracking furnaces) more efficiently
than can conventional hydrocarbon feeds.
[0011] In certain other aspects, this disclosure also provides
apparatus, systems, and equipment useful for producing the upgraded
hydrocarbon feed, for steam cracking the upgraded hydrocarbon feeds
to produce products such as light hydrocarbon including light
olefin.
[0012] In at least one embodiment, an apparatus includes a storage
tank in fluid connection with a first desalter, the first desalter
in fluid connection with at least a second desalter, the second
desalter being in fluid connection with a hydrocarbon recycle line,
a surge drum, and/or a steam cracker. The hydrocarbon recycle line
is in fluid connection with the storage tank. The surge drum is in
fluid connection with the steam cracker. The steam cracker is in
fluid connection with one or more recycle lines. The one or more
recycle lines are in fluid connection with the first desalter.
BRIEF DESCRIPTION OF THE DRAWING
[0013] So that the manner in which the above recited features of
the disclosure can be understood in detail, a more particular
description of the disclosure, briefly summarized above, may be had
by reference to implementations, some of which are illustrated in
the appended drawings. It is to be noted, however, that the
appended drawings illustrate only typical implementations of this
disclosure and are therefore not to be considered limiting of
scope, for the disclosure may admit to other equally effective
implementations.
[0014] FIG. 1 is a flow diagram of an embodiment of an apparatus
for removal of contaminants in a hydrocarbon feed while maintaining
flow to one or more downstream steam cracking furnaces, as
described in one or more embodiments.
[0015] FIG. 2 is a graph illustrating salt and water content after
a rate change of hydrocarbon feed to a first desalter and a second
desalter, as described in one or more embodiments.
DETAILED DESCRIPTION
[0016] Certain aspects of the invention will now be described in
more detail, which aspects relate to processes for producing an
upgraded hydrocarbon feed. These aspects include (i) removing
contaminants from a heavy hydrocarbon feed to produce an upgraded
feed for a steam cracking process to produce light olefins, and
(ii) managing fluctuations in the flow of the hydrocarbon feed. The
invention is not limited to these aspects, and this description
should not be interpreted as excluding other aspects within the
broader scope of the invention, such as those which utilize other
forms of hydrocarbon feed and/or other forms of pyrolysis.
[0017] At least part of the contaminant-removal can be carried out
in one or more desalters, in which clean water is vigorously mixed
with a hydrocarbon feed such as crude oil entering the bottom of
the desalter. When used in this sense, the term "clean water" means
water with relatively low salt content, e.g. one or more of
high-purity, clarified fresh, deionized, and/reverse osmosis water.
The water has the form of small water droplets, these typically
being in a size range selected to facilitate mass transfer. The
water and crude oil are combined to facilitate a transfer of
soluble contaminants such as various salts (e.g. NaCl) from the
crude oil to these small water droplets. Since the water has a
greater density than does the crude oil, the water tends to settle
towards a lower region (e.g., bottom) of the desalter vessel. An at
least partially-desalted crude oil of lesser density accumulates in
an upper region of the desalter vessel, by virtue of its lesser
density. Since the settling of the water proceeds relatively
slowly, particularly when the droplets are small, an emulsion layer
is observed to form between the water and the at least
partially-desalted crude oil. As such, a water layer forms in the
bottom of each vessel/stage, a crude layer at the top, and an
emulsion layer in between. An oleaginous phase comprising the at
least partially-desalted (e.g., "clean") crude oil is taken off the
top of the vessel. An aqueous phase comprising the contaminated
water (e.g., a salt-laden water known to those skilled in the art
as brine) is removed from the bottom of the desalter vessel.
[0018] Elevating temperature has been found to increase desalting
efficiency, it is believed by decreasing the density and viscosity
of the water and crude oil. This in turn aids both the initial
formation of small droplets, and the subsequent separation of the
aqueous (bottom) phase and the oleaginous (top) phase. Elevated
pressure can be used to lessen or substantially avoid vaporizing
the crude oil and/or water at the higher temperature.
[0019] Maintaining hydrocarbon feed flow rate and quality to steam
cracker furnaces during conventional desalting may increase the
cost of recycling and/or storage. Moreover, elevated temperatures
in a floating roof tank might imbalance the floating roof, e.g., as
a result of vapor pockets or increased fugitive emissions from tank
seals. This in turn may lead to a need to cool and/or depressurize
the desalted hydrocarbon feed prior to either recycling to the feed
tank or to another tank in between the desalter and steam cracker
furnace.
[0020] It has been discovered that these obstacles can be at least
partially overcome by utilizing the specified combination of one or
more desalters, recycle lines, spare pumps, and/or surge drums.
Doing so has be found to accommodate unexpected or anticipated feed
flow fluctuations to the steam cracking furnace (e.g., as may occur
when one or more of the steam cracking furnaces in the facility are
switched from pyrolysis mode to decoking mode or vice versa)
without an appreciable decrease in contaminant-removal efficiency
in comparison with conventional desalting processes, as would be
detrimental to the performance of a steam cracker furnace.
Definitions
[0021] The term "C.sub.n" hydrocarbon means hydrocarbon having n
carbon atom(s) per molecule, where n is a positive integer. The
term "C.sub.n+" hydrocarbon means hydrocarbon having at least n
carbon atom(s) per molecule, where n is a positive integer. The
term "C.sub.n-" hydrocarbon means hydrocarbon having no more than n
number of carbon atom(s) per molecule, where n is a positive
integer. The term "hydrocarbon" means a class of compounds
containing hydrogen bound to carbon, and encompasses (i) saturated
hydrocarbon, (ii) unsaturated hydrocarbon, and (iii) mixtures of
hydrocarbons, including mixtures of hydrocarbon compounds
(saturated and/or unsaturated), including mixtures of hydrocarbon
compounds having different values of n. A mixture of C.sub.n and
C.sub.m hydrocarbon, where m and n are integers and n<m, means a
mixture containing at least C.sub.n and C.sub.m hydrocarbon and
optionally one or more hydrocarbon compounds having a number of
carbon atoms greater than n but less than m.
[0022] The term "unsaturate" or "unsaturated hydrocarbon" mean a
C.sub.2+ hydrocarbon containing at least one carbon atom directly
bound to another carbon atom by a double or triple bond. The term
"olefin" means an unsaturated hydrocarbon containing at least one
carbon atom directly bound to another carbon atom by a double bond.
An olefin is a compound which contains at least one pair of carbon
atoms, where the carbon atoms of the pair are directly linked by a
double bond.
[0023] The term "non-volatile components" means the fraction of a
hydrocarbon stream with a nominal boiling point above 590.degree.
C. or greater, as measured by ASTM D-6352-98 or D-2887.
Non-volatile components may be further limited to components with a
boiling point of about 760.degree. C. or greater. The boiling point
distribution of a hydrocarbon stream may be measured by gas
chromatograph distillation according to the methods described in
ASTM D-6352-98 or D2887, extended by extrapolation for materials
above 700.degree. C. Non-volatile components may include coke
precursors, which are moderately heavy and/or reactive molecules,
such as multi-ring aromatic compounds, which can condense from the
vapor phase and then from coke under the operating conditions
encountered in a process of the present disclosure.
[0024] The term "steam cracker" and "steam cracker furnace" are
interchangeable with "thermal pyrolysis unit", "pyrolysis furnace",
or just "furnace." Steam, although optional, may be added for a
variety of reasons, such as to reduce hydrocarbon partial pressure,
to control residence time, and/or to decrease coke formation. In at
least one embodiment, the steam may be superheated, such as in the
convection section of the furnace, and/or the steam may be sour or
treated process steam.
[0025] The addition of steam at various points in the process is
not detailed in every embodiment described. It is further noted
that the steam added may include sour or treated process steam and
that the steam added, whether sour or not, may be superheated.
Superheating is common when the steam comes from sour water.
Hydrocarbon Feed
[0026] The hydrocarbon feed may include relatively high molecular
weight hydrocarbons (heavy hydrocarbon), such as those which
produce a relatively large amount of steam cracker naphtha (SCN),
steam cracker gas oil (SCGO), and steam cracker tar during steam
cracking. The heavy hydrocarbon typically includes C5+ hydrocarbon,
which may include one or more of residues, gas oils, heating oil,
jet fuel, diesel, kerosene, coker naphtha, hydrocrackate,
reformate, raffinate reformate, distillate, crude oil, atmospheric
pipestill bottoms, vacuum pipestill streams including bottoms,
condensates, heavy non-virgin hydrocarbon streams from refineries,
vacuum gas oils, heavy gas oil, naphtha contaminated with crude,
atmospheric residue, heavy residue, C4/residue admixture, naphtha
residue admixture, gas oil residue admixture, low sulfur waxy
residue, atmospheric residue, lubes extract steams, and heavy
residue. It may be advantageous to use a heavy hydrocarbon
feedstock including economically advantaged, minimally processed
heavy hydrocarbon streams containing non-volatile components and
coke precursors. The hydrocarbon feed can have a nominal final
boiling point of about 315.degree. C. or greater, such as about
400.degree. C. or greater, about 450.degree. C. or greater, or
about 500.degree. C. or greater.
[0027] Certain aspects of the invention will now be described which
related to feeds comprising heavy hydrocarbon, e.g., one or more
crude oils, crude oil fractions, or other resid-containing streams.
The invention is not limited to these feeds, and this description
is not meant to foreclose other feeds within the broader scope of
the invention, such as feeds containing one or more relatively low
molecular weight hydrocarbon (light hydrocarbon), such as C.sub.5-
hydrocarbon. The use of such heavy hydrocarbon is of increasing
interest due to lower costs and higher availability. The
hydrocarbon feed can include about 10 wt. % or more of heavy
hydrocarbon, based on the weight of the hydrocarbon feed, such as
about 25 wt. % or more, about 50 wt. % or more, about 75 wt. % or
more, about 90 wt. % or more, or about 99 wt. % or more.
Desalters (First Desalter and Optional Second Desalter)
[0028] Because of the desirably low concentration of sodium in the
radiant section of steam crackers, one or more desalters may be
included to remove salts and particulate matter from the
hydrocarbon feed prior to steam cracking. Certain forms of desalter
will now be described in more detail. The invention is not limited
to these, and this description should not be interpreted as
excluding other desalter forms within the broader scope of the
invention.
[0029] The desalting can be carried out in one or more conventional
desalter vessels such as a plurality of vessels in semi-continuous
operation, such as with one drum in use and the other under
maintenance, but the invention is not limited thereto. The vessels
and related equipment in the apparatus and system can be configured
in series, parallel, and/or series parallel. Optionally, at least
one of the vessels can include a mud-wash functionality and/or a
tri-line sampling functionality, and can further include auxiliary
equipment such as one or more brine tanks. While acceptable salt
and/or particulate matter concentration vary with furnace design,
the addition of a desalter may be advantageous when sodium chloride
is greater than a predetermined amount (in wppm) of the hydrocarbon
feed, and can further depend on the operating conditions of a
particular feed. Typically, desalting is carried out when the
hydrocarbon feed comprises salt in an amount .gtoreq.0.5 wppm,
e.g., .gtoreq.1 wppm, such as .gtoreq.2 wppm, or .gtoreq.3 wppm, or
.gtoreq.4 wppm, or in a range of from 1 wppm to 100 wppm.
[0030] As disclosed in U.S. Patent Application Publication No.
2006-0094918 (incorporated by reference herein), a partial
desalting of a hydrocarbon feed can be achieved using a
vapor-liquid separator that is fluidically and thermally integrated
with the steam cracking furnace's convection section. U.S. Patent
Application Publication No. 2007-0004952 (also incorporated by
reference herein) improves upon this by using a pair of cyclonic
separators operating in tandem. A partially desalted hydrocarbon
feed is conducted away from the cyclonic separators to the
vapor-liquid separator for additional desalting before cracking the
hydrocarbon feed in the steam cracking furnace's radiant section.
In aspects of the invention which utilize such a vapor-liquid
separator, the hydrocarbon feed can have an even greater salt
content, e.g., .gtoreq.100 wppm, such as .gtoreq.500 wppm, or
.gtoreq.1000 wppm, or .gtoreq.5000 wppm, or .gtoreq.10,000 wppm or
in a range of from 100 wppm to 50,000 wppm, or 200 wppm to 10,000
wppm. In these aspects, the first and second desalters (e.g., the
first and second desalters as shown in FIG. 1) produce a desalted
hydrocarbon feed having a salt content .ltoreq.1 wppm, e.g.,
.ltoreq.0.5 wppm, with the vapor separated from the vapor-liquid
separator having a salt content .ltoreq.0.125 wppm, such as
.ltoreq.0.0625 wppm.
[0031] Typically, wash water (or fresh water, or deionized water)
is mixed with a heated hydrocarbon feed to produce a water-in-oil
emulsion, which in turn extracts salt, brine and particulates from
the oil. The wash water used to treat the hydrocarbon feed may be
derived from various sources. For example, the water may be
recycled and/or recirculated water from other units in the
facility, e.g., sour water stripper bottoms, overhead condensate,
boiler feed water, with and/or without clarification, purification,
etc. Alternately, or in addition, water may be obtained from other
sources, e.g., from surface water sources such as from a river,
and/or or from geological water sources, such as from one or more
wells. The concentration of various salts in water can be expressed
in parts per thousand by weight (ppt), and typically salt
concentration is in the range of from that of fresh water (less
than 0.5 ppt of sodium chloride), brackish water (0.5-30 ppt of
sodium chloride), or saline water (30-50 ppt of sodium chloride) to
that of brine (more than 50 ppt of sodium chloride). 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. In certain aspects,
however, deionized water 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 are typically in
a range of from about 5% to about 7% by volume of the total crude
oil to be desalted, but may be higher or lower dependent upon the
crude oil source and quality. A variety of water sources may be
combined as determined by cost requirements, supply, salt content
of the water, salt content of the hydrocarbon feed, and other
factors specific to the desalting conditions such as the size of
the separator and the degree of desalting required.
[0032] During the separation phase of a desalting process, an
emulsion phase of varying composition and thickness may form at the
interface of the oil and aqueous layers. If unresolved, these
emulsions may carry-over with the desalted crude oil or carry-under
into the aqueous layer. If carried-over, the emulsions may lead to
coking or fouling of downstream equipment and disruption of the
downstream fractionation process. If carried-under, they can
disrupt the downstream water treatment process. Consequently,
refiners typically desire to either control the formation/growth of
these emulsions or remove the emulsions from desalter units and,
using an additional processing step, to resolve the emulsion into
its constituent parts (i.e., to break the emulsion, resulting in
separate oil, water and solid phases) to allow for reuse and/or
disposal of the oil, water, and solids.
[0033] Methods for separating the oil and water phases may include
gravitational or centrifugal methods. In a gravity method, the
emulsion is allowed to stand in the separator and the density
difference between the oil and the water causes the water to settle
through and out of the oil by gravity. In the centrifugation
method, the stable emulsion is moved from the desalter unit to a
centrifuge (not shown) which separates the emulsion into separate
water, oil and solids. The gravity method generally requires the
use of time-intensive, and thus inefficient, settling tanks as well
as costly methods for disposing of the partially resolved emulsion,
while the centrifugation method may require large centrifuges that
are costly to build and operate.
[0034] Typically, an electric field is established in a region
within the desalter to enhance water droplet coalescence. This in
turn breaks the emulsion to form an oleaginous continuous phase and
an aqueous continuous phase. Even when a relatively strong electric
field is established in the desalter, an emulsion layer (called a
"rag layer") may form, typically below the region in which the
electric field is established. This emulsion layer is observed to
be stable, even when adjacent to the strong electric field. The
strength of this emulsion layer (sometimes called a "persistent
emulsion", indicating its resistance to emulsion-breaking)
typically depends on factors such as feed hydrocarbon gravity
(e.g., the gravity of crude oil in the hydrocarbon feed), the
presence and amount of solids and semi-solids, such as particles,
etc.). Such a rag layer typically contains a high concentration of
oil, residual water, suspended solids and salts which, in a typical
example, might be about 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 transferred from the hydrocarbon feed. Conventional
methods for managing the rag layer can be used, but the invention
is not limited thereto. For example, introducing into the desalter
one or more de-emulsifier compositions and/or separating and
conducting away at least a portion of the emulsion.
[0035] Certain hydrocarbon feed contaminants have been identified
as being especially effective in establishing a persistent emulsion
layer. In hydrocarbon feeds comprising crude oil and/or
compositions derived from crude oil, such contaminants include
natural surfactants (asphaltenes and resins) and finely divided
solid particles. Since a persistent emulsion is typically observed
when desalting a hydrocarbon feed comprising crude oil, hydrocarbon
feeds having a high solids contents are typically not preferred.
While not wishing to be bound by any theory or model, it is
believed that the presence of such solids, often with particle
sizes under 5 microns, stabilizes the rag layer and the
oil/bulk-resolved-water interface, leading to a progressive
increase in the depth of the rag layer.
[0036] The invention is compatible with the use of de-emulsifiers
("demulsifiers") to decrease rag layer size (e.g., height, when the
plane of the rag layer is substantially parallel to the surface of
the earth) and persistence. Conventional demulsifiers, such as
those described in US. Patent Publication 2016/0208176
(incorporated by reference herein) can be used, but the invention
is not limited thereto. Suitable demulsifiers may be one or more
of: polyethyleneimines, polyamines, succinated polyamines, polyols,
ethoxylated alcohol sulfates, long chain alcohol ethoxylates,
long-chain alkyl sulfate salts, e.g. sodium salts of lauryl
sulfates, epoxies, and di-epoxides (which may be ethoxylated and/or
propoxylated). The addition of demulsifiers may be useful in the
desalting of hydrocarbon feeds containing high levels of
particulates or asphaltenes, which tend to stabilize the rag
layer.
[0037] FIG. 1 is a flow diagram an apparatus 100 for removal of
contaminants in a hydrocarbon feed while maintaining flow to one or
more downstream steam crackers. As shown in FIG. 1, the hydrocarbon
feed may be transferred from storage tank 101 through line 103 to
pump 105. Pump 105 may be supplemented by hydrocarbon transferred
from storage tank 101 through line 104 to spare auto-starting pump
106 in order to allow for consistent pressure and flow in the
system. The pressure and flow rate of the hydrocarbon feed is
determined by the salt content of the hydrocarbon feed and the size
and number of desalters and furnaces, but the pressure should be
sufficiently high as to avoid vaporization of the water and
hydrocarbon at the temperatures used in the desalting process. The
pressurized hydrocarbon feed is pumped through line 107 to heat
exchanger 109 to provide a heated hydrocarbon feed. Where a
stand-by auto-starting pump 106 is used, pressurized hydrocarbon
feed may flow through line 108 to join line 107 or flow directly to
heat exchanger 109. The heated hydrocarbon feed of line 111
(downstream of heat exchanger 109) may undergo further heating. The
additional heating can be carried out in one or more additional
heat exchangers (not shown), which can be located before and/or
after heat exchanger 109. The additional transfer of heat results
in an increased temperature of the heated hydrocarbon feed beyond
what can be achieved by heat exchanger 109 alone. Doing so
decreases the viscosity of the feed, and promote mixing with water,
as described below. Suitable heat transfer fluids for the
additional heat exchangers include, e.g., (i) steam such as low
pressure, medium pressure, high pressure, or super high pressure
steam (generally the lowest pressure steam that is effective for
carrying out the heat transfer is used, typically medium pressure
steam (15 bar-30 bar) or low pressure steam (<15 bar) steam is
sufficient), (ii) an oleaginous heat transfer fluid from
purification system 151, e.g., a bottoms pump around oil from a
primary fractionator, and (iii) an aqueous quench fluid, e.g., one
obtained from a quench tower included in purification system 151.
For example, in certain aspects heat exchanger 109 is located
upstream of a first additional heat exchanger utilizing low
pressure steam as a heat transfer fluid. The first additional heat
exchanger is located upstream of a second additional heat exchanger
utilizing a primary fractionator bottoms pump around oil as a heat
transfer fluid. Optionally, in these aspects, an emulsion recovered
(not shown in the figure) from purification system 151 is
introduced into the hydrocarbon feed or heated hydrocarbon feed at
a location upstream of heat exchanger 109 via line 167. The heated
hydrocarbon feed may be at a temperature of about 30.degree. C. or
greater, e.g., about 100.degree. C. or greater, such as about
120.degree. C. or greater, about 140.degree. C. or greater, or
about 150.degree. C. or greater. For example, the heated
hydrocarbon feed may have a temperatures of from about 100.degree.
C. to about 200.degree. C., from about 120.degree. C. to about
180.degree. C., from about 140.degree. C. to about 180.degree. C.,
or from about 150.degree. C. to about 200.degree. C.
[0038] The heated hydrocarbon feed passes through line 111 where it
is mixed with water from fresh water line 113 to form an emulsion.
The emulsion formed from the combination of fresh water in line 113
and heated hydrocarbon feed in line 111 may be passed through valve
115 and line 117 to first desalter 119 for optional additional
mixing followed by separation. In first desalter 119 the
hydrocarbon and salt water are separated producing (i) an aqueous
by-product (brine) sent away via line 121, and (ii) inter-stage
hydrocarbon feed removed from first desalter 119 via line 123. The
desalted oleaginous phase forms a top layer which is continuously
removed as inter-stage hydrocarbon feed via line 123 and the
resolved aqueous phase accumulates in the bottom of the desalter
and is continuously removed as a brine stream via line 121. The
brine stream may be sent for deionization and recycling or used
with or without further processing in other processes. In some
embodiments, a single desalter provides sufficient contaminant
removal that no additional desalting is necessary. The use of a
single desalter (with a recycle line to the desalter inlet and/or a
surge drum) may be sufficient if fluctuations in flow rate, such as
those caused by steam crackers being brought online or offline, are
managed to allow steady flow of the hydrocarbon feed through the
desalter.
[0039] One method of managing flow rate to steam crackers without
sacrificing removal of contaminants is to add an additional
desalter in series with the first desalter. In some embodiments,
the addition of a second desalter allows for sufficient removal of
contaminants even through rapid flow rate fluctuations. The
(optional) addition of a second desalter is shown in FIG. 1, where
the inter-stage hydrocarbon feed is passed through line 123 and
mixed with water from clean water line 125. The emulsion formed
from the combination of the inter-stage hydrocarbon feed and the
water is passed through valve 127 and line 129 into second desalter
131. In second desalter 131 the hydrocarbon and water are separated
producing (i) a clean water product stream sent away via line 133,
and (ii) desalted hydrocarbon feed removed at the hydrocarbon
outlet (not shown) from second desalter 131 via line 135. Line 135
is coupled with heat exchanger 109 to allow heat exchange between
the desalted hydrocarbon feed and the pressurized hydrocarbon feed.
The desalted hydrocarbon feed (after heat exchange) transferred via
line 136 is lower in temperature than the desalted hydrocarbon feed
in line 135, e.g., to meet furnace requirements that depend on
specific furnace design. The clean water product stream from the
second desalter may contain a sufficiently low sodium content (e.g.
about 10 wppm or less) and may be recycled via line 133 to line 113
for reuse in first desalter 119. Alternatively, the clean water
product may be used with or without further processing in other
processes at the facility (line not shown).
[0040] Typically the desalted hydrocarbon feed comprises .ltoreq.1
wppm of salt, e.g., .ltoreq.0.5 wppm, such as .ltoreq.0.25 wppm, or
.ltoreq.0.125 wppm, or .ltoreq.0.0625 wppm, or in a range of from
0.01 wppm to 0.125 wppm.
Surge Drum
[0041] The invention is compatible with the use of one or more
surge drums as an aid in providing a substantially-uninterrupted
flow rate of desalted hydrocarbon feed to steam cracker furnaces.
The surge drum can be filled with desalted hydrocarbon feed during
use. The desalted hydrocarbon feed in the filled surge drum could
be transferred into a steam cracker furnace's feed line. Doing so
can provide a short-term flow of desalted hydrocarbon feed during a
decrease in flow, as might occur when a pump fails or must be taken
offline for servicing while spare pumps are being started. The
volume of desalted hydrocarbon feed in the surge drum could be
transferred into the feed line at a similar pressure in a variety
of ways, e.g. using N.sub.2 as a motive force, along with automatic
valving. In certain aspects, e.g., where such a surge drum is not
used and/or where the surge drum's inventory of desalted
hydrocarbon feed is depleted, one or more of the desalters can be
by-passed to maintain a sufficient flow of feed to the stream
cracker furnaces.
[0042] The addition of a surge drum is shown in FIG. 1 where
desalted hydrocarbon feed in line 136 may be diverted through line
137 and valve 139 to surge drum 141 in order to fill the drum with
desalted hydrocarbon feed for use in the case of a loss in pressure
or of flow rate. If a drop in pressure or flow rate were to occur,
the desalted hydrocarbon feed stored in surge drum 141 could be
released through valve 143 and line 145 to rejoin line 136, thus
stabilizing the pressure and flow rate at levels acceptable to the
steam cracker(s).
Steam Cracker
[0043] Steam cracking can be carried out in at least one steam
cracker (also referred to as a steam cracker furnace or furnace).
Typically, a plurality of steam crackers in parallel may be used at
a facility to improve efficiency in production of light
hydrocarbons. Steam crackers are typically taken offline for
periodic maintenance and decoking, and having a plurality of
furnaces in parallel allows for continuous operation of the
remainder of the steam cracking and light hydrocarbon purification
process without undue downtime. Generally, a steam cracker furnace
includes a convection section where the desalted hydrocarbon feed
is pre-heated and steam is added before entering the steam
cracker's radiant section where the heat is sufficient for cracking
to occur. A steam cracker may have a vapor-liquid separator, e.g.,
a flash separation vessel, integrated by fluid connection between
the convection section and the radiant section. The radiant section
may include fired heaters, and flue gas from combustion carried out
with the fired heaters travels upward from the radiant section
through the convection section and then away as flue gas.
[0044] The heating of the desalted hydrocarbon feed in the
convection section of a steam cracker may include indirect contact
(e.g. within a line or tube within the furnace) with hot flue gases
from the radiant section of the furnace. The heating of the
hydrocarbon feed can be accomplished, for example, by passing the
desalted hydrocarbon feed through a bank of heat exchange tubes
located within the convection section of the steam cracker. The
heated desalted hydrocarbon feed may have a temperature from about
315.degree. C. to about 560.degree. C., such as about 370.degree.
C. to about 510.degree. C., or about 430.degree. C. to about
480.degree. C.
[0045] The heated desalted hydrocarbon feed may be combined with
steam and subjected to additional heating in the convection
section. The heated desalted hydrocarbon feed can include steam in
an amount from about 10 wt. % to about 90 wt. %, based on the
weight of the hydrocarbon and steam mixture, with the remainder
including the hydrocarbon feed. In certain embodiments, the weight
ratio of steam to hydrocarbon feed can be from about 0.1 to about
1, such as about 0.2 to about 0.6.
[0046] A stream cracker may be integrated with a vapor-liquid
separator, e.g., one or more flash separation vessels. Such
vessels, sometimes referred to as flash pot or flash drum, can
provide upgrading of the preheated desalted hydrocarbon feed. Such
flash separation vessels are suitable when the preheated
hydrocarbon feed includes about 0.1 wt. % or more of asphaltenes
based on the weight of the hydrocarbon components of the convection
product stream, e.g., about 5 wt. % or more. Upgrading the
preheated hydrocarbon feed through vapor/liquid separation may be
accomplished through flash separation vessels or other suitable
means. Examples of suitable flash separation vessels include those
disclosed in U.S. Pat. Nos. 6,632,351; 7,138,047; 7,090,765;
7,097,758; 7,820,035; 7,311,746; 7,220,887; 7,244,871; 7,235,705;
7,247,765; 7,351,872; 7,297,833; 7,488,459; 7,312,371; and
7,578,929; and, which are incorporated by reference herein.
[0047] One advantage of having a flash separation vessel downstream
of the convection section and upstream of the radiant section is an
increased breadth of hydrocarbon types available to be used
directly, without pretreatment, as hydrocarbon feed. For example,
the addition of a flash separation vessel allows for utilization of
a hydrocarbon feed that contains crude oil or heavy hydrocarbon in
about 50 wt. % or greater, such as about 75 wt. % or greater, or
about 90 wt. % or greater. The flash separation vessel may operate
at a temperature from about 315.degree. C. to about 560.degree. C.
and/or a pressure from about 275 kPa to about 1400 kPa, such as, a
temperature from about 430.degree. C. to about 480.degree. C.,
and/or a pressure from about 700 kPa to about 760 kPa. Typically,
only the vapor phase within the flash separation vessel is
conducted on to the radiant section of a steam cracker, while the
liquid phase can be conducted away from the flash separation
vessel, e.g., for storage and/or further processing. The portion
conducted to the radiant section is typically in the vapor phase at
the inlet of the radiant coils, e.g., about 90 wt. % or greater is
in the vapor phase, such as about 95 wt. % or greater, or about 99
wt. % or greater.
[0048] The vapor portion of the heated desalted hydrocarbon feed
may be pyrolysed in the radiant section of a steam cracker, where
the hydrocarbon is indirectly exposed to the combustion carried out
by the burners. Steam cracking conditions (pyrolysis conditions)
may include exposing the vapor portion of the heated desalted
hydrocarbon feed in the radiant section (within a radiant line) to
a temperature (measured at the outlet of the steam cracker) of
about 400.degree. C. or greater, such as, from about 400.degree. C.
to about 1100.degree. C., a pressure of about 10 kPa or greater,
and/or a steam cracking residence time from about 0.01 second to 5
seconds. For example, the steam cracking conditions can include one
or more of (i) a temperature of about 760.degree. C. or greater,
such as from about 760.degree. C. to about 1100.degree. C., or from
about 790.degree. C. to about 880.degree. C., or for hydrocarbon
feeds containing light hydrocarbon from about 760.degree. C. to
about 950.degree. C.; (ii) a pressure of about 50 kPa or greater,
such from about 60 kPa to about 500 kPa, or from about 90 kPa to
about 240 kPa; and/or (iii) a residence time from about 0.1 seconds
to about 2 seconds. The steam cracking conditions may be sufficient
to convert at least a portion of the steam cracking feed's
hydrocarbon molecules to C.sub.2+ olefins by pyrolysis.
[0049] The steam cracked effluent generally includes C.sub.2+
olefin, molecular hydrogen, acetylene, aromatic hydrocarbon,
saturated hydrocarbon, C.sub.3+ diolefin, and one or more of
aldehyde, acidic gases such as H.sub.2S and/or CO.sub.2, and
mercaptans. The steam cracked effluent may be categorized as (i)
vapor-phase products such as one or more of acetylene, ethylene,
propylene, butenes, and (ii) liquid-phase products including, e.g.,
one or more of C.sub.5+ molecules and mixtures thereof.
[0050] As shown in FIG. 1, desalted hydrocarbon feed passed through
line 136 may enter steam cracker 147. Within steam cracker 147, the
desalted hydrocarbon feed may be heated via indirect exposure to
flue gases in the convection section (not shown), semi-purified in
a flash separation vessel (not shown) and pyrolysed within the
radiant section (not shown) producing steam cracker effluent which
is transferred via line 149 to undergo further purification in
purification system 151. Purification system 151 may contain a
number of fractionators, separation columns, purification and/or
catalyst beds, cooling and/or quench towers, and/or other devices
for the production of purified light hydrocarbons transferred via
line 153.
Hydrocarbon Recycle Line
[0051] Another method of managing variations in flow of hydrocarbon
feeds used in an apparatus, such as apparatus 100, is using one or
more desalters large enough to maintain flow to the maximum number
of steam cracker furnaces that could be online and use of a
hydrocarbon recycle line downstream of one or both of the desalters
(and optionally one or more of the steam crackers) to allow
recycling of desalted hydrocarbon feed to the original storage tank
or another storage tank. Large storage tanks are typically external
floating roof tanks and are not suitable to store hydrocarbon (with
a flash point <60.degree. C.) above ambient pressure or
temperature. The desalted hydrocarbon feed sent to a large storage
tank (e.g. crude oil storage tanks) may be cooled and/or
depressurized so as not to cause fugitive emissions from tank seals
or imbalances in the floating roof due to vapor pockets.
[0052] A hydrocarbon recycle line for managing greater-than-needed
flow can be sized to offset the flow of one or more steam crackers
being taken offline, as is frequently done due to the need to
accommodate variations in the need for desalted hydrocarbon feed
flow to the furnaces, e.g., during periodic maintenance and
decoking. The hydrocarbon recycle line may have an automatic valve
that determines the necessity to divert a portion of the desalted
hydrocarbon feed to storage. For example, if ten steam crackers are
online and a single furnace comes offline, e.g., is switched from
pyrolysis mode to decoking mode, the valve in the hydrocarbon
recycle line will open to send the excess flow from the offline
furnace back a storage tank. In doing so the flow rate through the
desalter(s) will stay the same despite the change in the number of
furnaces online. Similarly when nine steam cracker furnaces are
online and a tenth is to be brought online, the valve in the
hydrocarbon recycle line can close to send the flow forward rather
than be recycled back to a storage tank.
[0053] Use of a hydrocarbon recycle line has also been found to be
beneficial when operating a desalter in "turndown", e.g., with a
reduced flow of hydrocarbon feed to the desalter. Various factors
influence the desalter turndown rate including the distributor
within the vessel that maintains emulsion uniformity, and mixing
valves intended to intimately mix the water and hydrocarbon feed.
At low flow rates, both the distributor and mixing valves operate
outside of their effective operating range, and may cause
contaminant removal to suffer. The use of a hydrocarbon recycle
line allows increased flow through the desalter even if flow to the
steam crackers is reduced. As steam crackers are brought offline,
it is common to turndown flow to maintain regular flow to the
remaining steam crackers, the turndown of flow is not typically
found in refinery processes. The addition of a recycle line can
improve desalting by allowing for greater flow through the
desalter, while accommodating the fluctuations in flow as steam
crackers are brought online or offline.
[0054] One embodiment of the hydrocarbon recycle line is shown
according to apparatus 100 in FIG. 1. Line 155 leads to valve 157,
which according to one embodiment is an automatic valve that
maintains the pressure and/or flow rate for one or more steam
crackers downstream and may divert a portion of the desalted
hydrocarbon feed. The valve is fluidly connected with heat
exchanger 159, which is configured to cool the portion of the
desalted hydrocarbon feed to a temperature suitable for entry into
a storage tank producing a cooled desalted hydrocarbon feed. In at
least one embodiment, the cooled desalted hydrocarbon feed is
recycled through line 161 to storage tank 101. In another
embodiment the cooled desalted hydrocarbon feed is sent for storage
in a separate tank (not shown) before use in a steam cracker.
[0055] The hydrocarbon recycle line may include a variety of
configurations with the result of maintaining desired flow and
pressure to downstream steam crackers. For example the recycle line
could be installed after a single desalter, or in some embodiments,
after the surge drum. The hydrocarbon recycle line could lead to
floating-roof storage tanks (typically after cooling) or to storage
vessels designed to contain the heated hydrocarbon, like the surge
drum discussed above. In other aspects, the hydrocarbon recycle
line is in fluidic communication with a desalter, e.g., via a
connection (not shown) to line 111. In these aspects, heat exchange
duty in heat exchanges 109 and/or 159 may be beneficially lessened,
which increases process efficiency.
Other Recycle Lines
[0056] The purification process of pyrolysis products may produce
difficult to manage small volumes of emulsified by-product streams
that can be recycled upstream of a desalter. It may be more
economical and efficient to recycle emulsified by-product streams
than conduct them away for further treatment and/or upgrading. One
example of a small volume emulsified by-product stream is disulfide
oil produced when spent caustic is treated by an oxidation process
(e.g. Merox) as described in U.S. Pat. Nos. 5,320,742; and
6,579,444, which are incorporated by reference herein in their
entireties. The disulfides may be separated from the caustic using
a light solvent and a separation vessel, producing a stream that is
mainly hydrocarbon with sulfur incorporated, but cannot be sent to
a steam cracker because the disulfide oil may contain traces of
caustic including sodium. By-product streams of similar types can
be recycled upstream of a desalter which can remove contaminants of
the hydrocarbon feeds down to an acceptable level for steam
cracking.
[0057] Example recycle lines from the post steam cracking
purification process are shown in FIG. 1. Recycle line 163 provides
recycling of certain process streams directly into hydrocarbon
recycle line 161 and from there return to storage tank 101.
Additionally or alternatively, process streams can be recycled
directly to storage tank 101 through recycle line 165. Where
purification process 151 produces emulsions at elevated
temperatures and/or pressures, and the emulsions may be recycled in
line 167 to line 111 to join the heated hydrocarbon feed (and/or
the hydrocarbon feed upstream of exchanger 109, not shown) sent to
desalter 119. Other recycle stream configurations may be suitable
for use with a hydrocarbon feed to one or more steam crackers that
is cleaned by passing through one or more desalters.
Other Embodiments of the Present Disclosure can Include:
[0058] Paragraph 1. A process for producing light hydrocarbons from
a hydrocarbon feed containing heavy hydrocarbons, the process
including pressurizing the hydrocarbon feed in one or more pumps
producing a pressurized hydrocarbon feed; heating the pressurized
hydrocarbon feed in one or more heat exchangers producing a heated
hydrocarbon feed; mixing the heated hydrocarbon feed with water and
separating an inter-stage hydrocarbon feed from inter-stage water;
mixing the inter-stage hydrocarbon feed with water and separating a
desalted hydrocarbon feed from outlet water; and pyrolysing the
desalted hydrocarbon feed in a steam cracker.
[0059] Paragraph 2. The process of paragraph 1, where pressurizing
includes pressurizing the hydrocarbon feed to a pressure of from
about 101 kPa (abs) to about 2000 kPa (abs) or higher.
[0060] Paragraph 3. The process of any of paragraphs 1 to 2, where
heating includes heating the pressurized hydrocarbon feed to a
temperature from about 100.degree. C. to about 150.degree. C.
[0061] Paragraph 4. The process of any of paragraphs 1 to 3,
further including storing at least a portion of the desalted
hydrocarbon feed in a surge drum.
[0062] Paragraph 5. The process of any of paragraphs 1 to 4,
further including recycling at least a portion of the desalted
hydrocarbon feed to a storage tank.
[0063] Paragraph 6. The process of any of paragraphs 1 to 5, where
pyrolysing is performed at a temperature from about 760.degree. C.
to about 1100.degree. C.
[0064] Paragraph 7. The process of any of paragraphs 1 to 6,
further including a pyrolysis pressure from about 60 kPa (gauge) to
about 500 kPa (gauge).
[0065] Paragraph 8. An apparatus for removing contaminants from a
hydrocarbon feed containing heavy hydrocarbons, the apparatus
including: a first desalter; a second desalter in fluid connection
with the first desalter; and a steam cracker in fluid connection
with the second desalter.
[0066] Paragraph 9. The apparatus of paragraph 8, further including
a storage tank in fluid connection with the first desalter.
[0067] Paragraph 10. The apparatus of any of paragraphs 8 to 9,
further including a surge drum in fluid connection with the second
desalter and the steam cracker.
[0068] Paragraph 11. The apparatus of any of paragraphs 9 to 10,
further including a hydrocarbon recycle line in fluid connection
with the second desalter and the storage tank.
[0069] Paragraph 12. The apparatus of any of paragraphs 8 to 11,
further including a recycle line in fluid connection with the steam
cracker and the first desalter.
[0070] Paragraph 13. The apparatus of any of paragraphs 9 to 12,
further including a recycle line in fluid connection with the steam
cracker and the storage tank.
[0071] Paragraph 14. The apparatus of any of paragraphs 11 to 13,
further including a recycle line in fluid connection with the steam
cracker and the hydrocarbon recycle line.
[0072] Paragraph 15. An apparatus for removing contaminants from a
hydrocarbon feed containing heavy hydrocarbons, the apparatus
including: a desalter; a storage tank in fluid connection with the
desalter; a hydrocarbon recycle line in fluid connection with the
desalter and the storage tank; and a steam cracker in fluid
connection with the desalter.
[0073] Paragraph 16. The apparatus of paragraph 15, further
including a surge drum in fluid connection with the desalter and
the steam cracker.
[0074] Paragraph 17. The apparatus of any of paragraphs 15 to 16,
further including a recycle line in fluid connection with the steam
cracker and the storage tank.
[0075] Paragraph 18. The apparatus of any of paragraphs 15 to 17,
further including a recycle line in fluid connection with the steam
cracker and the desalter.
[0076] Paragraph 19. The apparatus of any of paragraphs 15 to 18,
further including a recycle line in fluid connection with the steam
cracker and the hydrocarbon recycle line.
[0077] Paragraph 20. An apparatus for removing contaminants from a
hydrocarbon feed containing heavy hydrocarbons, the apparatus
including: a surge drum; a desalter in fluid connection with the
surge drum; and a steam cracker in fluid connection with the surge
drum.
[0078] Paragraph 21. The apparatus of paragraph 20, further
including a storage tank in fluid connection with the desalter.
[0079] Paragraph 22. The apparatus of any of paragraphs 20 to 21,
further including a recycle line in fluid connection with the steam
cracker and the storage tank.
[0080] Paragraph 23. The apparatus of any of paragraphs 20 to 22,
further including a recycle line in fluid connection with the steam
cracker and the desalter.
[0081] Paragraph 24. An apparatus for removing contaminants from a
hydrocarbon feed containing heavy hydrocarbons, the apparatus
including: a storage tank in fluid connection with a first
desalter; a second desalter in fluid connection with the first
desalter; a first hydrocarbon recycle line in fluid connection with
the second desalter and the storage tank; a steam cracker in fluid
connection with the second desalter; a surge drum in fluid
connection with the second desalter and the steam cracker; and a
purification system in fluid connection with the steam cracker.
[0082] Paragraph 25. The apparatus of paragraph 25, where the
apparatus further includes a recycle line in fluid connection with
the purification system and the first desalter.
[0083] Paragraph 26. A process for producing light hydrocarbons
from a hydrocarbon feed containing heavy hydrocarbons, the process
comprising: mixing a hydrocarbon feed with water and separating an
inter-stage hydrocarbon feed from inter-stage water; mixing the
inter-stage hydrocarbon feed with water and separating a desalted
hydrocarbon feed from outlet water; and pyrolysing the desalted
hydrocarbon feed in a steam cracker.
[0084] Paragraph 27. The process of paragraph 26, where
pressurizing includes pressurizing the hydrocarbon feed to a
pressure of from about 101 kPa (abs) to about 2000 kPa (abs) or
higher.
[0085] Paragraph 28. The process of any of paragraphs 26 to 27,
where heating includes heating the pressurized hydrocarbon feed to
a temperature from about 100.degree. C. to about 150.degree. C.
[0086] Paragraph 29. The process of any of paragraphs 26 to 28,
further including storing at least a portion of the desalted
hydrocarbon feed in a surge drum.
[0087] Paragraph 30. The process of any of paragraphs 26 to 29,
further including recycling at least a portion of the desalted
hydrocarbon feed to a storage tank.
[0088] Paragraph 31. The process of any of paragraphs 26 to 30,
where pyrolysing is performed at a temperature from about
760.degree. C. to about 1100.degree. C.
[0089] Paragraph 32. The process of any of paragraphs 26 to 31,
further including a pyrolysis pressure from about 60 kPa (gauge) to
about 500 kPa (gauge).
[0090] Paragraph 33. A process for producing light hydrocarbons
from a hydrocarbon feed containing heavy hydrocarbons, the process
comprising: mixing a hydrocarbon feed with water and separating an
inter-stage hydrocarbon feed from inter-stage water; mixing the
inter-stage hydrocarbon feed with water and separating a desalted
hydrocarbon feed from outlet water; recycling at least a portion of
the desalted hydrocarbon feed to a storage tank and pyrolysing the
remaining desalted hydrocarbon feed in a steam cracker.
[0091] Paragraph 34. The process of paragraph 33, further including
storing at least a portion of the desalted hydrocarbon feed in a
surge drum.
[0092] Paragraph 35. The process of any of paragraphs 33 to 34,
where pyrolysing is performed at a temperature from about
760.degree. C. to about 1100.degree. C.
[0093] Paragraph 36. The process of any of paragraphs 33 to 35,
further including a pyrolysis pressure from about 60 kPa (gauge) to
about 500 kPa (gauge).
[0094] Paragraph 37. A process for producing light hydrocarbons
from a hydrocarbon feed containing heavy hydrocarbons, the process
comprising: mixing a hydrocarbon feed with water and separating an
inter-stage hydrocarbon feed from inter-stage water; mixing the
inter-stage hydrocarbon feed with water and separating a first
desalted hydrocarbon feed from outlet water; introducing a second
desalted hydrocarbon feed from a surge drum to the first desalted
hydrocarbon feed and pyrolysing the combined first desalted
hydrocarbon feed and second desalted hydrocarbon feed in a steam
cracker.
[0095] Paragraph 38. The process of paragraph 37, further including
introducing a portion of the first hydrocarbon feed and/or a third
desalted hydrocarbon feed to the surge drum.
[0096] Paragraph 39. The process of any of paragraphs 37 to 38,
further including recycling at least a portion of the first
desalted hydrocarbon feed to a storage tank.
EXAMPLES
[0097] FIG. 2 shows a plant test evaluating the performance of two
desalters in series during a rapid rate change in the flow of
hydrocarbon feed. In the test, pressure was maintained at 1800 kPa,
and temperature at 130.degree. C., the rate of crude oil with 16
wppm of sodium was decreased from 60 kBD to 39 kBD (350 T/hr to 230
T/hr), and the rate change occurred at vertical line 201. Time is
shown on the x-axis, the sodium content of the oil is shown on one
y-axis, and the percent water (by volume) in the oil is shown on
the other y-axis. The salt content of the inter-stage hydrocarbon
feed (line 203) and hydrocarbon outlet (line 205) demonstrates that
the salt content of only the inter-stage hydrocarbon feed (203)
increases above the furnace limit (line 207), while the salt
content of the hydrocarbon outlet (205) remains under the furnace
limit (207). Therefore, a second desalting stage allows for
consistent flow to the furnace while providing a desalted
hydrocarbon feed to the furnace with a salt content below the
furnace limit. It is noted that the last sample of line 203 was
retested showing a salt content of 3.4 wppm instead of the 4.5 wppm
originally measured. By way of an additional comparison, the
desalting of crude oil in accordance with the process of U.S.
Patent Application Publication No. 2007/0004952 (at paragraph
[0016]) discloses a salt content of 0.01 wt. % or more in its
partially desalted hydrocarbon feed. Accordingly, stream 205
achieves a much greater degree of desalting than does the
conventional process. The desalted hydrocarbon feed (line 205) is
conducted to a vapor-liquid separator integrated with the
convection section of the steam cracker. Vapor transferred from the
vapor-liquid separator to the radiant section of the steam cracking
furnace typically has a salt content .ltoreq.0.125 wppm, e.g.,
.ltoreq.0.10 wppm, such as .ltoreq.0.050 wppm, based on the weight
of the transferred vapor.
[0098] Also, as shown by FIG. 2, the water content of the
hydrocarbon feed is kept within the furnace limit (line 209) with a
second desalting stage. The inter-stage water content (line 211)
crosses furnace limit 209, while the outlet water content (line
213) remains below furnace limit 209. The second sample of the
inter-stage water content was retested showing water content of
0.6% by volume, instead of the original 2% by volume, demonstrating
the accuracy of the high result.
[0099] Overall, it has been found that management of contaminants
in a hydrocarbon feed for steam cracking with limited to no feed
disruptions can be accomplished by (i) the combination of two or
more desalters, (ii) the combination of one or more desalters and a
surge drum, and/or (iii) the combination of one or more desalters
and a hydrocarbon recycle line. Additionally, it has been
discovered that the above management systems can allow for
recycling of emulsified by-product streams produced by the
purification of light hydrocarbons produced in the steam
cracker.
[0100] The phrases, unless otherwise specified, "consists
essentially of" and "consisting essentially of" do not exclude the
presence of other steps, elements, or materials, whether or not,
specifically mentioned in this specification, so long as such
steps, elements, or materials, do not affect the basic and novel
characteristics of this disclosure, additionally, they do not
exclude impurities and variances normally associated with the
elements and materials used.
[0101] For the sake of brevity, only certain ranges are explicitly
disclosed herein. However, ranges from any lower limit may be
combined with any upper limit to recite a range not explicitly
recited, as well as, ranges from any lower limit may be combined
with any other lower limit to recite a range not explicitly
recited, in the same way, ranges from any upper limit may be
combined with any other upper limit to recite a range not
explicitly recited. Additionally, within a range includes every
point or individual value between its end points even though not
explicitly recited. Thus, every point or individual value may serve
as its own lower or upper limit combined with any other point or
individual value or any other lower or upper limit, to recite a
range not explicitly recited.
[0102] All documents described herein are incorporated by reference
herein, including any priority documents and/or testing procedures
to the extent they are not inconsistent with this text. As is
apparent from the foregoing general description and the specific
embodiments, while forms of this disclosure have been illustrated
and described, various modifications can be made without departing
from the spirit and scope of this disclosure. Accordingly, it is
not intended that this disclosure be limited thereby. Likewise, the
term "comprising" is considered synonymous with the term
"including" for purposes of United States law. Likewise whenever a
composition, an element or a group of elements is preceded with the
transitional phrase "comprising," it is understood that we also
contemplate the same composition or group of elements with
transitional phrases "consisting essentially of," "consisting of,"
"selected from the group of consisting of," or "is" preceding the
recitation of the composition, element, or elements and vice
versa.
[0103] While this disclosure has been described with respect to a
number of embodiments and examples, those skilled in the art,
having benefit of this disclosure, will appreciate that other
embodiments can be devised which do not depart from the scope and
spirit of this disclosure.
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