Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 2022/225691
PCT/US2022/023235
PROCESSES AND SYSTEMS FOR STEAM CRACKING HYDROCARBON FEEDS
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to and the benefit of U.S. Provisional
Application No.
63/176,423 having a filing date of April 19, 2021, the disclosure of which is
incorporated herein
by reference in its entirety.
FIELD
[0002] Embodiments disclosed herein generally relate to processes and systems
for steam
cracking hydrocarbon feeds. More particularly, such embodiments relate to
processes and
systems for steam cracking a plurality of hydrocarbon feeds, where each feed
is cracked within
one or more radiant coils disposed within different segments of a firebox of a
steam cracking
furnace.
BACKGROUND
[0003] Steam cracking is the primary means to generate ethylene and other
products from a
variety of feedstocks. Modern plants employ optimization models and controls
to optimize
profit. At times, these models and controls call for multiple feeds or
multiple operating
conditions, sometimes in smaller increments than a full furnace can provide.
Steam cracking
two or more different feeds within different segments within the radiant
section of the steam
cracker has proved challenging.
[0004] Prior attempts to steam crack multiple hydrocarbon feeds within a
firebox of a single
steam cracking furnace have implemented a dividing wall to provide more
independent zones
within that exhausted flue gases from the independent zones to a single
convection section.
While this arrangement provides multiple feed capability, it comes at the
expense of a dividing
wall inside the extremely high temperature firebox, which must have structural
support and
refractory lining. In practice, this results in a similar plot space
requirement to a separate
furnace, reducing much of the economy of scale benefit for combining feeds in
a single furnace.
In addition, the complexity, cost, and physical space requirements for a
dividing wall naturally
limit segments in a furnace to at most two.
[0005] There is a need, therefore, for improved processes and systems for
steam cracking a
plurality of hydrocarbon feeds, where each feed is cracked within one or more
radiant coils
disposed within different segments of a firebox of a steam cracking furnace.
This disclosure
satisfies this and other needs.
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SUMMARY
[0006] Processes and systems for steam cracking a plurality of hydrocarbon
feeds, where
each feed is cracked within one or more radiant coils disposed within
different segments of a
firebox of a steam cracking furnace. In some embodiments, the process for
steam cracking
hydrocarbons can include introducing a first hydrocarbon feed into one or more
radiant coils
disposed within a first segment of a firebox of a steam cracker to produce a
first steam cracker
effluent having a first coil outlet temperature. The first segment can include
one or more
burners providing heat thereto. A second hydrocarbon feed can be introduced
into one or more
radiant coils disposed within a second segment of the firebox of the steam
cracker to produce
a second steam cracker effluent having a second coil outlet temperature. The
second segment
can include one or more burners providing heat thereto. The one or more
burners in the first
and second segments can be operated at substantially the same firing rate such
that an amount
of heat produced by each of the one or more burners in the first and second
segments is
substantially the same. A feed rate of the first hydrocarbon feed introduced
into the one or
more radiant coils disposed within the first segment can be controlled based,
at least in part, on
a composition of the first hydrocarbon feed and the first coil outlet
temperature.
[0007] In some embodiments, the system for steam cracking one or more
hydrocarbon feeds
can include a steam cracker that can include a firebox having one or more
radiant coils and one
or more burners disposed within a first segment of the firebox and one or more
radiant coils
and one or more burners disposed within a second segment of the firebox. The
one or more
radiant coils in the first segment can be configured to receive a first
hydrocarbon feed via a
first feed control valve and produce a first steam cracker effluent having a
first coil outlet
temperature. The one or more radiant coils in the second segment can be
configured to receive
a second hydrocarbon feed via a second feed control valve and produce a second
steam cracker
effluent having a second coil outlet temperature. The one or more burners in
the first and
second segments can be configured to operate at substantially the same firing
rate such that an
amount of heat produced by each of the one or more burners in the first and
second segments
is substantially the same. The first and second feed control valves can be
configured to
independently adjust a feed rate of the first and second hydrocarbon feeds
introduced into the
one or more radiant coils in the first and second segments, respectively, to
independently adjust
the first and second coil outlet temperatures of the first and second steam
cracker effluents,
respectively.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0008] So that the manner in which the above recited features of the present
invention can
be understood in detail, a more particular description of the invention,
briefly summarized
above, may be had by reference to embodiments, some of which are illustrated
in the appended
drawings. It is to be noted, however, that the appended drawings illustrate
only typical
embodiments of this invention and are therefore not to be considered limiting
of its scope, for
the invention may admit to other equally effective embodiments.
[0009] FIG. 1 depicts a schematic of an illustrative steam cracking furnace in
operation to
convert first and second hydrocarbon feeds within first and second segments,
respectively, of
a firebox in the stream cracking furnace, according to one or more embodiments
described.
[0010] FIG. 2 depicts a plan view of an illustrative firebox of a steam
cracking furnace having
a footprint area divided into four segments, according to one or more
embodiments described.
[0011] FIG. 3 depicts a plan view of the firebox shown in FIG. 2 where each of
the four
segments include a plurality of burners and a plurality of tubes disposed
therein, according to
one or more embodiments.
DETAILED DESCRIPTION
[0012] It is to be understood that the following disclosure describes several
exemplary
embodiments for implementing different features, structures, and/or functions
of the invention.
Exemplary embodiments of components, arrangements, and configurations are
described
below to simplify the present disclosure; however, these exemplary embodiments
are provided
merely as examples and are not intended to limit the scope of the invention.
Additionally, the
present disclosure may repeat reference numerals and/or letters in the various
exemplary
embodiments and across the Figures provided herein. This repetition is for the
purpose of
simplicity and clarity and does not in itself dictate a relationship between
the various exemplary
embodiments and/or configurations discussed in the Figures. Moreover, the
exemplary
embodiments presented below can be combined in any combination of ways, i. e.
, any element
from one exemplary embodiment can be used in any other exemplary embodiment,
without
departing from the scope of the disclosure.
[0013] The indefinite article "a" or "an", as used herein, means "at least
one" unless specified
to the contrary or the context clearly indicates otherwise. Thus, embodiments
using "a
separator" include embodiments where one or two or more separators are used,
unless specified
to the contrary or the context clearly indicates that only one separator is
used. Likewise,
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embodiments using "a separation stage" include embodiments where one or two or
more
separation stages are used, unless specified to the contrary.
[0014] Certain embodiments and features are described using a set of numerical
upper limits
and a set of numerical lower limits. It should be appreciated that ranges
including the
combination of any two values, e.g., the combination of any lower value with
any upper value,
the combination of any two lower values, and/or the combination of any two
upper values are
contemplated unless otherwise indicated. Certain lower limits, upper limits
and ranges appear
in one or more claims below. All numerical values are "about" or
"approximately" the
indicated value, and take into account experimental error and variations that
would be expected
by a person having ordinary skill in the art.
[0015] As used herein, the term "hydrocarbon" means a class of compounds
containing
hydrogen bound to carbon. The term "Cr," hydrocarbon means hydrocarbon having
n carbon
atom(s) per molecule, where n is a positive integer. The term "Cõ,"
hydrocarbon means
hydrocarbon having at least n carbon atom(s) per molecule, where n is a
positive integer. The
term "Cn." hydrocarbon means hydrocarbon having no more than n number of
carbon atom(s)
per molecule, where n is a positive integer. "Hydrocarbon" 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.
[0016] It has been surprisingly and unexpectedly discovered that two or more
hydrocarbon
feeds can each be steam cracked within one or more radiant coils disposed
within separate
segments of a firebox in a steam cracking furnace to produce two or more steam
cracker
effluents by operating one or more burners disposed within each segment at
substantially the
same firing rate by independently adjusting a feed rate of each hydrocarbon
feed. It has also
been surprisingly and unexpectedly discovered that two or more hydrocarbon
feeds can each
be steam cracked within one or more radiant coils disposed within separate
segments of the
firebox in the steam cracking furnace to produce the two or more steam cracker
effluents by
having one or more burners within one or more of the segments off while
operating the other
burners within the one or more segments at a substantially constant firing
rate by independently
adjusting the feed rate of each hydrocarbon feed. As used herein, the phrase
"substantially the
same firing rate" means that an amount of heat produced by each burner
disposed within each
segment is within 20%, within 15%, within 10%, within 7%, within 5%, within
3%, or within
1% of one another. Such control scheme of the steam cracking furnace, which
can also be
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referred to as a "coil outlet temperature to feed rate scheme", provides a
much more precise
and localized control as compared to independently adjusting the firing rate
of the burners to
adjust the coil outlet temperatures of the two or more hydrocarbon feeds,
which can also be
referred to as a "coil outlet temperature to firing scheme". The control
scheme of the steam
cracking furnace disclosed herein can also be accomplished without the use of
one or more
dividing walls being disposed between two or more segments. It should be
understood,
however, that in some embodiments, one or more dividing walls can optionally
be disposed
between two or more segments.
[0017] The feed rate of each hydrocarbon feed introduced into the radiant
coil(s) disposed
within each segment can be controlled based, at least in part, on the coil
outlet temperature of
each steam cracker effluent recovered from each segment. The coil outlet
temperature of each
steam cracker effluent can be monitored and the feed rate of a given
hydrocarbon feed can be
increased or decreased to reduce or increase the coil outlet temperature,
respectively, for the
given steam cracker effluent. One or more flow control devices, e.g., valves,
can be used to
control the amount of each of the hydrocarbon feeds introduced into the
radiant coil(s) disposed
within each segment.
[0018] In some embodiments, each of the two or more hydrocarbon feeds can be
mixed,
blended, combined, or otherwise contacted with steam to produce mixtures that
can be heated
by indirect heat exchange within a convection section of the steam cracking
furnace. In some
embodiments, the mixtures that include the hydrocarbon feeds can be heated to
a temperature
of 200 C, 300 C, 400 , or 450 C to 500 C, 600 C, 700 C, or 750 C within the
convection
section. The heated mixtures can then be steam cracked within the radiant
coil(s) disposed
within each segment to produce the steam cracker effluents. In such
embodiment, the steam
contacted with the hydrocarbon feeds can also be adjusted independently from
one another
such that at least one of the one or more hydrocarbon feeds can be mixed with
a different
amount of steam as compared to at least one other of the one or more
hydrocarbon feeds. One
or more flow control devices, e.g., valves, can be used to control the amount
of steam contacted
with each hydrocarbon feed.
[0019] In some embodiments, the steam cracking conditions can include, but are
not limited
to, one or more of: exposing the heated mixtures of the hydrocarbon feed and
steam in line (or
a vapor phase product separated therefrom) to a temperature (as measured at a
radiant outlet of
the steam cracking furnace) of > 400 C, e.g., a temperature of about 700 C,
about 800 C, or
about 900 C to about 950 C, about 1,000 C, or about 1050 C, a pressure of
about 10 kPa-
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absolute to about 500 kPa-absolute or more, and/or a steam cracking residence
time of about
0.01 seconds to about 5 seconds. In some embodiments, the hydrocarbon and
steam mixtures
can include steam in an amount in of about 10 wt% to about 95 wt%, based on
the weight of
the hydrocarbon and steam mixture. In some embodiments, the heated mixtures or
a vapor
phase product separated therefrom can be steam cracked according to the
processes disclosed
in U.S. Patent Nos. 6,419,885; 7,993,435; 9,637,694; and 9,777,227; and
International Patent
Application Publication No. WO 2018/111574.
[0020] In some embodiments, the steam cracker effluents can be cooled by
indirect heat
exchange in one or more heat exchange stages, e.g., via one or more transfer
line exchangers,
with water or steam to produce steam, e.g., medium pressure steam or
superheated steam, and
cooled steam cracker effluents. In some embodiments, the steam cracker
effluents can be
cooled by direct contact with a quench medium to produce the cooled steam
cracker effluents.
In other embodiments, the steam cracker effluents can be cooled by indirect
heat exchange and
by direct contact with a quench medium to produce the cooled steam cracker
effluent In some
embodiments, the steam cracker effluents can be mixed and cooled together. In
other
embodiments, the steam cracker effluents can be cooled separately and the
mixed with one
another. In still other embodiments, the steam crack effluents can be cooled
separately and can
be further processed separately.
[0021] In some embodiments, the quench medium that can be contacted with the
steam
cracker effluents can be or can include a utility fluid. In some embodiments,
the utility fluid
can be the same or similar to the utility fluids described in U.S. Patent Nos.
9,090,836;
9,637,694; and 9,777,227; and International Patent Application Publication No.
WO
2018/111574.
[0022] Suitable steam crackers, process gas recovery configurations, other
equipment, and
process conditions can include those disclosed in U.S. Patent Nos.: 6,419,885;
7,560,019;
7,993,435; 8,105,479; 8,197,668; 8,882,991; 9,637,694; 9,777,227; U.S. Patent
Application
Publication Nos.: 2014/0061096; 2014/0357923; 2016/0376511; 2018/0170832;
2019/0016975; and WO Publication No.: WO 2018/111574; WO/2020/096972;
WO/2020/096974; WO/2020/096977; and WO/2020/096979. Suitable dividing walls
that can
optionally be disposed between two or more segments can include those
disclosed in U.S.
Patent No. 7,718,052.
[0023] In some embodiments, an olefin plant recovery section can require at
least some
minimum amount of a given feed to function appropriately. For example,
recovery sections
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may need a minimum amount of a heavy feed for a suitable flow of the heaviest
furnace yields.
Such minimum heavy feed requirement can come at a significant economic debit
if the heavy
feed is a higher cost feed than lighter feeds but remains necessary to provide
any production
through the plant without significant costly modifications. By running a small
portion of a
furnace, e.g., only a single segment or a small number of segments of the
furnace, on this
minimized amount of heavy feed, the minimum feed requirement can be minimized
further
than if forced to process on an entire furnace or furnace segment with a
divided wall.
Additionally, by running this small portion of the heavy feed in a furnace
with manipulated
operating conditions (reduced feed or increased steam) the actual rate can be
turned down
further than if the segment of the furnace were running full of the minimized
heavy feed.
[0024] In some plants, some recovery sections operating at very cold
conditions can require
a minimum amount of heavy feeds for a suitable flow of fuel molecules to
achieve a desired
hydrogen to methane ratio for stable and desired refrigeration capacity. Gas
crackers, or
especially liquid crackers that have transitioned to gas crackers, typically
require a minimum
amount of methane for the right hydrogen-to-methane ratio to operate the
recovery section
"cold box" at optimum conditions. LPG or heavier feeds are typically used to
satisfy the
methane requirement. By running a small portion of a furnace, e.g., only a
single segment or
small number of segments of the furnace, on the minimized amount of heavy
feed, the
minimum feed requirement can be minimized further than if forced to process on
an entire
furnace or furnace segment with a divided wall. Additionally, by running this
small portion of
the heavy feed in a furnace with manipulated operating conditions (reduced
feed or increased
steam) or optimized firebox heat distribution (online burner pattern) the
actual rate can be
turned down further than if the segment of the furnace were running full of
the minimized
heavy feed.
[0025] In some plants, a feed slate can potentially leave one section of the
plant relatively
unloaded. While this may not present a feasibility constraint as discussed
above, an optimized
solution can select operating conditions on some feeds that would fill this
unloaded portion of
the plant to make products. An example could arise from a propylene/propane
fractionator in
a plant designed for higher propylene production now running mostly ethane
feed (with little
propylene production). By running much of a furnace on recycle or fresh
ethane, at maximum
conversion to maximize production against an ethylene fractionator constraint
(by minimizing
uncracked ethane that consumes capacity of the ethylene fractionator), and
running a portion
of a furnace on fresh or recycle propane streams at reduced conversion to
maximize propylene
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production and/or maximize methane production and/or minimize acetylene
production, both
the ethylene fracti onator and propylene fracti on ator can be filled for
increased profitability.
[0026] In plants, a refinery gas integration stream taken into the olefins
plant or pyrolysis
furnaces, where the refinery gas stream(s) require different operating
conditions to manage
unique content, even a small refinery gas integration stream can present a
significant impact to
plant operations through impacting operating conditions on larger feed
streams. In such
embodiment, a refinery gas that requires different operating conditions due to
contaminants or
different composition can be cracked separately from the other fresh or
recycle feed(s) to best
tailor operating conditions to each stream almost regardless of size.
[0027] In new furnace construction, the control scheme disclosed herein can
allow for a
single furnace with a single stack and single set of post-combustion emissions
reduction
facilities to accommodate multiple feeds or operating conditions while also
maximizing
economy of scale.
[0028] It has also been observed that the control scheme disclosed herein can
provide several
process advantages even when not utilized for multiple different hydrocarbon
feeds. For
example, the control scheme can mitigate process safety risks like furnace
flooding, e.g., a fuel-
rich firebox atmosphere, and/or furnace tube overheat.
[0029] Furnace flooding refers to a condition where insufficient air is
present in the firebox
to provide an excess of oxygen after combustion. Instead, an excess of fuel
exists after
combustion in the firebox and presents a potential deflagration or explosion
hazard if air were
suddenly introduced. Where this occurs, the heat released from a fuel input
that is not
completely combusted declines, causing the coil outlet temperatures to decline
for a given fuel
flow input. Coil outlet temperature to firing schemes do not explicitly
control firing heat input,
but rather only a fuel rate selected to deliver desired firing when the fuel
is fully combusted.
Therefore, declining coil outlet temperatures due to uncombusted fuel could
cause a coil outlet
temperature to firing control scheme to increase the fuel rate that could
result in even more
excess fuel remaining uncombusted (since air is the limiting reactant in a
flooding scenario).
On the other hand, a coil outlet temperature to feed rate scheme would not add
fuel and
aggravate the mismatch between fuel input and air input. Rather the coil
outlet temperature to
feed rate scheme can respond to a declining coil outlet temperature from
uncombusted fuel by
reducing the feed rate of the hydrocarbon feed(s) to maintain the same coil
outlet temperature
setpoint without the amount of fuel input to each of the burners increasing.
Therefore, the coil
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outlet temperature to feed rate scheme does not worsen the flooding situation
like the coil outlet
temperature to firing scheme_
[0030] Similarly, the coil outlet temperature to feed scheme has been found to
be
significantly more useful in preventing or mitigating furnace tube overheat in
a loss of feed or
firing excursion scenario. While industry standard furnaces use coil outlet
temperature to firing
to control coil outlet temperature because of the widespread impacts of firing
among multiple
temperature outlets and the overall firebox (including air input), these
firing controls tend to be
tuned very slowly to prevent upsets with too much fuel (and not enough air) or
too little fuel
(and a large temperature swing on the furnace). An effect of the slow tuning
is that a potential
overheat scenario is addressed too slowly to prevent significant furnace
damage due to
overheating. Conversely, the coil outlet temperature to feed scheme has a much
more localized
impact on just the set of tubes with the controlled coil outlet temperature.
Therefore, the coil
outlet temperature to feed scheme can be tuned much more rapidly to provide a
faster response
to any overheat scenario.
[0031] FIG. 1 depicts a schematic of an illustrative steam cracking furnace
100 in operation
to convert a first hydrocarbon feed in line 1001 and a second hydrocarbon feed
in line 1003,
within one or more first radiant coils 1025 and within one or more second
radiant coils 1027,
respectively, disposed within a radiant section 1029 of the steam cracking
furnace 100,
according to one or more embodiments. A feed rate of the first hydrocarbon
feed in line 1001
can be controlled via a first flow control device 1002 and a feed rate of the
second hydrocarbon
feed in line 1003 can be controlled via a second flow control device 1004.
[0032] In some embodiments, the first hydrocarbon feed in line 1001 and the
second
hydrocarbon feed in line 1003 can be mixed, blended, combined, or otherwise
contacted with
steam in lines 1007 and 1009, respectively, to produce first and second
hydrocarbon and steam
mixtures in lines 1011 and 1013, respectively. As shown, the steam in lines
1007 and 1009
can be provided from a common source, e.g., steam in line 1005. In other
embodiments,
however, the steam in lines 1007 and 1009 can be provided from different
sources. A feed rate
of the steam contacted with the first hydrocarbon feed in line 1001 can be
controlled by a third
flow control device 1008 and a feed rate of the steam contacted with the
second hydrocarbon
feed in line 1003 can be controlled by a fourth flow control device 1010. The
amount of steam
contacted with the first and second hydrocarbon feeds in lines 1001 and 1003
can be the same
or different with respect to one another.
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[0033] The first and second mixtures in lines 1011 and 1013 can each be heated
within one
or more convection coils 1015 and 1017, respectively, disposed within the
convection section
1019 of the steam cracking furnace 100 to produce first and second heated
mixtures via lines
1021 and 1023, respectively. In some embodiments, the first and second
mixtures in lines 1011
and 1013 can be heated to a temperature of 200 C, 300 C, 400', or 450 C to 500
C, 600 C,
700 C, or 750 C within the convection section 1019. The first and second
heated mixtures in
lines 1021 and 1023 can be further heated and subjected to steam cracking
conditions within
the one or more first radiant coils 1025 and within the one or more second
radiant coils 1027,
respectively, disposed within the radiant section 1029 of the steam cracking
furnace 100 to
produce first and second steam cracker effluents via lines 1031 and 1033,
respectively.
[0034] The first radiant coil(s) 1025 and the second radiant coil(s) 1027 can
be heated by a
plurality of burners (four are shown ¨ 1035, 1037, 1039, and 1041). The
burners 1035 and
1037 can be considered as being disposed within a first segment of the radiant
section 1029
and the burners 1039 and 1041 can be considered as being disposed within a
second segment
of the radiant section 1029. As such, the first segment of the radiant section
occupies the left
half of the radiant section 1029 and the second segment of the radiant section
1029 occupies
the right half of the radiant section 1029, as shown in FIG. 1. During
operation, the burners
1035, 1037, 1039, and 1041 can be operated at substantially the same firing
rate such that the
amount of heat produced by each burner in the first sand second segments is
substantially the
same.
[0035] The first steam cracker effluent in line 1031 can have a first coil
outlet temperature
upon exiting the first radiant coil(s) 1025 and the second steam cracker
effluent in line 1033
can have a second coil outlet temperature upon exiting the second radiant
coil(s) 1027. The
first coil outlet temperature of the first steam cracker effluent in line 1031
can he measured
with a first temperature measuring device, e.g., thermocouple, 1043 and the
second coil outlet
temperature of the second steam cracker effluent in line 1033 can be measured
with a second
temperature measuring device, e.g., thermocouple, 1045.
[0036] The feed rate of the first hydrocarbon feed in line 1001 and the feed
rate of the second
hydrocarbon feed in line 1003 can be controlled based, at least in part, on
the composition(s)
of the first and second hydrocarbon feeds and/or the first and second coil
outlet temperatures,
respectively. In some embodiments, the feed rate of the first hydrocarbon feed
in line 1001
can be reduced to increase the first coil outlet temperature of the first
steam cracker effluent in
line 1031. In other embodiments, the feed rate of the first hydrocarbon feed
in line 1001 can
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be increased to reduce the first coil outlet temperature of the first steam
cracker effluent in line
1031. The feed rate of the second hydrocarbon feed in line 1003 can be
controlled in a similar
manner as the feed rate of the first hydrocarbon feed in line 1001.
[0037] Similar to the feed rates of the first and second hydrocarbon feeds,
the feed rate of the
steam in line 1007 and the steam in line 1009 that can be contacted with the
first hydrocarbon
feed in line 1001 and the second hydrocarbon feed in line 1003, respectively,
can be controlled
based, at least in part, on the composition(s) of the first and second
hydrocarbon feeds and the
first and second coil outlet temperatures, respectively. By controlling the
feed rate of the first
and second hydrocarbon feeds and the steam contacted therewith, the feed rate
of the heated
first and second hydrocarbon feeds introduced via lines 1021 and 1023,
respectively, can be
increased or decreased as desired to control or otherwise adjust the first
coil outlet temperature
and the second coil outlet temperature as desired.
[0038] In some embodiments, the steam cracking conditions can include, but are
not limited
to, one or more of: exposing the heated mixtures of the hydrocarbon feed and
steam in line (or
a vapor phase product separated therefrom) to a temperature (as measured at a
radiant outlet of
the steam cracking furnace) of > 400 C, e.g., a temperature of about 700 C,
about 800 C, or
about 900 C to about 950 C, about 1,000 C, or about 1050 C, a pressure of
about 10 kPa-
absolute to about 500 kPa-absolute or more, and/or a steam cracking residence
time of about
0.01 seconds to about 5 seconds. In some embodiments, the hydrocarbon and
steam mixtures
can include steam in an amount in of about 10 wt% to about 95 wt%, based on
the weight of
the hydrocarbon and steam mixture.
[0039] FIG. 2 depicts a plan view of an illustrative firebox 200 of a steam
cracking furnace
having a footprint area divided into four segments, namely segments 2001,
2003, 2005, and
2007, according to one or more embodiments. FIG. 3 depicts a plan view of the
firebox 200
shown in FIG. 2 where each of the segments 2001, 2003, 2005, and 2007 include
a plurality of
burners A, B, C, and D and a plurality of tubes TA, TB, Tc, and TD,
respectively, disposed
therein, according to one or more embodiments. The firebox 200 can include any
desired
number of segments. In some embodiments, the firebox 200 can include 2, 3, 4,
5, 6, 7, 8, 9,
10, or more segments. During operation the burners A, B, C, and D in segments
2001, 2003,
2005, and 2007, respectively, can be operated at substantially the same firing
rate such that the
amount of heat produced by each of the burners A, B, C, and D, in the segments
2001, 2003,
2005, and 2007 is substantially the same.
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[0040] In some embodiments, one or more burners can be shut off during
operation. In some
embodiments, radiant heat in a hotter pass, i.e., the coil outlet temperature
of the steam cracker
effluent is greater than a colder pass, could be re-radiating the colder pass,
which could have
the effect of un-optimized cracking temperatures in the colder pass. In such
embodiment, one
or more burners primarily radiating heat to the hotter pass can be shut off to
reduce or eliminate
the amount heat being re-radiated to the colder pass. For example, if segment
2001 includes
the hotter pass and segment 2003 includes the colder pass, one or more burners
A and/or one
or more burners B disposed along the boundary between segment 2001 and segment
2003 can
be shut off. Similarly, if segment 2001 includes the hotter pass and segment
2005 includes the
colder pass, one or more burners A and/or one or more burners C can be shut
off.
Hydrocarbon Feeds
[0041] In some embodiments, the first and/or second hydrocarbon feeds in line
1001 and
1003, respectively, can be or can include, but are not limited to, relatively
high molecular
weight hydrocarbons ("heavy feedstocks"), such as those that produce a
relatively large amount
of steam cracker tar ("SCT") during steam cracking. Examples of heavy
feedstocks can include
one or more of steam cracked gas oil and residues, gas oils, heating oil, jet
fuel, diesel, kerosene,
coker naphtha, steam cracked naphtha, catalytically cracked naphtha,
hydrocrackate,
reformate, raffinate reformate, Fischer-Tropsch liquids, Fischer-Tropsch
gases, distillate, crude
oil, atmospheric pipestill bottoms, vacuum pipestill streams including
bottoms, gas oil
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, crude oil, or
any mixture
thereof. In some embodiments, the first and/or second hydrocarbon feeds in
lines 1001 and
1003, respectively, can be or can include, but are not limited to, lighter
hydrocarbons such as
C1-05 alkanes, naphtha distillate, aromatic hydrocarbons, or any mixture
thereof. In some
embodiments, as noted above, two or more hydrocarbon feeds can be introduced
into the steam
cracker and the two hydrocarbon feeds can be the same or different with
respect to one another.
In some embodiments, the first hydrocarbon feed in line 1001 can include one
or more lighter
hydrocarbons and the second hydrocarbon feed in line 1003 can include one or
more heavy
feedstocks. In some embodiments, the second hydrocarbon feed in line 1003 can
have a
nominal final boiling point > 315 C, > 399 C, > 454 C, or > 510 C. Nominal
final boiling
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point means the temperature at which 99.5 wt. 67o of a particular sample has
reached its boiling
point.
[0042] In other embodiments, the first and second hydrocarbon feeds in line
1001 and 1003,
respectively, can include one or more relatively low molecular weight
hydrocarbon (light
feedstocks), particularly those aspects where relatively high yields of C2
unsaturates (ethylene
and acetylene) can be desired. Light feedstocks can include substantially
saturated
hydrocarbon molecules having fewer than five carbon atoms, e.g., ethane,
propane, and
mixtures thereof (e.g., ethane-propane mixtures or "E/P- mix). For ethane
cracking, a
concentration of at least 75 wt. % of ethane is typical. For E/P mix, a
concentration of at least
75 wt. % of ethane plus propane is typical, the amount of ethane in the E/P
mix can be 20
wt. % based on the weight of the E/P mix, e.g., of about 25 wt. % to about 75
wt. %. The
amount of propane in the E/P mix can be, e.g., 20 wt. %, based on the weight
of the E/P mix,
such as of about 25 wt. % to about 75 wt. %. In some embodiments, the first
hydrocarbon
and/or the second hydrocarbon feed can be or can include, but is not limited
to, a refinery gas
stream that can include one or more C2 to C5, saturated or unsaturated
hydrocarbons. In some
embodiments, the first hydrocarbon feed can include primarily ethane, propane,
or a mixture
thereof, and the second hydrocarbon feed can include a refinery gas stream.
Suitable
hydrocarbon feeds can be or can include those described in U.S. Patent Nos.:
7,138,047;
7,993,435; 8,696,888; 9,327,260; 9,637,694; 9,657,239; and 9,777,227; and
International
Patent Application Publication No. WO 2018/111574.
[0043] Optionally, e.g., when the first and/or second hydrocarbon feeds in
lines 1001 and
1003, respectively, include certain heavy feedstocks, the system 100 can
include one or more
vapor/liquid separators (sometimes referred to as flash pot or flash drum)
integrated therewith.
When used, the vapor-liquid separator can be configured to upgrade the
hydrocarbon feed, e.g.,
by upgrading the hydrocarbon and steam mixture, upstream of the radiant
section 1029. In
some embodiments, it can be desirable to integrate a vapor-liquid separator
with the furnace
when the hydrocarbon feed includes > 1 wt% of non-volatiles, e.g., > 5 wt%,
such as about 5
wt% to about 50 wt% of non-volatiles having a nominal boiling point of > 760
C. In some
embodiments, it can be desirable to integrate a vapor/liquid separator with
the furnace when
the non-volatiles include asphaltenes, such as > about 0.1 wt% asphaltenes
based on the weight
of the hydrocarbon feed, e.g., about 5 wt%. Conventional vapor/liquid
separation devices
can be utilized to do this, though the invention is not limited thereto.
Examples of such
conventional vapor/liquid separation devices can include those disclosed in
U.S. Patent Nos.
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7,138,047; 7,090,765; 7,097,758; 7,820,035; 7,311,746; 7,220,887; 7,244,871;
7,247,765;
7,351,872; 7,297,833; 7,488,459; 7,312,371; 6,632,351; 7,578,929; and
7,235,705. A vapor
phase can be separated from the hydrocarbon feed in the vapor/liquid
separation device. The
separated vapor phase can be conducted away from the vapor/liquid separator to
the radiant
coil(s) for steam cracking. The liquid-phase separated from the hydrocarbon
feed can be
conducted away from the vapor/liquid separation device, e.g., for storage
and/or further
processing.
[0044] Various terms have been defined above. To the extent a term used in a
claim is not
defined above, it should be given the broadest definition persons in the
pertinent art have given
that term as reflected in at least one printed publication or issued patent.
Furthermore, all
patents, test procedures, and other documents cited in this application are
fully incorporated by
reference to the extent such disclosure is not inconsistent with this
application and for all
jurisdictions in which such incorporation is permitted.
[0045] While the foregoing is directed to embodiments of the present
invention, other and
further embodiments of the invention may be devised without departing from the
basic scope
thereof, and the scope thereof is determined by the claims that follow.
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