Note: Descriptions are shown in the official language in which they were submitted.
12~ 4~
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THE ~ET~OD OF S~PPLYING SOOT-FREE PROD~CTS
FRO~ THE PARTIAL OXIDATION OF HYDROCARBON
FUEL TO THE FUEL STREAM OF THE ACR PROCESS
TECHNICAL FIELD
This invention is concerned with a process
for a~vantageously practicing the Advanced Crac~ing
Reactor ~ACR) process. Vtilizing this invention, a
fuel oil ~uch as a heavy residual fuel oil, and
preferably the atmospheric vacuum residue fractions
from tbe distillation of crude oil, is partially
o~idized to produce a gaseous mi~ture of hydroaen
and carbon monoxide ~hereinafter termed "synthesi 5
gasn) and solid materials ~uch as soot and metal
o~ides. The gaseous products are ~eparated from the
601id material6 and are ~ed to the combustion zone
of an ACR where they are mixe~ with oxygen and
steam. The gaseous products act as the fuel for
effecting the combustion reaction in the ACR. The
product~ of tbe combustion reaction are thereafter
contacted with a liquid stream of hydro¢arbon
feedstock and the combination of the two are fed
tbrough a throat portion of the ACR into the
diverging diffuser/reactor ~ection ~f tbe ACR. The
hydrocarbon feedstream i~ therein converte~ into the
desired composition of cracked product~ wbich
contains a lar~e fraction of ethylene.
BACRGRO~ND ART
U. S. Patent No. 4,134,824, to Kamm, et
al., patented January 16, 1979, describes the
integration of some of the features of the partial
o~idation process into the ACR process. In the
prGcess ~e~cr~bed by Kamm, et al., the a6phaltic
residue ~f O ~rude oil feedstock whirh supplies a
crude oil di~tillate fraction stream for the
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reaction, is fed as a fuel to the combustion step of
the ACR process. In the combustion step, the
asphaltic stream is combined with a "fluid fuel" and
o~ygen to be partially combusted in the presence of
super-beated ~team to form a reducing stream of hot
combus~ion product~. The partial combu~tion
product~ are tber~after passed through the
combustion zone and during the course of such
passage, a crude oil distillate fraction stream is
injected into the partial combustion products
stream. The combination of hot partial combustion
products and the crude oil distillate fraction flow
at high velocities througb a converging zone, the
typical throat section of the ACR reactor, into a
diverging zone in which the streams increase in
velocity an~ cracking of the crude oil distillate
frac~ion occurs. The crac~ing ste~ is followed by
~uenching and product recovery~
~ he Advanced Cracking Reactor (ACR) process
is e~plained in detail in UO S. Patent No.
4,136,015. It is described therein as involving the
production of a hot gaseou~ combustion product
stream in a first-sta~e combustion zone in the
presence of ~uper-heated steam. The hydrocarbon
feedstock to be cracked is then injected and mi~ed
with the bot gaseous combustion product ~tream.
That ~i~ture is then ~ed into a crackinq zone. T~e
effluent from the reaction zone CQntainS a stream
whicb is rich in etbylene and contains varying
concentrations of acetylene, propylene and
butadiene~ The typical ACR process will produce
hydroaen, methane, acetylene, ethylene; ethane,
propylene, propane, butenes, 1,3-butadienef butanes,
carbon monoxide, carbon dioxide methyl acetylene,
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propadiene, and similar gaseous products. Typical
liquid products are pyrolysis gasoline, benzene,
toluene, xylenes, C8non-aromatics, tars and
pitches, and tbe like.
U. S. Patent ~o. 4,134,824 describes the
utilization of the partial oxidation proces~ to
produce a product stream containing hydrogen, carbon
mono~ide, carbon dioxide, steam, sulfur compounds,
and other minor components, ~ometimes referred to as
synthesis gas. The partial oxidation reaction
mechanis~ is therein described as involving an
exothermic partial combustion of a portion of a
hydrocarbon feedstream which supplies heat to the
endothermic steam cracking of the balance of the
feed. Besides carbon mono~ide, hydrogen, carbon
dioxide, hydrogen sulfide and other trace
impurities, partial o~idation produces soot in
non-equilibrium amounts. The composition of the
products, particularly hydroqen/carbon monoxide
ratio, sulfur and soot are generally determined by
the type of feedstock, the oxygen/fuel ratio and the
amount of steam used~ The process of U. S. Pa~ent
No. 4,134,824 utilizes the asphaltic fraction of a
fuel oil as part of ~he feed to the combustion
reaction that is utilized for generating tbe
temperature necessary ~or cracklng of tbe distillate
portion of the feedstock into the desired products
of tbe cracki~g reaction, as described above.
Con6e~uently, U. S. Patet No. 4,134,824 effects in
situ in the combustion zone, a partial oxidation
reacticn to thereby generate synthesis gas which is
carried through the ACR reactor. Indeed, the
~ynthesi~ gas in U. S. Patent No. 4,134,824 is
u~ilized as a beat carrier gas for transporting the
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ACR feedstock into tbe eeaction zone and for
supplyin~ the endothermic heat of reaction.
U. S. Patent Nol 4,264,435 is essentially
the ~ame process as U. S. Patent No. 4,134,824. The
alleged diffecence in U. S. Patent No. 4,264,435
resides in the sug~estion that a substantial amount
of ~uper-heated steam which is injected into the
combustion gases allegedly effects a shift in the
reaction resulting in a product with a ~ore
desirable composition having a temperature of 1200
to 1800C. This stream is thereafter contacted with
the hydrocaebon feed in the typical ACR manner. The
process of U. S. Patent No. 4,264,435, as i~ the
case with U. S. Patent No. 4,134,824 effects the
partial o~idation reaction in situ in the combustion
zone and the synthesis gas formed thereby serves to
carry tbe heat of the combustion reaction to the
cracking reaction downstream.
~ V. S. Patent No. 4,321,131, to Lower
patent~d March 23, 1982, describes a reforming step
in which ~team is combined with a fuel and fed to a
reforming catalyst sucb as a metal catalyst of GrouP
VIII, see column, lines 30 to 37 of Lowe, and the
~yntbesi~ gas product formed is fed to the
combustion zone of the ACR reactor with oxygen in
~he presence of steam to produce the com~ustion
products stream, a~ defined previously.
In the proce~ses of Kamm, et al., U. S.
Patent Mo. 4,264,435 and the Lowe patent, one
problem reoccurs. In each of tbe~e processes, the
technology that is utilized and with which synthesis
gas formation is involved, qenerates a carbonaceous
material which in one form or another must be
t~eated during the overall oper3tion of the ACR
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processD For e~ample, in U.S. Paten~ No. 4,134,824
and V. S. Patent No. 4,264,435 processes, the
partial oxidation process within the ACR process
causes the formation of soot which will be carried
through the reactor and deposited along the cracking
reactor zone wall6. Even though the typical ~CR
process will generate some carbonaceous de~osit, the
partial oxidation process will generate an increased
concentration of sucb carbonaceous deposits and will
tbereby necessitate a greater frequency of carbon
removal treatment in order to effectively operate
the ACR process. The Lowe process on the other
band, causes steam and fuel to be reformed within a
catalytic reaction step in which there ~ill be
generated a certain amount of carbonaceous material
and such carbonaceous material, instead of going to
the ACR reaction, will fcrm within the reforming
catalyst. This will necessitate a frequent
treatment of tbe catalyst ~eds in order to restore
their activity resulting from carbon deposits which
cause~ the catalyst to be deactivated.
Another problem ~hat is associated with the
DroCesS of ~. S. Patent No. 4,264,435 and U.S.
Patent No. 4,134,824 is that by virtue of starting
with an untreated crude oil product, the combu~tion
products will con~ain ash which will eventually
contaminate the ceramic linina of the ACR reactor.
Such ash can create an acid flu~ on the wall and
could therefore result in breakaqe of the ceramic as
well as corrosion.
SUM~ARY OE THE INVENTION
-
The process o~ this invention avoids tbe
aforementioned problems which are associated with
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pa~tial oxidation in the combustion portion of the
ACR or which are effected by a reforming process
over a reformin~ catalyst.
The process of this ivention provi~es a
two-~tep process in whicb any ~aseous, liquid, or
~olid hydrocarbon fuel can under~o a partial
o~idation step whereby the synthesi~ ~as product is
phy~ically ~eparated from ~he ~oot and ash which are
generated in ~uch a way as to retain much of its
sensible heat and such synthesis gas product is
thereafter fea to the combustion zone of the ACR
process and i~ utilized as a fuel to generate the
desired heat for tbe cracking reaction. Neither
U.S. Patent No. 4,134,824 nor U. S. Patent No.
4,264,435 utilize~ ~ynthesi~ gas as a fuel for
producing the de6ired temperature of the cracking
reaction, whereas the Lowe patent does describe a
proce6s which utilizes synthesi6 gas for that
purpose.
DETAILED DESCRIPTION OF THE INVENTION
There is a substantial body of art directed
to the manufacture of ~ynthe~is gas by the partial
oxidation of bydrocarbon fuels. Illustrative of
prior art is the followin~: British Patent
1,390,590; British Patent 1,445,549; British Patent
1,458,448: U. S. Pa~ent No. 2,698,830: U. S. Patent
No. 3,705,108: U~ SO Patent No. 3,743,606: U. S.
Patent No, 3,816,332; U. S. Patent No. 3,945,942t U.
S. Patent No~ 3,989,444; U. S. Patent No. 4,081,253:
U. S. Patent ~o. 4,007,018: U. S. Patent No.
4,007,019: U. S. Patent No. 3,990,865: U. S. Patent
No. 4,318,712 and U. S. Patent No. 4,282,010 and the
like.
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These patents variously describe the
partial oxidation of a gaseous liquid or solid
hydrocarbon fuel by reaction with oxygen in the
presence of ~team at a temperature ranging from
about 800C up to 2000C, preferably at a
temperature of about 1000 to about 1~00C, more
particularly at a tempera~ure ran~ing from about
1200C to about 1600C to produce a stream which
contains carbon monoxide, bydrogen~ water and carbon
dioxide as the gaseous products and soot and ash as
the solid products. These well-known methods for
producing syntbesis gas may be used in the present
invention.
There is also a substantial body of art
directed at quenching processes. IlIusteative of
this prior art are the following: U. S. Patent No.
3,719,029, U. S. Patent No. 3,576,519, U. S. Patent
No. 3,671,198, ~. S. Patent No. 3,~85,847, U. S.
Patent No. 3,907,661, U~ S. Patent No. 4,150,716 and
the like.
Since the hydrocarbon stream has not been
treated in advance to remove sulfur products, the
gas stream that comes from the reaction also
contains hydrogen sulfide and carbonyl sulide. The
hot gaseous effluent plu~ the soot in the ash are
~ed to a se~aration system whereby tbe soot and ash
are removed from the gaseous stream. T~is can be
accomplished by a number of procedures.
In the present invention, the qaseous
effluent from the partial oxidation process passes
directly from the reaction zone to a ~uencher. It
is here that the bulk of tbe soot is removed by
dir2ct contact with this hydrocarbon quench liquid.
In this quenching step, just enou~h heat i5 removed
to stop the partial oxidation
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reaction and lower the temperature of the gaseous
fuel to a point where it can be transported and
handled by normal equipmentr
This is in contrast to the common quenching
processes for partial oxidation reactions, whereby
the temperatures of the gases are lowered
considerably further ~o that the ~ases are suitable
for other processing steps, such as acid gas removal
or compre~sion. Since the gases of the instat
invention are to be used directly for fuel, the
temperatures are lowered ~ust to the point ~hat the
gases are usable in practical equipment. Thus, the
process does not entail the energy losses and
inefficiencies tbat are part of conventional
quenching steps, and whicb waste part of the heat
produced by tbe exothermic partial oxidation
reaction.
The quenching is done most conveniently by
direct contact with a recirculating heavy
hydrocarbon quench liquid. Several ty~es of
quenching apparatus whicb are direct liquid contact
are ~nown and are in use. Quenchers in which the
quencb liquid is ~prayed into the ~as stream would
be especially suitable: those in which the gas
stream flow~ through a body of quench li~uid
(immersion quenchers) are also suitable. However,
other types of quencher wbich would also be suitable
can be conceived of, and could be used to practice
this invention.
Some procedures utilize water to extract
the solid ~oot and ash from the ~aseous stream and
other techniques utilize a hydrocarbon oil to effect
tbe same results. The advantage of utilizing a
hyarocarbon oil iE that the oil plus the soot and
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g
ash products therein may be recycled directly back
to tbe feed of`the partial oxidation step and when
water is used to effect quenching, another
separation step ~u t be introduced.
When tbe solid products are separated from
the qaseous products, ~ome heat is removed by the
quench fluid, thus lowering the temperature of the
product gase6. As little of this sensible heat as
pos~ible sbould be removed so that ~uch heat can add
to the heat production by the combustion reaction of
the ACR. Therefore, the quenching and soot
extraction is carried out in a manner such that the
qases e~it at a fairly high temperature, while still
removing the bulk of the soot.
The gaseous effluent which is taken off
from ~be ~eparation ~tep is typically a bot stream
at a temperature ranging from about 300C up to
about 1200C, preferably at a temperature from about
600C to about 1000C. That stream will contain
hydrogen, carbon monoxide, carbon dioxide, water,
hydrogen sulfide, and carbonyl sulfide. Usually,
users of synthesis gas do not want hydro~en sulfide
and carbonyl sulfide in the products of that stream
and will take steps to remove them. However, in the
~ractice of the instant invention, hydrogen sulfide
and carbonyl sulfide do not adversely affect the
operation of the ACR process. Consequently, those
products may be left in the effluent comin~ from the
soo~/ash removal step. This provides the advantage
of using a hot ~ynthesis gas ~tream as a feedstream
to the ACR combustion step. Consequently, a savings
in fuel costs and oxy~en are provided.
The ~ynthesis~gas-containing steeam whicb
is obtained from the partial oxiBation reaction is
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fed while hot to the burner of the combustlon zone of
the ACR wherein it is mixed with oxygen in an amount
sufficient to effect essentially complete combustion of
the hydrogen and carbon monoxide values within the
synthesis gas. Utilizing the ratio of one-half mole of
oxygen for each mole of hydrogen and one-half mole of
oxygen for each mole of carbon monoxide, one should
select an amount of oxygen which will leave the gas
stream with a residual amount of synthesis gas still
present.
The oxygen can be preheated to temperatures of
up to approximately 80ooc before it is fed into the ACR
combustion zone. In the typical operation of the
process of the invention, approximately 90 per cent or
more of the ~ynthesis gas is converted to combustion
products. Since the usual synthesis gas whlch will be
obtalned will contain about a one-to-one molar ratio of
hydrogen to carbon monoxide, then one will utilize
approximately one-half mole of oxygen for each mole of
synthesis gas.
The remainder of the ACR process is practiced
exactly as is descrlbed in the prior art. The feedstock
which is fed to the ACR reaction may be shrouded in
steam as described ln U.~. Patent No. 4,136,015 and U.S.
Patent No. 4,142,963. The steam can be preheated to a
temperature of 300C-1200C before i~ is fed into the
Advanced Cracking Reactor combustion zones. The
combustion product stream and the hydrocarbon feedstock
can be thereafter fed to the cracking zone (termed in
the priQr art as the diffuser/reactor zonej wherein
cracking takes place to produce the desired products of
the ACR proce~s.
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~ he con~entional ACR ic characterized in U.
S. Patent No. 4,136,015. In particular the concept
of a throated region through which the gas streams
are passed at sonic velocity to obtain ~uper-sonic
velocities in a diverging difuser/reactor zone is a
preferred ~y~tem ~or carrying out tbe ACR prccess~
_ Quenching below the reactor zone as described in U.
S. Patent No. 4,136,015 and U. S. Patent No.
4,142,963 is a preferred method of operation as well
as tbe further quenching of the product streams as
described in U. S. Patent No. 4,150,716.
The feed of hydrocarbon feedstream into the
combustion chamber to ~e admixed with the combustion
product ~tream can be carried out in an angular
direction as described in U. S. Patent No.
3,855,339, utilizing the ~team ~hroud principal
described in U. S. Patent No. 4,142.963.
In the preferrea embodiment a steam shroud
can also be injected along the diffuser/reactor
wall~ by virtue of an inlet located at about the end
of the throate~ section.
Though this invention has ~een described
witb respect to a substantial number of 6pecific
embodiment~ it is not intended that the invention
should be ~o limited.
EXAMPLES
EXAMPLE I
A partial oxidation process produces a
product gas consi6ting of 50 mole percent hydro~en
and 50 mole percent carbon monoxide. This ~aseous
fuel is burned in essentially pure oxy~en, with
a~ded steam, to produce a beat carrier for the ACR
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process. ~he temperature of the heat carrier is
2000C, and the heat carrier i5 produced at the rate
of 7.5 lb.~moles/100 lbs of feed. Oxygen is used at
95 percent of tbe stoichiometric amount.
After it~ production by partial oxidation,
the fuel gas i5 quenched and cooled to 100C and fed
to the ACR burner. Oxygen is fed to the ACR burner
at 25C and ~team at 350C. With these
temperatures, the flow rates necessary to produce
the desired heat carrier at the requisite
temperature, and the resulting composition of the
heat carrier is illustrated in Table A.
Example I indicates how fuel can be
produced for the ACR, using a partial o~idation
process under the present ~tate of the art.
EXA~PLE II
A fuel gas for the ACR process is produced
and used in an identical way to EYamPle I, e~cept
that the gas is only partially quenched to 800C.
With the fuel gas at this temperature, the flow
rates necessary to produce the desired heat carrier
at the requisite temperature and the resulting
composition of the heat carrier are illustrated in
Table A.
Example II illustrates the results that can
be achieved when practicinq the process of this
invention. By reducing the quench temperature to a
range of appro~imately 600C-1900C, less fuel and
oxygen are needed to generate a heat of eeaction
temperature of 2000C. In Example II the quench
temperatuee was 800C, and there were fuel 6a~ings
of 3.06 lbs/100 lbs feed, and a 3.12 lbs/100 lbs
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feed reduction in the amount of oxygen utilized~Not only has a significant fuel and oxygen savings
been realized, but additionally the amounts of
carbon dio~ide and carbon monoxide in the ACR
effluent have ~een reduced. This allows for ~avings
in subse~uent acid-gas removal processeC.
_,
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Tabl~ A
_ AMPLE I EXA~PLE II
Temperature of Heat Carrier2000C 2000C
~uench Temperature 100aC 800C
Flow Rates Necessary to
Produce ~eat Carrier at
2000C~
Fuel 51b/100 lbs feed)35.75 32.69
Oxygen (lb/100 lbs feed)36.44 33.32
Steam (lb/100 lbs feed)80.61 84.2
Resultinq Composition of
Heat C3 rrier:
Hydrogen llbs/100 lbs feed) 0.15 0.15
Oxygen (lbs/100 lbs feed)0.36 0.33
Carbon ~onoxide (lbs/100 lbs feed)1.18 1.01
Carbon Dioxide (lbs/100 lbs feed)50.57 46.36
~team (lbs/100 lbs feed)112.07 113.99
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