U.S. patent application number 09/923147 was filed with the patent office on 2002-04-18 for cavitation enhanced liquid atomization.
Invention is credited to Draemel, Dean C., Ho, Teh Chung, Nahas, Nicholas C..
Application Number | 20020043478 09/923147 |
Document ID | / |
Family ID | 26955079 |
Filed Date | 2002-04-18 |
United States Patent
Application |
20020043478 |
Kind Code |
A1 |
Draemel, Dean C. ; et
al. |
April 18, 2002 |
Cavitation enhanced liquid atomization
Abstract
A cavitation enhanced atomizing process comprises forming a
flowing solution of the liquid to be atomized and a lower boiling
cavitating liquid. This flowing solution is then contacted with a
pressure reducing means, at a temperature below the bubble point of
the cavitating liquid in the solution, to produce cavitation
bubbles. These bubbles comprise cavitation liquid vapor and the
bubble nucleation produces a two-phase fluid of the bubbles and
liquid solution. The two-phase fluid is passed downstream into and
through an atomizing means, such as an orifice, and into a lower
pressure atomizing zone, in which the bubbles vaporize to form a
spray of liquid droplets. The nucleated bubbles also grow in size
as the so-formed two-phase fluid passes downstream to and through
the atomizing means.
Inventors: |
Draemel, Dean C.; (Kingwood,
TX) ; Nahas, Nicholas C.; (Chatham, NJ) ; Ho,
Teh Chung; (Bridgewater, NJ) |
Correspondence
Address: |
James H. Takemoto
ExxonMobil Research and Engineering Company
P.O. Box 900
Annandale
NJ
08801-0900
US
|
Family ID: |
26955079 |
Appl. No.: |
09/923147 |
Filed: |
August 6, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09923147 |
Aug 6, 2001 |
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09579678 |
May 26, 2000 |
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09579678 |
May 26, 2000 |
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09271707 |
Mar 18, 1999 |
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6171476 |
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Current U.S.
Class: |
208/113 ;
208/121 |
Current CPC
Class: |
B01J 8/1827 20130101;
C10G 11/18 20130101; B01J 19/008 20130101 |
Class at
Publication: |
208/113 ;
208/121 |
International
Class: |
C10G 011/00 |
Claims
1. A process for atomizing a liquid FCC feed comprises: (a)
contacting a flowing fluid, under pressure and comprising a
solution of FCC feed oil and a cavitating liquid which comprises
one or more hydrocarbon liquids or fractions containing material
which boils below the boiling range of said oil feed, with a
pressure drop means to reduce the pressure of said flowing fluid
and produce nucleation of bubbles comprising vapor of said
cavitating liquid at a temperature below the bubble point of said
solution, to form a two-phase fluid comprising said bubbles and
liquid solution; (b) passing said two-phase fluid downstream into
and through an atomizing means into an atomizing zone which is at a
pressure lower than that of said fluid upstream of said atomizing
means, to atomize said fluid and form a spray comprising liquid
droplets of said feed oil, wherein said atomizing zone comprises a
cat cracking reaction zone, and (c) contacting said spray with a
particulate, hot, regenerated cracking catalyst in said reaction
zone at reaction conditions effective to catalytically crack said
feed oil and produce lower boiling hydrocarbons.
2. A process according to claim 1 wherein said bubbles also grow in
size upstream of said atomizing means.
3. A process according to claim 2 wherein said lower boiling
hydrocarbons are separated from said spent catalyst particles and
are recovered.
4. A process according to claim 3 wherein said cracking reaction
also produces spent catalyst particles, which contain strippable
hydrocarbons and coke.
5. A process according to claim 4 wherein said spent catalyst
particles are stripped in a stripping zone, to remove said
strippable hydrocarbons to produce stripped, coked catalyst
particles.
6. A process according to claim 5 wherein said stripped, coked
catalyst particles are passed into a regeneration zone, in which
they are contacted with oxygen, at conditions effective to bum off
said coke and produce said hot, regenerated catalyst particles.
7. A process according to claim 6 wherein said pressure drop
produced by said pressure reducing means is less than 50 psi.
8. A process according to claim 7 wherein at least 0.5 wt. % of
said flowing fluid is vaporized by said bubble nucleation and
subsequent liquid atomization.
9. A process according to claim 8 wherein said hot, regenerated
catalyst particles are passed into said cracking reaction zone in
which they contact said spray to catalytically crack said feed
oil.
10. A process according to claim 9 wherein said pressure reducing
means comprises at least one static mixer means.
11. A process according to claim 9 wherein said atomizing means
comprises an atomizing orifice.
12. A process according to claim 9 wherein said pressure reducing
means reduces said pressure by less than 15 psi.
13. A process according to claim 12 wherein said recovered
hydrocarbons are further processed.
14. A process comprising the steps of: (a) combining an FCC feed
having a boiling range with a liquid cavitation fluid to form a
liquid solution, the cavitation fluid having a boiling range less
than the boiling range of the FCC feed; (b) reducing the pressure
of the liquid solution an amount sufficient to produce nucleation
of bubbles, the bubbles comprising vapor of the cavitation fluid,
thereby forming a two-phase fluid; (c) flashing the cavitation
fluid in the two-phase fluid, thereby atomizing the FCC feed; (d)
contacting the atomized FCC feed with a catalytic cracking catalyst
in a reaction zone of an FCC unit.
15. A process according to claim 14 wherein the pressure of the
liquid solution is reduced less than 50 psi.
16. A process according to claim 14 wherein the pressure of the
liquid solution is reduced between about 1 and about 5 psi.
17. A process according to claim 14 wherein at least 0.5 wt % of
the liquid solution has been vaporized before entering the reaction
zone.
18. A process according to claim 14 wherein at least 1.0 wt % of
the liquid solution has been vaporized before entering the reaction
zone.
19. A process according to claim 14 wherein the pressure of the
liquid solution is reduced in a static mixer.
20. A fluid catalytic cracking process comprising the steps of: (a)
combining an FCC feed having a boiling range with a liquid
cavitation fluid to form a solution, the cavitation fluid having a
boiling range less than the boiling range of the FCC feed; (b)
reducing the pressure of the liquid solution between about 1 and
about 5 psi to form bubbles comprising vapor of the cavitation
fluid, thereby forming a two-phase fluid; (c) flashing the
cavitation fluid in the two-phase fluid, thereby atomizing the FCC
feed; (d) contacting the atomized FCC feed with a catalytic
cracking catalyst in a reaction zone of an FCC unit to produce
cracked products, vaporized cavitation fluid, and spent catalyst;
(e) separating the cracked products from the spent catalyst
particles in a separation zone; (f) stripping the spent catalyst
particles in a stripping zone to remove the strippable
hydrocarbons; (g) recovering the cracked products, strippable
hydrocarbons, and the vaporized cavitation fluid; (h) passing the
stripped, spent catalyst into a regeneration zone and contacting
the catalyst particles with an oxygen-containing gas to produce
regenerated catalyst particles; and, (i) passing the regenerated
catalyst particles to the reaction zone.
21. A process comprising the steps of: (a) combining an FCC feed
having an initial boiling point above about 232.degree. C. with a
cavitation fluid to form a solution, the cavitation fluid having a
boiling range less than about 232.degree. C.; (b) reducing the
pressure of the solution an amount sufficient to form bubbles
comprising vapor of the cavitation fluid, thereby forming a
two-phase fluid; (c) flashing the cavitation fluid in the two-phase
fluid, thereby atomizing the FCC feed; (d) contacting the atomized
FCC feed with a catalytic cracking catalyst in a reaction zone of
an FCC unit.
22. A process according to claim 14 wherein the amount of liquid
solution is from 0.1 to 10 wt. %, based on flowing fluid.
23. A process according to claim 8 wherein the amount of cavitating
liquid is from 0.1 to 10 wt. %, based on flowing fluid.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 09/579,678 filed May 26, 2000, which is a
divisional of U.S. patent application Ser. No. 09/271,707 filed
Mar. 18, 1999, now U.S. Pat. No. 6,171,476. The Examiner's
attention is also directed to co-pending U.S. patent application
Ser. No. 09/677,251 filed Oct. 2, 2000, which is a continuation of
U.S. patent application Ser. No. 09/271,707 filed Mar. 18, 1999,
now U.S. Pat. No. 6,171,476.
FIELD OF THE INVENTION
[0002] The invention relates to cavitation enhanced liquid
atomization. More particularly, the invention relates to atomizing
a fluid comprising a solution of the liquid to be atomized and a
lower boiling cavitation liquid, by contacting the fluid under
pressure and while flowing, with a pressure reducing means to
reduce the fluid pressure and thereby produce nucleation and growth
of bubbles comprising vapor of the cavitation liquid in the fluid,
at a temperature below the bubble point of the solution, and then
passing the fluid through an atomizing means into a lower pressure
atomizing zone. Bubble nucleation is induced upstream of the
atomizing means. This is useful for atomizing a hot FCC feed oil
into a catalytic cracking reaction zone, using a lower boiling
hydrocarbon as the cavitation liquid.
BACKGROUND OF THE INVENTION
[0003] Fluid atomization is well known and used in a wide variety
of applications and processes. These include, for example, aerosol
sprays, the application of pesticides and coatings, spray drying,
humidification, mixing, air conditioning, and chemical and
petroleum refinery processes. For most applications, a fluid under
pressure, with or without the assistance of an atomizing gas, is
forced through a pressure reducing orifice in an atomization
nozzle. Atomization occurs as the fluid passes through the orifice
and into the lower pressure zone downstream. The degree of
atomization is determined by the orifice size, the pressure drop
across the orifice, fluid density, viscosity, and surface tension,
etc., as is known. Atomization is increased and the droplet size is
decreased, with decreasing orifice size and increasing pressure
drop. Atomizing relatively viscous fluids at high flow rates, such
as the heavy petroleum oil feeds used in fluidized catalytic
cracking (FCC) processes, or fluid cat cracking as it is also
called, is particularly challenging. FCC is an established and
widely used process in the petroleum refining industry, primarily
for converting high boiling petroleum oils to more valuable lower
boiling products, including gasoline and middle distillates such as
kerosene, jet and diesel fuel, and heating oil. In an FCC process,
the preheated oil feed is mixed with steam or a low molecular
weight (e.g., C.sub.4-) gas under pressure, to form a two phase,
gas and liquid fluid. This fluid is passed through a
pressure-reducing orifice into a lower pressure atomization zone,
in which the gas expands and the oil is atomized, and brought into
contact with a particulate, hot cracking catalyst. The atomization
is effected primarily by the shearing action between the gas and
liquid phases, as the fluid passes through the orifice and into the
lower pressure atomization zone. The FCC riser comprises both the
feed atomization zone and the cat cracking zone. Steam is more
often used than a light hydrocarbon gas, to reduce the vapor
loading on the on the gas compression facilities and the downstream
products fractionation. However, the use of steam produces sour
water, which enhances corrosion. Sour water is also environmentally
unfriendly and must therefore be treated before disposal. There is
a need therefore, for a process that either reduces or eliminates
the amount of steam or low molecular weight gas atomizing
agents.
SUMMARY OF THE INVENTION
[0004] The invention relates to a liquid atomizing process in which
a fluid comprising a solution of the liquid to be atomized and a
lower boiling cavitation liquid, is contacted under pressure and
while flowing, with a pressure reducing means to reduce the fluid
pressure and thereby produce nucleation of bubbles comprising the
cavitation liquid vapor in the fluid, at a temperature below the
bubble point of the solution, and then passing the fluid through an
atomizing means into a lower pressure atomizing zone. Thus, the
cavitation bubbles comprise vapor of the cavitation liquid.
Nucleation of the cavitation bubbles produces a two-phase fluid
comprising the vapor bubbles and the liquid solution. While bubble
nucleation is produced upstream of the atomizing means, typically
and preferably both nucleation and growth of the cavitation bubbles
will occur upstream of the atomizing means. Growth of the
cavitation bubbles is produced by one or more pressure reducing
means and also by the pressure drop in the fluid, as it flows
downstream to the atomizing means. A continued pressure drop, even
if only slight, assists in stabilizing the bubbles. Additional
growth of the cavitation bubbles occurs as the fluid passes through
the atomizing means and into the lower pressure atomizing zone, in
which it rapidly vaporizes. Passing the so-formed two-phase fluid
through the atomizing means also produces shear between the vapor
(the cavitation bubbles) and liquid phases, which increases the
surface area of the liquid, as reflected in the formation of
ligaments, membranes, smaller globules, etc. The atomization
produces a spray of liquid droplets into the lower pressure
atomizing zone. This is explained in detail below. By pressure is
meant a low pressure reducing means, such as one or more static
mixers in the fluid line upstream of the atomizing means. By low
pressure is meant that the static mixer(s) or other pressure
reducing means produces, in the flowing fluid, a pressure drop less
than 50 psi, preferably less than 15 psi and more preferably no
greater than 5 psi upstream of the atomizing means, with a typical
pressure drop ranging from 1 to 5 psi. Cavitation is a phenomena in
which a pressure drop induces bubble formation in a liquid, at a
temperature below the bubble point of the liquid. Thus, cavitation
occurs by reducing the pressure, while maintaining a constant
temperature. This is in contrast to boiling enhanced atomization,
in which bubble nucleation is induced by increasing the temperature
of the fluid above the bubble point, while maintaining the pressure
constant. The cavitation liquid is soluble in the liquid to be
atomized at the process conditions and either has a lower boiling
point than the liquid to be atomized or contains sufficient
material boiling below the boiling range of the liquid to be
atomized, to form bubbles which grow and expand for the
atomization. Typically this means that at least 0.5 wt. %,
preferably at least 1.0 wt. %, and more preferably greater than 1.0
wt. %, of the flowing fluid or liquid which comprises liquid to be
atomized and cavitating liquid will be vaporized during the initial
bubble formation and subsequent atomization of the flowing liquid
to be atomized. The cavitating liquid is from 0.1 to 10 wt. %,
preferably 0.3 to 5.0 wt. %, more preferably 0.5 to 2.0 wt. %,
based on flowing liquid to be atomized. From 1 to 100% of the
cavitating liquid can be vaporized depending on the process
conditions. Thus, the flowing fluid or liquid produced by mixing
the cavitating liquid with the liquid to be atomized is preferably
a single phase liquid mixture or solution, as opposed to two liquid
phases or an emulsion.
[0005] The process of the invention is useful for atomizing a wide
variety of liquids, including chemical and refinery process
liquids, such as atomizing a hot FCC feed oil into a cat cracking
reaction zone, using a lower boiling hydrocarbon as the cavitation
liquid. In, for example, an FCC process, a two-phase mixture of an
FFC oil feed liquid and an atomizing agent comprising steam flows
through a feed injector which terminates at its downstream end in
an atomizing means comprising an atomizing orifice. The downstream
side of the atomizing orifice opens downstream into a spray
distributor, as is known. In the practice of the invention, a
cavitating fluid, comprising one or more lower boiling hydrocarbons
or lower boiling hydrocarbon fractions, is mixed with the hot oil
either upstream of the injector or within the injector, to form the
fluid solution which, at this point, is a liquid. The injector
typically comprises one or more conduits for flowing one or more
liquids through and terminates at its downstream end in an
atomizing means. The liquid solution of FCC feed oil and the one or
more cavitating liquids is maintained at a pressure and
temperature, such that cavitation preferably does not occur until
the flowing fluid contacts one or more pressure reducing means in
the injector, to produce a pressure drop in the fluid and thereby
induce nucleation and growth of bubbles comprising the vapor of the
cavitating fluid(s) dissolved in the hot oil. This bubble
nucleating pressure drop may be as much as one-third of the
pressure drop of the fluid through the injector and into the FCC
cat cracking zone, as an oil spray comprising droplets of the
atomized oil. The pressure drop inducing means is located upstream
of the atomizing means. Such means will preferably include one or
more static mixing means located in the fluid conduit upstream of
the atomizing means. In one embodiment, a plurality of such means
may be located in the fluid conduit so that the flowing fluid
successively contacts more than one such means as it flows
downstream to the atomizing means. This embodiment will produce
bubble nucleation and growth in the oil feed as it approaches the
atomizing means. The fluid pressure upstream of the pressure drop
means is preferably maintained sufficiently high to prevent bubble
nucleation and this means a pressure greater than the vapor
pressure or bubble nucleation pressure of the solution at the
design temperature. The pressure in the atomizing zone is greater
than the vapor pressure of the liquid to be atomized, but lower
than the vapor pressure of the cavitating fluid and preferably
sufficiently lower to further promote and ensure rapid vaporization
or flashing of the cavitating liquid to assist in forming the spray
of liquid droplets. At any given temperature, the greater the
pressure differential between the pressure in the atomizing zone
and the vapor pressure of the cavitating fluid in the atomizing
zone, the more rapid and violent will be its expansion, which
translates into a smaller average droplet size of the atomized
liquid. The atomizing orifice may comprise the upstream entrance of
a controlled expansion atomizing zone, such as the fan-shaped
distributor of the type disclosed in U.S. Pat. No. 5,173,175 which
provides a fan-shaped spray of the atomized liquid into the FCC cat
cracking reaction zone. The orifice may also comprise a shaped slot
at the end of a conduit, for providing a more or less fan-shaped
spray as disclosed, for example, in U.S. Pat. Nos. 4,784,328 and
5,289,976. Other embodiments will be explained in detail below.
[0006] The process of the invention is useful for atomizing any
liquid, including aqueous liquids as well as hydrocarbonaceous
liquids. In the case of water, for example, the cavitating liquid
may be acetone, methanol and the like. When used in connection with
an FCC cat cracking process, the practice of the invention reduces
and preferably eliminates the use of steam for feed atomization and
the concomitant sour water production, clean-up and disposal. It
also reduces and preferably eliminates the use of a hydrocarbon gas
(e.g., C.sub.1-C.sub.5) to form a two-phase fluid for atomization.
In addition, the use of the liquid phase process of the invention
eliminates the hydraulic hammering and piping vibration problems
associated with conventional gas-liquid phase fluid atomization. In
a more detailed embodiment relating to FCC feed atomization, the
invention comprises a fluid cat cracking process which comprises
the steps of:
[0007] (a) contacting a flowing fluid, under pressure and
comprising a solution of FCC feed oil and a cavitating liquid which
comprises one or more hydrocarbon liquids or fractions containing
material which boils below the boiling range of said oil feed, with
a pressure drop means to reduce the pressure of said flowing fluid
and produce nucleation of bubbles comprising vapor of said
cavitating liquid at a temperature below the bubble point of said
solution, to form a two-phase fluid comprising said bubbles and
liquid solution;
[0008] (b) passing said two-phase fluid downstream into and through
an atomizing means into an atomizing zone which is at a pressure
lower than that of said fluid upstream of said atomizing means, to
atomize said fluid and form a spray comprising liquid droplets of
said feed oil, wherein said atomizing zone comprises a cat cracking
reaction zone, and
[0009] (c) contacting said spray with a particulate, hot,
regenerated cracking catalyst in said reaction zone at reaction
conditions effective to catalytically crack said feed oil and
produce lower boiling hydrocarbons.
[0010] The lower boiling hydrocarbons produced by the cracking
reaction are separated from the spent catalyst particles, in a
separation zone, are recovered and then typically sent to further
processing, including fractionation. The cracking reaction also
produces spent catalyst particles, which contain strippable
hydrocarbons and coke, as is known. The spent catalyst particles
are stripped in a stripping zone, to remove the strippable
hydrocarbons to produce stripped, coked catalyst particles. The
stripped, coked catalyst particles are passed into a regeneration
zone, in which they are contacted with oxygen, at conditions
effective to burn off the coke and produce the hot, regenerated
catalyst particles, which are then passed back up into the reaction
zone. The reaction zone of an FCC cat cracking process usually
comprises a riser and is known as a riser reaction zone.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIGS. 1(a) and 1(b) are simplified side and plan view
schematic illustrations of an FCC feed injection unit useful in the
practice of the invention.
[0012] FIG. 2 is a graph of vapor pressure as a function of
temperature for saturated hydrocarbon cavitating fluids.
DETAILED DESCRIPTION
[0013] The fluid passing through the atomizing means, which
typically comprises an atomizing orifice, having a cross-sectional
area perpendicular to the fluid flow direction smaller that that of
the fluid flow conduit upstream, as further described below, is a
two-phase fluid comprising a gas phase and a liquid phase. The gas
phase comprises cavitation liquid vapor and the liquid phase
comprises a solution of the cavitation liquid and the liquid to be
atomized. The two-phase fluid passing through the atomizing means
may be gas-continuous or liquid-continuous, or it may be a bubbly
froth, in which it may not be known with certainty if one or both
phases are continuous. This may be further understood with
reference to, for example, an open cell sponge and a closed cell
sponge. Sponges typically have a 1:1 volumetric ratio of air to
solid. An open cell sponge is both gas (air) and solid continuous,
while a closed cell sponge is solid continuous and contains
discrete (dispersed) gas cells. In an open cell sponge, the solid
can be said to be in the form of membranes and ligaments (such as
may exist in a two-phase gas-liquid froth or foam). In a closed
cell sponge, the gas can be envisioned as in the form of a
dispersion of discrete gas globules in the solid. Some sponges fall
in-between the two, as do some two-phase fluids comprising a gas
phase and a liquid phase. It is not possible to have a sponge that
is gas continuous and not also solid continuous, but it is possible
to have a two-phase gas and liquid fluid that is gas continuous
only. Therefore, the particular morphology of the fluid as it is
passed into and through the atomizing means, may not be always
known with certainty. Irrespective of this, there must be
sufficient vapor present in the fluid entering the atomizing means,
for the shear (and any other mixing upstream of the orifice, but
downstream of the bubble nucleation) mixing to increase the kinetic
energy of the fluid, by increasing the surface area of the liquid
phase. This is reflected in reducing (i) the thickness of any
liquid membranes, (ii) the thickness and/or length of any liquid
ligaments or rivulets, and (iii) the size of any liquid globules in
the fluid, either before or during the atomization. In the practice
of the invention, it is preferred that the fluid passed through the
atomizing means, to form the spray of oil droplets, comprise mostly
cavitating fluid vapor on a volumetric basis (e.g., a volumetric
vapor to liquid ratio of at least 2:1). A single phase fluid (e.g.,
liquid) passed through the nozzle, will have its kinetic energy
increased. With a two-phase fluid comprising a vapor phase and a
liquid phase, the vapor velocity may be increased relative to the
velocity of the liquid phase, (i) in mixing zones between the
bubble nucleation and pressure drop means, (ii) when the fluid
passes through an atomizing orifice of smaller cross-section,
perpendicular to the fluid flow direction, than the fluid conduit
means upstream of the orifice (a pressure-reducing orifice). This
velocity differential between the vapor and liquid phases is
believed to result in ligamentation of the liquid, particularly
with a viscous liquid, such as a hot FCC feed oil. By ligamentation
is meant that the liquid forms elongated globules or ligaments
which are sometimes referred to as rivulets. The atomizing zone is
at a lower pressure than the pressure upstream of the atomizing
orifice. Consequently, the vapor in the fluid passing through the
atomizing orifice rapidly expands, thereby further shearing,
squeezing and dispersing the liquid ligaments and/or droplets into
the atomizing zone. Any ligaments typically break into two or more
droplets during the atomization.
[0014] Referring to FIGS. 1(a) and 1(b), an FCC feed injection unit
10 comprises a hollow, liquid feed conduit 12, through which a hot,
liquid FCC oil feed is passed from an upstream source. At the same
time, a cavitation liquid comprising a lower boiling hydrocarbon
liquid is passed down into the conduit 12 via line 14, which
intersects the conduit at the tee joint, as shown. The cavitation
liquid is injected into the flowing hot oil, with it mixes, to form
a liquid solution comprising both liquids, in the vicinity of zone
16. This mixing to form the fluid solution, is shown here as
occurring in the fluid conduit upstream of the pressure drop means
18, for the purposes of illustrating one embodiment of the
invention. However, such mixing may be achieved further upstream
and even outside of the feed injector, if desired. The pressure in
the conduit is sufficient to maintain the cavitating fluid in the
liquid state, so that the so-formed mixture is essentially all
liquid. This fluid mixture progresses downstream (from left to
right) and passes through a low pressure drop static mixer 18,
which induces bubble nucleation. The so-formed fluid mixture having
nucleated microbubbles, continues downstream in the conduit to an
atomizing orifice 22, smaller in cross-section than that of the
conduit. By cross-section is meant the cross-sectional area of the
conduit (.pi.r.sup.2 for a cylindrical conduit) and the
cross-sectional area of the atomizing orifice perpendicular to the
fluid flow direction. Preferably, the wall of the conduit
terminates into the orifice by means of an arcuate or curved
surface, 20, which converges the flowing fluid stream into the
atomizing orifice with minimal coalescence, which might otherwise
occur if the fluid impinged onto the end of the conduit. The
downstream side of atomizing orifice 20, is contiguous with, and
opens into a hollow, fan-shaped spray distributor 26 containing
cavity 24. Cavity 24 comprises the controlled expansion zone, to
create a fan-shaped spray of the atomized feed droplets. The
pressure downstream of the atomizing orifice is sufficiently lower
than the pressure on the upstream side in the conduit, for the
cavitating fluid to flash or rapidly vaporize to atomize the FCC
feed liquid into droplets in the controlled expansion atomization
zone 24. The embodiment shown, of the conduit terminating by means
of an arcuate surface into the atomizing orifice, along with the
fan-shaped controlled expansion zone, is disclosed and claimed in
U.S. Pat. No. 5,173,175. However, other atomizing orifice and
nozzle configurations may also be used, such as those disclosed,
for example, in U.S. Pat. Nos. 4,784,328 and 5,289,976 and the
like.
[0015] An important and essential feature of the invention resides
in nucleating, in the liquid to be atomized, bubbles comprising
cavitating fluid vapor by pressure drop means, and preferably
upstream of the atomizing orifice. More preferably it will be
advantageous to permit the nucleated bubbles to grow by, i.e.,
additional pressure drop inducing means upstream of the atomizing
means. The pressure drop means preferably comprises one or more
static mixers, to provide the desired bubble nucleation with a
minimal pressure drop. If the two liquids, the feed and cavitating
liquid, are merely mixed together and then passed through an
atomizing means without bubble nucleation, the bubble expansion and
vaporization will be slower and the desired degree of atomization
of the feed liquid will not be achieved. The pressure drop across
one or more static mixers upstream of the atomizing means and
concomitant agitation of the so-formed bubble containing solution,
initiates bubble nucleation and preferably bubble nucleation and
growth, so that expansion of the bubble vapor is much more rapid
across the atomizing orifice, and feed atomization is therefore
enhanced. By analogy, if a bottle of soda is opened without
agitation, foaming either does not occur or occurs slowly. If the
soda is agitated before opening, rapid and violent foaming occurs
when the bottle is opened and the pressure is released. Shaking of
the bottle allows the soda to be sprayed out as a spray or mist,
due to the rapid bubble growth across the opening where the
pressure reduction occurs. In the present invention, the reduction
in pressure and agitation produced by the upstream mixer causes
bubble nucleation just as shaking the soda, and the resulting fine
atomization of the feed can be accomplished by the subsequent
depressurizing and the cavitating mechanism described, rather than
by the two phase shearing, as with conventional atomization
nozzles. The bubble nucleating means is preferably designed and/or
selected to produce the smallest pressure drop necessary to
vaporize from 1 to 100 wt. % of the cavitating liquid to provide
bubble nucleation, with the major portion of the pressure drop
occurring across the atomization nozzle, to generate the atomized
spray.
[0016] With respect to the above illustrations and the Example
below, FCC processes are well known and need not be described in
detail here. Cat cracker feeds used in FCC processes typically
include gas oils, which are high boiling, non-residual oils, such
as a vacuum gas oil (VGO), a straight run (atmospheric) gas oil, a
light cat cracker oil (LCCO) and coker gas oils. These oils have an
initial boiling point typically above about 450.degree. F.
(232.degree. C.), and more commonly above about 662.degree. F.
(350.degree. C.), with end points up to about 1150.degree. F.
(621.degree. C.), as well as straight run or atmospheric gas oils
and coker gas oils. In addition, one or more heavy feeds having an
end boiling point above 1050.degree. F. (e.g., up to 1300.degree.
F. or more) may be blended in with the cat cracker feed. Such heavy
feeds include, for example, whole and reduced crudes, resids or
residua from atmospheric and vacuum distillation of crude oil,
asphalts and asphaltenes, tar oils and cycle oils from thermal
cracking of heavy petroleum oils, tar sand oil shale oil, coal
derived liquids, syncrudes and the like. These may be present in
the cracker feed in an amount of from about 2 to 50 volume % of the
blend, and more typically from about 5 to 30 volume %. These feeds
typically contain too high a content of undesirable components,
such as aromatics and compounds containing heteroatoms,
particularly sulfur and nitrogen. Consequently, these feeds are
often treated or upgraded to reduce the amount of undesirable
compounds by processes, such as hydrotreating, solvent extraction,
solid absorbents such as molecular sieves and the like, as is
known. Typical cat cracking conditions in an FCC process include a
temperature of from about 800-1200.degree. F. (427-648.degree. C.),
preferably 850-1150.degree. F. (454-621.degree. C.) and still more
preferably 900-1150.degree. F. (482-621.degree. C.), a pressure
between about 5-60 psig, preferably 5-40 psig with feed/catalyst
contact times between about 0.5-15 seconds, preferably about 1-5
seconds, and with a catalyst to feed ratio of about 0.5-10 and
preferably 2-8. The FCC feed is preheated to a temperature of not
more than 850.degree. F., preferably no greater than 800.degree. F.
and typically within the range of from about 600-800.degree. F.
[0017] The invention will be further understood with reference to
the examples below.
EXAMPLES
Example 1
[0018] The lower boiling cavitating fluid must be soluble in, and
compatible with, the liquid to be atomized and with any upstream
processes conditions for each specific application. By way of an
illustrative example specifically for the practice of the invention
for atomizing the liquid oil feed to an FCC unit, reference is made
to a vapor pressure graph for hydrocarbons, shown in FIG. 2. For
the purposes of this example, this graph is a simplified version of
the one disclosed by Maxwell and Bonnell, in an article titled
Derivation and Precision of a New Vapor Pressure Correlation for
Petroleum Hydrocarbons, which appeared in Industrial and
Engineering Chemistry, v.49, pages 1187-1196 (1957). The pressure
in the fluid conduit upstream of the atomizing orifice is assumed
to be 7 atmospheres and the pressure on the downstream side of the
orifice, in the atomization zone, is assumed to be 3 atmospheres.
For an upstream temperature of 750-800.degree. F., the cavitating
liquid must be a liquid at 7 atmospheres and a vapor at 3
atmospheres. This suggests that a normal boiling point between 600
and 650.degree. F. is required for the cavitating liquid, although
the nominal boiling point for this cavitating liquid would be
adjusted based on the planned treat rate, as well as considering
the boiling range and miscibility of the fluid with the process
feed. In this example, the cavitating liquid could be a distillate
fraction produced from the FCC process or it could be obtained from
another source. A blend of 1-5 wt. % of the distillate, based on
the FCC feed, will generate a two phase volume expansion of 1.7-4.3
times the liquid feed volume, with a temperature drop of between
1-7 degrees, from an adiabatic flash. If the upstream conditions
are changed to 7 atmospheres and 400-450.degree. F., the required
boiling range for the cavitating fluid is approximately
290-315.degree. F. Similarly, for differing upstream and downstream
pressures, and differing FCC feed preheat temperatures, an optimum
cavitating fluid boiling range can be defined.
Example 2
[0019] Simple comparative experiments using an aqueous acetone
solution were conducted to demonstrate cavitation-enhanced
atomization. Sharp angle orifice plates were used for the atomizing
means, which in these experiments were bores in the plates and
their length to diameter (L/D) ratios were 1.4:1 and 7:1. Both were
cylindrical bores having an inner diameter of 350 .mu.m, with the
plate thickness determining the L/D ratio. The main components of
the experimental setup were a pressure vessel, a heated liquid
hose, a monosize drop generator, and a heated air chamber purged
with flowing nitrogen at atmospheric pressure. The atomizing
pressure was measured in the pressure vessel. Images of the
break-up of the fluid exiting each orifice and spray patterns were
taken with a Greenfield Speedview 700 imaging system. Droplet
images of the sprays were taken with a CCD camera. In every case,
the orifice opened into the heated air chamber at the downstream
side. The temperature in the chamber was identical to the liquid
temperature, to minimize fluid temperature changes due to the
atomization and evaporation.
[0020] Blank experiments with water at a temperature below the
boiling point at the atomizing pressure upstream of the orifice
plate, with a pressure drop of 30 psi across the orifice, indicated
that the orifice having the greater L/D ratio of 7:1, performed
better than the shorter one having the 1.4:1 L/D ratio. However,
fine sprays could not be obtained with either L/D ratio when the
water temperature was lower than the boiling point at the atomizing
pressure. Increasing the water temperature to above its bubble
nucleation temperature resulted in a fine spray in some cases.
Thus, with the single liquid alone (water), bubble nucleation by
cavitation did not occur and the water had to be heated above its
boiling point to produce bubble nucleation.
[0021] In contrast, a similar set of runs using a solution of 6.8
mole % acetone in water resulted in cavition-induced bubble
nucleation and fine sprays, at the same 30 psi pressure drop across
the orifice having the L/D ration of 7:1. The orifice having the
L/D ratio of 1.4:1 did not produce as fine a spray. In these runs,
the temperature of the acetone solution inside the chamber was
98.degree. C., which was below the bubble point of 104.degree. C.
for this acetone solution. For the case of the short nozzle or
orifice having an L/D ratio of only 1.4:1, substantially all of the
30 psi pressure drop occurred at the exit edge of the orifice. For
the long nozzle having the L/D ratio of 7:1, a portion of the
pressure drop took place inside the nozzle. These experiments
demonstrate that, the extra pressure drop incurred in the longer
nozzle having the L/D ratio of 7:1, produced stable cavitation
bubbles inside the nozzle or orifice bore.
[0022] It is understood that various other embodiments and
modifications in the practice of the invention will be apparent to,
and can be readily made by, those skilled in the art without
departing from the scope and spirit of the invention described
above. Accordingly, it is not intended that the scope of the claims
appended hereto be limited to the exact description set forth
above, but rather that the claims be construed as encompassing all
of the features of patentable novelty which reside in the present
invention, including all the features and embodiments which would
be treated as equivalents thereof by those skilled in the art to
which the invention pertains. Thus, the invention can be combined
with processes that use preformed gas or vapor to form a two-phase
gas and liquid fluid which is contacted with one or more mixing
means to induce bubble formation of the cavitating fluid. It may
also be combined with processes that initiate bubble nucleation by
temperature increase.
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