U.S. patent application number 09/735779 was filed with the patent office on 2001-05-03 for superheating atomizing steam with hot fcc feed oil.
Invention is credited to Draemel, Dean C., Ho, Teh C., Ito, Jackson I., Schoenman, Leonard, Swan, George A..
Application Number | 20010000600 09/735779 |
Document ID | / |
Family ID | 23514753 |
Filed Date | 2001-05-03 |
United States Patent
Application |
20010000600 |
Kind Code |
A1 |
Ito, Jackson I. ; et
al. |
May 3, 2001 |
Superheating atomizing steam with hot FCC feed oil
Abstract
An atomizing gas, such as steam, and a hot fluid comprising a
hot liquid to be atomized, are passed under pressure, through
separate fluid conduits in a heat exchange means, in which the hot
liquid heats the steam to a superheat temperature, by indirect heat
exchange. The superheated steam is then injected into the hot
fluid, which comprises a two-phase fluid comprising steam and the
hot liquid, subsequent to the superheated steam injection. The
two-phase fluid is passed through an atomizing means, such as an
orifice, into a lower pressure atomizing zone, which causes the
steam to expand and atomize the liquid into a spray of liquid
droplets. The two-phase fluid is formed before or as a consequence
of the superheated steam injection and is preferably
steam-continuous when passed through the atomizing means. This
process is useful for atomizing a hot feed oil for a fluid cat
cracking (FCC) process.
Inventors: |
Ito, Jackson I.;
(Sacramento, CA) ; Schoenman, Leonard; (Citrus
Heights, CA) ; Draemel, Dean C.; (Kingwood, TX)
; Ho, Teh C.; (Bridgewater, NJ) ; Swan, George
A.; (Baton Rouge, LA) |
Correspondence
Address: |
ExxonMobil Research and Engineering Company
P. O. Box 900
Annandale
NJ
08801-0900
US
|
Family ID: |
23514753 |
Appl. No.: |
09/735779 |
Filed: |
December 13, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09735779 |
Dec 13, 2000 |
|
|
|
09383794 |
Aug 26, 1999 |
|
|
|
Current U.S.
Class: |
208/113 ;
208/153; 208/157; 239/8 |
Current CPC
Class: |
B01J 2219/00119
20130101; B01J 2219/00159 20130101; B01J 2219/00092 20130101; B01J
2219/00123 20130101; C10G 11/18 20130101; B01J 2219/00094 20130101;
B05B 7/0433 20130101; F28F 7/02 20130101; B05B 7/0483 20130101;
F28C 3/06 20130101; B01J 8/1827 20130101; F28F 13/08 20130101; B01J
19/26 20130101 |
Class at
Publication: |
208/113 ;
208/153; 208/157; 239/8 |
International
Class: |
C10G 011/00; B05D
001/00 |
Claims
What is claimed is:
1. A fluid cat cracking process which comprises the steps of: (a)
injecting steam into a flowing, hot, liquid FCC feed oil under
pressure, to form a two-phase fluid comprising said hot oil and
steam; (b) passing an atomizing gas comprising steam and said hot,
two-phase fluid formed in (a) through separate conduits in a heat
exchange means, in which said flowing hot fluid heats said steam to
a superheat temperature, by indirect heat exchange with said fluid;
(c) injecting superheated heated steam formed in (b) into said hot
fluid to increase the surface area of said liquid phase and form a
steam-continuous two-phase fluid; (d) passing said steam-continuous
fluid through an atomizing means into a lower pressure atomizing
zone to atomize said fluid and form a spray comprising droplets of
said feed oil, and (e) passing said spray into a cat cracking
reaction zone.
2. A process according to claim 1 wherein said superheated steam
formed in (b) is injected into said fluid in one or more of (i)
upstream of said means, (ii) downstream of said means and (iii) in
said means.
3. A process according to claim 2 wherein said superheated steam is
injected into said fluid at a Mach number of at least 0.5.
4. A process according to claim 3 wherein said atomizing means is
located downstream of said heat exchange means.
5. A process according to claim 4 wherein said spray is
fan-shaped.
6. A process according to claim 2 wherein said heat exchange means
includes atomizing means.
7. A process according to claim 2 wherein said heat exchange means
includes means for mixing said two-phase fluid flowing
therethrough.
8. A process according to claim 7 wherein said two-phase fluid
mixed in said heat exchange means is steam continuous.
9. A process according to claim 8 wherein said steam heated in said
heat exchange means and then injected into said fluid is at a Mach
number of at least 0.5.
10. A process according to claim 2 wherein said heat exchange means
comprises part of an FCC feed injection unit which injects said
atomized hot oil spray into said cat cracking reaction zone.
11. A liquid atomization process in which a hot fluid comprising
the liquid to be atomized flows through a heat exchange means, in
indirect heat exchange with an atomizing gas to heat said gas,
wherein said hot gas is injected into said flowing hot fluid which
comprises a hot, two-phase fluid comprising said gas and liquid,
subsequent to said gas injection, to reduce the surface area of
said liquid and assist in atomizing said liquid in said fluid into
a spray comprising drops of said liquid.
12. A process according to claim 11 wherein said two-phase fluid
comprises a gas continuous fluid, which is atomized by passing it
through an atomizing means and into a lower pressure atomizing
zone, to form said spray.
13. A process according to claim 12 wherein said fluid flowing
through said heat exchange means comprises a single liquid
phase.
14. A process according to claim 12 wherein a two-phase fluid
comprising said liquid to be atomized and said atomizing gas flows
through said heat exchange means.
15. A process according to claim 11 wherein said two-phase fluid is
formed either before injecting said heated gas into said fluid, or
as a consequence of injecting said heated gas into said fluid.
16. A process according to claim 15 wherein said two-phase fluid
comprises a gas-continuous, two-phase fluid after injecting said
hot gas into said fluid.
17. A process according to claim 15 wherein said heat exchange
means includes means for mixing said two-phase fluid flowing
therethrough.
18. A process according to claim 16 wherein said heat exchange
means includes means for mixing said two-phase fluid flowing
therethrough.
19. A process according to claim 11 wherein said gas heated in said
heat exchange means and then injected into said fluid is at a Mach
number of at least 0.5.
20. A process according to claim 16 wherein said gas heated in said
heat exchange means and then injected into said fluid is at a Mach
number of at least 0.5.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
1. This application is a continuation of U.S. patent application
Ser. No. 09/383,794 filed Aug. 26, 1999.
BACKGROUND OF THE DISCLOSURE
2. 1. Field of the Invention
3. The invention relates to liquid atomization, in which atomizing
gas is heated by indirect heat exchange with the hot liquid to be
atomized. More particularly, the invention relates to a liquid
atomization apparatus and process in which atomizing steam is
heated to a superheat temperature and a high velocity, by indirect
heat exchange with the hot liquid to be atomized. This is useful
for atomizing the hot feed oil in an FCC process.
4. 2. Background of the Invention
5. Atomizing hot, 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 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 fluid comprising the steam or gas
phase and the liquid oil phase. This fluid is passed through an
atomizing means, such as an orifice, into a lower pressure
atomizing zone, to atomize the fluid into a spray of oil droplets
which contact a particulate, hot cracking catalyst. Feed
atomization is initiated immediately downstream of the atomizing
orifice or means, and may continue into the downstream riser
reaction zone. Steam is more often used than a light hydrocarbon
gas, to reduce the vapor loading on the gas compression facilities
and the downstream products fractionation. With the trend toward
increasing the fraction of the very heavy and viscous residual oils
used in FCC feeds, more and hotter steam is needed for atomization.
However, many facilities have limited steam capacity and the steam
is typically saturated, which constrains their ability to
effectively process heavier feeds.
SUMMARY OF THE INVENTION
6. The invention relates to a fluidized cat cracking (FCC) process
in which the hot feed oil is atomized with an atomizing gas, and
wherein at least a portion of the atomizing gas has been heated by
indirect heat exchange with the hot oil feed. The heat exchange
takes place upstream of the atomizing means, in at least one heat
exchange means which may comprise, for example, a heat conductive
apparatus or body having a plurality of fluid passage means
therein, with each fluid passage means having at least one fluid
entrance and exit, to permit the gas and the hot oil to flow
separately into and through, in indirect heat exchange, during
which the hot oil heats the gas. By atomization is meant that the
liquid feed oil is formed into a spray comprising discrete and
dispersed, small drops or droplets of the oil. Atomization is
achieved by conducting the fluid through at least one atomizing
means, into a lower pressure atomizing zone. When more than one
atomizing means is used, they may be in a series or parallel flow
arrangement, preferably parallel. The heated atomizing gas
preferably comprises steam, which may or may not be in admixture
with one or more other gases, such as hydrocarbon gases and vapors.
Thus, the term "steam" as used herein is not meant to exclude the
presence of other gases in admixture with the steam. However, the
atomizing gas preferably comprises at least 95 volume % steam and
more preferably all steam. In the practice of the invention, the
steam is heated to a superheat temperature and, in a preferred
embodiment, the superheated steam exits the heat exchange means and
is injected into the flowing, hot, oily fluid at a high velocity.
By high velocity is meant a steam Mach number of preferably greater
than 0.5, more preferably greater than 0.8, and still more
preferably greater than 0.9. The hot oil flowing through the heat
exchange means may be a single-phase fluid comprising the hot feed
oil or a two-phase fluid comprising gas, as in preferably steam,
and the hot oil. Hereinafter, the term "fluid" as used herein is
meant to include both a single liquid phase, and a two-phase
mixture comprising a gas phase and a liquid phase. The superheated
steam, preferably at a high velocity, is injected into the flowing
fluid to increase the surface area of the liquid phase. Increasing
the velocity reduces the amount of steam required and increases the
kinetic energy available for increasing the liquid surface area
(e.g., e=mv.sup.2), which is ultimately manifested by smaller
droplet sizes of the atomized oil spray. The superheated steam may
be injected into the flowing hot fluid either inside, outside,
upstream or downstream of the heat exchange means. The superheated
steam injection results in either (i) a two-phase fluid comprising
the steam and hot feed oil or (ii) a two-phase fluid in which the
surface area of the liquid phase has been increased. That is, if
the hot fluid into which the steam is injected is a single-phase
liquid, injecting the steam into the liquid produces a two-phase
fluid comprising a steam phase and a liquid phase. If the fluid
into which the steam is injected is a two-phase fluid comprising
steam (or gas) and the hot liquid oil, injecting the steam into the
fluid increases the surface area of the liquid phase of the fluid.
The two-phase fluid is passed into and through an atomizing means
and into a lower pressure atomization zone, in which the steam
expands and forms a spray comprising atomized droplets of the oil.
The atomizing means typically comprises a pressure reducing and
velocity increasing orifice, as is known, but it may also comprise
a pressure reducing and velocity increasing region or zone, just
upstream of the lower pressure atomizing zone, in which the steam
expands sufficiently to form the spray of oil droplets. The
atomizing means may or may not comprise part of the heat exchange
means, as is described in detail below. If it comprises part of the
heat exchange means, it will typically be located proximate to its
fluid exit. In another embodiment, all or a portion of the
superheated steam formed in the heat exchange means may be directed
as "shock steam" into the two-phase fluid, as it exits the
atomizing means and enters the lower pressure atomizing zone, to
provide a more uniform drop size distribution of the atomized
oil.
7. In an FCC process in which at least a portion of the atomizing
steam is heated to a superheat temperature according to the
practice of the invention, the hot feed oil will typically be
injected or mixed with a portion of the atomizing steam to form the
two-phase fluid, prior to being injected with the superheated steam
produced in the heat exchange means. This will typically occur
upstream of the heat exchange means. A portion of this prior or
upstream steam may be superheated, but is more typically all
saturated steam. In one embodiment, the heat exchange means may
include atomizing means such as an orifice. In another embodiment
it will include means for mixing the two-phase fluid formed
upstream to increase the surface area of the liquid feed oil phase.
In the practice of the invention, the temperature drop incurred by
the hot oily fluid flowing through the heat exchange means, as it
heats the steam to a superheat temperature, will be typically less
than 6.degree. C. If saturated steam is passed into the heat
exchange means, then passage of the steam through this means
superheats the steam and this superheated steam is injected or
impacted into the flowing hot fluid. If superheated steam is passed
into the heat exchange means, its superheat temperature will be
increased. In either case, the superheated steam heated or formed
in the heat exchange means is directed into the flowing hot fluid
as atomizing gas. Both the heat exchange and atomizing means will
typically comprise part of a feed injection unit, which sprays the
hot, atomized oil droplets into a cat cracker reaction zone, in
which they contact hot catalyst particles which catalytically crack
the hot oil into more valuable, and generally lower boiling,
material. The injection unit will generally comprise a feed conduit
in which a steam sparger is located, to form a two-phase fluid
comprising the hot oil feed and the steam. The conduit feeds this
two-phase fluid into the heat exchange means and the superheated
steam formed in this means is injected into the flowing fluid to
increase the surface area of the liquid phase. While a single-phase
liquid fluid may be passed into the heat exchange means, in an FCC
process it will more typically be a two-phase fluid comprising
steam and the liquid feed oil. In an embodiment in which the heat
exchange means also mixes the flowing fluid, the fluid will be a
two-phase, steam-continuous fluid comprising a steam phase and the
liquid feed oil phase. In any case, a two-phase fluid is formed
before, or as a consequence of, the superheated steam injection and
is preferably steam-continuous when passed through the atomizing
means. The two-phase fluid is passed into and through atomizing
means into a lower pressure atomizing zone in which the steam
expands and the fluid is atomized to form a spray of oil droplets.
A spray distribution means or tip, is preferably used to shape the
spray of liquid droplets into the desired shape and is typically
located proximate the downstream end of the injection unit. This
spray distribution means is located downstream of the atomizing
means or its upstream entrance may comprise atomizing means.
8. In the practice of the invention, the fluid pressure upstream of
the downstream side of the atomizing means is higher than that in
the atomizing or expansion zone(s). In an FCC process, the pressure
of the fluid in the injector is above that in the atomizing zone
which, in an FCC cat cracking reaction process either comprises, or
opens into and is in direct fluid communication with, the cat
cracking reaction zone. This reaction zone typically comprises a
riser, as is known. Superheating the steam so that it is injected
into the fluid at a high velocity will produce a smaller Sauter
mean droplet diameter of the resulting atomized liquid, even with a
very low fluid pressure drop (e.g., .about.69 kPa) through the
atomizing means or orifice. Injecting high velocity steam at a Mach
number greater than 0.5 into the fluid, reduces the amount of steam
needed for atomization, without increasing the size of the atomized
liquid droplets. Vaporization of the feed in the shortest time
possible leads to greater amounts of useful crackate products. Feed
vaporization is a function of many factors, including the droplet
size of the atomized feed liquid and the shape and uniformity of
the atomized spray of liquid droplets.
9. In a broad sense, the process comprises an atomization process
in which a hot fluid, comprising the liquid to be atomized flows
through a heat exchange means, in indirect heat exchange with an
atomizing gas, to heat the gas. In the context of the invention,
the term "gas" is meant to include steam and/or any other gaseous
material suitable for use as an atomizing fluid, such as for
example, C.sub.4- hydrocarbon vapors, nitrogen and the like.
However, in an FCC process it is typically all steam. The heated
atomizing gas is injected at high velocity into the flowing hot
fluid, to assist in atomizing the liquid in the fluid, into a spray
of small droplets. As discussed, this fluid is atomized, by passing
it through at least one atomizing means, such as an orifice and
into a lower pressure atomizing zone. The fluid flowing through the
heat exchange means may be a single phase of the liquid to be
atomized or a two-phase fluid comprising the liquid and an
atomizing gas. The fluid will comprise a two-phase fluid, and most
preferably a gas-continuous, two-phase fluid, when passing through
an atomizing orifice. This two-phase fluid is formed either before
injecting the superheated steam into the fluid, or as a consequence
of the superheated steam injection. In either case, the fluid will
comprise a gas-continuous, two-phase fluid after the superheated
steam injection. The pressure in the heat exchange means and
upstream of the atomizing means is greater than that in the
downstream atomizing zone. In a more detailed embodiment with
respect to a typical FCC process, the invention comprises the steps
of:
10. (a) injecting atomizing steam into a flowing, hot, liquid FCC
feed oil under pressure, to form a two-phase fluid comprising the
hot oil and steam;
11. (b) passing steam and the hot, two-phase fluid formed in (a)
through separate conduits in a heat exchange means, in which the
flowing hot fluid heats the steam to a superheat temperature, by
indirect heat exchange with the fluid;
12. (c) injecting superheated heated steam formed in (b) into the
hot fluid to increase the surface area of the liquid phase and form
a steam-continuous two-phase fluid;
13. (d) passing the steam-continuous fluid through at least one
atomizing means into at least one lower pressure atomizing zone to
at least partially atomize said fluid and form a spray comprising
droplets of said feed oil.
14. The spray may be formed in or near a cat cracking zone, or it
may be conducted into the cat cracking reaction zone.
15. Further embodiments include: (i) contacting the spray with a
particulate, hot, regenerated cracking catalyst in the reaction
zone at reaction conditions effective to catalytically crack said
feed oil and produce lower boiling hydrocarbons and spent catalyst
particles which contain strippable hydrocarbons and coke; (ii)
separating said lower boiling hydrocarbons produced in step (e)
from said spent catalyst particles in a separation zone and
stripping said catalyst particles in a stripping zone, to remove
said strippable hydrocarbons to produce stripped, coked catalyst
particles; (iii) passing the stripped, coked catalyst particles
into a regeneration zone in which the particles are contacted with
oxygen at conditions effective to burn off the coke and produce the
hot, regenerated catalyst particles, and (iv) passing the hot,
regenerated particles into the cat cracking zone.
BRIEF DESCRIPTION OF THE DRAWINGS
16. FIG. 1 is a simplified cross-sectional, schematic side view of
an FCC feed injector employing the heat exchange means of the
invention.
17. FIGS. 2(a) and 2(b) are simplified, cross-sectional, schematic
side and plan views of an FCC feed injector of the invention, in
which the heat exchange means also mixes the two-phase fluid.
18. FIG. 3 is a view showing the steam injection ports on the
downstream outer end of the heat exchange means shown in FIG.
1.
19. FIG. 4 is a schematic of a cat cracking process useful in the
practice of the invention.
DETAILED DESCRIPTION
20. Important parameters include the mean droplet diameter and the
droplet size distribution in the atomized oil feed sprayed into the
riser reaction zone of an FCC process. Both smaller oil drop size
and a more evenly distributed oil spray pattern may influence the
oil feed vaporization rate and effective contact of the oil with
the uprising, hot cracking catalyst particles in the riser. While
not wishing to be bound, it is believed that the oil evaporation
rate is inversely proportional to the droplet diameter to a power
greater than unity. For example, a 25% reduction in the Sauter mean
oil droplet diameter will boost the oil vaporization rate by from
35-50%. Longer oil vaporization times result in lower naphtha
selectivity and higher yields of undesirable, low value thermal
reaction products, such as hydrogen, methane, ethane, coke and high
molecular weight material. Rapid vaporization of the oil feed
becomes more important as the amount of heavier material, such as
resids, reduced crudes and the like, added to the feed is
increased. In general, as the amount of heavy material in the FCC
feed is increased, the amount of gas added to the feed in the feed
injector, to form a two-phase fluid comprising the feed liquid and
gas upstream of the atomizing orifice, is increased to achieve
adequate feed atomization. For FCC feed atomization, this gas is
typically steam, the pressure drop across the atomizing orifice is
less than 0.4 MPa and the atomized feed drop size is no more than
1,000 micrometers. It is preferred to achieve lower drop sizes and
pressure drops across the orifice, such as no more than 300
micrometers and 0.2 MPa. It is also desirable to limit the amount
of the steam used for atomization, to less than 5 wt. % steam based
on the oil feed. The present invention reduces the amount of steam
required and also the Sauter mean droplet size of the atomized
oil.
21. The two-phase fluid fed into and through the atomizing means
and also into a fluid mixing means or chamber in the process of the
invention, may be gas or liquid continuous, or it may be a bubbly
froth, in which it is not 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 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 discrete gas globules
dispersed throughout the solid material. 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 heat exchange means of the invention,
is not always known with certainty. Therefore, increasing the
surface area of the liquid phase in the practice of the invention
includes (i) forming a two-phase fluid of gas (e.g., steam) and
liquid, (ii) reducing the thickness of any liquid membrane, (iii)
reducing the thickness and/or length of any liquid rivulets, and
(iv) reducing the size of any liquid globules in the fluid, either
before or during the atomization. With a two-phase fluid comprising
a gas phase and a liquid phase, the gas velocity is increased
relative to the velocity of the liquid phase in a mixing zone. This
velocity differential also occurs when the fluid passes through an
orifice or zone of smaller cross-section perpendicular to the fluid
flow direction, than the fluid passage or conduit means upstream of
the orifice or zone (a pressure-reducing and velocity increasing
orifice or zone). This velocity differential between the gas and
liquid phases results 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 rivulets. The
velocity differential is greatest during impingement mixing and
decreases during shear mixing. Thus, passing a two-phase fluid
through a pressure-reducing orifice, or impingement and/or shear
mixing it, produces a velocity differential between the gas and
liquid which results in ligamentation of the liquid and/or
dispersion of the liquid in the gas due to shearing of the liquid
into elongated ligaments and/or dispersed drops. The atomizing zone
is at a lower pressure than the pressure upstream of the atomizing
orifice. Consequently, the gas in the fluid passing through the
atomizing orifice or means rapidly expands, thereby dispersing the
liquid rivulets and/or droplets into the atomizing zone. Any
rivulets present break into two or more droplets during the
atomization. The atomizing orifice may be a discrete, readily
discernable orifice, or it may be in the form of a region or zone
of the smallest cross-sectional area upstream of the atomizing
zone. In the strictest technical sense, atomization sometimes
refers to increasing the surface area of a liquid and this occurs
when the steam or other atomizing gas is mixed with, or injected
into, the liquid to be atomized. However, in the context of the
invention, atomization means that as the fluid passes through the
atomizing orifice or zone, the liquid phase breaks up, or begins to
break up, into discrete masses in the gas phase and this continues
as the fluid continues downstream and the liquid is atomized into a
spray of droplets dispersed in the gas phase. In the embodiment in
which the superheated steam formed in the heat exchange means is
injected into the flowing liquid prior to the formation of a
two-phase fluid, the steam injection will form a two-phase
fluid.
22. Turning to FIG. 1, an FCC feed injector 10 is shown as
comprising a hollow, cylindrical conduit 12, connected at its
downstream end to heat exchange means 14 by means of flange 16,
which is fastened (preferably bolted) (not shown) to the upstream
end of the heat exchange means. The downstream or exit end of the
heat exchange means is fastened preferably bolted or welded) (not
shown) to a fan-type of atomizing means 18, via flange 20. A steam
sparger comprising a cylindrical, hollow pipe or conduit 22,
extends into the upstream end of conduit 12. Sparger 22 terminates
at its downstream end in a wall means 26, and has a plurality of
holes 24 circumferentially spaced around its outer periphery at its
downstream end portion. These holes are radially drilled through
the cylindrical wall of 22, into the interior portion of the pipe
and define the sparging zone. Hot feed oil enters conduit 12 via
feed line 28 and flows downstream, past the steam sparging holes
24, which comprise a first sparging zone, and towards heat exchange
means 14. Sparging steam is passed into and through sparger 22
until it reaches the sparging holes 24, at which point it passes
radially out into the flowing hot oil feed, to form a two-phase
fluid comprising steam and the hot oil feed. The pressure drop
through steam sparging holes 24 is typically less than 69 kPa,
resulting in relatively low sparging steam velocity. Both the
sparging steam and hot oil are at a pressure above atmospheric and
above the pressure in the downstream atomization or expansion zone.
The end wall 26 could have a diameter greater than that of conduit
22, to provide a baffle type of static mixing means at the
downstream end of the first sparging zone. In an embodiment, in
which all of the atomizing steam is injected as superheated high
velocity steam into the hot oil at the downstream end of the heat
exchange means, there is no need for an upstream sparger. The
two-phase fluid formed by the sparging steam flows towards heat
exchange means 14, which comprises a solid, heat-conducting metal,
cylindrical body having, in this embodiment, an interior
cylindrical bore 30, through which the two-phase fluid flows
towards the atomizing means 18. Heat exchange means 14 also
contains a plurality of steam passages circumferentially arranged
in the thick wall 32 of the nozzle, of which only two, are shown
for convenience. In this embodiment, each steam passage is
identical and comprises a conduit 34, having a steam entrance 36,
into which steam is passed by steam lines (not shown) indicated by
the two arrows. Alternately, one or more separate, annular
cavities, concentric with bore 30 and with each other, may be in
wall 32, with each cavity comprising a steam passage, having at
least one steam entrance and terminating in a plurality of
superheated steam exits located circumferentially around the fluid
exit of the heat exchange means. This embodiment is not shown. The
steam exits may be located in the exterior downstream end wall as
shown in FIG. 1 and in FIG. 3, or extending through and
circumferentially arrayed around the interior wall of the bore 30,
proximate the downstream end, as shown in FIG. 2. These are merely
two illustrative, but non-limiting examples, as will be appreciated
by those skilled in the art. In this embodiment, the bore 30 is
approximately of the same diameter as that of feed conduit 12, to
minimize the pressure drop of the fluid through the heat exchange
means. A plurality of baffles, tabs, or longitudinal ribs extending
radially inward from the surface of the bore, could be used to
increase the available heat transfer surface for the fluid flowing
through the heat exchange means and/or as static mixing means. In
the embodiment shown, each steam passage makes two passes through
the interior of the thick heat exchange means wall 32, parallel to
the longitudinal axis of the heat exchange means, although more or
less passes and configurations may be used, if necessary or
desired, depending on relative temperatures, flow rates, etc. In
this embodiment, the heat transfer surface for heating the steam is
determined by the length and diameter of the channel or bore. The
superheated steam produced in the heat exchange means exits at a
plurality of orifices 38 in the downstream wall 40 of the heat
exchange means and is injected into the fluid flowing out of the
heat exchange means and into cavity 42, of the atomizing means 18.
The steam is injected into the exiting fluid at an angle preferably
greater than 60.degree. to the longitudinal axis of the bore of the
heat exchange means, as shown by the two dashed arrows. In the case
where the fluid flowing through the heat exchange means is a single
phase comprising the liquid oil, the steam forms a two-phase fluid
comprising the steam and liquid oil for the subsequent atomization.
For a two-phase fluid comprising steam and liquid oil, the impact
of the hot steam into the fluid exiting the heat exchange means
increases the surface area of the liquid phase. This steam is at a
higher velocity than the upstream sparging steam. When the injected
steam is high velocity steam at a Mach number of greater than 0.5,
then it acts as shock steam which is more effective for converting
the kinetic energy to surface tension energy, as reflected in
increased surface area of the liquid phase. The convergence zone 42
of the atomizing means 18, minimizes coalescence of the dispersed
oil globules, by directing the flowing fluid into the atomizing
orifice 44. In this embodiment, the atomizing orifice 44 is
rectangular in shape, with its plane normal to the longitudinal
axis of the injector and fluid flow. In plan view (not shown) the
width of the orifice is greater than the height shown in FIG. 1.
The cross-sectional area of the plane of the atomizing orifice
opening normal to the fluid flow direction, is smaller than the
internal cross-sectional area of the feed conduit 12 and bore 30 in
heat exchange means 14, normal to the fluid flow direction. This
increases the velocity of the fluid flowing through the atomizing
orifice 44 and results in both a pressure drop across the orifice
and an increase in the velocity of the fluid flowing through, which
farther shears the fluid and initiates fluid atomization. The fluid
passes through the atomizing orifice into a lower pressure
atomizing zone 46, in which it expands and forms a spray of
dispersed liquid droplets. Atomization begins just downstream of
orifice 44 in the hollow interior 46 of atomizing tip 48 and
continues into the interior of the riser reaction zone (not shown),
into which tip 48 extends. In plan view (not shown), tip 48 is
fan-shaped, like that shown in FIG. 2(b), to produce a relatively
flat and uniform, fan-shaped spray of the atomized oil, for maximum
uniform contact of the oil with the hot, uprising regenerated
catalyst particles in the riser reaction zone. This type of
atomizing unit is known and disclosed in U.S. Pat. No. 5,173,175,
the disclosure of which is incorporated herein by reference. As an
illustrative, but non-limiting example of operation of the steam
injector of FIG. 1, preheated feed oil (with or without the
upstream or first sparger-added steam to form a two-phase fluid or
foam) for the FCC enters the injector at a temperature above
260.degree. C., with a typical flow rate ranging between 4.5 to
13.6 kg/sec. With 1.1 MPa saturated steam at 182.degree. C., the
steam flow rate into the heat exchange means will vary from 0.5 to
5 wt. % of the oil feed, or between about 0.02 to 0.7 kg/sec. Heat
exchange between the hot oil and steam flowing through the heat
exchange means will achieve from 28 to 139.degree. C. of steam
superheat, with negligible cooling of the oil (e.g., <6.degree.
C.). The multi-point injected, superheated steam impacting the hot
oil near the heat exchange means outlet, facilitates the breakup of
the oil into small diameter droplets and can be considered as
"shock" steam. In the embodiment of FIG. 1, a small fraction of the
saturated process steam (e.g., 0.1 to 1.0 wt. % of the oil) is
separately sparged into the oil upstream of the heat exchange
means, to create the steam-continuous, two phase fluid which can be
described as a "foam". In this case, the amount of superheated
steam formed in the heat exchange means and injected into the
two-phase fluid will typically comprise from 0.5 to 2.5 wt. % of
the oil feed. This is less than what would typically be required
without the superheated steam and process of the invention, to
achieve comparable oil atomization.
23. FIGS. 2(a) and 2(b) illustrate respective side and top
cross-sectional views of another embodiment of the practice of the
invention, in which the superheated steam from the heat exchange
means is injected into the fluid from inside the heat exchange
means bore, proximate the fluid exit which, in this embodiment,
comprises the atomizing orifice. Thus, an FCC feed oil injector 50,
comprises a hot feed conduit 12, steam pipe 22 with holes 24
radially drilled through it around the downstream end, for sparging
saturated steam into the incoming hot oil, a heat exchange means 52
which produces superheated steam and a combination spray
distributor and atomizing means 54, having a fan-shaped spray
distributor or tip 74. The hot oil conduit and sparger are the same
as in FIG. 1 and provide the same functions in this embodiment.
Heat exchange means 52 also comprises a heat conducting,
cylindrical metal body containing a longitudinal bore 56 within,
which is open at both ends and extends through the heat exchange
means from its upstream to its downstream end. The bore provides
the fluid flow path through the heat exchange means and has a
stream divider 58 at its upstream entrance. The interior of bore 56
is somewhat venturi-shaped, with its cross-sectional area normal to
the fluid flow direction, gradually decreasing to a minimum at the
downstream exit end. Referring to FIG. 2(a), the stream splitter 58
splits the incoming fluid into two separate streams to provide both
impingement and shear mixing in the chamber, with a minimal
pressure drop through the bore. Preferably, the two streams are
symmetrical and diametric. The downstream exit of the bore
comprises the atomizing orifice. The combination of impingement and
shear mixing in the chamber increases the surface area of the
liquid phase in the two-phase fluid flowing fluid. This surface
area increase is manifested by smaller oil droplets dispersed in
the steam continuous phase. Unlike the embodiment of FIG. 1, in
which the use of sparging steam (or comprising superheated steam
produced by the means) upstream of the heat exchange means may be
optional, in this embodiment it is particularly preferred, in order
to obtain the full benefits of the mixing in the heat exchange
means. That is, in the embodiment of FIG. 2, it is preferred that a
two-phase fluid, and most preferably a steam continuous two-phase
fluid, is passed into and through the heat exchange means 52. Two
different pairs of opposing walls form bore 56. Thus, as shown in
FIG. 2(a), the surface of identical and opposing walls 60 and 60'
is in a direction normal to the plane of the paper and convexly or
inwardly curved, with respect to the longitudinal axis of the heat
exchange means as shown. The maximum curvature is shown at the
upstream portion of the bore, with the amount of curvature
decreasing in a downstream direction. The other pair of identical
and opposing walls that define the bore are shown in FIG. 2(b) as
62 and 62'. Walls 62 and 62' are shown as slightly converging in
the downstream direction and have a surface perpendicular to he
plane of the paper. A rectangular-shaped bore 56 is formed by the
intersection of the two wall pairs, which comprises the fluid
mixing chamber, having a rectangular cross-section normal to the
longitudinal axis of the heat exchange means (parallel to the flat
fluid entrance and exits at opposite ends of the means) and overall
fluid flow direction, with the cross-sectional area of the chamber
progressively decreasing along the downstream direction, and which
form a rectangular-shaped atomizing orifice 64, at the downstream
exit end of the heat exchange means. Stream divider 58 divides the
two-phase, steam continuous fluid formed by the upstream steam
injection into the hot oil, into two diametrically symmetrical and
separate streams. The two separate streams flow into the upstream
portion of the bore where the convex curvature provides both
radially inward and axially downstream flow vectors. The radially
inward flow component imparted to the inflowing fluid forces a
portion of each stream to impinge against the other, for maximum
mixing forces, to increase the surface area of the liquid phase of
the flowing fluid. However, continued violent impingement mixing
may coalesce a portion of the now-dispersed droplets. Therefore,
the inward curvature of walls 60 and 60' continuously decreases in
the downstream flow direction, to provide primarily mild shear
mixing from friction along the walls down to the orifice 64. Fluid
mixing is maximized as the two streams first enter bore 56, but
continuously decreases in intensity as the fluid progresses
downstream through the bore. This provides a fluid having maximum
area increase of the liquid phase, with little subsequent
coalescence and a low pressure drop through the heat exchange
means. The other pair of opposing walls 62 and 62', gradually
approach each other in the downsteam direction to the orifice 64,
in order to minimize pressure loss of the fluid through the bore to
the atomizing orifice and maximize the fluid velocity through the
orifice. Only two identical steam channels 66 are shown in FIG.
2(a), for convenience, each with a steam inlet 68 and outlet 70.
These channels extend through the thick, outer metal wall portion
72, of the heat exchange means. The outlets 70 are angled acute to
the outflowing fluid and are positioned in the bore wall upstream
and proximate to the orifice 64, to impact the outflowing fluid
with the superheated, and preferably also high velocity steam, for
further reducing the droplet size of the subsequently atomized oil
spray. In the feed conduit and heat exchange means, the fluid is
under superatmospheric pressure. The riser reaction zone (not
shown), into which the downstream portion of the injector (e.g.,
the atomizing tip) protrudes, is at a lower pressure than that in
the feed injector. As the two-phase, steam continuous fluid passes
through to the downstream end of the heat exchange means, the
superheated steam is injected into the fluid as a plurality of
jets, further increasing the liquid phase surface area, to form a
more uniform spray of smaller oil droplets during fluid
atomization. The superheated steam injected into the fluid inside
the heat exchange means is at a higher pressure than the fluid.
This increases the volumetric flow rate of the fluid and
contributes to a further reduction in the droplet size of the
dispersed and ultimately atomized oily liquid. This steam is either
shock steam or shear steam, depending on whether the steam is
injected at supersonic or subsonic velocity, respectively. The
two-phase fluid passes through the rectangular atomizing orifice,
which comprises the fluid exit of the heat exchange means and the
adjacent fluid entrance of the atomizing means 54. The heat
exchange means exit and upstream entrance to the interior 76 of the
fan-shaped atomizing tip, are identical in size and shape. As
mentioned above, this orifice is rectangular in shape, with a
cross-sectional area perpendicular to the longitudinal axis of the
injector, substantially less than that of the cross-sectional area
of the fluid conduit 12 and the fluid entrance of the heat exchange
means. The spray distributor or tip 74 of the atomizing unit 54 is
fan-shaped and hollow, as shown by FIGS. 2(a) and 2(b). This
provides a fan-shaped, controlled expansion-atomization zone 76,
for injecting a flat, fan-shaped atomized spray of the small oil
droplets, into the uprising hot, regenerated catalyst particles, in
the riser reaction zone of the FCC unit. Atomizing unit 54 may be
metallurgically bonded, welded, or brazed to the heat exchange
means via flange 78. In FIG. 2(b), only two, identical steam
passages 80 are shown in the thick and otherwise solid
circumferential wall portion 72, of the heat exchange means. The
steam, which may be saturated or superheated steam, enters the
steam passages by inlet means 82, as indicated by the two
respective arrows. The steam outlets 84 are angled so as to inject
the steam at an acute angle into the flowing fluid, as indicated by
the two arrows. In this embodiment, the steam is injected into the
flowing oily fluid at a forward acute angle greater than
60.degree., to impart both a radially inward and a forward flow and
shear component to the injected steam. This maximizes the
differential steam velocity between the injected steam and the
flowing oily fluid. In yet another embodiment (not shown), the
steam shown in FIG. 2(a) could be injected at an acute angle into
the fluid in the upstream direction. In yet another embodiment (not
shown) the cross-sectional area of the bore 56 could progressively
decrease in the downstream direction and then increase. In this
case, atomization will initiate at the point or region of smallest
cross-section, which will comprise the atomization region or zone,
as opposed to a readily discernable orifice. FIG. 3 is a simplified
downstream end view of the heat exchange means 14 shown in FIG. 1,
to illustrate the plurality of superheated steam exits 38,
circumferentially arrayed around the downstream exit of the heat
exchange means. While these steam outlets are depicted as circular,
they could be rectangular slits or any other shape. The heat
exchange means of the invention can be fabricated in a number of
different ways, at the discretion of the practitioner. Thus a lost
wax or investment casting process could be employed, as well as
forging and other casting processes. The nozzle may be fabricated
of a ceramic, metal or combination thereof. Fabrication of a nozzle
using a plurality of stacked, relatively thin metal plates or
platelets, having fluid passage means therein, is known and
disclosed as useful for rocket motors and plasma torches in, for
example, U.S. Pat. Nos. 3,881,701 and 5,455,401. This fabrication
technique is also useful in fabricating nozzles of the invention.
The choice of fabrication method is left to the discretion of the
practitioner.
24. FIG. 4 is a simplified schematic of a fluid cat cracking
process used in conjunction with the feed injection method of the
invention. Turning to FIG. 4, an FCC unit 100 useful in the
practice of the invention is shown as comprising a catalytic
cracking reactor unit 112 and a regeneration unit 114. Unit 112
includes a feed riser 116, the interior of which comprises the
catalytic cracking reaction zone 118. It also includes a
vapor-catalyst disengaging zone 120 and a stripping zone 122
containing a plurality of baffles 124 within, in the form of arrays
of metal "sheds" which resemble the pitched roofs of houses. A
suitable stripping agent such as steam is introduced into the
stripping zone via line 126. The stripped, spent catalyst particles
are fed into regenerating unit 114 via transfer line 128. A
preheated FCC feed is passed via feed line 130 into a feed injector
(not shown) containing a heat exchange means of the invention,
which heats at least a portion of the dispersion steam according to
any of the embodiments of the invention. Steam, from steam line
132, is fed into the hot oil feed according to any of the
embodiments of the invention, to form a two-phase, gas continuous
mixture of the steam and hot oil which is passed through an
atomizing orifice in the injector and into the base of riser 116 as
a flat, fan-shaped spray, at feed injection point 134. The feed
injector is not shown in FIG. 5 for the sake of simplicity. In a
preferred embodiment, a plurality of feed injectors may be
circumferentially located around the feed injection area of riser
116. A preferred feed comprises a mixture of a vacuum gas oil (VGO)
and a heavy feed component, such as a resid fraction. The hot feed
is contacted with particles of hot, regenerated cracking catalyst
in the riser. This vaporizes and catalytically cracks the feed into
lighter, lower boiling fractions, including fractions in the
gasoline boiling range (typically 38-204.degree. C.), as well as
higher boiling jet fuel, diesel fuel, kerosene and the like. The
cracking catalyst is a mixture of silica and alumina containing a
zeolite molecular sieve cracking component, as is known to those
skilled in the art. The catalytic cracking reactions start when the
feed contacts the hot catalyst in the riser at feed injection point
134 and continue until the product vapors are separated from the
spent catalyst in the upper or disengaging section 120 of the cat
cracker vessel 112. The cracking reaction deposits strippable
hydrocarbonaceous material and non-strippable carbonaceous material
known as coke, to produce spent catalyst particles which must be
stripped to remove and recover the strippable hydrocarbons and then
regenerated by burning off the coke in the regenerator. Vessel 112
contains cyclones (not shown) in the disengaging section 120, which
separate both the cracked hydrocarbon product vapors and the
stripped hydrocarbons (as vapors) from the spent catalyst
particles. The hydrocarbon vapors pass up through the reactor and
are withdrawn via line 136. The hydrocarbon vapors are typically
fed into a distillation unit (not shown) which condenses the
condensable portion of the vapors into liquids and fractionates the
liquids into separate product streams. The spent catalyst particles
fall down into stripping zone 122 in which they are contacted with
a stripping medium, such as steam, which is fed into the stripping
zone via line 126 and removes, as vapors, the strippable
hydrocarbonaceous material deposited on the catalyst during the
cracking reactions. These vapors are withdrawn along with the other
product vapors via line 136. The baffles 122 disperse the catalyst
particles uniformly across the width of the stripping zone or
stripper and minimize internal refluxing or backmixing of catalyst
particles in the stripping zone. The spent, stripped catalyst
particles are removed from the bottom of the stripping zone via
transfer line 128, from which they are passed into fluidized bed
138 in regenerator 144. In the fluidized bed they are contacted
with air entering the regenerator via line 140 and some pass up
into disengaging zone 142 in the regenerator. The air oxidizes or
burns off the carbon deposits to regenerate the catalyst particles
and in so doing, heats them up to a temperature which preferably
doesn't exceed about 760.degree. C. and typically ranges from about
650-700.degree. C. Regenerator 114 also contains cyclones (not
shown) which separate the hot regenerated catalyst particles from
the gaseous combustion products which comprise mostly CO, N.sub.2,
H.sub.2O and CO.sub.2 and conveys the regenerated catalyst
particles back down into fluidized catalyst bed 138, by means of
diplegs (not shown), as is known to those skilled in the art. The
fluidized bed 138 is supported on a gas distributor grid, which is
briefly illustrated as dashed line 144. The hot, regenerated
catalyst particles in the fluidized bed overflow the weir 146
formed by the top of a funnel 148, which is connected at its bottom
to the top of a downcomer 150. The bottom of downcomer 150 turns
into a regenerated catalyst transfer line 152. The overflowing,
regenerated particles flow down through the funnel, downcomer and
into the transfer line 152 which passes them back into the riser
reaction zone 118, in which they contact the hot feed entering the
riser from the feed injector. Flue gas comprising the combustion
products referred to above is removed from the top of the
regenerator via line 154.
25. 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 (LCGO) 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 650.degree. F. (343.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
565.degree. C. (e.g., up to 705.degree. C. 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 0.14-0.52 MPa, preferably 0.14-0.38 MPa, 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 454.degree. C., preferably no greater
than 427.degree. C. and typically within the range of from about
260-427.degree. C.
26. 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. For example, although an FCC feed
injector for atomizing an FCC oil feed has been disclosed, as a
specific use of the process of the invention, the invention itself
is not intended to be so limited. The practice of the invention may
be employed with any liquid atomization process, in which it is
advantageous to heat at lest a portion of the atomizing gas or to
heat steam to a superheat temperature, by indirect heat exchange
with the liquid or fluid flowing through the heat exchange means
for any reason, including, but not limited to (i) forming a
two-phase fluid comprising the liquid to be atomized and the
atomizing gas and/or steam, and (ii) injecting the heated gas or
steam into the hot liquid or fluid for atomization.
* * * * *