Note: Descriptions are shown in the official language in which they were submitted.
L8~
BACKGROUND OF THE INVENTION
The invention is concerned with increasin~ the portion
10 of heavy petroleum crudes which can be utilized as catalytic
cracking feed stock to produce premium petroleum products,
particularly motor gasoline of high octane number, or as
high quality heavy ~uel~ The heavy ends of many crudes are
high in Conradson Carbon (sometimes reported as Ramsbottom
15 Carbon) and metals which are undesirable in catalytic cracking
feed stocks and in products such as heavy fuel. ~he present
invention provides an economically attractive method for
selectively removing and utilizing these undesirable com-
ponents from whole crudes and from the residues of atmospheric
20 and vacuum distillations, commonly called atmospheric and
vacuum residua or 'Iresids". The terms "residual stocks",
"resids" and similar terminology will be used here in a
somewhat broader sense than is usual to include any petroleum
fraction remaining after fractional distillation to remove
25 some more volatile components. In that sense "topped crude"
remaining ater distilling off gasoline and lighter is a
resid. The undesirable CC (for Conradson Carbon) and metal
bearing compounds present in the crude tend to be concen-
trated in the resids because most of them have low volatility.
30 The terms "Conradson Carbon" and "Ramsbotlom Carbon" have
reference to the two most used tests for this undesirable
c~nstituent. Some difference in numerical values by the two
tests may be found for the same sample, but generally the
test results from either are indicative of the same
35 ~haracteristic.
3~
. .
-2-
1 When catalytic cracking was irst introduced to the
petroleum industry in the 1930's the process consti~uted a
major advance in its advantages over the previous technique
for increasing the yield of motor gasoline from petroleum
5 to meet a fast growing demand for that premium product. The
catalytic process produces abundant yields of high octane
naphtha from petroleum fractions boiling above the gasoline
xange, up~ards of about 400F. Catalytic cracking has been
greatly improved by intensive research and development eforts
lO and plant capacity has expanded rapidly to a present day
status in which the catalytic cracker is the dominant unit,
the "workhorse" o~ a petroleum refinery.
As installed capacity of catalytic cracking has
increased, there has been increasing pressure to charge to
15 those units greater proportions of the crude entering the
refinary. Two very efective restraints oppose that pressure,
namely Conradson Carbon and metals content of the feed. As
these values rise, capacity and e~ficiency of the catalytic
cracker are adversely affected~
Quality of heavy fuels such as Bunker Oil and heavy
gas oil is also increasingly affected as it becomes necessary
to prepare these from crudes of high CC, metals and salt
contents.
The e~fect of higher Conradson Carbon in catal~tic
25 cracking is to increase the portion of the charge converted
to "coke" deposited on the catalyst~ As coke builds up on
the catalyst, the active surfaca of the catalyst is masked
and rendered inactive fF the d~sired conversion. It has
-3-
1 been conventional to burn off the inactivating coke with air
to "regenerate" the active surfaces, after which the catalyst
is returned in cyclic fashion to the reaction stage for contact
with and conversion of additional charge. The heat generated
5 in the burning regeneration stage is recovered and used, at
least in part, to supply heat of vaporization of the charge
and endothermic heat of the cracking reaction. The regeneratiOn
stage operates under a maximum temperature limitation to avoid
heat damage of the catalyst. Since the rate of co~e burning
10 is a function of temperature, it follows that any regeneration
stage has a limit of coke which can be burned in unit time.
As CC of the charge stock is increased, coke burning capacity
becomes a bottle-neck which forces reduction in the rate of
charging feed to the unit. This is in addition to the dis
15 advantage that part of the charge has been diverted to an
undesirable reaction product.
Metal bearing fractions CQntain~ inter alia, nickel
and vanadium which are potent catalysts for production of coke
and hydrogen. These metals, when present in.the charge, are
20 daposited on the catalyst as the molecules in which they occur
are cracked and tend to build up to levels which become very
troublesome. The adverse effects of increased coke are as
reviewed a~ove~ Excessive hydrogen also raises a bottle-neck
problem. The lighter ends o~ the cracked product, butane and
25 lighter, are processed through fractionation equipment to
separate components of value greater than fuel to furnaces,
primarily propane, butane and the olefins of like carbon
number. Hydrogen, being incondensible in the "gas plant"
occupies space as a gas in the compression and fractionation
O
- 35
~ 4~ .r
~, .
1 train and can easily overload the system when excessive
amounts are produced by high metal content catalyst, c2using
reduction in charge rate to mai~tain the FCC Unit and
auxiliaries operative.
In heavy fuels, used in stationary furnaces, turbines,
marine and large stationary diesel engines, quality is a
significant factor. ~or example, petroleum ash, particularly
vanadium and sodium, attacks furnace reractories and turbine
blades.
These problems have long been reco~nized in the art
and ma~Yexpedients have been proposed. Thermal conversions
of resids produce large quantities of solid fuel (coke) and
the pertinent processes are characterized as coking, of which
two varieties are presently practiced commercially. In
15 delayed coking, the feed is heated in a furnace and passed
to large drums maintained at 780-840F. During the long
residence time at this temperature, the charge is converted
to coke and distillate products taken off the top of the drum
for recovery of "coker gasoline", "coker gas oil" and ~as.
20 The other coking process now in use employs a fluidized bed
of coke in the form of smzll granules at about 900 to 1050F.
The resid charge undergoes conversion on the surface o~ the
coke particles during a residence time on the order of two
minutes, depositing additional coke on the surfaces of
25 particles in the fluidized bed. Coke particles are transferred
to ~ bed fluidized by air to burn some of the coke at
temperatures upwards of 1100F., thus heating the residual
coke which is then returned to the coking vessel for conversion
of additional charge~ Higher temperature coking for production
30 of olefinic products is described in Beuther, et al. Patent No.
O 2,874,092 where volatile products are pro~ptly removed from the
coking reactor to inhibit secondary reactions.
- i
1 These coking processes are known to induce extensiv~
cracking of components which would be valuable for ~CC charge,
resulting in gasoline o~ lower octane number (from thermal
cracking) tha~ would be obtained by catalytic cracking of the
5 same components. The gas oils produced are olefinic, contain-
ing significant amounts of diolefins which are prone to
degradation to coke in furnace tubes and on cracking catalysts.
It is often desirable to ~reat the gas oils Dy expensive
hydrogenation techniques before charging to catalytic cracking
10 or blending with other fractions for fuels. Co~ing does
reduce metais and Conradson Carbon, but still leaves an
inferior gas oil for charge to catalytic cracking.
Catalytic charge stock and fuel stocks may also ~e
prepared from resids by "deasphalting" in which an asphalt
15 precipitant such as liquid propane is mixed with the oil~
Metals and Conradson Carbon are drastically reduced but at
low yield o~ deasphalted oil.
Solvenk extractions and various other techniaues have
been proposed for preparation of FCC charge stock from resids.
20 Solvent extraction, in common with pxopane deasphalting,
functions by selection on chemical type, rejecting from the
charge stock the aromatic compounds which can crack to yield
high octane components of cracked napththa. Low temp~rature,
liquid phase sorption on catalytically inert silica gel is
25 proposed b~ Shuman and Brace, Oil and Gas Journal, April 6,
1353, page 113. See also U.S~ patents 2,378,531, 2,462,891
and 2,472,723
.
e~ .
~ .
The above noted patents numbered 2,462,891 (Noll) and
2,378,531 (~ecker) utilize a solid heat transfer medium to vaporize
and preheat catalytic cracking charge stock utili`zing heat from a
catalytic regenerator. The intent of those patentees is to
vaporize the total quantity of a catalytic charge stock, although
it is recognized that a heavy portion of the charge may remain in
liquid state and be converted to vaporized products of cracking
and coke by prolonged contact with the heat transfer material, a
conversion related to the coking processes earlier noted.
Patent No. 2,472,723 proposes the addition of an
adsorptive clay to the charge for a catalytic cracking process.
The clay is used on a "once-through" basis to adsorb the polynuclear
aromatic compounds which are believed to be coke precursors and
thus reduce the ~uantity of coke deposited on the active cracking
catalyst also present in the cracking zone.
It is known to use solid heat transfer agents to induce
extensive cracking of hydrocarbon charge stocks àt the high tempera-
tures and short reaction times which maximize ethylene and other
olefins in the product. An example of such teachings is patent
3,074,878 to Pappas.
S~MMARY OF THE INVENTION
.
According to the present invention, there is now provided
in a selective vaporization process for decarbonizing and demetal-
lizing heavy petroleum fractions by contacting such fraction and
an inert gas for reduction of hydrocarbon partial pressure with a
~inely divided inert solid contact matexial at low cracking
severity conditions o~ high temperature and short hydrocarbon
-- 6 --
residence time in a confined column, separa-ting vaporous products
of said contac-tin~ from said contact material bearing a combustible
deposit of unvaporized high Conradson Carbon or high metal content
constituents of said petroleum fraction, cooling said vaporous
products to a temperature below that at which subs-tantial thermal
cracking occurs, contacting said separated contact material wi-th
an oxidizing gas to burn said combus-tible deposit and heat the
contac-t material -to high temperature and returning -the so heated
contact material -to the lower portion of said confined column for
renewed contact with said heavy petroleum fraction; the improvement
providing flexibility in rate of charging said fraction, or in
control of said residence time or both which comprises establishing
a rising confined column of said solid contact material in said
inert gas at the lower portion of said confined column, reversing
the direction of flow of said confined column and discharging the
same as a downwardly flowing stream into an enlarged separation
zone for conduct of the aforesaid separation of said va orous
products from said contact material, injecting said heavy petroleum
fraction to a point in said column at or downstream of said lower
portion and preferably varying the said point of injection to vary
the said residence time.
In another aspect, there is provided an apparatus for
selective vaporization of a heavy pet~oleum fraction comprising a
riser contactor in the form of a vertical conduit having a reverse
bend at the upper portion to provide a downwardly directed dis-
charge opening, a hot solids standpipe connected to the bottom of
said riser contactor for supply thereto of finely divided hot inert
- 6a -
,
., ,
solid contact material, means to supply an inert carrier gas to
tlle bottom of said riser contactor to suspend said solid contact
material in a rising confined column of gases and contact material
in said riser contactor, a plurality of injection means for the
introduction of a heavy petroleum fraction to said riser contactor
spaced at different downstream points along s,aid riser contactor,
an enlarged separation vessel surrounding said downwardly directed
discharge opening for separation of vapors from solid contact
material bearing a combustible deposit, a burner, means to transfer
the so separated solid contact material -to said burner, air inlet
means to said burner for supply of air thereto for combustion of
said combustible deposit whereby the temperature of said solid
contact material is increased and means, to transfer the so heated
contact material from said burner to the said hot solids standpipe.
- 6b -
--7--
~.
1 Briefly, the selective va~orization process is
conducted by contacting a heavy charge stock such as whole
crudes, topped crudes, resids and the like with an inert,
finely divide~ solid material in a confined vertical
5 column under conditions to deposit heavy components of high
f-~ 'CC and/or metal content on the solid and vaporize other
components of the charge. This results from temperatures
high enough to cause the desired vaporization and ve~y short
hydrocarbon residence times to avoid substantial cracking.
10 The operation is thus held to a low crac~ing severity to
accomplish the desired purpose of separating vaporizable,
more valuable components from those which are regarded as
contaminants. Steam, light hydrocarbons or the li};e are
added to the rising confined column in the selective
15 vaporization facility to reduce partial pressure of hydro-
carbons in the charge and thus aid in vaporization.
Vaporous hydrocarbons are separated at the top of
the column from inert solids bearing the unvaporized
components as a deposit thereon. The vapors are promptly
20 cooled to a temperature belo~ that at which substantial
thermal cracklng occurs and processed as desired in a
eatalytic cracker or the like.
According to certain embodiments of the inventlon~ the
eontact is conducted in a riser. In other e~bodiments, a rising
25 column of inert solids in steam, hydrocarbon gases or both is
established and the direction of flow i5 reversed to a confined
descending column into which the charge is injected.
~ The separated inert solids bearing the deposit of un-
vaporized components of the charge are transferred to a burner
30 for combustion of the deposit in air or other oxygen containing
gas. Heat generated by combustion of the deposit raises the
temperature of the inert solids ~hich are then retur~ed ~o the
lower portion of the rising ~on~i~ed column to supply the heat
for selective vaporization of a~ditional heavy charge.
- 8 -
The present :lnvention provides a process and an apparatus
for varying the hydrocarbon residence time in the confined column
which defines the contactor in which selective vaporizatlon is
conducted. That result is accomplished by providing a plurality of
points for injection of charge stock to the selective vaporization
contactor to compensate for changes in quantity or quality of feed stock.
DESCRIPTION OF THE DRAWINGS
Apparatus suited to practice of the invention is illustrated
diagrammatically in Figure 1 of the annexed drawings. Figure 2
represents an embodiment in which the charge is injected to a
descending column produced by reversing direction of flow of a stream
of suspended inert solids which is initially established as a rising
column.
- 9 - ~
DESCRIPTION OF SPECIFIC EMBODIMENTS
As shown in Figure 1, the principal vessels used are a
riser 1 for conducting the short time, high tempexature contact between
hot inert solids and charge stock which terminates in a disengaging
chamber 2 from which inert solids bearing a deposit of unvaporized
material are transferred to a burner 3 by standpipe 4. The hot inert
solids resulting from combustion in burner 3 are returned to the
base of riser 1 by a standpipe 5 through a control valve 6.
A charge stock containing high boiling components which are
characterized by high CC, metals content or both is admitted to the
riser 1 by line 7 to rise at high velocity in riser 1 while in intimate
contact with the hot inert solids from standpipe 5. The major portion
of the charge stock is vaporized at the temperature prevailing in the
riser by reason of the hot solids from standpipe 5. That vaporization
;5 is extremely rapid to result in a rapidly rising column of vapor with
hot inert solids suspended therein. The portions of the charge which
are not vaporized coalesce on the inert solids to provide a combustible
deposit constituted primarily by feed stock components of high CC and
metals content.
The solids are separated from the vaporous hydrocarbons
at the top of riser 1 by any of the systems developed for the same
purpose ~n the well-known FCC process for riser cracking of hydro-
carbons in the presence of an active cracking catalyst. A system
of preference in the present invention is the vented riser described
in Meyers et al U. S. patents 4,066,533 and ~,070,1~9. The upper
end of riser 1 i.s open whereby inertia of the suspended solids causes
them to be projected into the vessel 2. Vapors leave the riser
~,
2~
,j . ~. 1
.
-10-
l through a side vent in the riser to cyclone sepa.rator 8 where
solids still suspended in the vapors are removed and discharged
by dip leg 9 to the lower portion of vessel 2. The solids
projected from the top of riser 2 ànd those from dip leg 9
5 pass downwardly to a stripper lO where steam from line ll
aids in vaporization of any remaining volatile hydrocarbons
before the solids bearing combustible deposit enter standpipe
4 for transfer to burner 3.
The vapors separated from entrained solids in cyclone
lO 8 pass by conduit 12 to transfer line 13 where the vapors are
cooled to a t~m.perature below that at which substantial
t~.e~mal cracking occurs as by mixture with a suitable quench
medium such as a cold hydrocarbon stream or water.
The burner 3 may be any of the various structures
15 developed for burning of combustible deposits from finely
divided solids, for example, the regenerators for Fluid
Cracking Catalyst. Air admitted to the burner 3 by line 15
provides the oxygen for combustion of the deposit on the
inert solid, resulting in gaseous products of combustion
20 discharged by flue gas outlet 16~ The burner 3 is preferably
operated to maintain the temperature in the burner at
the maximum value, usually limited by metallurgy of the burner.
This is accomplished by controlling temperature of the riser 1
to the minimum temperature which will provide the amount of
25 fuel (as deposit on the inert solids) which will sustain the
maximum temperature of the burner. As is common in heat
- balanced FCC Units, valve 6 is controlled responsive to the
temperature at the top of riser 1 in a manner to maintain the
riser temperature at a preset value. That preset temperature
30 is reset as needed in selective vaporization to maintain a
L026
~ , , ~
--11--
1 desired maximum temperature in burner 3. A trend to lower
temperature in burner 3 is compen~ated by reduction of the
preset temperature of riser 1, and vice versa. Inert solids
heated by the combustion in burner 3 are stripped with steam
5 in the burner 3 or the standpipe 5 before being returned to
riser 1.
The solid contacting agent is e~sentially inert in
the sense that it induces minimal cracking of heavy hydro-
carbons by the standard microactivity test conducted by
10 measurement of amount of gas oil converted to gas, gasoline
and coke by contact with the solid in a fixed bed. Charge
in that test is 0.8 grams of mid-Continent gas oil of 27 ~PI
contacted with 4 grams of catalyst during 48 second oil
delivery time at 910F. This results in a catalyst to oil
15 ratio of 5 at weight hourly space velocity ~WHSV~ of 15.
By that test, ~he solid here employed exhibits a microactivity
less ~han 20, preferably about 10. A preferred solid is
microspheres of calcined kaolin clay. Othex suitable inert
solids include, in ~eneral~ an~ s~lid which satisfies the
20 ~ta~ed cr~teria,
The microspheres of calcined kaolin clay preferably
used in the process of the invention are known in the art and
are employed as a chemical reactant with a sodium hydroxide
solution in the manufacture of fluid zeolitic cracki~g
25 catalysts as descri~ed in U.S. 3,647,718 to Haden et al. In
practice o the instant inventionO in contrast, the micro-
spheres of calcined kaolin clay are not used as a chemical
reactant. Thus the chemical composition of the microspheres
of calcined clay used in practice of this invention corresponds
30 to that of a dehydrated kaolin cla~. Typically, the calcined
~ -12-
r
1 microspheres analyze about 51~ to 53% (wt~) sio2, 41 to 45%
A12O3, and from 0 to 1~ H2O, the balance being minor amounts
of indigenous impurities, notably iron, titar.ium and alkaline
earth metals. Generally, iron content (expressed as Fe203)
5 is about 1~2% by weight and titanium ~expressed as Tio2)
is approximately 2%.
The microspheres are preferabl~ produced by spray
drying an aqueous suspension of kaolin clay~ The ~erm "kaolin
clay" as used herein embraces clays, the predominating mineral
lO constituent of which kaolinite, halloysite~ nacrite, dickite,
anauxite and mixtures thereof. Preferably a fine particle
size plastic hydrated clay~ i.e., a clay containing a sub-
stantial amount of submicron size particles, is used in order
~ to produce microspheres having adequate mechanical strengthO
While it is preferable in some cases to calcine the
microspheres at temperatures in the range of abou~ 1600F.
to 2100F. in order to produce particles of maximum hardness,
it is possible to dehydrate the microspheres by calcination
at lower temperatures, for example, temperatures in the range
20 Of 1000F~ to 1600F., thereby converting the clay into the
material known as "metakaolin". After calcination the micro-
- spher~s should be cooled and fractionated, i~ necessary, to
recover the portion which is in the desired si~e range, say
20-150 microns.
Pore volume of the microspheres will vary slightly
with the calcination temperature and duration of calcination.
Pore size distribution analysis of a representative sample
obtained with a Desorpta analyzer using nitrogen desorption
indicates that most of the pores have diameters in the range
3O of 150 to 600 Angstrom units.
~ -13- 1
- 1 The surface area of the calcined microspheres is
usually within the range of 10 to 15 m2/g. as measured by
the well-known B.E.T. method using nitrogen absorption. It
is noted that the sùrface areas of commercial fluid zeolitic
5 catalysts is considerably higher, generally exceeding values
of 100 m /g. as measured by the B.E.T. method.
Although the system just described bears superficia
resemblance to an FCC Unit, its operation is very differcnt
~rom FCC. Most importantly, the riser contactor 1 is
10 operated to remove from the charge an amount not gre2tly in
excess of the Conradson Carbon number of the feed. This
contrasts with normal FCC "conversion" o~ 50~70ga~ measured
as the percent2ge of FCC product not boiling within the range
of the charge. Percent removed by the present process is pre-
15 ferably on the order of 10% to 20~ on charge and constituted bygas, gasoline and deposit on the solid contacting agent. Rarely
will the amount removed as gas, gasoline a~d deposit on the in-
ert sQlid exceed a Yalue, by wei~ht, more ~n 3 to 4 tir~es the
Conradson Car~on value of th~ charge. This result is achieved
20 by a very low severity of cracking due to inert character
of the solid and the very short residence time at cracking
temperature. As is well knot~ cracking severity is a function
of time and temperature. Increased temperature may be
compensated by reduced residence time, and vice versa.
The new process affords a control aspect not
~ available to FCC Units in the supply of hydrocarkons or
steam to the riser contactor. When processing stocks of
high CC, the burner temperature will tend to rise because of
increased supply of fuel to the burner. This may be compen-
O
- 35 -
-14-
1 sated ~y increasing the hydrocarbons or steam supplied to
reduce partial pressure of hydrocarbons in the riser contac-
tor or by recycling water from the overhead recei~er to be
vaporized in the riser to produce steam.
The riser contact with inert solid thus provides a
novel sorption technique for removing the polynuclear aromatic
compounds of resids (high CC and metals) while these are
carried in a stream of low hydrocarbon partial pressure by
reason of hydrocarbons or steam supplied to the riser.
The decarbonized, desalted and/or demetallized resid
is good quality FCC charge stock and may be transferred to
the feed line of an FCC reactor operated in the conventional
- manner.
It is found that the nature of the selective vaDor-
15 izatio~ is a function of temperature, total pressure, par~i.al
pressure of hydrocarbon vapors 7 residence time, charge stoc~
and the li}~e. One effect of temperature is a tendency to
decrease the combustible deposit on the contact material
as contact temperature is increased. Thus greater portions
20 of the charge are vapori3ed at higher temperatures and ~he
secondary effect of thermal cracking of deposited hydrocarbons
increases at higher temperatures. These effects o~ higher
temperature enhance the yield of product from the operation
and reduce the fuel supplied to the combustion zone i~ the form
25 of,combustible deposit.
In general, the temperature of selective vaporization
will be above the averaye boiling point of the charge stoc~,
calculated as the sum of the 10~ to 90% points by ASTM
distillation of the charge divided by nine. For the heavy
30 stocks contemplated by the invention, the contact temperature
35 '-
.
- 15 ~ 6
will usually be not substantially below 900F. and will be below the
temperatures at which severe cracking occurs to produce large yields
of olefins. Thus even at residence times as short as 0.1 second or
less, selective vaporization temperatures will be below about 1050F.
Residence time for selective vaporization is not accurately
calculated by the methods generally used in FCC cracking where the
volume of vapors increases to a major extent as the hydrocarbons remain
in contact with an active cracking catalyst along the length of a
riser. In selective vaporization, the vapors are quickly generated
on contact wlth the hot inert solid and remain substantially constant
in composition along the length of the riser, increasing slightly with
modest thermal cracking believed to be cracking of the deposit on the
inert solid. Residence time of hydrocarbons in selective vaporization
is therefore calculated with reasonable accuracy as the length of the
riser from point of hydrocarbon injection to point of disengagement
from inert solids divided by superficial velocity of vapors (hydro-
carbons, steam, etc.) at the top of the riser. So calculated,
hydrocarbon residence time in selective vaporization will be not
substantially greater than about 3 seconds and is preferably much
shorter, one second or less, such as 0.1 second. As previously
indicated, residence time and temperature will be correlated to
provide conditions of low cracking severity. The quantity removed
from the charge is very nearly equal to CC value of the charge when
operating under preferred conditions and will rarely exceed a value
3 to 4 times the CC of the charge. Further, the hydrogen content
of the deposit is about 3% to 6%, below the 7-8% normal in FCC coke.
~.
-16~ ~
1 The invention provides a rle~ns to vary h~drocarbon
residence time while maintaining charge rate constant or to
maintain a constant residence time at reduced charge rate.
It will be apparent that the invention also provides other
5 flexibilities for the process, i.e., residence times and/or
charge rates may be varied without holding either at constant
levels.
That effect results from use of a riser 1 which has
multiple injection points along the length thereof. When
lO hydrocarbon feed is inje~cted at a point above the bottom of
the riser, an inert gas is injected at the bottom o the riser
to carry the inert solids upwardly to the region of hydrocarbon
injection. That inert gas also serves the function of
reducing hydrocarbon partia~ pressure above the point of
15 hydrocar~on injection, thus promoting selective vaporization.
The inert gas is preferably supplied as stèam or ~ater but
may ~e any gas which will not undergo substantial reaction
at the conditions prevailing in the riser. Thus the process
may use nitrogen as the lift gas or may use a hydrocarbon
~O which will not undergo substantial thermal cracking at the
riser conditions. Methane and other light hydrocarbons which
boil below about 450F. are preferred examples of such
materialsv
As shown in Figure 1, the riser 1 is provided with
25 injection means to supply charge from valved lines 17 and 18
which may be convaniently spaced at 25~ and 50% of the height
of riser 1, respectively. In a riser so modified, injection
line 7 at the ~ottom of the riser is provided with valved
lines 19 and 20 for supply of steam or other recycle materials
3O such as sour water, recvcle gas or hydrocarbon liquids to the
bottom of riser 1 ~lith or without hydrocarbon char~e stock.
'
.
.
26
1 In the embodiment of Figure 2 the flow in riser
contactor 1 is reversed to enter the vessel 2 by downward flow
through the top of vessel 1. Various structures for that pur-
pose have been designed for parallel use in the FCC process,
5 such as cyclone separators as generally discussed in column 4,
lines 42-59 of the above-cited Myers, et al. Patent 4,070,159.
As shown in Figure 2, a column of rising hot inert solids is
established in riser contactor 1 by injecting steam, liquid
water, recycle gas or stable light hydrocarbon liquid to the
10 bottom of the riser by line 7 to mix with and suspend hot
inert solids added by standpipe 5 from the burner. Charge
residual fractions may be added at points along riser 1 from
lines 17 and 18 as in Figure 1. At the highest point of
riser 1, flow is directed horizontally through portion 23 of
15 the contactor and then downwardly throush vertical section 24
to the open end of the contactor with diversion of vapors
to cyclones 8.
Significant advantages are realized by adding some
or all of the charge to the upper end of contactor section 24.
20 Extremely short contact times charac-terize this embodiment.
In addition, the force of gravity on the inert solid does not
induce the i'slippage" which causes the inert solid to have a
longer residence time in the contactor than does the hydrocar-
bon vapor generated by contact o~ charge stock with hot inert
25 solids in the embodiment o Figure 1. With some types of
residual fractions, it will be found that hest results are
achieved by injecting the total charge by line 25 to the
downwardly directed section 24 of the contactor 1. In that
type of operation, the xiser portion of the con~actor serves
30 to establish the suspension of hot inert solids in the gaseous
medi~m which also acts to reduce partial pressure of hydrocar-
bon vapors produced by contacting the residual fraction charge
with hot inert solids.
. . . _
, q `-18~ 26
1 This system allows the operator increased 1exibility
in the conduct of selective vaporization. Taken with the
flexibility inherent in ability to vary the ratio between
charge and steam, a unit can be operated over a wide range
5 of charge stocks and residence time to adapt the operation
to changes in quantity and/or quality of charge available.
. .,
..
~ .
.
_
