Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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1 BACKGROUND ~ THE INVENTION
The invention is concerned with increasing the portion
of heavy petroleum crudes which can be utilized as catalytic
cracking feedstock to produce premium petroleum products, partic-
ularly motor gasoline of high octane number. The heavy ends of
many crudes are high in Conradson Carbon and metals which are
undesirable in catalytic cracking feedstocks. The present invention
provides an economically attractive method for selectively removing
and utilizing these undesirable components from the residues of
atmospheric and vacuum distillations, commonly called atmospheric
and vacuum residua or "resids." The undesirable CC (for Conradson
Carbon) and metal bearing compounds present in the crude tend to
be concentrated in the resids because most of them are of high
boiling point.
When catalytic cracking was first introduced to the petroleum
industry in the 1930's, the process constituted a major advance in
its advantages over the previous technique for increasing the yield
of motor gasoline from petroleum 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 range, upwards of about 400F. Catalytic cracking has
been greatly improved by intensive research and development efforts
and plant capacity has expanded rapidly to a present-day status in
which the catalytic cracker is the dominant unit, the workhorse"
of a petroleum refinery.
As installed capacity of catalytic cracking has increased
there has been increasing pressure to charge to those units greater
proportions of the crude entering the refinery. Two very effective
restraints oppose that pressure, namely Conradson Carbon and metals
content of the feed. As these values rise, capacity and efficiency
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1 of the catalytic cracker are adversely affected.
The effect of higher Conradson Carbon is to increase the
portion of the charge converted to "coke" deposited on the catalyst.
As coke builds up on the catalyst, the active surface of the
catalyst is masked and rendered inactive for the desired conversion.
It has 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 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 coke burning 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 bottleneck which forces reduction
in the rate of charging feed to the unit. This is an addition to
the disadvantage that part of the charge has been diverted to an
undesirable reaction product.
Metal bearing fractions contain, inter alia, nickel and
vanadium which are potent catalysts for production of coke and
hydrogen. These metals, when present in the charge, are deposited
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 above. The
lighter ends of the cracked product, butane and 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
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1 in the gas plant," occupies space as a gas in the compression and
fractionation train and can easily overload the system when excessive
amounts are produced by high metal content catalyst, causing
reduction in charge rate to maintain the FCC unit and auxiliaries
operative.
These problems have long been recognized in the art and
many expedients 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 delayed coking, the feed is
heated in a furnace and passed to large drums maintained at 780
to 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 gas. The other coking process now in use employs a fluidized
bed of coke in the form of small granules at about 900 to 1050F.
The resid charge undergoes conversion on the surface of the coke
particles during a residence time on the order of two minutes,
depositing additional coke on the surfaces of particles in the
fluidized bed. Coke particles are transferred to a 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.
These coking processes are known to induce extensive
cracking of components which would be valuable for FCC charge,
resulting in gasoline of lower octane number (from thermal cracking)
than would be obtained by catalytic cracking of the same components.
The gas oils produced are olefinic, containing significant amounts
of diolefins which are prone to degradation to coke in furnace tubes
and on cracking catalysts. It is often desirable to treat the gas
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oils by expensive hydrogenation techniques before charging to
catalytic cracking. Coking does reduce metals and Conradson
Carbon but still leaves an inferior gas oil for charge to
catalytic cracking.
Catalytic charge stock may also be prepared by resids by
"deasphalting" in which an asphalt precipitant such as liquid
propane is mixed with the oil. Metals and Conradson Carbon are
drastically reduced but at low yield of deasphalted oil.
Solvent extractions and various other techniques have
been proposed for preparation of FCC charge stock from resids.
Solvent extraction, in common with propane 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 naphtha. Low temperature, liquid phase sorption on
catalytically inert silica gel is proposed by Shuman and Brace,
OIL AND GAS JOURNAL, April 16, 1953, page 113.
SUMMARY OF THE INVENTION
According to the present invention; there is provided a
process for upgrading a petroleum charge which contains high
boiling components of substantial Conradson Carbon number which
comprises contacting said charge in a confined vertical column
with a finely divided solid contact material consisting essential-
ly of an inert solid material having a microactivity for catalytic
cracking not substantially greater than 20 at low severity, at
a temperature of at least about 900F. and for a period of time
less than that which induces substantial thermal cracking of said
charge, at the end of said period of time separating from said
inert solid a decarbonized hydrocarbon fraction of reduced
Conradson Carbon number as compared with said charge and reducing
the temperature of said separated decarbonized hydrocarbon
fraction to a level below that at which substantial thermal
cracking takes place to terminate said period of time.
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Furthermore, the invention provides a process for
preparing premium products from crude petroleum by fractionally
distilling the crude petroleum to separate gasoline and distil-
late gas oil from a residual fraction having high boiling
components of substantial Conradson Carbon number and charging
the distillate gas oil to catalytic cracking; the improvement
which comprises upgrading said residual fraction by contacting
said residual fraction in a confined vertical column with an
inert solid material having a microactivity for catalytic crack-
ing not substantially greater than 20 at low severity, at atemperature of at least about 900F. for a period of time less
than two seconds and less than that which induces substantial
thermal cracking of said residual fraction, at the end of said
period of time separating from said inert solid material a
decarbonized residual hydrocarbon fraction of reduced Conradson
Carbon number as compared with said residual fraction, and
reducing the temperature of the said separated decarbonized
residual fraction to a level below that at which substantial
thermal cracking takes place, said decarbonized residual fraction
then being added to said distillate gas oil as additional charge
to said catalytic cracking.
Thus, a resid may be contacted with an inert solid of
low surface area but finely divided at temperatures above about
900F. for very short residence times of two seconds or less,
more preferably less than 0.5 seconds. The separated oil may be
quenched below cracking temperature as rapidly as possible. The
necessary short residence time is conveniently achieved by supply
of the solid in a size of about 20 to 150 microns particle
diameter mixed with the resid charge in a riser. The oil is
introduced at a temperature below thermal cracking temperature in
admixture with steam and/or water to reduce partial pressure of
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volatile components of the charge. The catalytically inert solid
is preferably supplied to a rising column of charge at a
temperature and in an amount such that the mixture is at a
temperature upwards of 900F. to 1050F. and higher,
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1 sufficient to vaporize most of the charge.
At the top of the riser the solid is rapidly separated
from oil vapors and the latter are quenched to temperatures at
which thermal cracking is essentially arrested. During the
course of this very short contact, the heavy components of high
Conradson Carbon value containing the majority of the metal content
are laid down on the solid particles. This deposition may be a
coalescing of liquid droplets, adsorption, condensation or some
combination of these mechanisms. In any event, there appears to ~ ;
be little or no conversion of a chemical nature. Particularly,
thermal cracking is minimal. The quantity removed from the charge
under preferred conditions is very nearly that indicated by
Conradson Carbon of the resid charged. Further, the hydrogen content
of the deposit on the solids is believed to be about 6%, below
the 7 to 8% normal in FCC coke.
The solids, now bearing deposits of the high CC and metals
components of the resid, are then contacted with air, for example,
by any of the techniques suited to regeneration of FCC catalyst,
; preferably under conditions of full CO combustion to less than 1000
p.p.m. CO in the flue gas. Combustion of the deposited material
from the inert solids generates the heat required in the contacting
step when the inert solid is returned to the riser.
DESCRIPTION OF THE DRAWINGS
A system for preparing charge stock to an FCC unit is
shown in the single figure of the annexed drawing.
DESCRIPTION OF PREFERRED EMBODIMENTS
The decarbonizing, demetallizing step which characterizes
the present invention is preferably conducted in a contacter very
similar in construction and operation to riser reactors employed in
modern FCC units. Typically a resid feed, either a vacuum resid
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1 boiling above 900F. or an atmospheric resid which may contain
components boiling as low as 500F., is introduced to the lower
end of a vertical conduit. Steam and/or water in amounts to
substantially decrease hydrocarbon partial pressure is added with
the feedstock. Pressures will be sufficient to overcome pressure
drops, say 15 to 50 p.s.i.a. The charge may be preheated in a
furnace, not shown, before introduction to the riser contactor, to
any desired degree below thermal cracking temperature, e.g., 200 to
800F., preferably 300 to 700F. Higher temperatures will induce
thermal cracking of the feed with production of low octane naphtha.
The feed diluted by steam rises in the contactor 1 at
high velocity such as 40 feet per second. Hot inert solid in finely
divided form is introduced to the feed from a standpipe 2 in a quan-
tity and at a temperature to provide a mixture at a temperature in
excess of 900F. to volatilize all components of the feed except the
very heavy compounds of high CC and high metal content.
The solid contacting agent is essentially inert in the
sense that it induces minimal cracking of heavy hydrocarbons by
the standard microactivity test conducted by measurement of amount
of gas oil converted to gas, gasoline and coke by contact with the
solid in a fixed fluidized bed. Charge in that test is 0.8 grams
of mid-Continent gas oil of 27 API contacted with 4 grams of
catalyst during 48 second oil delivery time at 910F. This results
in a catalyst to oil ratio of 5 at weight hourly space velocity
(WHSV) of 15. By that test, the solid here employed exhibits a
microactivity less than 20, preferably about 10. A preferred solid
is microspheres of calcined kaolin clay.
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 in the manufacture of
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1 fluid zeolitic cracking catalysts as described in U. S. 3,647,718
to Haden et al. In practice of the instant invention, in contrast,
the microspheres 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 to that
of a dehydrated kaolin clay. Typically the calcined microspheres
analyze about 51% to 53% (wt.) Si02, 41 to 45% A1203, and from 0 to
1% H20, the balance being minor amounts of indigenous impurities,
notably iron, titanium and alkaline earth metals. Generally, iron
content (expressed as Fe203) is about 1/2% by weight and titanium
(expressed as Ti02) is approximately 2%.
The microspheres are preferably produced by spray drying
an aqueous suspension of kaolin clay. The term "kaolin clay" as
used herein embraces clays, the predominating mineral constituent
of which is kaolinite, halloysite, nacrite, dickite, anauxite and
mixtures thereof. Preferably a fine particle size plastic hydrated
clay, i.e., a clay containing a substantial amount of submicron si~e
particles, is used in order to produce microspheres having adequate
mechanical strength.
To facilitate spray drying, the powdered hydrated clay
is preferably dispersed in water in the presence of a deflocculating
agent exemplified by sodium silicate or a sodium condensed phosphate
salt such as tetrasodium pyrophosphate. By employing a deflocculating
agent, spray drying may be carried out at higher solids levels and
harder products are usually obtained. When a deflocculating agent
is employed, slurries containing about 55 to 60% solids may be
prepared and these high solids slurries are preferred to the 40 to
50% slurries which do not contain a deflocculating agent.
Several procedures can be followed in mixing the ingre-
dients to form the slurry. One procedure, by way of example, is to
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1 dry blend the finely divided solids, add the water and then incor-
porate the deflocculating agent. The components can be mechanically
worked together or individually to produce slurries of desired
viscosity characteristics.
Spray dryers with countercurrent, cocurrent or mixed
countercurrent and cocurrent flow of slurry and hot air can be
employed to produce the microspheres. The air may be heated
electrically or by other indirect means. Combustion gases obtained
by burning hydrocarbon fuel in air can be used.
Using a cocurrent dryer, air inlet temperatures to 1200F.
may be used when the clay feed is charged at a rate sufficient to
produce an air outlet temperature within the range of 250 to 600F.
At these temperatures, free moisture is removed from the slurry
without removing water of hydration (water of crystallization) from
the raw clay ingredient. Dehydration of some or all of the raw clay
during spray drying is contemplated. The spray dryer discharge may
be fractionated to recover microspheres of desired particle size.
Typically particles having a diameter in the range of 20 to 150
microns are preferably recovered for calcination. The calcination
may be conducted in the manufacturing operation or by adding the
spray dried particles to the burner described below.
While it is preferable in some cases to calcine the micro-
spheres at temperatures in the range of about 1600 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 of 1000 to 1600F., thereby
converting the clay into the material known as "metakaolin."
After calcination the microspheres should be cooled and fractionated,
if necessary, to recover the portion which is in desired size
range.
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1 Pore volume of the microspheres will vary slightly withthe 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 of 150 to 600 Angstrom units.
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
surface areas of commercial fluid zeolitic catalysts is considerably
higher, generally exceeding values of 100 m2/g. as measured by the
B.E.T. method.
Other solids of low catalytic activity and of like particle
size may be employed. In general, solids of low cost are recommended
since it may be desirable to discard a sizeable portion of the contact
agent in the system from time to time and replace it with fresh agent
to maintain a suitable level of metals. Since the solid is preferably
of low porosity, resulting in deposition primarily on external
surfaces, the invention contemplates abrading the particles as in a
column of air at velocity to permit refluxing of solids for removal
of external metal deposits.
Length of the riser contacting 1 is such to provide a very
short time of contact between the feed and the contacting agent, less
than 2 seconds, preferably 0.5 second or less. The contact time
should be long enough to provide good uniformity of contact between
feed and contacting agent, say at least 0.1 second.
At the top of the riser, e.g., 15 to 20 feet above the
point of introduction of contacting agent from standpipe 2 at a feed
velocity of 40 feet per second, vaporized hydrocarbons are separated
as rapidly as possible from particulate solids bearing the high CC
deposits and metals, if any. This may be accomplished by discharge
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1 from the riser into a large disengaging zone defined by vessel 3. However,it is preferred that the riser vapors discharge directly into cyclone
separators 4 from which vapors are transferred to vapor line 5 while
entrained solids drop into the disengaging zone by diplegs 6 to stripper 7
where steam admitted by line 8 evaporates traces of volatile hydrocarbons
from the solids. The mixture of steam and hydrocarbons, together with
entrained solids enters cyclone 9 by mouth 10 to disengage the suspended
solids for return to stripper 7 by dipleg 11. As well known in the Fluid
Cracking art, there may be a plurality of cyclones 4 and cyclones 9 and the
cylcones may be multi-stage, with gas phase from a first stage eyclone
discharging to a seeond stage eyelone.
In one embodiment, the eyclones 4 may be of the stripper cyclone
type described in U.S. Patent No. 4,043,899. In such case, the stripping
steam admitted to the cyclone may be at a low temperature, say 400 to 500
F., and serve to perform part or all of the quenching function presently
to be described.
The vaporized hydrocarbons from cyclones 4 and 10 passing by way
of line 5 are then mixed with eold hydroearbon liquid introdueed by line 12
to queneh thermal eracking. The quenched product is cooled in condenser 13
and passed to aecumulator 14 from which gases are removed for fuel and
water, if any, is taken from sump 15, preferably for recyele to the
eontaetor for generation of steam to be used as an aid in vaporizing eharge
at the bottom of the riser and/or removing heat from the burner. Condenser
13 is advantageously set up as a heat exchanger to preheat eharge to the
eontaetor or preheat charge to the FCC Unit hereinafter deseribed and the
like.
In one embodiment, the quenehing is advantageously eondueted in a
eolumn equipped with vapor-liquid eontaet zones sueh as dise and doughnut
trays and valve trays. Bottoms from such column quencher
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1 could go directly to catalytic cracking with overhead passing to
condenser 13 and accumulator 14.
The liquid hydrocarbon phase from accumulator 14 is a
decarbonized and demetallized resid fraction which is now satisfact-
ory charge for catalytic cracking. This product of contact in
riser 1 may be used in part as the quench liquid at line 12. The
balance is preferably transferred directly to a catalytic cracker
by line 16.
Returning now to stripper 7, the inert solid particle
bearing a deposit of high CC and metallic compounds passes by a
standpipe 17 to the inlet of burner 18. Standpipe 17 discharges
to a riser inlet 19 of burner 18 where it meets a rising column
of air introduced by line 19 and is mixed with hot inert particles
from burner recycle 20 whereby the mixture is rapidly raised to a
temperature for combustion of the deposits from treating resid,
1200 to 1400F. The mixture enters an enlarged zone 21 to form
a small fluidized bed for thorough mixing and initial burning of
deposits. The flowing stream of air carries the burning mass through
a restricted riser 22 to discharge at 23 into an enlarged dis-
engaging zone. The hot, burned particles, now largely free of
combustible deposit, fall to the bottom of the disengaging zone
from which a part enters recycle 20 and another part enters the
standpipe 2 for supply to contactor 1 after steam stripping. By
reason of the very high temperatures attainable in this type of
burner and in the presence of a stoichiometric excess of oxygen, C0
will burn to provide a flue gas containing very little of that gas.
In other types of burners, the combustion products may contain
substantial amounts of C0 which can be burned for its heating value
in C0 boilers of the type commonly used in FCC units.
In the type of burner shown, the gaseous products of
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.
1 combustion, containing earbon dioxide, some residual oxygen, nitrogen, I
oxides of sulfur and perhaps a trace of C0, enter a cyclone 25 (one of a I -
plurality of such devices) to disengage entrained solids for discharge by
displeg 26. The clarified gases pass to a plenum 27 from which flue gas is
removed by outlet 28.
Although the system just deseribed bears superfieial resemblance
to an FCC unit, its operation is very different from FCC. Most
importantly, the riser contacting 1 is operated to remove from the charge
an amount not greatly in exeess of the Conradson Carbon number of the feed.
This contrasts with normal FCC "conversion of 50 to 70%, measured as the
percentage of FCC product not boiling within the range of the charge.
Percent removed by the present process is preferably on the order of 10 to
20% on charge and constituted by gas, gasoline and deposit on the solid
eontacting agent. Rarely will the amount removed from boiling range of the
charge exeeed a vaIue, by weight, more than three to four times the
Conradson Carbon value of the charge. This result is aehieved by a very
low severity of eracklng due to inert character of the solid and the very
short residenee time at eraeking temperature. As is well known, eracking
severity is a function of time and temperature. Increased temperature may
be compensated by reduced residence time, and viee versa.
The new process affords a eontrol aspeet not available to FCC
units in the supply of steam to the riser eontactor. When proeessing
stoeks of high CC, the burner temperature will tend to rise beeause of
inereased supply of fuel to the burner. This may be eompensated by
inereasing the hydroearbon or steam supplied to reduce partial pressure of
hydroearbons in the riser eontaetor or by recyeling water from the overhead
reeeiver to be vaporized in the riser to produee steam.
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1 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 steam
supplied to the riser.
The decarbonized, demetallized resid is good quality
FCC charge stock and is transferred by line 16 to feed line 30
of an FCC reactor 31 operated in the conventional manner. Hot
regenerated catalyst is transferred from FCC regenerator 32 by
standpipe 33 for addition to the reactor charge. Spent catalyst
from reactor 31 passes by standpipe 34 to the regenerator 32,
while cracked products leave reactor 31 by transfer line 35 to
fractionation fGr recovery of gasoline and other conversion
products.
Many residual fractions are high in sulfur content,
particularly in the heavy components. The sulfur is oxidized to
sulfur oxides (S0 ) in the burner 18 and these undesirable gases
form part of the flue gas discharged at 28. In a preferred
embodiment of the invention, the FCC unit operates on a catalyst
designed for reduction of S0 emissions. Several such catalysts
are known in the art. Such catalysts will absorb S0 in the
oxidizing environment of the regenerator. Catalyst which contains
sorbed sulfur is then transferred to the reducing atmosphere of
the reactor. In that reducing atmosphere and in the presence of
water, the sulfur is converted to hydrogen sulfide, readily removed
from reactor products in the usual gas plant and treating facili-
ties of a refinery. See Belgain Patents 849,635, 849,636 and 849,637.
As shown in the drawing, a drag stream of catalyst from
regenerator 32 is passed by standpipe 36 to mix with cooled flue
gas passed from burner 18 through heat exhanger 29. The
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1 mixture is then transferred to a fluidized bed contactor 37
resulting in sorption of SO from the flue gas of burner 18.
! Catalyst carrying sorbed (reacted) SO is conveyed by stand-
pipe 38 back to regenerator 32 for ultimate reaction in reactor
31. After cyclonic separation of entrained catalyst, flue gas
from which SO has been removed is then discharged by line 39
for recovery of the heat energy contained therein as by expansion
turbines driving air blowers for regenerator 32 and burner 18;
by waste heat boilers or the like.
EXAMPLES
The effect of contacting in the manner described above
has been demonstrated in laboratory scale equipment. The apparatus
employed is a circulating fluidized bed pilot plant which simulates
behavior of commercial FCC riser reactors. The reactor is equipped
to provide a stream of nitrogen through the riser and for addition
of catalyst and charge. The riser is lagged and heated to maintain
isothermal conditions. The nitrogen flow serves the same function
as the steam described above for reduction in partial pressure of
hydrocarbons. In the runs described below residual stocks and the
microspheres set forth above were contacted under the conditions
recited. Inspection data on the charge stock are given in Table
I.
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1 TABLE I
DESCRIPTION OF CHARGE STOCKS
____
Example 1 2
Gravity, API 27.9 23
Ramsbottom Carbon, % 0.35 2.5
Metals, p.p.m.
Ni 1 10
Cu
V 1 20
Distillation, F.
IBP 438 420
10% 554 478
30% 659 711
50% 750 829
70% 847 979
76% - 1046
90% 991
94% 1050
20 Conditions of contact and resultant products are shown in
Table II.
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1 TABLE II
CONTACT CONDITIONS AND PRODUCTS
Example 1 2
Rise contactor temp., F. 915 935
Contact time, seconds 0.66 0.97
Contact solid Temp., F. 1203 1185
Oil partial pressure, p.s.i.a. 2.83 4.62
Oil preheat temp., F. 641 659
Solids/Oil, wt. 12.5 12.2
Mol ratio, N2/oil 3.7 2.2
Products, wt. % -~
Gas 7.9 7.6
Liquid 90.4 85.5
Deposit on solid 1.7 6.9
Liquid Product
Metals, p.p.m.
Ni - 1.5
Cu - 1.0
V - 1.0
Ramsbottom Carbon - 0.6
Distillation, F.
IBP 170 173
10% 466 475
30% 597 610
50% 684 704
70% 775 803
90% 894 967
93% 1033
EP 1028
