Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a process for the fluid
catalytic cracking of hydrocarbons whereby hydrocarbon
charges contaminated with high contents of metal can
be processed.
: The cracking process concerned consists of pro-
paring a suspension made up of a hydrocarbon, a crack-
in additive, and a cracking catalyst, constantly mixing
said suspension with a fresh stream of hydrocarbons,
and marina the mixture undergo cracking.
Under the usual fluid catalyst cracking processes-
referred to hereinafter as FCC - the catalyst is
brought into contact with the charge and the mixture
flows through a riser where the cracking reactions
take place towards the reactor. At the reactor the
catalyst is separated, usually by means of cyclones,
from the output of the reaction, the latter going on
to the distilling stage and the catalyst to be stripped
and then to the regenerator.
m e steam stripping treatment withdraws the
weaker compounds adsorbed at the surface of the gala-
lust, while treatment in the regenerator burns out the
ooze also lying on the surface of the catalyst, active
middle portions of which become obstructed, thus
bringing about a drop in catalytic action.
The particles of the catalyst dragged or carried away by
combustion gases are also reassured by means of
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cyclones lying within the regenerator. After having
been regenerated, the catalyst rejoins the process,
to meet up with a fresh stream of coarse.
The output which goes on to be distilled is led
Jo a fractionator where it is broken up into gases,
naphtha, light gas oil, heavy ohs oil, clarified
oil and slurry oil. Such slurry oil will also contain
particles of the catalyst, carried away by the reaction
products upon separation from the catalyst at reactor
outlet.
Though the latest FCC units are equipped with
sets of one or more stage cyclones, catalyst losses
in such units are still considerable.
The fluid catalytic cracking process covered
by this invention makes use of a catalyst charging
method (described further on) which enables a drastic
cut to be made in such losses.
cause of the oil crisis, efforts have been world-
wide towards developing processes to make ever greater
use of such oil as is available. Thus cracking processes
have come into being which enable use to be made of
the heavier fractions of crude as a raw material for
such processes, while at the same time catalysts
that are more active and less susceptible to being
poisoned than those used in the seventies are being
developed. ____
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It is a well-known fact that the presence of
certain metals, such as No and V, in the charge to
be cracked, represents a serious obstacle when the
usual catalysts are employed, since such metals
soon poison them. Furthermore, in the heavier cuts
of crude the proportion of such metals is considerably
greater than in the lighter cuts.
-To overcome this trouble research ha been
undertaken towards finding a way of lessening the
o effect of such poisons upon the catalysts then known.
- m is led to substances nowadays known as cracking pass- -
vapors or additives. The presence of such substances
on the reaction medium enables high No and V content
hydrocarbon charges to be processed.
It was found that compounds containing B, Sun,
To, Sub, My, Bit W, To, In, Go and others have such
powers. Nowadays there is a trade in products for such
purpose. Meanwhile further passivation process technic
quest have been described in publications on the subject.
Jo Fresh processes directed towards the more effective use of crude,
plus such Tahitian have led to other discoveries
in recent years.
One of the purposes of the process of the present invention is
that of providing a process for the fluid catalytic
cracking of hydrocarbons in which catalyst losses can be
drastically reduced, by about 50 to 80%.
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Another purpose of the process invented is that
of enabling catalyst fines (particles of G-40 microns
on size) to play their part in cracking reactions.
A further purpose of the process invented is
what of enabling metal contaminated hydrocarbon charges
to be processed.
Such purposes were achieved thanks to the change
made in the way of supplying the coolest to the
process. Instead of employing the usual method of replace
it in catalyst losses, namely, by means of a pressurized
silo leading to the regenerator, in this invention the
catalyst is supplied wet, directly to the reaction
medium;
By supplying the process with wet virgin catalyst,
that is, by means of a suspension within a hydrocarbon,
there is the advantage to be gained of enabling catalyst
- fines to play a part in the cracking reaction.
The process invented enables stricter control to
be kept over the quantities of catalyst and of cracking
additive (if any) which it is intended to add to the
stream of the charge.
The catalyst is suspended in a stream of a hydra-
carbon, for instance, heavy vacuum gas oil, heavy
recycle gas oil, LOO or FCC diesel, naphtha, FCC fuel
oil, etc., said suspension being mixed with the charge
or else directly injected into the riser, after which
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the cracking takes place. When the charge is contami-
noted with metals, a cracking additive is incorporated
to inhibit any poisoning of the catalyst. The basis
of such additives is usually antimony and there are
several kinds on the market.
This invention resides in a process for the
fluid catalytic cracking of hydrocarbons, which
comprises the following steps:
a) preparing a suspension comprising (i) a
hydrocarbon and (ii) a virgin cracking catalyst or a
virgin cracking catalyst and a cracking additive;
b) continuously mixing said suspension with
a stream of a hydrocarbon feed stock having a density
of from 10 to 25 APT to form a joint charge; and
c) subjecting said joint charge to cracking,
said process being conducted in the substantial absence
of added water.
The invention further provides a process for
the fluid catalytic cracking of hydrocarbons comprising:
(a) preparing a suspension comprising (i) a
hydrocarbon and (ii) a virgin cracking catalyst or a
virgin cracking catalyst and a cracking additive;
(b) directly and continuously injecting said
suspension into a riser unit; and
(c) subjecting said hydrocarbon to cracking,
said process being conducted in the
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substantial absence of added water.
An alternative process would be to inject the
catalyst suspension directly into the riser and then
make it undergo cracking.
To determine the quantities of the suspension
to be added to the process from time to time, certain
operational aspects have to be considered.
The method of checking on the degree of metal
contamination of the catalyst by measuring hydrogen and
methane produced during the process is a well-known one.
When the catalyst is poisoned by I and V,
dehydrogenation and the creation of coke reactions take
place at the
.
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.
same time, being catalyzed by such metals. Therefore,
a sign that the catalyst is being contaminated is
that there is a higher proportion of hydrogen in the
fuel gas.
Usually, what is done is to control catalytic
action by making piecemeal replacements o, tune spent
catalyst with regenerated or even virgin catalyst
and also by striving to keep the relationship between
the hydrogen and the methane present in the fuel
gas within bounds regarded as acceptable. It is worth-
whole keeping such bounds as low as possible.
For the purpose of comparing performance under
the process invented with that under processes already
described in publications, a suspension was prepared,
as yet on an experimental scale, containing the gala-
lust, and according to methods described further on,
and the invented process was carried out. Afterwards,
merely for the sake of comparison, a know cracking
process was completed.
It was found that when the method invented is
employed, and whether or not a cracking additive is
added to the catalyst suspension, catalyst losses are
substantially less.
It was also found that when the method of the present
invention is employed, less cracking additive has to be used
to arrive at the same hydrogen/methane ratio in the
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fuel gas, other variables in the operation being
the same. This means that about half as much cracking
additive has to be employed.
Furthermore, it was discovered that lower hydrogen/
methane ratios within the fuel gas could be
arrived at than those under the usual kind of process,
regardless of what quantity of cracking additive
might be employed in the usual process. This means that under
the usual process the hydrogen/methane ratio in the fuel
gas cannot be brought down below a given f guru no matter
what quantity of cracking additive be employed.
Therefore the fluid catalytic cracking process
covered by this invention has proved to be more efficient than
those previously described in publications.
The invented process will next be described in
terms of the drawing which is appended to this specification
so as to make it clearer though such description must in no
way be construed as a limitation of the process.
The single drawing figure is a schematic representation
of the invention.
The cracking reactor is shown under 1 and consists
of the riser unit and the product separator, the catalyst
regenerator, under I, and the tank for preparing the suspension,
under 3.
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To the mixing tank (3), provided with a mechanic
eel stirrer (4), a hydrocarbon I is added, which is to
act as the dispersing medium for the catalyst, plus a
cracking additive (6), if needed, and a virgin catalyst
(7), in suitable proportions. The suspension stream thus
secured for the catalyst (8) is being continually mixed
with the stream of the fresh charge (9), which gives rise
to a joint charge stream (10), which is led into the
cracking reactor (1), more specifically, into the riser.
The stream of reaction products (11) is separated
and led to the fractionator - not shown in the figure -
while the stream of spent catalyst (12) is led to the
regenerator (2), in which regeneration of the catalyst
will take place.
A stream of combustible gas (13) is introduced
into the regenerator (2) to burn up the coke deposited upon
the spent catalyst, which gives rise to a stream of
combustion gases (14), which is then withdrawn from the
regenerator (2). From the regenerator a stream of regenerated
catalyst (15) also runs back to the process and joins up
with the stream of the combined charge (10) which enters
the cracking reactor (1).
In carrying out this invention heavy gas oil was
so
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employed as the charge and as the dispersing agent,
and air as the combustible gas.
An alternative process under the invention
consists of preparing a suspension of the catalyst in a
hydrocarbon (8), either with or without cracking additive,
and injecting such suspension continuously into the riser,
that is, without going through the stage of having to mix
it with the stream of fresh charge (9).
The usual method which was employed for the sake
of comparison was as follows.
X
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g
The catalyst stored in a silo was transferred
to the regenerator by pressurizing the silo and the
catalyst was added continuously to the process. The
cracking additive was diluted with gas oil in a drum
and continuously injected into the stream of the
charge, in quantities big enough to arrive at the
desired results. The mixture so secured was made to
undergo cracking.
In order to bear out results arrived at on the
workbench a prototype unit was put up for trials.
Such trials were meant to arrive at more reliable
figures than those ascertained at a work bench scale,
amongst others, those for catalyst losses, as well
as ideal operating conditions and a study comparing
usual process with that invented.
The examples given below show the results of
such trials which are not however to be regarded
as limits of the invention.
he catalysts that can be used for the process
invented are the usual ones, e.g.: low alumina,
high alumina, zealots, etc.
Operating conditions followed for the trials
were also the ones that usually apply.
Throughout the trials the quality of the charge
was kept the same.
' 1 ! '
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.
EXAMPLE I
The purpose of this example is to check the
efficiency of the feed system under the process
invented as compared with that for the usual process.
In tests 1 and 2 the catalyst was replaced continuously
as provided for in the usual method, that is from the
silo to the regenerator. In tests 3 and 4 the invented
method was employed, namely:
A suspension of the catalyst in gas oil was
prepared in a mixing tank provided with a mechanical
stirrer. Such suspension was fed continuously. to the
process, along with the charge.
he charge used for such tests was a heavy gas oil
derived from Leon crudely the catalyst used was
high alumina In all the tests, replacement was
exactly equal to quantity of catalyst lost.
'rABLE (I)
Ten Charge (m Davy) Replacement (tons/dzy)
1 153 0.45
2 285 0.66
3 239 . 0.13
4 255 0.20
ordinary comparison of test 3 against test 2
. shows a drop of 80.3% in ca~al~st~replaced, in the
former.
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,
- EXAMPLE II
In these tests the intention was to discover
optimum operating conditions for tune process. Runs
were done in which the usual process turn 5) was come
pared with that of the invention (run reaction
temperature, catalyst/oil ratio, and combined charge
ratio were all kept as steady as possible. A cork nod
charge of 1.0 means that no recycling was done.
Table II shows average results of the runs.
TABLE (II)
Runs _ 5 6
charge (m day) 186 - 186
charge temperature (C) 165 169
circulation of catalyst (ton/min.) 3.0 2.4
catalyst/oil ratio 22.8 18.3
reaction temperature (C) 492 490
dense stage 607 623
regenerator temperature diluted
(SUE stage 612 628
cyclone 639
combined charge ratio 1.0 1.0
hydrogen/methane ratio in fuel
gas 3.17 2.72
cracking additive (kg/day~* 24 8
replacement catalyst (kg/day)200 100
* antimony type commercial ad Five
replacement exactly equal to catalyst lost -
- 12 12 2 8 3 I
The above serves to show that, under the process of the
present invention, catalyst losses were half as much. It
should also be noted that even with only a third of
the additive the hydrogen/methane ratio was lower,
Which means that the cracking additive was more
efficiently used.
EXP~IPLE III
The object of this example was to find out if
by raising the quantity of cracking additive employed,
as in the usual catalyst replacement method, the
hydrogen/carbon (H2/Cl) ratio would become lower
than that arrived at under the process invented.
, under the process invented a clue ratio of
2.7 was arrived at and 2.7k~ of Sub pox day was used.
Doses of Sub were worked out in terms of the common-
coal cracking additive employed. Table III shows the
results secured.
TABLE (III)
kg Sb/day ~2/C
1.80 3.8
2.76 3.17
3.50 3.3
4.00 3.5
- Under the usual process no matter what quantity
of additive was used the Ho/ old not be brought down
to below 3.17.
