EP1170355B1 - Process and apparatus for hydrocarbon cracking with two successive reaction zones - Google Patents

Abstract

The effluents from each chamber are fractionated in a separate part of the same fractionating column (12) which is partially divided and at least one resulting section (13,44a) from the separate fractionating is totally or partially reinjected into the other chamber. Hydrocarbon cracking in a fluidized bed reactor in which the heat bearing particles, which are also catalytic, circulate in two successive reaction chambers (1,16) in each of which they are put in contact with at least one section of hydrocarbons. The reaction effluents from each chamber are sent to the same fractionating unit. The hydrocarbons injected into the first reaction chamber spend less time there than the hydrocarbons injected into the second reaction chamber, with the time in the first chamber being 0.05 to 5 seconds, preferably 0.1 to 1 second and the time in the second chamber being 0.1 to 10 seconds, preferably 0.4 to 5 seconds. The flow through the first chamber is essentially downwards and that in the second is essentially upwards. In the partially divided fractionating column, the heavier effluents from each chamber are fractionated separately whilst the lighter effluents are combined. The section which is reinjected is a slurry or heavy distillate containing HCO and/or a diesel section containing LCO. The heavy effluents from the first chamber are reinjected into the second. Alternatively, the lighter effluents are fractionated separately and the heavy effluents are combined, with the petrol section from the second chamber reinjected into the first. The reinjected fraction can be mixed with other fractions and/or undergo intermediate treatments before reinjection, such as hydrogenation, hydrodearomatization, hydrodesulfurization or hydrodenitrogenation. Upstream of the second chamber particles are injected both from the first chamber and from a regenerator. Device to carry out this process, comprising a partially divided fractionating column with a zone containing two separate fractionating compartments (38,39) and a common compartment (41). This divided zone can be at the top or bottom of the column and the means of division is a flat or cylindrical vertical wall.

Description

The present invention relates to the cracking of hydrocarbons in the presence of heat transfer particles, catalytic or not, circulating in the fluidized phase. It relates more particularly to a cracking process in a fluidized bed, in which heat-transfer particles circulate in two successive reaction chambers, in each of which they are brought into contact with one or more cuts of hydrocarbons to be cracked.

The invention also relates to a device designed for implementing the method according to the invention.

In a manner known per se, the petroleum industry makes use of processes for converting heavy hydrocarbon charges, in which high molecular weight and high boiling point hydrocarbon molecules are split into smaller molecules, which can boil in lower temperature ranges, suitable for the intended use.

To carry out this type of conversion, it has in particular so-called cracking processes in the fluid state. In this type of process, the hydrocarbon charge, generally sprayed in the form of fine droplets, is brought into contact with heat-carrying particles at high temperature and which circulate in the reactor in the form of a fluidized bed, that is to say in suspension more or less dense within a gaseous fluid ensuring or assisting their transport. On contact with hot particles, the charge vaporizes, followed by cracking of the hydrocarbon molecules. The cracking reaction is of the thermal type, when the particles have only a heat transfer function. It is of the catalytic type, when the heat-carrying particles also have a catalytic function, that is to say have active sites promoting the cracking reaction, as is the case in particular in the so-called catalytic cracking process in the state fluid (commonly known as FCC process, from English “Fluid Catalytic Cracking”):

After, following the cracking reactions, the desired molecular weight range has been reached, with a corresponding lowering of the boiling points, the reaction effluents are separated from the particles. The latter, deactivated due to the coke which is deposited on their surface, are generally stripped in order to recover the entrained hydrocarbons, then regenerated by combustion of the coke, and finally brought back into contact with the charge to be cracked.

The reactors used are most often vertical reactors of the tubular type, in which the charge and the particles move in an essentially ascending flow (the reactor is then called “riser”) or in an essentially descending flow (the reactor is then called "Dropper" or "downer").

A major difficulty in such methods consists in carrying out a cracking which is both complete and selective of the charge, that is to say to succeed in cracking the entire charge, so as to obtain a maximum amount of it. recoverable hydrocarbons, while minimizing the quantity of undesirable by-products. This objective is all the more difficult to achieve since the charges to be cracked have relatively wide boiling intervals, and are made up of very diverse compounds which crack under significantly different conditions to lead to various products.

This is why the methods currently implemented carry out a generally incomplete conversion of the charge. In these processes, the cracking is carried out in a single reactor, the operating conditions of which, chosen as a function of the average nature of the hydrocarbons constituting the feed, do not allow the entire range of hydrocarbons present to be cracked correctly so as to selectively obtain the products desired. This results in reaction effluents made up of very diverse products, a large proportion of which result from insufficient cracking of the feedstock and which constitute undesirable products for the refiner, which are difficult to recover.

A first solution consists in recycling all or part of these products in the cracking reactor, so as to subject them to a second cracking step. However, such a measure proves not only ineffective, but also harmful, insofar as such recycling often has the effect of appreciably affecting the quality of the cracking of the fresh charge.

A second solution consists in increasing the severity of the cracking, in order to crack the charge injected further and convert all the types of hydrocarbons present. However, such measure, if it makes it possible to increase the conversion rate of the charge, on the other hand favors overcracking phenomena, which result in a reduction in the selectivity of the conversion: an increased production of dry gases and coke is observed to the detriment intermediate hydrocarbons sought.

Several solutions have been proposed in the prior art, in order to remedy the aforementioned problems.

From 1947, US Patent No. 2,488,713 proposes a catalytic cracking process using two successive reactors, in each of which circulate catalytic particles. In the first reactor, a heavy recycle cut (residue from the fractionation of cracked effluents, of the type known as a “slurry”) is cracked on contact with the catalytic particles coming from the regenerator. In the second reactor, a fresh charge as well as an intermediate recycle cut of the distillate type are cracked on contact with the particles coming from the first reactor. At the outlet of each of the two reactors, the hydrocarbon effluents are separated from the particles, then are combined and directed to a conventional fractionation column.

The first drawback of such a process is that the fresh charge is treated, in the second reactor, in the presence of particles which have already been largely coked and deactivated in the first reactor, in contact with the heavy recycle charge, which is particularly rich in refractory polyaromatic compounds. As a result, in the second reactor, poor catalytic activity of these particles, hence poor quality of cracking of the fresh feed, a conversion that is both low and not very selective.

A second disadvantage comes from the fact that the heavy recycle cut progressively enriches itself with the most refractory heavy compounds, which, even recycled in the first reactor, do not crack or crack in an incomplete manner, and "go around in circles" in the unit. . This exacerbates the problems described above of premature coking of the particles in the first reactor. A purge planned on the recycling line does not solve the problem satisfactorily. In fact, the recycle being made up of the fractionation residue of the combined effluents from the two reactors, the purge not only extracts only part of the most refractory compounds that are desired eliminate from the unit, but additionally extracts a fraction of compounds directly originating from the fresh charge, which were not converted during their passage through the second reactor, but which could have been cracked in the first reactor in contact with regenerated particles. The poor selectivity of this purge system thus induces an additional loss of yield in desired products.

Furthermore, patent EP No. 573316 describes a catalytic cracking process in which the reaction takes place in two successive reactors, the first reactor being in downward flow, and the second being in upward flow (riser). The charge to be cracked is brought into contact with the regenerated particles at the inlet of the downflow reactor, at the bottom of which the charge / particle mixture is transferred into the upflow reactor. The charge therefore flows in contact with the particles in two successive reactors, which makes it possible to increase the overall yield of cracked hydrocarbons. However, this process is absolutely not selective: the hydrocarbons already converted in the first reactor continue to crack in the second reactor, resulting in an overcracking phenomenon generating increased production of dry gases and coke, to the detriment of intermediate cuts sought.

Continuing its research in the field of cracking in a fluidized bed, the Applicant is interested in these processes in which two cracking reactors are used, in order to improve the rate and the selectivity of the conversion compared to the traditional processes using a single reactor. In doing so, it has developed a method making it possible to remedy the drawbacks of the systems of the prior art.

To this end, the present invention relates to a process for cracking in a fluidized bed a hydrocarbon feedstock in which heat-carrying particles, optionally catalytic, circulate in two successive reaction chambers? in each of which they are brought into contact with at least one section of hydrocarbons, and the reaction effluents from each of said chambers are directed to the same fractionation unit.

This process is characterized in that the effluents from each of the reaction chambers are partially fractionated separately in the same partially partitioned fractionation column, and in that that at least one section resulting from the separate fractionation of the effluents from one of the two reaction chambers is, in whole or in part, reinjected into the other chamber.

In the present description, the term “reaction chamber” designates any enclosure provided with means for introducing heat-transfer particles (catalytic or not), means for injecting one or more cuts of hydrocarbons to be cracked, a reaction zone of cracking and means for separating cracking effluents and particles. This term includes in particular any type of thermal or catalytic cracking reactor in a fluidized bed, whatever its operating mode (ascending or descending).

According to the invention, hydrocarbons are cracked in a first reaction chamber, in contact with fully active particles coming from the regenerator. At the exit from this first chamber, the effluents are separated from the particles, and the latter continue their journey in a second reaction chamber in which their residual activity is used to crack an additional quantity of hydrocarbons.

Considering the charge to be cracked, it undergoes a first conventional cracking step in one of these two reaction chambers. The corresponding effluents are then fractionated in the same fractionation column as the effluents from the other chamber, but partly separately. We then recover, from the separate fractionation of the effluents from the first cracking step, one or more cuts comprising undesirable products. These sections are then, in whole or in part, reinjected into the other reaction chamber. They undergo a second cracking step independent of the first, and whose operating conditions can be adjusted according to the nature of these reinjected hydrocarbons and the type of products that one wishes to obtain.

Such a process diagram is possible thanks to the specific fractionation column involved in the invention. This column is in fact partially partitioned, which makes it possible to fractionate the effluents from each of the two reactors partly separately, that is to say without there being contact between them. Of course, the part of the effluents from the two reactors thus fractionated separately corresponds to the part containing cuts rich in undesirable products, to which the refiner wishes to undergo a second cracking step. The other part of said effluents is combined in the non-partitioned zone of the column, in which the effluents are fractionated in common.

Compared to traditional systems with a single reactor, the process according to the invention allows a more thorough and more selective conversion of the charge to be cracked. It allows the refiner to re-inject low-value products obtained during a first conventional cracking step, so as to subject these products to a second cracking step. The fact that the recycling of said products takes place in a different reactor has the advantage, on the one hand, of being able to carry out this second cracking under appropriate conditions and, on the other hand, of avoiding affecting the quality of the first step of cracking the load.

Compared to the two-reactor systems proposed in the prior art, the method according to the invention makes it possible to subject the hydrocarbons constituting the charge to separate cracking circuits, perfectly adapted to the various natures of these hydrocarbons, so as to obtain a maximum quantity of recoverable products. Indeed, the charge to be cracked undergoes a first conversion, as a result of which the undesirable products obtained are fractionated separately from the effluents of the other reactor, in a compartment of the partitioned zone of the fractionation column. These products are then reinjected into a separate reactor, in which they undergo a second cracking step, under conditions specifically suited to their nature.

The effluents resulting from this second cracking are then fractionated in the same column as the effluents from the first cracking, and the partitioned fractionation system of this column makes it possible to prevent the residual undesirable compounds, not converted after passing through the two reactors (in particularly compounds that are particularly refractory to cracking), are not recycled a second time and "go around in circles" in the unit. Indeed, such compounds are recovered, in the fractionation column, in the compartmentalized fractionation compartment of the effluents from the second cracking step. These compounds are thus recovered separately from the effluents from the first cracking step, and they can for example be eliminated from the unit. This system makes it possible to reinject into one of the reaction chambers only hydrocarbons coming exclusively from the other chamber. This avoids any phenomenon of enrichment of the recycled cuts in refractory compounds, which would gradually degrade the quality of the cracking of said cuts, while causing excessive coking of the particles circulating in the unit.

Thus, the method according to the invention makes it possible to make the most of undesirable products originating from a first conventional cracking step, in order to produce an additional quantity of products with greater added value. For the same feedstock, it offers the refiner the possibility of carrying out a cracking that is both more complete and more selective in favor of the type of products he wishes to obtain. The profitability of the unit is significantly improved.

Furthermore, the Applicant has developed a device allowing an efficient implementation of the method according to the invention.

The present invention therefore also relates to a cracking device in a fluidized bed of a hydrocarbon feedstock, using two reaction chambers connected to each other by means of transfer of the heat-carrying particles, a fractionation column and supply lines for the hydrocarbon effluents from each of the two chambers at said fractionation column.

• ladite colonne de fractionnement comporte dans sa partie interne au moins deux zones distinctes : une première zone de fractionnement cloisonné constituée de deux compartiments, communiquant chacun avec une seconde zone de fractionnement commun ;
• les conduites d'amenée des effluents issus de la première et de la deuxième chambre réactionnelle débouchent respectivement dans le premier et le deuxième compartiment de ladite zone de fractionnement cloisonné ;

   des moyens sont prévus pour le recyclage et l'injection dans l'une des chambres réactionnelles d'au moins une coupe soutirée du compartiment de fractionnement cloisonné des effluents de l'autre chambre réactionnelle.This device is characterized in that:

• said fractionation column comprises in its internal part at least two distinct zones: a first partitioned fractionation zone consisting of two compartments, each communicating with a second common fractionation zone;
• the effluent supply lines from the first and second reaction chambers open respectively into the first and second compartments of said partitioned fractionation zone;

means are provided for recycling and injecting into one of the reaction chambers at least one section withdrawn from the partitioned compartment for partitioning the effluents from the other reaction chamber.

A first advantage of the device according to the invention is linked to the fact that the hydrocarbon effluents from the two reaction chambers are partly treated separately, but in a single fractionation column. This system makes it possible to avoid having to use two separate columns, therefore to have a compact unit and to limit investments.

A second advantage of this device is linked to the fact that it allows optimal implementation of the method according to the invention. In fact, said partitioned fractionation zone is advantageously dimensioned as a function of the boiling ranges of the undesirable products to which the refiner wishes to subject a second cracking step. The common fractionation zone, on the other hand, is used for the fractionation of products for which the refiner does not wish to differentiate those from each of the two reaction chambers, for example because these are directly recoverable products, which he does not wish to reverse.

The two reaction chambers involved in the invention are designated in the present description by "first" and "second" reaction chamber, it being understood that this order is adopted by reference to the direction of circulation of the heat-carrying particles from the regenerator. In each of these two chambers, the injection of hydrocarbons can be done co-current and / or against the current of the flow of heat-transfer particles.

These two reaction chambers can in particular be made up of any type of downward (or downward) or riser (riser) flow reactors. Although the two chambers can completely be identical, the method according to the invention is all the more advantageous when said chambers are different. This makes it possible in particular to make different operating conditions prevail in these two chambers, adapted to the type of hydrocarbons injected into each.

In particular, according to a preferred variant of the process according to the invention, the residence time of the hydrocarbons injected into the first reaction chamber is less than the residence time of the hydrocarbons injected into the second reaction chamber. Indeed, the cracking in the first reaction chamber takes place in the presence of particles coming directly from the regenerator, therefore at particularly high temperature and maximum activity. In fact, it has proved preferable to avoid prolonged contact between these particles and the hydrocarbons, so as, on the one hand, to avoid overcracking, on the other hand, to limit the quantity of coke deposited on the particles. , which thus preserve part of their heat and their activity for the cracking of the hydrocarbons injected into the second reaction chamber.

In the second reaction chamber, on the other hand, the cracking takes place under milder conditions, since the particles have partly cooled, or even deactivated, during their passage through the first reaction chamber. Consequently, it has proved advantageous to prolong the contact there between the particles and the hydrocarbons, so as to allow a sufficiently complete cracking of the latter.

Advantageously, the residence time of the hydrocarbons injected into the first reaction chamber is between 0.05 and 5 seconds, preferably between 0.1 and 1 seconds. As for the residence time of the hydrocarbons injected into the second reaction chamber, it is advantageously between 0.1 and 10 seconds, preferably between 0.4 and 5 seconds.

According to a preferred embodiment, the flow of the charge and the catalyst in the first reaction chamber takes place in an essentially descending direction. Said reaction chamber can then consist of a substantially vertical downward flow reactor of the type known under the name of "downer", as described for example in international patent application WO 98/12279. In fact, this type of reactor allows a particularly short contact time between the hydrocarbons and the fluidized bed of particles.

According to an equally preferred embodiment, the flow of the charge and the catalyst in the second reaction chamber takes place in an essentially ascending direction. Said reaction chamber can then consist of a substantially vertical reactor with upward flow, of the type known under the name of "riser". Indeed, this type of reactor allows access to longer contact times between the hydrocarbons and the fluidized bed of particles.

The present invention presents numerous modes of implementation, among which the refiner will be able to choose the one which is the most adapted to the types of products he wishes to obtain, taking into account the type of fillers available.

A first particularly advantageous embodiment consists in partitioning the fractionation of the heavy part of the effluents from the two reactors. Thus, the heaviest effluents from each of the two reaction chambers are fractionated separately, while the lightest effluents are combined.

This configuration allows heavy products from a first cracking step to be subjected to a second cracking step. Advantageously, said cut resulting from the separate fractionation of the effluents from one of the reaction chambers and which is, in whole or in part, reinjected into the other chamber, comprises slurry and / or a heavy distillate of the HCO type.

In the field of petroleum refining, HCO (from the English term "heavy cycle oil") is usually used to designate a heavy fraction whose boiling range can extend from an initial point generally between 320 and 400 ° C. up to an end point generally between 450 and 480 ° C. It is a poorly recoverable product, rich in sulfur and aromatic compounds, which is generally used as a diluent for heavy fuels.

As for the product commonly called "slurry", it consists of the fractionation residue from the cracked effluents. It is a very heavy, very viscous product, the initial cutting point of which is generally between 450 and 480 ° C. This residue is all the more difficult to develop as it is particularly rich in polyaromatic compounds, and that it comprises an appreciable proportion of fines, that is to say dust from the erosion of the heat-carrying particles circulating in unit.

It is therefore particularly advisable to subject a second cracking step to heavy products of the HCO and slurry type, all the more since this makes it possible to produce more valuable intermediate products such as diesel, petrol, LPG.

Furthermore, for these embodiments in which heavy-type sections are recycled, it has been found to be preferable to inject such sections into the second reaction chamber. This avoids the risk of premature coking of the heat transfer particles in the first reaction chamber. We can then advantageously inject all or part of the fresh charge into the first reaction chamber. Thus, according to a particularly advantageous configuration, at least one section resulting from the separate fractionation of the heaviest effluents from the first reaction chamber is, in whole or in part, reinjected into the second reaction chamber.

A second particularly advantageous embodiment consists in partitioning the fractionation of the light part of the effluents from the two reactors. Thus, the lightest effluents from each of the two reaction chambers are fractionated separately while the heaviest effluents are combined.

This configuration allows light products from a first cracking step to be subjected to a second cracking step. Advantageously, said cut resulting from the separate fractionation of the effluents from one of the reaction chambers and which is, in whole or in part, reinjected into the other chamber, comprises gasoline. Usually, cuts are designated by essence whose boiling range can extend from an initial point generally greater than or equal to 20 ° C up to an end point generally between 140 and 220 ° C. It can be particularly advantageous for the refiner to subject a second cracking step to this type of product, insofar as this increases the production of light olefins such as, for example, propenes and butenes, which are very sought after products, in particular for uses in petrochemicals.

For these modes of implementation in which light-type sections are recycled, it may be preferable to inject these recycled sections into the first reaction chamber. Indeed, the cracking of gasolines into light olefins requiring particularly high temperatures, it has proved more effective to carry out such a conversion in the presence of particles coming directly from the regenerator. The fresh charge can then be injected, in whole or in part, into the second reaction chamber. Thus, according to a particularly advantageous configuration, at least one section resulting from the separate fractionation of the lightest effluents from the second reaction chamber is, in whole or in part, reinjected into the first reaction chamber.

According to the present invention, at least one section resulting from the separate fractionation of the effluents from one of the reaction chambers is, in whole or in part, reinjected into the other chamber. The reinjected proportions depend in particular on the nature (more or less dense, more or less difficult to crack, ...) of the cuts concerned. These proportions must also take into account the operating conditions prevailing in the reactor in which such cuts are reinjected, so as to ensure complete vaporization and cracking of the recycled hydrocarbons. For each cut thus recycled, the proportion reinjected advantageously comprises from 10 to 100% of the flow of said cut. More preferably, this proportion is between 50 and 100%.

Furthermore, each of the reinjected cuts can be, prior to this reinjection, combined with other cuts of hydrocarbons.

For example, in the case of the separate fractionation of heavy effluents with reinjection of a viscous slurry-type cup, it may be particularly advantageous to dilute the fraction reinjected from this slurry by a lighter cut, so as to facilitate reinjection . The diluent can, for example, include fresh feed, in particular conventional fillers such as diesel or distillates. The diluent can moreover comprise for example light recycling oils ("light cycle oils", LCO) or heavy recycling oils ("heavy cycle oils", HCO).

Finally, each of the reinjected sections can, before this reinjection, be subjected to one or more intermediate treatments. Advantageously, such an intermediate treatment includes a hydrotreatment, such as for example a hydrogenation, a hydrodearomatization, a hydrodesulfurization, a hydrodenitrogenation. Such treatments are usually carried out in the presence of catalysts known to those skilled in the art, and which generally comprise, deposited on a refractory mineral oxide support, one or more metals from Group VIII of the Periodic Table of the Elements, sometimes associated with other metals such as those of Group VI of the Periodic Table of the Elements.

In the second reaction chamber, the cracking of the hydrocarbons is carried out in the presence of the heat-transfer particles coming from the first chamber, in which they have been partially coked, or even deactivated, in contact with the charge injected into this first chamber. A particularly advantageous variant of the invention consists in introducing upstream of this second reaction chamber, in addition to the particles coming from the first reaction chamber, an addition of particles coming from the regenerator. This variant is particularly beneficial when the heat provided by the particles from said first chamber is insufficient to vaporize the hydrocarbons injected into the second reaction chamber. Adding regenerated particles then makes it possible to provide an additional quantity of heat, and to control the temperature prevailing in said second chamber. Furthermore, when said particles are of the catalytic type, this system has the additional advantage of introducing into the second chamber an addition of fully active catalytic sites, so as to optimize the cracking reactions of the hydrocarbons injected into this second chamber.

Preferably, the addition of particles is introduced between the zone where the separation of the particles and effluents takes place from the first reaction chamber and the zone where the injection of the hydrocarbon fractions takes place in the second reaction chamber. Said make-up is advantageously introduced so as to ensure a homogeneous mixture with the particles coming from the first reactor. To this end, a system for homogenizing the fluidized beds of particles as described in patent application EP No. 99.401112 in the name of the Applicant may prove to be particularly useful.

The invention uses a specific fractionation column. Indeed, this must allow the simultaneous distillation of the effluents from the two reactors, and be arranged so that the fractionation of these two types of effluents is carried out partly separately, partly in common.

• une zone de fractionnement cloisonné, dans laquelle les effluents issus des deux réacteurs sont fractionnés séparément, chacun dans un compartiment, de manière à éviter tout contact entre eux, et
• une zone de fractionnement commun, dans laquelle les effluents issus des deux réacteurs sont mélangés.

For this purpose, the interior volume of said column comprises two zones:

• a partitioned fractionation zone, in which the effluents from the two reactors are fractionated separately, each in a compartment, so as to avoid any contact between them, and
• a common fractionation zone, in which the effluents from the two reactors are mixed.

This partial segregation of the effluents from the two reactors is carried out using a partitioning disposed inside the column, which partitioning separates part of said column into two compartments which constitute said partitioned fractionation zone.

This partially partitioned fractionation column can be arranged in many ways, depending on the part of the effluents for which it is desired that the fractionation be carried out separately.

For example, if it is desired to partition the fractionation of the heavy part of the effluents from each of the two reactors, the partitioned fractionation zone corresponds to the lower part of the fractionation column. In this case, different modes of partitioning can be envisaged for the device according to the present invention.

According to a first embodiment, the partitioned fractionation zone is separated into two compartments by means of a substantially vertical separation means, extending from the bottom of the fractionation column over part of the height thereof. It may for example be a flat vertical wall. It may also be a cylindrical vertical wall whose axis of revolution is parallel to the longitudinal axis of the fractionating column.

According to a second embodiment, the partitioned fractionation zone is separated into two compartments by means of a substantially horizontal separation means, for example consisting of a tray extending over a horizontal section of the column, and provided with one or more several chimneys allowing the passage upwards, towards the common fractionation zone, of light effluents from the lower compartment to said tray.

Similarly, if it is desired to partition the fractionation of the light part of the effluents from each of the two reactors, the partitioned fractionation zone corresponds to the upper part of the fractionation column. Again, different modes of partitioning can be implemented.

According to a first embodiment, the partitioned fractionation zone is separated into two compartments by means of a substantially vertical separation, extending from the head of the fractionation column over a part of the height thereof, such as for example a flat vertical wall or a vertical cylindrical wall whose axis of revolution is parallel to the longitudinal axis of the fractionating column.

According to a second embodiment, the partitioned fractionation zone is separated into two compartments by means of a substantially horizontal separation means, for example consisting of a tray extending over a horizontal section of the column, and provided with one or more several chimneys allowing the passage downwards, towards the common fractionation zone, of the heavy effluents coming from the upper compartment to said tray.

The operating conditions under which each of the two reaction chambers operates can vary. They are preferably different in each of these two chambers, taking into account the different natures of the hydrocarbons which are injected there. In general, these operating conditions include a reaction temperature between 450 and 900 ° C, and a pressure close to atmospheric pressure. A person skilled in the art knows perfectly how to optimize these conditions according to the type of petroleum cuts to be cracked.

The hydrocarbon charges liable to be cracked in the context of the present invention can be extremely diverse. They include in particular, but are not limited to, the usual fillers for cracking processes, such as for example distillates and / or gas oils obtained from atmospheric or vacuum distillation, distillates and / or visbreaking gas oils, deasphalted residues.

The process according to the invention is, moreover, perfectly suited to the conversion of heavier feedstocks, containing fractions normally boiling up to 700 ° C. and more, which may contain high quantities of asphaltenes and have a Conradson carbon content. up to 4% and beyond. Thus, the feed can include heavy distillates, atmospheric distillation residues, or even vacuum distillation residues.

The injected fillers may if necessary have received a preliminary treatment such as, for example, a hydrotreatment in the presence of an appropriate catalyst, for example a catalyst based on cobalt and molybdenum deposited on a porous refractory oxide.

In order to facilitate its injection, especially when it is viscous, the charge to be cracked can moreover be diluted by one or more lighter cuts, which can include intermediate cuts coming from the fractionation zone of the cracking effluents. For this purpose, the LCOs or HCOs mentioned above can constitute excellent diluents.

In the context of the present invention, it does not appear necessary to mention the type of heat transfer particles, catalytic or not, used, nor the means for circulating such particles in the form of fluidized beds more or less diluted by fluids gaseous dilution, insofar as these are data well known to those skilled in the art.

The various embodiments of the invention mentioned above will be described below in more detail, with reference to the accompanying drawings. These are only intended to illustrate the invention and therefore have no limiting character, the process which is the subject of the present invention being able to be implemented according to very numerous variants.

• La figure 1 est une vue schématique d'un premier mode de mise en oeuvre du procédé de craquage selon l'invention, dans lequel on cloisonne le fractionnement de la partie lourde des effluents issus des deux réacteurs.
• Les figures 2 et 3 représentent deux variantes possibles pour la colonne de fractionnement partiellement cloisonnée intervenant dans le procédé illustré sur la figure 1.
• La figure 4 est une vue schématique d'un second mode de mise en oeuvre du procédé de craquage selon l'invention, dans lequel on cloisonne le fractionnement de la partie légère des effluents issus des deux réacteurs.
• La figures 5 représente une variante possible pour la colonne de fractionnement partiellement cloisonnée intervenant dans le procédé illustré sur la figure 4.

In these drawings:

• FIG. 1 is a schematic view of a first embodiment of the cracking method according to the invention, in which the fractionation of the heavy part of the effluents from the two reactors is partitioned.
• FIGS. 2 and 3 represent two possible variants for the partially partitioned fractionation column involved in the process illustrated in FIG. 1.
• FIG. 4 is a schematic view of a second embodiment of the cracking method according to the invention, in which the fractionation of the light part of the effluents from the two reactors is partitioned.
• FIG. 5 represents a possible variant for the partially partitioned fractionation column involved in the process illustrated in FIG. 4.

FIG. 1 represents a catalytic cracking unit comprising two successive reaction chambers, the first with downward flow and the second with upward flow.

This unit comprises a first reaction chamber consisting of a tubular reactor 1 with downflow, known as name of "downer". This reactor is connected in its upper part to an enclosure 2, from which it is fed by a flow of regenerated catalyst particles, with a flow rate regulated by means of a valve 3.

The charge to be cracked is conveyed by line 4 and injected into reactor 1 by means of injectors 5. The catalyst particles and the hydrocarbons then flow from top to bottom in reactor 1.

At the base of reactor 1, the mixture emerges in enclosure 6, in the upper part of which a separator, not shown, separates the catalyst particles from the reaction effluents, which are directed to the fractionation zone by line 7. In the lower part of the enclosure 6, the particles are stripped, by means of water vapor brought by the line 8 to the diffuser 9.

The particles are then evacuated via line 10 out of the enclosure 6, and transferred to the base of the second reaction chamber. The latter consists of a reactor 16 in the form of a column, of a type known per se, known as a load elevator, or riser. The reactor 16 is supplied at its base by the conduit 10 with particles of catalyst.

As an option, it is possible to provide a conduit, not shown, for conveying an addition of regenerated particles coming directly from the regenerator 23 which will be described in more detail below, with a regulated flow rate so as to optimize the cracking conditions. in this second reactor.

A riser gas, for example water vapor, is introduced into column 16 through line 11, by means of a diffuser 19, while a charge comprising a substantial proportion of a cut resulting from the separate fractionation of heaviest effluents from the first reactor 1, is conveyed by means of line 13 and injected into the reactor 16 by means of the injector-sprayers 14. The catalyst particles and the hydrocarbons then flow from bottom to top in the reactor 16 .

The column 16 opens at its top in an enclosure 15, which is for example concentric and in which the separation of the cracked charge takes place and the stripping of the deactivated particles of catalyst. The particles are separated from the charge treated by means of a cyclone 17, which is housed in the enclosure 15, at the top of which is provided a discharge line 18 for the effluents from the second reactor 16, which are routed to the fractionation zone. The deactivated particles move by gravity towards the base of the enclosure 15. A line 20 supplies stripping fluid, generally steam, to injectors or diffusers 21 of fluidizing gas regularly arranged at the base of the pregnant 15.

The particles are then evacuated at the base of the enclosure 15 to a regenerator 23, via the conduit 22. In the regenerator 23, the coke deposited on the particles is burned using air or a another oxygen-rich gas, injected at the base of the regenerator 23 by a line 24, which feeds regularly spaced injectors or diffusers 25. The particles entrained by the combustion gas are separated by cyclones 26, and the combustion gas is evacuated by a line 27, while the particles flow towards the base of the enclosure 23, from where they are recycled by the conduit 28 towards the enclosure 2 supplying the first reactor 1.

The reaction effluents from each of reactors 1 and 16 are routed respectively by lines 7 and 18 to the fractionation column 12. The latter consists of two zones: a lower zone 40 for partitioned fractionation, and an upper zone 41 for fractionation common. The partitioned fractionation zone 40 is divided into two compartments 38 and 39 by a separation means 37, consisting of a flat vertical wall, extending from the bottom of the column 12 over part of the height thereof. .

In accordance with the invention, the lines 7 and 18 for supplying the effluents from the two reactors open on either side of the separation means 37, into the respective compartments 39 and 38, in which the corresponding heavy products are fractionated separately. These products correspond to distillation residues or "slurry", the initial cutting point of which is preferably chosen at a value between 450 and 480 ° C.

The two compartments 38 and 39 communicate with the common fractionation zone 41, located in the upper part of the column 12, and in which the lighter products contained in the combined effluents from the two reactors 1 and 16 are carried out.

• les produits gazeux aux conditions normales de température et de pression (hydrocarbures en C1 à C4), soutirés par la ligne 43 ;
• une coupe d'essences, dont l'intervalle d'ébullition peut aller de 20°C jusque vers 140-220°C, soutirée par la ligne 44 ;
• une coupe de type gazole ou LCO, dont l'intervalle d'ébullition s'étend généralement de 140-220°C jusque vers 320-400°C, soutirée par la ligne 45.
• une coupe de type distillat ou HCO, dont l'intervalle d'ébullition s'étend généralement de 320-400°C jusque vers 450-480°C, soutirée par la ligne 46.

The fractionation by distillation of these lighter fractions is carried out in a conventional manner, in order to obtain the desired products. In in particular, the skilled person knows perfectly how to choose the cutting points according to the products he wishes to obtain. Traditionally, this distillation is carried out so as to isolate:

• gaseous products at normal temperature and pressure conditions (C1 to C4 hydrocarbons), drawn off by line 43;
• a section of essences, the boiling range of which can range from 20 ° C to around 140-220 ° C, drawn off by line 44;
• a diesel or LCO type cut, the boiling range of which generally ranges from 140-220 ° C to around 320-400 ° C, drawn off by line 45.
• a distillate or HCO type cut, the boiling range of which generally extends from 320-400 ° C up to around 450-480 ° C, drawn off by line 46.

Of course, the fractionation zone can perfectly comprise conventional additional columns, not shown, coupled to column 12, in which part of the fractionation of the common effluents described above and / or subsequent fractionations can be carried out.

In the process shown here, only the effluent residues from the two reactors are fractionated separately. It is of course entirely possible to separate other heavy products separately, such as in particular HCO or even LCO, so as to recycle all or part of these to the second reactor 16, alone or mixed with the slurry. For this, it suffices to use a separation means 37 extending over a greater height of the column 12, so that the partitioned fractionation zone 40 also includes the zone for distillation and withdrawal of HCO (or even LCO).

The condensed residues in compartments 38 and 39 are drawn off respectively by lines 42 and 13. The section drawn off by line 13, which corresponds to the slurry resulting from the separate fractionation of the effluents from the first reaction chamber 1, is, in accordance with invention, recycled to the second reaction chamber 16. Optionally, line 47 makes it possible to dilute this bottom fraction by a less viscous cut, for example all or part of the HCO cut drawn off by line 46. Optionally, the line 48 makes it possible to withdraw part of said bottom fraction, so as to inject only a given proportion into the reactor 16.

As for the section drawn off by line 42, it corresponds to the slurry resulting from the separate fractionation of the effluents from the second reaction chamber 16. This section, which comprises particularly refractory compounds which are not converted after successive cracking in each of the two reactors, can be by example removed from the unit.

FIG. 2, in which the members already described in relation to FIG. 1 are designated by the same reference numbers, shows a first alternative embodiment of the fractionation column 12, which shows another means of partitioning the lower part 40 of said column.

In this figure, the column 12 comprises a separation means consisting, as in FIG. 1, of a substantially vertical partitioning, extending from the bottom of the column 12. However, this partitioning element here consists of a cylindrical vertical wall 37 ′ whose axis of revolution is parallel to the longitudinal axis of the column 12. This cylindrical element is disposed internally and concentrically with the wall of the column 12, and it extends from the bottom of this over a sufficient height, thus dividing the partitioned fractionation zone 40 into two compartments 39 and 38, into which lead respectively the line 7 for conveying effluents from the first reaction chamber 1, and the line 18 for conveying effluents from the second reaction chamber 16. In this configuration, the two compartments 38 and 39 are therefore concentric.

Each compartment 38 and 39 communicates directly with the common fractionation zone 41 situated above, in which is carried out, in a conventional manner, the fractionation of the lighter products contained in the combined effluents of the two reactors.

In the variant shown in Figure 2, the partition element 37 'extends over a greater height of the column 12, so as to also cover the distillation zone of HCO type cuts. Furthermore, the HCO is not separated from the slurry, so that the residues, drawn off by lines 42 and 13 in the bottom of each of the two respective compartments 38 and 39, consist of a mixture of these two types of products. .

The residue drawn off by line 13, consisting of a mixture of HCO and slurry from the separate fractionation of heavy effluents from the first reaction chamber 1, is, in accordance with the invention, recycled in whole or in part to the second reaction chamber 16.

Of course, the supply lines 7 and 18 can completely be inverted, provided that the two lines 13 and 42 for drawing off the corresponding products are also inverted.

FIG. 3, in which the members already described in relation to FIG. 1 are again designated by the same reference numbers, represents a second alternative embodiment of the fractionation column 12 of this FIG. 1, in which the means 37 " for separating the lower partitioned partitioning zone 40 is of the horizontal type.

In this figure, the zone 40 comprises an internal partitioning constituted by a horizontal plate 37 ", which is dimensioned so as to cover the entire cross section of the column 12 and to be in sealed contact with the internal vertical wall of that -this.

This partitioning delimits a first upper compartment 39, into which opens the line 7 for transporting the effluents from the first reaction chamber 1, and a second lower compartment 38, into which opens the line 18 for transporting the effluents from the second reaction chamber. 16. In this configuration, the two compartments 38 and 39 are therefore arranged one above the other.

Each compartment, 38, 39, communicates directly with the common fractionation zone 41 situated above. Indeed, the tray 37 "is provided with at least one chimney 50, which allows the passage upwards, towards said common fractionation zone 41, of the vaporized products coming from the compartment 38 below the tray 37". Thus, the lightest effluents from the second reaction chamber 16 rise via this chimney towards the common area 41, where they are fractionated and drawn off by lines 43, 44 and 45, in mixture with the light effluents from first reaction chamber 1.

The chimney 50 is surmounted by a cap 51, for example conical, which makes it possible to prevent hydrocarbons from passing from the upper compartment 39 to the lower compartment 38. This system therefore ensures perfect segregation of the heavy effluents from the two reactors 1 and 16.

The section drawn off by line 13 of the compartment 39 for partitioning heavy effluents from the first reaction chamber 1 is, in accordance with the invention, recycled in whole or in part to the second reaction chamber 16.

In this variant, as in that presented in FIG. 2, the supply lines 7 and 18 can be inverted (the separate fractionation of the heavy effluents from the first reactor 1 is then carried out in the lower compartment 38, while the separate fractionation of the effluents heavy of the second reactor 16 is carried out in the upper compartment 39), provided that the two lines 13 and 42 for drawing off the corresponding products are also reversed.

FIG. 4 also represents a catalytic cracking unit comprising, like that presented in FIG. 1, a first reaction chamber 1 with downward flow and a second reaction chamber 16 with upward flow. This unit has many elements common to the unit shown in Figure 1 and designated by the same reference numerals, so that only the different elements will be described below.

The process illustrated in this FIG. 4 corresponds to an embodiment of the invention, in which the lightest effluents from each of the two reactors 1 and 16 are fractionated separately, in order to reinject into one of them products light from the other.

To this end, the fractionation column 12 comprises an upper zone 40 for partitioned partitioning of light effluents, and a lower zone 41 for common fractionation of heavy effluents. The partitioned fractionation zone 40 is divided into two compartments 38 and 39 by a separation means 37, consisting of a flat vertical wall extending downwards from the head of the column 12, over part of the height of it.

• les produits gazeux aux conditions normales de température et de pression (hydrocarbures en C1 à C4), soutirés respectivement des compartiments 38 et 39 par les lignes 43a et 43b ;
• deux coupes de type essences, dont l'intervalle d'ébullition peut aller de 20°C jusque vers 140-220°C, soutirées respectivement des compartiments 38 et 39 par les lignes 44a et 44b.

In accordance with the invention, the lines 7 and 18 for supplying the effluents from the respective reactors 1 and 16 open on either side of the separation means 37, in the respective compartments 39 and 38, in which the corresponding light products are fractionated separately, so as to isolate:

• gaseous products at normal temperature and pressure conditions (C1 to C4 hydrocarbons), drawn off from compartments 38 and 39 respectively by lines 43 a and 43 b ;
• two gasoline-type cups, the boiling range of which can range from 20 ° C to around 140-220 ° C, drawn from compartments 38 and 39 respectively by lines 44 a and 44 b .

The gasoline fraction removed through line 44 is separated after splitting of the lightest effluents from the second reaction chamber, is fed to injectors 5, from which it is fed back into the first reaction chamber 1. In fact, although, in the context of the invention, it is entirely possible to recycle this section to the second reaction chamber 16, it has been found to be more effective in cracking such a section in the first chamber 1, in contact with the particles of maximum temperature coming directly from the regenerator 23. Consequently, the fresh charge can be wholly or partly injected into the second reactor 16. For this purpose, it is sent to the injectors 14 via the line 52.

• une coupe de type gazole ou LCO, dont l'intervalle d'ébullition s'étend généralement de 140-220°C jusque vers 320-400°C, soutirée par la ligne 45 ;
• une coupe de type distillat ou HCO, dont l'intervalle d'ébullition s'étend généralement de 320-400°C jusque vers 450-480°C, soutirée par la ligne 46 ;
• un résidu de distillation ou « slurry », dont le point de coupe initial est généralement choisi à une valeur comprise entre 450 et 480°C, soutiré par la ligne 53.

In the common fractionation zone 41 of column 12, the heavier products contained in the combined effluents from the two reactors 1 and 16 are conventionally fractioned, so as to isolate:

• a cut of the diesel or LCO type, the boiling range of which generally extends from 140-220 ° C up to around 320-400 ° C, drawn off by line 45;
• a distillate or HCO type cut, the boiling range of which generally extends from 320-400 ° C up to around 450-480 ° C, drawn off by line 46;
• a distillation residue or "slurry", the initial cutting point of which is generally chosen at a value between 450 and 480 ° C., drawn off by line 53.

FIG. 5, where the members already described in relation to FIG. 4 are designated by the same reference numerals, represents an alternative embodiment of the fractionation column 12 of this FIG. 4, in which the means 37 "for separating the upper zone 40 of partitioned fractionation is of horizontal type.

In this FIG. 5, the zone 40 comprises an internal partitioning constituted by a horizontal plate 37 ", dimensioned so as to cover the entire cross section of column 12 and be in leaktight contact with the internal vertical wall of that.

This partitioning delimits a first upper compartment 39, into which opens the line 7 for transporting the effluents from the first reaction chamber 1, and a second lower compartment 38, into which opens the line 18 for transporting the effluents from the second reaction chamber. 16.

Each compartment 38, 39 communicates directly with the common fractionation zone 41 located below. Indeed, the tray 37 "is provided with at least one chimney 50, which allows the passage downward, towards said common fractionation zone 41, of the heavy products coming from the compartment 39 above the tray 37". Thus, the heaviest effluents from the first reaction chamber 1 descend via this path to the common area 41, where they are fractionated and drawn off by lines 45, 46 and 53, mixed with the heavy effluents from the second reaction chamber 16.

The chimney 50 is provided with a baffle 51, for example conical, which makes it possible to prevent hydrocarbons from passing from the lower compartment 38 to the upper compartment 39. This system therefore makes it possible to ensure perfect segregation of the light effluents from the two reactors 1 and 16.

The gasoline section drawn off by line 44 a from the compartment 38 for partitioning partitioned light effluents from the second reaction chamber 16 is, in accordance with the invention, recycled in whole or in part to the first reaction chamber 1.

The examples below, which are not limiting, are only intended to illustrate the implementation of the invention and the advantages thereof.

EXAMPLES Example 1:

Two catalytic cracking tests were carried out using a heavy petroleum charge, consisting of a mixture of 50% by weight of atmospheric residue and 50% by weight of vacuum distillate, both originating from the distillation of a Kirkuk-type crude oil.

The first test was carried out in an experimental catalytic cracking unit in accordance with that shown in Figure 1, which comprises two successive reaction chambers (1; 16), the first (1) with downflow ("downer"), and the second (16) with upward flow ("riser"). The catalyst used is a conventional commercial catalyst, of the zeolitic type. According to the invention, the effluents from each of these two reaction chambers are directed to the same fractionation column (12), partitioned in its lower part (40) by a flat vertical wall (37). The fresh charge is injected into the first reaction chamber (1), while in the second reaction chamber (16) a section is recycled from the separate fractionation of the effluents from the first chamber (1).

In addition, a comparative test (test No. 2) was carried out under the same conditions, but by replacing the partially partitioned fractionation column (12) with a conventional column, in which the effluents from each of the two chambers (1; 16 ) are combined and split in the traditional way. The fresh charge is injected into the first reaction chamber (1), while in the second reaction chamber (16) a section is recycled from the fractionation of the combined effluents from the two chambers.

In these two tests, the fraction recycled in the second reaction chamber (16) corresponds to a heavy distillate or HCO, with a boiling range extending from 380 ° C. to 480 ° C. In test 1 according to the invention, all of the HCO from the partitioned fractionation of the effluents from the first reaction chamber (1) is injected into the second reaction chamber (16). In comparative test 2, the recycling rate (ratio of the amount of HCO recycled in the second reaction chamber to the total amount of HCO produced in the unit) is 0.8.

• Température de sortie de la première chambre réactionnelle (1) : 540°C
• Température de sortie de la deuxième chambre réactionnelle (16) : 515°C
• Rapport C/O dans la première chambre réactionnelle (1) (rapport massique entre la quantité de catalyseur C et celle O de la charge injectée dans cette chambre) : 6
• Rapport C/O dans la deuxième chambre réactionnelle (16) : 8
• Température du régénérateur (23) : 690°C

The operating conditions, identical in the two tests, are as follows:

• Exit temperature of the first reaction chamber (1): 540 ° C
• Second reaction chamber (16) outlet temperature: 515 ° C
• C / O ratio in the first reaction chamber (1) (mass ratio between the quantity of catalyst C and that O of the feed injected into this chamber): 6
• C / O ratio in the second reaction chamber (16): 8
• Regenerator temperature (23): 690 ° C

The table below summarizes the results obtained, in terms of conversion rate of the HCO cut recycled in the second reaction chamber (ie quantity of HCO converted / quantity of HCO recycled), and of yield of conversion products (ie weight of product obtained / weight of HCO converted). Trial 1 Trial 2 (comparative) returns: Conversion rate (% by weight) 34.6 24.5 Dry gas yield (% by weight) 2.2 1.5 LPG yield (% by weight) 5.8 4.3 Fuel efficiency (% by weight) 13.1 10.1 LCO yield (% by weight) 20.0 20.8 Slurry yield (% by weight) 45.4 54.7 Coke yield (% by weight) 13.5 8.6

• gaz secs: hydrocarbures légers à 1 ou 2 atomes de carbone et hydrogène sulfuré (H₂S);
• GPL: hydrocarbures légers à 3 ou 4 atomes de carbone;
• essence: coupe d'hydrocarbures dont l'intervalle d'ébullition s'étend de 20°C jusqu'à 220°C;
• LCO: coupe d'hydrocarbures dont l'intervalle d'ébullition s'étend de 220°C jusqu'à 380°C;
• slurry: résidu de distillation, qui contient des quantités importantes de poussières de catalyseur et dont l'intervalle d'ébullition s'étend à partir de 480°C.

In the table above, the products obtained are defined as follows:

• dry gases: light hydrocarbons with 1 or 2 carbon atoms and hydrogen sulfide (H ₂ S);
• LPG: light hydrocarbons with 3 or 4 carbon atoms;
• gasoline: cut of hydrocarbons with a boiling range from 20 ° C to 220 ° C;
• LCO: cut of hydrocarbons with a boiling range from 220 ° C to 380 ° C;
• slurry: distillation residue, which contains significant quantities of catalyst dust and whose boiling range extends from 480 ° C.

The above results show that it is much more advantageous to recycle HCO from the partitioned effluent fractionation from the first reactor to the second reactor (test 1) than to recycle HCO from the fractionation of the combined effluents from the two reactors (test 2).

Indeed, in the first case, the recycled HCO cut contains only hydrocarbons from a first cracking of the fresh charge, while in the second case it also contains hydrocarbons from the second chamber, not converted after passing through the two successive reactors, therefore particularly refractory to cracking, and which "go around in circles" in the unit. In test 1 carried out in accordance with the invention, the elimination of such compounds by means of the partitioned fractionation system notably improves the quality of the cracking in the second reaction chamber. It can be seen that this conversion is both more complete (10-point increase in the conversion rate), and more selective (sharp reduction in yield of slurry, which is a particularly undesirable product, in favor of an increase in yields sought intermediate products, such as gasolines and LPG).

Example 2:

In this example, two tests (respectively 3 and 4) were carried out in the same units and under the same operating conditions as the respective tests 1 and 2 of Example 1, with the difference that this time the cut recycled in the second reaction chamber (16) is a section of the diesel or LCO type (with a boiling range extending from 220 ° C. to 380 ° C.). In test 3 according to the invention, all of the LCO originating from the partitioned fractionation of the effluents from the first reaction chamber (1) is injected into the second reaction chamber (16). In comparative test 4, the recycling rate (ratio of the amount of LCO recycled in the second reaction chamber to the total amount of LCO produced in the unit) is 0.8. The fresh charge used is the same as in Example 1.

For each of these two tests, the properties of the cut of recycled LCO in the second reaction chamber were determined. The table below illustrates the results obtained: Trial 3 Trial 4 (comparative) Properties of the recycle cut: Density (at 15 ° C) .9522 .9543 Viscosity (at 50 ° C) 2.76 2.98 Sulfur content (% by weight) 2.59 2.71 Molecular hydrogen content (% by weight) 10,10 9.79

The above results illustrate, in a manner complementary to those of Example 1, certain advantages provided by the invention.

In fact, it can be seen that, in test 3 carried out in accordance with the invention, the recycle cut is of clearly superior quality to that obtained in comparative test 4. In test 3, this cut is lighter, less viscous, less rich in sulfur impurities; the hydrogen content of the hydrocarbons it contains is higher. This cut is therefore less rich in heavy hydrocarbons, in particular in polyaromatic compounds which are particularly refractory to cracking.

This example therefore illustrates the fact that, in the process according to the invention, the qualities of the recycle cut are higher, which contributes to better yields, better selectivity and better quality of the products obtained during the cracking of this cut. in the second reaction chamber 16.

Example 3:

In this example, an experimental catalytic cracking unit conforming to that shown in FIG. 4 is used, which comprises two successive reaction chambers (1; 16), the first (1) with downward flow, and the second (16) upward flow ("riser"). The catalyst used is a conventional commercial catalyst, of the zeolitic type.

A first test (test No. 5) is carried out in accordance with the invention: the effluents from each of these two reaction chambers are directed to the same fractionation column (12), partitioned in its upper part (40) by a vertical wall plane (37). The fresh charge is injected into the second reaction chamber (16), while in the first reaction chamber (1) a section is recycled from the separate fractionation of the effluents from the second chamber (16).

Furthermore, a comparative test (test no. 6) was carried out under the same conditions, but by replacing the partially partitioned fractionation column (12) with a conventional column, in which the effluents from each of the two chambers (1; 16 ) are combined and split in the traditional way. The fresh charge is injected into the second reaction chamber (16), while in the first reaction chamber (1) a section is recycled from the fractionation of the combined effluents from the two chambers.

In these two tests, the cut recycled in the first reaction chamber (1) is a light gasoline (with a boiling range extending from 20 ° C. to 220 ° C.). In test 5 according to the invention, all of the petrol coming from the partitioned fractionation of the effluents from the second reaction chamber (16) is injected into the first reaction chamber (1). In comparative test 6, the recycling rate (ratio of the quantity of petrol recycled in the first reaction chamber to the total quantity of petrol produced in the unit) is 0.8.

• Température de sortie de la première chambre réactionnelle (1) : 540°C
• Température de sortie de la deuxième chambre réactionnelle (16) : 515°C
• Rapport C/O dans la première chambre réactionnelle (1) : 8
• Rapport C/O dans la deuxième chambre réactionnelle (16) : 6
• Température du régénérateur (23) : 690°C

The fresh charge used is the same as in Example 1, and the operating conditions, identical in the two tests, are as follows:

• Exit temperature of the first reaction chamber (1): 540 ° C
• Second reaction chamber (16) outlet temperature: 515 ° C
• C / O ratio in the first reaction chamber (1): 8
• C / O ratio in the second reaction chamber (16): 6
• Regenerator temperature (23): 690 ° C

For each of these two tests, the properties of the cut of recycled gasoline in the first reaction chamber (1) were determined. The table below illustrates the results obtained: Trial 5 Trial 6 (comparative) Properties of the recycle cut: Density (at 15 ° C) .7130 .7289 Sulfur content (% by weight) 0,063 0.078 Molecular hydrogen content (% by weight) 14,30 13.77 Aromatic content (% by weight) 16.0 17.5

Here again, it can be seen that in test 5 carried out in accordance with the invention, the recycle cut is of clearly superior quality to that obtained in comparative test 6. In fact, in test 5 this cut is lighter, less rich in sulfur impurities; its molecular hydrogen content is higher, and its aromatic hydrocarbon content is lower. This results in cracking such a cut in the first reaction chamber (1), not only higher yields, but also better qualities of the cracked products.

In general, the above examples perfectly illustrate some of the many advantages provided by the present invention. In particular, they show that the invention makes it possible to optimally recycle certain hydrocarbon fractions resulting from a first step of cracking the fresh charge, which makes it possible to substantially increase the total conversion efficiency of this charge. , with increased selectivity in favor of the specific products sought.

Claims (28)

1. A process for cracking a hydrocarbon charge in a fluidised bed, in which heat-conducting particles, optionally catalytic, circulate in two successive reaction chambers (1;16), in each of which they are brought into contact with at least hydrocarbon fraction, and the reaction effluents originating from each of said chambers are directed towards the same fractional distillation unit, characterised in that the effluents of each of the reaction chambers (1;16) are fractionated partly separately in the same partly compartmented fractionating column (12), and in that at least one fraction (13,44a) originating from the separate fractional distillation of the effluents of one of the reaction chambers (1;16) is, wholly or partly, reinjected into the other chamber.
2. A process according to any one of the preceding claims [sic], characterised in that the residence time of the hydrocarbons injected into the first reaction chamber (1) is less than the residence time of the hydrocarbons injected into the second reaction chamber (16).
3. A process according to any one of the preceding claims, characterised in that the residence time of the hydrocarbons injected into the first reaction chamber (1) is between 0.05 and 5 seconds, preferably between 0.1 and 1 second.
4. A process according to any one of the preceding claims, characterised in that the residence time of the hydrocarbons injected into the second reaction chamber (16) is between 0.1 and 10 seconds, preferably between 0.4 and 5 seconds.
5. A process according to any one of the preceding claims, characterised in that the flow of the charge and of the particles into the first reaction chamber (1) takes place in an essentially descending direction.
6. A process according to any one of the preceding claims, characterised in that the flow of the charge and of the particles into the second reaction chamber (16) takes place in an essentially ascending direction.
7. A process according to any one of the preceding claims, characterised in that, in said partly compartmented fractionating column (12), the heaviest effluents originating from each of the two reaction chambers are fractionated separately, whereas the lightest effluents are combined.
8. A process according to the preceding claim, characterised in that said fraction (13) originating from the separate fractional distillation of the effluents from one of the reaction chambers and which, wholly or partly, is reinjected into the other chamber, comprises slurry and/or a heavy distillate of the HCO type and/or fraction of the gas oil type, such as LCO.
9. A process according to either one of claims 7 and 8, characterised in that at least one fraction (13) originating from the separate fractional distillation of the heaviest effluents from the first reaction chamber (1) is, wholly or partly, reinjected into the second reaction chamber (16).
10. A process according to any one of claims 1 to 6, characterised in that, in said in said partly compartmented fractionating column (12), the lightest effluents originating from each of the two reaction chambers are fractionated separately, whereas the heaviest effluents are combined.
11. A process according to the preceding claim, characterised in that said fraction (44a) originating from the separate fractional distillation of the effluents from one of the reaction chambers and which is, wholly or partly, reinjected into the other chamber, is gasoline.
12. A process according to either one of claims 10 and 11, characterised in that at least one fraction (44a) originating from the separate fractional distillation of the lightest effluents from the second reaction chamber (16) is, wholly or partly, reinjected into the first reaction chamber (1).
13. A process according to any one of the preceding claims, characterised in that said fraction (13;44a) originating from the separate fractional distillation of the effluents from one of the reaction chambers and which is, wholly or partly, reinjected into the other chamber, is combined with other hydrocarbon fractions prior to this reinjection.
14. A process according to any one of the preceding claims, characterised in that said fraction (13;44a) originating from the separate fractional distillation of the effluents from one of the reaction chambers and which is, wholly or partly, reinjected into the other chamber, is subjected to one or more intermediate treatments prior to this reinjection.
15. A process according to claim 14, characterised in that said intermediate treatment includes a hydrotreatment, for example hydrogenation, hydrodearomatisation, hydrodesulphurisation, hydro-denitrogenation.
16. A process according to any one of the preceding claims, characterised in that upstream of the second reaction chamber (16), in addition to the particles originating from the first reaction chamber (1), there is introduced the remainder of particles originating from the regenerator (23).
17. An apparatus for cracking a hydrocarbon charge in a fluidised bed, utilising two reaction chambers (1;16) connected to one another by a transfer means (10) for heat-conducting particles, a fractionating column (12) and ducts (7;18) for the inlet of the hydrocarbon effluents originating from each of the two chambers (1;16) into said fractionating column (12), characterised in that:

    - said fractionating column (12) comprises, in its inner portion, at least two distinct zones: a first compartmented fractional distillation zone (40) formed by two compartments (38;39) each communicating with a second common fractional distillation zone (41);

    - the inlet ducts (7;18) for effluents originating from the first and second reaction chambers (1;16) discharge respectively into the first and second compartments (39;38) of said compartmented fractional distillation zone (40);

    - means (13;44a) are provided for recycling and injecting into one of the reaction chambers (1;16) at least one fraction drawn off from the compartmented fractional distillation compartment of the effluents of the other reaction chamber.
18. An apparatus according to the preceding claim, characterised in that said reaction chambers (1;16) are different.
19. An apparatus according to either one of claims 17 and 18, characterised in that the first reaction chamber (1) is formed by a substantially vertical reactor with descending flow of the type known as a downer.
20. An apparatus according to any one of claims 17 to 19, characterised in that the second reaction chamber (16) is formed by a substantially vertical reactor with ascending flow of the type known as a riser.
21. An apparatus according to any one of claims 17 to 20, characterised in that the compartmented fractional distillation zone (40) corresponds to the lower part of the fractionating column (12).
22. An apparatus according to claim 21, characterised in that the compartmented fractional distillation zone (40) is divided into two compartments (38;39) by a substantially vertical separating means (37;37') extending from the bottom of the fractionating column (12) over part of the height thereof.
23. An apparatus according to claim 21, characterised in that the compartmented fractional distillation zone (40) is divided into two compartments (38;39) by a substantially horizontal separating means formed by a plate (37") extending over a horizontal section of the column (12) and provided with one or more flues (50) allowing the upward passage, towards the common fractional distillation zone (41), of the light effluents originating from the compartment (38) below said plate (37").
24. An apparatus according to any one of claims 17 to 20, characterised in that the compartmented fractional distillation zone (40) corresponds to the upper part of the fractionating column (12).
25. An apparatus according to claim 24, characterised in that the compartmented fractional distillation zone (40) is divided into two compartments (38;39) by a substantially vertical separating means (37;37') extending from the top of the fractionating column (12) over part of the height thereof.
26. An apparatus according to claim 24, characterised in that the compartmented fractional distillation zone (40) is divided into two compartments (38;39) by a substantially horizontal separating means formed by a plate (37") extending over a horizontal section of the column (12) and provided with one or more flues (50) allowing the downward passage, towards the common fractional distillation zone (41), of the heavy effluents originating from the compartment (38) above said plate (37").
27. An apparatus according to either claim 22 or 25, characterised in that said separating means comprises a flat vertical wall (37).
28. An apparatus according to either claim 22 or 25, characterised in that said separating means comprises a cylindrical vertical wall (37') whose axis of revolution is parallel to the longitudinal axis of the fractionating column (12).