EP0323297B1 - Fluidised bed hydrocarbon conversion process - Google Patents

Description

The present invention relates to a conversion process allowing, in the same reaction zone, catalytic cracking from heavy hydrocarbon charges and the simultaneous production of olefins, in particular olefins comprising from 2 to 4 carbon atoms, by gentle steam cracking of light hydrocarbon charges.

It is known that hydrocarbon cracking processes are commonly used by the petroleum and oil services industries; they consist in dividing, by raising the temperature, hydrocarbon molecules into smaller molecules. There are two types of cracking, thermal cracking and catalytic cracking, which involve either the only influence of temperature or the active sites of a catalyst.

In a conventional steam cracking unit, that is to say thermal cracking with water vapor, the hydrocarbon charge is gradually heated in a tubular furnace, and the thermocracking reaction, which is a globally endothermic reaction, takes place mainly in the part of the tubes receiving the maximum heat flux. The temperature of these tubes is determined by the nature of the hydrocarbons to be cracked (they are generally either ethane or liquefied petroleum gases or LPG, or gasolines, or naphthas, or finally sometimes gas oils). Whatever the nature of the load, this temperature is always very high and greater than 700 ° C; it is however limited to a maximum of the order of 850 ° C. by the conditions of implementation of the method and by the complexity of operation of the ovens which use auxiliary heating energy.

• le préchauffage de la charge liquide,
• la vaporisation de cette charge,
• l'apport de calories exigé par les réactions impliquées, lesquelles sont globalement endothermiques.

In a catalytic cracking unit in a conventional fluidized bed (in English Fluid Catalytic Cracking, or FCC process), the hydrocarbon charge, generally composed of gas oils or heavier charges such as distillation, is brought into contact with a cracking catalyst, which is kept in suspension in the vapors of the feed. After the desired molecular weight range has been reached by cracking, with corresponding reduction in the boiling weights, the catalyst is separated from the products obtained, stripped, regenerated by combustion of the coke formed, then brought back into contact with the charge to crack. This catalytic cracking reaction takes place in a temperature range generally between 450 and 550 ° C. It is implemented so that the cracking unit is in thermal equilibrium without using energy annexed to the heating. In other words, the supply of hot catalyst regenerated by combustion of the coke deposited during the reaction must be such that it can meet the various thermal requirements of the reaction section, namely, in particular:

• preheating of the liquid charge,
• the vaporization of this charge,
• the intake of calories required by the reactions involved, which are generally endothermic.

The steam cracking and catalytic cracking processes therefore make it possible to treat hydrocarbon charges of different natures under reaction conditions no less different.

The subject of the present invention is a process for carrying out, in the same reaction zone, in dilute fluidized phase, of ascending or descending type, on the one hand, a thermal cracking reaction with steam of hydrocarbon feedstocks light, which may include saturated light gases or cuts ranging from gasoline to diesel, and, on the other hand, a catalytic cracking reaction of heavy hydrocarbon charges, of which a substantial part of the boiling range is located above 500 ° C.

It is known, in fact, that the catalytic cracking of heavy feedstocks (see EP-A-208.609, belonging to the Applicant) requires temperatures greater than or equal to the vaporization temperature of the hydrocarbons, in order to allow a subsequent reaction in the gas phase. When this vaporization temperature is significantly higher than that required by the actual cracking reaction, it is possible, after a controlled contact time, to bring the temperature of the suspension of catalyst grains and of hydrocarbons to a more suitable level to the catalytic cracking reaction, by introducing, into this suspension, fluids with a lower boiling point, such as light recycling oils or LCOs (from the "Light Cycle Oil") and heavy oils or HCO (from Heavy Cycle Oil).

It is also known that, because of their content of compounds such as asphaltenes, resins or polyaromatics, these heavy loads tend to supply, under the reaction conditions, substantial amounts of coke, which are sometimes much greater than those required to satisfy the unit's thermal balance.

The present invention aims to use this feature of heavy loads to produce coke, not only to provide the catalyst, during the combustion of coke, the energy necessary for the vaporization of the heavy load, but also to provide energy to the catalyst. additional and thus create, in the upstream part of the reaction zone, the conditions required for carrying out a gentle steam cracking of lighter hydrocarbons, comprising in particular ethane, propane, butane, light gasolines, naphthas and gas oils .

• le vapocraquage est réalisé par mise en contact, dans un lit fluidisé des particules de catalyseur, desdits hydrocarbures légers et d'une quantité de vapeur d'eau égale au moins à 20% en poids et de préférence comprise entre 30 et 50% en poids de la quantité d'hydrocarbures légers, la température résultant de ladite mise en contact étant comprise entre 650 et 850°C et, de préférence entre 700 et 800°C;
• le craquage catalytique des hydrocarbures lourds est réalisé par injection dans la suspension de catalyseur des effluents provenant de la partie amont de la zone réactionnelle de façon telle que la température de mélange soit d'abord supérieure à la température de vaporisation de la charge et comprise entre 500 et 650°C, puis soit ramenée à une température comprise entre 475 et 550°C par pulvérisation, immédiatement en aval de l'injection de la charge lourde, d'une coupe d'hydrocarbures entièrement vaporisable dans les conditions de sortie de la zone réactionnelle.

The present invention therefore relates to a process for the conversion of petroleum hydrocarbons, in the presence of catalyst particles in the fluidized phase, in a tubular reaction zone with ascending or descending flow, this process comprising at least one step of steam cracking of at least one cut of light hydrocarbons, in the upstream part of the reaction zone, and a catalytic cracking step of at least one cut of heavy hydrocarbons, in the downstream part of said reaction zone, a step of ballistic separation of the spent catalyst particles, a step of regenerating this catalyst in at least one zone for burning the coke deposited on these particles and a step of recycling the regenerated particles to the supply of the reaction zone, this process being characterized in what:

• the steam cracking is carried out by bringing into contact, in a fluidized bed, the particles of catalyst, said light hydrocarbons and an amount of water vapor equal to at least 20% by weight and preferably between 30 and 50% by weight the quantity of light hydrocarbons, the temperature resulting from said contacting being between 650 and 850 ° C and preferably between 700 and 800 ° C;
• the catalytic cracking of heavy hydrocarbons is carried out by injecting effluents from the upstream part of the reaction zone into the catalyst suspension in such a way that the mixing temperature is first above the vaporization temperature of the charge and between 500 and 650 ° C, then be brought back to a temperature between 475 and 550 ° C by spraying, immediately downstream of the injection of the heavy load, with a cut of hydrocarbons entirely vaporizable under the conditions of exit from the reaction zone.

Light hydrocarbons intended for steam cracking may be introduced into the reaction zone using one or more injection lines, depending on the nature of the hydrocarbons to be steam cracked. In particular, according to a particularly advantageous embodiment of the process according to the present invention, the various cuts of hydrocarbons capable of being injected, will be introduced one after the other from upstream to downstream in said reaction zone by Ascending of their boiling temperature, the lightest cup being introduced into the hottest area. For example, it will be possible to introduce ethane into the most upstream part of the reactor, that is to say into the injection zone where the regenerated catalyst is the warmest, and to introduce petrol in the area immediately downstream, the temperature of which will be lower, due to the contacting of the catalyst and the ethane, but will nevertheless remain sufficient for the thermal cracking of petrol. It will likewise be possible to introduce thereafter and according to the same principle, cuts of naphthas, then of diesel.

Thus, the steam cracking zone may be subdivided into as many zones, operating with decreasing severity, as there are sections of light saturated hydrocarbons intended for steam cracking.

The quantity of water vapor injected into the upstream part of the reaction zone is here significant compared to the usual cracking conditions in a fluidized bed. However, it remains appreciably lower than the values practiced in the conventional steam cracking process, in particular because the process described here accommodates without problem the possible formation of a certain amount of coke. Indeed, the amount of water vapor will usually be between 20 and 60% and, preferably, between 30 and 50% by weight, relative to the amount of hydrocarbons to be converted by steam cracking. As a result, maintaining the fluidized phase at the temperatures desired for steam cracking requires an increase in calories which is all the more important when a greater quantity of water vapor is injected into the reaction zone intended to avoid or at the very least to minimize the polymerization of olefins and diolefins. This supply of calories can be obtained, in accordance with the present invention, by catalytic cracking of a heavy load of hydrocarbons from the downstream part of the reaction zone.

Technological difficulties related, in part, to metallurgy of the apparatus and, in part, to the problems of stability of the catalyst at the temperatures required by the implementation of the process according to the present invention, preferably driving the use of a catalyst regeneration device operating with two separate combustion chambers, thus making it possible to supply the required quantities of catalytic particles at the appropriate elevated temperature (see for this purpose EP-A-184,517 filed by the Applicant).

A first advantage of the process according to the invention is linked to the fact that the steam cracking reaction, in the upstream part of the reactor, requires significant amounts of calories due, essentially, to the very high endothermicity of this reaction (5 to 10 times higher than that of the catalytic cracking reaction). This significant absorption of calories, in the upstream part of the reactor, acts as a heat sink, which results, as in any catalytic cracking unit, by an increased flow rate of the catalyst circulation. As a result, the catalytic cracking reaction will be carried out with a ratio of quantity of catalyst to quantity of filler to be cracked (generally called "C / O ratio") much higher than according to the prior art (see for this purpose EP-A -208.609), with the consequence of a significant improvement in the yield of gasoline and diesel compared to the amount of heavy load to be cracked. In particular, this C / O ratio may advantageously be between 4 and 12 in the downstream part of the reaction zone.

A second advantage of the process according to the invention resides in the fact that it makes it possible to convert into ethylene, propylene and butenes, light cuts of low recovery, such as ethane or certain gasoline cuts, and this under selectivity conditions superior to conventional steam cracking. For example, according to a particularly advantageous embodiment of the invention, the cracking unit will comprise a device for fractionating the reaction effluents making it possible to selectively fractionate, in a manner known per se, the abovementioned hydrocarbons as well as light gases and hydrocarbons with two, three or four carbon atoms. It will in particular be possible to separate the ethane from the other gaseous effluents and to recycle it, possibly in combination with cuts from other units, in the hottest part of the reaction zone, that is to say in upstream of the injection of petrol or diesel, where the regenerated and hot catalyst is introduced.

According to this configuration, the gentle steam cracking will be carried out in the upstream part of the reactor in at least two zones of decreasing severity, by injection in the presence of water vapor of at least two separate cuts: a cut containing mainly ethane, but also possibly propane and butane, then a cut containing light essences, then possibly naphtas or gas oils.

• d'une part, l'éthane n'ayant pas réagi, qui sera recyclé à l'entrée de la partie amont de la zone réactionnelle, conformément à la présente invention.
• d'autre part, des essences légères résultant de ladite oligomérisation, qui pourront pour leur part, être éventuellement recyclées avec d'autres essences dans la zone de vapocraquage fonctionnant à plus basse sévérité, en vue d'augmenter la production de propylène et de butènes, si tel est le but recherché.

According to a particularly advantageous embodiment of the process according to the present invention, the production of propylene can also be significantly increased by judicious reuse of the hydrocarbons with two carbon atoms produced during the reaction. For this purpose, it will suffice to use the mixture of ethylene ethane coming from the fractionation zone, of a type known per se, and to send this mixture to a trimerization or oligomerization reactor of the ethylene, for example of the type described by the prior art (for this purpose refer to patents EP-A-12 685, 24 971, 215 609 or US-A-4 605 807), to recover, after fractionation of the effluents :

• on the one hand, the unreacted ethane, which will be recycled at the inlet of the upstream part of the reaction zone, in accordance with the present invention.
• on the other hand, light essences resulting from said oligomerization, which can for their part, be optionally recycled with other essences in the steam cracking zone operating at a lower severity, with a view to increasing the production of propylene and butenes, if this is the aim sought.

An additional advantage arising from the present invention resides in the fact that the hydrogen necessarily produced by steam cracking in the upstream part of the reactor is capable of reacting under the reaction conditions of the downstream part of the reactor and, therefore, of improving the yield effluents from the conversion unit into the best valued products.

The steam cracked hydrocarbon fractions usable according to the present invention therefore comprise saturated light gases, such as ethane, propane or butanes, or heavier hydrocarbons, saturated or not, such as light gasolines, naphthas or gas oils, or even certain cuts with a higher boiling point but highly paraffinic, such as paraffins or slack wax. These hydrocarbon fractions can come either from different refinery units, such as atmospheric distillation, visbreaking, hydrocracking, oil manufacturing or olefin oligomerization units, or effluents from the unit of conversion itself.

The main charge injected downstream of the mild steam cracking zone could be a standard charge of a catalytic cracking unit, but with the possibility, compared to the known precedents, of also using heavier charges.

Mention may be made, for example, as fillers capable of being treated according to the present invention, gas oils under vacuum and heavier hydrocarbon oils, such as crude oils, possibly topped, as well as residues from atmospheric distillation or from distillation under empty. These fillers may, if necessary, have received a preliminary treatment, such as, for example, a hydrotreatment. They may, in particular, contain fractions rich in asphaltenes and having a Conradson carbon content. equal to or greater than 10%. These charges may or may not be diluted by conventional lighter cuts, which may include cuts of hydrocarbons which have already undergone a cracking operation and which are recycled, such as cracked gas oils, LCOs or HCOs Finally, these charges can be preheated in a temperature range generally between 100 and 400 ° C.

All these charges of high boiling hydrocarbons can easily be vaporized by carrying out an appropriate spraying in the reaction zone, due to the presence of a high quantity of catalyst at high temperature coming from the upstream part of the zone. reactive. The heaviest compounds and, in particular, the asphaltenes contained in the feed will then be liable to undergo instantaneous and very selective thermal cracking, giving rise to the formation of lighter products capable of being catalytically cracked in the reaction zone located in downstream.

To this end, the injection of hydrocarbons into the downstream part of the reaction zone is carried out using high-performance sprayers, such as nozzle sprayers of the venturi type, so as to give the droplets of liquid the smallest possible diameter. , generally less than 100 microns and preferably less than 50 microns. This fine spray allows the droplets formed to be vaporized almost instantaneously, when they are brought into contact with the catalyst flow at high temperature.

The temperature for mixing the charge with the catalyst particles may be as high as necessary to obtain complete vaporization of all the constituents of the charge, while remaining independent of the final catalytic cracking temperature of the zone located further downstream, thanks to the injection, downstream of the residual main charge, of another cut of hydrocarbons, such as a cut HCO or LCO liquid, the latter cut being injected at a temperature and in an amount such that the temperature prevailing in the rest of the reaction zone can be adjusted, so that the catalytic cracking is carried out under optimal conditions. To this end, the device will include means for regulating the feed rate of the recycle so that the final reaction temperature is maintained equal to a set value adapted to the load to be cracked, to the cracking conditions and to the type of market sought (for example, petrol market: final temperature 500-530 ° C, or diesel market: final temperature 480-510 ° C). The mixing temperature of the vaporized charge to be cracked and the catalyst can thus be maintained above the dew point of the charge, while adapting the cracking temperature to the selectivity desired for the cracking effluents.

The process according to the invention can advantageously be implemented in a device comprising a reaction zone for bringing petroleum fractions at high temperature into contact with catalyst particles in a tubular type reactor with essentially ascending or descending flow, means for ballistic separation of said particles and cracked cuts, means for stripping the catalyst particles, means for regenerating them by combustion of the coke deposited on these particles, and means for recycling the regenerated particles in the supply to said reactor , this device comprising means for injecting at least one section of light hydrocarbons such as saturated light gases, gasoline or diesel in the upstream part of the tubular reactor in the presence of water vapor in an amount equal to less than 20% by weight and preferably between 30 and 50% by weight relative to the quantity hydrocarbons, so that the resulting mixture is maintained at a temperature between 650 and 850 ° C in a dilute fluidised bed, said device further comprising in the downstream part of the tubular reactor first means for spraying at least one cut of heavier hydrocarbons under conditions such that the mixing temperature is higher than the vaporization temperature of said hydrocarbons and between 500 and 650 ° C, as well as second spraying means disposed immediately downstream of the injection zone of said heavier hydrocarbons with a view to injecting a fraction of hydrocarbons entirely vaporizable under the conditions for leaving the reaction zone.

This temperature of the conversion effluents will in particular be kept constant between 475 and 550 ° C. by spraying, downstream of the injection zone of the heavy load, with a determined quantity of LCO or HCO. This spraying, like that of the heavy load to be catalytically cracked, will be carried out using injectors of a type known per se, making it possible to obtain, at the outlet of the injector (s), droplets of which at least 80% have a diameter less than 100 micrometers.

It goes without saying that many variants of the process according to the invention can be implemented and that, consequently, the ratio between the flow rate of heavy hydrocarbon feed introduced into the downstream part and the flow of lighter hydrocarbons ( in particular ethane and petrol) introduced into the upstream part can vary in significant proportions, for example in a ratio of between 0.20 and 1.50 by weight.

All the classes of catalysts having catalytic cracking capacities can be used to carry out the process according to the present invention. A particularly advantageous category is that of catalysts having porous structures in which molecules can be brought into contact with active sites located in the pores; in this class, there are in particular silicates or aluminosilicates. In particular, catalysts containing zeolite are commercially available with supports containing a variety of metal oxides and combinations of said oxides, in particular silica, alumina, magnesia, oxides of titanium, barium, and mixtures of these substances, as well as mixtures of said oxides with clays, bridged or not. The catalyst composition can naturally contain one or more agents promoting one or the other step of the process. The catalyst may therefore, in particular, contain agents promoting the combustion of coke during regeneration.

The present invention will be described below in more detail, with reference to the single figure in the appendix, which illustrates the application of the invention to a fluidized bed, riser or riser conversion assembly and to two combustion chambers, particularly suitable for the complete regeneration of a catalyst capable of being brought to high temperature.

The upward fluidized phase conversion device shown in this figure essentially comprises a column 1, called a load elevator, or riser. It is supplied at its base by line 2 with particles of regenerated catalyst particles, in a quantity regulated by a valve 3. The regenerated particles are fluidized by injection of steam or gas arriving by line 4 at the base of the riser , using a diffuser 5.

Light saturated gases comprising in particular ethane are then introduced into the column using the diffuser 7 supplied by line 6 with additional steam supplied by line 10. The temperature above 750 ° C., and, preferably, at 800 ° C., which prevails in this part of the chamber, therefore allows thermal cracking with steam of these saturated light gases. Downstream of this first steam cracking zone, a gasoline or diesel cut, injected by a diffuser 8 supplied by the line 9, can in turn be cracked at a lower temperature level, of the order of 150 to 750 ° C. A complement of steam can also be supplied by line 10 ′.

The load of hydrocarbons heavier than diesel is then introduced into the reactor using one or more injectors 11 supplied by line 12, in an amount such that the temperature prevailing in this part of column 1 is higher or equal to the vaporization temperature of said charge. It is then necessary to reduce the mixing temperature to a value more conducive to catalytic cracking, that is to say of the order of 475 to 550 ° C., by spraying with hydrocarbons such as light diluents (LCO) or heavy (HCO), using line 13 which supplies the injector (s) 14.

Column 1 opens at its top into an enclosure 15, which is for example concentric with it and in which, on the one hand, the separation of the cracked charge takes place and, on the other hand, the stripping of the used particles. The ballistic separation system, cyclonic or not, is housed in the enclosure 15 and the effluent hydrocarbons are evacuated by an evacuation line 16, provided at the top of the enclosure 15, while the used catalytic particles descend to the base. enclosure 15 where a line 17 supplies stripping gas (generally steam) to diffusers 18 regularly arranged at the base of this enclosure 15. The particles thus stripped are evacuated towards the regenerator, via of a duct 19, on which a regulating valve 20 is provided.

The regenerator shown in this figure here comprises a first combustion zone 21, in the presence of oxygen, of the coke deposited on the catalyst particles. The coke is thus mainly burnt using air, injected into the regenerator bar by a line 22, which feeds the diffuser 23. The combustion gas is separated from the catalyst grains in the cyclone 24, whence the combustion gas is evacuated via a line 25, while the partially regenerated catalytic particles are transferred to the second stage 26 by the central duct 27, supplied with air by the line 28. The base of the stage 26 can also be supplied with air by the diffuser 29, supplied by the line 30. The grains of this regenerated catalyst are discharged laterally in a buffer enclosure 31 and recycled through line 2 to the supply to the elevator 1. The combustion gases discharged at the upper part of the chamber 26 are treated in a cyclone 32, which is here external to the chamber and from the base of which the particles of the catalyst are returned via the conduit 33 into the chamber 26, while the combustion gases are evacuated via line 34.

• par la ligne 36, les gaz légers ou gaz secs, (composés en particulier d'hydrogène, de méthane, d'éthane, d'éthylène, d'hydrocarbures en C₃ à C₅ de NH₃ et d'H₂S), lesquels peuvent être ensuite traités dans un autre dispositif 37 de fractionnement, permettant, de façon connue en soi, de séparer l'éthane et l'éthylène par la ligne 38 et les hydrocarbures en C₃ à C₅ qui sortent par la ligne 39;
• par la ligne 40, la coupe essence, dont l'intervalle d'ébullition s'étend généralement de la coupe C₅ jusque vers 160-220°C;
• par la ligne 41, la coupe gazole, souvent appelée aussi LCO, dont l'intervalle d'ébullition s'étend généralement depuis 160-220°C (début de coupe) jusque vers 320-380°C (fin de coupe);
• par la ligne 42, la coupe diluant lourd, souvent appelée aussi HCO, moins bien valorisée (base de fuel à faible viscosité) et dont l'intervalle d'ébullition est généralement compris entre 320-380°C (début de coupe) et 480-500°C (fin de coupe);
• et, enfin, par la ligne 43, une coupe de résidu de distillation, qui contient les produits les plus lourds et les plus difficiles à craquer et des quantités plus ou moins importantes de fines de catalyseurs; ce résidu, qui a un point d'ébullition généralement supérieur à 400°C (mais qui peut également inclure tout le résidu de distillation de point d'ébullition supérieur à 320-380°C), est généralement appelé "slurry catalytique".

Furthermore, the reaction effluents leaving the stripping zone via line 16 are sent to a fractionation device schematically represented at 35, making it possible to separate:

• via line 36, light gases or dry gases (in particular composed of hydrogen, methane, ethane, ethylene, C₃ to C₅ hydrocarbons of NH₃ and H₂S), which can then be treated in another fractionation device 37, making it possible, in a manner known per se, to separate ethane and ethylene via line 38 and the C₃ to C₅ hydrocarbons which exit through line 39;
• by line 40, the gasoline section, the boiling range of which generally extends from section C₅ to around 160-220 ° C;
• by line 41, the diesel cut, often also called LCO, whose boiling range generally extends from 160-220 ° C (start of cut) until around 320-380 ° C (end of cut);
• by line 42, the heavy thinner cut, often also called HCO, less well valued (low viscosity fuel base) and whose boiling range is generally between 320-380 ° C (start of cut) and 480 -500 ° C (end of cut);
• and, finally, by line 43, a section of distillation residue, which contains the heaviest products and the most difficult to crack and more or less large quantities of catalyst fines; this residue, which has a boiling point generally greater than 400 ° C (but which can also include all the distillation residue with a boiling point greater than 320-380 ° C), is generally called "catalytic slurry".

According to a particularly advantageous embodiment of the present invention, the ethane and the ethylene coming from line 38 are introduced into an oligomerization reactor 44. A fractionation device 45 then makes it possible to evacuate via line 46 unreacted ethane and ethylene, while light olefinic gasolines (whose boiling temperature is generally between 30 and 100 ° C) are extracted by line 47. Line 46 then allows to return the ethane thus recovered in the upstream part of the reactor by line 6, while the light gasolines can either be recovered as such, or steam cracked by recycling in line 9, in order, for example, to maximize the production of propylene.

Finally, part of the HCO from the fractionation zone 35 is here recycled by line 42 to line 13 to regulate the reaction temperature downstream of column 1. This regulation is done using a valve 48, the flow rate of which is for example adjusted as a function of the temperature measured using a probe preferably located at the outlet of the reactor.

Likewise, valves 49 and 50 make it possible to regulate the quantities of light hydrocarbons introduced by lines 9 and 6 into the upstream part of the reaction zone, as a function of the temperature measured in this part, so that this temperature , between 650 and 850 ° C, allows to ensure steam cracking, in accordance with the present invention.

EXAMPLE

The following tests were carried out in the same unit in ascending fluidized phase, having two regeneration zones of the type shown in FIG. 1, from a gasoline cut (straight-run cut) and a charge A which is here an atmospheric distillation residue of a crude oil of the SHENGLI type.

These charges have the following characteristics:

A commercial catalyst is used comprising ultra-stabilized zeolites and a matrix capable of cracking the heaviest hydrocarbon molecules. The conditions of this test, in which ethane and petrol are successively injected into the upstream part of the reaction zone, then successively the charge A and a determined quantity of HCO in the downstream part, are as follows:

After recovery of the effluents from the conversion reaction, the nature of the latter is analyzed. The analysis results (in% by weight relative to the total amount of hydrocarbons to be converted, that is to say relative to ethane, petrol and the atmospheric distillation residue) alone demonstrate the advantages of the present invention compared to conventional type methods. These results are as follows:

Claims (9)

1. A process for the conversion of petroleum hydrocarbons, in the presence of catalyst particles in the fluidised phase, in a tubular reaction zone with ascending or descending flow, said process comprising at least one steam cracking stage of at least one fraction of light hydrocarbons, in the upstream part of the reaction zone, and a catalytic cracking stage of at least one fraction of heavy hydrocarbons, in the downstream part of said reaction zone, a ballistic separation stage for spent catalyst particles, a stage for regenerating this catalyst in at least one combustion zone of the coke deposited on these particles and a stage for recycling the regenerated particles to the feed of the reaction zone, said process being characterised in that:

- the steam cracking is carried out by bringing into contact, in a fluidised bed, catalyst particles, said light hydrocarbons and a quantity of steam equal to at least 20% by weight and, preferably, between 30 and 50% by weight of the quantity of light hydrocarbons, the temperature arising from said bringing into contact being between 650 and 850°C and, preferably, between 700 and 800°C;

- the catalytic cracking of the heavy hydrocarbons is carried out by injecting into the catalyst suspension effluents originating from the upstream part of the reaction zone, in such a way that the mixing temperature is initially higher than the vaporisation of the charge and is between 500 and 650°C, is then reduced to a temperature of between 475 and 550°C by atomising, immediately downstream of the injection of the heavy charge, a hydrocarbon fraction which can be completely vaporised under the outlet conditions of the reaction zone.

2. A process according to claim 1, characterised in that the light hydrocarbon fractions to be steam cracked comprise saturated light gases, motor fuels, naphthas and/or gas oils.

3. A process according to claim 2, characterised in that said light hydrocarbons are injected into at least two zones from upstream to downstream of said reaction zone, in ascending order of their boiling point, the lightest fraction being introduced into the hottest zone.

4. A process according to any one of claims 1 to 3, characterised in that the heavy hydrocarbon fractions to be catalytically cracked comprise charges of an atmospheric or vacuum distillation residue type, of which at least 20% by weight have a boiling point above 550°C.

5. A process according to any one of claims 1 to 4, characterised in that the majority of the hydrocarbons atomised immediately downstream of the injection of the heavy charge are composed of recycles of HCO or LCO arising from the fractional distillation of the effluents coming from the reaction zone.

6. A process according to any one of claims 1 to 5, characterised in that the hydrocarbons injected into the downstream part of the reaction zone are atomised in the form of droplets of which at least 80% are of a diameter of less than 100 micrometres.

7. A process according to any one of claims 1 to 6, characterised in that the catalyst particles are regenerated by combustion of the coke deposited on them in two separate combustion chambers each having their own means for discharging gaseous effluents.

8. A process according to any one of claims 1 to 7, characterised in that the ratio of the quantity of catalyst to the quantity of charge to be cracked is between 4.0 and 12.0 in the downstream part of the reactor.

9. A process according to any one of claims 1 to 8, characterised in that the ethylene arising from the fractionation of the reaction effluents is fed into an oligomerisation reactor, the effluents of which are recycled into the upstream part of the reactor.

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