WO1991003527A1

WO1991003527A1 - Method and device for vapor-cracking of hydrocarbons in fluidized phase

Info

Publication number: WO1991003527A1
Application number: PCT/FR1989/000437
Authority: WO
Inventors: Jean-Bernard Sigaud; Jean-Louis Mauleon
Original assignee: Compagnie De Raffinage Et De Distribution Total France
Priority date: 1989-09-01
Filing date: 1989-09-01
Publication date: 1991-03-21
Also published as: AU641367B2; AU4225289A

Abstract

Methods for converting by vapor-cracking at high temperature and in the presence of a diluted fluidized phase of essentially heat-conveying particles, on the one hand at least one light hydrocarbon charge which is little contaminated by metals and of which the boiling temperature is lower than 400 °C approximately and, on the other hand a heavier hydrocarbon charge essentially comprised of compounds of which the boiling temperature is higher than 400 °C approximately. According to the invention, the heavier hydrocarbon charge is injected between the step for the separation of the particles and the hydrocarbons issued from vapor-cracking and the step of fractionation of said hydrocarbons. Part of the rest of the distillation of hydrocarbons issued from vapor-cracking is injected in the downstream portion of the reactor.

Description

Process and device for steam cracking of hydrocarbons in the fluidized phase.

The present invention relates to a steam cracking method and device for converting petroleum hydrocarbon fractions, in the fluidized phase of heat-carrying particles and at high temperature, for the production of olefins and, in particular, olefins comprising 2 to 4 carbon atoms, butadiene and monoaromatic compounds, such as benzene, or which can be branched, such as toluene, xylenes, etc.

It is known that hydrocarbon cracking processes are commonly used in the petroleum and parapetroleum industries; they consist of dividing, by increasing 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 thermal cracking unit, the hydrocarbon charge is gradually heated in a tube furnace. The thermocracking reaction takes place mainly in the part of the tubes receiving the maximum heat flux, where the temperature is determined by the nature of the hydrocarbons to be cracked: - for the so-called visbreaking processes, in which only the heaviest molecules are split into smaller molecules, the cracking temperature is between 450 and 600 ° C depending on the case;

- when the molecules to be thermocracked are lighter molecules such as gasoline or liquefied petroleum gas (LPG) and that one seeks to produce light olefins and monoaromatic compounds, the necessary temperature is much higher and generally between 780 and 850 ° C, depending on the type of charge to be cracked, but it remains however limited by the conditions of implementation of the process and by the complexity of operation of the ovens, which use additional heating energy. Obtaining and maintaining the required temperature levels is all the more delicate since it gradually deposits unwanted coke on the walls of the tubes and the heat flow is limited. In addition, the higher wall temperature than that of the process is the cause of the formation of coke and degradation products such as gums and acetylenic compounds. Coke affects the quality of heat exchange; it leads to an increase in the pressure drop inside the tubes and an increase in the skin temperature imposing an excessive mechanical stress, which contributes to reducing the conversion rate of the load of hydrocarbons entering the unit. thermocracking and causes periodic stops for decoking. It also follows, on the one hand, that the process must be modular, so as to allow decoking operations in operation, and, on the other hand, that the loads to be treated must be "clean", so that that the duration of the cycles between two decokings is not too short. In practice, these charges are limited to LPG, gasoline, and certain favorable or hydrotreated gas oils.

In addition, the heat transfer in a tube is not instantaneous and the thermocracking reaction is very endothermic. There are therefore problems of temperature regulation and maintenance and, consequently, of selectivity, which are very difficult to solve.

To overcome these drawbacks and perform thermal cracking of hydrocarbons, it has been proposed for a long time to use the technique of fluidized beds. So, for example:

- US Pat. No. 3,074,878 (Esso) and European Patent Application No. 26,674 (Stone) use a tubular reactor with fluidized phase with downward flow of heat-carrying particles, with a short contact time, to achieve thermal cracking of charges petroleum, thanks to the heat supplied by the combustion of the coke deposited on the particles heat carriers;

- US patent 4,427,538 (Engelhard) uses a tubular reactor to perform cracking at low severity and elimination of the heaviest hydrocarbons contained in a charge, using an ascending fluidized phase reaction of inert heat-carrying particles .

None of these techniques is however capable of allowing, under satisfactory industrial conditions, the simultaneous conversion into light olefins and into monoaromatic compounds of several petroleum hydrocarbon fractions such as LPG, petroleum gasoline or, even more so, highly contaminated residual charges. Indeed, to thermocrack petroleum hydrocarbon fractions which include light paraffins such as butanes, propane and especially ethane, as well as petroleum fractions such as gasolines, naphthas and diesel fuels, it is necessary to maintain the reaction temperature at a very high level, generally of the order of 750 to 850 ° C, for a very short time, but strictly controlled. In the absence of precise control of the residence time in this temperature zone, olefin molecules formed during the conversion could polymerize to the detriment of the overall selectivity of the reaction. However, it turns out that the separation systems used until now to separate the reaction effluents from the heat-carrying particles do not generally allow a sufficiently rapid separation and quenching of the effluents, so that certain molecules formed are capable of continuing to react and to polymerize.

This results in a constant risk of clogging or fouling in the separation and stripping zone, as well as in the effluent hydrocarbon pipes between said zone and that of fractionation.

Furthermore, maintaining in the gas phase, at the temperatures desired for thermocracking, requires an instantaneous and very important supply of calories, due to the high endothermicity of the thermal conversion by steam cracking and the fact that a fairly large quantity of steam is injected into the reaction zone intended to lower the partial pressure of the hydrocarbons and to minimize coke production. In addition, in the case of steam cracking of light hydrocarbon fractions into olefins and monoaromatic compounds, the quantity of coke deposited on the heat-carrying particles would be entirely insufficient to ensure the thermal equilibrium of the system and would require the systematic addition of external energy.

Finally, this balance and the level of temperatures to be achieved impose very high temperatures on the heat transfer mass. However, the technological difficulties linked in part to the metallurgy of the equipment concerned have meant that only the most recent techniques make it possible to supply the required quantities of heat-carrying particles at the appropriate high temperature. The present invention aims to remedy these drawbacks by proposing a process for the conversion by steam cracking at high temperature of petroleum hydrocarbon fractions into olefins such as ethylene, propylene and butenes, butadiene and monoaromatic compounds, for example. introduction of said cuts into a dilute fluidized phase of heat-carrying particles and water vapor at high temperature, under reaction conditions of fluidization, of temperature and of strictly determined duration. The invention also aims to allow satisfactory conversion, by cracking the cuts introduced into the reactor, with a high selectivity for light olefins, butadiene and monoaromatic compounds. The invention also aims to allow effective control of the polymerization reactions of the reaction products.

The invention finally aims to produce coke only reduced quantity, but sufficient to satisfy the thermal balance of the unit.

To this end, the subject of the invention is a process of conversion by steam cracking, at high temperature and in the presence of a dilute fluidized phase of essentially heat-transferable particles, on the one hand, of at least one cut of light hydrocarbons little contaminated with metals, the boiling point of which is less than about 400 ° C and, on the other hand, a heavier hydrocarbon charge, consisting essentially of compounds with a boiling point above about 400 ° C, this process comprising a step of bringing said cut, then said load, in a staged manner and with decreasing severity, with heat transfer particles, catalytic or not, in a continuous reactor of tubular type with ascending flow or descending, a separation and stripping step making it possible to separate, on the one hand, at least 90% of said particles, which are then preferably regenerated by combustion of the coke deposited on r these before recycling them at a higher temperature to the feed to said continuous reactor and, on the other hand, the effluent hydrocarbons, which are recovered during a fractionation stage by distillation, this process being characterized in that at least a fraction of the heavier hydrocarbon charge is injected between said step of separation of the particles and of effluent hydrocarbons and that of fractionation, and in that at least a part is recycled in the downstream part of said reactor of the residue from said distillation fractionation step.

The cut or cuts of lightly contaminated light hydrocarbons distilling at less than 400 ° C. may be advantageously chosen from the group consisting of light paraffins such as ethane, propane and butanes, and heavier hydrocarbons such as essences, naphthas and gas oils, or even certain cuts with higher boiling point, but strongly paraffinic or naphthenic, such as paraffins or slack oil or oil recycles. 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 conversion unit itself. These various cuts can also be injected alone or in combination with steam and possibly other fluidizing gases such as hydrogen and light gases.

Preferably, according to a particularly advantageous embodiment, the steam cracking will be carried out in the continuous reactor in several zones of decreasing severity, by successive injections in the presence of steam and / or gaseous fluids of several distinct cuts, the first cut must necessarily have a boiling temperature lower than that of the next. This temperature profile is in fact particularly advantageous for optimizing the selectivity of the reactions involved. It is possible, for example, to successively inject a first cut containing mainly ethane, then optionally propane and butane, then in the liquid phase , a cut containing light gasolines, then possibly naphthas or gas oils and finally the heavier hydrocarbon charge, having a boiling point higher than about 400 ° C. The latter can advantageously be chosen from the group consisting of atmospheric or vacuum distillation residues, deasphalting pitches, catalytic slurries, or synthetic hydrocarbons. These charges can therefore be very heavy charges containing hydrocarbons whose boiling point can go up to 750 ° C. and more, and whose density can vary between 0 and 25 ° API. The quantity injected of these heavy hydrocarbon charges may advantageously, depending on the desired temperature profile and the needs of the thermal balance, represent 0.25 to 4 times the quantity of light cut injected in upstream.

In its most elaborate configuration, including successive injections of increasingly heavy cuts, for example of ethane or LPG (liquefied petroleum gas), then of petrol or diesel and, finally, of the heavier load , of the distillation residue type, in the continuous reactor zone located downstream, the continuous reactor will therefore, in fact, comprise several distinct reaction zones, operating successively under conditions of decreasing severity (decrease in temperature, in duration of contact with the heat transfer mass, the possibly catalytic activity of the heat transfer mass and the ratio between the flow rate of this mass and that of the hydrocarbons) and adapted to the nature of the charges to be treated and of the products sought. It will thus be possible, for example, to convert ethane by steam cracking, in the presence of water vapor, in the area of injection of heat-carrying particles where the temperature is the highest (of the order of 850 to 950 ° C. ), that is to say in the most upstream zone of the continuous reactor, then use the drop in temperature which results from the endothermicity of the reaction to inject at a temperature of the order of 800 to 900 ° C. a cut of propane or butane, and so on until the injection of an intermediate cut of hydrocarbons, such as a cut of the diesel type or a cut of light gasolines. Finally, we can use the resulting new temperature drop to crack the heavier charge, as well as the heavier residues from the steam cracking reaction, by recycling all or part of the fractionation residue in the downstream part of the reactor in conditions better suited to its nature.

In the course of its numerous works in this field, the Applicant has indeed observed that, while it is relatively easy to control the conditions of reaction time and temperature in the reactor by using each injection zone as quench zone ( "quench") compared to the previous zone, it is not the same in the part of the reaction zone which immediately precedes the separation and stripping of the heat transfer particles. Indeed, at the always very high temperature levels required for steam cracking, the separation of gaseous hydrocarbons and solids must be almost instantaneous, so as to preserve, on the one hand, the production of desired olefins, while minimizing the formation of coke or heavy products by polymerization reaction. So far, we have been limited in the matter of steam cracking in a fluidized bed to the following dilemma:

- or else the separation system, generally ballistic, often made up of cyclones, is effective and, in this case, the duration of the separation is too long to be able to optimize production and avoid coking and the formation of acetylene-type contaminants;

- or else the separation system is instantaneous but less efficient, this time resulting in either an excessive loss of hydrocarbons by entrainment of the latter in the regeneration zone, or an excessive entrainment of solid particles with the gaseous effluents and in particular fines, which it is very expensive to isolate distillates, the latter then becoming difficult to recover, with the risk of undesirable side reactions, when the solid particles have a certain catalytic activity.

The present invention aims to remedy the problems associated with the formation of coke and degradation products in the conduits leading the reaction effluents from the steam cracking units to the fractionation zone of these effluents. In order to be able to fractionate the effluent hydrocarbons from steam cracking units of the conventional type by distillation, the temperature of these must be lowered very sharply and above all very quickly, so as to obtain a fractionation tower inlet temperature lower than the "dew point" of effluents (ie at a temperature at which the heaviest fractions condense). However, at During this sudden drop in temperature, it is known that the heaviest compounds produced by the steam cracking reaction tend to deposit on the wall of the pipes, which causes regular and costly shutdowns of the steam cracking units for decoking these pipes. .

The present invention also makes it possible to remedy the drawbacks mentioned above, insofar as the injection of a major part of the heaviest charge necessary for the thermal equilibrium of the steam cracking reaction is carried out after step separation of at least 90% of the particles and of the hydrocarbons and before that of fractionation by distillation.

This particular mode of charge injection makes it possible to completely control the temperature and duration conditions of the steam cracking reaction for the following reasons:

the quenching effect necessary for the instantaneous cessation of the thermal reactions is ensured by spraying the charge itself, which is thereby preheated, which, combined with the dilution effect of the condensed liquid effluents, allows effectively deactivate all the coke precursors present in the steam cracking effluents, by dissolving in the still liquid petroleum charge (this quenching effect can optionally be completed before the fractionation step, either by passing the hydrocarbons through a heat exchanger, or by a new injection of water, steam or any other cut of hydrocarbons); - 0.01 to 10% and, preferably 0.05 to 5%, of heat transfer particles entrained in the reactor effluents allow both permanent sweeping of the walls, thus preserving them from any fouling, and absorption of erasers being formed in the effluent transfer lines to the fractionation zone;

- the recycling of distillation residues in the downstream part of the reactor not only ensures the thermal equilibrium of the unit and the transformation into olefins and monoaromatics of heavy loads hitherto not used in steam cracking, but also the consumption of the heaviest products, often difficult to recover, until they are exhausted.

The vaporization then being almost instantaneous and homogeneous, the recycle is thus preheated to a temperature close to its bubble point and therefore placed in the excellent conditions to crack very selectively.

In addition, the entrained heat transfer particles can be fully recycled and it is then possible, without excessive loss of heat transfer particles, to promote the rapid separation between the heat transfer particles and the gaseous effluents, even if this must be done at the expense of the efficiency of separation.

According to a particularly advantageous embodiment of the present invention, an almost instantaneous heat transfer is provided between the heavier hydrocarbon charge and the effluents of the steam cracking reaction by spraying in a manner known per se (see, for this purpose , European Patent No. 312,428) said filler in the liquid state. The quality of the heat transfer being linked to the exchange surface between liquid and gas, the injector (s) will be adapted to allow spraying of the charge in drops of diameter less than 200 microns and, preferably, 100 microns. Said injectors may advantageously be equipped with mixing chambers making it possible to introduce certain quantities of water or steam, or other petroleum fractions, with the charge. In addition, it is advantageous to introduce with the charge a substantial amount of fractionation residue. Furthermore, the quality of the quenching will be optimum, insofar as the temperature of the hydrocarbons entering the fractionation zone and resulting from the dissolution of the steam cracking effluents in the feed. the heaviest to steam will be below the "dew point" of these hydrocarbons.

The heat transfer thus carried out makes it possible to bring the hydrocarbons to a temperature which will preferably be between 300 and 450 ° C. in less than 0.3 seconds and, preferably, in less than 0.1 seconds.

In particular, the charge of hydrocarbons entering the fractionation zone will have a temperature less than 100 ° C and, preferably, less than 50 ° C than the temperature corresponding to the "bubble point" of said charge (c (i.e. at a temperature where it is in the liquid state, but at which the first bubbles of gaseous hydrocarbons are formed).

According to an equally advantageous embodiment of the present invention, the production of olefins and of monoaromatic compounds can be notably increased by judicious reuse of the saturated hydrocarbons produced during the reaction: it will suffice, for this purpose, to separate from each cuts C2, C, C Λ and others produced, these hydrocarbons saturated with olefins and to recycle the hydrocarbons in the corresponding injection zone of the upstream part of the reactor described above.

As a variant, it will also be possible to use for example the mixture of ethane and ethylene coming from the fractionation zone and to send this mixture to a ethylene trimerization or oligomerization reactor, for example of the type described by the prior art (for this purpose refer to European patents N ° 12 685, 24 971, 215 609 or to American patent N ° 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 gasolines resulting from said oligomerization, which can for their part, be optionally recycled with other gasolines in the steam cracking zone operating at a lower severity, which allows 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 selectivity of the effluents from the conversion unit into better-valued and possibly more stable products.

As explained above, the deposition of coke resulting from thermal or catalytic cracking must, for economic reasons, be minimized, but nevertheless be sufficient to ensure the thermal balance in the upstream and downstream parts of the tubular reactor (failing this, the heat balance can be ensured by the introduction of an auxiliary fuel into the regenerator); also, at least 50% and preferably 80% by weight of the heavy feed should preferably have a boiling temperature above about 400 ° C. This value of approximately 400 ° C. being mainly linked to the cutting point of the distillation residues, it may of course vary between 300 and 550 ° C. without departing from the scope of the present invention.

Among these fillers, mention may be made of vacuum gas oils and heavier hydrocarbon oils such as crude oils, whether or not topped, as well as residues from atmospheric distillation or vacuum distillation, pitches, bitumen emulsions, aromatic extracts , catalytic slurries, or synthetic or used oils. These fillers may, if necessary, have received a preliminary treatment such as, for example, a hydrotreatment. They may, in particular, contain fractions whose boiling point can go up to 750 ° C. and more, which may contain high percentages of asphaltenic products, and have a carbon content. Conradson high (10% and above). 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 LCOs ("Light Cycle Oils"), the interval d boiling is generally between 160-220 ° C (start of cut) and 320-380 ° C (end of cut), heavy recycling oils or HCOs ("Heavy Cycle Oils"), including the boiling range is generally between 300-380 ° C (start of cut) and 460-500 ° C (end of cut), or even catalytic residues (slurries) of which a major fraction distills above 500 ° C. According to a preferred embodiment of the invention, the charges can advantageously be preheated in a temperature range generally between 100 and 400 ° C., preferably close to the bubble point, so as to promote instant and homogeneous vaporization when brought into contact with the hot solid grains. ° ⁿ can use, to implement the process according to the present invention, inert heat transfer particles of a type known per se, such as kaolin or silicate microspheres; it is also possible to use all the classes of catalysts having catalytic cracking capacities. A particularly advantageous class is constituted by 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 comprising stable zeolites are commercially available with supports containing a variety of metallic cv-ydes and combinations of said oxides, in particular silica, alumina, magnesia and mixtures of these. substances, as well as mixtures of said oxides with clays. The catalytic composition can naturally contain one or more agents promoting one or more the other step of the process; the catalyst may therefore contain, in particular, agents promoting the combustion of coke, during regeneration, or contain agents capable of promoting the cyclization of olefins into aromatics and vice versa, if the production of aromatics becomes a priority objective .

Given the high temperatures and the operating pressure (generally between 0.3 and 5 kg / cm), and the short duration of the residence time of the hydrocarbons in the reaction zone (of the order of a few hundredths to a few tenths of seconds), as well as the conditions of quenching and recycling of the charge to steam crack the implementation of the process requires a certain number of specific means, which form an integral part of the present invention.

The invention therefore also relates to a steam cracking device, by conversion by direct contact, in the fluidized phase of heat-carrying particles and at high temperature, of petroleum hydrocarbon charges comprising, on the one hand, at least one light, slightly contaminated cut. by metals, the boiling point of which is less than about 400 ° C and, on the other hand, a charge of heavier hydrocarbons consisting essentially of compounds whose boiling point is above 400 ° C, this device comprising a continuous reactor for bringing petroleum fractions at high temperature into contact with heat transfer particles, catalytic or not, the continuous reactor being of tubular type with essentially ascending or descending flow, means in particular ballistic capable of effecting the separation of minus 90% of said particles and cracked hydrocarbons, means for stripping separate particles, means for r generation under combustion conditions of the coke deposited on these particles by air or steam, and means for recycling the regenerated particles to the feed of said reactor, as well as means for fractionating the gaseous effluents by distillation, said device being characterized in that it comprises, on the one hand, between said separation means and said fractionation means, means for injecting a fraction of said heavier hydrocarbon charge into the effluents and, on the other hand , means for recycling and injecting at least part of the distillation residue in the liquid phase, but at a temperature close to its bubble point, in the downstream section of the reactor. As with the charge injectors in the effluents, the injectors of the fractionation residues recycled in the downstream part of the continuous reactor will be adapted to allow spraying of the charge in drops with a diameter of less than 200 microns and, preferably, less than 100 microns. They will preferably be of the venturi type with a wide neck (see European patent n ° 312 428) to limit as much as possible the problems of attrition linked to the presence of recycled heat transfer particles. In addition, certain types of devices for separating effluents from steam cracking intended to limit the duration of the transfer of effluents to the fractionation zone by distillation could more advantageously be used in accordance with the present invention. In particular, when the reactor will operate in ascending mode ("riser"), due to the production of a large quantity of gaseous hydrocarbons, the heat-transfer particles will reach the reaction zone at high speeds (between 20 and 200 m / s and, preferably, between 40 and 100 m / s), and a simple device for separation by centrifugation can therefore possibly be used. The generally expensive use of cyclonic systems can thus be avoided. Likewise, when the reactor is operating in descending mode ("dropper"), the heat-transfer particles will be collected in an enclosure arranged at the base of the dropper, where they will be stripped after being separated from the steam cracking effluents by simple ballistic effect.

The accompanying drawings, which are not limiting, illustrate different modes of implementing the invention. In these drawings:

FIG. 1 illustrates the application of the invention to a set of steam cracking in an ascending column or riser or "riser" and to a single regeneration chamber at high temperature of the heat-carrying particles, suitable in particular for the regeneration of contact masses ; in this application, the ballistic separation device is provided with a simple centrifugal ballistic separation device;

FIGS. 2 and 3 illustrate the application of the invention to a steam cracking assembly with an essentially descending reaction zone ("dropper").

The ascending fluidized phase steam cracking device shown diagrammatically in FIG. 1 comprises a reaction column 1, known as a load riser, or "riser". This is supplied at its base, via line 2, with regenerated heat-transfer particles, in a quantity determined for example by the opening or closing of a valve 3. The regenerated particles are fluidized by injection at the base of the riser, using a diffuser 5, steam arriving via line 4, or any other suitable gas flow.

A first line 6 here supplies a diffuser 7, making it possible to inject a saturated light gas such as ethane into the upstream part of the reactor. A cut, which here is a propane cut, but which could just as well be a butane cut or a mixture of the two, can then be injected identically by line 8 using the diffuser 9. A cut of gasoline or diesel can finally be vaporized here using an injector 11 supplied by line 10. A charge of distillation residue coming from line 14 from the fractionation zone 12 is introduced, possibly mixed with a little of fresh charge supplied by the line 40, using an injector 13, in the downstream part of the reactor, under temperature conditions close to the bubble point of said residue, in order to facilitate instant and homogeneous vaporization. Column 1 opens at its top in an enclosure

15, which is for example concentric and in which are effected, on the one hand, thanks to the ballistic separator

16, the separation between the reaction effluents and the heat transfer particles and, on the other hand, the stripping of the coke particles. The effluent hydrocarbons are evacuated from the centrifugal system 16 by the evacuation line

17, in which the cold charge arriving via the line 18 is sprayed using the injectors 19, while at least 90% of the heat-carrying particles descend towards the base of the enclosure 15, where a line 20 supplies stripping gas , generally water vapor, diffusers 21, regularly arranged at the base of the enclosure 15.

The quenching effect of the effluents from the steam cracking reaction, caused in 17 by the direct contact between the droplets of the fresh charge and said effluents, is here reinforced by the injection by line 50 of a residue recycle of the distillation carried out in the fractionation zone 12. The distillation residue can be cooled by passing through a heat exchanger 51 and the calories thus recovered can be used to form water vapor for the entire installation, without that it is necessary to use additional quenching, as is the case with conventional methods. In addition, the presence of a small quantity of grains or fines of the solid heat carrier in the reactor effluents not only allows effective sweeping of the walls, but also constitutes a means of adsorption of the gum precursors and of coke deposits. To this end, it is possible to modify the content of particles circulating in line 17 by providing an injector of fresh particles arriving via line 53. The heat transfer particles stripped at the base of the enclosure 15 are discharged to a regenerator 22, via a conduit 23, on which a regulating valve 24 is provided here. The regenerator 22 shown in this figure only has '' a single combustion zone for the coke deposited on the heat transfer particles in the presence of oxygen or water vapor. This regeneration is carried out in such a way that a large part of the heat released by the combustion of the coke is transferred to the particles to enable them to reach the high temperatures necessary for the reaction in zone 1. The coke deposited on the particles is thus eliminated, using air injected at the base of the regenerator by a line 25, which feeds the diffuser 26. Optionally, to adjust the temperature to the desired thermal level, additional fuel can be injected. The regeneration gas is separated from the heat-carrying particles entrained in the cyclone 27, from which the regeneration gas is evacuated by a line 28, while the regenerated and hot heat-carrying particles are extracted from the regulator, from where they are recycled by the conduit 2 to the elevator supply or riser 1.

Furthermore, after the quenching by injection of the charge in 19, the reaction effluents and the charge introduced in 19 are led by line 17 in the fractionation device schematically represented at 12, making it possible to separate:

- by line 29, the light gases which can then be treated in another gas fractionation device, also schematic, making it possible, in a manner known per se, to separate ethane in particular by line 30, and propane by line 31;

- via line 36, a gasoline section, the boiling range of which generally extends from section c ₅ to around 200-220 ° C;

- via line 37, a diesel type cut, the boiling range of which generally extends from 160-220 ° C (start of cut) up to around 320-400 ° C (end of chopped off ) ;

- and, finally, via line 14, a fraction of the fraction of distillation residue, which contains the heaviest products from both the feedstock and the reaction effluents and relatively large quantities of fines (this residue, a a boiling point between 300 and 550 ° C and generally of the order of 400 ° C).

Part of this fractionation residue is therefore injected at 13 into the steam cracking reactor, in accordance with the present invention; depending on the case and after recovery of the heat by passing through the exchanger 51, another part can either be recycled for quenching, by the line 50, in mixture with the charge to be steam cracked, or withdrawn from the device by the purge line 52.

In addition, ethane, propane, gasoline cut, from this fractionation device can be recycled in the reaction section by lines 30, 31, 36, then 6, 8 and 10, while the olefins in C ₂ , C3 produced by steam cracking are isolated by lines 33 and 34 respectively.

An essential advantage of this fluidized phase steam cracking device lies in the fact that good use of the temperature profile in the reaction zone 1 makes it possible to selectively crack several petroleum fractions. In particular: in the zone for the introduction of heat transfer particles, where there is a maximum temperature of the order of 800 ° C. and more, steam can be introduced via line 4, as well as ethane through line 6, coming from either from the fractionation device via line 31, or from another unit of the refinery;

- given the high energy demand of this reaction (3 to 6 times higher than in a catalytic cracking reaction), the temperature of the reaction zone decreases appreciably, and it is then possible to inject saturated hydrocarbons downstream more heavy, such as propane (in 8) or butane (in 11) or even light gasolines (in 11) or naphthas, with possible addition of water vapor by lines 38, 39 and 40. regulation, 41 to 44, can also make it possible, in a manner known per se, to modulate the quantities injected into the reaction zone, in order to maintain the desired temperature profiles thanks to temperature probes placed for this purpose in said zones.

It will be noted that, compared to a conventional type steam cracking, all the energy necessary for the reaction is supplied at one time by the heat-transfer mass, at the time of mixing with the fillers, that is to say at the start of the reaction. The temperature therefore reaches its maximum at this time and then decreases under the effect of the endothermicity of the reactions, thus causing a natural effect of progressive quenching and therefore of decreasing severity, unlike conventional methods. The resulting temperature profile, combined with the extremely short reaction time allowed by this device, leads to a significantly higher selectivity of the reaction than that obtained with traditional methods and to the elimination of coke or tars formed on the walls. , where the skin temperature is higher.

The fluidized phase steam cracking devices represented in FIGS. 2 and 3 are variants of that of FIG. 1, in which the reaction zone is operating this time in descending mode. The reactor will therefore be called "dropper", by reference to the English term. The parts of this device identical to those of FIG. 1 are designated therein by the same reference numerals, assigned the index 'for Figure 2 and the index' 'for Figure 3.

According to FIG. 2, a different type of regenerator is used, capable of better withstanding the high temperatures required by steam cracking. The regeneration fumes leave the unit in 28 'after passing through a cyclone 27' external to the regeneration chamber 22 '. In order to allow the withdrawal well 54 'of the regenerated heat transfer particles to be placed above the dropper, the regeneration chamber 22' is located in the upper part of the unit, and the particles to be regenerated come from the stripping zone by line 23 'must be transported by an ascending column 55'. This transport is carried out by fluidization with a gas diffused in 26 'by line 25'. During this transport, a primary combustion of the coke deposited on the catalyst particles can take place under conditions known per se with a fluidizing gas containing air or oxygen. The particles of the catalyst and the fluidizing gas are then separated ballistically by means of the device 56 'and the particles of the catalyst are regenerated in a manner known per se in the chamber 22', where the particles are burned against the flow of oxygen. brought by line 45 'to diffuser 46 •.

The regenerated particles of the catalyst can be introduced without thermal losses into the upstream part of the reactor l 'in an amount determined by the flow rate of the diffuser 57'; the homogeneity of the grain distribution is ensured by a device of a type known per se and not shown here. At the outlet of the dropper, the particles dive directly into the dense fluidized stripping zone 15 ', while the hydrocarbon vapors as well as the stripping vapor coming from the diffuser 21' supplied by the line 20 'and the stripped hydrocarbons are evacuated almost instantaneously by line 17 ', where they are immediately quenched by dissolution in the heavy load which enters the unit by line 18'. In the variant of FIG. 3, in order to allow operation in dropper mode without requiring an expensive elevation of the regeneration zone 22 ", the regenerated and hot particles coming from line 2" are first transported inside an ascending column 58 "by injection of a fluid such as water vapor arriving via line 4". After passing through the two elbows 59 "and 60", at right angles, the particles are discharged homogeneously into the dropper 1 ", into which, for example, are successively injected, in 7" and 8 ", ethane and gasoline Then, the effluents are quenched by the heavy load at 19 ", and the distillation residue from the fractionation zone 12" is injected at 13 "at a temperature close to its bubble point.

At the exit of the dropper, the particles are stripped and leave zone 15 "by line 23", at the bottom of which an injection of fluid, such as steam or air, makes it possible to transfer them by line 55 "to the regeneration chamber 22". In it, a ballistic separation device 56 "allows them to be poured into the combustion zone in a fluidized bed.

EXAMPLE This example shows the advantages of a device according to the present invention, of the type shown in FIG. 3. The tests were carried out using ethane, a gasoline cut (straight-run cut) and two charges A and B, which are respectively an atmospheric distillation residue and a vacuum distillation residue of a crude oil of the SHENGLI type.

The charges have the following characteristics:

CHARGED TO CHARGED B

- density (at 15 ° C): 0.675 0.955 0.985

CHARGED TO CHARGED B

As heat transfer particles, contact mass particles composed of microspheres, mainly kaolin, with a specific surface of approximately 10 m ² / g and an average diameter of approximately 70 microns are used. The charge injectors in the quenching zone and in the reactor are of the type described in European patent application No. 312,428.

The conditions of the two tests carried out successively with load A, then load B, are as follows (extrapolated for 100 t / H of total load):

LOAD TO LOAD B

Upstream area of the reactor:

- Regenerated catalyst temperature (° C): 880 880

- Flow rate of regenerated catalyst (t / h): 2000 2160

- Steam flow at

320 ° C (t / h): 15 15 - Ethane flow rate (t / h): 10 10

- Mixing temperature (° C): 862 868

Central reactor area

- Steam flow at 320 ° C (t / h)

- Fuel flow at 150 ° C (t / h) 30

- Mixing temperature 825 LOAD TO LOAD B

Downstream area of the reactor:

- Steam flow at 320 ° C (t / h)

- Charging flow A or B at 380 ° C (t / h) 90 60

- Mixing temperature (° C) 785,780

- Temperature at the end of the reaction (° C) 740 750

Quenching zone:

- Effluent temperature after ballistic separation (° C) 730 740

- Charge temperature (° C) 80 90

- Mixing temperature (° C) 450 470

- Concentration of particles in effluents (% by weight) 3.2 2.2

- Cutting temperature of the fractionation residue (° C) 420 440

After recovering the effluents from the steam cracking reaction, the nature of these effluents is analyzed. The analysis results (in% by weight), which are collated below, alone demonstrate the advantages of the present invention over conventional methods:

H ₂ S + NH ₃ H

C ₂ (olefins) ^c 3

C (olefinic) C ^ (olefinic) C ^ (diolefinic)

^• 5,220 - 360 ° C

> 360 ° C

Coke

It can therefore be seen, in this example, that the invention has numerous advantages over the steam cracking processes used up to now. Indeed, with olefin yields at least equivalent to those of the best performing units, - it allows:

- Use in the loading of distillation residues hitherto excluded from steam cracking;

- Unmatched operational flexibility (throughput, nature of loads, etc.); - And a continuous operation (without stop for decoking) and without additional energy (since the production of coke makes it possible to satisfy the thermal balance of the unit).

Claims

1.- Method of conversion by steam cracking, at high temperature and in the presence of a dilute fluidized phase of essentially heat-transferable particles, on the one hand, of at least one cut of light hydrocarbon, little contaminated with metals, the boiling point is less than about 400 ° C and, on the other hand, a heavier cut of hydrocarbons, consisting essentially of compounds whose boiling temperature is above about 400 ° C, this process comprising a step of bringing said cut then of said charge into contact, in a staged manner and with decreasing severity, with heat-carrying particles, catalytic or not, in a continuous reactor of tubular type with ascending or descending flow, a separation and stripping step making it possible to separate, on the one hand, at least 90% of said particles, which are then preferably regenerated by reaction of the coke deposited on them before recycling them further high temperature towards the supply of said continuous reactor and, on the other hand, the effluent hydrocarbons, which are recovered during a fractionation stage by distillation, this process being characterized in that at least a fraction of the charge d heavier hydrocarbon is injected between said step of separation of particles and effluent hydrocarbons and that of fractionation, and in that one recycles in the downstream part of said reactor at least a part of the residue of said fractionation step by distillation.

2.- Method according to claim 1, characterized in that the heavier hydrocarbon charge is injected in the liquid state by spraying in drops of diameter less than 200 microns and preferably less than 100 microns.

3.- Method according to one of claims 1 and 2, characterized in that the effluents from the steam cracking reaction are brought by injection of the heavier load at a temperature below the dew point.

4- Method according to one of claims l to 3, characterized in that the hydrocarbons entering the fractionation zone contain between 0.01 and 10% by weight and, preferably, between 0.05 and 5% by weight of heat-carrying particles.

5- Method according to one of claims 1 to 4, characterized in that, prior to the fractionation step by distillation of the effluents of the steam cracking reaction, these effluents are brought to a temperature preferably between 320 and 450 ° vs.

6- Method according to one of claims l to 5, characterized in that the effluents from the steam cracking zone are brought back to the liquid state at a temperature between 300 and 450 ° C in less than 0.3 seconds and, preferably in less than 0.1 seconds.

7- Method according to one of claims 1 to 6, characterized in that the heavier hydrocarbon charge is chosen from the group consisting of atmospheric or vacuum distillation residues, catalytic slurries, deasphalting pitches, or synthetic or used oils.

8- Method according to one of claims 1 to 7, characterized in that the fraction of the distillation residue recycled in the reactor is ^• at a higher temperature of less than 100 ° C and, preferably, of less than 50 ° C at the bubble point temperature of this cut.

9- Method according to one of claims 1 to 8, characterized in that said liquid heavy charge is constituted at least in part by at least a fraction of the distillation residue of said fractionation step.

10- A method according to claim 9, characterized in that the distillation residue of said fractionation step is cooled by heat exchange at its outlet from the fractionation tower.

11- Method according to one of claims 1 to 10, characterized in that the or light cuts of hydrocarbons are chosen from the group comprising light paraffins such as ethane, propane. butanes, and gasolines, - naphthas and gas oils.

12- The method of claim 11 comprising the injection of a plurality of light cuts of hydrocarbons in the upstream part of the reactor, characterized in that this injection is carried out in stages in order of decreasing severity of said cuts.

13- The method of claim 12, characterized in that one successively injects into the reactor, from upstream to downstream, light gases comprising ethane, then, optionally, propane and butanes, in an amount such that the temperature of the mixture with the heat-carrying particles remains above 800 ° C and, preferably, at 825 ° C, then cuts of hydrocarbons such as light essences, and / or possibly naphthas or gas oils, in such quantities that the temperature of the mixture immediately downstream is greater than 750 ° C and, preferably, 800 ° C, and finally a fraction of the distillation residue to bring the reaction temperature to a temperature between 650 and 750 ° C.

14.- Method according to one of claims 1 to 13, characterized in that at least part of the ethane and / or propane and / or butane produced by steam cracking is recycled to the reactor.

15- Method according to one of claims 1 to 14, characterized in that the operating pressure of the reaction zone is between 0.3 and 5 kg / cm ² .

16- Steam cracking device, by conversion by direct contact, in a fluidized phase of heat-carrying particles and at high temperature, of petroleum hydrocarbon charges comprising, on the one hand, at least one light cut little contaminated with metals, the temperature of which boiling point is less than around 400 ° C. and, on the other hand, a charge of heavier hydrocarbons essentially consisting of compounds whose boiling point is higher than 400 ° C., this device comprising a continuous reactor (1) from contact to high temperature of petroleum fractions with heat transfer particles, catalytic or not, the continuous reactor (l) being of tubular type with essentially ascending or descending flow, in particular ballistic means (16) capable of effecting the separation of at least 90% said particles and cracked hydrocarbons, means (20,21) for stripping the separated particles, means (22) for regenerating under conditions of combustion of the coke deposited on these particles by air or steam water, and means (2) for recycling the regenerated particles to the feed of said reactor (1), as well as means (12) for fractionating gaseous effluents by distillation, said device being characterized in that it comprises, on the one hand, between said separation means (16) and said fractionation means (12), means for injecting (18,19) a fraction of said heavier hydrocarbon charge in the effluents and, d 'aut re part, recycle means (14) and injection (13) of at least part of the distillation residue in the liquid phase, but at a temperature close to its bubble point, in the downstream section of the reactor (1 ).

17- Device according to claim 16, characterized in that said injection means (18,19; 14,13) of said heaviest hydrocarbon charge between the ballistic separation means (16) and the fractionation means ( 12), on the one hand, and in the downstream section of the reactor (1), on the other hand, are fed from the residue from the means (12) for fractionation by distillation of the effluents from the reaction zone.

18- Device according to one of claims 16 and 17, characterized in that it comprises means (7, 9, 11) for successively injecting into the reactor, from upstream to downstream, light gases comprising ethane , then optionally, propane and / or butanes, in an amount such that the temperature of the mixture with the heat-carrying particles is greater than 800 ° C. and preferably at 825 ° C., followed by hydrocarbon fractions such as light essences and / or possibly naphthas and gas oils, in an amount such that the temperature of the resulting mixture, immediately downstream of the injection point, is greater than 750 ° C and, preferably, 800 ° C, finally, in the downstream part of the reactor, in the form of fine liquid droplets with an average diameter preferably less than 100 microns, the charge (s) of heavier hydrocarbons.

19- Device according to one of claims 16 to 18, characterized in that it comprises means for injecting (53) grains of cool heat transfer particles in the steam cracking effluents.