FR2628436A1 - Fluidised bed high temp. vapour cracking - useful for prodn. of olefin(s) - Google Patents

Abstract

Method of high temp. vapour cracking whereby (a) at least one light hydrocarbon cut, slightly contaminated with metals with b.pt. less than 400 deg.C, and (b) a heavier cut with b.pt. above 400 deg.C are converted in the presence of a fluid phase diluted with heat-carrying particles. The process comprises a stage where the hydrocarbon cuts are contacted with heat carriers (catalytic or otherwise) in a tubular-type reactor in a fluidised bed ascending or descending, a stage of particle stripping from the cracked hydrocarbons after reaction, a re-generation stage by combustion of the coke deposited on the particles and a re-cycling step of the re-generated particles at high temp. to supply the reactor. Vapour cracking takes place by injection into the fluidised bed of heat-carrying particles of: in the up-stream section of the reactor at least one light hydrocarbon cut and steam so that the temp. is between 750-850 deg.C, steam content being 40-80% and contact time less than 0.1 sec., and in the down-stream part of reactor zone, the heavy cut is injected in form of fine droplets, the temp. being 700-800 deg.C, steam content being 20-60% of total wt. of hydrocarbons injected and contact time of less than 0.1 sec. USE/ADVANTAGE - The process can treat all hydrocarbons from light saturated gases to heavy residues. It is important for producing olefins with C = 2-4 partic. butadiene. The fluidised bed technique obviates the need for de-coking operations and the use of heat carriers is advantageous to the endo-thermicity of the vapour cracking process.

Description

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

 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, as well as butadiene.

 It is known that hydrocarbon cracking processes are commonly used in the petroleum and oil services industries; they consist in 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 so-called visbreaking processes, in which only the heaviest molecules are split into smaller molecules, the cracking temperature is between 450 and 6000C 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, the necessary temperature is much higher, but remains however limited by the conditions of implementation of the method and by the complexity of operation of the ovens which use an auxiliary energy of heating.

 Obtaining and maintaining the required temperature levels is all the more delicate since it gradually deposits unwanted coke on the walls of the tubes.

This coke harms the quality of the heat exchanges and leads to an increase in the pressure drop inside the tubes, which contributes to reducing the conversion rate of the hydrocarbon charge entering the thermo-cracking unit and causes periodic stops for decoking. It also results, on the one hand, from the fact that the process is modular, so as to allow decoking operations in operation, and, on the other hand, that the charges to be treated must be "clean", so 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 diesel oils.

 In addition, the heat transfer in a tube is not instantaneous and the thermocracking reaction is very endothermic. I1 therefore poses problems of temperature regulation 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) uses a fluidized phase tubular reactor with a downward flow of heat-carrying particles, with a short contact time, to achieve thermal cracking of heavy petroleum charges, thanks to a supply of heat supplied by the combustion of the coke deposited on the heat-carrying particles;
- US patent 4,427,538 (Engelhard) uses a tubular reactor to achieve cracking with 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 conversion to light olefins of petroleum hydrocarbon fractions such as petroleum spirits or, a fortiori, highly contaminated residual charges.

 Indeed, to thermocrack petroleum hydrocarbon cuts which include light paraffins such as butanes, propane and especially ethane, as well as petroleum cuts such as gasolines, naphthas and diesel fuels, it is necessary to maintain the temperature of the charge at a very high level, generally of the order of 750 to 8500C, for a very short period, but strictly controlled. In the absence of a rigorous 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 Ballistics 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.

 In addition, and in particular with the ascending fluidized phases used up to now, it is known that part of the heat-carrying particles will tend to accumulate in the vicinity of the walls, and even to descend, carrying with it a part of the hydrocarbons. ; this effect is called back mixing or, in English, "back mixing", and it constitutes another important source of heterogeneity in the duration of the reaction.

 Furthermore, maintaining the fluidized phase, at the temperatures desired for thermocracking, requires a very high caloric intake, due to the high endothermicity of the thermal conversion by steam cracking and the fact that a quantity is injected into the reaction zone. significant vapor intended to lower the partial pressure of the hydrocarbons and to minimize the production of coke. In addition, in the case of steam cracking of light hydrocarbon cuts into olefins, the quantity of coke deposited on the heat transfer particles would be entirely insufficient to ensure the thermal equilibrium of the system.

 Finally, this balance and the temperature level 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 transfer 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, as well as butadiene, by introduction of the said cuts in a diluted 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 a satisfactory conversion, by cracking the cuts introduced into the reactor, with a high selectivity in light olefins and in butadiene.

 The invention also aims to allow effective control of the reactions. polymerization of the reaction products.

 The invention finally aims to produce coke in sufficient quantity 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 lower than approximately 4000C and, on the other hand, a heavier cut of hydrocarbons such as a cut consisting essentially of compounds whose boiling point is higher than around 4000C, this process comprising a step of bringing the petroleum cut into contact with heat-carrying particles, catalytic or not, in a tubular type reactor with rising or falling flow, a step 'of ballistic separation of said particles and cracked hydrocarbons , a step of stripping the particles, a step of regeneration under conditions of combustion of the coke deposited on the particles, and a step of recycling at high temperature of the particles s regenerated towards the supply to said reactor, said process being characterized in that the steam cracking is carried out by injection into the fluidized bed of heat-carrying particles, in the upstream part of the tubular reactor, of at least one of said light cuts and of water vapor under conditions such that the resulting mixture is at a temperature between 700 and 9000C and, preferably, between 750 and 8500C and that it contains an amount of water vapor representing between 40 and 80% by weight of the total quantity of water vapor injected into the reactor, and in that, after having maintained these contact conditions for a period of between 0.01 and 0.5 seconds and, preferably, less than 0.1 second, said heavier charge, in the form of fine droplets, is injected into the downstream part of the reaction zone, -so that the resulting mixture in a diluted fluidized bed is at a temperature between 600 and 8500C and, preferably between 700 and 800 0C and that it contains a quantity of water vapor representing between 20 and 60% by weight of the total quantity of hydrocarbons injected, this mixture being maintained under these conditions for a period of between 0.01 and 0.5 second and preferably less than 0.1 second.

 The cut of lightly contaminated light hydrocarbons, distilling at less than 4000C, may be chosen from the group consisting of light paraffins such as ethane, propane, butanes, and gasolines, naphthas and gas oils.

 The heavier cut of hydrocarbons, having a boiling temperature above 4000C, - may be chosen from the group consisting of atmospheric or vacuum distillation residues, deasphalting pitches, catalytic slurries, synthetic hydrocarbons or solid hydrocarbons, with no quality limit.

 The C / O ratio where C denotes the mass of heat transfer particles and O the mass quantity of hydrocarbons present will advantageously be between 10 and 30 and, preferably, between 15 and 25, at the outlet of the reactor.

 At the entry of the first reaction zone (injection zone of the light cup little contaminated with metals), this ratio C, 0 will be at least 40 and may even be greater than 200.

The ratio of the quantity of vapor injected to the quantity of hydrocarbons present is also an important parameter of the process according to the invention. At the outlet of the reactor, this ratio may be between 20 and 60% and, at the inlet of the engine, it may be between 30 and 200%
The fluidized bed into which the section of hydrocarbons to be steam-cracked is introduced is therefore made up of a mixture of heat-transfer particles of small diameter, possibly having catalytic power, and of an auxiliary fluid composed in particular of steam.

This fluid is introduced by a diffuser in a quantity such that the average speed of the particles at the entrance to the reaction zone is between 5 and 200m / s and preferably between 20 and 50m / s, which avoids any risk of back-mixing and ensuring a very short reaction time of the hydrocarbons at high temperature.

 The auxiliary fluid can, of course, consist solely of steam; however, in addition to the vapor mentioned above, it is also possible to inject inert gases capable of minimizing the polymerization of the olefins formed during the reaction, as well as additives capable of influencing the selectivity of the reaction .

As indicated above, the injection of heavier hydrocarbons than petrol and diesel, downstream of the first steam cracking zone, has two specific goals:
- allow, by cracking, the deposition on the heat transfer particles of the quantity of coke necessary for the equilibrium of the thermal balance of the unit, because the deposition due to the steam cracking of the light hydrocarbon fraction (s), in the upstream of the reaction zone, is relatively small and therefore insufficient to ensure thermal equilibrium in the upstream part; this condition will be all the more easily fulfilled as the pulverized hydrocarbons contain a significant proportion of hydrocarbons of high boiling temperature, since the latter generally contain significant quantities of coke-generating contaminants such as heavy metals, asphaltenes or d 'other unstable compounds;
- allow, at the same time, the production of a large quantity of light olefins from these heavy hydrocarbons and reduce the temperature to an acceptable level so that the ballistic separation of the reaction effluents is carried out without risking promoting polymerization olefins obtained.

 This reduction in temperature will be achieved by vaporization and cracking of the said charge of hydrocarbons heavier than petrol and diesel. To vaporize this charge as instantaneously as possible and to control the duration of the reaction upstream well, the charge of hydrocarbons with high boiling point must imperatively be sprayed into extremely fine droplets.

The numerous studies carried out for this purpose have in fact shown that, when a hydrocarbon is sprayed in droplets of which at least 80% have a diameter of less than 100 microns, in a flow of heat-transfer particles under the conditions of the present invention, the vaporization by heat transfer then takes place in less than a hundredth of a second.

 In its most elaborate configuration, including successive injections of heavier and heavier cuts, for example ethane or LPG (liquefied petroleum gas), then petrol or diesel and, finally, a more heavy, of the distillation residue type, in the reaction zone located downstream, the reactor will in fact comprise several distinct reaction zones, operating successively under conditions of decreasing severity (decrease in temperature, in activity of the heat-transfer mass and the relationship between the flow rate of this mass and that of the hydrocarbons) and adapted to the nature of the charges to be treated and the products sought. In this way, it will be possible, for example, to convert ethane by steam cracking, in the presence of water vapor , in the injection zone of heat transfer particles where the temperature is the highest, then use the drop in temperature which results from the endothermicity of the reaction to inject an intermediate cut of hydrocarbon s such as a diesel type cut or a cut of light gasoline, and finally use the new temperature drop that results from it to crack the heavier load, in conditions better suited to its nature.

In addition, when, as an alternative to the operating mode described above, the heat-transfer particles used in this device are catalyst particles, the upstream part of the tubular reactor operates in mild steam cracking mode of light hydrocarbons, while the downstream part operates in catalytic cracking mode of heavier loads, at an appropriate temperature level. It is therefore possible, in this case, to advantageously regenerate the catalyst in a manner arranged in two regeneration zones as described in the patent.
European No. 191,695 filed by the Applicant.

 The cuts of steam cracked hydrocarbons which can be used according to the present invention therefore include, unlike conventional methods, all hydrocarbons, from saturated light gases such as ethane and propane or butanes, to the heaviest residues, those -this bringing, thanks to the coke they produce, the heat necessary for the thermal equilibrium of the assembly, while also contributing significantly to the production of light olefins in the same way as conventional fillers.

 An additional advantage arising from the present invention resides in the fact that the hydrogen 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. into the best valued products, from the heaviest load.

 The introduction of the light section (s) into the upstream part of the reaction zone can be carried out in a manner known per se by injection of these sections, alone or in combination with steam and possibly other fluidizing gases such as hydrogen, and light gases.

 The hydrocarbon feedstocks capable of being injected into the downstream part of the tubular reactor can contain hydrocarbons having boiling temperatures above 4000C and their density can vary between 10 and 35 API. These charges can be very heavy charges containing hydrocarbons whose boiling point can go up to 7500C 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 temperature profile sought and the needs of the heat balance, represent 0.25 to 4 times the quantity of light cut injected upstream.

 As defined above, the deposition of coke resulting from thermal or catalytic cracking must, for economic reasons, be as much as possible sufficient to ensure the thermal balance in the upstream and downstream parts of the tubular reactor (failing this, the balance thermal can be ensured by the combustion of an auxiliary fuel in the regenerator); also, at least 50% by weight and preferably 80% of the load must have a temperature above 4000C.

 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 atmospheric distillation or vacuum distillation residues, pitches, bitumen emulsions, aromatic extracts , catalytic slurries, synthetic or used oils, coal-water mixtures. 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 7000C and more, which may contain high percentages of asphaltenic products, and have a high Conradson carbon content (10% and beyond). diluted or not 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"), whose boiling range is generally between 160-220 C (start of cut) and 320-38O0C (end of cut), or heavy recycling oils or H.C.O. ("Heavy Cycle Oils"), whose boiling range is generally between 300-3800C (start of cut) and 460-500 C (end of cut).

According to a preferred embodiment of the invention, the charges can be preheated in a temperature range generally between 100 and 4000C.

 Can be used 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 zeolite are commercially available with supports containing a variety of metal oxides 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 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 avoiding the cyclization of olefins to aromatics.

 Given the high temperatures and the short duration of the residence time of the hydrocarbons in the reaction zone, 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 device for steam cracking, by conversion, in a fluidized phase of heat-carrying particles and at high temperature, of petroleum hydrocarbon cuts comprising, on the one hand, at least one light cut little contaminated with metals, including the boiling temperature is below 4000C and, on the other hand, a cut of heavier hydrocarbons, whose boiling temperature is above 4000C, comprising a reaction zone for bringing petroleum fractions to high temperature heat transfer particles, catalytic or not, in a tubular type reactor with essentially ascending or descending flow, means capable of effecting ballistic separation of said particles and cracked hydrocarbons, means for stripping the particles, means for regeneration in -conditions for combustion of the coke deposited on these particles, and means for recycling the regenerated particles to the feed of said reactor ur, said device being characterized in that it comprises, in the upstream part of the tubular reactor, means for injecting the light cut or cuts of hydrocarbons in the presence of an amount of water vapor of between 40 and 80% and, preferably, between 50 and 70% by weight of the total amount of water vapor injected into the reactor, so that the resulting mixture or mixtures are maintained at a temperature of between 700 and 9000C and, preferably between 7500C and 8500C for about 0.01 to 0.5 seconds, in that it comprises, in the downstream part of the tubular reactor, means for spraying said cut of heavier hydrocarbons, so that the temperature of the mixture resulting from this spraying is brought to a temperature of between 600 and 8500C and preferably between 700 and 8000C and that it contains an amount of water vapor representing between 20 and 60% by weight of the total quantity of hydrocarbons injected, the mixture was ant maintained under these conditions for a period of between 0.01 and 0.5 seconds and, preferably, less than 0.1 seconds after the injection of said heavier hydrocarbons, said device further comprising regulating means allowing adapt the introduction of said hydrocarbons so that the quantities of coke necessary for the thermal equilibrium of the device are formed by combustion of this coke during the regeneration step.

The device according to the invention preferably comprises, from upstream to downstream of the reaction zone:
on the one hand, in the upstream part of the reactor, means for injecting light gases preferably comprising ethane, but also optionally propane and butanes, in a quantity determined so that the temperature of the mixture with the particles heat transfer is greater than 8000C and preferably at 8250C, then cuts of hydrocarbons such as light gasolines, but also possibly naphthas or gas oils, in a quantity determined so that the temperature of the mixture immediately downstream is greater than 7500C and preferably at 8000C,
- on the other hand, in the downstream part of the reactor, injection means by spraying into fine droplets, the average diameter of which will preferably be less than 100 microns, of the charge of heavier hydrocarbons.

 In a particularly advantageous embodiment of the device of the present invention, this device will further comprise means for injecting a fluid for cooling the reaction effluents, with a view to limiting the parasitic reactions of polymerization of olefins, thus than coking, likely to occur between the effluent separation zone and that of fractionation. The fluids intended for quenching the effluents will preferably be sprayed to facilitate heat transfer; they may advantageously consist of water, steam, or various petroleum fractions, which may in particular come from the fractionation device located downstream from the steam cracking reactor.

 These fluids may also include the charge of heavy hydrocarbons proper, which then makes it possible to ensure the heating of this charge and the washing of the circuits by the latter. In this case, the residue from the steam cracking reaction is recycled as a mixture with the heavy feed to the reaction section.

 In particular, with ballistic devices for separating particles and effluents of the conventional type, the quenching of the effluents will be carried out by injection or spraying of hydrocarbon fractions, in the part situated completely downstream of the reaction zone, that is to say ie immediately before the ballistic separation step. This quenching will have the effect, while lowering the temperature of the tributaries, of diluting the latter and therefore, in a manner known per se, of preventing the deposition of coke in the parts of the unit situated further downstream.

 In addition, other 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 may advantageously be used in accordance with the present invention. In particular, when the reactor is operating in ascending mode ("riser"), it will be possible to take advantage of the fact that the heat-carrying particles move within the reaction zone, after the injection of gasolines, at a high speed, between? 0 and 200 m / s and, preferably, between 40 and 100 m / s, to use a device capable of separating the heat-carrying particles by centrifugation.

 Likewise, when the reactor operates 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 ballistic effect.

 In the latter two cases, it is also advantageously possible to quench the steam cracking effluents directly in the pipe connecting the effluent separation device to that of fractionation by distillation.

 This quenching, generally carried out by injection of a diesel-type cut, possibly originating from the recycling of the effluent fractionation unit, may further advantageously consist of the heavy feed, as will be shown in the description below. The device which is the subject of the present invention therefore advantageously comprises means making it possible to fractionate the effluent-reaction hydrocarbons by distillation. I1 may also include recycling means, in the conversion zone, in particular of saturated light gases, such as ethane, and possibly of light essences, as well as means of recycling the cuts intended for quenching the effluents. steam cracking, as previously described.

The invention will be described below in more detail, with reference to the accompanying schematic drawings, in which:
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 ;
FIG. 2 illustrates the application of the invention to a steam cracking assembly of the same type, but fitted with a centrifugal ballistic separation device;
FIG. 3 illustrates the application of the invention to a set of steam cracking with a substantially descending reaction zone (dropper).

 The ascending fluidized phase steam cracking device shown diagrammatically in FIG. 1 essentially comprises a column 1, known as a load elevator, or riser; this is supplied at its base, via line 2, with regenerated heat-transfer particles, in a quantity determined by the opening or closing of a valve 3. The regenerated particles are fluidized by injection at the base of the riser, at the using a diffuser 5, of steam arriving by line 4.

 A first line 6 here supplies a diffuser 7, making it possible to inject a light saturated gas such as ethane into the upstream part of the reaction zone. A section of petrol or diesel is then vaporized using an injector 8 supplied by line 9. The charge of hydrocarbons heavier than petrol is introduced into the downstream part of the reactor with the help of an injector 10 supplied by the line 11. An injector 12, supplied by the line 13, here makes it possible to quench the steam cracking effluents, while keeping these effluents above their dew point.

 Column 1 opens at its apex in an enclosure 14, which is for example concentric with it and in which, on the one hand, thanks to the ballistic separator 15, the separation between the cracked charge and the heat-carrying particles takes place and, on the other hand, the stripping of coked particles. The effluent hydrocarbons are evacuated by a cyclonic system 16, which is housed in the enclosure 14, at the top of which is provided an evacuation line 17, while the spent heat-carrying particles descend to the base of the enclosure 14, where a line 18 supplies stripping gas, generally water vapor, to the diffusers 19, regularly arranged at the base of the enclosure 14.

 The particles thus stripped are evacuated towards a regenerator 20, by means of a conduit 21, on which is provided a regulating valve 22. The regenerator 20 represented in this figure comprises only one zone for combustion of the deposited coke on heat transfer particles in the presence of excess oxygen.

This regeneration is carried out in such a way that a large part of the heat released by the combustion of the coke into carbon dioxide is transferred to the particles, so as to allow them to reach the high temperatures necessary for the reaction in zone 1. The coke deposited on the particles is thus burned with the help of air, injected at the base of the regenerator by a line 23, which feeds the diffuser 24. The combustion gas is separated from the heat-carrying particles entrained in the cyclone 25, d '' where the combustion gas is evacuated via a line 26, while the regenerated and hot heat-transfer particles are extracted at the base of the regulator, from where they are recycled via line 2, to the elevator or riser supply .

Furthermore, the reaction effluents leave the ballistic separation zone and are led by line 17 in a fractionation device schematically represented at 27, making it possible to separate
- by line 28, the light gases or dry gases, which can then be treated in another fractionation device 29, schematically represented here, and making it possible, in a manner known per se, to separate the dry gases by line 30, from ethane via line 31, and the other gases, which exit via line 32;
- by line 33, a gasoline cup, the boiling range of which generally extends from the C5 cup until around 200-2200C;
- via line 34, a diesel type cut, the boiling range of which generally extends from 1602200C (start of cut) to around 320-4000C (end of cut);
- and, finally, by line 35, a section of distillation residue, which contains the heaviest products and significant quantities of fines, this residue, which has a boiling point generally higher than 400-5000C, being called 'Bslurry ".

The superiority of this fluidized phase steam cracking device lies in particular in the fact that good use of the temperature profile in 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 8000C and above, the vapor can be introduced via line 4, as well as ethane through line 6, coming either from the fractionation by line 31, that is to say from another refinery unit;
- given the high energy demand of this reaction (3 to 4-times higher than in a catalytic cracking reaction), the temperature of the reaction zone decreases appreciably, and it is then possible to inject gasolines in 8 , with possible addition of steam via line 36; ;
- similarly, the charge of heavy hydrocarbons will be introduced with atomizing steam through the injectors 10 supplied by line 11.

 Regulatory systems 37, 38 and 39 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 required temperature profile in the zones located immediately downstream of each of the injections, thanks to temperature probes placed for this purpose in said zones.

 It will be noted that, with respect to a conventional type steam cracking, all the energy necessary for the reaction is supplied at once 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.

 The resulting temperature profile, combined with the extremely short reaction time allowed by this device, leads to a selectivity of the reaction significantly higher than that obtained with traditional methods.

 The fluidized phase steam cracking device shown in FIG. 2 is a variant of the previous unit, in particular at the level of the separation of the effluents from the reaction zone. To facilitate the description, the parts of this device identical to those of FIG. 1 are designated by the same reference numbers. As mentioned above, use is made of the fact that the mixture of particles and hydrocarbon vapors circulates in reaction zone 1 at a high speed, generally between 50 and 200 meters per second. This high speed is used here to separate the effluent hydrocarbons from the heat-carrying particles in an extremely short time, using a centrifugal device 40, formed by the upper part of the reactor 1, in the form of a question mark, in which the particles circulating at the.

periphery fall directly into the stripping zone 41, while the hydrocarbon vapors are collected in the central part and evacuated by line 42.

 A system for separation by centrifugation of heat transfer particles, which can be used in the context of the invention, is described, for example, in the U.S. patent.

N02 901 420.

 A particularly advantageous characteristic of the device according to the invention is the use of the heavy load of hydrocarbons to quench the hydrocarbon vapors directly at the outlet of the ballistic separation system 40. The heavy load is thus injected via line 43 and , while avoiding coking in line 42, it will be preheated by the reaction effluents. The feedstock having a boiling temperature higher than that of the gasolines and gas oils, which leave the fractionation zone 27 by the lines 33 and 34, will leave at the bottom of the tower by the line 35, with the heaviest hydrocarbons n ' having not reacted in the reaction zone, and will then be injected into the latter by spraying using the injectors 10.

In addition to the functions of rinsing the bottom of the tower circuits and preheating the heavy load, this device allows the elimination of entrained particles towards the fractionation column and their recycling towards the reaction section. It follows that the ballistic separation between reaction effluents and the heat-transfer particles does not need to be very thorough and that it can therefore be carried out in a simpler and faster manner.

 It will also be noted that, unlike traditional steam cracking devices, the device according to the invention does not use an additional source of thermal energy and does not require that the charge be clean, but that, on the contrary, it completely exhaust the hydrocarbons. the heaviest, mainly transformed into lighter hydrocarbons and partly into coke necessary for the thermal equilibra of the unit, with an appreciable additional advantage the concentration of the main contaminants in the combustion gases (with regard to the sulfur) and heat transfer particles (for heavy metals), a concentration that makes the elimination or recovery of these elements easier and less expensive.

 The fluidized phase steam cracking device shown in FIG. 3 is a variant of that of FIG. 2, in which the reaction zone this time operates in descending mode. The reactor will therefore be called "dropper" by reference to the English term. The identical parts of this device will be designated by the same references as the corresponding parts of the units shown in FIGS. 1 and 2.

 In order to allow operation in dropper mode without requiring a costly raising of the regeneration zone 20, the regenerated and hot particles coming from line 2 are first transported inside an ascending column 50 by injection of a fluid such as water vapor through line 4; after passing through the two elbows 51 and 52, 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 gasolines, then, by injectors 10, the heavy load with the unconverted heavy hydrocarbons.

 At the outlet of the dropper, the particles dive directly into the dense fluidized stripping zone 41, while the hydrocarbon vapors as well as the stripping vapor coming from line 18 are evacuated almost instantaneously by line 15, where they are immediately quenched by introduction of the heavy load which enters the unit via line 43.

 The stripped particles leave zone 41 via line 21, at the bottom of which an injection of fluid, such as water vapor or air, makes it possible to transfer them via line 53 to the regeneration chamber 20.

In this, a ballistic separation device makes it possible to discharge them into the combustion zone in a fluidized bed, while the transport fluid and the hydrocarbons entrained with these particles leave the chamber 20 with the combustion gases via line 26, after passing through the cyclonic system 25.

EXAMPLE
The example which follows 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 (straightrun 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:
ESSENCE CHARGE TO CHARGE B - density (at 150C) 0.675 0.955 0.985 - Z in distilled volume at 500C: 20 -
at 700C: 70 -
at 1000C: 99 - - Z by weight distilled at 4500C: - 20
at 5500C: - 45 10
at 6500C: - 70 55 - P / N / A (Z by weight): 77/17/6 - H2 (% by weight): 15.4 12.1 11.7 - S (Z by weight): - 1 , 0 1.3 - Total nitrogen (Z by weight): - 0.6 0.8 - Carbon (Z by weight): - 8.1 14.2 - Ni + V (ppm): - 40 70
As heat transfer particles, particles of contact mass 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 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 riser zone: - Catalyst temperature
regenerated (OC): 880 880 - Catalyst flow
regenerated (t / h): 2000 2160 - Steam flow at
3200C (t / h): 15 15 - Ethane flow rate (t / h): 10 10 - Mixing temperature (OC): 862 868
Central riser area: - Steam flow at
3200C (t / h): - 3 - Fuel flow at
1500C (t / h): - 30 - Mixing temperature: - .825
Downstream riser area: - Steam flow at
3200C (t / h): 9 6 - Charging flow A or B
at 3800C (t / h): 90 60 - Mixing temperature (OC): 785 780 - Temperature at the end of
reaction (OC): 740,750
After recovering the effluents from the steam cracking reaction, the nature of these tributaries is analyzed. The analysis results (in% by weight), which are collated below, alone demonstrate the advantages of the present invention compared to the methods of conventional type:
LOAD TO LOAD B
H2S + NH3 0.90 0.80
H2 0.90 0.70
C1 7.90 9.70
C2 5.60 5.90
C2 (olefinic) 20.50 25.30
C3 0.5 0.60
C3 (olefinic) 11.00 11.00
C4 (olefinic) 3.20 3.10
C4 (diolefinic) 2.80 3.10
C5 -2200C 13.90 14.80 220 - 3600C 14.40 7.80> 3600C 4.9 3.70
Coke 13.50 13.50

Claims (19)

 1.- Method of conversion by steam cracking, at high temperature and in the presence of a dilute fluidized phase of essentially heat-carrying particles, on the one hand, of at least one coupa of light hydrocarbon, little contaminated with metals, the boiling temperature is less than approximately 4000C and, on the other hand, a heavier cut of hydrocarbons whose boiling temperature is greater than approximately 4000C, this process comprising a step of bringing the cuts into contact hydrocarbons with heat transfer particles, catalytic or not, in a tubular type reactor with rising or falling flow, a ballistic separation step of said particles and cracked hydrocarbons, a stripping step of the particles, a regeneration step under conditions combustion of the coke deposited on the particles, and a step of recycling at high temperature the regenerated particles to the supply of said reactor, said process being characterized in that the steam cracking is carried out by injection into the fluidized bed of heat transfer particles, in the upstream part of the tubular reactor, of at least one of said light cuts and of steam under conditions such that the resulting mixture is at a temperature between 700 and 9000C and, preferably, between 750 and 8500C and that it contains an amount of water vapor representing between 40 and 80% by weight of the total amount of water vapor injected into the reactor, and in that , after having maintained these contact conditions for a period of between 0.01 and 0.5 seconds and preferably less than 0.1 seconds, said heavier load is injected, in the form of fine droplets, into the downstream part of the reaction zone, so that the resulting mixture in a diluted fluidized bed is at a temperature between 600 and 8500C and, preferably, between 700 and 8000C that it contains a quantity of water vapor representing between 20 and 60Z by weight of la-q total quantity of injected hydrocarbons, this mixture being maintained under these conditions for a period of between 0.01 and 0.5 seconds and, preferably, less than 0.1 seconds.  2.- Method according to claim 1, characterized in that the light hydrocarbon cut is selected from the group comprising light paraffins such as ethane, propane, butanes, and gasolines, naphthas and gas oils.  3.- Method according to one of claims 1 and 2, characterized in that the heavier hydrocarbon fraction is chosen from the group consisting of atmospheric or vacuum distillation residues, catalytic slurries, deasphalting pitches, synthetic or used oils, solid hydrocarbons or coal-water emulsions.  4.- Method according to one of 'claims 1 to 3, characterized in that is successively injected into the reactor, from upstream to downstream, light gases comprising ethane and, optionally, propane and butanes, in an amount such that the temperature of the mixture with the heat-carrying particles is greater than 8000C and, preferably, at 8250C, then cuts of hydrocarbons such as light essences, and possibly naphthas or gas oils, in quantities it that the temperature of the mixture immediately downstream is greater than 7500C and preferably 8000C, finally, in the downstream part of the reactor, in the form of fine droplets of average diameter preferably less than 100 microns, the charge (s) heavier hydrocarbons.  5.- Method according to one of claims 1 to 4, characterized in that the ratio C / 0 where C denotes the mass of heat transfer particles and O the mass of hydrocarbons. present, is between 10 and 30 at the outlet of the reactor and preferably between 15 and 25.  6.- Method according to one of claims 1 to 5, characterized in that the ratio C / 0 where C denotes the mass of heat transfer particles and O the mass of hydrocarbons present at the inlet of the injection zone of the light cut is at least 40 and is preferably between 40 and 200.  7.- Method according to one of claims 1 to 6, characterized in that the ratio between the quantity of steam injected and the mass of hydrocarbons present is between 20 and 60% at the outlet of the reactor.  8.- Method according to one of claims 1 to 7, characterized in that the ratio between the quantity of steam injected and the mass of hydrocarbons present is. between 30 and 200% between the injection area of the light cup.  9.- Method according to one of claims 1 to 8, characterized in that the speed of the heat-transfer particles, at the entry- of the injection zone of the light cut, is between 5 and 200 m / s and preferably between 20 and 50 m / s.  10.- Method according to one of claims 1 to 10, characterized in that said heat transfer particles consist of inert microspheres or catalytic particles.  11.- Method according to one of claims 1 to 11, characterized in that at least part of the ethane produced by steam cracking is recycled to the reactor.  12.- Method according to one of claims 1 to 10, characterized in that one carries out a quenching of the reaction effluents as soon as after the ballistic separation step to avoid secondary reactions and limit the formation of coke in the downstream circuits .  13.- Method according to claim 12, characterized in that said quenching is carried out using the heavier hydrocarbon feed.  14.- Steam cracking device, by conversion into a fluidized phase of heat transfer particles and at high temperature of petroleum fractions comprising, on the one hand, at least one light fraction little contaminated with metals, the boiling point of which is between 20 and 4000C and, on the other hand, a cut of heavier hydrocarbons, the boiling temperature of which is higher than 4000C, comprising a reaction zone for bringing petroleum fractions into contact at high temperature with heat-carrying particles, catalytic or not , in a reactor (1) of tubular type with essentially ascending or descending flow, means (15) capable of effecting ballistic separation of said particles and cracked hydrocarbons, means (19) for stripping the particles, means (20) of regeneration in. conditions for combustion of the coke deposited on these particles, and means (2) for recycling the regenerated particles to the supply of said reactor, said device being characterized in that it comprises means for injecting (7, 8) the or light cuts of hydrocarbons in the upstream part of the tubular reactor in the presence of an amount of water vapor of between 40 and 80% and, preferably, between 50 and 70% by weight of the total amount of vapor d water injected into the reactor, so that the resulting mixture (s) are maintained at a temperature between 700 and 9000C and preferably between 7500C and 8500C for about 0.01 to 0.5 seconds, in that it comprises in the downstream part of the tubular reactor means (10) for spraying said cut of heavier hydrocarbons, so that the temperature of the mixture resulting from this spraying is brought to a temperature between 600 and 8500C and, preferably between 700 and 80 00C and that it contains an amount of water vapor of between 20 and 60% by weight of the total amount of injected hydrocarbons, the mixture being maintained under these conditions for a period of between 0.01 and 0.5 seconds and preferably less than 0.1 seconds after the injection of said heavier hydrocarbons, said device further comprising regulating means (37, 38, 39) making it possible to adapt the introduction of said hydrocarbons in such a way that the quantities of coke necessary for the thermal equilibrium of the device are formed by combustion of this coke during the regeneration stage.  15.- Device according to claim 14, characterized in that it comprises means (7, 8, 10) for injecting successively into the reactor, from upstream to downstream, light gases comprising ethane and, optionally , propane and butanes, in an amount such that the temperature of the mixture with the heat-carrying particles is greater than 8000C and, preferably, at 8250C, then cuts of hydrocarbons such as light gasolines and possibly naphthas and gas oils , in a quantity such that the temperature of the resulting mixture, immediately downstream of the injection point, is greater than 7500C and, preferably, at 8000C, finally, in the downstream part of the reactor, in the form of fine droplets with an average diameter of preferably less than 100 microns, the heavier hydrocarbon charge (s).  16.- Device according to one of claims 14 and 15, characterized in that it comprises centrifugal ballistic means (40) for separating the cracked charge from the heat transfer particles.  17.- Device according to claim 16, characterized in that the upper part (40) of the tubular reactor with ascending flow has the form of a question mark and acts as a ballistic separator by centrifugation.  18.- Device according to one of claims 14 to 17, characterized in that the tubular reactor is in downward flow, in that it is supplied at its upper part with particles regenerated by a particle elevator and in that at its lower part is provided an enclosure (41) supplied with a stripping fluid such as water vapor, where the heat transfer particles separated from the effluents by centrifugal ballistic effect are stripped.  19.- Device according to one of claims 17 and 18, characterized in that it comprises means for spraying the heavy load to be steam cracked immediately downstream of the ballistic separation of the reaction effluents, and means for recovering it at the base in the downstream part of the steam cracking zone.