FR2659346A1 - CRACKING PROCESS WITH OLIGOMERIZATION OR TRIMERIZATION OF OLEFINS PRESENT IN EFFLUENTS. - Google Patents

Abstract

The invention relates to a process for cracking in a fluid bed of a hydrocarbon feed, carried out in an elongated reaction zone (1) in which solid particles are introduced at the lower base of the elongated zone, through a pipe (2). , and the load is introduced by at least one pipe (3). At least part of the heavy oil obtained at a level above the inlet level of the load is recycled via a line (5) and, on the other hand, at least part of the oil is recycled via a line 3A. gasoline obtained in the cracking reaction, at a level intermediate between the admission levels of the catalysts and the feed; In the present invention, the gasoline injected through line 3A is gasoline (line 23) obtained by oligomerization or trimerization of olefins present in the cracking effluents, and is recycled (via at least one line 3-A) into a intermediate point between the points of admission of the catalyst and the charge.

Description

The present invention relates to a cracking process in the fluid state

  of a hydrocarbon charge intended to produce in particular olefins It more particularly has the object of producing a

  maximum of olefins comprising from 2 to 4 carbon atoms.

  To produce olefins from hydrocarbon feedstocks, there are two types of cracking, thermal cracking and catalytic cracking which involve either the

  temperature or the active sites of a catalyst.

  We know that in a conventional thermal cracking unit, the charge

  of hydrocarbons is gradually heated in a tube furnace.

  The thermocracking reaction takes place mainly in the parts of the tubes receiving the maximum heat flux and whose final temperature is that required for the cracking of the charge introduced This thermocracking temperature is generally limited to a maximum of 8500 C by the conditions of implementation of the process and by the complexity of operation of the ovens which use an auxiliary energy of heating Obtaining and maintaining this temperature are all the more delicate as it gradually deposits unwanted coke on the walls of the tubes However, this coke harms the quality of the heat exchanges, lowers the cracking temperature inside the tube, which contributes to greatly reducing the rate of conversion of the charge of hydrocarbons entering the thermocracking unit. build up of coke in an oven can cause the tubes to clog and therefore cause the oven to shut down completely, which is costly them for the operator Failure to remove contaminants from the feed such as nickel, sodium or vanadium is also a major drawback for the

maintenance of ovens.

  We also know how to make olefins in catalytic cracking units. Mention may in particular be made of US Patents 3,284,341 and US 3,074,878 The disadvantage of these patents is notably the reaction time at high temperature. A necessary solution would be to be able to determine an adequate temperature thanks to the addition of hot catalyst and for a short and strictly limited period, avoiding back-mixing of catalysts and / or droplets and limiting the duration of separation of the effluents. The present invention consists in carrying out thermal or catalytic cracking of a charge in a tube, in combination with a steam cracking reaction carried out in the same tube, upstream of the cracking reaction. The steam cracking reaction carried out according to the invention, on petrol coming from, for example, effluents from the cracking reaction, will be carried out with an ideal residence time because this steam cracking reaction will be stopped by injection upstream, at a temperature below that of a steam cracking reaction, of the cracking charge

thermal or catalytic.

  The present invention relates to a process for thermal or catalytic cracking in the fluid state of a hydrocarbon charge in a tubular reaction zone; the method is characterized in that it comprises a prior step of bringing upward or downward flow into contact in one end of the tubular reaction zone with a fluid comprising at least 50 to 100% by weight of a section of gasoline whose boiling point is preferably between 40 C and 2200 C, in a fluidized bed diluted with heat-carrying particles and water vapor; the process carried out with a view to producing in particular olefins, is carried out as follows: (a) said preliminary step is carried out by injecting a mixture of solid particles (the temperature of which is between 600 and 9000) at one end of the tubular reaction zone C) and water vapor, which represents approximately 15 to 60% by weight relative to said fluid and by injecting through at least one pipe, downstream of the mixture of solid particles and water vapor, said fluid containing said cut gasoline, at a temperature

  below 7000 C, to produce olefins.

  (b) a pulverized cracking charge is injected downstream of the intake pipe of said fluid containing said gasoline cut (droplet diameter generally less than 150 microns, ie 150 × 10 -6 m) so as to lower the temperature in the tubular reaction zone, at the intake level of said

  load, between 450 and 6000 C, this lowering of temperature provokes

  as for the stopping of the production of olefins carried out in step (a).

  (c) thermal or catalytic cracking of the heaviest constituents of said charge is carried out, said cracking generating the quantities of coke necessary to subsequently enable, by combustion of the solid particles on which most of this coke has deposited, d '' obtain the calories necessary to maintain between 600 and 900 C the temperature of the particles

  heat carriers, used in step (a).

  Different aspects of the invention could be the following: the fluid which is injected downstream of the particles in step (a) is a gasoline This gasoline can be obtained by fractionation of the effluents withdrawn from the tubular reaction zone It is this aspect which was the subject of patent EP-B-325502; this gasoline can also be any hydrocarbon gasoline for example a direct distillation gasoline. According to the invention, the hydrocarbons with two carbon atoms (essentially ethylene) coming from the effluents of the tubular reaction zone are sent to a trimerization unit or oligomerization in order to produce a gasoline, which is at least partly recycled as said fluid defined in paragraph (a) of the process In addition, the ethane produced in said oligomerization or trimerization zone can be sent at least in part at the end of the tubular reaction zone with the

  heat transfer particles and / or water vapor.

  In addition, the reagents involved can circulate from bottom to top in the tubular reaction zone ("riser" type or in English: "riser") Likewise the reagents involved can circulate from top to

  low in the tubular reaction zone (English term: "dropper").

  The heat-carrying particles may be catalytic particles, in which case, there is a catalytic cracking unit,

  type FCC ("fluid catalytic cracking").

  In step (a), the chosen amount of water vapor is relatively large to avoid triggering radical reactions which can be caused by the presence of the ethylene formed and which

  lead to parasitic polymerizations.

  In general, the speed of the gasoline cut between its injection point in the tubular reaction zone and the charge intake pipe is less than 1 m / sec. The speed of the

  load in the tubular area is generally less than 20 m / sec.

  and for example between 18 and 20 m / sec, the residence time

  being of the order of 2 to 5 seconds, sometimes 1 to 4.

  The advantage of the invention is to be able, in the tubular reaction zone, to carry out catalytic or thermal cracking of a hydrocarbon charge while maximizing the production of olefins by injecting a gasoline between the point of catalytic or non-catalytic heat transfer particles and the charge admission point Conventional cracking is not intended to obtain olefins We could of course choose operating conditions allowing the production of olefins but we do not would not, in any case, produce enough olefins for the process to be profitable and furthermore, obtaining olefins would be at the expense of other products

obtained by cracking.

  However, the process according to the invention for the production of olefins therefore consists in operating a steam cracking (or "steam-cracking") using steam injected with the heat-carrying particles in order to carry out fluidization of the charge The optimization of this steam cracking reaction can be carefully controlled here, in particular its temperature and its duration, precisely because of the injection of the charge downstream of the injection of petrol, at relatively cold temperature, (English term: "quench"), thanks to which temperature, the steam cracking operation will be stopped, with conventional cracking starting at this stage, as described for example in patent EP BF 191 695 CFR It is therefore possible, by the process according to the invention, to benefit, for the production of olefins, simultaneously from the advantages (a) of a steam cracking reaction, which here is controlled contrary to what was happening in the art er, with an ideal residence time,

(b) a cracking reaction.

  The advantage of the invention is to be able to use, as a gasoline cut, a recycled gasoline cut obtained as follows. It is possible, as explained above, to perform an oligomerization or a trimerization of the C 2 cuts obtained during the fractionation of the cracking effluents, thus obtaining a gasoline, in particular C 6 5 and advantageously recycling at least part of this gasoline The process of the invention also makes it possible also to obtain more hydrogen (produced by cracking with steam) at the top of the fractionation zones for effluents from steam cracking and catalytic cracking or not, therefore to obtain a sought-after raw material in refining In accordance with the invention, a catalyst described in EP- is also used in the present invention B 325502 containing by weight: (a) 20 to 95% of a matrix (b) 1 to 70% of a so-called open structure zeolite (c) 0.05 to 40% of a z Wlithe of the family of erionite having a e

  potassium content less than 0.4% by weight.

  The following descriptions illustrate and specify the invention, its

  scope, its various means of implementation.

  The contact mass playing the essential role of heat-transfer mass must withstand temperatures close to 1000 ° C. and can advantageously consist for example of kaolin, notably calcined clay, sand, etc., of a catalytic cracking catalyst and

  mixtures of the solids mentioned above.

  Apart from the regulation of the cracking temperature by the contact mass and the injection of steam into the cracking zone, another of the important parameters of the cracking reaction of the process according to the invention is the good atomization-vaporization of the charge when the latter is brought into contact with the heat-transfer grains of the contact mass and of the vapor in the cracking zone. The atomized charge can vaporize before coming into contact with these grains, due to the good distribution of the grains of contact mass in the tube obtained according to a known mode of the technique relating to fluidized beds. The accompanying drawings illustrate, in schematic form, various devices for implementing the method according to the prior art or according to the invention; FIGS. 1 to 3 relate here to a diagram of a device, either for thermocracking or for catalytic cracking with a fluid bed comprising a regenerator. They have been described in

  Applicant's patents FR-A-2621322 and EP-B-325502.

  Figure 4 illustrates the injection of a gasoline obtained by

oligomerization or trimerization.

  The gasoline injection is made via line 3 A. The column or riser 1 opens at its top in a chamber (not shown) which is concentric with it and in which the cracked charge is separated on the one hand , on the other hand, stripping of the contact mass covered with hydrocarbon materials. The treated charge is separated by a cyclone, not shown, which is housed in said enclosure, at the top of which is provided a discharge line 6 for the cracked charge, while the contact mass grains covered with hydrocarbonaceous materials

  are rejected at the base of the enclosure.

  The spent catalyst particles are generally stripped by steam and are evacuated at the base of the enclosure, to at least one regenerator. In this regenerator, the coke deposited on the grains of the contact mass is burnt to using air The treated clean grains are recycled through line 2, fitted with a

  regulation, to the elevator or column supply or riser 1.

  The effluent withdrawn through line 6 is subjected to fractionation in zone 7 Generally, by way of illustration, light gases C 1-C 4 and hydrogen are collected through line 12, gasoline through line 11, which can be recycled to

  line 3 A fuel intake at the bottom of the elevator 1.

  a relatively light oil LCO, via line 10, a relatively heavy oil HCO, via line 9,

a residue, through line 8.

  The light products drawn off through line 12 can be split into 27 and thus methane and hydrogen are collected for example through line 13; the C 2, C 3, C 4 hydrocarbons of line 14 are fractionated at 26 with the obtaining, on the one hand, in lines 25 and 15, of C 2 hydrocarbons (ethane and ethylene) and on the other hand, in line 17, C 3 and / or C 4 hydrocarbons. The object of the invention consists in transporting the ethylene from line 15, via line 16, in a zone 18 in which it is possible to carry out either an oligomerization reaction or a trimerization reaction, obtaining gasoline; these reactions are now well known and their operating conditions are described in particular in US patents 3,795,712, 4,270,929, 4,268,701, 4,532,370 and in

  European patents 170,537, 183,604.

  The gasoline obtained is collected by lines 20 and 22 At least part of this gasoline is advantageously recycled through line 23, to line 3 A of gasoline injection at level C,

  in the lower part of the elevator 1; Note that advantageously

  You could also use at least part of the ethane collected through lines 19 and 24 and return this ethane through line 21 to a non-steam injection line.

  shown at the bottom of the elevator 1.

  In practice, as already indicated on page 4 above, the catalyst regenerated at a temperature generally above 6000 ° C. and the charge to be treated are brought into continuous contact at the base of a vertical or inclined tubular reactor known as a charge ", which the technicians often designate by the English term of" riser "One can also introduce the load to be treated and the catalyst at the top of a vertical or inclined tubular reactor which the technicians often designate by the English term" dropper " In these two techniques ("riser" or "dropper"), the charge, usually preheated to a temperature of 80 to 4000 C and injected at a pressure between 0.7 105 and 3.5 105 relative Pascals, vaporizes then cracks in contact with the active sites of the catalyst, while ensuring pneumatic transport of the grains thereof, the

  desired average size is around 70 microns (1 micron = 10-6 m).

  After a contact time of the order of 1 to 4 seconds, the hydrocarbon vapors, at a temperature of the order of 450 to 6000 C, are separated from the catalyst downstream of the reactor, and sent to the fractionation section of the various products The spent catalyst, generally charged with 0.5 to 2.0% by weight of coke, is first stripped with steam, then evacuated to a regenerator, where its activity is restored by combustion of the coke The heat of combustion of this coke, which can contain 5 to 10% by weight of hydrogen, is divided between the catalyst (about 70%) and the regeneration fumes The regenerated catalyst is recycled to the reaction zone, where the fraction of the heat of combustion of the coke transmitted to the catalyst in the regenerator is used to vaporize the charge, provide the reaction heat (endothermic) and compensate for the various heat losses The duration of an average cycle, for the catalyst, is

about 15 minutes -

  So, after having separated the cracked and / or vaporized charge, the catalyst covered with a carbonaceous material containing coke resulting from the cracking reaction is recovered, this carbonaceous material is burned using an oxidizing gas at high temperature. in an oven often called a regenerator and this regenerated catalyst is returned in the presence of another part of the hydrocarbon charge in the

tubular reactor.

  The coke can be burned between 500 and 10,000 C in one or two stages of regeneration; the cracking reaction using the regenerated catalyst, heated to these temperatures can be carried out in the elevator up to a temperature of 6500 C (see US Pat. Nos. 4,331,533, 4,332,674 and 4,336,160) The coking rate during the cracking reaction is generally a function of the percentage of Conradson carbon in the feed and the temperature of the regenerated catalyst. The catalyst regeneration temperature cannot exceed 750 C in the presence of water and approximately 1000 C in the absence of water, otherwise the latter will be damaged, i.e. weaken its catalytic activity and therefore decrease the selectivity of the

  cracking reaction in petrol and light distillates.

  The hydrocarbon charge is vaporized and brought into contact at high temperature with a cracking catalyst, which is kept in suspension in the vapors of the charge After the desired molecular weight range has been reached by cracking, with a lowering corresponding to the boiling points, the catalyst is separated from the products obtained, stripped, regenerated by combustion of the coke

  formed, then brought back into contact with the load to be cracked.

  The charges to be cracked are usually injected into the reaction zone at a temperature generally between 80 and 4000 ° C., under a relative pressure of 0.7 to 3.5 bars, while the temperature of the regenerated catalyst which arrives in this zone can be of the order of 600 to 950 C. The hydrocarbon charges capable of being injected into the units of the type described above may contain hydrocarbons having boiling ranges between 200 and 550 C or more, and their density can vary between 10 and 350 API These charges can also be heavy loads containing hydrocarbons whose boiling point can go up to 7500 C and more, and whose density can vary between 10 and 350 API, or even between

0 and 25 API.

  For example, there may be mentioned as fillers, those having final boiling points of the order of 4000 C, such as gas oils under vacuum, but also heavier hydrocarbon oils, such as crude and / or de-essential oils, and atmospheric distillation or vacuum distillation residues; these fillers may if necessary have received a preliminary treatment such as, for example, a hydrotreatment in the presence for example of catalysts of the cobalt-molybdenum or nickel-molybdenum type. The preferred fillers of the invention will be those containing fractions normally boiling up to at 7000 C and above, which may contain high percentages of asphaltenic products, and have a Conradson carbon content of up to 10% and above These fillers may or may not be diluted by conventional lighter cuts, which may include cuts of hydrocarbons that have already undergone the cracking operation, which are recycled, such as for example light recycling oils ("light cycle oils", LCO) or heavy recycling oils ("heavy cycle oils"; HCO) Next the preferred mode of the invention, these charges are preheated in a range of

  temperature between 300 and 450 C before their treatment.

  The catalysts usable in the devices described above include cracking catalysts of the crystalline aluminosilicate type, certain types of silica-alumina, silica-magnesia, silica-zirconium, all having relatively cracking activities.

  or having such activities.

  The crystalline aluminosilicates can be in their natural state or be prepared by synthesis, according to techniques well known to those skilled in the art. They can be chosen from synthetic zeolites or clays, such as faujasite, certain mordenites, montmorillonite, bridged clays, alumino-phosphates, or the like, offretites, zeolites A, Y, L, X, omega, erionites, etc. The present invention therefore relates to a catalytic cracking process which allows d '' improving flexibility on the structure of product yields It often happens that a customer requests, in the context of a catalytic cracking, obtaining a maximum of liquefied petroleum gases (C 3-C 4) (LPG) and the simultaneous obtaining of a maximum of light distillate (Light cycle oil or "LCO") However, such an operation is incompatible since it would be necessary to be able to increase the severity of the catalytic cracking to obtain the maximum of LPG and decrease it to maximize the production of L C O.

  In the present invention, it is sought to remedy this incompatibility

  For this purpose, a process is proposed which consists in judiciously recycling part of the gasoline obtained in the effluent from the catalytic cracking zone and produced from this effluent. Thus, as explained above, the recycled fraction of gasoline or LP G in the reactor 1 is carried out by at least one line 3 A. The cracking of this light fraction recycled in this way is carried out under conditions of severity more favorable than , if this recycling had been carried out for example by a line 3, essentially because it is near the level C of the line 3 A that the temperature of the catalyst is the warmest So there are locally at this level C conditions severe cracking (high temperature, high C / O) which are generally required for cracking light loads (petrol, LPG) This is the level C where cracking of petrol and / or recycled LPG occurs, thus causing at this level C, a drop in the temperature of the catalyst. Thus at level B, point of arrival of the charge, the temperature is lower, allowing cracking to be carried out under milder conditions (moderate temperature, ca talyseur already amortized) which precisely are suitable for cracking the load with obtaining a maximum of L C O We were therefore able

  thus reconcile two objectives apparently incompatible by the user-

  sation of at least two zones of different severity, namely on the one hand a first zone of great severity disposed at the bottom of the riser, situated between the admission of recycling and the admission of the load and where maximum production occurs of LPG by cracking recycled fractions of the reaction effluent lighter than LCOs and on the other hand another zone of milder severity, arranged in the riser above a pipe 3 for admission of the charge, this last zone which can, according to the objective, be itself subdivided into zones with different severities as the temperature decreases when one rises in the riser In accordance with the main request, a recycling of HCO then occurs via line 5, to maximize the efficiency of the system according to the invention. In these examples, it is proposed to treat a heavy load whose characteristics are as follows: Density (20 C) Viscosity c St (80 C) c St (100 C) Conradson% (weight) Na ppm Ni ppm V ppm C% (weight) H% (weight) N% (weight) S% (weight) N Basic% (weight) C aromatic% (weight) H aromatic% (weight) Disti 1 ation% (weight)%%%% PBF 0.968 ( solid at 60 C) 119.8 (119.8 mm 2 / s) 52.2 (52.2 mm 2 / s), 1 11.6 1.2 86.9 12.2 0.35 0.21 0.055 22.3 2.7 simulated (C) In tests NI, N 2, N 4 and N 5, a conventional ultrastable Y zeolite USY diluted in a matrix which is a mixture of silica alumina rich in silica and kaolin is used as catalyst. (30% of zeolite by weight relative to the mass of catalyst, 70% of matrix The balanced catalyst circulating in the unit has the following characteristics: Alumina present: 37% by weight Surface in m 2 g 1: 110 Rare earth oxide : 1.6% by weight Na 20: 0.3% by weight Vanadium: 4800 ppm Nickel: 2800 pp m Iron: 10200 ppm In the first test N I, an FCC is operated in a conventional manner, in a lifting tube; we operate without recycling H C O, and without

  fuel injection, as shown in Figure 1.

  Catalyst injection temperature: 771 C Charge injection temperature: 210 C Level B temperature: approximately 537 C Temperature at the top of the riser: 516 CC / O = 6 o C is the catalyst flow rate and O charge flow

  heavy ("catalyst / oil ratio", catalyst / oil ratio).

  In a second test N 2, the operation is carried out as in the first test, in addition carrying out an injection of a direct distillation essence upstream of the injection of the charge. We therefore operate in accordance with FIG. 2 This direct distillation essence is a 50-160 C cut, non-olefinic, of the following composition: paraffins% weight: 58 olefins% weight: O naphthenes% weight: 29.5 aromatics% weight: 12.5 This essence contains less than 2% by weight of compounds with 5 carbon atoms The mass of petrol injected through line 3 a represents 20% of the mass of the cracking charge The temperature T 3 in the vicinity of the inlet of line 3 is approximately 5370 C; the temperature T 4 at the top of the riser is 516 ° C. In test N O 3, the procedure is as in test N 02, but using a catalyst prepared according to example 2 of European patent EP-B-325502

  incorporated herein by reference.

  In test N 04, the procedure is as in the first test, but here by operating in accordance with FIG. 1; 40% of the heavy diluent obtained is thus recycled, via a line (5) The catalyst grains are injected through a line (2) at 7710 C, the charge is injected through a line (3) at 210 ° C. The temperature T 3 riser near the intake pipe (3) is around 5370 C The temperature T 4 at the top of the riser is 5160 C The temperature is 5560 C

at level A of the pipe (5).

  In test N 05, the procedure is carried out both in accordance with the second and

  fourth test, according to the technique illustrated in FIG. 3.

  In test N 06, the procedure is as in test N 05, but in the presence of the

  catalyst according to the invention, used in test N 03.

  During all of the tests, except the first, the operating conditions were therefore as follows: Temperature T 1 of catalyst injection (OC) 771 Temperature T 2 of charge injection (OC) 210 Temperature T 3 at level B (OC) approximately 537 Temperature T 4 (OC) 516 In the fourth, fifth and sixth tests, the temperature at level A of the pipe (5) is 5560 C. The gasoline is injected in test N 06, at a temperature of 2100 C, and in the same

  proportions as in tests N 2,3 and 5. The results obtained in the six tests are presented in the table

  next The yields are expressed in% by weight relative to

load.

  In the second, fifth and sixth trials, the conversion of

  the gasoline injected is 56% by weight.

  The system (second and third tests) of injection of a light gasoline of first distillation at the bottom of the elevator on a very hot catalyst, allows to obtain an improved yield in propylene but also in olefins with 4 carbon atoms, and this more particularly when instead of using a conventional catalyst (2nd test), a catalyst according to the invention is used. When a gasoline injection and a recycling of H C 0 are carried out simultaneously (5 and 6 tests) the results are not raised in a highly surprising manner but the gains (notably in propylene, unsaturated hydrocarbons at 4 carbon atoms and gasoline) without increasing the coke and slurry contents are appreciable in high-capacity industries, using a conventional catalyst and become very appreciable using the

catalyst according to the invention.

  1 ER TEST 2 nd TEST 13 th TEST | 4 th TEST 5 th TEST 16 th ESSAII injection I j injection catalyst injection 1 injection I petrol j recycling of petrol and petrol and conventional petrol Icatalyst 1 HC O; I recycling Irecycling | catalyst 1 according to catalyst I HCO; 1 HCO; conventional Il'inventionl convention Icatalyseur Icatalyseur nel Iconvention-1 according to I 1 nel invention

H 2 S 0.10 0.10 0.10 0.10 0.10 0.10

  H 2 + C 1 + C 2 4.6 5.5 6.4 3.2 4.0 4.7

C 3 1.4 2.1 3.0 1.4 2.0 3.0

C 3 = 4.4 6.5 1 0.3 4.6 6.8 10.6

  C 3 saturated 4.1 5.1 1 6.1 4.3 1 5.3 1 6.2 (âont i C) (3.3) (4.1) (4.9) (3.5) ( 4.2) (5.0) C 4 = total 5.9 9.3 12.7 6.1 9.6 12.7 l ll ll Total gasoline Gas C -221 C

LCO (221- 50 C)

  heavy thinner HCO and slurry (350 C +) coke conversion Total Octane number for gasoline search Octane index for gasoline engine, 50 44.9, 1 11.4 8.1 92.2, 1 32, 70, 0, 8 12.2 8.5, 9 79.5 38.6 52.8 13.9 11.0 8.7 93.7 82.2 19.7, 4, 4 11.6 7.9 27.70, 7 16.0 12.3 8.3 37.20, 6 11.8 8, 4 r, u M (o r_.

Claims (10)

  1 Method for the thermal or catalytic cracking in the fluid state of a hydrocarbon feed, in a tubular reaction zone, the method comprising a prior step of bringing into contact with ascending or descending flow in one end of the zone of tubular reaction of a fluid comprising at least 50 to 100% by weight of a gasoline cup whose boiling temperature is preferably between 40 ° C. and 220 ° C., in a fluidized bed diluted with heat-carrying particles and vapor of water, said process being carried out as follows: (a) said preliminary step is carried out by injecting at one end of the tubular reaction zone a mixture of solid heat-carrying particles (whose temperature is between 600 and 900 ° C.) and steam of water which represents approximately 15 to% by weight relative to said fluid and by injecting through at least one pipe, downstream of the mixture of solid particles and water vapor, said fluid, at a time temperature below 700 ° C., in order to produce olefins, (b) a pulverized cracking charge is injected downstream of the intake pipe of said fluid, so as to lower the temperature in the tubular reaction zone, at the level of admission of said charge, between 450 and 600 C, this lowering of temperature causing the stopping of the production of olefins carried out in step (a). (c) thermal or catalytic cracking of the heaviest constituents of said charge is carried out, said cracking generating the quantities of coke necessary to subsequently enable, by combustion of the solid particles on which most of this coke has deposited, d '' obtaining the calories necessary to maintain between 600 and 900 C the temperature of the heat transfer particles used in step (a), the catalyst used containing by weight: 95% of a matrix 1 to 70% of a so-called zeolite open structure 0.05 to 40% of a zeolite of the eronite family, having a potassium content of less than 4% by weight, the process being characterized in that the hydrocarbons with two carbon atoms originating from the effluents of the tubular reaction zone are sent at least partly to a trimerization or oligomerization unit in order to produce a gasoline, which is at least partly recycled as indicated in paragraph (a) above at fluid title.   2. The method of claim 1 wherein further, the ethane produced in said oligomerization or trimerization zone is sent at least partially to the end of the reaction zone   tubular with heat transfer particles and water vapor.   3. Method according to one of claims 1 and 2 wherein the   reagents involved circulate from top to bottom in the reaction zone tubular.   4. Method according to one of claims 1 and 2 in which the reagents involved circulate from bottom to top in the tubular reaction zone.   5. Method according to one of claims 1 to 4 wherein the   at least most of the heat-carrying particles are catalytic particles.   6 Method according to one of claims 1 to 5 wherein the   recycled fraction represents, by volume, 5 to 50% of the charge.   7. Method according to one of claims 1 to 6 wherein the   recycled fraction represents, in volume, 10 to 30% of the load.   8. Method according to claim 5, for catalytic cracking of a hydrocarbon charge in a fluid bed or entrained bed in an elongated zone of substantially vertical tubular shape, the catalytic particles being introduced at the lower base of the elongated zone, the charge being introduced through at least one pipe into the lower part of the elongated zone at a level B higher than the intake level of the catalytic particles, said catalytic particles being separated from the reaction effluent at the upper part of the elongated zone, l the reaction effluent then being fractionated in order to obtain various fractions in particular hydrogen, ethylene, a relatively light oil "LCO" and a relatively heavy oil "HCO", the process being characterized in that a part at least ethylene is subjected to an oligomerization or trimerization reaction and in that the products thus obtained during this reaction is recycled at least in part in the elongated zone to a level C higher than the level of admission of the catalytic particles and lower than the level B of charge admission. 9 The method of claim 8 wherein the recycled fraction   represents, by volume, 5 to 50% of the charge.   10. The method of claim 8 wherein the recycled fraction   represents, by volume, 10 to 30% of the load.