AU641367B2 - Method and device for vapor-cracking of hydrocarbons in fluidized phase - Google Patents

Description

OPI DATE 09/04/91 AO.JP DATE 16/05/91 APPLN. 1I) 42252 89

PCT

PCT NUMBER PCI/FR89/0O437 DEMANDE INTERNATIONALE PUBLIEE EN VERTU DU TRAITE DE COOPERATION EN MATIERE DE BREVETS (PCT) Classification Internationale des brevets 5 (11) Numiro de publication internationale: WVO 91/03527 ClOG 9/00, 9/32, 11/18 Al (43) Date de publication internafionale: 21 mars 1991 (21.03.91) (21) Numiro de la demnande Internationale: PCT/FR89/00437 (81) Etats disignis: AT (brevet europ~cn), AU, BE (brevet curop~en), ClH (brevet europ~en), DE (brevet europcen)*, FR (22) Date de d~p6t international: Iler septembre 1989 (01.09.89) (brevet europ~cn), GB (brevet europeen), IT (brevet curop~en), JP, LU (brevet europ~en), NL (brevet euro- (71) Diposant (pour rous ics Etals d~sign&s satuf US): COMPA- pe) E(rvtcrpe)

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GNIE DE RAFFINAGE ET DE DISTRIBUTION TO- TAL FRANCE [FR/FR]; 84, rue de Villiers, F-92538 Le- Publiie vallois-Perret Avec rappori de recherch~e interrnationale.

(72) Inventeurs; et Inventeurs/Diposants (US seulement) :SIGAUD, Jean-Bernard [FR/FR]; 18, boulevard de la R~publique, F-92430 Vaucresson MAULEON, Jean-Louis [FR/FR); 22, avenue do l'Abreuvoir, F-78160 Marly-le-Roi 616; (74) Mandataire: CABINET BROT JOLLY; 83, rue d'Ams- 61 terdam, F-75008 Paris (FR1).

(54) Title: METHOD AND DEVICE FOR VAPOR-CRACKING OF HYDROCARBONS IN FLUIDIZED PHASE (54) Titre: PROCEDE ET DISPOSITIF DE VAPOCRAQUAGE D'HYDROCARBURES EN PHASE FLUIDISEE (57) Abstract 3 Methods for converting by vapor-cracking at high temperature and in the presence of a diluted fluidized phase of essentially heatconveying particles, on the one hand at least one light hydrocarbon 3 charge which is little contaminated by metals and of which the boiling163 temperature is lower than 400 'C approximately and, on the other30

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hand a heavier hydrocarbon charge essentially comprised of com- 11 pounds of which the boiling temperature is higher than 400 *C ap- 21 proximately. According to the invention, the heavier hydrocarbon 3 2 charge is injected between the step for the separation of the particles 21 13 U I and the hydrocarbons issued from vapor-cracking and the step of frac- 22 1 24 11t? tionation of said hydrocarbons. Part of the rest of the distillation of 5 10 _ehydrocarbons issued from vapor-cracking is injected in the down- 4 stream portion of the reactor.- (57) Abrijg6 Proc6d6 de conversion par vapocraquage, A haute temp~rature et en prisence d'une phase fluidis~e diluie de particules essentiellement caloporteuses, d'une part, d'au momns une coupe d'hydrocarbures 16g~re, peu contamin~e par des m~taux, dont la temperature cl' bullition est inf6rieure i environ 400 'C et, d'autre part, d'une coupe d'hydrocarbures plus lourde, constitute essentiellement de composes dont la temperature d6bullition est sup~rieure Ai environ 400 Selon l'invention, la charge d'hydrocarbures plus lourde est inject~e entre 1'6tape de separation des particules et des hydrocarbures issus du vapocraquage et 'Etape de fractionnement de ces hydrocarbures. Une partie du r~sidu de distillation des hydrocarbures issus du vapocraquage est inject~e dans la partie aval du r~acteur.

*Voir au verso 1 Process and device for vapour-cracking hydrocarbons in the fluidized phase The present invention relates to a processand device for vapourcracking permitting the conversion of fractions of petroleum hydrocarbons in a fluidized phase of heat-carrying particles and at hig, temperature with a view to the production of olefines and, in particular, olefines containing 2 to 4 atoms of carbon, butadiene and monoaromatic compounds such as benzene, or possibly being branched, such as toluene, xylenes, etc.

It is known that the processes of cracking hydrocarbons are commonly used in the petroleum and para-petroleum industries; they consist in splitting molecules of hydrocarbons into smaller molecules by raising the temperature. There are two types of cracking, thermal cracking and catalytic cracking which make use either only of the influence of the temperature, or the active sites of a catalyst.

In a conventional thermal cracking unit the charge of hydrocarbons is heated progressively in a tubular furnace. The thermal cracking reaction takes place mainly in the part of the tubes that receives the maximum of the heat flux, where the temperature is determined by thenature of the hydrocarbons to be cracked: for the so-called "viscoreduction" processes, in which only the heaviest molecules are cracked into smaller molecules, the cracking temperature is between 450 and 600'C, depending on cases; when the molecules to be thermally cracked are lighter molecules, such as petrols or liquefied petroleum gases (LPG) and it is required to produce light olefines and monoaromatic compounds, the temperature necessary is much higher, and generally between 780 and 850'C, depending on the type of charge to be cracked, but it nevertheless remains limited by the conditions of application of the process and by the complexity of operation of the furnaces, which use an extra heating energy.

The obtaining and the maintenance of the required temperature levels are all the more delicate as undesirable coke is deposited on the walls of the tubes and the thermal flux is limited. Furthermore, the wall temperature higher than that of the process is the cause of the formation of coke and degradation products of the type of gums and acetylene compounds. The coke has an adverse effect on the quality of the heat exchanges; it brings aboutan increase in the charge loss inside the tubes and an increase in the skin temperature, imposing an excessive mechanical stress, which contributes to reducing the rate of conversion of the charge of hydrocarbons penetrating into the thermal cracking unit and causing periodic halts for decoking. The result is also, on the one hand, that the process must be modular, so as to permit the decoking operations while working and, on the other hand, that the charges to be treated must be "clean", so that the duration of the cycles between two decoking operations is not too short. In practice, these charges are restricted to LPG, to petrols and to certain favourable or hydrotreated gas oils.

Furthermore, the transfer of heat in a tube is not instantaneous and the thermal cracking reaction is extremely endothermal. Problems therefore arise with regard to temperature regulation and maintenance and, consequently, to selectivity, which are very difficult to solve.

To remedy these disadvantages and carry out a thermal cracking of hydrocarbons it was proposed very long ago to use the fluidized bed technique. Thus, for example, U.S. patent 3,074,878 (Esso) and European patent application no.

26,674 (Stone) use a tubular reactor with a downward-flow fluidized phase of heat-bearing particles, with a short contact time, to effect a thermal cracking of petroleum charges by the application of heat provided by the combustion of coke deposited on the heat-bearing particles; U.S. patent 4,427,538 (Engelhard) uses a tubular reactor to effect a low-severity cracking and the elimination of the heaviest hydrocarbons contained in a charge by means of a reaction in a rising fluidized phase of inert heat-bearing particles.

Neither of these techniques, however, is likely to permit, under I t d 3 satisfactory industrial conditions, the simultaneous conversion into light olefines and monoaromatic compounds of several fractions of petroleum hydrocarbons such as LPG, petroleum spirits or, a fortiori, severely contaminated residual charges.

Indeed, for the thermal cracking of petroleum hydrocarbon fractions which contain light paraffins, such as butanes, propane and especially ethane, as well as petroleum fractions such as petrols, naphthas and gas oils, it is necessary to keep the ieaction temperature at a very high level, generally of the order of 750 to 850'C, for a very short time, but strictly controlled. Without a precise control of the holding time in this temperature zone, molecules of olefines formed during the conversion might be polymerized, to the detriment of the overall selectivity of the reaction. Now, it is found that the separation systems used up to the present to separate the reactive outflowing materials from the heat-bearing particles do not generally permit a sufficiently rapid separation and quenching of the outflowing material, so that some molecules formed are likely to continue to react and become polymerized.

The result of this is a constant risk of blocking or fouling in the separation and stripping zone, as well as in the hydrocarbon outlet ducts between said zone and the fractionation zone.

In addition, holding in the gas phase at the temperatures required for thermal cracking necessitates an instantaneous and very considerable application of calories on account of the highly endothermal nature of the thermal conversion by vapour-cracking and in view of the fact that a fairly large quantity of steam, intended to reduce the partial pressure of the hydrocarbons and minimize coke production, is injected into the reaction zone. In addition, in the case of the vapour-cracking of fractions of light hydrocarbons into olefines and monoaromatic compounds, the quantity of coke deposited on the heat-carrying particles would be quite insufficient to ensure the thermal equilibrium of the system and would necessitate the systematic addition of external energy Finally, this equilibrium and the level of temperatures to be reached necessitate very high temperatures in the heat-carrying material. Now, 1, 4 S I the technological difficulties associated in part with the metallurgical properties of the equipment concerned have made the situation such that only the most recent techniques make it possible to provide the required quantities of heat-carrying particles at the appropriate high temperature.

The present invention aims to remedy these disadvantages by proposing a process for the conversion of fractions of petroleum hydrocarbons into olefines such as ethylene, propylene and butenes, butadiene and monoaromatic compounds by high-temperature vapour-cracking, by the introduction of said fractions into a diluted fluidized phase of heatcarrying particles and high-temperature steam under strictly determined reaction conditions of fluidization, temperature and duration.

The invention also has the aim of permitting a satisfactory conversion by cracking the fractions introduced into the reactor with high selectivity into light olefines, butadiene and monoaromatic compounds.

A further aim of the invention is to. permit an effective control of the polymerization reactions of thereaction products.

Finally, the invention aims at producing coke only in a reduced quantity, but a quantity sufficient to mect the requirements of the heat balance of the unit.

To this end, the object of the invention is a process for the conversion, by vapour-cracking at high temperature and in the presence of a diluted fluidized phase of essentially heat-carrying particles, of, in the first place, at least one fraction of light hydrocarbons which is not severely contaminated by metals and the boiling temperature of which is less than about 400'C, and, in the second place, of a heavier charge of hydrocarbons composed essentially of compounds the boiling temperature of which is greater than about 400'C, said process comprising a stage of bringing said fraction, then said charge, in stages of decreasing severity into contact with heat-carrying particles, catalytic or otherwise, in a continuous reactor of the tubular rising-flow or descending-flow type, a separation and stripping stage permitting the separation, in the first place, of at least 90% of said particles, which are then regenerated, preferably by combustion of coke deposited on them, before recycling them at a higher temperature to the feed of said continuous reactor and, in the second place, the outflowing hydrocarbons, which are then recovered from a fractionation stage by distillation, said process being characterized in that at least one fraction of the heavier charge of hydrocarbons is injected between said stage of the separation of the particles and outflowing hydrocarbons and that of fractionation, and in that at least part of the residue of said stage of fractionation by distillation is recycled to the downstream part of said reactor.

Since the lightly contaminated fraction or fractions of light hydrocarbons are distilled at less than 400'C, it will be possible to choose them to advantage from the group formed by light paraffins, such as ethane, propane and butanes, and heavier hydrocarbons, such as petroleum spirits, naphthas and gas oils, even some fractions with a higher boiling point, but strongly paraffinic or naphthenic, such as paraffins or paraffin sludge or recycled :hydrocarbon substances. These hydrocarbon fractions may come either from various units of the refinery, such as the atmospheric distillation, viscoreduction, hydrocracking, oil production or olefine oligomerization plants, or effluents from the conversion unit itself. These various fractions may, in addition, be injected alone or in combination with steam and possibly other fluidization gases, such as hydrogen and light gases.

According to one particularly advantageous mode of application, the vapour-cracking is preferably carried out in the contiuous reactor in a plurality of zones of decreasing severity by successive injections, in the presence of steam and (or) gaseous fluids, of a plurality of separate fractions, the first fraction necessarily having a boiling temperature lower than that of the next. This temperature profile is, in fact, particularly convenient for optimizing the selectivity of the reactions involved. It will be possible, for ex .mple, to inject in succession a first fraction containing mainly ethane, then possibly propane and butane, next, in the liquid phase, a fraction containing light spirits, then possibly naphthas or gas oils and finally the heavier

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6 charge of hydrocarbons which have a boiling temperature higher than about 400'C. The latter can be chosen to advantage from the group made up of the residues from atmospheric or vacuum distillation, pitches from deasphalting, catalytic slurries or synthetic hydrocarbons. These charges may thus be very heavy charges containing hydrocarbons, the boiling point of which may extend to 750'C and above and the density of which may vary between 0 and 250 API. The quantity of the charges of heavy hydrocarbons injected may, depending on the temperature profile sought and the requirements of the heat balance, conveniently represent 0.25 to 4 times the quantity of light fraction injected upstream.

In its most elaborate configuration, including successive injections of increasingly heavy fractions, for example ethane or LPG (liquefied petroleum gas), then petroleum spirit or gas oil and, finally, the heaviest charge, of the distillation residue type into the zone of the continuous reactor located downstream, the continuous reactor will therefore, in fact, comprise a plurality of separate reaction zones operating successively under conditions of decreasing severity (decrease in temperature, in the duration of contact with the heat-carrying material, in the possibly catalytic activity of the heat-carrying material and the ratio between the delivery of this material and that of the hydrocarbons) and adapted to the nature of the charges to be treated and that of the products sought. It will thus be possible, for example,to convert ethane by vapour-cracking in the presence of steam in the zone for the injection of heat-carrying particles, where the temperature is highest (of the order of 850 to 950C0), i.e. in the zone furthest upstream of the continuous reactor, then to make use of the drop in temperature which results from the endothermal nature of the reaction to inject at a temperature of the order of 800 to 900'C a propane or butane fraction, and so on, until the injection of an intermediate fraction of hydrocarbons such as a fraction of the gas oil type or a fraction of light petrols.

It will finally be possible to make use of the new drop in temperature which results from this to crack the heaviest charge, as well as the heaviest residues of the vapour-cracking reaction by recycling all or part of the fractionation residue in the downstream part of the reactor to conditions better suited to its nature.

7 During their considerable work in this field, the applicants have, in fact, observed that although it is relatively easy to control the time and reaction conditions in the reactor by using each zone as a quenching zone in relation to the preceding zone, the same is not the case in the part of the reaction zone that immediately precedes the separation and stripping of the heat-carrying particles. Indeed, at the always very high temperature levels required for vapour-cracking, the separation of gaseous hydrocarbons and solids must be quasi-instantaneous, so as to preserve, in the first place, the production of required olefines, while minimizing the formation of coke or heavy products by polymerization reaction.

One was therefore, until now, confined to the following dilemma as regards vapour-cracking in a fluidized bed: either the separation system, which is generally ballistic, often composed of cyclones, was efficient and in this case the duration of separation was too long for it to be possible to optimize production and avoid coking and the formation of contaminants of the acetylene type; or the separation system was instantaneous, but less efficient, with the result, this time, either of an excessive loss of hydrocarbons by entrainment of them into the regeneration zone, or an excessive entrainment of solid particles with the effluents, both gaseous and, in particular, fines, which it was very costly to isolate from the distillates, these then becoming difficult to put to use, with the risk of undesirable secondary reactions, when the solid particles had a certain catalytic activity.

The aim of the present invention is to remedy the problems associated with the formation of coke and degradation products in the ducts carrying the reaction effluents from the vapour-cracking units to the fractionation zone for these effluents. In fact, to be able to fractionate by distillation the effluent hydrocarbons from vapour-cracking units of the conventional type the temperature of them must be reduced very considerably, and in particular very rapidly, so as to obtain a temperature on entry to the fractionation tower which is lower than the "dew point" of the effluents at a temperature at which the heaviest fractions condense). During this abrupt reduction in temperature it is known that the heaviest compounds produced by the vapour-cracking reaction tend to be deposited on the walls of the ducts, which entails regular and costly stoppages of the vapour-cracking units in order to decoke these ducts.

The present invention makes it possible, moreover, to remedy the disadvantages mentioned, inasmuch as the injection of a major part of the heaviest charge necessary for the thermal equilibrium of the vapourcracking reaction is effected after the stage in which at least 90% of the particles and hydrocarbons are separated and before that of fractionation by distillation.

This particular manner of injecting the charge makes it possible to control completely the temperature conditions and those of the duration of the vapour-cracking reaction for he following reasons: the quenching effect necessary for the instantaneous halting of the thermal reactions is assured by pulverizing the charge itself, which is there even preheated, which, combined with the dilution effect of the condensed liquid effluents, makes it possible effectively to deactivate all the precursors of coke present in the vapour-cracking effluents by dissolving in the still liquid petroleum charge (this quenching effect may possibly be supplemented before the fractionation stage either by the passage of the hydrocarbons into a heat exchanger or by a fresh injection of water, steam or any other hydrocarbon fraction); the 0.01 to 10% of heat-carrying particles entrained in the effluents from the reactor make possible at the same time a permanent sweeping of the walls, thus keeping them free of any fouling, and an absorption of the gums in the course of formation in the ducts used to transfer the effluents towards the fractionation zone; the recycling of the distillation residues in the downstream part of the reactor makes it possible not only to assure the thermal 9 equilibrium of the unit and the transformation into olefines and monoaromatic compounds of heavy charges hitherto not used in vapourcracking, but also the consumption of the heaviest products, which are often difficult to utilize, until they are exhausted.

Since vaporization is then almost simultaneous and homogeneous, the recycled material is thus preheated to a temperature close to its bubble point and thus placed under excellent conditions for cracking very selectively.

In addition, the entrained heat-carrying particles may be entirely recycled and it is then possible, without excessive losses of heatcarrying particles to promote rapidity of separation between the heatcarrying particles and the gaseous effluents, even if this has to be done to the detriment of the efficiency of separation.

According to one particularly convenient manner of application of the present invention, an almost instantaneous transfer of heat is effected between the heavier charge of hydrocarbons and the effluents from the vapour-cracking reaction by pulverizing, by a method in itself known (see in this connexion European patent no. 312,428), said charge in the liquid state. Since the quality of the heat transfer is linked to the exchange surface between the liquid and the gas, the injector or injectors will be adapted to permit a pulverization of the charge in drops of diameter less than 200 microns, and preferably less than 100 microns. Said injectors can be equipped to advantage with mixing chambers which make it possible to introduce with the charge certain quantities of water or steam, or else other petroleum fractions. In addition, it will be possible conveniently to introduce with the charge a substantial quantity of fractionation residue.

Furthermore, the quality of the quenching will be optimum, inasmuch as, the temperature of the hydrocarbons entering the fractionation zone and resulting from the dissolving of the vapour-cracking effluents in the heaviest charge to be vapour-cracked will be below the "dew point" of these hydrocarbons.

The heat transfer effected in this way makes it possible to bring the hydrocarbons back to a temperature which will preferably be between 300 and 450C in less than 0.3 second, and preferably in less than 0.1 second.

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

According to an equally advantageous manner of application of the present invention, the production of olefines and monoaromatic compounds can be notably increased by a judicious reuse of the saturated hydrocarbons produced during the reaction: it will suffice, for this purpose, to separate from each of the fractions C 2

C

3 C4 and othe..

produced, these saturated hydrocarbons from the olefines and to recycle the hydrocarbons to the corresponding injection zone of the upstream part of the reactor previously described.

By way of variant it will also be possible to use, for example, the mixture of ethane and ethylene emanating from the fractionation zone and to pass this mixture into an ethylene trimerization or oligomerization reactor, for example of the type described by the prior art (see in this connexion European patents nos. 12,685, 24,9711, 215,609, or American patent no. 4,605,807), in order to recover, after fractionation of the effluents: firstly, the ethane that has not reacted, which will be recycled to the entry up the upstream part of the reaction zone in accordance with the present invention; secondly, light petrols resulting from said oligomerization, which, for their part, may possibly be recycled with other petrols into the vapour-cracking zone ope'ating with less severe conditions, whic permits the production of propylene and butenes, if such is the objective sought.

1 11 A further advantage deriving from the present invention lies in the fact that the hydrogen necessarily produced by vapour-cracking in the upstream part of the reactor is capable of reacting under the reaction conditions of the downstream part of the reactor and thus improving the selectivity of the effluents from the conversion unit in relation to the best utilized and possibly most stable products.

As was shown above, the deposit of coke resulting from thermal or catalytic cracking must, for economic reasons, be kept to a minimum, but must nevertheless be sufficient to satisfy the thermal balance in the :pstream and downstream sections of the tubular reactor (if it is insufficient, the thermal balance can be produced by the introduction of an additional fuel into the regenerator); also, at least and preferably 80% of the heavy charge, must preferably have a boiling temperature higher than about 400°C. Since this figure of about 400°C is linked mainly to the fractionation point of the distillation residues, it may, of course, range between 300 and 550 0 C without going beyond the scope of the present invention.

Among these charges, mention can be made of vacuum gas oils and heavier hydrocarboF oils such as crude petroleums, topped or not, as well as residues from atmospheric or vacuum distillation, pitches, bitumen emulsions, aromatic extracts, catalytic slurries or synthetic or used oils. These charges may, should the occasion arise, have received a preliminary treatment such as, for example, a hydroskimming treatment.

They may, in particular, possibly contain fractions the boiling point of which may rise to as much as 750"C and above and may possibly contain high percentages of asphaltene products and have a high Conradson carbon content (10% and above). These charges may be diluted or otherwise by conventional lighter fractions, possibly including fractions of hydrocarbons which have already undergone a cracking operation and which are recycled, such as L.C.O. (light cycle oils), the boiling range of which is generally between 160-220°C (start of the fraction) and 320- 380 0 C (end of fraction), recycled heavy oils or H.C.O. (heavy cycle oils), the boiling range of which is generally between 300-380°C (start of fraction) and 460-500°C (end of fraction), or even catalytic residues (slurries), a major fraction of which distils above 500 0 C. According

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12 tr, a preferred application of the invention, the charges may to advantage be preheated in a temperature range generally between 100 and 40000, preferably close to the bubble point, so as to promote an instantaneous and homogeneous vaporization when brought into contact with the hot solid particles.

To apply the process in accordance with the present invention it is possible to use inert heat-carrying particles of a type in itself known, such as kaolin or silicate micro-spheres: it is also possible to use all classes of catalysts that have the capacity for catalytic cracking. One particularly advantageous class is composed of catalysts which have porous structures in which molecules may be brought into contact with active sites existing in the pores; silicates or aluminosilicates in particular are found in this class. In particular, catalysts comprising stable zeolites are available commercially 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 may naturally contain one or more agents which promote one stage of the process or another: the catalyst may therefore contain in particular agents promoting coke combustion during regeneration or contain agents capable of promoting the cyclization of olefines into aromatic compounds and vice versa, if the production of aromatic compounds becomes a priority objective.

In view of the high temperatures and the operating pressure (generally between 0.3 and 5 kg/cm 2 and the short duration of the period for which the hydrocarbons are held in the reaction zone (of the order of a few hundredths to a few tenths of a second) as well as the conditions for the quenching and recycling of the charge to be vapour-cracked, the application of the process necessitates a number of specific means which form an integral part of the invention.

The invention therefore also relates to a device for vapour-cracking by conversion through direct contact, in a fluidized phase of heatcarrying particles at high temperature, of petroleum hydrocarbons comprising, in the first place, at least one light fraction with little 13 contamination by metals, the boiling tempev" 're of which is less than about 4000C, and, secondly, a charge of heavier kydrocarbons composed essentially of compounds the boiling temperature of which is higher than 4000C, this device comprising a continuous reactor for bringing petroleum fractions into contact at high temperature with heat-carrying particles, catalytic or otherwise, the continuous reactor being of the tubular type with essentially rising or descending flow, means, in particular ballistic means, capable of effecting the separation of at least 90% of said particles and cracked hydrocarbons, means for stripping the separated particles, means for regeneration under conditions of combustion of the coke deposited on these particles by air or steam, and means for the recycling of the regenerated particles to the feed of said reactor, as well as means of fractionating the gaseous effluents by distillation, said device being characterized in that it comprises, firstly, between said separation means and said fractionation means, means for injecting a fraction of said heavier charge of hydrocarbons into the effluents and, secondly, means for recycling and injecting at least a part of the residue from liquid-phase distillation, but at a temperature close to its bubble point, in the downstream section of the reactor.

This device may possibly comprise means for injecting successively into i the reactor, from upstream to downstream, light gases comprising ethane, then 20 possibly propane and/or butanes, in a quantity such that the temperature of mixing with the heat-carrying particles is higher than 8000C, and preferably than }"825 0 C, then hydrocarbon fractions such as light petrols and/or possibly naphthas and gas oils, in a quantity such that the temperature of the resultant S:mixture immediately downstream of the point of injection is higher than 7500C 25 and preferably than 8000C, and finally, in the downstream part of the reactor, in the form of fine liquid droplets of mean diameter preferably less than 100 microns the charge or charges of heavier hydrocarbons.

Like the injectors for introducing the charge into the effluents, the Sinjectors for introducing the recycled fractionation residues into the downstream part of the continuous reactor will be adapted to permit an atomization of the charge into drops of diameter less than 200 microns, and preferably less than 100 microns. They will preferably be of the wide-necked venturi type (see 14 European patent 312,428) in order to limit as far as possible the problems of attrition associated with the presence of the recycled heat-carrying particles.

Furthermore, some types of devices for separating the effluents from vapour-cracking, the purpose of which is to restrict the time taken to transfer the effluents to the distillation fractionation zone will possibly be able to be used to greater advantage in accordance with the present invention. In particular, when the reactor operates in the "riser" mode, on account of the production of a large quantity of gaseous hydro-carbons the heat-carrying particles will reach the reaction zone at high speeds (between 20 and 200 m/s, and preferably between 40 and 100 m/s) and it will thus perhaps be possible to use a simple centrifugal separation device. It will thus be possible to avoid the generally expensive use of cyclone systems.

Similarly, when the reactor is operating in the "dropper" mode, the heatcarrying particles will be collected in an enclosed space disposed at the base of the dropper, where they will be stripped after having been separated from the vapour-cracking effluents by a simple ballistic effect.

The attached drawings, which are not of a limiting nature, illustrate S. various applications of the invention. In these drawings: Figure 1 illustrates the application of the invention to a fluidized-bed 20 vapour-cracking unit with a rising column or "riser" and a single hightemperature regeneration chamber for the heat-carrying particles, and suitable in particular for the regeneration of contact masses. In this application the ballistic separation device is fitted with a simple centrifugal ballistic separation device.

Like the injectors for introducing the charge into the effluents, the injectors for introducing the recycled fractionation residues into the downstream part of the continuous reactor will be adapted to permit an atomization of the charge into drops of diameter less than 200 microns, and preferably less than 100 microns. They will preferably be of the wide-necked venturi type (see European patent 312,428) in order to limit as far as possible the problems of attrition associated with the presence of the recycled heat-carrying particles.

Furthermore, some types of devices for separating the effluents from vapour-cracking, the purpose of which is to restrict the time taken to transfer the effluents to the distillation fractionation zone will possibly be able to be used to greater advantage in accordance with the present invention. In particular, when the reactor operates in the "riser" mode, on account of the production of a large quantity of gaseous hydrocarbons the heat-carrying particles will reach the reaction zone at high speeds (between 20 and 200 m/s, and preferably between 40 and 100 m/s) and it will thus perhaps be possible to use a simple centrifugal separation device. It will thus be possible to avoid the generally expensive use of cyclone systems.

Similarly, when the reactor is operating in the "dropper" mode, the heat-carrying particles will be collected in an enclosed space disposed at the base of the dropper, where they will be stripped after having been separated from the vapour-cracking effluents by a simple ballistic effect.

The attached drawings, which are not of a limiting nature, illustrate various applications of the invention. In these drawings: Figure 1 illustrates the application of the invention to a fluidizedbed vapour-cracking unit with a rising column or "riser" and a single high-temperature regeneration chamber for the heat-carrying particles, and suitable in particular for the regeneration of contact masses. In this application the ballistic separation device is fitted with a simple centrifugal ballistic separation device.

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16 Figures 2 and 3 illustrate the application of the invention to a vapour-cracking unit with an essentially descending reaction zone ("dropper").

The vapour-cracking unit with a rising fluidized phase shown schematically in figure 1 comprises a reaction column 1, known as a charge lifter or "riser". This is fed at its base, by way of the line 2, with regenerated heat-carrying particles in a quantity determined, for example, by the opening or closing of a valve 3. The regenerated particles are fluidized by the injection at the base of the riser, by means of a diffuser 5, of steam delivered by the line 4, or any other appropriate flow of gas.

A first line 6 here feeds a diffuser 7, making it possible to inject into the upstream section of the reactor a saturated light gas, such as ethane. A fraction, which is here a propane fraction, but which might equally well be c butane fraction or a mixture of the two, can then be injected in an identical manner through the line 8 by means of the diffuser 9. A petrol or gas oil fraction may finally be vaporized here by means of an injector 11 fed by the line 10. A charge of distillation residue coming by way of the line 14 from the fractionation zone 12 is introduced, possibly mixed with a small quantity of fresh charge fed by way of the line 40, by means of an injector 13 into the downstream section of the reactor under temperature conditions close to the bubble point of said residue, in order to facilitate an instantaneous and homogeneous vaporization of it.

The column 1 opens at the top into an enclosed space 15, which is, for example, concentric with it, and in which are carried out, firstly, by means of the ballistic separator 16, the separation between the reaction elements and the heat-carrying particles and, secondly, the stripping of the coked particles. The effluent hydrocarbons are evacuated from the centrifugal system 16 by the evacuation line 17, in which the cold charge arriving by the line 18 is atomized by means of the injectors 19, while at least 90% of the heat-carrying particles fall back towards the base of the enclosed space 15, where a line 20 feeds stripping gas, 17 generally steam, to the diffusers 21 disposed at regular intervals at the base of the chamber The quenching effect of the vapour-cracking reaction effluents produced at 17 by the direct contact between the droplets of the fresh charge and said effluents is here reinforced through the injection, by way of the line 50, of recycled distillation residue effected in the fractionation zone 12. The distillation residue may be cooled by passage through a heat exchanger 51 and the calories recovered in ths way may be used to generate steam for the entire installation, without the necessity of an extra quenching, as is the case with conventional processes. Furthermore, the presence of a small quantity of grains or fines of the heat-carrying solid in the reactor effluents makes possible not only an efficient scouring of the walls, but also constitutes a means of adsorbing gum precursors and coke deposits. To this end it is possible to modify the content of particles circulating in the line 17 by providing an injector of fresh particles arriving by the line 53.

The heat-carrying particles stripped at the base of the chamber are evacuated to a regenerator 22 by means of a conduit 23, on which is provided here a regulating valve 24. The regenerator 22 represented in this figure comprises only a single zone for the combustion of the coke deposited on the heat-carrying particles in the presence of oxygen or steam. This regeneration is effected in such a way that a large proportion of the heat released by the combustion of the coke will be transferred to the particles to enable them ;o reach the high temperatures necessary for the reaction in zone 1. The coke deposited on the particles is thus removed by means of air injected at the base of the regenerator by means of a line 25 which feeds the diffuser 26. Possibly, in order to adjust the temperature to the level required, additional fuel may be injected. The regeneration gas is separated from the entrained heatcarrying particles in the cyclone 27, from where the regeneration gas is evacuated through a line 28, while the hot, regenerated heat-carrying particles are extracted from the regenerator, whence they are recycled through the conduit 2 to feed the riser 1.

In addition, after quenching by the injection of the charge at 19, 4, I I 18 the reaction effluents and the charge introduced at 19 are passed by the line 17 into the fractionation device shown schematically at 12, making it possible to separate: through the line 29, the light gases, which may then be treated in another gas fractionation device, also schematic, making it possible in a manner in itself known to separate, in particular, ethane by the line 30 and propane through the line 31; through the line 36 a petrol fraction, the boiling range of which generally extends from the fraction C 5 to about 200-220 0

C;

through the line 37 a gas oil fraction, the boiling range of which generally extends from 160-220°C (start of the fraction) to about 320- 400 0 C (end of the fraction); and finally, through the line 14, a fraction of the distillation residue fraction, which contains the heaviest products stemming from both the charge and the reaction effluents and relatively large quantities of fines (this residue has a boiling point between 300 and 550 0 C and generally of the order of 400C).

Part of this fractionation residue is therefore injected at 13 into the vapour-cracking reactor in accordance with the present invention; depending on the case and after recovery of the heat by passage through the heat exchanger 51, another part may be either recycledfor quenching, through the line 50, mixed with the charge to be subjected to vapourcracking, or drawn off from the device through the purge line 52.

Furthermore, the ethane, propane and the petrol fraction coming from this fractionation device may be recycled to the reaction section by the lines 30, 31, 36, then 6, 8 and 10, while the C2 and C3 olefines produced by vapour-cracking are isolated by the lines 33 and 34 respectively.

An essential advantage of this device for fluidized-phase vapourcracking lies in the fact that a good use of the temperature profile I I 19 in the reaction zone 1 makes it possible to crack selectively several petroleum fractions. In particular: in the zone in which heat-carrying particles are introduced, where a maximum temperature of the order of 800 0 C and more prevails, the steam may be introduced by the line 4 and the ethane through the line 6, coming either from the fractionation device by the line 31, or from another unit in the refinery; in view of the high energy requirements of this reaction (3 to 6 times as great as in a catalytic cracking reaction) the temperature of the reaction zone decreases appreciably and it iL then possible to inject downstream heavier saturated hydrocarbons, such as propane (at 8) or butane (at 11), or also light petrols (at 11) or naphthas, with a possible addition of steam through the lines 38, 39 and Regulation systems, 41 to 44, may, moreover, make it possible to modulate, in a manner in itself known, the quantities injected into the reaction zone in order to maintain the :required temperature profiles, using temperature sensors installed for this purpose in said zones.

It will be noted that, in comparison with vapour-cracking of the conventional type, all the energy necessary for the reaction is applied in a single operation by the heat-carrying material at the time of mixing with the charges, i.e. at the start of the reaction. The temperature therefore reaches its maximum at that moment and then decreases under the effect of the endothermal nature of the reactions, thus producing a natural effect of progressive quenching, and therefore of decreasing severity, unlike conventional processes.

The temperature profile which result, combined with the extremely short reaction time permittedby this device, leads to a reaction selectivity significantly superior to that obtained with the traditional processes and to the elimination of the coke or tars formed on the walls, where the skin temperature is higher.

The fluidized-phase vapour-cracking devices shown in figures 2 and I I I 3 are variants of that in figure 1 in which the reaction zone this time functions in the descending mode. The reactor will therefore, using the English term, be known as a "dropper". The parts of this device identical with those in figure 1 are indicated by the same reference iumbers, with the addition of the index for figure 2 and for figure 3.

According to figure 2, a different type of regenerator is used which is better able to resist the high temperatures required by vapourcracking. The regeneration fumes leave the unit at 28' after passage through a cyclone 27' outside the regeneration chamber 22'. In order to make it possible to place the removal shaft 54' for the regenerated heat-carrying particles above the dropper, the regeneration chamber 22' is located in the upper part of the unit and the particles to be regenerated, which come from the stripping zone by way of the line 23' must be transported by a rising column 55'. This transport is effected by fluidization with a gas diffused at 26' by the line 25'. During this transport a primary combustion of the coke deposited on the catalyst particles may take place, under conditions which are in themselves known, with a fluidization gas containing air or oxygen. The particles of the catalyst and the fluidization gas are then separated ballistically by means of the device 56' and the catalyst particles are regenerated, in a manner in itself known, in the chamber 22', where the particles are burned in counter-current to the flow of oxygen brought by the line 45' to the diffuser 46' The regenerated catalyst particles may be introduced without heat losses into the upstream section of the reactor 1' in a quantity determined by the delivery rate of the diffuser 57': the homogeneity of the particles is assured by a device of a type in itself known, which is not shown here. At the outlet of the dropper 1' the particles plunge directly into the dense fluidized stripping zone 15', while the hydrocarbon vapours and the stripping vapour coming from the diffuser 21', fed by the line 20', and the stripped hydrocarbons are evacuated practically instantaneously by way of the line 17', where they are immediately quenched by dissolving in the heavy charge which enters the unit by the line 18'.

t' 21 In the variant shown in figure 3, in order to permit operation in the dropper mode without the necessity of a costly elevation of the regeneration zone 22", the hot regenerated particles coming from the line 2" are first transported to the interior of a rising column 58" by the injection of a fluid such as steam, delivered by the line 4".

After passage through the two right-angled elbows 59" and 60", the particles are poured homogeneously into the dropper where, for example, ethane and petrols are injected successively at 7" and The quenching of the effluents is then effected by the heavy charge 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 outlet of the dropper the particles are stripped and leave the zone 15" by the line 23", below which an injection of fluid, such as steam or air, makes it possible to transfer them by way of the line to the regeneration chamber 22". In this, a ballistic separation device 56" makes it possible to pour them into the fluidized-bed combustion zone.

EXAMPLE

This example shows the advantages of a device accoriing to the present invention and of the type shown in figure 3. The tests were made with ethane, a petrol fraction (straight-run fraction) and two charges, A and B, which were, respectively, a residue of atmospheric distillation and a residue from vacuum distillation of a crude of the SHENGLI type.

The charges had the following characteristics: PETROL CHARGE A CHARGE B Density (at 15°C) 0.675 0.955 0.985 by volume distilled at 500C 20 at 700C 70 at 100°C 99 by weight distilled at 4500C 20 at 5500C 45 at 650 0 C 70 P/N/A by weight) 77/17/6

H

2 by weight) 15.4 12.1 11.7 S2(% by weight) 1.0 1.3 Tnal nitrneen hy weih 0.6 0.8 22 PETROL CHARGE A CHARGE B Carbon by weight) 8.1 14.2 Ni V (ppm) 40 Contact mass particles composed of micro-spheres, mainly kaolin, of about 10 m'/g specific surface and mean diameter about 70 microns were used as heat-carrying particles. The charge injectors in the quenching zone and in the reactor were of the type described in European patent no. 312,428.

The conditions of the two tests made in succession with the charge A, then charge B, were as follows (extrapolated for 100 t/h total charge): CHARGE A CHARGE B Upstream zone of the reactor Temperature of regenerated catalyst (OC) 880 880 Delivery of regenerated catalyst .2000 2160 Delivery of steam at 320 0 C 15 Delivery of ethane 10 Mixing temperature 862 868 Central zone of the reactor Delivery of steam at 320 0 C 3 Delivery of petrol at 150 0 C Mixing temperature 825 Downstream zone of the reactor Delivery of steam at 320 0 C 9 6 Delivery of charge A or B at 380°C 90 Mixing temperature 785 780 Temperature at end of reaction 740 750 Quenching zone Temperature of effluents after ballistic separation 730 740 Temperature of charge (OC) 80 Mixing temperature (OC) 450 470 Concentration of particles in effluents by weight) 3.2 2.2 Fractionation temperature of fractionation residue (OC) 420 440 After recovery of the effluents of the vapour-cracking reaction, the nature of these effluents is analysed. The analytical results (as by weight) which are summarized below, by themselves show the advantages of the present incention over processes of the conventional type.

Claims (23)

1. A process for the vapour-cracking conversion of at least one light hydrocarbon fraction having a low metal contamination and a boiling point of below about 4000C and a heavier hydrocarbon feedstock, which heavier feedstock comprises of compounds having a boiling point of above about 4000C, said process taking place at high temperature and in the presence of a dilute fluidized phase of heat-transfer particles, said process comprising contacting the light hydrocarbon fraction and then the heavier feedstock, in a sequential manner and with decreasing severity, with heat-transfer particles in a continuous-flow reactor of the tubular upflow or downflow type, and separating and stripping the contacted materials to permit the separation of at least 90 percent of the particles, which particles are then regenerated, by the combustion with air or steam of coke, which coke is deposited on the go particles, before recycling the particles at a higher temperature to the inlet of the .i continuous-flow reactor, thereby permitting the separation of the effluent hydrocarbons, which are then recovered by fractionating by distillation, the process further comprising injection of a fraction of the heavier feedstocK between the separation and fractionation of the particles and effluent hydrocarbons, wherein at least a portion of residue resulting from the fractionation is recycled downstream in the reactor.

2. The process as defined in claim 1, wherein the heavier hydrocarbon feedstock is injected in the liquid state as atomized drops of a diameter of less than about 200 microns.

3. The process as defined in claim 2, wherein the atomized drops are of a diameter of less than about 100 microns.

4. The process as defined in claim 1, wherein the effluents from the vapour- cracking reaction are brought to a temperature below the dew point by means of injection of the heavier feedstock.

The process as defined in claim 1, wherein the hydrocarbons to be fractionated contain from about 0.01 to 10 percent, by weight, of heat-transfer particles.

6. The process defined in claim 5, wherein the hydrocarbons contain from about 0.05 to 5 percent, by weight, of heat-transfer particles.

7. The process as defined in claim 1, wherein prior to fractionation by distillation of the effluents from the vapour-cracking reacion, the effluents are brought to a temperature range of from 300 to 4500C.

8. The process as defined in claim 1, wherein the effluents from the vapour- cracking reaction are brought to a liquid state, at a temperature range of from 300 to 450 0 C, in less than 0.3 second. i• co

9. The process, as defined in claim 8, wherein the effluents are brought to the liquid state, at a temperature range of from 300 to 4500C, in less than 0,1 second.

The process as defined in claim 1 wherein the heavier hydrocarbon feedstock is chosen from the group consisting of the residues from atmospheric or vacuum distillation, catalyst slurries, pitches from deasphalting, synthetic and o reclaimed oils. o*

11. The process as defined in claim 1, wherein the distillation-residue fraction recycled to the reactor is at a temperature of less than 100C below the temperature of the bubble point of that fraction.

12. The process as defined in claim 11, wherein the distillation residue fraction recycled to the reaction is at a temperature of less than 50°C below the temperature of the bubble point of that fraction. U i:i:

13. The process as defined in claim 1, wherein the heavy liquid feedstock consists at least in part of a portion of the distillation residue from fractionation.

14. The process as defined in claim 13, wherein the distillation residue from the fractionation is cooled by heat exchange upon its exit from the fractionating column.

The process as defined in claim 1, wherein the light hydrocarbon fraction is chosen from the group consisting of light paraffins, ethane, propane, butane, gasolines, naphthas and gas oils.

16. The process as defined in claim 15 further comprising the injection upstream into the reactor, of a plurality of light hydrocarbon fractions, wherein the injection of said fractions is effected in a sequential manner, in an order of decreasing severity. i

17. The process as defined in claim 16, wherein light gases, selected from the group consisting of ethane, propane or butane, are injected successively from upstream to downstream, into the reactor, in such quantity that the temperature of the heat-transfer particle mixture remains above 8000C, and hydrocarbon fractions such as light gasolines, naphthas or gas oils are then injected, in such quantity that the temperature of the mixture directly downstream of the point of injection is above 7500C, and then a fraction of the distillation residue is injected to bring the reaction temperature to a temperature range of from 650 to 7500C.

18. The process as defined in claim 17, wherein the temperature of the mixture directly downstream is above 8000C.

19. The process as defined in claim 1, wherein a portion of light gases which are produced by the vapour-cracking is recycled to the reactor.

The process as defined in claim 1, wherein an operating pressure for the reaction is applied which ranges from 0,3 to 5 kg/cm2,

21. An apparatus for the high temperature vapour-cracking conversion in the presence of a dilute fluidized phase of heat-transfer particles of at least one light hydrocarbon fraction having a low metal contamination and a boiling point of below about 400 0 C, and a heavier hydrocarbon feedstock, which heavier feedstock comprises compounds having a boiling point of above about 400 0 C, said apparatus comprising a continuous-flow reactor for contacting, at high temperature, petroleum fractions with heat-transfer particles, the continuous-flow reactor being of the upflovi or downflow tubular type; ballistic separating means adapted to separate at least 90 percent of the particles and the cracked hydrocarbons; stripping means for stripping the separated particles; Sok regenerating means for regenerating, under conditions of combustion, coke deposited on the particles, with air or steam; recycling means for recycling the regenerated particles to the inlet of the reactor; ""fractionating means for fractionating gaseous effluents by distillation; a means for injecting between the separating means and the fractionating means, a fraction of the heavier hydrocarbon feedstock into the effluents; and means for recycling and injecting downstream into the reactor a portion of the distillation residue in the liquid phase, at a temperature close to its bubble point.

22. The apparatus as defined in claim 21, wherein the means for injecting the heaviest feed.tock between the ballistic separating means and the fractionating means downstream into the reactor is supplied with residue from the fractionating means which means fractionates, by distillation, effluents from the reaction. ,i) 0, i 27

23. The apparatus as defined in claim 22, further comprising means for injecting into the reactor, successively from upstream to downstream, light gases selected from the group consisting of ethane, propane or butane, in such quantity that the temperature of the heat-transfer particle mixture is above 8000C, then means for injecting hydrocarbon fractions such as light gasolines, naphthas or gas oils, in such quantity that the temperature of the resulting mixture directly downstream of the point of injection is above 750°C, and finally, means for injecting the heavier hydrocarbon feedstock downstream into the reactor, in the form of fine liquid droplets having an average diameter of less than 100 microns. An apparatus as defined in claim 23, further comprising means for injecting fresh heat-transfer particles into the vapour-cracking effluents. TOTAL RAFFINAGE DISTRIBUTION S.A. WATERMARK PATENT TRADEMARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 S. EAUSTRALIA D LPS/ML DOC 27 AU4225289.WP v, "7 s,