FR2706479A1 - Cracking plant including common means and means specific to each reactor for separating and recycling solid particles, and its use - Google Patents

Abstract

Plant for thermal cracking in vapour phase, including: - at least one cracking furnace (Fn) comprising means for introducing feedstock to be cracked, - for each furnace, downstream of the latter, at least one indirect quenching exchanger (Tn) for the effluents leaving the furnace, the said plant including at least two indirect quenching exchangers - upstream of each indirect quenching exchanger at least one means (1, Gp) for injecting solid particles, connected to at least one conduit (10n) for introducing solid particles into the furnace(s) and/or just upstream of the exchangers, each of the conduits comprising, upstream of each quenching exchanger, at least one valve (Vfn), - at least one means (Cg) common to all the furnaces and/or exchangers, for separating at least a part of the solid particles, and comprising downstream of each furnace (Fn) at least two primary separators (Cn) performing the separation of the solid particles and of the gases, each of the primary separators comprising a gas exit conduit (3n) connected to a means (4) for collecting the gases, and each of the primary separators also comprising an exit conduit (6n) for the solid particles, connected to a means (7) for collecting the said solid particles enabling the solid particles to be conveyed and introduced into the means (Cg), common to all the furnaces and/or exchangers, for separating at least a part of the solid particles, including a gas exit conduit (5) and an exit conduit (9) for the solid particles, connected to at least one means (STO) for storage including means for discharging and transferring the recovered particles.

Description

 The present invention relates to an installation for thermal cracking in the vapor phase of a charge (such as for example a hydrocarbon charge or a charge of halogenated hydrocarbons) and more particularly to a steam cracking installation of a hydrocarbon charge comprising, means for introducing, recovering, storing and / or recycling solid particles used for at least partial, continuous or discontinuous decoking, cracking ovens and / or exchangers for the indirect quenching of furnace effluents.

 The main technical problem for installations with at least partial decoking operating on the principle of the injection of erosive solid particles consists in ridding the effluents of most of the injected particles, so as to avoid pollution of the downstream sections, and this economically and reliably.

 Several patent documents already describe installations and methods for cracking and more particularly steam cracking of hydrocarbons comprising the use of solid particles (for example silica or alumina or hard metals or coke) qualified as erosives, for continuous or generally sequential decoking of cracking ovens and / or indirect quenching exchangers of the effluents from these ovens.

 Thus, patent application WO-A-90 / 12,851 describes an installation, and a method, for steam cracking of hydrocarbons comprising decoking means allowing the decoking of ovens and / or indirect quenching exchangers during the unit walk. The erosive solid particles used according to this embodiment to carry out decoking are recovered from the effluents leaving the indirect quenching exchangers by means of separation and recycling, specific to each oven, comprising an airlock for recompressing the erosive solid particles recovered (c that is to say a means for raising the pressure level in the solid particles recovery zone, for reinjecting them upstream of the cracking zone and / or of the indirect quenching zone). This embodiment, although proposing an effective solution allowing the continuous running of the unit, has the disadvantage of imposing the use of one or two cyclones per oven and especially of means of storage and evacuation of the recovered particles. and an oven recompression airlock, which are relatively complex systems and whose maintenance is delicate. Indeed, such equipment requires the frequent operation of valves which must remain sealed although crossed by abrasive solids.

 We could, in a steam cracking installation, use only one set of separation, storage, transfer and possibly recycling of the particles by collecting all the effluents from all the ovens to treat them in a cyclone unique. This would lead to the installation of a cyclone of considerable dimensions (whose inlet pipe would be, for example, 1 meter in diameter), the price and the conditions of implantation of which would generally be unacceptable, and which would require for its installation, I ' complete shutdown of the steam cracker.

 Patent application WO-A-91/05 031 also describes an installation and a process for steam cracking of hydrocarbons, comprising decoking means allowing the decoking of ovens and / or indirect quenching exchangers during the operation of the 'unit. When the installation comprises several ovens, the erosive solid particles used according to this embodiment to carry out decoking are recovered from the effluents leaving the indirect quench exchangers by means, of separation and recycling, common to all of the ovens. which allows to use only one storage module, transfer and a single airlock for recompression of solid particles and therefore has a definite advantage over the embodiment described in the patent document cited above.

According to the description of this request, the installation comprises pipes and valves making it possible to direct the cracked gases sequentially either to this module, during the phases of injection of the erosive solid particles, or to the direct quenching means, outside the phases injection. Despite the definite advantage of having only one separation, storage and recycling set for solid particles, this installation requires the use of numerous bypass pipes connecting the outputs of the quench exchangers to the common separation module, storage, transfer and recycling; However, these pipes have the disadvantage of being of large diameter (for example around 35 centimeters in diameter (14 inches)) since they must convey a very large flow of fluid and solids which is the total flow of outgoing material. from an oven. These large-diameter pipes include valves of suitable diameter (identical or slightly smaller than the diameter of the pipe, therefore also of large diameter) making it possible to sequentially direct the flows of material leaving the exchangers, either to the common means for separating solid particles erosive, either towards the common means of quenching. These valves, which those skilled in the art call maneuvering valves, are complex, expensive elements, of delicate maintenance and of life possibly limited by the circulation of erosive solids. For large dimensions such as 8 inches (1 inch equals 2.54 centimeters) or more, these valves are special (not standard).

 Likewise, large diameter pipes, capable of transporting all the effluents loaded with solid particles, are very expensive, in particular because of the need to strengthen the elbows to increase their resistance to abrasion.

 Another drawback of this installation comes from the fact that the particles which circulate in the ovens and the exchangers outside the injection phases of the erosive solid particles in these ovens, such as for example coke particles or erosive particles having been injected previously and having sojournées in dead zones, will not be recovered in the common means of separation and could thus pollute and / or damage the downstream circuits such as those going towards the direct quenching zone as well as this quenching zone itself.

 Thus, it is not possible in the prior art to avoid a certain number of significant drawbacks - either a storage, transfer module, and possibly an air lock by oven are used, which increases the price and difficulty of maintenance.

- Either all the effluents are collected in a pipe of considerable diameter supplying a cyclone of considerable size connected to a single module for processing the recovered powders.

- Either the furnace effluents are collected sequentially and it is then necessary to install pipelines and operating valves of large dimensions of high price and delicate maintenance.

The present invention relates to an installation making it possible to avoid the drawbacks of the installations described above while retaining their main advantages. According to the present invention the recovery,
The injection, circulation and recycling of erosive solid particles use only means of relatively current design, relatively inexpensive, or having a long service life.

 Among the many advantages of the installation according to the present invention, the following can be emphasized - the decoking of the various ovens and / or exchangers can be carried out sequentially, without the need to use specially designed large-diameter operating valves. for the passage of gas loaded with erosive solid particles which are extremely expensive, and without it being necessary to increase the capacity of the common means of separation of solid particles and gases.

- the reliability of the installation is very important because it does not include large diameter valves, on cracked gas pipes loaded with particles and that it can include only one storage module, transfer and a single airlock for particle recompression. In addition, the installation will generally be able to operate without the valves (of small diameter) arranged on the pipes carrying the particles, being maneuverable, unlike the prior process.

the efficiency of the separation of solid particles from the gaseous effluents can be extremely high, which avoids any risk of pollution, downstream circuits such as those going to the direct quenching zone, as well as from this quenching zone itself even.

- Finally, the installation according to the present invention also makes it possible to prevent the solid particles which circulate in the furnaces and / or the exchangers outside the injection phases of the erosive solid particles upstream of these exchangers such as for example particles coke or erosive particles having been injected previously and having stayed in dead zones do not pollute and / or damage the downstream circuits such as those going to the direct quenching zone as well as this quenching zone itself.

Finally, the installation according to the invention is applicable to numerous variants of the decoking process.
It is applicable to the process with recycling of particles, or to the process with recovery of particles without recycling, which increases the simplicity of the installation by eliminating the airlock.

 Likewise, it is applicable to the process where the injection of the particles is carried out during the operation of the installation under normal cracking conditions but also to the variant of the process, which is particularly advantageous in the case of cracking of heavy loads, where the '' the load is modified during the injections (for a lighter load or even steam alone) in order to avoid any sticking of the recovered particles.

 The present invention therefore provides an installation for cracking a charge and will be described below in conjunction with the appended figures representing specific cases of embodiment of the invention. This description is made in conjunction with the figures for the sole purpose of allowing better ease of understanding without this being able to be considered as any limitation of the invention.

 In the five appended figures, similar bodies are designated by the same numbers and reference letters.

 The invention relates to a thermal cracking installation in the vapor phase and its uses. It can in particular be used for the cracking of preferably chlorinated halogenated hydrocarbons. However, it is most often used for steam cracking of hydrocarbons or hydrocarbon cuts. Examples of feedstocks for steam cracking include: light hydrocarbons of the C2 to C4 type, in particular ethane, propane, naphtha, gas oils or even heavy petroleum distillates and in particular vacuum distillates . The fillers can also include recycled olefinic fractions, with 3, 4, 5 or 6 carbon atoms.

The thermal cracking installation in the vapor phase, according to the present invention, comprises: (FIG. 1) - at least one and generally in parallel at least two ovens (F1, F2, Fi,
Fn) of cracking, comprising means (I) for introducing the charge to be cracked, - for each oven (F1, F2, Fi, Fn), downstream thereof, at least one exchanger (T1, T2, Ti, Tn) of indirect quenching of the effluents leaving said furnace, said installation comprising several (that is to say at least two) indirect quenching exchangers of effluents (Ti, T2, Ti, Tn), (TiA, TiB) , - upstream of each indirect quenching exchanger, at least one means (1,
Gp) for transferring solid particles connected to at least one pipe (101, 102, 10i, 10n), for introducing solid particles, into the furnace (s) and / or just upstream of the quench exchangers, said pipes each comprising at least one valve (Vfl, Vf2, Vfi, Vfn) (or equivalent technical means), - at least one means (Cg), common to all the ovens and / or exchangers, for separating at least one part of said solid particles.

Said installation is characterized in that it comprises downstream of the furnace (s) (F1, F2, Fi, Fn), and preferably downstream of the exchangers for indirect quenching of the effluents (sorting, T2, Ti, Tn), (TiA . TiB), a plurality (that is to say at least two) primary separators (C1, C2, Ci, Cn), (CiA or CiB), (Ci being relative to the furnace i), performing in parallel on the current which feeds it the at least partial separation of solid particles from most of the gaseous effluents of said supply stream of said separator, said primary separators each comprising a main gas outlet pipe (31, 32 3i, 3n), diameter (D1, D2, Di, Dn), each of said pipes (31, 32, 3i, 3n) being connected to a means for collecting said gases such as a pipe (4), and said primary separators each also comprising a pipe ( 61, 62, 6i, 6n) outlet of the solid particles and a minor part of the gas contained in the supply stream d a separator, each of said pipes (61, 62, 6i, 6n) having a diameter (d1, d2, di, dn) smaller than the diameter (D1, D2, Di, Dn) of the corresponding gas outlet pipe (31, 32 , 3i 3n), each of said pipes (61, 62, 6i, 6n) being connected to a means for collecting said solid particles such as a pipe (7) for conveying and introducing said solid particles into the means (Cg) , common to all the ovens and / or exchangers, for separating at least a portion of said solid particles, said means (Cg) common to all the ovens and / or exchangers comprising a line (5) for gas outlet and an outlet pipe (9) for solid particles connected to at least one storage means (STO) comprising means for evacuating and transferring the recovered particles.

 The common separation means (Cg) may typically be a cyclone (or two stages of cyclones) or any gas / solid particle separator of the centrifugal, inertial or ballistic type.

 The means (STO) for storing, evacuating and transferring solid particles can be a silo for storing particles comprising evacuation means such as a valve, screw, lock, fluidized evacuation means, or any means equivalent of evacuation and transfer of particles from a silo. If the installation operates with recycling of particles, the means of storage, evacuation and transfer of particles (STO) is then connected to a means of raising pressure, for example an airlock such as one of those described in patent application WO-A-90 / 12,851 or in application WO-A-90 / 12,852 or also in application WO-A-91 / 05,031 and shown diagrammatically in FIGS. 1 and 2 of these applications.

 The airlock is itself connected to the particle transfer means (1, Gp) generally comprising a source of pressurized gas, for example superheated steam, as well as a pneumatic transfer pipe.

 The remainder of the description relates to the preferred forms of installation. These preferences or some of them may or may not be associated.

 Solid particles can be introduced (Figure 5) just upstream of the quench exchangers (T1, T2, Ti, Tn), for example at the outlet of the reaction zone (radiation zone) They can also be introduced into ovens (F1 , F2, Fi, Fn) cracking, upstream or at the entrance of the reaction zone of these ovens, or radiation zone for example at the exit of the convection zone (at the entry of the coils in radiation zone ). Generally, each primary (C1, C2, Ci, Cn) primary separator for separating solid particles and gases will be located just downstream of an indirect quenching exchanger and will be supplied by the effluent from this exchanger.

 Alternatively, each primary separator Ci can be supplied by the effluents from two or more quench exchangers belonging to the same furnace.

 Thus, the primary separators are in an area where the effluents are cooled, but remain essentially gaseous (there may be traces of condensed heavy products, but in infinitesimal quantities, so that there is no real phase recoverable liquid). In the present description, the term gas is therefore also used for a gas which can lead to the trace state of condensed products (liquids).

 In a variant, the installation will include in series at least two common means for separating solid particles and gases. According to this variant illustrated in FIG. 2, the pipe (5) for leaving the gases of the common means (Cg), for separating at least part of the solid particles, is connected to at least one common means (Cg2) of secondary separation. solid particles and gases comprising a gas outlet pipe (12) connected to a means for collecting said gases such as the pipe (4), and a solid particles outlet pipe.

 According to a particular arrangement of the invention, the means (STO) comprises at least one means (Vg) (not shown in the figures) for discharging solid particles; the solids outlet pipes (61, 62, 6i, 6n) each comprise at least one valve (V1, V2, Vi, Vn), the valve (Vi) relating to a furnace i being open during the phases in which injects the particles into the furnace i (or upstream of the exchangers), the installation also comprising means for maintaining the means (Cg) at a pressure lower than the pressure of the primary separators (Cl, C2, Ci, Cn).

 Thus, according to this particular arrangement, when particles are injected into an oven, or upstream of the exchanger, these particles are separated in the primary separator, the outlet of the solids of which is in communication with a network at lower pressure, so that the particles are extracted and transported directly by pneumatic transport without being stored in an atmosphere of cracked gas promoting the condensation of traces of heavy products. This arrangement is very effective in limiting the pollution of the particles recovered.

 The means for maintaining the common separation means (Cg) at a pressure lower than those of the primary separators (C1, C2, Ci, Cn) (at least during the particle injection phases) may consist of a connection of the outlet gas 5 of the medium (Cg) at a point downstream of the line 4 where the pressure is sufficiently low; it is also possible to modify the pressures of the different lines by means of orifices or ejectors.

 The pipes (61, 62, 6i, 6n) for transporting the particles from the primary separators (C1, C2, Ci, Cn) can advantageously be of small diameter, for example between 2 and 6 inches (50 to 150 mm), as well as the associated valves (V1, V2, Vi, Vn) because they only carry a limited gas flow taken from the total gas flow.

 These valves are much less delicate, expensive than non-standard large diameter valves (10 to 20 inches), of quality compatible with the circulation of solids, which would be necessary to convey the entire gas flow.

Preferably, these valves Vi and lines 6i will be dimensioned for a gas flow rate (particle vector) of less than 20% and even 10% of the gas flow supplying the separators (C1, C2, Ci, Cn), for example between 0 , 3 and 10% of the gas flow supplying the separators (Ci, C2,
Ci, Cn). Thus the primary separators (Ci, C2, Ci, Cn) act as concentrators, by purifying most of the gas flow, and by concentrating the particles in a very reduced gas flow, sufficient to allow their pneumatic transport, and allowing these particles to be transported in small diameter, inexpensive pipes (61, 62, 6i, 6n), as well as the valves located on these pipes (price reduced by more than half). The primary separators are therefore not only separators but separator-concentrators, that is to say means of separation and concentration of solid particles.

 Compared to the installation described previously in the patent documents cited above where the particles were transported by the entire effluent it is clear that the invention provides considerable advantages in terms of cost and reliability.

 According to a first variant, each oven (Fi) of rank i can comprise one or more reactors (Ri) (not shown diagrammatically in FIG. 4) and each quench (Fi) or each reactor (Ri) can correspond to a quench exchanger ( Ti) or a plurality of quench exchangers (Ti) (for example for the furnace (Fi) shown diagrammatically in FIG. 4 two quench exchangers (TiA) and (TiB)) and at each furnace (Fi) or at each reactor (Ri) can also be associated with one or more primary separators (Ci) for separating solid particles and gases (for example for the furnace (Fi) shown diagrammatically in FIG. 4, two primary separators (CiA) and (CiB) each connected to the exchangers (TiA) and (TiB)).

 When several primary separators for the separation of gases and solids are associated with an oven (Fi) or with a reactor (Ri), they are used in parallel. Each oven (Fi) or each reactor (Ri) or each quench exchanger (Ti) can comprise a means for injecting solid particles and comprise at least one line (10i) for introducing solid particles into the oven (Fi) or in the reactor (Ri) or in the quench exchanger (Ti) each pipe comprising a valve (Vfi). It would not go beyond the scope of the present invention in the case where the introduction of the solid particles would be carried out by means of a single pipe (10i), comprising a valve (Vfi), and possibly subdividing into several pipes, not fitted with valves, for introducing these solid particles into each furnace (Fi) or into each reactor (Ri) or into each quench exchanger (Ti). It is also conceivable that several reactors (Ri) are associated together with a single quenching exchanger (Ti), each furnace (Fi) remaining associated with at least one primary separation means (Ci). Each furnace (Fi) or each reactor (Ri) can comprise at least one means (I) for introducing the charge or this means for introducing the charge can be a means common to several reactors (Ri) or even to several ovens (Fi).

 Likewise, the installation according to the invention may comprise only a single oven comprising a plurality of reactors and quench exchangers.

In fact, very large capacity furnaces are now being built (for example 120,000 tonnes / year of ethylene compared to typically 25,000 tonnes / year in the past). In this case the installation comprises a plurality of primary separators located downstream of the quench exchangers; these primary separators comprise relatively small diameter pipes which make it possible to convey the recovered particles, concentrated in a low gas flow rate, to the common separation means (Cg) and the common storage (STO).

 The installation according to the invention is also applicable to part of a steam cracker (not all of the ovens).

 The decoking, which can be partial or complete, can relate to the indirect quenching exchangers alone or all the ovens or reactors and exchangers. This decoking can be intermittent or continuous on all the elements of the installation that one wishes to decoker, in this case the valves (Vfi) are all open during the period of introduction of the particles or are permanently open. Most often decoking will be carried out sequentially, that is to say that for a reactor (Ri) or an oven (Fi) there are periods of introduction of solid particles and periods when one does not introduce solid particles. In other words, this sequential decoking is equivalent to decoking a certain number of elements of the installation for a certain period of time, then stopping the decoking of this or these elements and carrying out the decoking of a or several other elements of the installation during a subsequent phase of operation of the installation.

 Several operating modes of the installation are therefore possible. Thus, the installation comprises on each pipe (31, 32, 3i, 3n), of diameter (Dl, D2, Di, Dn), of main gas outlet, at least one valve (V'1, V '2, V'i, V'n) and on each pipe (61, 62, 6i, 6n) of diameter (dl, d2, di, dn), leaving the solid particles at least one means of action on the passage of solid particles and / or gases such as a valve (vol, V2, Vi, Vn).

A very important point compared to the prior art lies in the fact that the valves (of large diameter) located on the pipes (31, 32, 3i, 3n) (or downstream on the union of several pipes) operate on gases. free of solid particles and remain open during normal operation of the installation, in particular during the solid particle injection phases These valves, which are the sectioning valves existing on any installation, are therefore not manoeuvrable and are of known design and common. Typically, these valves remain open, except in the event that the operation of the oven is stopped, for example if air decoking is carried out in the oven. In a preferred embodiment, each pipe (61, 62, 6i, 6n) for leaving the solid particles has a diameter (dl, d2, di, dn) less than or equal to 80% and preferably less than or equal to 50% the value of the diameter (D1, D2, Di, Dn) of each pipe (31, 32, 3i 3n) for the main gas outlet. According to the invention, the installation comprises conduits (1, 61, 62, 6i, 6ns 101, 102, 10i, 10ns 11) in which solid particles circulate; these pipes being of relatively small dimensions make it possible to have valves (Vf1, Vf2, Vfi,
Vfn, V1, V2, Vi, Vn, Vg) of reduced dimensions, of relatively common design and therefore of very substantially reduced cost.

 The primary separators (Ci, C2, Ci, Cn) for separating at least a portion of said solid particles can be cyclones or any gas / solid particle separator of the centrifugal, inertial or ballistic type.

Likewise, each primary separator may consist of a cyclone, two stages of cyclone, or any other known means of separation of gas / solid particles. These primary separators are usually cyclones having a very high separation efficiency, for example at least 95% or even at least 99%. It would not go beyond the scope of the present invention if each pipe (31, 32, 3i, 3n) of each primary separator (Ci, C2, Ci, Cn) for separating solid particles and gases is connected to a second separation means, before being connected to the means (4) for collecting said gases (for example a second cyclone stage).

 Depending on the operating mode chosen, it is sometimes desirable that each primary separator (Ci, C2, Ci, Cn) has a retention volume (S1, S2, Si, Sn) located upstream of the valve (Vi, V2, Vi , Vn). These retention volumes are most often reservoirs having for example a volume of 40 to 400 liters. This volume can stop large solid pieces whose pneumatic transport would be difficult.

 According to a particular embodiment of the invention, the particles injected do not stagnate in the retention volume (Si) because the discharge valve (Vi) is open. The retention volumes are also used to collect solid particles outside the injection phases in an operating mode of the installation detailed below.

When decoking is carried out sequentially, at least two modes of operation of the installation can be distinguished. According to a first mode, one introduces during a certain
Vf2, Vfi, Vfn) and the valves (V1, V2, Vi, Vn) which correspond to the elements of the installation which one wishes to decoker are open. During this same period of time all the valves (V'1, V'2, V'i, V'n) remain open. According to this first operating mode the valves (V1, V2, Vi, Vn) are necessarily open when the valves (Vfl, Vf2, Vfi, Vfn) which correspond to them are, and that solid particles are introduced into the ovens , but it is possible to open these valves (V1, V2, Vi, Vn) a little before the opening of the corresponding valves (Vfl, Vf2, Vfi, Vfn) and to keep these valves (Vi, V2, Vi, Vn ) open for a certain time after closing the corresponding valves (Vf1, Vf2, Vfi, Vfn). According to this first operating mode, the retention volumes (S 1, S2, Si, Sn) located upstream of the valves (V1, V2, Vi, Vn) allow, even after the valves are closed (V1, V2, Vi, Vn ), recover and optionally store the residual solid particles leaving an exchanger after the introduction of solid particles has stopped in the furnace or upstream of this exchanger, these particles being able to be removed later, for example during 'Another period of decoking these same elements of the installation when the valve (Vi) is opened again. For the injection part of the particles in an oven i, the valve (Vfi) is necessarily open during the injection (operation of (Vg) if the particles are recycled), but can open or close with a delay before and after the injection phases.

 During the decoking periods and during the periods when at least one valve (V1, V2, Vi, Vn) remains open, the solid particles and part of the gases introduced into the primary separators (Ci, C2, Ci, Cn) which exit by the pipes (61, 62, 6i, 6n) are collected and conveyed by the pipe (7) in the means (Cg), common to all the ovens, for separation of at least a portion of the solid particles. The solids recovered from this means (Cg) are sent via line (9) to the storage means (STO), comprising means for evacuating and transferring solid particles.

As for the gases recovered from this means (Cg), they are sent via the pipe (5) to the means (4) for collecting the gases. The gases introduced into the primary separators (Ci, C2, Ci, Cn) and leaving through the pipes (31, 32, 3i, 3n) major fraction of the gases supplying the primary separators, are recovered by the means (4) for collecting the gas and preferably sent to the direct quenching means (TD).

According to a second mode of operation the valves (Vi, V2, Vi, Vn) are permanently open and are introduced for a certain time into the element or elements of the installation (that is to say into the furnace (s) (F1,
F2, Fi, Fn) and exchangers (T1, T2, Ti, Tn) that we want to decoke erosive solid particles. According to this operating mode the valves (V'1, V'2, V'i,
V'n) are non-operable and also permanently open and a minor part of the gas flow leaving the exchangers passes through the valves (V1, V2, Vi, Vn) and is evacuated by the pipes (61, 62, 6i, 6n) and the collecting means (7) towards the means (Cg), common to all the ovens, for separating at least a part of the solid particles. In this operating mode the gas flow rate leaving the primary separators (C1, C2, Ci,
Cn) via the pipes (31, 32, 3i, 3n) and the gas flow rate leaving the common means (Cg) for separating solid particles and gases via the pipe (5) are recovered by the collecting means (4) gases. Compared to the first operating mode, there is a higher total flow of gas passing through (Cg) because all of the pipes (61, 62, 6i, 6n) convey gas permanently, but the advantage that the valves ( Vi) are not maneuverable.

 For the implementation of at least certain operating modes, the installation usually includes means allowing the sequential injection and introduction of solid particles upstream of a limited number of indirect quenching exchangers (sorting, T2 , Ti, Tn) coordinated to the valves (Vi, V2, Vi, Vn), on the pipes (61, 62, 6i, 6n) for the exit of solid particles from the primary separators (Ci, C2, Ci, Cn). These means may include, for example, a programmable controller.

 In the various operating modes envisaged, the gas flow rate passing through the valves (V1, V2, Vi, Vn) depends in particular on the respective dimensions of the pipes (61, 62, 6i, 6n) and (31, 32, 3i 3n) Ce flow rate will be for example from 0.1% to 50%, preferably from 1% to 40 iG, and often from 1% to 20% by volume of the total flow rate of gas entering the primary separator (s) (Ci, C2, Ci , Cn) and therefore the pipes and the valves or shutters therein are inexpensive and more reliable. In addition, if an error occurs in the programming of valve openings or closings, the installation allows, in particular thanks to the retention volumes (Si, S2, S i, Sn), to stop the residual particles passing through the installation by outside the injection phases.

The cracking installation usually comprises at least one means (TD) of direct quenching into which is introduced, by means (4) collectors, the gases leaving the primary separators (cry, C2,
Ci, Cn) and / or those emerging from the common separation means (Cg). This direct quenching means can be a means common to all of the elements of the installation or this installation can comprise a plurality of common direct quenching means, each of these means being supplied with gas coming from one or more quenching exchangers indirect.

 According to an embodiment (FIG. 3) particularly desirable in the case of steam cracking of heavy loads, but also usable for cracking other loads, the installation will comprise upstream common separation means (Cg) and downstream of the separators primary (CI, C2, Ci, Cn), at least one means (I ') for introducing gases of a nature or composition different from the feedstock introduced into the cracking furnaces. For example in the case of steam cracking of heavy hydrocarbon feedstocks (gas oils, vacuum distillates) these gases, introduced by the means (I ′), will for example be formed from cracked gases of a chemical nature different from that of the cracked gases supplying the primary separators (Cl, C2, Ci, Cn). This charge, introduced by the means (I ′), will preferably comprise a rate of heavy hydrocarbons lower than the rate of heavy hydrocarbons contained in the feed of the primary separators (Cl, C2, Ci, Cn). This charge, introduced by the means (I ′), can be water vapor or can, for example, come from the thermal cracking of hydrocarbons having less than 10 carbon atoms, advantageously less than 5 carbon atoms in their molecules, in particularly those for example from thermal cracking of ethane, or light naphtha.

During operation of the installation, the charge introduced by the means (I ′) is often at a temperature higher than that of the cracked gases leaving the primary separators (C1, C2, Ci, Cn). The temperature of this charge is most often at least 10 ° C., preferably at least 20 ° C. and most often at least 40 ° C. at the temperature of the cracked gases leaving the primary separators (C1, C2, Ci, Cn). The gas introduced by the means (I ') is most often introduced in a quantity greater than the quantities of gas leaving the primary separators (Ci, C2, Ci, Cn) via the pipes (61, 62, 6i, 6n). The flow rate of the charge introduced by the means (I ′) will for example be of the order of 5 to 10 times the flow rate of gas leaving a primary separator (Cl, C2,
Ci, Cn). This flow rate may for example be of the same order of magnitude as the flow rate of gas entering a primary separator (C1, C2, Ci, Cn). The main function of this charge is to dilute the effluents and dry the traces of heavy hydrocarbons present.

 The erosive solid particles which are used usually have a diameter of less than approximately 250 Wm (micrometers) and for example of approximately 5 μm to approximately 150 tim without the present invention being linked to these values (higher values which can be considered). The average flow rate of particles injected into the installation during decoking periods is most often less than 10% by weight relative to the flow rate of the feed (hydrocarbons + water vapor). This flow rate will be for example from about 0.1 to about 8% by weight relative to the flow rate of the load. These particles can be of several types and mixtures of particles of different types can be used. These particles can be metallic particles or mineral particles as is for example described in patent applications WO-A-9012851 and WO-A-9012852. They can be angular and / or substantially spherical. Mention may thus be made of silica-alumina particles, particles of a metal alloy of high hardness. Coke particles can also be used, for example ground metallurgical coke.

 If it is desired to recycle the solid particles, as described in the abovementioned patent applications, means can be used to increase the static pressure in the solid particle storage part of the means (STO), for example an airlock and a source of pressurized gas (Gp), the main function of which is also to supply the carrier gas for transferring solid particles into the elements of the installation which it is desired to decoke. The carrier gas, in particular in the case of steam cracking, can be a light hydrocarbon (C1, C2 for example) or a mixture of gaseous hydrocarbons under the conditions of use, but will most often be a gas containing a significant proportion of vapor water or even steam alone.

 In a particular embodiment the cracking installation according to the invention comprises means making it possible to introduce into the cracking furnace (s) a charge different from the cracked charge during part of the operation of the installation and preferably during minus part of the solid particle introduction phases. One could for example introduce water in place of the cracked charge.

 The invention makes it possible to reduce the cost of the means for recovering solid particles by a factor of 2 to 3 compared to the prior art, and to increase reliability by using valves of more common design.

Claims (12)

1 - Installation for thermal cracking in the vapor phase, comprising - at least one cracking oven (Fi, F2, Fi, Fn), comprising means (I) for introducing the charge to be cracked, - for each oven (Fi, F2, Fi, Fn) downstream thereof, at least one exchanger (T1, T2, Ti, Tn) for indirect quenching of the effluents leaving said furnace, said installation comprising at least two indirect quenching exchangers for effluents (T1, T2, Ti, Tn), (TiA, TiB), - upstream of each indirect quench exchanger, at least one means (1, Gp) for transferring solid particles connected to at least one pipe (101, 102, 10i, 10n), for introducing solid particles, into the furnace (s) and / or just upstream of the quench exchangers, said pipes each comprising , at least one valve (Vfl, Vf2, Vfi, Vfn) - at least one means (Cg), common to all of the ovens and / or exchangers, for separating at least part of said solid particles, said installation being characterized in that it comprises downstream of the oven (s) (F1, F2, Fi, Fn) at least two primary separators (C1, C2, Ci, Cn), (CiA or CiB), (Ci being relative to the oven i), performing in parallel on the current which feeds it the at least partial separation of solid particles from the major part of the gaseous effluents of said supply stream of said separator, said primary separators each comprising a pipe (31, 321 3i, 3n ) main gas outlet, of diameter (Dl, D2, Di, Dn), each of said pipes (31, 32, 3i, 3n) being connected to a means for collecting said gases such as a pipe (4), and said primary separators each also comprising a pipe (61, 62, 6i, 6n) for leaving solid particles and a minor part of the gas contained in the feed stream of said separator, each of said conduits (61, 62, 6i, 6n) having a diameter (dol, d2, di, dn) smaller than the diameter (Di, D2, Di , Dn) of the corresponding gas outlet pipe (31, 32, 3i, 3n), each of said pipes (61, 62, 6i, 6n) being connected to a means for collecting said solid particles such as a pipe (7) allowing to convey and introduce said solid particles into the means (Cg), common to all the ovens and / or exchangers, for separation of at least a portion of said solid particles, said means (Cg) common to the set of ovens and / or exchangers comprising a gas outlet pipe (5) and a solid particle outlet pipe (9) are connected to at least one storage means (STO) comprising means for evacuation and transfer of the recovered particles. 2 - Cracking installation according to claim 1 comprising means for maintaining the means (Cg) of separation at a pressure lower than the pressure of the primary separators (cry, C2, Ci, Cn). 3 - Cracking installation according to claim I or 2 wherein the solid particles are introduced into the cracking ovens, upstream or at the entrance of the reaction zone of the ovens. 4 - Cracking installation according to claim 1 or 2 in which the solid particles are introduced just upstream of the quench exchanger, at the outlet of the reaction zone of the ovens 5 - Cracking installation according to one of claims 1 to 4 in which each primary separator (Cl, C2, Ci, Cn) has a solid retention volume (S1, S2, Si, Sn) upstream of the valves (V1, V2, Vi, Vn). 6 - Cracking installation according to one of claims 1 to 5 wherein each pipe (61, 62, 6i, 6n) for the exit of solid particles has a diameter (dl, d2, di, dn) less than or equal to 80% and preferably less than or equal to 50% of the value of the diameter (Dl, D2, Di, Dn) of each pipe (31, 32, 3i, 3n) of gas outlet. 7 - Cracking installation according to one of claims 1 to 6 characterized in that it comprises upstream means (Cg) of common separation and downstream of the primary separators (Ci, C2, Ci, Cn), at least one means (I ′) for introducing a gas of a nature or composition different from the charge introduced into the cracking ovens. 8 - Cracking installation according to claim 7 wherein the gas introduced by the means (I ') is introduced in an amount greater than the amounts of gas leaving the primary separators (Cl, C2, Ci, Cn) through the pipes (61, 62 , 6i, 6n) and has a content of heavy hydrocarbons lower than that of the gas leaving the primary separators (C1, C2, Ci, Cn). 9 - Cracking installation according to claim 7 or 8 wherein the gas introduced by the means (I ') is selected from the group formed by water vapor, the effluents from cracking of hydrocarbons having less than 10 carbon atoms in their molecules. 10 - Cracking installation according to one of claims 1 to 9 characterized in that it comprises means allowing the sequential injection and introduction of solid particles upstream of a limited number of indirect quenching exchangers (Ti , T2, Ti, Tn) coordinated to the valves (Vf1, Vf2, Vfi, Vfn), on the passage of solid particles in the pipes (lOi, 102, lOi, 10n) 11 - Cracking installation according to one of claims 1 to 9 characterized in that it comprises means allowing the sequential injection and introduction of solid particles upstream of a limited number of indirect quenching exchangers (T1, T2, Ti, Tn) coordinated with the valves (Vi , V2, Vi, Vn) on the passage of solid particles in the pipes (61, 62, 6i, 6n) for the exit of solid particles from the primary separators (cry, C2, Ci, Cn). 12 - Cracking installation according to one of claims 1 to 11 characterized in that it comprises means making it possible to introduce into the cracking furnace (s) a charge different from the cracked charge during part of the operation of the installation and preferably during at least part of the phases of introduction of the solid particles. 13 - Use of an installation according to one of claims 1 to 12 for the cracking of halogenated hydrocarbons, preferably chlorinated hydrocarbons. 14 - Use of an installation according to one of claims 1 to 12 for the steam cracking of hydrocarbons or hydrocarbon cuts.