Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
  • C10G9/00—Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils
  • C10G9/14—Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils in pipes or coils with or without auxiliary means, e.g. digesters, soaking drums, expansion means
  • C10G9/16—Preventing or removing incrustation

Definitions

• the steam cracking process is the basic process of petrochemicals. It consists in thermally cracking a mixture of hydrocarbons and steam at high temperatures of the order of 800 to 850 ⁇ C, then quenching the effluents in a quench exchanger generally designated by TLX or TL ⁇ (Transfer Une Exchanger "), then split the cooled effluents.
• the problem ope main tory of the method resides in the ae coke deposit ⁇ ans cracking tubes and those of the transfer line exchanger.
• the particles are injected "in-line", that is to say either during normal operation of the steam cracking process (preferred operation ⁇ or during phases where one interrupts temporarily and briefly, the hydrocarbon feed, ovens then being swept by the steam of water alone and remaining connected to the downstream processing sections ⁇ es effiuents.
• one cup r e ry the injected particles, because if p aration gas / soii ⁇ e (e.g. a cyclone) downstream of the exchangers tremoe. so as not to pollute the downstream sections.
• p aration gas / soii ⁇ e e.g. a cyclone
• the spent catalyst powders are recovered under pressure (operating pressure of the reactor), and these powders are transferred to a regeneration zone (combustion of the coke), which is itself under pressure, close to that of the reactor, before transferring the regenerated catalyst back to the reactor (in a fluidized bed, "moving bed", or by bucket elevations in the first versions of the TCC)
• the particles fall by gravity into a filter placed below the recovery cyclone and join an airlock, to allow their recycling by means of a current of steam.
• the installation uses a filter directly receiving the powder collected in the cyclone, typically at a temperature of 400 to
• the object of the invention is to solve this technical problem, not with a new filtration method, difficult to make reliable, but thanks to a new conception of the process, and of the corresponding installation, making it possible to carry out the operation of filtration that is both simple, economical and reliable, easy to maintain, and with existing equipment.
• the invention proposes a process for steam cracking of hydrocarbons in an installation comprising at least one steam cracking oven, comprising at least one cracking zone with pyrolysis tubes connected downstream to a quenching exchanger for the effluents of this zone. for their sudden cooling, the process comprising the injection of powders containing erosive solid particles, upstream of the quench exchanger for the on-line elimination of at least part of the coke deposited in this exchanger, also comprising the separation, by primary separation means effluent / solid gases, of at least part of the injected powders and the recovery and recycling of at least part of the separated powders, the process being characterized in that:
• a step D is carried out, discontinuously, of depressurization of the powders recovered up to substantially atmospheric pressure
• a step T is carried out, beforehand, simultaneously, or after step D, of pneumatic transfer of these powders in a transfer pipe, the powders being conveyed by an inert, non-coking transport gas, and from point of atmospheric dew below 1 10 ° C, the temperature of the transport gas at its supply point being lower than the temperature of the effluent leaving the exchanger, • a step is carried out after the pneumatic transfer step so-called secondary separation of the transport gas and the powders conveyed by said gas,
• the transport gas used for the circulation of the powders recovered in the transfer pipe can be steam, at a temperature below for example 200 ° C., or preferably fuel gas (produced by the steam cracker, or external) such as methane or a methane / hydrogen mixture. Nitrogen can also be used. When using fuel gas or nitrogen as the transport gas, it will also be preferable to use a supply of this gas at a temperature below 250 ° C, or even below 200 ° C; it is also possible in this case to use a transport gas at a temperature below 150 ° C and even a cold gas at room temperature.
• This gas has a main role in pneumatic transport of the particles, in dense or diluted phase, for example at a gas speed of between 2 and 60 m / s and preferably 5 to 50 m / s, for example in the diluted phase at a speed of 20 to 35 m / s, according to techniques well known to those skilled in the art; these techniques generally use pressurization of the shipping container, isolated from upstream, and / or downstream, then the pneumatic evacuation of the powder in a controlled flow of transport gas (for example by means of a ve ⁇ turi ).
• the powder can also be extracted from the shipping container by a screw, a lock or other known components.
• This transport gas also has two other functions, which contribute to the cooling of the transported powder: by simple mixing, it allows a first cooling of this powder, since it is at a temperature lower by at least 50 ° C., in particular d 'at least 100 ° C, and even preferably at least 150 ° C relative to the temperature of the effluent of the TLE (powder arrival temperature).
• the pneumatic transport of particles whether in dense or diluted phase, accelerates heat exchange with the wall of the transfer duct (in particular with respect to a fall of particles in a gravity flow); indeed, the turbulent gas / particle flow achieves an efficient particle / wall heat transfer via the gas.
• this step T of pneumatic transfer of the recovered powders achieves a second effective cooling of the powders, the wall of the transfer duct forming exchanger.
• the temperature of this conduit, over a length of at least several meters is lower by at least 50 ° C, in particular by at least 100 ° C, and preferably by at least 150 ° C by relative to the temperature of the effluent from the TLE (powder arrival temperature).
• the powder can be cooled to a level such that the subsequent sieving operation of the powder, to remove large fragments, for example greater than 3 or 4 mm, can be carried out at an operating temperature relatively low, less than about 250 ° C, and preferably 180 ° C, for example between 40 and 150 ° C.
• This low temperature and the use of atmospheric pressure then makes it possible to use existing vibrating screens (or vibrating screens), perfectly reliable, the arrival of powder and the outlets of sieved powders on the one hand, and fragments of other part, which can be connected to the vibrating screen by conventional flexible cuffs (for example rubber).
• the invention therefore makes it possible, thanks to a significant modification of the recycling process, to solve in a completely reliable manner the problem of filtration (or indifferently screening, or sieving) consisting in eliminating the large solid fragments present in the recovered powder.
• Screening can be carried out with existing materials, which are very common and therefore economical.
• simple maintenance can be carried out, the screen being at atmospheric pressure, low temperature, and under nitrogen. This easy maintenance therefore makes the process more reliable, insofar as possible clogging problems can be resolved in a very short time, which is not detrimental to the continuity of the steam cracking.
• the pneumatic transfer stage T is carried out using a transport gas with a very low condensation point at atmospheric pressure: less than 110 ° C., but very generally at ambient temperature, according to the preferred version of the process where uses nitrogen or a light aliphatic hydrocarbon gas (H2 / C 1 / C2 / C3 / C4) and in particular fuel gas Ci or C1 / H2;
• this pneumatic transport by a gas under conditions far from its condensation point dry gas, noncondensable at room temperature, or overheated
• the drying of the powders and elimination of traces of liquid that may be present on the recovered powder humidity, or pyrolysis essence entrained with the powder at the time of its recovery during its gravity fall in the receiving container located below the cyclone (or gas separator / solid).
• This drying of the powder in a circulating bed is a new essential element making the operation of the screen more reliable and preventing it from clogging.
• the particles of the transport gas are separated, at the downstream end of the transfer duct, in at least one cyclone (or a gas / particle separator, called a secondary separator, in contrast to the primary separator having separated the powders from the cracked gases), to recover the dry particles and eliminate the vapors, that is to say the traces of liquid evaporated in the transport gas, before the screening operation.
• a cyclone or a gas / particle separator, called a secondary separator, in contrast to the primary separator having separated the powders from the cracked gases
• this separation is typically made for this separation to be carried out at a temperature of between approximately 40 and 180 ° C., and preferably between 80 and 160 ° C., this temperature being at least higher 25 ° C at the dew point of the transport gas at the pressure of the secondary separator; this can possibly be achieved by heating the transfer duct just before the cyclone.
• the powders, separated in the secondary separator at this temperature at the end of step T are then dry, and can be sent to the screening step.
• the steam cracking installation comprises a plurality of quench exchangers equipped with the erosive decoking process, and a plurality of effluent gas / primary solid separators and of collected powder collection points; in this case, according to a characteristic arrangement of the invention, at least part of the powders, recovered at several collection points, is transferred to a single point using the transfer conduits, during step T of the method, according to the 'invention.
• these 10 collection points being divided into two groups of 5 points, the 5 points of a group being connected by their pneumatic transfer conduits to a secondary separator and a treatment module comprising a vibrating screen; such an installation therefore comprises 20 TLEs, 10 primary separators,
• Step T characteristic according to the invention, has in this case a triple function - cooling of powders (in circulating bed)
• This method according to the invention has considerable advantages compared to the previously described method where the powders were conveyed by a large flow of cracked gases, towards a single point and a common module, by directing the effluent from the different TLEs, sequentially towards the module common, during particle injections, thanks to large diameter valves since they are crossed by the total flow of cracked gases from a TLE; the advantages are:
• the method according to the invention is therefore both much more reliable, easy to operate, and economical from the investment point of view.
• the pneumatic transfer stage T and the secondary separation stage are carried out prior to the depressurization stage.
• the secondary separator can be in direct communication (that is to say without depressurization valve) with a discharge line of cooled cracked gases, to allow the evacuation of the transport gas, downstream the secondary separator, mixed with the cooled cracked gases circulating in this line; so we carry out the transfer of the powders recovered in the different cans of reception, under pressure, to a single point (the secondary separator).
• There is therefore only one depressurization system downstream for example an airlock comprising at least two controlled valves, for depressurizing the powders to atmospheric pressure.
• the atmospheric pressure zone typically comprising the vibrating screen
• the atmospheric pressure zone will be connected directly inside the enclosure of a furnace, or to a chimney (zones at atmospheric pressure, but confined, the gaseous discharges being emitted on top of a chimney), rather than directly in the open air.
• the powders are injected upstream of the cracking zone, in order to carry out a preponderant decoking of both the cracking zone and quench exchanger.
• a large portion of powders is injected, and more particularly 70% by weight at least during a steam cracking cycle, into the transfer zone, located between the outlet of the cracking zone, that is to say conventionally at the level of the exit from the oven enclosure (radiation zone), and the entry into the quench exchanger, the inlet cone of this exchanger forming part of this transfer area.
• This second variant of the process is advantageously used to make flexible an oven intended for cracking light loads (naphtha, liquefied petroleum gases), and also to treat, under variable conditions, condensates, diesel, heavy distillates. or under vacuum; unlike the first variant, it does not allow a substantially continuous steam cracking requiring the injection upstream of the cracking zone of large quantities of erosive powders, for example several thousand ppm of angular mineral powders, relative to the gases cracked, but allows to strongly limit the fouling of the quench exchanger, whatever the loads treated, without technological risks for the installation and without modifying it in an expensive way (without strengthening the elbows of the cracking zone ).
• This second variant requires much lower quantities of powders, injected for the most part or even entirely in an area where the tubes of the quench exchanger, which do not include bends, are at relatively low temperature (350 ° C approximately), and where the gas circulation speed is relatively low, typically less than 120 m / s.
• the control of the process is very easy to implement: it consists in injecting a sufficient quantity of powder, generally by discontinuous injections at intervals between 0.3 and 72 hours, in particular between 1 and 30 hours, to limit the increase in the outlet temperature of the quench exchanger to an acceptable value for the industrial operation of the installation: 100 ° C per month, or preferably 30 ° C per month, or even to substantially stabilize this temperature.
• the particles which can be used according to the invention comprise particles of average diameter (diameter at point 50% by weight) of between 0.02 and 4 mm and preferably between 0.07 and 0.8 mm, preferably comprising at least 20% by weight angular particles, which can be chosen from, in particular, coke, calcined at high temperature, silicon carbide, simple or mixed oxides of silicon, aluminum and zirconium. Other particles (angular metal, crushed ores, sand, spent FCC fluid cracking catalyst) can also be used.
• the decoking of the pyrolysis tubes of the cracking zone can be done, in a conventional manner, by decoking in air or by an air / water vapor mixture, or with water vapor alone, optionally with the addition of hydrogen.
• This decoking, chemical, by gasification of coke, accelerated with respect to the (limited) gasification occurring during the steam cracking itself, can also be strongly accelerated by injecting chemical compounds which are catalysts for the gasification of coke by vapor of water, upstream of the cracking zone.
• These gasification catalyst compounds comprise at least one mineral salt of at least one element from the group of sodium, potassium, lithium and barium, active for the gasification of coke.
• an equimolar mixture of potassium carbonate and sodium carbonate or an equimolar mixture of sodium acetate, potassium acetate, lithium acetate and barium acetate, are effective for decoking or limiting the coking of the cracking zone.
• aqueous solution preferably diluted with at least 90% water and preferably 95 99.9% water; this solution is preferably atomized, or sprayed very finely into the charge of hydrocarbons and water vapor downstream from the dry point, for example at the outlet of the convection zone, at a level where the charge is at a temperature of around 500 to 650 ° C.
• a steam cracking installation is also proposed, making it possible to implement the method according to the invention, comprising at least one steam cracking oven, comprising at least one cracking zone with pyrolysis tubes connected downstream via a zone for transferring cracked gases to at least one quench exchanger for these cracked gases, and comprising means for injecting upstream of the quench exchanger, powders containing erosive particles, also comprising primary separation means for cracked gases / solids, downstream of the quench exchanger, for the recovery, in at least one receiving container, of at least part of the injected particles, characterized in that the installation comprises means for pneumatically transferring the powders recovered in the receiving can adapted to cool the powders, comprising in particular a supply of a non-coka ⁇ t transport gas, with an atmospheric dew point below 1 10 ° C, the pneumatic transfer means also comprising a transfer pipe connected upstream to the receiving container and downstream to a secondary gas / solid separator, comprising a powder outlet connected downstream to a screen operating substantially at atmospheric pressure and under an essentially
• the screen is of the vibrating screen type, with a maximum operating temperature below 250 ° C., and in particular at 180 ° C.
• this screen has an operating temperature below 150 ° C., and comprises flexible cuffs, for example made of elastomer or reinforced elastomer, for its connection to the inlet and outlet of the powders, passing through the screen before being at least partially recycled, and also at the exit of "refusals", or large fragments, which are eliminated.
• flexible cuffs for example made of elastomer or reinforced elastomer
• centrifugal screen (frequently called a centrifugal screen), chosen from existing conventional materials, thanks to the specific operating conditions according to the invention, a vibrating screen (or vibrating screen) being however preferred.
• the mesh size of the screen will preferably be between 2 and 6 mm and greater than the maximum dimension of the "new" particles.
• An installation is also proposed such that at least part of the powder recycling means are connected and directly connected to the cracked gas transfer zone, for the injection into this transfer zone of at least 70% by weight of the injected powders. upstream of the quench exchanger during a steam cracking cycle; this installation is particularly suitable for flexible cracking of various loads.
• the powders are preferably injected into the inlet cone of the quench exchanger, and in particular at one or more points of this cone where the passage section offered to the cracked gases (effiuents from the cracking zone) is increased d 'at least 25%, and for example 40 to 400% relative to the passage section of these cracked gases in the terminal part of the transfer duct.
• the powders are therefore injected at a point where the speed of the cracked gases is already greatly reduced, which reduces or eliminates the risks of erosion of the tube plate; more we will inject preferably new and recycled powders conveyed by a gas such as nitrogen, fuel gas or water vapor, at a gas speed of between 5 and 50 m / s, just upstream of a playing impactor also a role of diffuser of these particles, to better distribute them in the different tubes of the quench exchanger.
• a gas such as nitrogen, fuel gas or water vapor
• the quantity of powder required for limiting the fouling of the quench exchanger can be reduced, if necessary, by increasing the gas circulation speed at the time of the injections, for example by increasing the volume flow rate of cracked gases by 10 at 50%; this speed can also be increased permanently, by closing off some of the tubes of the quench exchanger, for example from 4 to 25% of the tubes.
• an installation comprising means for metering and injecting mineral salts catalysts for the gasification of coke, these means being connected upstream of the cracking zone; these means such as a storage tank, a metering pump, for example for injecting mineral salts comprising at least one salt of an element from the group of sodium, potassium, lithium and barium, active as a catalyst gasification of coke by steam.
• An installation comprising a plurality of quench exchangers (TLE), a plurality of primary gas / solid separators, for the recovery of powders in a plurality of receiving cans arranged at a plurality of collection points, characterized in that that it comprises a plurality of pipes for the pneumatic transfer of the powders recovered in the said receiving containers, by means of said non-coking transport gas, each of these transfer pipes being connected upstream to one of the receiving containers and downstream to the same secondary separator, the outlet of the powders of which is connected to the screen.
• TLE quench exchangers
• TLE quench exchangers
• This installation is particularly economical, in comparison with the installation described in the prior art, where the powders are conveyed by cracked gases at high temperature, by means of large-diameter valves, very expensive, and the elimination system of which large fragments are placed in a high temperature pressure area, excluding the use of conventional equipment.
• the reliability of the installation according to the invention is also higher, due to the implementation of a reliable system for removing large fragments, as well as drying of the powders by the transport gas, beforehand. at the screening stage.
• FIG. 1 schematically illustrates an embodiment of a steam cracking installation according to the invention
• FIG. 2 shows schematically and in a simplified way, part of a steam cracking installation according to the invention, comprising a plurality of primary separators and containers for receiving the recovered powders, a single secondary separator and a single vibrating screen.
• FIG. 1 where a part of a steam cracking oven (1) has been represented comprising a cracking zone (2) with pyrolysis tubes, located in the radiation zone of the oven, connected downstream to a quench exchanger (4), or (TLE), via a zone (3) for transferring cracked gases, this zone comprising the inlet cone of the TLE, which contains an impactor-diffuser (24) located just downstream of at least one point of introduction of powders by a line (25).
• a part of a steam cracking oven (1) has been represented comprising a cracking zone (2) with pyrolysis tubes, located in the radiation zone of the oven, connected downstream to a quench exchanger (4), or (TLE), via a zone (3) for transferring cracked gases, this zone comprising the inlet cone of the TLE, which contains an impactor-diffuser (24) located just downstream of at least one point of introduction of powders by a line (25).
• This impactor-diffuser consists of two rows of surfaces, offset relative to each other, so that it is substantially opaque, seen from the entry of cracked gases into the cone, while being permeable to gas.
• temperature measurement means (27) make it possible to know the temperature of the cooled cracked gases circulating in a discharge line (15), which indirectly makes it possible to know the degree of fouling of the TLE by coke.
• the cracked gases pass through a primary cracked / solid gas separator (5), constituted by a cyclone, which makes it possible to recover almost all of the solid particles in a receiving container (6).
• This container contains a grid (32) with a large mesh passage, for example 20 mm, making it possible to stop any large pieces of coke which could hinder the pneumatic transfer downstream of the powders. These large pieces being very rare, this grid can operate for long periods without maintenance.
• a supply of nitrogen (9) under pressure, or of another non-coking gas with an atmospheric dew point, ie of initial condensation temperature at the pressure of 1 atmosphere below 110 ° C., such as fuel gas (methane or methane / hydrogen), or water vapor introduced at about 200 ° C, allows to inject such a gas, called “incondensable” to simplify, in the receiving container (6); this allows this balloon to be placed under an incondensable gas atmosphere, to introduce an incondensable barrier gas, by a line (10), to avoid the presence of cracked gases in the can (6), to stripping the powders recovered in making them pass through a stream of incondensable gas, introduced by a line (33), and evacuating them by a stream of transport gas, introduced by a line (1 1).
• This gas can also be used to pressurize the container (6), by a line (34), at the time of the pneumatic evacuation of the powders.
• the container (6) can be isolated upstream side by a valve (7) and downstream side by a valve (8). These valves (7) and (8), controlled, make it possible, with the container (6), to form a pneumatic airlock, to empty the container, and discharge the powder only by pneumatic means, that is to say without screws, lock or other mechanical extractor.
• the powder contained in the container (6) When the powder contained in the container (6) is pneumatically emptied, it is evacuated by a transfer pipe (12), conveyed by the non-coking "noncondensable" transport gas, over a length of several meters and preferably between 5 and 150 m, for example between 10 and 60 meters, to carry out step T of the process.
• the mixture of powder and transport gas is separated in a secondary separator (13), preferably a cyclone.
• the transport gas leaving the secondary separator, and which comprises the "incondensable" gas, possibly supplemented with hydrocarbon vapors, for example traces of pyrolysis gasoline, evaporated, originating from the powder joins the general evacuation line cracked gas cooled (15) by a line (14).
• This airlock performs step D of the process (depressurization to the atmosphere), and comprises a valve (18) for depressurization, connected to the atmosphere, preferably inside the enclosure of one of the steam cracking furnaces. , or to a fireplace.
• This airlock also includes means (16) for introducing sweeping nitrogen, making it possible to put the powders under a nitrogen atmosphere before their depressurization. This nitrogen sweep could possibly be suppressed when the transport gas supplied with (9) is already nitrogen.
• the depressurization airlock also includes means (35) for removing used powders.
• Means (36) for introducing new powders, to compensate for the consumption and loss of used powders, can be connected to the container (17), or to another place in the installation, for example just upstream of the secondary separator ( 13).
• the powder After depressurization, downstream of the airlock consisting of the container (17) and its isolation valves, the powder falls into a vibrating screen (19), of the conventional type, with flexible sleeves allowing connections with the inlet and the outlet of powders and fragments compatible with the vibrations of the device.
• the screen (1 9) is connected to the atmosphere directly (without depressurization valve) by a line (23).
• the mesh size of the screen for a conventional powder with a particle size between 70 and 800 microns, can typically be 3, or 4 millimeters, making it possible to eliminate all "rejects", larger than this mesh size, which are collected in a container (22).
• This container which can also be isolated by controlled valves 20a and 20b, upstream and downstream, is the airlock for shipping the powder to recycle it in the installation.
• the pneumatic transfer of the powders from the shipping container (20) is also advantageously carried out by means of a "noncondensable" gas, supplied with (21) such as fuel gas or nitrogen.
• a noncondensable gas supplied with (21) such as fuel gas or nitrogen.
• Water vapor is also a possible transport gas, but presents constraints for maintaining the temperature of the lines, to avoid any condensation of water liable, with the powders, to block these lines.
• the preferred transport gases both for the pneumatic transport of step T and for the pneumatic transport of the powders for recycling, from the canister (20), are gases noncondensable at room temperature, more specifically nitrogen or fuel gas. Then, the powder transport lines are advantageously unheated and not insulated.
• the recycled powders, circulating in the line (25), in dense phase or in diluted phase, are generally reinjected into the inlet cone of the quench exchanger, for example at 4 points, by means of injectors whose diameter internal can typically vary from 10 to 35 mm, for example from 10 to 20 mm, without risk of clogging, thanks to the elimination of large fragments in the vibrating screen (or sieve) (19). If the load of the installation is well known, and relatively constant, and the coil (2) of pyrolysis tubes is adapted to this load, the powders can be reinjected not by the line
• the load of the installation is variable, at least 70% of the particles are injected via the line (25), or even 100%, the quantity injected for the line (26) being less than 200 ppm compared to cracked gases (average value over a steam cracking cycle), and preferably less than 100 ppm.
• the installation also includes means (28) for injecting anti-coking chemical compounds, and more particularly mineral salts which are catalysts for gasification of coke by water vapor. These compounds are injected upstream of the cracking zone (2), during the steam cracking operation, to limit or cancel the coking speed, and / or during decoking phases with steam alone, to accelerate this decoking. .
• the installation also obviously includes means (30) for supplying hydrocarbons (charge to be cracked) and (29) for supplying dilution water vapor.
• the assembly (31), contained in the drawn rectangle, and constituted by the secondary separator (13), the can (17) for the depressurization of the powders, the vibrating screen (19), and the re-shipment airlock (20), as well as all the power supplies and related materials, is a powder processing module.
• This processing module can be arranged differently without departing from the scope of the invention, and may possibly include other functions (for example weighing the recovered powders, and / or removing very fine particles, before recycling, by sieving , elutriation, or other means).
• FIG. 2 there is shown schematically and simplified, two quench exchangers (4) belonging to the same oven (1) or to two different ovens, equipped with powder injectors in accordance with method according to the invention.
• the powders, injected into the two TLEs, are separated in two primary cyclonic separators (5), and recovered in two collection points, different and distant, constituted by the two receiving drums (6).
• Two sources (9) of "incondensable" transport gas make it possible to evacuate, respectively, the powders contained in the cans (6).
• This installation also includes two lines (25), common along part of their length, for recycling the powders upstream of the two TLEs, and two lines for discharging cooled cracked gases (15).
• This installation therefore includes a number of devices of the installation of Figure 1, duplicated.
• This installation typically contains a single module
• the installation according to FIG. 1 operates as follows: according to a preferred version of the process, the installation makes it possible to carry out steam cracking of various charges, ranging from ethane to atmospheric diesel. Some of these charges very quickly foul the quench exchanger and make the installation inoperable without frequent removal of the coke from the quench exchanger.
• powder is injected into the inlet cone of the quenching exchanger by means of the shipping container (20), and its valves (20a) and (20b) upstream and downstream, forming pneumatic shipping lock.
• the powders are conveyed by a stream of nitrogen, fed at (21), and circulate in the line (25), before being introduced into the inlet cone of the quench exchanger (4).
• the powder, brought by the line (25) is then transported by the cracked gases, circulates in the exchanger (4) then in the line (15) downstream of the exchanger, and is separated in the primary cyclone (5) ; it then falls into the receiving container (6), the valve (7) being open during the injection of powders into the exchanger, while the valve (8) is closed.
• the powder is then stripped, to obtain at least partial drying, by a controlled injection of nitrogen by the line (33), coming from the feed (9).
• Another controlled flow of barrier nitrogen, introduced into the line (10) opposes the arrival of cracked gases in the can (6), which is therefore kept under an incondensable atmosphere.
• the valve (7) is closed, and simultaneously the nitrogen circulation in the lines (10) and (34) is interrupted.
• the powder is therefore trapped in the balloon (6), isolated from upstream and downstream.
• We can then perform the pneumatic transfer step T of this powder by pressurizing the container (6), with nitrogen introduced through the line (33), and by opening the valve (8), with the introduction of gas. transport (nitrogen) flow controlled by line (11).
• the container (6) then empties pneumatically, the powder being transferred in the phase diluted by nitrogen. transport in the transfer line (12) long at least several meters, for example 25 meters.
• the powder is separated from the transport gas in the secondary cyclone (13), and falls into the container (17), the valve 17a being open during step T, after having optionally swept the container (17) with an additional current d nitrogen introduced through line (16), the valve 17a is closed.
• the powder dose which has been dried and cooled by its circulation in the pipe (12), is therefore dry, at a typical temperature of 120 ° C., for example, in the can (17).
• the valve (18) is then opened, for placing the container (17) in communication with the atmosphere, in order to carry out step D of depressurization of the powder to substantially atmospheric pressure; in fact, before this depressurization phase, the container (17), like the cyclone (13), is in direct communication with the line (15) for discharging the cooled cracked gases, which is under a pressure typically close to 1. 7 bar absolute.
• valve 17b is opened immediately downstream of the container (17), so that the powder falls, by gravity, into the vibrating screen (19). Large fragments, greater than 3 mm, are discharged into the container (22) while the powder, without large fragments, falls into the container (20); the powder has therefore returned to its starting point and can be recycled, by pressurizing the can
• this spent powder is eliminated by the line (35), when it arrives in the can (17) and it is introduced by the line (36), a dose of new powder, for example 30 kg of new powder.
• this powder can be angular silicon carbide, with a particle size between 70 and 250 micrometers, with an average diameter of 150 micrometers. It is also possible to use corundum, ground coke, or other powders, mineral, metallic, preferably partially angular.
• a small amount of injected is injected, by the means (28) comprising a reservoir for storing coke gasification catalysts chemicals and a metering pump.
• these products preferably in a highly dilute aqueous solution, for example 96% water, atomized in the steam cracking charge vaporized and preheated to 550 ° C., for example, in the convection zone of the oven.
• An equimolar mixture of sodium carbonate and potassium carbonate can in particular be used.
• FIG. 2 works exactly in the same way as that of FIG. 1, the dose of powder circulating either in the quench exchanger presented on the left part of the figure or in that presented on the right part.
• Orientation valves located on the lines (25) allow direct the powders towards the part of the installation where the heat exchanger is the most dirty.
• Comparative Example 1 A steam cracking installation with powder injection (for example silicon carbide), comprises 20 quench exchangers (TLE), and a single module for processing and recycling these powders.
• powder injection for example silicon carbide
• TLE quench exchangers
• this module operates under pressure (for example 1.7 bar absolute), and in a water vapor atmosphere.
• the injected powders are conveyed to the common module for treatment by the effluent cracked gases from each of the TLEs, oriented successively towards this common module by means of sets of orientation valves.
• This installation therefore comprises, for each TLE, two large diameter valves (typically 300 mm), to direct the effluent either to the downstream sections for the treatment and fractionation of cracked gases, or to the common module for recovery and treatment of powders when 'we inject particles into this TLE.
• two large diameter valves typically 300 mm
• This installation includes, before recycling the powders, a static grid (for example with a mesh diameter close to 5 mm) to remove large fragments.
• a static grid for example with a mesh diameter close to 5 mm
• This installation not in accordance with the invention, has very limited reliability, because of the risks of clogging of the static grid, and of the fact that the powders, conveyed towards the common module by cracked gases, are not dried, and can therefore sometimes contain traces of liquid, and be sticky. Access for maintenance of the grid is relatively difficult and requires a long time, due to the pressure and the operating temperature of this grid (close to 400 ° C.).
• Example 2 The same steam cracking installation is fitted in accordance with the invention. For example, 20 primary cyclones (5) and receiving drums (6) are installed, connected by 20 transfer pipes (12) to a single module (31) comprising a single secondary separator and a single vibrating screen (19), operating at atmospheric pressure, under nitrogen.
• the screening operation can be carried out with great reliability, by reducing the mesh size to 3 mm, thanks to the standard vibrating screen, whose flexible cuffs are compatible with the operating conditions (moderate temperature, atmospheric pressure).
• the operating conditions moderate temperature, atmospheric pressure.
• access to the screen is very easy and can be achieved in a very short time.
• cyclones (5) and canisters (6) are less expensive than large-diameter controlled valves, compatible with a powder service.
• the transfer pipes (12) do not convey very hot cracked gases but very low flow rates of cooler gases (for example 1000 m 3 / h of noncondensable transport gas, in instantaneous flow, against typically around 10 000 m 3 / h of cracked gas, for each TLE, in Example 1).
• the lines (12) can be made of carbon steel, and of much smaller diameter (for example 50 to 100 mm) than those of the lines of Example 1 (typically of diameter around 300 mm), which are necessarily made of alloy steel, because it carries cracked gases.
• the invention which presents both a much more reliable process, in a less expensive installation, therefore achieves significant progress compared to the prior art.

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• 1994
  • 1994-12-26 FR FR9415745A patent/FR2728579A1/fr active Granted
• 1995
  • 1995-12-22 WO PCT/FR1995/001720 patent/WO1996020258A1/fr active Application Filing
  • 1995-12-26 TW TW084113869A patent/TW343995B/zh active

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