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
  • C10G9/002—Cooling of cracked gases
• • 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
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28G—CLEANING OF INTERNAL OR EXTERNAL SURFACES OF HEAT-EXCHANGE OR HEAT-TRANSFER CONDUITS, e.g. WATER TUBES OR BOILERS
  • F28G1/00—Non-rotary, e.g. reciprocated, appliances
  • F28G1/12—Fluid-propelled scrapers, bullets, or like solid bodies
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
  • B01J2208/00796—Details of the reactor or of the particulate material
  • B01J2208/00823—Mixing elements
  • B01J2208/00831—Stationary elements
  • B01J2208/0084—Stationary elements inside the bed, e.g. baffles
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S585/00—Chemistry of hydrocarbon compounds
  • Y10S585/949—Miscellaneous considerations
  • Y10S585/95—Prevention or removal of corrosion or solid deposits

Definitions

• the invention relates to an installation for steam cracking of hydrocarbons and to an implementation method, comprising a decoking step with controlled injection of solid particles.
• the technological background is illustrated by patent FR-A-1,433,702.
• the steam cracking process is the basic process of the petrochemical industry and consists of cracking at high temperature and then brutally cooling a load of hydrocarbons and water vapor.
• the main operational problem results from the deposition of carbonaceous products on the internal walls of the installation. These deposits, consisting of coke or heavy tars of condensed pyrolysis and more or less agglomerated, limit the heat transfer in the cracking zone (coil with pyrolysis tubes) and the indirect quenching zone (effluent quench exchanger), requiring frequent stops to decoker the installation.
• the erosive solid particles can be injected upstream of the cracking zone of each oven so that they pickle the coke deposited in the pyrolysis tubes, then downstream, that of the effluent quenching exchangers.
• the injections are carried out online, that is to say either preferably during the normal operation of the furnace, or during periods when the supply of hydrocarbons is briefly interrupted, the furnace then being swept by a flow of water vapor and remaining connected to the downstream sections of the installation (primary oven, compression of cracked gases, etc.).
• This passage under steam, in the absence of oxygen, can also be used for steam decoking of the furnace tubes, when it is carried out for longer periods of time.
• erosive particles was very difficult to implement reliably with flexible operation under necessarily variable conditions: the geometry of the pyrolysis tubes cannot in fact be adapted for all of the charges, to ensure a correspondence between the erosive intensity local and the local coking speed (the nature of the coke and its hardness can also vary greatly from one charge to another); on the other hand, in flexible operation, therefore under variable operating conditions, type of charge and dilution rate, the pressure drop and the skin temperature of the tubes are no longer reliable indicators of the coking state of a bundle of pyrolysis tubes which cannot therefore be known and controlled in real time.
• a new method is proposed combining chemical decoking, at least preponderant, of the pyrolysis tubes with erosive decoking, at least preponderant, of the quench exchangers.
• This process therefore includes an erosive decoking of the tubes of the quenching exchangers, which requires suitable means for introducing erosive particles into these exchangers.
• quench exchangers are of the multitubular type with an inlet tubular plate which may comprise, for example, from 50 to 100 cracked gas circulation tubes, each tube being cooled, most often, by circulation of pressurized water in an annular space around this tube.
• Each exchanger comprises an "inlet cone” of evolving geometry connected to the cracked gas transfer duct, itself connected to the pyrolysis tubes of the corresponding upstream cracking zone.
• the technical problem for which a solution object of the invention has been found concerns the distribution of the particles in the different tubes of the exchanger.
• the process does not require a strictly equal distribution of the quantities of particles in each tube, but relatively small differences in distribution are sought, and it is in particular necessary to prevent one of the tubes from collecting, for example 10%, or on the contrary 10 times more particles than the average value.
• a tube poorly supplied with erosive particles could become clogged, due to insufficient decoking, while a tube supercharged would risk being eroded by the particles in excessive quantity.
• the distribution of the particles must moreover be carried out without causing significant erosion of the tubular plate of the exchanger.
• the device for introducing and distributing particles must therefore be:
• the injection manifolds are generally straight or circular conduits, comprising injection nozzles or orifices.
• One of the objects of the invention is to remedy the drawbacks of the prior art and to respond to the technical problem mentioned above.
• the invention therefore relates to an installation for steam cracking of hydrocarbons comprising at least one cracking furnace comprising at least one cracking furnace comprising at least one cracking zone with at least one pyrolysis tube connected downstream via a transfer duct (1) to an inlet cone (2) of an exchanger (3) for quenching the effluents of this zone, of the multitubular type with inlet tubular plate (5), the installation also comprising at least a pipe (I) for injecting solid particles for at least partial elimination, carried out online, of the coke deposited in the tubes of the exchanger, characterized in that it comprises:
• an impactor-diffuser (6) of particles, comprising solid surfaces arranged opposite the transfer duct (1), inside said cone (2) of inlet, said impactor-diffuser being permeable to gases in a plurality of gas passages, but opaque at least to 70% seen from said transfer conduit (1) located upstream, b) said injection conduit (I) opening at a point of introduction of the particles arranged at a distance L upstream of the impactor-diffuser not exceeding
• inlet cone a transition zone of substantially increasing cross section, generally at least partially frustoconical in shape, connected upstream to the cracked gas transfer duct originating from the pyrolysis tubes, this duct being of cylindrical section, and downstream to the tubular plate of the quench exchanger.
• This cone can also be flared "in trumpet”, as shown in the figures below.
• This term “exchanger cone”, well known to those skilled in the art, can in fact cover various geometries making it possible to pass from the cylindrical transfer duct (or sometimes two ducts) to the much larger diameter of the exchanger tubular plate (typically around 1 m).
• injection of particles "in line” means injections of particles during the operation of the steam cracking (general case), or possibly injections during short-term phases, less than 2 hours and preferably 0.5 hours, of circulation water vapor only, the supply of hydrocarbons being interrupted. This possibility can be used when cracking particularly heavy loads, by recovering the particles, and when one wants to eliminate any risk of tar condensations on the recovered particles, making them sticky, and making the installation inoperable.
• the furnace In all cases of in-line injection, the furnace is not disconnected from the downstream sections (direct quenching, compression, fractionation, etc.).
• impactor-diffuser designates a solid body, generally metallic located on the path of the flow and being able to deflect the gases according to several directions, and to obtain the direct impact, on itself, of a significant part of the particles incident solids carried by the gases, in order to avoid the direct impact of these particles on the downstream tube plate.
• impactor-diffuser opaque at least at 70%
• the projected surface of the various elements of the impactor-diffuser, on the section of the transfer duct represents at least 70% of this section.
• the section of the pipe is the area delimited by the circle corresponding to the inside diameter of the cylindrical pipe, just upstream of the cone, the surface being projected parallel to the axis of the pipe).
• the gas passages can be non-communicating or communicating, for example at the ends of solid surfaces which constitute the diffusing impactor, as will be described in FIG. 6. -., n ⁇ _ nM n
• the impactor-diffuser has a jet breaker function because of its position and its partial permeability to gases, according to a plurality of gas passages. There is therefore a burst of the main current into a plurality of secondary currents. These currents, or secondary jets tend to disperse and weaken much faster than a single central jet whose power is much greater; more these jets do not generally meet the tubular plate in the same place. This jetbreaking effect therefore effectively limits the risks of erosion.
• the impactor-diffuser has a second function of protection of the downstream tubular plate: as it is opaque at least 70% with respect to the current lines of the upstream flow, it therefore avoids the direct impact of the major part of the particles incident on the tubular plate.
• the injectors are arranged at a reduced distance upstream of the impactor-diffuser, the particle jets (which do not mix instantly with the cracked gases) are only very partially accelerated or dispersed at the time of their arrival at the impactor-diffuser level. These jets, poorly distributed in the cracked gases, therefore arrive at relatively slow speed, rebound, "burst" on the impactor-diffuser and disperse in the different free spaces of the impactor-diffuser.
• the injectors do not perform the spatial distribution function of the injection points by themselves, they do not need to be penetrating into the cone, which considerably limits their mechanical fragility and the risks of deformation .
• the impactors can all be arranged identically (no "spatial" distribution) there is no aerodynamic effect causing downstream pressure distortions between the different injectors, which considerably limits the risks of clogging .
• the distance L from the ends of the injectors upstream of the impactor-diffuser is between 0.1 x D and 1.0 x D (D being the diameter of the tubular plate), and preferably between 0.15 x D and 0.8 x D.
• the impactor-diffuser is at least 90% opaque, or substantially 100% opaque, seen from the transfer duct, which limits or substantially cancels the amount of particles passing through the impactor without bouncing, being braked and dispersed .
• the number of injection pipes is advantageously between 1 and 8, in particular and preferably between 2 and 6 (terminals included): in fact, due to the role of spatial dispersion of the particles played by the impactor-diffuser, it there is no need to ensure significant spatial dispersion by a very large number of injection points. Likewise, there is no need to use injection conduits comprising end pieces penetrating the flow of cracked gases.
• the ends of the injection pipes are situated substantially at the level of the internal surface of the assembly formed by the transfer pipe and the inlet cone.
• the ends of these injection conduits are located in the region of the inlet cone of the exchanger, and in particular are flush with the internal surface of this inlet cone. The use of injection points in the area of the inlet cone brings these injection points closer to the impactor-diffuser, which is favorable from the point of view of protection against erosion.
• the ends of the injection conduits may advantageously be situated at the same level, in the direction of flow of the effluents, for example at the same level of the internal surface of the cone d 'Entrance.
• the inlet cones of the quenching exchangers comprise, on the upstream side, a portion of the cone of frustoconical internal surface with an apex angle (overall) less than or equal to 20 °, and preferably 15 ° and typically close to 10 °.
• the particle injection conduits open out at this slowdown zone, in particular in the second downstream half of this zone. In this way, the speeding up of the particles is reduced since the cracked gases are already slowed down, or begin their slowdown immediately downstream of the injection points.
• the injection points are situated at a level where the cross-section of the flow is increased by at least 25%, and preferably between 40 and 400%, relative to the cross-section. passage of the terminal part of the transfer duct upstream of the quench exchanger.
• the permeability of the impactor-diffuser can be defined as the minimum vacuum fraction obtained by projecting the various sections of this impactor-diffuser, perpendicular to the axis of the cone, on the section of the transfer duct.
• this porosity will be at least 30%, and preferably between 40 and 60%.
• the impactor-diffuser can comprise solid surfaces and empty spaces, arranged according to at least two levels in the direction of flow of the effluents, the empty spaces at one of the two levels being substantially facing to solid surfaces on the other level.
• the impactor may consist of discs or O-rings of substantially circular, rectangular or square section, which can be mechanically connected together, as well as to the inlet cone of the exchanger, by fixing lugs, or a technical equivalent, compatible with expansion problems.
• the diffusing impactor may comprise a plurality of rectilinear bars, of rectangular, square or preferably circular section, substantially parallel and arranged in at least one level, preferably in two levels.
• the bars are supported by a single spacer, central and substantially perpendicular to the axis of these bars.
• the end of the bars is advantageously located at a distance d from the cone of at least 30 mm and preferably at least 50 mm. This allows evacuation of coke fragments from flaking in the furnace or in the pyrolysis tubes, upstream, in the substantially annular space around the impactor. This prevents obstruction of the impactor by coke fragments.
• the invention also provides a steam cracking process, which can be implemented in one of the installations described above, characterized in that effluent cracked gases are introduced from a steam cracking zone, via a transfer duct, flared at an angle less than or equal to 20 ° at the top, upstream of the tubular plate of a quench exchanger, so as to reduce the speed of these gases to a value between 0.07 and 0, 7 times their speed in the terminal part of the transfer duct, in that one injects into these gases whose speed is reduced, erosive solid particles, in a discontinuous manner, at a suitable distance at most 1 meter, upstream a gas permeable impactor-diffuser in a plurality of passages and opaque at least at 70% seen from the transfer duct, and that the mixture of particles and cracked gases is circulated downstream of the impactor-diffuser in the exchange tubes eur quenching, to limit its fouling, the quantities of particles injected being sufficient so that the outlet temperature of the quenching exchanger does not increase by more than 100 °
• This method makes it possible to greatly flexibilize a steam cracking installation intended for naphtha and to crack, for example, condensates, gas oils, or distillates under vacuum; process control (quantities of solid particles required) is very simple and follows from the examination of the outlet temperature of the quench exchanger, which provides reliable information on its degree of fouling, even under flexible conditions.
• the quantities of adequate solid particles depend very much on the charges, operating conditions, and on the choice of the erosive particles. Generally, between 20 and 3000 ppm will be injected, in particular between 20 and 1500 ppm of solid particles (average weight value relative to the cracked gases on a steam cracking cycle).
• the instantaneous flow rate may be, at the time of the injections, between 0.5 and 25% by weight relative to the cracked gases, in particular between 1 and 10%.
• the suitable particles are typically particles of average diameter (at point 50% by weight) of between 0.02 and 4 mm, in particular between 0.07 and 0.8 mm.
• angular for example at least 20%
• they can consist mainly of materials from the group formed by stabilized coke (in particular coke having been calcined at 850 ° C minimum), carbide silicon, and single or mixed oxides of silicon, aluminum and zirconium.
• FIG. 1 represents a supply of particles, according to a mode known from the prior art, with a multi-point spatial distribution.
• an indirect quenching exchanger (3) for the steam cracking effluents coming from a cracking zone with pyrolysis tubes, not shown, is connected to this zone by a transfer duct (1), opening into the cone. inlet (2) of the exchanger.
• This exchanger is of the multitubular type and comprises a plurality of tubes (4) for the circulation of cracked gases for their sudden cooling, connected to a tubular plate (5).
• injection ramps I
• injection points In
• the large number of points In, and the thermal, aerodynamic and chemical conditions (coking), are very unfavorable for this device, and in particular cause problems of blockage and deformation of the ramps.
• FIG. 2 represents the characteristic part of an installation according to the invention: injectors (I), in limited number (1 to 8 and preferably 2 to 6) make it possible to inject particles at the same level of the cone (2 ) of the quench exchanger.
• the injection conduits (I) open at the injection points, on the internal surface of the cone (2), just upstream of an impactor-diffuser, comprising a plurality of surfaces (A, B, C, F), as well as empty spaces (E) forming several gas passages.
• This impactor-diffuser is located opposite the transfer duct (1), downstream of the current lines of this transfer duct, symbolized by arrows.
• FIG. 2A schematically illustrates a top view of the surfaces ABCF of the impactor-diffuser seen from the tubular plate (5).
• the injection points located at the ends of the injection conduits (I) are arranged at a reduced distance L, upstream of the impactor-diffuser (by definition, of position defined by the solid surfaces the most downstream).
• L is smaller than the diameter (D) of the tubular plate (5) of the exchanger.
• this impactor comprises two levels of solid surfaces: A and C on the one hand, and B and F on the other hand, the empty spaces (E) at one of the levels being substantially opposite solid surfaces on the other level.
• A, B, C, F are O-rings (A, B, C) or a disc (F), of rectangular section; they can be made of refractory alloy (for example HK 40), and connected together and to the cone (2) by fixing lugs, or other mechanical devices not shown.
• refractory alloy for example HK 40
• the total angle of the cone at the level of the taps of the conduits (I) is preferably less than 20 ° and generally close to 10 °, which is not shown in the figure, for simple drawing reasons.
• the injectors (I) can be arranged perpendicular to the axis of the cone (according to the figure), or inclined upstream or even inclined downstream.
• FIGS. 3 and 4 show two other geometries of the impactor, comprising O-rings of circular section for FIG. 3, and rectangular for FIG. 4A.
• FIG. 5 presents various possible embodiments of the inlet cone, comprising a frustoconical zone of deceleration (FIGS. 5A and 5B) of total angle ⁇ ⁇ 15 °, or else without zone of deceleration , but with a "trumpet" profile (Figure 5C).
• FIGS. 5A and 5B show the channels I opening into the slowdown zone (in its second downstream half). The impactor-diffusers have not been shown in FIGS. 5A, B, C for simple drawing reasons.
• FIG. 6 illustrates another variant of a diffuser impactor (6) comprising a plurality of bars (6a, 6b, 6c), rectilinear, of circular section, substantially parallel and arranged in two levels. These bars are supported by a single central spacer (7) and substantially perpendicular to the axis of the bars. The end of the bars is located at a distance d from the cone of at least 30 mm.
• the projections of the bars are not contiguous, the projected free space being at most 30% of the total space seen from the duct.
• the bars of one row occupying the interstices of the other row.
• the installation according to the invention operates as follows: continuous or preferably discontinuous injections of solid particles are carried out, sequentially for each of the quench exchangers (or ovens, comprising several quench exchangers).
• the erosive solid particles are transported by pneumatic transport to the injection pipes (I), by a carrier gas such as fuel gas, nitrogen, or water vapor.
• the particles can be fed from a silo of new particles, or on the contrary be separated downstream from the quench exchangers and, at least in part, recycled.
• the pneumatic mode of transport can be transport in a dense phase, or in a diluted phase, in continuous or pulsed regime, and use means well known to those skilled in the art, such as valves, locks, feed screws. , referral.
• the non-homogeneous mixture of cracked gases / particles arrives at the level of the impactor-diffuser, where the gas is diffused by passages (E) in several directions; the majority (70% or 90% or 100%) of the particles rebound on the solid surfaces of the impactor-diffuser and are themselves diffused and dispersed secondarily through the passages (E), and around the impactor-diffuser , and are distributed correctly in the different tubes (4) of the exchanger.
• the quantities of particles which it is necessary to inject can be easily determined from the outlet temperature of the quench exchanger, the drift of which is sought to limit to a value below 30 ° C. per month, for example.
• the invention therefore makes it possible to respond favorably to all of the specifications of the technical problem posed, unlike the known devices.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Thermal Sciences (AREA)
• Physics & Mathematics (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Combustion & Propulsion (AREA)
• Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
• Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)
• Details Of Heat-Exchange And Heat-Transfer (AREA)

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• 1994
  • 1994-12-26 FR FR9415744A patent/FR2728582A1/fr active Granted
• 1995
  • 1995-12-22 ES ES95943265T patent/ES2146797T3/es not_active Expired - Lifetime
  • 1995-12-22 WO PCT/FR1995/001721 patent/WO1996020259A1/fr active IP Right Grant
  • 1995-12-22 EP EP95943265A patent/EP0800565B1/fr not_active Expired - Lifetime
  • 1995-12-22 DE DE69515699T patent/DE69515699T2/de not_active Expired - Fee Related
  • 1995-12-22 US US08/836,148 patent/US5965013A/en not_active Expired - Fee Related

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