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
• • 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 a single controlled injection of solid particles.
• 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. It is also possible to inject particles during air decoking phases, during the circulation of air or air / vapor mixtures in the installation.
• 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 load and dilution rate, pressure drop and skin temperature of the tubes are no longer reliable indicators of the state of coking of a bundle of pyrolysis tubes which cannot therefore be known and controlled in real time.
• a new process which combines chemical decoking (for example with air), at least preponderant, of pyrolysis tubes with decoking, at least in part by erosion, of the quench exchangers.
• This process comprises therefore 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 pressurized water circulation 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 upstream cracking zone corresponding.
• This term of inlet cone used generally, must be considered in a non-restrictive manner and represents the intermediate part at the inlet of the exchanger, making it possible to pass from the transfer duct to the tubular plate of the exchanger, much larger diameter.
• This transformation can be conical in the strict sense, in trumpet, or according to other evolutionary forms
• the process does not require a strictly equal distribution of the quantities of particles in each tube, but relatively small distribution differences are sought, and it is in particular necessary to avoid that one of the tubes collects 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 tube plate of the exchanger.
• the particle introduction and distribution device must therefore be both: • robust to withstand high temperatures, the risk of impact and erosion,
• the injection manifolds are generally straight or circular conduits, comprising injection nozzles or orifices. This known solution was expei imentee for the application considered, and quickly abandoned for multiple reasons
• One of the objects of the invention is to remedy the drawbacks of the prior art and to respond to the technical problems mentioned above.
• This device has a large number of advantages with respect to technical problems l)
• the particles injected immediately upstream of the impactor-diffuser do not have time to be fully accelerated before their impact on the impactor-diffuser, which reduces the risk of erosion.
• the impactor-diffuser comprising a plurality of gas passages makes it possible to diffuse the gases and the particles in a plurality of directions and to improve the distribution (distribution) of the particles in the different tubes of the exchanger.
• the impactor-diffuser being essentially opaque seen from upstream avoids the direct impact of at least most of the particles on the tube plate; the particles which rebound on the impactor-diffuser lose part of their kinetic energy, which reduces the risks of erosion, and rebound with variable angles, which gives a dispersing effect and improves the distribution of the particles in the various exchanger tubes.
• the permeability of the impactor-diffuser finally makes it possible to properly supply particles to the tubes placed just behind the impactor-diffuser.
• a number of injection points has been described between 1 and 8, but preferably between 2 and 6 (in sufficient number to improve the distribution of the particles), the injectors being oriented mainly in a substantially radial manner, in directions directed towards or near the axis of the cone.
• the devices described effectively make it possible to obtain the desired technical results, but at the cost of a plurality of injection lines, which requires the implementation of a plurality of injection lines and upstream particle distribution means. between the different injection lines.
• These multiple injection lines typically each comprising a shut-off valve provided for the high temperatures of the downstream injection point (for example 850 ° C.) are therefore relatively complex and expensive.
• the object of the installation and of the method according to the invention is to propose a technical solution to the problem posed, notably simpler to implement and therefore also less expensive and more reliable.
• a single axial injection is used placed immediately upstream of the multitubular quench exchanger.
• the furnace comprises several tubular exchangers arranged in parallel, there will therefore be, according to the invention, several injection lines but a single line for each of the exchangers.
• 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 1 direct impact, on itself, of a significant part of the solid particles incident 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 terminal section of the transfer duct represents at least 70% of this section.
• the section of the duct is the area delimited by the circle corresponding to the inside diameter of the transfer duct just upstream of the cone, the surface being projected parallel to the axis of the cone).
• the section considered is that of the terminal part of the duct, downstream of the Y or the bend, parallel to the tube plate
• the gas passages can be non-communicating or communicating, for example at the ends of solid surfaces which constitute 1 diffusing impactor, as will be dec ⁇ t later
• the distance L from the ends of the injector to the impactor-diffuser is between 0.1 x D and 1.5 x D, D being the diameter of the tube plate and preferably between 0.15 x D and 1.2 x D
• the impactor-diffuser will advantageously be approximately 90% opaque, seen from the transfer duct, and even 100%
• the impactor-diffuser advantageously comprises surfaces arranged according to two levels, and offset so that the surfaces at one level are facing voids at the other level.
• the impactor-diffuser comprises a plurality of straight bars, preferably of circular section, substantially parallel and arranged according to at least two levels substantially perpendicular to the axis of the cone, the bars being offset so that the solid surfaces of the bars of one of said levels are substantially opposite empty spaces at the other level
• the transfer duct comprises a bend disposed immediately upstream of the inlet cone, the injection duct being connected to the transfer duct just at this bend
• the transfer conduit comprises two branches connected in Y immediately upstream of the inlet cone, the injection conduit being connected to the transfer conduit just at the point of connection of the two branches forming a Y
• the invention also provides a steam cracking process in a steam cracking installation, characterized in that one injects, preferably discontinuously, just upstream of a multitubular quench exchanger comprising an inlet cone, solid particles erosive by a single injection line, arranged substantially on the axis of the exchanger inlet cone, in sufficient quantity to limit the increase in the temperature of the exchanger effluents to a value below 100 ° C per month and preferably less than 30 ° C per month.
• the hydraulic decokings of the exchanger can thus be spaced at intervals of at least 6 months and preferably at least 18 months.
• 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 ramps (I), only one of which is shown, with a plurality of injection points (In) to achieve the spatial distribution of the particles.
• FIGS. 2A and 2B represent the characteristic part of an installation according to the invention.
• a single injector or injection pipe (I) typically tubular, arranged along the axis of the cone (2) and opening into the cone, makes it possible to inject particles just upstream of an impactor-diffuser (6), 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 parallel arrows
• FIG. 2B schematically illustrates a top view of the surfaces ABCF of the impactor-diffuser seen from the tube plate (5)
• the injection point located at the end of the injection pipe (I) is disposed at a reduced distance (L), upstream of the impactor-diffuser (by definition, of defined position by the most downstream solid surfaces)
• (L) is smaller than the diameter (D) of the tube 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 the solid surfaces on the other level
• A, B, C, F are either straight bars or O-rings (A, B, C) or a disc (F), and are of rectangular section, they can be made of refractory alloy (for example HK 40) , and connected to each other and to the cone (2) by fixing lugs, or other mechanical devices not shown
• FIGS. 3A, 3B illustrate another variant of a diffuser impactor (6) comprising a plurality of bars (6a, 6b, 6c), rectilinear, substantially perpendicular to the axis of the exchanger, 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, and preferably 80 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.
• a totally opaque impactor seen from the upstream duct (1) will be used, the bars of one row occupying the space opposite the interstices of the other row
• Figure 4 shows a part of an installation, according to a first characteristic variant
• the gas transfer conduit c ⁇ qués (l) has a bend immediately upstream of the inlet cone (2) of the exchanger
• the injection pipe (I) which opens inside the transfer pipe is connected at the elbow, which allows the particles to be well injected in the direction of the axis of the cone.
• This device is much more effective for particle distribution that a device where the injection pipe (I) would bend inside an axial transfer pipe (1)
• the impactor-diffuser (6) comprises rectilinear bars perpendicular to the plane shaped by the elbow and the axis of the cone (2)
• the cone (2) has a substantially conical internal part (8), made of a refractory metal alloy opening opposite the impactor-diffuser (6)
• This impactor-diffuser (6) is mechanically fixed to the internal cone (8) by fixing lugs (1 1) shown in dotted lines
• Refractory concrete (9) is placed between the internal metallic cone (8) and the external metallic wall (10) of the cone (2) in order to reduce the internal free volume of the cone (2 ) and lower the temperature of the outer wall of the cone (2)
• the cracked gas transfer duct (1) comprises two branches which are connected by forming a Y, just upstream of the inlet cone (2)
• the injection pipe (I) is connected to the transfer pipe (1) substantially at the point of connection of the two branches of the Y. This symmetrical arrangement is very efficient from the point of view of the distribution of the particles in the exchanger tubes
• the installation according to the invention operates in the following manner, injections, preferably discontinuous, of solid particles are carried out, sequentially for each of the quenching exchangers (or ovens, comprising several quenching exchangers)
• the erosive solid particles are transported by transport pneumatic to the injection pipes (I), by a carrier gas such as fuel gas, nitrogen, or water vapor
• the particles can be supplied from a silo of new particles, or on the contrary, be separated downstream of the quench exchangers and, in part at least, recycled.
• the pneumatic transport mode can be transport in dense phase, or in dilute phase, in continuous or pulsed regime, and use movens well known in the art. skilled in the art, such as valves, locks, feed screws, switches
• the non-homogeneous gas / particle mixture arrives at the level of the impactor-diffuser, or the gas is diffused by passages (E) (fig 2A) in several directions; the majority (50%, 70% or 90% or 100%) of the particles bounce off 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
• This injection mode according to the invention with a single injection pipe disposed substantially on the axis of the inlet cone of the exchanger and directed substantially along this axis, has unexpectedly proved to be as effective as devices ⁇ multiple injection pipes such as three or four pipes radially substantially radially

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)

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• 1996
  • 1996-06-25 FR FR9607871A patent/FR2750139B1/fr not_active Expired - Fee Related
• 1997
  • 1997-06-24 EP EP97930571A patent/EP0907695A1/de not_active Ceased
  • 1997-06-24 WO PCT/FR1997/001118 patent/WO1997049784A1/fr not_active Application Discontinuation
  • 1997-06-24 JP JP10502445A patent/JP2000512681A/ja active Pending
  • 1997-06-24 US US09/202,787 patent/US6160192A/en not_active Expired - Fee Related

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