Classifications

• • 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
• • 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

Definitions

• the invention relates to a flexible hydrocarbon steam cracking process, that is to say compatible with a wide variety of fillers to be cracked and a wide variety of operating conditions. It also relates to a process for decoking the steam cracking installation.
• 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 conventional cycle times (operation between two complete chemical decokings of the cracking zone, in air and / or steam) are either fixed (programmed stops), or variable depending on the coking of the installation, and s typically range from 3 weeks to 12 weeks for fillers such as naphtha and liquefied petroleum gases.
• This process consists, for a determined charge, in allowing a layer of coke to form and mature on the internal walls of the cracking coil, then to inject erosive particles (for example hard mineral particles, of diameter less than 150 micrometers, spherical , or angular) in sufficient quantity to substantially stabilize the coking state of the tubes, without completely eliminating the coke pre-layer which has a protective role for these tubes.
• erosive particles for example hard mineral particles, of diameter less than 150 micrometers, spherical , or angular
• This process requires a good knowledge of the coking speeds of the charge in question, and a coil design such that there is a certain correspondence between the local coking speeds linked to the progression of cracking along the coil and the erosive intensity. linked to the velocity profile along the coil and to the nature of the erosive particles.
• the decoking efficiency has been found to depend significantly on the charges and operating conditions (different nature of the coke).
• the light charges C3, C4, light Naphtha produce at the start of the reaction zone a catalytic coke much more fragile (5 to 10 times) than the asymptotic coke predominant in the middle and at the end of the reaction zone It is therefore desirable for these charges to limit the speed of circulation in this zone, to maintain a protective coke layer and / or avoid the risk of erosion of the cracking tubes.
• the carbon deposits of the quenching exchanger in particular in the case of heavy loads, were much more fragile than the coke of the cracking tubes. It was, in fact, found that the brittleness, with respect to the erosion by the solid particles tested, was at least 25 times greater for the coke of the quench exchanger than for the asymptotic coke of the pyrolysis tubes.
• the absence of erosion noted for the exchanger tubes themselves is explained by the fact that the circulation speed of the particles is much lower in the quench exchanger than in the pyrolysis tubes, and that their temperature is very low (approximately 330 ° C against typically 1000 to 1100 ° C for the pyrolysis coil).
• the tubes of the quenching exchangers are straight, without bends, which eliminates the risks of occasional erosion
• the object of the process according to the present invention is to provide a flexible, efficient, reliable steam-cracking process with moderate investment, suitable for modern ovens comprising a large number of primary quench exchangers.
• a process for steam cracking hydrocarbon feedstocks is proposed in an installation comprising at least one steam cracking oven comprising a plurality of pyrolysis tubes connected by a plurality of pipes to means for indirectly quenching the effluents of the pyrolysis tubes, these means comprising at least one secondary quenching multitubular exchanger connected upstream to a plurality of primary quenching exchangers and downstream to direct quenching and fractionation, the process comprising the injection of erosive solid particles to remove at least part of the carbon deposits located on the internal walls of the installation, the process being characterized in that.
• solid erosive particles of average diameter between 0.02 and 4 mm, at at least one point of the installation located downstream of said primary transfer line exchangers and upstream of the secondary quench exchanger, the particles then circulating in the secondary quench exchanger conveyed by a carrier gas whose average speed is advantageously between 20 and 180 m / s, and preferably 40 to 130 m / s .
• the overall average quantities [Q + q] of erosive particles injected being determined to limit the increase in the outlet temperature of the effluents from the secondary quench exchanger to a value less than 100 ° C. per month and preferably less than 50 ° C per month, and to allow an operation of the steam cracking oven for at least 6 months and preferably at least 12 months, and more particularly at least 18 months, without hydraulic decoking of the indirect quenching means
• mineral erosive particles are injected during the steam cracking phases, downstream of the primary exchangers and upstream of the secondary exchanger, at fixed or variable intervals between 0 , 3 and 72 hours and at least most of the particles are separated, downstream of the secondary exchanger, the amounts of particles injected being sufficient to limit the increase in the temperature of the exchanger effluents to a value not exceeding 50 ° C. per month.
• solid erosive coke particles are injected during the steam cracking phases, downstream of the primary quench exchangers and upstream of the secondary exchanger, these particles being conveyed without separation, downstream of the secondary exchanger to the downstream direct quenching and fractionation means, the quantities injected being sufficient to limit the increase in the temperature of the effluents in the exchanger to a value not exceeding 50 ° C. per month.
• At least 90% by weight or even 100% of the quantities of particles injected are during air and / or steam decoking phases and are removed by a decoking line.
• all of the erosive solid particles injected upstream of the secondary exchanger is injected downstream of the primary exchangers.
• the invention also provides a steam cracking installation comprising at least one steam cracking oven comprising a cracking zone comprising a plurality of pyrolysis tubes connected downstream by a plurality of transfer pipes to a plurality of primary quench exchangers, these exchangers of primary quenching being connected downstream to at least one secondary quenching exchanger itself connected downstream to direct quenching and fractionation means, characterized in that it comprises:
• metering and injection means for erosive solid particles connected to at least one point of the installation located downstream of the primary exchangers and upstream of the secondary exchanger, for the introduction downstream of these exchangers by 70% weight at least of the solid particles introduced upstream of the secondary exchanger, • means for measuring the temperature of the effluent from the exchanger to allow control of its degree of fouling, and
• decoking means in the presence of air connected to the pyrolysis tubes upstream, for establishing decoking conditions in the pyrolysis tubes and the primary exchangers.
• the process according to the invention is a mixed decoking process
• the pyrolysis tubes and the primary quenching exchangers are mainly decoked in air (generally in a mixture with steam), with a reduced or zero circulation of erosive solid particles, to prevent any risk of erosion.
• the decoking of the secondary quenching exchanger (s) includes elimination of coke by erosion (there may also be partial decoking in air during the decoking phases of the pyrolysis tubes and of the primary exchangers).
• the process which therefore differs from the process with particle injection upstream of all the quenching exchangers, is based on the following analysis and technical results:
• the cracked gases are only partially cooled (by example from 850 ° C to 500/550 ° C)
• the high gas temperatures tend to limit condensations of heavy polyaromatics precursors of coke, and also to increase the skin temperatures at the gas / coke wall interface of the heat exchanger. quenching.
• the coking of these exchangers remains relatively moderate, even with heavy or coking charges.
• the permissible outlet temperature of these exchangers is high (for example 550/620 ° C.) They can therefore operate with long durations.
• the secondary quench exchangers operate with much lower temperatures (360 to 450 ° C at the outlet), which favors condensation of polyaromatic compounds, and much faster coking, in particular with charges heavy or coking
• the process according to the invention which therefore comprises essentially air decoking of the primary exchangers and at least partially erosive decoking of the secondary quench exchangers is therefore very well suited to these technical results.
• the advantage of this process compared to that previously described (injection upstream of all the quench exchangers) is very important for the type of ovens considered:
• the injection is easier to carry out, since it is carried out in an area at a lower temperature.
• FIG. 1 shows a part of a steam cracking oven (1) according to the invention.
• a plurality of pyrolysis tubes (2) supplied with a hydrocarbon feedstock and water vapor by lines (10) and (1 1) and located in the radiation zone of the furnace. They are connected downstream by a plurality of transfer pipes (3) to a plurality of primary quench exchangers (4a). These exchangers are connected downstream to a secondary quench exchanger (4b) by a line (12). Downstream of this exchanger, the effluents are sent to the means (5) of direct quenching and fractionation by a line (6a), or else evacuated, during the decoking phases (air and / or steam) via the decoking line (6).
• the oven also includes means (7, 7a) for metering and injecting erosive solid particles immediately upstream of the secondary exchanger (4b).
• This oven operates in a conventional manner, with cracking phases, and decoking phases, in air and / or in steam, after the injection of the hydrocarbons has been stopped.
• particles are injected continuously or preferably discontinuously by the means (7 and 7a) to reduce or eliminate the coking problems of the exchanger (4b).
• the particles can be injected during the operating phases of the furnace, that is to say either during periods of steam cracking or during periods of decoking.
• the particles can be mineral (for example corundum), made up of coke, possibly metallic.
• the particles are not made up of coke, it will be necessary either to collect them downstream of the exchanger (4b) or to inject them only during decoking phases so that they are evacuated by the decoking line ( 6). Separation means, not shown, such as a cyclone can be installed, downstream of the exchanger (4b) or on the decoking line (6).
• the installation described in FIG. 1 could also include means for injecting limited quantities of erosive particles (less than 30% by weight on annual average) upstream of the pyrolysis tubes (2) or between the tubes (2) and the primary exchangers (4a), but the preferred variant consists in injecting all of the particles immediately upstream of the exchanger (4b).
• a steam cracking furnace comprising 40 pyrolysis tubes (2) in a U (pins), connected to 20 primary quench exchangers (4a) of the double tube type, connected to two secondary quench exchangers (4b).
• the primary exchangers cool the cracked gases to a temperature between 480 and 620 ° C, the secondary exchangers lowering their temperature between 360 and 450 ° C.
• the cycle time between two air decoking is typically 2 months, and the duration between two hydraulic decoking exchangers is 6 to 8 months.
• the cycle times can drop significantly below three weeks, and the hydraulic decoking of the exchangers is necessary at intervals of 3 to 4 months or less.
• erosive particles for example corundum
• the air decoking times are extended: 36 to 48 hours, against 15 to 24 hours strictly necessary for decoking the pyrolysis tubes, in order to properly decoke the primary exchangers.
• coking charges it is possible, with coking charges, to increase the cycle times notably beyond 1 month, and almost eliminate the hydraulic decoking, which eliminates a major easement.
• the invention therefore provides a very significant improvement in the case of ovens comprising a large number of primary quench exchangers.

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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 FR9607870A patent/FR2750138B1/fr not_active Expired - Fee Related
• 1997
  • 1997-06-24 JP JP10502444A patent/JP2000512680A/ja active Pending
  • 1997-06-24 US US09/202,925 patent/US6183626B1/en not_active Expired - Fee Related
  • 1997-06-24 EP EP97930570A patent/EP0907694A1/de not_active Ceased
  • 1997-06-24 WO PCT/FR1997/001117 patent/WO1997049783A1/fr not_active Ceased

Non-Patent Citations (1)

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