US3597494A - Steam-cracking of hydrocarbons - Google Patents

Steam-cracking of hydrocarbons Download PDF

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US3597494A
US3597494A US855134A US3597494DA US3597494A US 3597494 A US3597494 A US 3597494A US 855134 A US855134 A US 855134A US 3597494D A US3597494D A US 3597494DA US 3597494 A US3597494 A US 3597494A
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fraction
temperature
gaseous
recycled
liquid
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US855134A
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English (en)
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Francois Bigache
Michel Lemee
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IFP Energies Nouvelles IFPEN
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IFP Energies Nouvelles IFPEN
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    • 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
    • C10G2400/00—Products obtained by processes covered by groups C10G9/00 - C10G69/14
    • C10G2400/20—C2-C4 olefins
    • 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 resulting liquid fraction is separated from the gaseous, uncondensed fraction in a first fractionation zone, a portion of the said liquid fraction, after passage through a first indirect heat exchange zone to lower its temperature, is used as first recycled liquid hydrocarbon stream, the gaseous fraction withdrawn from the first fractionation zone is admixed with a third, relatively cool stream of recycled liquid hydrocarbon, in order to further lower the temperature of this gaseous fraction down to about 140190 C.
  • the resulting gaseous frac tion is separated from the resulting liquid fraction in a second fractionation zone, a portion of the latter liquid fraction after passage through a second indirect heat exchange zone to lower its temperature, is used as the second and third recycled hydrocarbon streams, and the gaseous fraction of the second fractionation zone is withdrawn, said fraction containing the desired olefins.
  • the steam-cracking processes are broadly used for converting hydrocarbon feedstocks to lighter products.
  • the feedstock is contacted with steam at a temperature between 500 and 1200 C., preferably 750 to 900 C.
  • the feedstock may be a pure or substantially pure compound, for example ethane, or a hydrocarbon cut, for example a naphtha, a gas oil, or a mixture thereof.
  • olefins such as ethylene, light gases, gasolines, fuels or heavier products.
  • the outflow from the cracking zone may be subjected to a quick chilling elfected by various means, for example by admixing the eflluent with a cool liquid or by indirect thermal exchange.
  • a quick chilling elfected by various means, for example by admixing the eflluent with a cool liquid or by indirect thermal exchange.
  • the cracked material is maintained in the gaseous state in order to avoid the formation of coke deposits.
  • the cool effluent is usually subjected to a fractionation step in a separation column: gaseous products are removed at the top thereof.
  • gaseous products are removed at the top thereof.
  • 3 phases may appear: a gaseous phase containing the desired products, for example ethylene, an aqueous phase and an intermediary hydrocarbon phase, for example of the gasoline type.
  • a portion of the hydrocarbon phase is usually refluxed to the separation column.
  • condensed heavy products usually contain ing monoand poly-cyclic aromatic compounds. Under 3,5WAM Patented Aug. 3, l97i the usual distillation conditions, these heavy products have a boiling point of approximately 200 C.
  • Deposits of hard materials such as coke, may be formed at the bottom of this first separation column, which results in the plugging of the pipes, the stopping of the operation of the column and consequently that of the cracking furnace,
  • a main object of this invention is to avoid these inconveniences.
  • the cooling of the recycled portion of these heavy products usually permits to obtain steam at a relatively low pressure by indirect heat exchange, this steam being hardly usable in the process.
  • the dilution rate i.e. the ratio of steam to feedstock at the inlet of the cracking furnace, must be higher in order to obtain the same yield of olefins.
  • This rate may be, for example, 0.5/1 by weight for a naphtha and from 1/1 to 2/1 for a light or heavy gas-oil, these figures being not limitative.
  • the temperature of the gaseous outflow from the cooling zone must be higher: 500 to 700 C. for a gas oil instead of 300 to 500 C. for a naphtha in order to avoid coke deposits at the beginning of the condensation stage.
  • the further cooling necessary to obtain the inlet temperature of the primary separation column is thus greater. It is thus more important to recover thermal energy at a satisfactory level in that case than in the case of the cracking of lighter materials.
  • Another object of this invention is to improve the recovery of thermal energy.
  • Still another object of this invention is to crack heavy feedstocks while avoiding the above inconveniences.
  • the condensation of the heavy materials of the cooled cracking effluent is carried out in at least two separate zones having different average temperatures.
  • this invention relates to a process for producing olefins, wherein a mixture of steam with a hydrocarbon feedstock is heated up to a high temperature, the resulting gaseous cracked product is admixed successively with a first relatively cool stream of recycled liquid hydrocarbons and a second relatively cool stream of recycled liquid hydrocarbons so as to subject the temperature of the cracked product to a first decrease and condense a part thereof, the resulting liquid fraction is separated from the gaseous, uncondensed fraction in a first fractionation zone, a portion of the said liquid fraction, after passage through a first indirect heat exchange zone to lower its temperature, is used as first recycled liquid hydrocarbon stream, the gaseous fraction withdrawn from the first fractionation zone is admixed with a third, relatively cool stream of recycled liquid hydrocarbon, in order to further lower the temperature of this gaseous fraction and condense another portion thereof, the resulting gaseous fraction is separated from the resulting liquid fraction in a second fractionation zone, a portion of the latter liquid fraction, after passage
  • FIG. 1 is given for comparison purposes only and illustrates a conventional cracking unit.
  • FIG. 2 is an example of a unit operated according to the process of this invention, said process being welladapted for cracking heavy feedstocks.
  • a mixture of feedstock (for example naphtha or gas oil) introduced through line 1 and steam introduced through line 2 is passed through a cracking furnace 3 of the thermal or catalytic type.
  • the ratio of water to hydrocarbons of the feedstock is higher than 0.5 by weight and usually between 0.65 and 10.
  • the temperature is generally between 750 and 900 C. and the pressure between 1 and kg./cm.
  • the outflow from the cracking furnace may be conveyed through line 4 to the cooling zone 5.
  • the latter may consist of an indirect heat exchange device cooled by water, so as to produce steam.
  • the cooling zone 5 may be omitted and the cooling may be achieved by direct contact with the hydrocarbons of line 19.
  • the gaseous products at a temperature of, for example, 300 to 500 C. (case of naphtha) or 500 to 900 C. (case of gas oil) are admixed with the hydrocarbons recycled through line 19.
  • the resulting mixture at a temperature of about 140 to 190 C., is introduced through line 6 in the separation column 7. From the top thereof there is recovered gases through line 8, the latter being cooled in 9 and conveyed through line 10 to the separating vessel 11 in which two liquid phases may be separated: the aqueous phase is withdrawn through line 12 and an intermediary hydrocarbon phase is partly recycled to the column 7 as reflux, through line 13, and partly withdrawn through line 14.
  • the uncondensed gases evolve from the separating vessel 11 through line 15.
  • the partial condensation of the gaseous outflow 8 may be achieved in several different manners.
  • the exchanger 20 According to the temperature of the heavy products of lines 16 and 18, the exchanger 20 will be able or not to produce steam under a pressure useful on the industrial scale. Practically, these products are at a temperature of about 140 to 190 C. in line 16 and 100 to 150 C. in line 19.
  • FIG. 2 The same devices as those shown in FIG. 1 may be found in FIG. 2, i.e. the furnace, the cooling zone, the separation zone and others. All these devices are referenced by the same numerals as in FIG. 1.
  • the outlet temperature of the heat exchanger 5, the inlet temperature of column 7 and the temperatures of lines 16, 17, 18 and 19 are those given hereabove.
  • the temperature of pipe 26 is also about-100 to 150 C.
  • An additional device 21 is provided in the embodiment of FIG. 2, in order to condense and further partially separate heavy products at a temperature of about 195 to 230 C.
  • the latter are withdrawn in part through line 22 at the said temperature, while another part of this liquid outflow is admixed with the gaseous outflow from the cooling zone after passage through line 23, the heat exchanger 24 and line 25.
  • the outlet temperature of the heat exchanger 24 is about 165 to 200 C. In pipe 25, the temperature is about 150 to 190 C. In line 6, the temperature is about 195 to 230 C.
  • a unit such as shown in FIG. 2 is adapted for cracking heavy feedstocks of the light or heavy gas oil type, i.e. feedstocks normally boiling over C. with a 10% distillation point over 200 C. and a final point over 250 C.
  • the outflow from the cooling zone i.e. the gaseous product issued from device 5
  • the cooling zone is usually at a high temperature, for example about 500 to 900 C., preferably 550 to 650 C.
  • This vapor is valuable since it may be used directly for cracking the feedstock.
  • Lighter feedstocks such as naphthas may be also subjected to the treatment of this invention.
  • this invention offers other advantages. It has been shown that the outflow from the cracking zone contains solid particles such as coke which, in conventional processes, are deposited on the lower plates of column 7.
  • these solid particles are more selectively deposited in device 21. This is not inconvenient since this condensation device 21 has usually no plate (this is commonly a flask) so that it can be easily cleaned up. It is also possible to make use of several devices such as 21 in parallel so that the operation of one or more thereof is stopped for cleaning while at least one other is on run without requiring the stopping of the operation of the separation column 7.
  • temperatures given herebefore are illustrative and by no way limitative. Since the steam-cracking may be carried out within a broad temperature range even for a feedstock of a given type, it is obvious that the temperatures at the different steps are partly dependent on this cracking temperature.
  • distillation column may be operated with a water reflux at its upper part.
  • the heavy liquid from the separating vessel 21 runs in a circle through line 22, line 23, the cooling vessel 24, lines 25 and 6 and the device 21 while remaining in the liquid state. It withdraws from the chilled outflow a large amount of heat at a high level, the latter being recovered in the exchanger 24. Simultaneously it contributes to condense in 21 a part of the cooled heavy products.
  • the recycling of the heavy liquid of line 26 also contributes to cool down the gaseous outflow from the cooling zone. It also vaporizes at least in part, which increases the dew point of the mixture introduced in device 21, thus the temperature of the liquid of line 22 and also the amount of heat at a high temperature which is available in the exchanger 24.
  • the ratio of the liquid feed rates through lines 23 and 26 is preferably from 10/1 to 30/1 respectively, although ratios from 2/1 to 50/1 are convenient.
  • ratios by weight are advantageously selected between /1 and 30/1 (pipes 23 and 4), between 0.2 and 2 (pipes 26 and 4) and between 0.1 and 2 (pipes 19 and 4).
  • the ratio by weight of the heavy products condensed in the two zones, i.e. in apparatuses 21 and 7, may be selected, for example, between 0.5 and 2 and preferably at about 1.
  • the yield of ethylene was 21% by weight (without recycling at the furnace inlet).
  • the ratio of the feed rates in pipes 23 and 26 was 20.
  • a process for producing olefins wherein a mixture of steam with a hydrocarbon feedstock of the naphtha to gas oil range inclusive is heated up to about 5500-1200 C.
  • the resulting gaseous cracked product is admixed successively with a first relatively cool stream of recycled liquid hydrocarbons and a second relatively cool stream of recycled hydrocarbons so as to subject the cracked product to a first decrease of temperature down to about 195-230 C. and condense a part thereof, the resulting liquid fraction is separated from the gaseous, uncondensed fraction in a first fractionation zone, a portion of the said liquid fraction, after passage through a first indirect heat exchange zone to lower its temperature, is used as first recycled liquid hydrocarbon stream, the gaseous fraction withdrawn from the first fractionation zone is admixed with a third, relatively cool stream of recycled liquid hydrocarbon, in order to further lower the temperature of thsi gaseous fraction down to about 190 C.
  • the resulting gaseous fraction is separated from the resulting liquid fraction in a second fractionation zone, a portion of the latter liquid fraction after passage through a second indirect heat exchange zone to lower its temperature, is used as the second and third recycled hydrocarbon streams, and the gaseous fraction of the second fractionation zone is withdrawn, said fraction containing the desired olefins.

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  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
US855134A 1968-09-04 1969-09-04 Steam-cracking of hydrocarbons Expired - Lifetime US3597494A (en)

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FR165110 1968-09-04

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3718709A (en) * 1967-02-23 1973-02-27 Sir Soc Italiana Resine Spa Process for producing ethylene
US3907661A (en) * 1973-01-29 1975-09-23 Shell Oil Co Process and apparatus for quenching unstable gas
US3923921A (en) * 1971-03-01 1975-12-02 Exxon Research Engineering Co Naphtha steam-cracking quench process
US4096163A (en) * 1975-04-08 1978-06-20 Mobil Oil Corporation Conversion of synthesis gas to hydrocarbon mixtures
EP0031609A1 (fr) * 1979-12-21 1981-07-08 Shell Internationale Researchmaatschappij B.V. Procédé pour la récupération de chaleur d'un effluent d'un réacteur de pyrolyse d'hydrocarbures
US5073249A (en) * 1989-11-21 1991-12-17 Mobil Oil Corporation Heavy oil catalytic cracking process and apparatus
US20090326301A1 (en) * 2008-06-30 2009-12-31 Adam Kanyuh Two stage contact cooler design for hot water generation

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1390382A (en) * 1971-03-01 1975-04-09 Exxon Research Engineering Co Steam-cracking process
FR2463177A1 (fr) * 1979-08-07 1981-02-20 Uop Inc Procede de traitement thermique d'huiles hydrocarbonees lourdes
AU1800083A (en) * 1982-08-18 1984-09-27 Allis-Chalmers Corp. Condensing particles from gas using a fraction of the condensate as the primary coolant
AU3151793A (en) * 1991-12-11 1993-07-19 Exxon Chemical Patents Inc. Method for simplifying quench and tar removal facilities in steam crackers
US7101463B1 (en) 1999-05-05 2006-09-05 Metso Minerals Industries, Inc. Condensation and recovery of oil from pyrolysis gas
KR20020010633A (ko) * 1999-05-05 2002-02-04 추후제출 열분해 가스로부터 오일의 응축 및 회수

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3718709A (en) * 1967-02-23 1973-02-27 Sir Soc Italiana Resine Spa Process for producing ethylene
US3923921A (en) * 1971-03-01 1975-12-02 Exxon Research Engineering Co Naphtha steam-cracking quench process
US3907661A (en) * 1973-01-29 1975-09-23 Shell Oil Co Process and apparatus for quenching unstable gas
US4096163A (en) * 1975-04-08 1978-06-20 Mobil Oil Corporation Conversion of synthesis gas to hydrocarbon mixtures
EP0031609A1 (fr) * 1979-12-21 1981-07-08 Shell Internationale Researchmaatschappij B.V. Procédé pour la récupération de chaleur d'un effluent d'un réacteur de pyrolyse d'hydrocarbures
US5073249A (en) * 1989-11-21 1991-12-17 Mobil Oil Corporation Heavy oil catalytic cracking process and apparatus
US20090326301A1 (en) * 2008-06-30 2009-12-31 Adam Kanyuh Two stage contact cooler design for hot water generation
US8735642B2 (en) * 2008-06-30 2014-05-27 Uop Llc Two stage contact cooler design for hot water generation

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FR1604213A (fr) 1971-10-04
DE1944383A1 (de) 1970-03-12
GB1234499A (fr) 1971-06-03

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