US3557241A - Decoking of onstream thermal cracking tubes with h20 and h2 - Google Patents

Decoking of onstream thermal cracking tubes with h20 and h2 Download PDF

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Publication number
US3557241A
US3557241A US768065A US3557241DA US3557241A US 3557241 A US3557241 A US 3557241A US 768065 A US768065 A US 768065A US 3557241D A US3557241D A US 3557241DA US 3557241 A US3557241 A US 3557241A
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tubes
decoking
cracking
steam
feed
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US768065A
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English (en)
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John A Kivlen
Ihor Koszman
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ExxonMobil Technology and Engineering Co
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Exxon Research and Engineering Co
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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
    • C10G9/14—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
    • 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

  • This invention relates to a process for decoking the tubes of a cracking furnace. More particularly, this invention relates to an improved process for decoking steam cracking tubes while maintaining the furnace onstream and continuing the cracking process. Still more particularly, this invention relates to an onstream decoking process whereby the hydrocarbon feed to at least one tube in the cracking furnace is cut out and a decoking feed comprising steam and/or water and hydrogen is passed through said tube or tubes and the coke is removed.
  • Coke deposition is believed to be due to the formation of free radicals, e.g., when ethane is cracked methylene radicals can -be formed, which may then polymerize with other unsaturate components into long chain compounds and dehydrogenate to form coke on the tube walls.
  • the coke tends to build up and, therefore, reduces the effective cross-sectional area of the tube necessitating higher pressures to maintain a constant throughput.
  • coke is an excellent thermal insulator
  • its formation is accompanied by a sharp increase in furnace tube temperature, in order to maintain l 3,557,241 ce Patented Jan. 19, 1971 cracking efficiency, thereby resulting in a decrease in tube life and the limiting of the craking temperature that can be employed (which also limits conversions and yields).
  • the coke lbuildup is such that the furnace must be shut down for decoking with a consequent loss in production capacity.
  • an im,- proved process of the decoking of steam cracking tubes whereby the hydrocarbon feed to at least one tube is cut out and a decoking feed comprising steam and/or water and hydrogen is passed through said tube or tubes while maintaining the remaining tubes onstream, i.e., in normal service, continuing to crack hydrocarbon feed in the remaining tubes, and maintaining the temperature level of the tube or tubes rbeing decoked essentially the same as the temperature level in the tubes remaining onstream.
  • This invention has the advantage of lending a decoking capability to the steam cracking process which allows decoking of one or more tubes while maintaining furnace temperatures and continuing to make product.
  • this invention contemplates the decoking of only a single tube at a time in the furnace, thereby not substantially reducing the conversion capacity of the furnace as a whole, or the decoking of any number of tubes simultaneously or successively, or the decoking all of the tubes of the furnace simultaneously. Nevertheless, because the vapor load on downstream equipment increases with an increase in the number of tubes being simultaneously decoked by this method, it is preferred that only a minor portion of the tubes in a steam cracking furnace :be decoked by this method at any one time. After the decoking operation has been completed, the clean tubes are returned to normal service by reintroducing the hydrocarbon feed, adjusting the steam/water rate, and cutting out the hydrogen.
  • This induction period is believed to be caused by the presence of sulfur (which is present in some amount in almost every steam cracking feed) which coats the trace elements thereby masking their catalytic effect. Only when the sulfur is removed do the trace metals become active catalysts.
  • the process of this invention eliminates or substantially decreases this induction period due to the presence of hydrogen in the decoking feed, the hydrogen acting as a desulfurization agent:
  • the quantities of steam and/or water that are used during the decoking process are predetermined to Imeet the following criteria.
  • the temperature of the decoking feed, i.e., steam/ water and hydrogen, entering the section of the furnace to be decoked i.e., cracking section, should be about 700 F. or higher. If water is employed, it must be vaporized and superheated while steam need only be superheated.
  • the mass rate of decoking feed entering the furnace section to be decoked should preferably be greater than pounds per second per square foot of tube internal cross-sectional area when tube outlet pressure is in the order of -25 p.s.i.a.
  • Higher mass rates at constant temperature reduce the time required for decoking.
  • Higher operating pressures in the furnace tubes being decoked require higher mass rates of steam for the same decoking time. (It is noted, however, that in this invention it is preferable to conduct the decoking operation at pressures as low as possible, e.g., atmospheric, since lower pressures tend to increase the decoking rate.)
  • the supply of' steam and/or water and hydrogen can be cut off from the decoked tube and feed may be simultaneously reintroduced.
  • the completion of the decoking operation can be monitored by any one of several methods, such as l) decrease in pressure drop across the section of the furnace being decoked, (2) decrease in tube metal temperature, or (3) rate of carbon monoxide formation (cf. Equation l, CO will increase during decoking but fall off sharply when little or no coke is left in the tube).
  • FIG. l wherein the flow path of the reactants through an apparatus for thermal cracking of hydrocarbons is illustrated diagrammatically.
  • the cracking furnace 10 comprises an upper, convection or preheat section 11 and a lower, cracking zone 12.
  • Burners 13 are provided on the side walls and/or on the bottom of the furnace to supply heat. The number of burners provided is dependent upon the heat required and may vary considerably.
  • the furnace contains several conduits or passes in parallel. Each pass may contain a number of connected tubular members or tubes that provide a flow path through the convection section and into the cracking section. ln the drawing, one pass is shown, with the tubes in the convection section 11 designated by the numeral 15 and thecracking coils or tubes in the cracking zone 12 designated by the numeral 16. It is to be understood that the number of conduits or tubes in the furnace is a function of the size of the furnace and is dictated solely by design considerations.
  • Hydrocarbon feed stock is supplied to the steam cracker via supply conduit 20 and manifold or distributor conduit 21 to the several parallel cracking conduits or passes.
  • a control valve 22 is provided on each conduit 23 connecting the feed distributor 21 to each of the cracking conduits or tubes.
  • Steam, ⁇ or in the decoking operation, steam and/or water are supplied through inlet line 24and valve 25 to the conduit 23. (In some cases, steam and water are supplied through separate lines and not necessarily at the identical point in the convection section.) Hydrogen is mixed with the steam or water inlet from line 26 through valve 27.
  • reaction products are discharged from the coils or tubes 16 of the cracking furnace via conduits 28 into conduit or header 29 from which they are discharged into conduit 30.
  • quenching agents such as higher boiling hydrocarbons and/or water are supplied through conduit 31 and control valve 32.
  • the mixture of quenched reaction products and quenching agent is discharged via conduit 30 into fractionating tower 33.
  • Aromatic tar product is withdrawn from the bottom of fractionating tower 33 through line 34 and product is taken overhead via line 35.
  • Other intermediate boiling range fractions may be withdrawn as product or recycled to a higher plate in the fractionating tower as one or more reflux streams.
  • the quench oil may be Withdrawn from the fractionating tower 33 through line 36 and passed through heat exchanger 37 where it is passed in indirect heat exchange relation to the hydrocarbon feed stock for preheat thereof or to water for steam formation while cooling the quench oil to a suitable temperature for discharge through line 31 and valve 32 into the reaction product stream in line 30 as described above.
  • the onstream decoking procedure requires the closing of one of the hydrocarbon feed valves 22 and the opening of the steam water valve 25.
  • the amount of steam and water passed through the decoking conduit 24 is adjusted so that the steam temperature inside the pass is about 700 F. or higher at the point'of transition from convection'tubes 15 to cracking tubes 16.
  • valves 25 and 27 are closed and valv 22 is opened.
  • FIG. 2 depicts a graphical portrayal of the increase in decoking rate due to the presence of hydrogen in a steam/ water decoking feed.
  • the figure shows carbon monoxide formation plotted against the mole fraction of water in a decoking feed of water and hydrogen as a function of temperature.
  • decoking by steam/water involves the water gas reaction and, therefore, carbon monoxide make is directly related to decoking rate.
  • Examination of FIG. 2 shows that an H2O mole fraction of zero, the rate of decoking is zero.
  • the steam cracking operation is vold and Well known (see, for example, Chemical Week, Nov. 13, 1965, p. 72 et seq), and will only be briefly described hereinbelow.
  • the petroleum feed fraction is admixed with steam, i.e., in amounts ranging from about 20-95 mole percent steam, prior to entry into the steam cracking furnace which may be heated by any suitable means, e.g., gas firing, etc.
  • the furnace itself normally contains two sections, a convection section wherein the feed is vaporized, if not already in that form and preheated, and a radiant or cracking section, the feed being passed in admixture with steam through one or more furnace tubes located within the furnace.
  • the convection section is normally employed to increase heating eiciency and the petroleum-steam mixture is heated therein to intermediate temperatures, i.e., about 100G-1100" F. How.
  • the heated feed then passes into the radiant section, i.e., the cracking zone, where the temperature of the reactants is quickly raised to about 1200-1700 F., preferably 1500-1700 F., or higher, as tube metal materials permit, and the feed is cracked.
  • raising the temperature of the reactants to the mentioned ranges requires heating the tubes to about 1400-2000" F., preferably 1600-2000 F. and higher as tube materials permit.
  • Residence times in the radiant section are carefully controlled to minimize polymerization and other undesirable reactions. Thus, residence times in the cracking zone will range from about 0.1-10 seconds, preferably 0.1-1 second.
  • Pressures within the tubes may range from about -50 p.s.i.g. but are not critical, and higher pressures e.g., up to about 100 p.s.i.g. can be tolerated.
  • the reaction products are immediately quenched to stop further reaction and/or minimize loss primary conversion products.
  • hydrocarbon feeds consisting essentially of cyclic or acyclic saturated hydrocarbons.
  • hydrocarbons that may be utilized herein include such cyclic hydrocarbons as cyclopropane, cyclobutane, cyclopentane, cyclohexane, cyclooctane, cyclododecane, etc., and mixtures thereof.
  • Acyclic hydrocarbon feeds include any alkane, namely, aliphatic hydrocarbons of the methane series or mixtures of alkanes with cycloalkanes.
  • Preferred feeds are those saturated hydrocarbons containing from 2 to about 24 carbon atoms, more preferably alkanes containing 2 to about 12 carbon atoms, e.g., ethane, propane, butane, isobutane, hexanes, heptanes, etc., n-hexadecane, eicosane, and light naphthas boiling in the range of 90- 430" F., gas oils of 450-800 F., or higher boiling points, and kerosenes of 430-550" F. boiling points can also be effectively cracked in this process.
  • the improvement which comprises taking at least one of the tubes oifstream by cutting out the ow of hydrocarbon fed and passing a decoking feed containing hydrogen and a component selected from the group consisting of water, steam, and mixtures thereof, the mole ratio of said component to hydrogen being from about 1:1 to about 3:1, through the tubes in suicient amount to maintain the temperature of the decoking feed in the offstream tubes at essentially the same level as in the tubes remaining onstream, thereby effecting the removal of coke from the interior of the offstream tubes, and thereafter returning the offstream tubes to onstream operation.
  • the lmprovement which comprises taking at least one of the tubes offstream by cutting out the flow of hydrocarbon feed and passing a decoking feed containing hydrogen and a component selected from the group consisting of steam, water, and mixtures thereof, the mole ratio of said component to hydrogen being from about 2:1 to about 3:1, through the tubes in sufficient amount to maintain the temperature of the decoking feed in the oifstream tubes at essentially the same level as in the tubes remaining onstream, continuing the supply of decoking feed through the offstream tubes fol a period sufficient to effect removal of coke on the interior of the offstream tubes, and thereafter returning the offstream tubes to onstream operation.

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  • Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (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)
US768065A 1968-10-16 1968-10-16 Decoking of onstream thermal cracking tubes with h20 and h2 Expired - Lifetime US3557241A (en)

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BE (1) BE739923A (enrdf_load_stackoverflow)
CA (1) CA926799A (enrdf_load_stackoverflow)
DE (1) DE1948635C3 (enrdf_load_stackoverflow)
FR (1) FR2020790B1 (enrdf_load_stackoverflow)
GB (1) GB1266433A (enrdf_load_stackoverflow)
NL (1) NL161494C (enrdf_load_stackoverflow)
SE (1) SE344961B (enrdf_load_stackoverflow)

Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3818975A (en) * 1971-07-13 1974-06-25 Idemitsu Petrochemical Co Method of removing carbonaceous matter from heat exchange tubes
US4203963A (en) * 1977-12-12 1980-05-20 United Technologies Corporation Staged vaporization of liquid hydrocarbon fuels
EP0036151A1 (de) * 1980-03-15 1981-09-23 BASF Aktiengesellschaft Verfahren zur thermischen Entkokung von Spaltgaskühlern
US4469587A (en) * 1983-09-02 1984-09-04 Intevep, S.A. Process for the conversion of asphaltenes and resins in the presence of steam, ammonia and hydrogen
US4902403A (en) * 1987-10-30 1990-02-20 Ashland Oil, Inc. Heat treatment of exchangers to remove coke
US4904368A (en) * 1987-10-30 1990-02-27 Ashland Oil, Inc. Method for removal of furfural coke from metal surfaces
US4908121A (en) * 1986-05-12 1990-03-13 The M. W. Kellogg Company Flexible feed pyrolysis process
US4917787A (en) * 1983-10-31 1990-04-17 Union Carbide Chemicals And Plastics Company Inc. Method for on-line decoking of flame cracking reactors
US5932089A (en) * 1997-01-24 1999-08-03 Atlantic Richfield Company Petroleum coker cooling method with minimum coke drum stress
US20070031307A1 (en) * 2004-05-21 2007-02-08 Stell Richard C Process and apparatus for removing coke formed during steam cracking of hydrocarbon feedstocks containing resids
US20100174130A1 (en) * 2009-01-05 2010-07-08 Spicer David B Process for Cracking a Heavy Hydrocarbon Feedstream
US20100191031A1 (en) * 2009-01-26 2010-07-29 Kandasamy Meenakshi Sundaram Adiabatic reactor to produce olefins
US20100252072A1 (en) * 2009-04-06 2010-10-07 Synfuels International, Inc. Secondary reaction quench device and method of use
CN102083944A (zh) * 2008-07-11 2011-06-01 埃克森美孚化学专利公司 裂解烃原料的炉的在运转中脱焦的方法
WO2013093640A2 (en) 2011-12-21 2013-06-27 Hyl Technologies, S.A. De C.V. Method and apparatus for production of direct reduced iron (dri) utilizing coke oven gas
US20180291283A1 (en) * 2017-04-07 2018-10-11 Citgo Petroleum Corporation Online coke removal in a heater pass
US20220315421A1 (en) * 2019-04-12 2022-10-06 Synhelion Ag Process and apparatus for cracking hydrocarbon gases

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3920537A (en) * 1974-06-05 1975-11-18 Toscopetro Corp Process for on-stream decoking of vapor lines
CA1232856A (en) * 1983-10-31 1988-02-16 Akinobu Fukuhara Method for on-line decoking of flame cracking reactors
US5190634A (en) * 1988-12-02 1993-03-02 Lummus Crest Inc. Inhibition of coke formation during vaporization of heavy hydrocarbons

Cited By (26)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3818975A (en) * 1971-07-13 1974-06-25 Idemitsu Petrochemical Co Method of removing carbonaceous matter from heat exchange tubes
US4203963A (en) * 1977-12-12 1980-05-20 United Technologies Corporation Staged vaporization of liquid hydrocarbon fuels
EP0036151A1 (de) * 1980-03-15 1981-09-23 BASF Aktiengesellschaft Verfahren zur thermischen Entkokung von Spaltgaskühlern
US4420343A (en) * 1980-03-15 1983-12-13 Basf Aktiengesellschaft Process for the thermal decoking of cracked gas coolers
US4469587A (en) * 1983-09-02 1984-09-04 Intevep, S.A. Process for the conversion of asphaltenes and resins in the presence of steam, ammonia and hydrogen
US4917787A (en) * 1983-10-31 1990-04-17 Union Carbide Chemicals And Plastics Company Inc. Method for on-line decoking of flame cracking reactors
US4908121A (en) * 1986-05-12 1990-03-13 The M. W. Kellogg Company Flexible feed pyrolysis process
US4904368A (en) * 1987-10-30 1990-02-27 Ashland Oil, Inc. Method for removal of furfural coke from metal surfaces
US4902403A (en) * 1987-10-30 1990-02-20 Ashland Oil, Inc. Heat treatment of exchangers to remove coke
US5932089A (en) * 1997-01-24 1999-08-03 Atlantic Richfield Company Petroleum coker cooling method with minimum coke drum stress
US20070031307A1 (en) * 2004-05-21 2007-02-08 Stell Richard C Process and apparatus for removing coke formed during steam cracking of hydrocarbon feedstocks containing resids
US7670573B2 (en) * 2004-05-21 2010-03-02 Exxonmobil Chemical Patents Inc. Process and apparatus for removing coke formed during steam cracking of hydrocarbon feedstocks containing resids
CN102083944A (zh) * 2008-07-11 2011-06-01 埃克森美孚化学专利公司 裂解烃原料的炉的在运转中脱焦的方法
CN102083944B (zh) * 2008-07-11 2016-05-04 埃克森美孚化学专利公司 裂解烃原料的炉的在运转中脱焦的方法
US20100174130A1 (en) * 2009-01-05 2010-07-08 Spicer David B Process for Cracking a Heavy Hydrocarbon Feedstream
US8684384B2 (en) 2009-01-05 2014-04-01 Exxonmobil Chemical Patents Inc. Process for cracking a heavy hydrocarbon feedstream
US8815080B2 (en) * 2009-01-26 2014-08-26 Lummus Technology Inc. Adiabatic reactor to produce olefins
US20100191031A1 (en) * 2009-01-26 2010-07-29 Kandasamy Meenakshi Sundaram Adiabatic reactor to produce olefins
US20100252072A1 (en) * 2009-04-06 2010-10-07 Synfuels International, Inc. Secondary reaction quench device and method of use
US8137476B2 (en) 2009-04-06 2012-03-20 Synfuels International, Inc. Secondary reaction quench device and method of use
US8434505B2 (en) 2009-04-06 2013-05-07 Synfuels International, Inc. Secondary reaction quench device and method of use
WO2013093640A2 (en) 2011-12-21 2013-06-27 Hyl Technologies, S.A. De C.V. Method and apparatus for production of direct reduced iron (dri) utilizing coke oven gas
US9725778B2 (en) 2011-12-21 2017-08-08 Hyl Technologies, S.A. De C.V. Method and apparatus for production of direct reduced iron (DRI) utilizing coke oven gas
US20180291283A1 (en) * 2017-04-07 2018-10-11 Citgo Petroleum Corporation Online coke removal in a heater pass
US10968399B2 (en) * 2017-04-07 2021-04-06 Citgo Petroleum Corporation Online coke removal in a heater pass
US20220315421A1 (en) * 2019-04-12 2022-10-06 Synhelion Ag Process and apparatus for cracking hydrocarbon gases

Also Published As

Publication number Publication date
NL161494C (nl) 1980-02-15
DE1948635A1 (de) 1970-07-16
DE1948635C3 (de) 1978-10-26
GB1266433A (enrdf_load_stackoverflow) 1972-03-08
FR2020790B1 (enrdf_load_stackoverflow) 1973-12-21
NL6914981A (enrdf_load_stackoverflow) 1970-04-20
NL161494B (nl) 1979-09-17
DE1948635B2 (de) 1978-02-23
FR2020790A1 (enrdf_load_stackoverflow) 1970-07-17
CA926799A (en) 1973-05-22
BE739923A (enrdf_load_stackoverflow) 1970-04-07
SE344961B (enrdf_load_stackoverflow) 1972-05-08

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