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
  • C10G9/14—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

• the invention relates to a method for thermal decoking of a device for the thermal cracking of hydrocarbons, the cracking tubes arranged in a cracking zone and a subsequent cracking gas cooler for cooling the cracked products by indirect heat exchange with a.
• Has cooling medium a gas stream containing water vapor and oxygen is passed through the can and the can gas cooler.
• a common decoking process for the cracked gas cooler therefore consists in cooling the system and then separating the cracked gas cooler from the cracking zone and cleaning it mechanically.
• This cleaning can be carried out by means of a water jet which emerges from a nozzle under very high pressure, for example 700-1000 bar, and causes the deposits to come off.
• This method This usually takes about three days, but is not only time-consuming, but also leads to thermal stress on the system due to the periodically repeated heating and cooling cycles, which limits the life of the can.
• the invention therefore has for its object to embody a method of the kind referred to so that the cost and time is reduced for the "decoking.
• cooling medium is passed through the cracked gas cooler even during decoking, that in a first process stage the gas stream is passed through the device in such an amount that the temperature of the deposits on the heat-exchanging surfaces of the cracked gas cooler in the area the operating temperature prevailing in the thermal fission and that in a second process stage the gas flow is amplified to such an extent that the temperature of the deposits on the heat-exchanging surfaces of the fission gas cooler is increased.
• a major disadvantage of this known cracked gas cooler can be seen in the fact that the temperature of the tubes in the cracked gas cooler is subject to large fluctuations. This is particularly important because the pipes are arranged in a high-pressure container, which has an operating pressure in the order of 100 bar, for example. If in such a container, compared to the operating temperature in the order of magnitude of 300 ° C, heating to over 700 ° C is carried out at regular intervals, special measures must be taken for the operational safety of such a cracked gas cooler. In addition, this well-known fission gas cooler deviates from the most commonly used type.
• straight heat exchange tubes In contrast to conventional cracked gas coolers, it does not use straight heat exchange tubes, but rather spirally arranged coils. A transfer of this known concept to straight tube constructions would not be possible due to the thermal expansion or shrinkage when the temperature rises or when cooling back to operating temperature. Straight tube constructions are preferred, among other things, because a corrosion-inhibiting magnetite layer is formed on the outside of the tubes during operation, which is retained in the event of larger temperature fluctuations, while in the case of tube coils this layer is chipped and thus a. increased susceptibility to corrosion occurs.
• a gas mixture containing water vapor and oxygen usually a mixture of water vapor and air, is passed through the cracking plant, the deposits in the cracking tubes being burnt off in the manner customary hitherto.
• the major part of the coke is removed from the can, while the can gas cooler is cleaned only slightly, since the temperature is too low for it to burn up.
• the second process stage follows, in which a substantially larger amount of the gas mixture is passed through the plant.
• the canned tubes are cleaned further and the coke in the cracked gas cooler is largely broken down. This is due to the fact that the gas mixture is passed through the cracked gas cooler in such an amount that the temperature of the coke deposits on the inner wall of the tubes increases to such an extent that a noticeable water gas reaction begins. This temperature increase is possible despite the cooling of the pipes because the thermal conductivity of the coke layer is very low.
• a gas mixture containing water vapor and oxygen is also used in the second stage of the process, although only water vapor is actually required for the water gas reaction.
• the presence of oxygen is advantageous for the rate at which the coke is broken down in the cracked gas cooler. This is due to the fact that the water gas reaction is catalyzed by trace components from the pipe materials, in particular chromium and nickel, which are contained in the coke by diffusion from the pipe materials. However, this catalytic effect only occurs when the sulfur components contained in the coke have always been broken down.
• the presence of oxygen in the gas stream now causes that the pivoting elspuren f are mainly converted to S0 2, so that they can no longer act as a catalyst poison.
• the temperature of the decolourization gases at the outlet from the cracked gas cooler is at least 400.degree. It has been shown that the rate of coke degradation in the cracked gas cooler is too low at lower temperatures to ensure an effective decoking treatment. If the amount of decoking gas is kept constant during the second stage of the process, it is expedient to choose the outlet temperature at the beginning of the second stage of the process considerably above the minimum temperature of approximately 400 ° C., since the outlet temperature increases as the temperature increases Decoking decreases and the minimum temperature should not be fallen below.
• the deposition layer in the tubes is continuously thinner, thereby improving the heat exchange with the refrigerant so that the outlet temperature decreases with the progress of decoking.
• a termination of the decoking process can therefore be easily determined by checking the outlet temperature, since in this case it remains practically constant.
• the high-severity fission of a heavy atmospheric gas oil resulted in a fission gas cooler outlet temperature of 634 ° C after 60 days of operation at an oven outlet temperature of 800 ° C, which indicated strong coking.
• a steam-air mixture to a ground speed of 25 kg / sm 2 is used in the cracking gas cooler, the furnace outlet temperature was 750 0 C.
• the mass velocity in the cracked gas cooler was increased to 45 kg / sm 2 and the furnace outlet temperature to 800 ° C. After a two hour induction period during which the coke breakdown rate was slow, there was a marked increase in the coke breakdown rate.
• the coke extraction rate is the lowering of the cracked gas cooler outlet temperature during decoking under completely constant conditions.
• the coke extraction rate during the induction period was 2 K / h, but then reached a maximum value of 15 K / h. This second phase of decoking was ended after 16 hours.
• the cracked gas cooler is decoked step by step, whereby in each step the gas flow is only passed through part of the heat-exchanging surface. It is essential here that the heat-exchanging surface is reduced during the decoking of the cracked gas cooler, in order in this way to achieve a temperature increase in the sections through which flow occurs.
• this can be done, for example, by passing the entire stream of decoking gas through only part of the cooling tubes while other tubes are being shut down.
• the heat supply to the individual sections of the coked cracked gas cooler can hereby be increased to such an extent that the temperatures required for a sufficiently strong water gas reaction are reached.
• this increase in temperature is not possible by exclusively increasing the mass throughput because the gas stream is then no longer heated to the required high temperature when it passes through the gap zone.
• the complete decoking of the cracked gas cooler takes place in this embodiment of the invention in that after decoking a first part of the heat-exchanging surface, the latter is shut off and the gas flow is then passed through a further part in which the process is repeated. This process is continued until the entire cracked gas cooler is decoked.
• the process according to the invention can be carried out in the cracking of heavy hydrocarbons using the cracked gas coolers usually used for this purpose.
• a modified cracked gas cooler is used, which, in addition to the usual features such as a gas inlet hood, a gas outlet hood, and cooling pipes surrounded by a coolant, also has shut-off devices that allow part of the cooling pipes to be shut down becomes. It has proven to be advantageous to arrange the shut-off elements in the area of the gas outlet hood of the cracked gas cooler. Since the shut-off elements are arranged in the colder part of the cracked gas cooler in this way, a structurally simpler design is possible.
• shut-off devices arranged in the area of the gas inlet hood must remain functional at temperatures of, for example, 850 ° C. it is sufficient to provide valves in the area of the outlet hood which are functional at temperatures up to, for example, 550 ° C.
• a particularly simple way of dividing the heat-exchanging surface of the cracked gas cooler has been found to be to split the gas outlet hood into several separate areas. Each region is associated with a 'number of cooling tubes in each compound, and has a closable gas outlet on.
• the only structural change compared to conventional cracked gas coolers is the subdivision of the gas outlet hood and can therefore be carried out at low cost even with existing systems.

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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)

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Citations (3)

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• 1980
  • 1980-06-04 DE DE8080103123T patent/DE3060219D1/de not_active Expired
  • 1980-06-04 EP EP80103123A patent/EP0021167B1/fr not_active Expired
  • 1980-07-28 IN IN863/CAL/80A patent/IN153444B/en unknown
• 1981
  • 1981-07-08 US US06/281,344 patent/US4376694A/en not_active Expired - Fee Related

Patent Citations (3)

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