EP0036151A1 - Process for thermally decoking coolers for cracked gases - Google Patents

Process for thermally decoking coolers for cracked gases Download PDF

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Publication number
EP0036151A1
EP0036151A1 EP81101665A EP81101665A EP0036151A1 EP 0036151 A1 EP0036151 A1 EP 0036151A1 EP 81101665 A EP81101665 A EP 81101665A EP 81101665 A EP81101665 A EP 81101665A EP 0036151 A1 EP0036151 A1 EP 0036151A1
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EP
European Patent Office
Prior art keywords
cracked gas
gas cooler
cracked
air
heated
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EP81101665A
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German (de)
French (fr)
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EP0036151B1 (en
EP0036151B2 (en
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Artur Dr. Sliwka
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BASF SE
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BASF SE
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B08—CLEANING
    • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
    • B08B9/00—Cleaning hollow articles by methods or apparatus specially adapted thereto 
    • B08B9/02—Cleaning pipes or tubes or systems of pipes or tubes
    • B08B9/027—Cleaning the internal surfaces; Removal of blockages
    • B08B9/032—Cleaning the internal surfaces; Removal of blockages by the mechanical action of a moving fluid, e.g. by flushing
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B08—CLEANING
    • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
    • B08B2230/00—Other cleaning aspects applicable to all B08B range
    • B08B2230/01—Cleaning with steam

Definitions

  • the present invention relates to a method for thermal decoking of cracked gas coolers for indirect cooling by means of water of ethylene-containing cracked gases which are obtained by thermal cracking of hydrocarbons in the presence of steam in an indirectly heated tubular cracking furnace.
  • Thermal cracking of hydrocarbons in the presence of water vapor in an indirectly heated tube cracking furnace is widely used in ethylene plants (steam crackers), in which, in addition to ethylene, there are other valuable unsaturated compounds such as propylene and butadiene as well as pyrolysis gasoline with a high proportion of aromatic hydrocarbons such as benzene , Toluene and xylene can be obtained.
  • steam crackers in which, in addition to ethylene, there are other valuable unsaturated compounds such as propylene and butadiene as well as pyrolysis gasoline with a high proportion of aromatic hydrocarbons such as benzene , Toluene and xylene can be obtained.
  • dwell times for the hydrocarbons in the cracked tubes of the tubular cracking furnace of 0.1 to 0.5 seconds and exit temperatures of the cracked gases from the cracked tubes of more than 750 ° C., generally between 800 and 900 ° C., are preferably observed .
  • the cracked gas has to be cooled immediately after leaving the tubular cracking furnace in order to prevent undesired side reactions which lead to a reduction in the yield of valuable products.
  • This can be done directly by injecting liquid hydrocarbons or water into the hot cracked gas.
  • direct cooling has the disadvantage that when the heat is recovered in the form of water vapor, the water vapor obtained has only a low pressure level.
  • the process has a considerable disadvantage, namely the deposition of coke on the inner walls of both the cracked tubes in the tube furnace and the inlet hood and the cooling tubes in the downstream cracked gas cooler. Due to the insulating effect of the coke, the tube wall temperature of the canned tubes of the tubular cracking furnace increases and the pressure loss increases. In the downstream cracked gas cooler, the heat transfer is deteriorated by the coke deposit, so that the temperature of the cracked gas rises at the outlet of the cracked gas cooler. Once the coke deposits have reached a certain strength, the tube cracking furnace must be switched off together with the downstream cracking gas cooler and the coke removed.
  • the canned tubes are generally freed of coke with a water vapor / air mixture or only with water vapor or with a mixture of water vapor and hydrogen (cf. DE-OS 19 48 635) at temperatures of 700 ° C to 1000 ° C .
  • the cracked gas cooler is cleaned mechanically.
  • This method is very complex and requires a longer one '' Shutdown time of the tube cracking furnace and therefore a corresponding loss of production in the ethylene plant.
  • the tube cracking furnace is usually cooled.
  • the cracked gas cooler is opened and the individual pipes of the cracked gas cooler, for example with more than 50 pipes, are used for mechanical cleaning, e.g. with a high-pressure water device, at a water pressure of usually 300 to 700 bar or in the case of very hard coke deposition by means of water / sand blasting from the coke freed.
  • a major disadvantage of this method is that the material of the furnace is subjected to excessive stress as a result of the frequent cooling and subsequent heating, and damage often occurs as a result.
  • the method described above is modified in such a way that one first cools the tube cracking furnace at 200 0 C to 400 ° C, then separating the gas cooler of the tube cracking furnace and performs the mechanical cleaning of completely cooled cleavage gas cooler, while the cracking tubes the cracked gas cooler with a water vapor / air mixture. But even here, only a small amount of time is saved, especially since the change in temperature and the stress on the canned tubes of the tubular cracking furnace can cause coke to separate from the inside of the canned tubes and thus create additional problems.
  • the coke in the cracked gas cooler is only removed to a small extent due to the lower temperatures that arise in the one-line decoking in the cracked gas cooler.
  • the disadvantage that the temperature at which the cracking gas emerges from the cracking gas cooler does not drop to the value of a mechanically cleaned cooler, but is only slightly lower than before the shutdown, so that a correspondingly smaller amount of high pressure steam is generated in the cracked gas cooler.
  • mechanical cleaning of the cracked gas cooler with all the disadvantages described is necessary.
  • the invention was therefore based on the object of a method for the thermal decoking of cracked gas coolers to make available, which does not have the disadvantages of the known methods.
  • the cracked gas coolers can be decoked thermally without the need for additional mechanical cleaning of the cracked gas cooler and the associated cooling of the upstream tube cracking furnaces.
  • the known methods for example in the one-line decoking described above, only annual runtimes of the tube cracking furnaces of 85 to 95% are achieved, annual runtimes of more than 97% and thus correspondingly are reduced by reducing the downtimes get higher ethylene production.
  • fewer replacement tube cracking furnaces are required in the ethylene plant due to the increased operating time, which reduces the investment costs for the ethylene plant.
  • cracked gas coolers are thermally decoked, which are used for indirect cooling by means of water of ethylene-containing cracked gases, the cracked gases being obtained by thermal cracking of hydrocarbons in the presence of steam in an indirectly heated tubular cracking furnace at gas outlet temperatures above 750 ° C.
  • Suitable starting hydrocarbons for thermal cracking are ethane, propane, butane, LPG, gasoline fractions such as light petrol, e.g. light petrol with a boiling range of approx. 30 to 150 ° C, gasoline (full-range naphtha), e.g. gasoline with a boiling range of approx. 30 up to 180 ° C, heavy gasoline, e.g. heavy gasoline with a boiling range of approx.
  • the method is preferably used for cracked gas coolers for cooling cracked gases obtained from gasoline fractions, kerosene and / or gas oils.
  • the Austrittstem p eraturen of the cracking gas from the tubular cracking furnace amount to more than 750 ° C, preferably 780-900 ° C, in particular 800 to 900 ° C.
  • the residence times in the tube cracking furnaces are generally 0.05 to 1 sec., Preferably 0.1 to 0.6 sec., In particular 0.1 to 0.5 sec.
  • the thermal loads on the canned tubes in the tubular cracking furnaces are expediently 40,000 to 80,000 kcal / m 2 . h, v o rz UGS as 50,000 to 70,000 kcal / m 2 .h.
  • the weight ratio of water vapor to the hydrocarbon used is L.
  • thermal splitting generally 0.1: 1, preferably 0.2: 0.8, in particular 0.3: 0.7.
  • heated air is passed through the cracked gas cooler to be decoked without the addition of water vapor. It is also possible to use heated mixtures of air and oxygen instead of heated air to accelerate decoking.
  • the volume ratio of air to oxygen is generally 100: 1 to 1: 100, preferably 100: 1 to 1:50, in particular 100: 1 to 1:10 however, because of the easy availability, use heated air alone without additional oxygen for decoking.
  • the cracked gas cooler inlet temperature for the heated air or the air / oxygen mixture is generally 600 to 1100 ° C, preferably 700 to 1050 ° C, in particular 800 to 1000 ° C.
  • Decoking can be carried out while maintaining slightly reduced pressure in the cracked gas cooler, e.g. in the range of 0.5 to 1 bar.
  • atmospheric pressure or increased pressure are used in the cracked gas cooler.
  • the pressures are expediently 1 to 50 bar, preferably 1 to 20 bar, in particular 1 to 10 bar.
  • elevated pressures of 2 to 50 bar, preferably 5 to 40 bar.
  • the thermal decoking of the cracked gas cooler is expedient in the cracked gas cooler on the boiling side Water maintain a vapor pressure of 80 to 160 bar, preferably 90 to 150 bar, in particular 100 to 130 bar.
  • the ratio of the amount of heated air or the heated air / oxygen mixture passed through per hour during the thermal decoking to the amount of hydrocarbon passed through per hour during the thermal cracking is 0.05 to 5, preferably 0.1 to 3 , in particular 0.1 to 2.
  • the cracked gas cooler is decoked to such an extent that the exit temperature of the cracked gas from the cracked gas cooler corresponds to the initial value of the exit temperature of the cracked gas cooler from the cracked gas cooler at the start of the first start-up of the cracked gas cooler or after mechanical cleaning of the cracked gas cooler.
  • the cracked gas cooler is completely freed of the coke after about 20 to 30 hours and then has the above-mentioned initial value of the starting temperature of the cracked gas after restarting.
  • the course and the end of the decoking process can be followed in a simple manner by determining the carbon dioxide concentration in the gas mixture introduced into the cracked gas cooler and the gas mixture emerging from the cracked gas cooler.
  • the air or the air / oxygen mixture can be heated in a separate oven, bypassing the tube cracking furnace or tubes belonging to the cracked gas cooler, to the cracked gas cooler inlet temperatures and passed through the cracked gas cooler.
  • the air or the air / oxygen mixture in the associated tubular cracking furnaces is preferably heated to the inlet temperature for the cracked gas cooler and passed through the downstream cracked gas cooler.
  • the cracked tubes of the upstream tube cracking furnace are first decoked. This is expediently carried out in such a way that, after the addition of the hydrocarbon to be split has been prevented, a water vapor / air mixture is passed through the indirectly heated cracking tubes of the tube cracking furnace and at the same time through the downstream cracking gas cooler, and after the decoking of the cracking tubes of the tube cracking furnace has ended, the water vapor supply is prevented and only air or the air / oxygen mixture are passed through the indirectly heated canned tubes of the tubular cracking furnace and the downstream cracked gas cooler.
  • outlet temperatures for the gas mixture leaving the tube cracking furnace are generally used, which are between 600 and 11000C, preferably between 700 and 1050 ° C, in particular between 700 and 900 ° C .
  • the water vapor / air mixture used expediently has a weight ratio of water vapor to air of 100: 1 to 2: 8, preferably 9: 1 to 3: 7, expediently using a water vapor / air mixture with a very low air content , for example less than 10% by weight of air, or water vapor alone begins and then rises 'Mixing sufficient amounts of air, for example up to an air content of 70% by weight in the water vapor / air mixture.
  • a mixture of 2.2 t / h of a gasoline fraction (naphtha) with a boiling range of 40 to 180 ° C and 1.05 t / h of water vapor is passed through in a tube cracking furnace, which contains four cracking tubes, and at a furnace exit temperature of 850 ° C split.
  • the cracked gas from 2 cracked tubes is cooled in a downstream cracked gas cooler.
  • the cooler outlet temperature is 350 ° C.
  • this cracked gas cooler outlet temperature finally rises to 450 ° C, the highest outlet temperature permitted for the cracked gas cooler.
  • the hydrocarbon flow through the tube cracking furnace is interrupted and the cracked tubes and the cracked gas cooler are decoked in a conventional manner by passing a water vapor / air mixture through the cracked tubes and the downstream cracked gas cooler.
  • 1.0 t / h of water vapor and 0.08 t / h of air are initially passed through each can.
  • the air throughput is slowly increased and the water vapor throughput is reduced until finally a water vapor / air mixture with 70 vol.% Air is passed through each can. This state is maintained for a further 6 hours, so that the entire decoking process takes 16 hours.
  • the tubular cracking furnace is operated as described in the first paragraph of the comparative example, initially to produce the cracked gas with the addition of naphtha and water vapor and, after reaching the maximum permissible cracked gas cooler outlet temperature of 450 ° C., is subjected to the decoking of 16 hours described in the first paragraph of the comparative example.
  • the water vapor throughput is then completely prevented and only air in an amount of 1.3 t / h per can is passed through. This corresponds to a weight ratio of 0.59 of the amount of air passed per hour per can to the amount of hydrocarbon passed per hour during the thermal cracking.
  • a furnace exit temperature of 850 0 C is maintained.
  • a cracked gas cooler outlet temperature of 335 ° C is reached.
  • High pressure steam of 125 bar continues to be generated during these 30 hours.
  • the tube cracking furnace is again passed through by passing 2.2 t / h of naphtha and 1.05 t / h of steam each Canned tube put into operation.
  • 2.2 t / h of gas oil and 1.7 t / h of water vapor are split in a tube cracking furnace at a furnace exit temperature of 830 ° C.
  • the cracked gas cooler outlet temperature in the clean state is 550 ° C with a steam pressure on the water side of 125 bar.
  • the cracked gas cooler outlet temperature rises to 650 ° C, the highest outlet temperature permitted for the cracked gas cooler.
  • the hydrocarbon stream is interrupted and, as described in Example 1 and in the comparative example, first a mixture of water vapor and air with a slowly increasing air content (until a water vapor / air mixture with 70% by volume of air is reached) through the can and the downstream gas cooler passed.
  • the canned tubes of the tubular cracking furnace are completely cleaned, while the cracked gas cooler has only been cleaned slightly.
  • air alone is first heated without passing water vapor while passing through the cracking tubes of the tubular cracking furnace and then passed through the cracking gas cooler.
  • a complete removal of coke from the cracked gas cooler is achieved after only 15 to 20 hours of passage of air, so that when the tube cracking furnace is put back into operation with the addition of gas oil and steam, the temperature of the cracked gas leaving the cracked gas cooler is again 550 ° C. in accordance with a mechanically cleaned one Cooler.

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Abstract

Die vorliegende Erfindung betrifft ein Verfahren zur thermischen Entkokung von Spaltgaskühlern für die indirekte Abkühlung mittels Wassers von ethylenhaltigen Spaltgasen, die durch thermische Spaltung von Kohlenwasserstoffen in Gegenwart von Wasserdampf in einem indirekt beheizten Röhrenspaltofen bei Spaltgasaustrittstemperaturen oberhalb 750°C erhalten werden, durch Indurchleiten eines erhitzten Gasgemisches aus Wasserdampf und Luft durch die mit Koks belegten Rohre des Spaltgaskühlers, bei dem anstelle des erhitzten Wasserdampf-/Luft-Gemisches erhitzte Luft ohne Zuführung von Wasserdampf durch die zu entkokenden Rohre des Spaltgaskühlers geleitet wird.The present invention relates to a process for the thermal decoking of cracked gas coolers for indirect cooling by means of water of ethylene-containing cracked gases, which are obtained by thermal cracking of hydrocarbons in the presence of water vapor in an indirectly heated tubular cracking furnace at cracked gas outlet temperatures above 750 ° C., by passing a heated gas mixture through it from water vapor and air through the coke-coated pipes of the cracked gas cooler, in which heated air is passed through the pipes of the cracked gas cooler to be decoked instead of the heated steam / air mixture.

Description

Die vorliegende Erfindung betrifft ein Verfahren zur thermischen Entkokung von Spaltgaskühlern für die indirekte Abkühlung mittels Wasser von ethylenhaltigen Spaltgasen, die durch thermische Spaltung von Kohlenwasserstoffen in Gegenwart von Wasserdampf in einem indirekt beheizten Röhrenspaltofen erhalten werden.The present invention relates to a method for thermal decoking of cracked gas coolers for indirect cooling by means of water of ethylene-containing cracked gases which are obtained by thermal cracking of hydrocarbons in the presence of steam in an indirectly heated tubular cracking furnace.

Das thermische Spalten von Kohlenwasserstoffen in Gegenwart von Wasserdampf in einem indirekt beheizten Röhrenspaltofen findet eine weit verbreitete Anwendung in Ethylenanlagen (Steamcracker), in denen neben dem Ethylen noch weitere wertvolle ungesättigte Verbindungen wie Propylen und Butadien sowie Pyrolysebenzin mit einem hohen Anteil an aromatischen Kohlenwasserstoffen wie Benzol, Toluol und Xylol gewonnen werden. Die weitere Entwicklung des Verfahrens hat zu immer kürzeren Verweilzeiten in den Spaltrohren des Röhrenspaltofens und zu immer höheren Spalttemperaturen geführt. Bei den modernen Verfahren werden bevorzugt Verweilzeiten für die Kohlenwasserstoffe in den Spaltrohren des Röhrenspaltofens von 0,1 bis 0,5 sec. und Austrittstemperaturen der Spaltgase aus den Spaltrohren von mehr als 750°C, in der Regel zwischen 800 und 900°C, eingehalten. Bei diesen extremen Bedingungen muß das Spaltgas nach Verlassen des Röhrenspaltofens sofort abgekühlt werden, um unerwünschte Nebenreaktionen, die zur Herabsetzung der Ausbeute an wertvollen Produkten führen, zu unterbinden. Dies kann auf direkte Art durch Einspritzen von flüssigen Kohlenwasserstoffen oder von Wasser in das heiße Spaltgas erfolgen. Die direkte Abkühlung hat jedoch den Nachteil, daß bei der Zurückgewinnung der Wärme in Form von Wasserdampf der erhaltene Wasserdampf nur ein niedriges Druckniveau aufweist. Im allgemeinen zieht man es daher vor, die Abkühlung der Spaltgase indirekt vorzunehmen, indem die Spaltgase durch einen Spaltgaskühler geleitet werden, in welchem die Spaltgase in indirektem Wärmeaustausch mit Wasser gekühlt werden. Dabei erzeugt man hochgespannten Dampf mit einem Druck bis zu 150 bar,. vorzugsweise bis 130 bar. Dieser Hochdruckdampf trägt zur Wirtschaftlichkeit des Verfahrens bei, da er den überwiegenden Teil der Antriebsenergie für die Rohgas- und Kältekompressoren der Ethylenanlagen liefert.Thermal cracking of hydrocarbons in the presence of water vapor in an indirectly heated tube cracking furnace is widely used in ethylene plants (steam crackers), in which, in addition to ethylene, there are other valuable unsaturated compounds such as propylene and butadiene as well as pyrolysis gasoline with a high proportion of aromatic hydrocarbons such as benzene , Toluene and xylene can be obtained. The further development of the process has led to shorter and shorter dwell times in the cracked tubes of the tubular cracking furnace and to ever higher cracking temperatures. In the modern processes, dwell times for the hydrocarbons in the cracked tubes of the tubular cracking furnace of 0.1 to 0.5 seconds and exit temperatures of the cracked gases from the cracked tubes of more than 750 ° C., generally between 800 and 900 ° C., are preferably observed . Under these extreme conditions, the cracked gas has to be cooled immediately after leaving the tubular cracking furnace in order to prevent undesired side reactions which lead to a reduction in the yield of valuable products. This can be done directly by injecting liquid hydrocarbons or water into the hot cracked gas. However, direct cooling has the disadvantage that when the heat is recovered in the form of water vapor, the water vapor obtained has only a low pressure level. Generally you pull it therefore intends to cool the cracked gases indirectly by passing the cracked gases through a cracked gas cooler in which the cracked gases are cooled in indirect heat exchange with water. This produces high-tension steam with a pressure of up to 150 bar. preferably up to 130 bar. This high-pressure steam contributes to the economics of the process, since it supplies the major part of the drive energy for the raw gas and refrigeration compressors of the ethylene plants.

Obwohl die thermische Spaltung von Kohlenwasserstoffen in Gegenwart von Wasserdampf einen hohen technischen Stand erreicht hat, haftet dem Verfahren ein beträchtlicher Nachteil an, nämlich der Ablagerung von Koks auf den Innenwänden sowohl der Spaltrohre im Röhrenofen als auch der Eintrittshaube und der Kühlrohre im nachgeschalteten Spaltgaskühler. Durch die isolierende Wirkung des Kokses erhöht sich die Rohrwandtemperatur der Spaltrohre des Röhrenspaltofens und der Druckverlust steigt an. Im nachgeschalteten Spaltgaskühler wird durch die.Koksablagerung der Wärmeübergang verschlechtert, so daß die Temperatur des Spaltgases im Ausgang des Spaltgaskühlers ansteigt. Haben die Koksablagerungen eine gewisse Stärke erreicht, muß der Röhrenspaltofen zusammen mit dem nachgeschalteten Spaltgaskühler abgestellt und vom Koks befreit werden. Die Spaltrohre werden in der Regel mit einem Wasserdampf-/Luft-Gemisch oder auch nur mit Wasserdampf oder mit einem Gemisch von Wasserdampf und Wasserstoff (vgl. DE-OS 19 48 635) bei Temperaturen von 700°C bis 1000°C vom Koks befreit.Although the thermal cracking of hydrocarbons in the presence of water vapor has reached a high technical level, the process has a considerable disadvantage, namely the deposition of coke on the inner walls of both the cracked tubes in the tube furnace and the inlet hood and the cooling tubes in the downstream cracked gas cooler. Due to the insulating effect of the coke, the tube wall temperature of the canned tubes of the tubular cracking furnace increases and the pressure loss increases. In the downstream cracked gas cooler, the heat transfer is deteriorated by the coke deposit, so that the temperature of the cracked gas rises at the outlet of the cracked gas cooler. Once the coke deposits have reached a certain strength, the tube cracking furnace must be switched off together with the downstream cracking gas cooler and the coke removed. The canned tubes are generally freed of coke with a water vapor / air mixture or only with water vapor or with a mixture of water vapor and hydrogen (cf. DE-OS 19 48 635) at temperatures of 700 ° C to 1000 ° C .

Um einen verschmutzten Spaltgaskühler zu säubern, bieten sich mehrere Möglichkeiten an. Nach einer ersten Methode wird der Spaltgaskühler mechanisch gereinigt. Diese Methode ist sehr aufwendig und erfordert eine längere 'Abstellzeit des Röhrenspaltofens und somit einen entsprechenden Produktionsausfall in der Ethylenanlage. Dazu wird in der Regel der Röhrenspaltofen abgekühlt. Nach der Abkühlung wird der Spaltgaskühler geöffnet, und die einzelnen Rohre des Spaltgaskühlers mit beispielsweise mehr als 50 Rohren werden zu mechanischen Reinigung, z.B. mit einem Hochdruckwassergerät, bei einem Wasserdruck von gewöhnlich 300 bis 700 bar oder bei sehr harter Koksablagerung mittels Wasser/Sandstrahlung vom Koks befreit. Ein großer Nachteil dieser Methode besteht darin, daß durch das häufige Abkühlen und anschließende Hochheizen das Material des Ofens übermäßig beansprucht wird und dadurch häufig Schäden auftreten.There are several ways to clean a dirty cracked gas cooler. According to a first method, the cracked gas cooler is cleaned mechanically. This method is very complex and requires a longer one '' Shutdown time of the tube cracking furnace and therefore a corresponding loss of production in the ethylene plant. For this purpose, the tube cracking furnace is usually cooled. After cooling, the cracked gas cooler is opened and the individual pipes of the cracked gas cooler, for example with more than 50 pipes, are used for mechanical cleaning, e.g. with a high-pressure water device, at a water pressure of usually 300 to 700 bar or in the case of very hard coke deposition by means of water / sand blasting from the coke freed. A major disadvantage of this method is that the material of the furnace is subjected to excessive stress as a result of the frequent cooling and subsequent heating, and damage often occurs as a result.

Bei einer weiteren Methode wird die vorstehend beschriebene Methode in der Weise abgewandelt, daß man den Röhrenspaltofen zunächst auf 2000C bis 400°C abkühlt, danach den Spaltgaskühler von dem Röhrenspaltofen trennt und die mechanische Reinigung des völlig abgekühlten Spaltgaskühlers durchführt, während gleichzeitig die Spaltrohre des Spaltgaskühlers mit einem Wasserdampf-/Luftgemisch entkokt werden. Aber auch hierbei wird nur ein geringer Zeitgewinn erzielt, zumal durch den Temperaturwechsel und die Beanspruchung der Spaltrohre des Röhrenspaltofens sich Koks von der Innenseite der Spaltrohre lösen und dadurch zusätzliche Probleme schaffen kann.In another method, the method described above is modified in such a way that one first cools the tube cracking furnace at 200 0 C to 400 ° C, then separating the gas cooler of the tube cracking furnace and performs the mechanical cleaning of completely cooled cleavage gas cooler, while the cracking tubes the cracked gas cooler with a water vapor / air mixture. But even here, only a small amount of time is saved, especially since the change in temperature and the stress on the canned tubes of the tubular cracking furnace can cause coke to separate from the inside of the canned tubes and thus create additional problems.

Es ist weiter versucht worden, das Abkühlen des Röhrenspaltofens und das mechanische Reinigen des Spaltgaskühlers durch eine besondere Konstruktion des Kühlers (DE-AS 19 26 495) zu vermeiden. Die Kühlrohre sind in diesem Kühler spiralförmig angeordnet und das Material aus teurem hitzebeständigem Material gefertigt. Zum Reinigen des Kühlers muß das Wasser aus dem Kühler abgelassen werden, um dann mit einem Wasserdampf-/Luft-GeL misch den Koks abzubrennen. Aber auch diese Methode hat sich wegen der extremen Beanspruchung des Materials und der damit verbundenen Reparaturhäufigkeit in der Technik nicht durchsetzen können.Attempts have also been made to avoid the cooling of the tubular cracking furnace and the mechanical cleaning of the cracked gas cooler by a special design of the cooler (DE-AS 19 26 495). The cooling tubes are spirally arranged in this cooler and the material is made of expensive heat-resistant material. To clean the cooler, the water must be drained from the cooler and then with a steam / air gel mix to burn the coke. However, even this method has not been able to establish itself in technology due to the extreme stress on the material and the associated frequency of repairs.

Schließlich ist die sogenannte On-line-Entkokung von Röhrenspaltofen und Spaltgaskühler bekannt (CZ-Chemie-Technik, 3. Jahrgang, 1974, Nr. 2, Seite 53, linke Spalte, Ziffer 2.5), bei der man bei der herkömmlichen Entkokung der Spaltrohre des Röhrenspaltofens mit dem Wasserdampf-/Luft-Gemisch die Entkokungsgase durch den nachgeschalteten Spaltgaskühler führt in der Absicht, diesen gleichzeitig zu entkoken. Hierzu wird vor Erreichen der höchsten zulässigen Austrittstemperatur des Spaltgases aus dem Spaltgaskühler der Röhrenspaltofen früher als erforderlich .außer Betrieb genommen. Nach beendeter Entkokung der Spaltrohre des Röhrenspaltofens ist wegen der tieferen Temperaturen, die sich bei der One-line-Entkokung im Spaltgaskühler einstellen, der Koks im Spaltgaskühler nur zu einem geringen Teil entfernt. Gegenüber dem Vorteil, den Spaltofen nicht abkühlen und die Hauben des Spaltgaskühlers nicht demontieren zu müssen, nimmt man den Nachteil in Kauf, daß die Austrittstemperatur des Spaltgases aus dem Spaltgaskühler nicht auf den Wert eines mechanisch gereinigten Kühlers abfällt, sondern nur geringfügig niedriger liegt als vor der Abstellung, so daß eine entsprechend geringere Menge an Hochdruckdampf im Spaltgaskühler erzeugt wird. Hinzu kommt, daß spätestens nach der dritten One-line-Reinigung doch eine mechanische Reinigung des Spaltgaskühlers mit all den geschilderten Nachteilen erforderlich wird.Finally, the so-called on-line decoking of tube cracking furnace and cracking gas cooler is known (CZ-Chemie-Technik, 3rd year, 1974, No. 2, page 53, left column, number 2.5), in which conventional cracking of the cracking tubes is carried out of the tube cracking furnace with the steam / air mixture leads the decoking gases through the downstream cracking gas cooler with the intention of decoking it at the same time. For this purpose, before reaching the highest permissible outlet temperature of the cracked gas from the cracked gas cooler, the tube cracking furnace is taken out of operation earlier than necessary. After decoking of the canned pipes of the tubular cracking furnace, the coke in the cracked gas cooler is only removed to a small extent due to the lower temperatures that arise in the one-line decoking in the cracked gas cooler. Compared to the advantage of not having to cool the cracking furnace and not having to dismantle the hoods of the cracking gas cooler, one accepts the disadvantage that the temperature at which the cracking gas emerges from the cracking gas cooler does not drop to the value of a mechanically cleaned cooler, but is only slightly lower than before the shutdown, so that a correspondingly smaller amount of high pressure steam is generated in the cracked gas cooler. In addition, after the third one-line cleaning at the latest, mechanical cleaning of the cracked gas cooler with all the disadvantages described is necessary.

Der Erfindung lag daher die Aufgabe zugrunde, ein Verfahren zur thermischen Entkokung von Spaltgaskühlern zur Verfügung zu stellen, welches die Nachteile der bekannten Verfahren nicht aufweist.The invention was therefore based on the object of a method for the thermal decoking of cracked gas coolers to make available, which does not have the disadvantages of the known methods.

Es wurde nun ein vorteilhaftes Verfahren gefunden zur thermischen Entkokung von Spaltgaskühlern für die indirekte Abkühlung mittels Wasser von ethylenhaltigen Spaltgasen, die durch thermische Spaltung von Kohlenwasserstoffen in Gegenwart von Wasserdampf in einem indirekt beheizten Röhrenspaltofen bei Spaltgasaustrittstemperaturen oberhalb 750°C erhalten werden, durch Hindurchleiten eines erhitzten Gasgemisches aus Wasserdampf und Luft durch die mit Koks belegten Rohre des Spaltgaskühlers, welches dadurch gekennzeichnet ist, daß anstelle des erhitzten Wasserdampf-/Luft-Gemisches erhitzte Luft ohne Zuführung von Wasserdampf durch die zu entkokenden Rohre des Spaltgaskühlers geleitet wird.An advantageous method has now been found for the thermal decoking of cracked gas coolers for indirect cooling by means of water of ethylene-containing cracked gases, which are obtained by thermal cracking of hydrocarbons in the presence of steam in an indirectly heated tubular cracking furnace at cracked gas outlet temperatures above 750 ° C. by passing a heated one through Gas mixture of water vapor and air through the coke-coated pipes of the cracked gas cooler, which is characterized in that heated air is passed through the pipes of the cracked gas cooler to be decoked instead of the heated steam / air mixture.

Bei diesem Verfahren können die Spaltgaskühler thermisch entkokt werden, ohne daß eine zusätzliche mechanische Reinigung des Spaltgaskühlers und eine damit verbundene Abkühlung der vorgeschalteten Röhrenspaltöfen erforderlich werden. Während nach den bekannten Verfahren, z.B. bei der vorstehend beschriebenen One-line-Entkokung, lediglich jährliche Laufzeiten der Röhrenspaltöfen von 85 bis 95 % erzielt werden, werden nach dem erfindungsgemäßen Verfahren durch Senkung der Stillstandszeiten jährliche Laufzeiten von mehr als 97 % und damit eine entsprechend höhere Ethylenproduktion erhalten. Gleichzeitig sind wegen der erhöhten Laufzeit weniger Ersatzröhrenspaltöfen in der Ethylenanlage erforderlich, wodurch die Investitionskosten für die Ethylenanlage gesenkt werden. Außerdem wird durch den Wegfall der Ab- und Aufheizperiode die Lebensdauer der Spaltrohre des Röhrenspaltofens erhöht. Weitere Vorteile des erfindungsgemäßen Verfahrens bestehen darin, daß die Hochdruckdampferzeugung L im Spaltgaskühler während des gesamten Entkokungsvorganges nicht unterbrochen wird und daß die Betriebskosten der Entkokung gesenkt werden.With this method, the cracked gas coolers can be decoked thermally without the need for additional mechanical cleaning of the cracked gas cooler and the associated cooling of the upstream tube cracking furnaces. While according to the known methods, for example in the one-line decoking described above, only annual runtimes of the tube cracking furnaces of 85 to 95% are achieved, annual runtimes of more than 97% and thus correspondingly are reduced by reducing the downtimes get higher ethylene production. At the same time, fewer replacement tube cracking furnaces are required in the ethylene plant due to the increased operating time, which reduces the investment costs for the ethylene plant. In addition, by eliminating the heating-up and heating-up period, the life of the canned tube furnace is increased. Further advantages of the method according to the invention are that the high pressure steam generation L is not interrupted in the cracked gas cooler during the entire decoking process and that the operating costs of the decoking are reduced.

Nach dem erfindungsgemäßen Verfahren werden Spaltgaskühler thermisch entkokt, die für die indirekte Abkühlung mittels Wasser von ethylenhaltigen Spaltgasen verwendet werden, wobei die Spaltgase durch thermische Spaltung von Kohlenwasserstoffen in Gegenwart von Wasserdampf in einem indirekt beheizten Röhrenspaltofen bei Gasaustrittstemperaturen oberhalb 750°C erhalten werden. Geeignete Ausgangskohlenwasserstoffe für die thermische Spaltung sind Ethan, Propan, Butan, LPG, Benzinfraktionen wie Leichtbenzin, z.B. Leichtbenzin mit dem Siedebereich von ca. 30 bis 150°C, Benzin (full-range Naphtha), z.B. Benzin mit dem Siedebereich von ca. 30 bis 180°C, Schwerbenzin, z.B. Schwerbenzin mit dem Siedebereich von ca. 150 bis 220°C, Kerosin, z.B. Kerosin mit dem Siedebereich von ca. 200 bis 260°C, Gasöle wie leichtes Gasöl, z.B. leichtes Gasöl mit dem Siedebereich von ca. 200 bis 360°C, schweres Gasöl, z.B. schweres Gasöl mit dem Siedebereich von ca. 310 bis 4300C und Vakuumdestillate. Das Verfahren wird vorzugsweise für Spaltgaskühler für die Abkühlung von Spaltgasen, die aus Benzinfraktionen, Kerosin und/oder Gasölen erhalten worden sind, verwendet. Die Austrittstemperaturen des Spaltgases aus dem Röhrenspaltofen betragen mehr als 750°C, vorzugsweise 780 bis 900°C, insbesondere 800 bis 900°C. Die Verweilzeiten in den Röhrenspaltöfen betragen im allgemeinen 0,05 bis 1 sec., vorzugsweise 0,1 bis 0,6 sec., insbesondere 0,1 bis 0,5 sec.In the process according to the invention, cracked gas coolers are thermally decoked, which are used for indirect cooling by means of water of ethylene-containing cracked gases, the cracked gases being obtained by thermal cracking of hydrocarbons in the presence of steam in an indirectly heated tubular cracking furnace at gas outlet temperatures above 750 ° C. Suitable starting hydrocarbons for thermal cracking are ethane, propane, butane, LPG, gasoline fractions such as light petrol, e.g. light petrol with a boiling range of approx. 30 to 150 ° C, gasoline (full-range naphtha), e.g. gasoline with a boiling range of approx. 30 up to 180 ° C, heavy gasoline, e.g. heavy gasoline with a boiling range of approx. 150 to 220 ° C, kerosene, e.g. kerosene with a boiling range of approx. 200 to 260 ° C, gas oils such as light gas oil, e.g. light gas oil with a boiling range of approx 200 to 360 ° C, heavy gas oil, for example heavy gas oil with a boiling range of approx. 310 to 430 0 C and vacuum distillates. The method is preferably used for cracked gas coolers for cooling cracked gases obtained from gasoline fractions, kerosene and / or gas oils. The Austrittstem p eraturen of the cracking gas from the tubular cracking furnace amount to more than 750 ° C, preferably 780-900 ° C, in particular 800 to 900 ° C. The residence times in the tube cracking furnaces are generally 0.05 to 1 sec., Preferably 0.1 to 0.6 sec., In particular 0.1 to 0.5 sec.

Zweckmäßig betragen die Wärmebelasgungen der Spaltrohre in den Röhrenspaltöfen 40 000 bis 80 000 kcal/m2.h, vorzugs- weise 50 000 bis 70 000 kcal/m2.h. Das Gewichtsverhältnis von Wasserdampf zum eingesetzten Kohlenwasserstoff beträgt L 'bei der thermischen Spaltung im allgemeinen 0,1 : 1, vorzugsweise 0,2 : 0,8, insbesondere 0,3 : 0,7.The thermal loads on the canned tubes in the tubular cracking furnaces are expediently 40,000 to 80,000 kcal / m 2 . h, v o rz UGS as 50,000 to 70,000 kcal / m 2 .h. The weight ratio of water vapor to the hydrocarbon used is L. In the case of thermal splitting, generally 0.1: 1, preferably 0.2: 0.8, in particular 0.3: 0.7.

Nach dem Verfahren nach der Erfindung wird zur thermischen Entkokung des Spaltgaskühlers erhitzte Luft ohne Zuführung von Wasserdampf durch den zu entkokenden Spaltgaskühler geleitet. Es ist weiter möglich, zur Beschleunigung der Entkokung anstelle der erhitzten Luft erhitzte Mischungen von.Luft und Sauerstoff zu verwenden. Bei der Verwendung von Luft-/Sauerstoff-Mischungen beträgt im allgemeinen das Volumenverhältnis von Luft zu Sauerstoff 100 : 1 bis 1 : 100, vorzugsweise 100 : 1 bis 1 : 50, insbesondere 100 : 1 bis 1 : 10. In der Regel wird man jedoch wegen der leichten Verfügbarkeit erhitzte Luft allein ohne weiteren Sauerstoffzusatz für die Entkokung verwenden.According to the method according to the invention, for the thermal decoking of the cracked gas cooler, heated air is passed through the cracked gas cooler to be decoked without the addition of water vapor. It is also possible to use heated mixtures of air and oxygen instead of heated air to accelerate decoking. When using air / oxygen mixtures, the volume ratio of air to oxygen is generally 100: 1 to 1: 100, preferably 100: 1 to 1:50, in particular 100: 1 to 1:10 however, because of the easy availability, use heated air alone without additional oxygen for decoking.

Die Spaltgaskühlereintrittstemperatur beträgt für die erhitzte Luft bzw. das Luft-/Sauerstoff-Gemisch im allgemeinen 600 bis 1100°C, vorzugsweise 700 bis 1050°C, insbesondere 800 bis 1000°C.The cracked gas cooler inlet temperature for the heated air or the air / oxygen mixture is generally 600 to 1100 ° C, preferably 700 to 1050 ° C, in particular 800 to 1000 ° C.

Die Entkokung kann unter Einhalten von leicht vermindertem Druck im Spaltgaskühler, z.B. im Bereich von 0,5 bis 1 bar, durchgeführt werden. Im allgemeinen werden im Spaltgaskühler atmosphärischer Druck oder erhöhter Druck angewendet. Zweckmäßig betragen die Drucke 1 bis 50 bar, vorzugsweise 1 bis 20 bar, insbesondere 1 bis 10 bar. Aus Gründen des geringeren technischen Aufwandes kann es vorteilhaft sein, bei atmosphärischem Druck zu arbeiten. Es kann jedoch auch zweckmäßig sein, erhöhte Drücke von 2 bis 50 bar, vorzugsweise 5 bis 40 bar anzuwenden.Decoking can be carried out while maintaining slightly reduced pressure in the cracked gas cooler, e.g. in the range of 0.5 to 1 bar. In general, atmospheric pressure or increased pressure are used in the cracked gas cooler. The pressures are expediently 1 to 50 bar, preferably 1 to 20 bar, in particular 1 to 10 bar. For reasons of less technical effort, it can be advantageous to work at atmospheric pressure. However, it can also be expedient to use elevated pressures of 2 to 50 bar, preferably 5 to 40 bar.

Bei der thermischen Entkokung des Spaltgaskühlers wird zweckmäßig im Spaltgaskühler auf der Seite des siedenden Wassers ein Dampfdruck von 80 bis 160 bar, vorzugsweise 90 bis 150 bar, insbesondere 100 bis 130 bar aufrechterhalten. In der Regel beträgt das Verhältnis der während der thermischen Entkokung je Stunde durchgesetzten Gewichtsmenge an erhitzter Luft bzw. des erhitzten Luft-/Sauerstoffgemisches zu der je Stunde während der thermischen Spaltung durchgesetzten Menge an Kohlenwasserstoff 0,05 bis 5, vorzugsweise 0,1 bis 3, insbesondere 0,1 bis 2. Im allgemeinen wird der Spaltgaskühler soweit entkokt, daß die Austrittstemperatur des Spaltgases aus dem Spaltgaskühler dem Ausgangswert der Austrittstemperatur des Spaltgases aus dem Spaltgaskühler zu Beginn der ersten Inbetriebnahme des Spaltgaskühlers bzw. nach mechanischer Reinigung des Spaltgaskühlers entspricht.In the thermal decoking of the cracked gas cooler is expedient in the cracked gas cooler on the boiling side Water maintain a vapor pressure of 80 to 160 bar, preferably 90 to 150 bar, in particular 100 to 130 bar. As a rule, the ratio of the amount of heated air or the heated air / oxygen mixture passed through per hour during the thermal decoking to the amount of hydrocarbon passed through per hour during the thermal cracking is 0.05 to 5, preferably 0.1 to 3 , in particular 0.1 to 2. In general, the cracked gas cooler is decoked to such an extent that the exit temperature of the cracked gas from the cracked gas cooler corresponds to the initial value of the exit temperature of the cracked gas cooler from the cracked gas cooler at the start of the first start-up of the cracked gas cooler or after mechanical cleaning of the cracked gas cooler.

In der Regel ist der Spaltgaskühler nach der erfindungsgemäßen Behandlung mit Luft bzw. dem Luft-/Sauerstoff-Gemisch nach ca. 20 bis 30 Stunden vollständig vom Koks befreit und weist dann nach der Wiederinbetriebnahme den vorstehend genannten Ausgangswert der Ausgangstemperatur des Spaltgases auf. Der Ablauf und die Beendigung des Entkokungsvorgangs kann in einfacher Weise durch Bestimmung der Kohlendioxidkonzentration in dem in den Spaltgaskühler eingeleiteten und dem aus dem Spaltgaskühler austretenden Gasgemisch verfolgt werden.As a rule, after the treatment according to the invention with air or the air / oxygen mixture, the cracked gas cooler is completely freed of the coke after about 20 to 30 hours and then has the above-mentioned initial value of the starting temperature of the cracked gas after restarting. The course and the end of the decoking process can be followed in a simple manner by determining the carbon dioxide concentration in the gas mixture introduced into the cracked gas cooler and the gas mixture emerging from the cracked gas cooler.

Es war überraschend, daß nach dem erfindungsgemäßen Verfahren Spaltgaskühler vollständig entkokt werden können, da alle Versuche, mit einem Wasserdampf-/Luftgemisch einen Spaltgaskühler völlig von Koks zu befreien, gescheitert waren. Auch Versuche im Laboratoriumsmaßstab, bei denen Koks, wie er im Spaltgaskühler erhalten wird, bei den im Spaltgaskühler herrschenden Temperaturen mit Luft behandelt wurde, hatten ergeben, daß praktisch keine Reaktion zwischen dem Koks und der Luft erfolgte.It was surprising that cracked gas coolers can be completely decoked using the process according to the invention, since all attempts to completely remove coke from a cracked gas cooler with a water vapor / air mixture have failed. Laboratory-scale experiments in which coke, as obtained in the cracked gas cooler, was treated with air at the temperatures prevailing in the cracked gas cooler, had shown that there was practically no reaction between the coke and the air.

Man kann die Luft bzw. das Luft-/Sauerstoff-Gemisch unter Umgehung des bzw. der zum Spaltgaskühler gehörenden Röhrenspaltöfen in einem getrennten Ofen auf die Spaltgaskühlereintrittstemperaturen erhitzen und durch den Spaltgaskühler leiten. Vorzugsweise wird jedoch die Luft bzw. das Luft-/Sauerstoff-Gemisch in den zugehörigen Röhrenspaltöfen auf die Eintrittstemperatur für den Spaltgaskühler erhitzt und durch den nachgeschalteten Spaltgaskühler geleitet.The air or the air / oxygen mixture can be heated in a separate oven, bypassing the tube cracking furnace or tubes belonging to the cracked gas cooler, to the cracked gas cooler inlet temperatures and passed through the cracked gas cooler. However, the air or the air / oxygen mixture in the associated tubular cracking furnaces is preferably heated to the inlet temperature for the cracked gas cooler and passed through the downstream cracked gas cooler.

In einer bevorzugten Ausführungsform des Verfahrens werden vor der thermischen Entkokung des Spaltgaskühlers zunächst die Spaltrohre des vorgeschalteten Röhrenspaltofens entkokt. Dies erfolgt zweckmäßig in der Weise, daß nach Unterbindung der Zugabe des zu spaltenden Kohlenwasserstoffs ein Wasserdampf-/Luft-Gemisch durch die indirekt beheizten Spaltrohre des Röhrenspaltofens und gleichzeitig durch den nachgeschalteten Spaltgaskühler geleitet wird und nach beendeter Entkokung der Spaltrohre des Röhrenspaltofens die Wasserdampfzufuhr unterbunden und nur noch Luft oder das Luft-/Sauerstoff-Gemisch durch die indirekt beheizten Spaltrohre des Röhrenspaltofens und den nachgeschalteten Spaltgaskühler geleitet werden. Beim gleichzeitigen Hindurchleiten des Wasserdampf-/Luft--Gemisches durch Röhrenspaltofen und nachgeschalteten Spaltgaskühler werden im allgemeinen Austrittstemperaturen für das den Röhrenspaltofen verlassende Gasgemisch angewendet, die zwischen 600 und 11000C, vorzugsweise zwischen 700 bis 1050°C, insbesondere zwischen 700 und 900° C liegen. Das eingesetzte Wasserdampf-/Luft-Gemisch weist zweckmäßig ein Gewichtsverhältnis von Wasserdampf zu Luft von 100 : 1 bis 2 : 8, vorzugsweise 9 : 1 bis 3 : 7 auf, wobei man zweckmäßig mit einem Wasserdampf-/Luft-Gemisch mit sehr geringem Luftgehalt, z.B. weniger als 10 Gew.% Luft, oder auch Wasserdampf allein beginnt und dann stei- 'gende Mengen Luft zumischt, z.B. bis zu einem Gehalt an Luft im Wasserdampf-/Luft-Gemisch von 70 Gew.%.In a preferred embodiment of the method, before the thermal decoking of the cracked gas cooler, the cracked tubes of the upstream tube cracking furnace are first decoked. This is expediently carried out in such a way that, after the addition of the hydrocarbon to be split has been prevented, a water vapor / air mixture is passed through the indirectly heated cracking tubes of the tube cracking furnace and at the same time through the downstream cracking gas cooler, and after the decoking of the cracking tubes of the tube cracking furnace has ended, the water vapor supply is prevented and only air or the air / oxygen mixture are passed through the indirectly heated canned tubes of the tubular cracking furnace and the downstream cracked gas cooler. When the steam / air mixture is simultaneously passed through a tube cracking furnace and a downstream cracking gas cooler, outlet temperatures for the gas mixture leaving the tube cracking furnace are generally used, which are between 600 and 11000C, preferably between 700 and 1050 ° C, in particular between 700 and 900 ° C . The water vapor / air mixture used expediently has a weight ratio of water vapor to air of 100: 1 to 2: 8, preferably 9: 1 to 3: 7, expediently using a water vapor / air mixture with a very low air content , for example less than 10% by weight of air, or water vapor alone begins and then rises 'Mixing sufficient amounts of air, for example up to an air content of 70% by weight in the water vapor / air mixture.

Die folgenden Beispiele veranschaulichen die Erfindung.The following examples illustrate the invention.

VergleichsbeispielComparative example

In einem Röhrenspaltofen, der vier Spaltrohre enthält, werden je Spaltrohr eine Mischung von 2,2 t/h einer Benzinfraktion (Naphtha) mit dem Siedebereich von 40 bis 180°C und 1,05 t/h Wasserdampf durchgeleitet und bei einer Ofenaustrittstemperatur von 850°C gespalten. Das Spaltgas von je 2 Spaltrohren wird in einem nachgeschalteten Spaltgaskühler abgekühlt. Zu Beginn bei sauberem Spaltgaskühler beträgt die Kühleraustrittstemperatur 350°C. Diese Spaltgaskühleraustrittstemperatur steigt nach mehreren Monaten Laufzeit schließlich auf 450°C an, der höchsten für den Spaltgaskühler zulässigen Austrittstemperatur. Danach wird der Kohlenwasserstoffstrom durch den Röhrenspaltofen unterbrochen und die Spaltrohre und der Spaltgaskühler auf herkömmliche Art entkokt, indem ein Wasserdampf-/Luft-Gemisch durch die Spaltrohre und den nachgeschalteten Spaltgaskühler geleitet wird. Dazu werden zunächst pro Spaltrohr 1,0 t/h Wasserdampf und 0,08 t/h Luft durchgesetzt. Im Verlauf von 10 Stunden wird der Luftdurchsatz langsam angehoben und der Wasserdampfdurchsatz zurückgenommen bis schließlich ein Wasserdampf-/Luft-Gemisch mit 70 Vol.% Luft je Spaltrohr durchgeleitet wird. Dieser Zustand wird noch weitere 6 Stunden aufrecht erhalten, so daß der gesamte Entkokungsvorgang 16 Stunden dauert.A mixture of 2.2 t / h of a gasoline fraction (naphtha) with a boiling range of 40 to 180 ° C and 1.05 t / h of water vapor is passed through in a tube cracking furnace, which contains four cracking tubes, and at a furnace exit temperature of 850 ° C split. The cracked gas from 2 cracked tubes is cooled in a downstream cracked gas cooler. At the beginning with a clean cracked gas cooler, the cooler outlet temperature is 350 ° C. After a period of several months, this cracked gas cooler outlet temperature finally rises to 450 ° C, the highest outlet temperature permitted for the cracked gas cooler. Thereafter, the hydrocarbon flow through the tube cracking furnace is interrupted and the cracked tubes and the cracked gas cooler are decoked in a conventional manner by passing a water vapor / air mixture through the cracked tubes and the downstream cracked gas cooler. For this purpose, 1.0 t / h of water vapor and 0.08 t / h of air are initially passed through each can. In the course of 10 hours, the air throughput is slowly increased and the water vapor throughput is reduced until finally a water vapor / air mixture with 70 vol.% Air is passed through each can. This state is maintained for a further 6 hours, so that the entire decoking process takes 16 hours.

Wird der Röhrenspaltofen nach diesem Entkokungsvorgang abgekühlt und einer visullen Kontrolle unterzogen, so stellt man fest, daß die Spaltrohre bis zum Eingang des Spaltgas- 'kühlers vollständig gesäubert sind, nicht jedoch der Spaltgaskühler selbst, der besonders zum Ausgang hin noch einen starken Koksbelag aufweist. Wird der Röhrenspaltofen unter den eingangs angeführten Bedingungen wieder in Betrieb genommen, so stellt sich eine Spaltgaskühleraustrittstemperatur von nur 420 bis 4300C ein. Um auf Kühleraustrittstemperaturen von 3500C zu gelangen, war bisher als einziger Ausweg nur die mechanische Reinigung des Spaltgaskühlers möglich.If the tube cracking furnace is cooled after this decoking process and subjected to a visual inspection, it can be seen that the cracked tubes up to the entrance of the cracked gas '' coolers are completely cleaned, but not the cracked gas cooler itself, which still has a thick coke coating, especially towards the exit. If the tubular cracking furnace is put into operation again under the conditions mentioned at the beginning, a cracked gas cooler outlet temperature of only 420 to 430 ° C. is established. In order to reach cooler outlet temperatures of 350 0 C, the only way out so far was only mechanical cleaning of the cracked gas cooler.

Beispiel 1example 1

Der Röhrenspaltofen wird wie im ersten Absatz des Vergleichsbeispiels beschrieben, zunächst zur Herstellung des Spaltgases unter Zugabe von Naphtha und Wasserdampf betrieben und nach Erreichen der maximal zulässigen Spaltgaskühleraustrittstemperatur von 450°C der im ersten Absatz des Vergleichsbeispiels beschriebenen Entkokung von 16 Stunden unterzogen. Anschließend wird der Wasserdampfdurchsatz vollständig unterbunden und nur Luft in einer Menge von 1,3 t/h je Spaltrohr durchgeleitet. Dies entspricht einem Gewichtsverhältnis der je Stunde pro Spaltrohr durchgeleiteten Menge Luft zu der je Stunde während der thermischen Spaltung durchgesetzten Menge an Kohlenwasserstoff von 0,59. Dabei wird eine Ofenaustrittstemperatur von 8500C eingehalten. Während des 30stündigen Durchleitens von Luft stellt sich eine Spaltgaskühleraustrittstemperatur von 335°C ein. Während dieser 30 Stunden wird weiterhin Hochdruckdampf von 125 bar erzeugt. Nach der l6stündigen Wasserdampf-/Luftentkokung der Spaltrohre und der anschließenden 30stündigen thermischen Behandlung des Spaltgaskühlers mit Luft allein wird der Röhrenspaltofen, ohne daß eine Abkühlung erfolgte, wieder unter Durchleiten von 2,2 t/h Naphtha und 1,05 t/h Dampf je Spaltrohr in Betrieb genommen.The tubular cracking furnace is operated as described in the first paragraph of the comparative example, initially to produce the cracked gas with the addition of naphtha and water vapor and, after reaching the maximum permissible cracked gas cooler outlet temperature of 450 ° C., is subjected to the decoking of 16 hours described in the first paragraph of the comparative example. The water vapor throughput is then completely prevented and only air in an amount of 1.3 t / h per can is passed through. This corresponds to a weight ratio of 0.59 of the amount of air passed per hour per can to the amount of hydrocarbon passed per hour during the thermal cracking. A furnace exit temperature of 850 0 C is maintained. During the 30-hour passage of air, a cracked gas cooler outlet temperature of 335 ° C is reached. High pressure steam of 125 bar continues to be generated during these 30 hours. After the steam and air decoking of the cracking tubes for 16 hours and the subsequent 30-hour thermal treatment of the cracking gas cooler with air alone, the tube cracking furnace, without cooling down, is again passed through by passing 2.2 t / h of naphtha and 1.05 t / h of steam each Canned tube put into operation.

Beispiel 2Example 2

In einem Röhrenspaltofen werden je Spaltrohr 2,2 t/h Gasöl und 1,7 t/h Wasserdampf bei einer Ofenaustrittstemperatur von 830°C gespalten. Die Spaltgaskühleraustrittstemperatur im sauberen Zustand beträgt 550°C bei einem Dampfdruck auf der Wasserseite von 125 bar. Nach mehrwöchigem Betrieb steigt die Spaltgaskühleraustrittstemperatur auf 650°C, der höchsten für den Spaltgaskühler zulässigen Austrittstemperatur an. Danach wird der Kohlenwasserstoffstrom unterbrochen und, wie im Beispiel 1 und im Vergleichsbeispiel beschrieben, zunächst ein Gemisch aus Wasserdampf und Luft mit langsam zunehmendem Luftgehalt (bis zum Erreichen eines Wasserdampf-/Luft-Gemisches mit 70 Vol.% Luft) durch die Spaltrohre und die nachgeschalteten Spaltgaskühler geleitet. Nach einer Entkokungsdauer von 16 Stunden sind die Spaltrohre des Röhrenspaltofens vollständig gesäubert, während nur eine geringfügige Reinigung des Spaltgaskühlers erfolgt ist. Anschließend wird, wie in Beispiel 2 beschrieben, Luft allein ohne Zugabe von Wasserdampf zunächst unter Hindurchleiten durch die Spaltrohre des Röhrenspaltofens erhitzt und anschließend durch den Spaltgaskühler geleitet. Hierdurch wird bereits nach 15- bis 20stündigem Hindurchleiten von Luft eine vollständige Befreiung des-Spaltgaskühlers von Koks erreicht, so daß bei Wiederinbetriebnahme des Röhrenspaltofens unter Zuführung von Gasöl und Wasserdampf sich wieder die Austrittstemperatur des Spaltgases aus dem Spaltgaskühler von 550° C entsprechend einem mechanisch gereinigten Kühler einstellt.2.2 t / h of gas oil and 1.7 t / h of water vapor are split in a tube cracking furnace at a furnace exit temperature of 830 ° C. The cracked gas cooler outlet temperature in the clean state is 550 ° C with a steam pressure on the water side of 125 bar. After several weeks of operation, the cracked gas cooler outlet temperature rises to 650 ° C, the highest outlet temperature permitted for the cracked gas cooler. Then the hydrocarbon stream is interrupted and, as described in Example 1 and in the comparative example, first a mixture of water vapor and air with a slowly increasing air content (until a water vapor / air mixture with 70% by volume of air is reached) through the can and the downstream gas cooler passed. After a decoking time of 16 hours, the canned tubes of the tubular cracking furnace are completely cleaned, while the cracked gas cooler has only been cleaned slightly. Then, as described in Example 2, air alone is first heated without passing water vapor while passing through the cracking tubes of the tubular cracking furnace and then passed through the cracking gas cooler. As a result, a complete removal of coke from the cracked gas cooler is achieved after only 15 to 20 hours of passage of air, so that when the tube cracking furnace is put back into operation with the addition of gas oil and steam, the temperature of the cracked gas leaving the cracked gas cooler is again 550 ° C. in accordance with a mechanically cleaned one Cooler.

Claims (6)

1. Verfahren zur thermischen Entkokung von Spaltgaskühlern für die indirekte Abkühlung mittels Wassers von ethylenhaltigen Spaltgasen, die durch thermische Spaltung von Kohlenwasserstoffen in Gegenwart von Wasserdampf in einem indirekt beheizten Röhrenspaltofen bei Spaltgasaustrittstemperaturen oberhalb 7500C erhalten werden, durch Hindurchleiten eines erhitzten Gasgemisches aus Wasserdampf und Luft durch die mit Koks belegten Rohre des Spaltgaskühlers, dadurch gekennzeichnet, daß anstelle des erhitzten Wasserdampf-/Luft-Gemisches erhitzte Luft ohne Zuführung von Wasserdampf durch die zu entkokenden Rohre des Spaltgaskühlers geleitet wird.1. Process for the thermal decoking of cracked gas coolers for indirect cooling by means of water from ethylene-containing cracked gases, which are obtained by thermal cracking of hydrocarbons in the presence of steam in an indirectly heated tubular cracking furnace at cracked gas outlet temperatures above 750 ° C., by passing a heated gas mixture of steam and Air through the coke-coated pipes of the cracked gas cooler, characterized in that instead of the heated water vapor / air mixture, heated air is passed through the pipes of the cracked gas cooler to be decoked instead of supplying steam. 2. Verfahren nach Anspruch r, dadurch gekennzeichnet, daß man anstelle der erhitzten Luft erhitzte Mischungen von Luft und Sauerstoff durch die Rohre des Spaltgaskühlers leitet.2. The method according to claim r, characterized in that instead of heated air passes heated mixtures of air and oxygen through the tubes of the cracked gas cooler. 3. Verfahren nach Anspruch 1 und 2, dadurch gekennzeichnet, daß im Spaltgaskühler auf der Seite des siedenden Wassers ein Dampfdruck von mindestens 80 bar aufrecht erhalten wird.3. The method according to claim 1 and 2, characterized in that a vapor pressure of at least 80 bar is maintained in the cracked gas cooler on the boiling water side. 4. Verfahren nach Anspruch 1 bis 3, dadurch gekennzeichnet, daß der Spaltgaskühler soweit entkokt wird, daß die Austrittstemperatur des Spaltgases aus dem Spaltgaskühler dem Ausgangswert der Austrittstemperatur des Spaltgases aus dem Spaltgaskühler zu Beginn der ersten Inbetriebnahme des Spaltgaskühlers bzw. nach mechanischer Reinigung des Spaltgaskühlers entspricht.4. The method according to claim 1 to 3, characterized in that the cracked gas cooler is decoked so far that the outlet temperature of the cracked gas from the cracked gas cooler is the initial value of the exit temperature of the cracked gas from the cracked gas cooler at the beginning of the first commissioning of the cracked gas cooler or after mechanical cleaning of the cracked gas cooler corresponds. 5. Verfahren nach Anspruch 1 bis 4, dadurch gekennzeich- net, daß das Verhältnis der während der thermischen Entkokung je Stunde durchgesetzten Gewichtsmenge an erhitzter Luft bzw. des erhitzten Luft-/Sauerstoffgemisches zu der je Stunde während der thermischen Spaltung durchgesetzten Menge an Kohlenwasserstoff 0,05 bis 5 beträgt.5. The method according to claim 1 to 4, characterized in that the ratio of the amount of weight of heated air or the heated air / oxygen mixture passed through per hour during the thermal decoking to the amount of hydrocarbon passed through per hour during the thermal cracking , 05 to 5. 6. Verfahren nach Anspruch 1 bis 5, dadurch gekennzeichnet, daß vor der thermischen Entkokung des Spaltgaskühlers zunächst die-Spaltrohre des vorgeschalteten Röhrenspaltofens entkokt werden, indem nach Unterbindung der Zugabe des zu spaltenden Kohlenwasserstoffs ein Wasserdampf-/Luftgemisch durch die indirekt beheizten Spaltrohre des Röhrenspaltofens und den nachgeschalteten Spaltgaskühler geleitet wird und nach beendeter Entkokung der Spaltrohre des Röhrenspaltofens die Wasserdampfzufuhr unterbunden und nur noch Luft oder ein Luft-/Sauerstoffgemisch durch die indirekt beheizten Spaltrohre des Röhrenspaltofens und den nachgeschalteten Spaltgaskühler geleitet werden.6. The method according to claim 1 to 5, characterized in that before the thermal decoking of the cracked gas cooler, the cracking tubes of the upstream tube cracking furnace are first decoked by a water vapor / air mixture through the indirectly heated cracking tubes of the tube cracking furnace after the addition of the hydrocarbon to be cracked has been prevented and the downstream cracked gas cooler is passed and after the decoking of the cracked tubes of the tube cracking furnace the water vapor supply is cut off and only air or an air / oxygen mixture is passed through the indirectly heated cracked tubes of the tube cracking furnace and the downstream cracked gas cooler.
EP81101665A 1980-03-15 1981-03-07 Process for thermally decoking coolers for cracked gases Expired EP0036151B2 (en)

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DE19803010000 DE3010000A1 (en) 1980-03-15 1980-03-15 METHOD FOR THERMAL DECOKING OF COLD GAS COOLERS
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EP0497155A1 (en) * 1991-01-31 1992-08-05 Linde Aktiengesellschaft Decoking of pyrolysis furnaces
EP0591856A1 (en) * 1992-10-05 1994-04-13 Stone & Webster Engineering Corporation Pulsed air decoking
FR2711374A1 (en) * 1993-10-20 1995-04-28 Schmidt Sche Heissdampf Method of thermal decoking of a cracking furnace and the downstream cracking gas cooler.
FR2728578A1 (en) * 1994-12-26 1996-06-28 Inst Francais Du Petrole PROCESS FOR FLEXIBLE VAPOCRAQUING AND CORRESPONDING VAPOCRACKING INSTALLATION
FR2750140A1 (en) * 1996-06-25 1997-12-26 Inst Francais Du Petrole SPRAYING SYSTEM WITH EROSION PROTECTION MEANS
EP2048217A2 (en) 2007-10-12 2009-04-15 Linde Aktiengesellschaft Method for decarbonising cracking furnaces

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US8524070B2 (en) * 2005-07-08 2013-09-03 Exxonmobil Chemical Patents Inc. Method for processing hydrocarbon pyrolysis effluent
US7749372B2 (en) * 2005-07-08 2010-07-06 Exxonmobil Chemical Patents Inc. Method for processing hydrocarbon pyrolysis effluent
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CN104327904A (en) * 2014-10-30 2015-02-04 北京晟辉兴业科技有限公司 Liquid boiler coking inhibitor
WO2024089443A1 (en) * 2022-10-25 2024-05-02 Dow Global Technologies Llc A method of decoking a cracking furnace

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EP0497155A1 (en) * 1991-01-31 1992-08-05 Linde Aktiengesellschaft Decoking of pyrolysis furnaces
EP0591856A1 (en) * 1992-10-05 1994-04-13 Stone & Webster Engineering Corporation Pulsed air decoking
FR2711374A1 (en) * 1993-10-20 1995-04-28 Schmidt Sche Heissdampf Method of thermal decoking of a cracking furnace and the downstream cracking gas cooler.
FR2728578A1 (en) * 1994-12-26 1996-06-28 Inst Francais Du Petrole PROCESS FOR FLEXIBLE VAPOCRAQUING AND CORRESPONDING VAPOCRACKING INSTALLATION
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FR2750140A1 (en) * 1996-06-25 1997-12-26 Inst Francais Du Petrole SPRAYING SYSTEM WITH EROSION PROTECTION MEANS
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EP2048217A3 (en) * 2007-10-12 2012-06-06 Linde AG Method for decarbonising cracking furnaces

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AU6835381A (en) 1981-09-24
JPH0113515B2 (en) 1989-03-07
EP0036151B1 (en) 1984-01-18
ATE5891T1 (en) 1984-02-15
AU540068B2 (en) 1984-11-01
US4420343A (en) 1983-12-13
JPS56142217A (en) 1981-11-06
EP0036151B2 (en) 1987-05-13
DE3161916D1 (en) 1984-02-23
CA1164385A (en) 1984-03-27
DE3010000A1 (en) 1981-09-24

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