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EP0252355B1 - Verfahren und Ofen für das Dampfkracken von Kohlenwasserstoffen für die Zubereitung von Olefinen und Diolefinen - Google Patents

Verfahren und Ofen für das Dampfkracken von Kohlenwasserstoffen für die Zubereitung von Olefinen und Diolefinen Download PDF

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Publication number
EP0252355B1
EP0252355B1 EP87108911A EP87108911A EP0252355B1 EP 0252355 B1 EP0252355 B1 EP 0252355B1 EP 87108911 A EP87108911 A EP 87108911A EP 87108911 A EP87108911 A EP 87108911A EP 0252355 B1 EP0252355 B1 EP 0252355B1
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EP
European Patent Office
Prior art keywords
cracking
tube
hydrocarbons
mixture
outlet
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EP87108911A
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English (en)
French (fr)
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EP0252355A1 (de
Inventor
André Martens
Serge Bellet
Pierre Crouzet
Jean-Pierre Toulet
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Naphtachimie SA
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Naphtachimie SA
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Priority claimed from FR8609218A external-priority patent/FR2600666B1/fr
Priority claimed from FR8609217A external-priority patent/FR2600665B1/fr
Priority claimed from FR8609220A external-priority patent/FR2600641B1/fr
Application filed by Naphtachimie SA filed Critical Naphtachimie SA
Publication of EP0252355A1 publication Critical patent/EP0252355A1/de
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
    • F28F13/06—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by affecting the pattern of flow of the heat-exchange media
    • F28F13/08—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by affecting the pattern of flow of the heat-exchange media by varying the cross-section of the flow channels
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G2400/00—Products obtained by processes covered by groups C10G9/00 - C10G69/14
    • C10G2400/20—C2-C4 olefins

Definitions

  • the present invention relates to a process for cracking hydrocarbons in the presence of water vapor, intended for manufacturing olefins and diolefins, and in particular ethylene.
  • the present invention also relates to a device consisting of a cracking oven intended for the implementation of this process.
  • hydrocarbons are thus in particular transformed, on the one hand, into a gaseous hydrocarbon fraction comprising in particular olefins containing from 2 to 6 carbon atoms, such as ethylene, propylene and isobutene, and diolefins such as butadiene, and, on the other hand, in a liquid hydrocarbon fraction, called "steam cracking gasoline", comprising hydrocarbons containing from 5 to 12 carbon atoms, as well as undesirable by-products, such as methane.
  • steam cracking processes known until now, using in particular liquid hydrocarbons and in particular that described in GB-A 1 165 907 are carried out with the aim, obviously, of obtaining the highest possible yield of olefins and as diolefins, but under conditions which favor the production of ethylene over those of other olefins and diolefins.
  • steam cracking ovens are generally designed to operate under conditions known as high severity. These conditions are such that the mixture of hydrocarbons and water vapor, circulating in the cracking tube arranged in the form of a coil inside the radiant part of an oven, is subjected to a high temperature. and at low pressure, for a relatively short time.
  • steam cracking processes can use relatively higher cost gaseous hydrocarbons, such as liquefied petroleum gas, also called LPG, or ethane, a secondary product resulting from steam cracking of hydrocarbons.
  • gaseous hydrocarbons such as liquefied petroleum gas, also called LPG, or ethane
  • liquids such as naphtha or gas oil.
  • LPG liquefied petroleum gas
  • ethane a secondary product resulting from steam cracking of hydrocarbons.
  • liquids such as naphtha or gas oil.
  • an urgent need has also appeared to modify the steam cracking processes for gaseous hydrocarbons, in order to significantly increase the ethylene selectivity of steam cracking reactions.
  • a process and an oven for cracking liquid or gaseous hydrocarbons have now been found in the presence of water vapor, making it possible, in the case of liquid hydrocarbons, not only to very significantly increase the production of proplyene, isobutene and butadiene with respect to the production of ethylene, but also to significantly increase the yield of cracking into olefins and diolefins, and in the case of gaseous hydrocarbons very significantly increase the selectivity for ethylene of the steam cracking reaction and at the same time very significantly reduce the amount of methane produced, while also avoiding the drawbacks mentioned above.
  • the method and the device of the invention can, moreover, be easily adapted to already existing steam cracking installations.
  • the cracking temperature of the mixture of hydrocarbons and steam increases along the cracking tube, between the inlet and the outlet of the radiation area of the furnace, i.e. in the direction of flow of the mixture.
  • the mixture of hydrocarbons and water vapor is subjected to preheating before it enters the radiation zone of the oven, this preheating can be carried out by any known means, in particular in a zone of convection heating of the oven. .
  • the cracking temperature of the mixture of hydrocarbons and water vapor is at the entry of the radiation region of the oven between 400 ° C and 650 ° C, preferably between 430 ° C and 580 ° C; it is at the exit of this zone comprised between 720 ° C and 860 ° C, preferably comprised between 760 ° C and 810 ° C.
  • the cracking temperature of the mixture of hydrocarbons and steam is at the entry of the radiation zone of the furnace between 500 ° C and 700 ° C, preferably between 550 ° C and 660 ° C; it is at the exit of this zone between 800 ° C and 880 ° C, preferably between 810 ° C and 850 ° C.
  • the method according to the present invention is characterized by an average residence time of the mixture of hydrocarbons and water vapor, circulating in the cracking tube between the inlet and the outlet of the radiation zone of the furnace.
  • This average residence time can be relatively longer than that usually existing in steam cracking processes for hydrocarbons operating under conditions of high severity. It is generally between 300 and 1800 milliseconds, preferably com taken between 400 and 1400 milliseconds, especially when the hydrocarbons used are gaseous. It is, moreover, between 850 and 1800 milliseconds, preferably between 870 and 1500 milliseconds, and more particularly between 900 and 1400 milliseconds, when the hydrocarbons used are liquid.
  • the method according to the present invention is also characterized by the reaction volume of the cracking tube which in the first half of the length of the tube, located towards the entrance to the radiation zone, is 1.3 to 4 times greater, preferably 1.5 to 2.5 times greater than that of the second half of the length of the tube, located towards the exit of this area. More particularly, the reaction volume per unit length of the cracking tube decreases continuously or discontinuously from the entry to the exit from the radiation zone of the furnace. In practice, it is preferred to carry out this reduction in a discontinuous manner, in stages along the cracking tube.
  • the average residence time of the mixture per unit length of the cracking tube also called partial residence time
  • the average residence time of the mixture circulating in the first half of the length of the tube, located towards the entrance to the radiation area of the furnace is 2 to 4 times greater, preferably 2.6 to 3 times greater than that existing in the second half of the length of the tube, located towards the exit of this zone. It is also observed that the apparent surface speed of the mixture of hydrocarbons and water vapor circulating in the cracking tube increases in the direction of flow of the mixture.
  • this speed is relatively low in the first half of the length of the cracking tube, located towards the entrance to the radiation zone, for example between 30 and 80 m / sec, and higher in the second half of the length of the tube, located towards the exit of the radiation zone, for example between 90 and 150 m / sec.
  • the method according to the present invention allows the mixture of hydrocarbons and steam to pass relatively slowly through the part of the cracking tube where the temperature is relatively low, and on the contrary more quickly through the part of the cracking tube where the temperature is higher.
  • the cracking temperature of the mixture of hydrocarbons and steam does not increase uniformly along the tube, between the inlet and the outlet of the radiation zone of the furnace. More specifically, the increase in the cracking temperature of the mixture is relatively moderate in the first half of the length of the tube, located towards the entrance to the radiation zone of the furnace, while the increase in the cracking temperature of the mixing is more important in the second half of the length of the tube, located towards the exit of the radiation area of the oven.
  • the regulation of the cracking temperature of the mixture of hydrocarbons and steam, circulating in the tube between the inlet and the outlet of the radiation area of the furnace is obtained by a graded distribution of the thermal power applied to the pipe.
  • thermal power applied to the second half of the length of the tube, located towards the exit from the radiation area of the furnace is 1.5 to 5 times greater, preferably 2 to 4 times greater than that applied at the first half of the length of the tube, located towards the entrance to this area.
  • thermal power is meant here the quantity of heat supplied per unit of time and per unit of volume of the oven surrounding the cracking tube.
  • This combination also has the result of increasing the ethylene selectivity of the steam cracking reaction and of significantly reducing the quantity of methane produced, when gaseous hydrocarbons are used in particular. This result is also obtained with an improved thermal radiation efficiency compared to previously known methods, due to a relatively lower average cracking temperature.
  • the method according to the present invention also provides other advantages.
  • it makes it possible to reduce the coking phenomena occurring inside the cracking tube. It allows, in in addition, to increase the service life of a steam cracking installation, thus operating at a relatively low average cracking temperature.
  • composition of the mixture of hydrocarbons and steam, used in the process according to the invention is such that the weight ratio of the quantity of hydrocarbons to the quantity of steam is between 1 and 10, preferably between 2 and 6, in the case of gaseous hydrocarbons in particular, and preferably between 3 and 6, when it is in particular liquid hydrocarbons.
  • the liquid hydrocarbons used in the mixture with the water vapor, can be chosen from naphtha, consisting of hydrocarbons containing approximately from 5 to 10 carbon atoms, light gasolines consisting of hydrocarbons comprising approximately 5 or 6 carbon atoms, the diesel oil consisting of hydrocarbons containing approximately from 8 to 15 carbon atoms, as well as their mixtures. They can also be used in admixture with saturated and unsaturated hydrocarbons containing from 3 to 6 carbon atoms.
  • the gaseous hydrocarbons used in the mixture with water vapor, consist of alkanes comprising from 2 to 4 carbon atoms, in particular ethane, propane or butane, or by their mixtures. These alkanes can optionally be used in admixture with alkenes containing from 2 to 6 carbon atoms and / or methane and / or alkanes containing from 5 to 6 carbon atoms. It is possible, in particular, to use in the process of the invention natural gas or liquefied petroleum gas, also called LPG, or ethane, a secondary product resulting from the steam cracking of liquid hydrocarbons, such as naphtha or diesel.
  • LPG liquefied petroleum gas
  • ethane a secondary product resulting from the steam cracking of liquid hydrocarbons, such as naphtha or diesel.
  • the process of the present invention is particularly advantageous for increasing the production of higher olefins and diolefins compared to that of ethylene, in particular the production of olefins having 3 or 4 carbon atoms, such as propylene and isobutene and the production of diolefins such as butadiene.
  • This advantage is appreciated, in particular, by defining, on the one hand, a selectivity, Ss, in produced hydrocarbons comprising 3 carbon atoms, and on the other hand a selectivity, S 4 , in produced hydrocarbons comprising 4 carbon atoms, according to the following equations: and
  • the method makes it possible to carry out the steam cracking of liquid hydrocarbons with a selectivity S 3 equal to or greater than 0.73 and a selectivity S 4 equal or greater than 0.51, when the thermal power is applied in a homogeneous manner along of the cracking tube.
  • the selectivities S 3 and S 4 can become equal to or greater than 0.78 and 0.57 respectively, when the thermal power is applied in a non-homogeneous manner along the cracking tube, according to the process of the invention .
  • the steam cracking furnace comprises a thermal radiation enclosure through which at least one cracking tube passes, arranged in the form of a horizontal or vertical coil.
  • This cracking tube must have a ratio between the length and the mean internal diameter of between 200 and 600, preferably between 300 and 500.
  • the mean internal diameter of the cracking tube is preferably equal to or greater than 100 mm, so that the average residence time of the mixture in the cracking tube can be relatively long and that the pressure drops of the mixture circulating in the powerful cracking tube to be weak.
  • the mean internal diameter and the length of the tube must remain within ranges of values compatible with the mechanical and thermal stresses to which the materials constituting the cracking tube are subjected.
  • the average internal diameter of the cracking tube cannot exceed approximately 250 mm.
  • the internal mean diameter of the cracking tube can be between 70 mm and 160 mm, preferably between 80 and 150 mm.
  • the internal diameter of the cracking tube decreases continuously or discontinuously from the inlet to the outlet of the thermal radiation enclosure of the furnace, that is to say in the direction of the flow of the mixture of hydrocarbons and water vapor.
  • the reduction in the internal diameter of the cracking tube is such that the ratio between the internal diameters of the tube at the inlet and at the outlet of the thermal radiation enclosure is between 1.2 and 3, preferably included between 1.4 and 2.2, more particularly between 1.4 and 2.
  • the internal diameter of the cracking tube at the inlet of the thermal enclosure radiation is preferably between 140 and 220 mm, and that at the outlet of this enclosure is preferably between 70 and 120 mm.
  • the internal diameter of the cracking tube at the inlet of the thermal radiation enclosure is preferably between 110 and 180 mm, and that at the outlet of this enclosure is preferably between 60 and 100 mm.
  • the cracking tube is arranged in the form of a coil made up of a succession of straight sections connected together by elbows, these straight sections having decreasing internal diameters from the inlet to the outlet of the pipe. thermal radiation enclosure.
  • Figure 1 schematically illustrates a horizontal steam cracking furnace comprising a thermal radiation enclosure (1) through which passes a cracking tube arranged in the form of a coil consisting of eight horizontal straight sections connected together by elbows, the sections (2) and (3) having an internal diameter of 172 mm, the sections (4) and (5) an internal diameter of 150 mm, the sections (6) and (7) a diameter of 129 mm and the sections (8 ) and (9) an internal diameter of 108 mm, the inlet and outlet of the cracking tube in the thermal radiation enclosure being in (10) and (11) respectively.
  • a variant may consist in using a cracking tube which, upon entering the thermal radiation chamber of the furnace, is divided into a bundle of parallel tubes whose internal diameter can be constant and whose number decreases since l entry to the exit of the thermal enclosure, so that the reaction volume constituted by the set of tubes corresponding to the first half of the length of the cracking tube is 1.3 to 4 times greater, preferably 1.5 to 2.5 times greater than that corresponding to the second half of the length of the tube.
  • the steam cracking oven comprises a thermal radiation enclosure provided with heating means consisting of burners, arranged for example in rows on the floor and / or on the walls of the enclosure.
  • the arrangement, adjustment and / or size of the burners in the thermal enclosure are such that the thermal power can be distributed uniformly along the tube, and the mixture of hydrocarbons and steam is subjected to a temperature which increases rapidly in the first half of the tube, then more slowly in the second half of the tube.
  • the maximum heating power must be such that the skin temperature does not exceed the limit compatible with the nature of the metal or alloy constituting the cracking tube.
  • the steam cracking furnace comprises heating means constituted by burners whose thermal power increases along the cracking tube, from the inlet to the outlet of the enclosure.
  • thermal radiation so that the ratio between the thermal power of the burners applied to the first half of the length of the cracking tube, located towards the inlet of the thermal radiation enclosure, and that applied to the second half of the length of the tube, located towards the outlet of this enclosure, is between 40/60 and 15/85, preferably between 33/67 and 20/80.
  • the arrangement, adjustment and / or size of the burners in the thermal enclosure are such that the thermal power increases along the cracking tube from the inlet to the outlet of the enclosure.
  • This increasing profile of the thermal power of the burners applied along the cracking tube can be easily obtained by appropriately adjusting the gas or fuel-gas supply rate of each of the burners.
  • Another way is to have burners of the appropriate size and heating capacity in the thermal enclosure.
  • the maximum heating power must be such that the skin temperature does not exceed the limit compatible with the nature of the metal or alloy constituting the cracking tube.
  • a steam cracking furnace as shown diagrammatically in FIG. 1, comprises a thermal radiation enclosure (1) in brickwork, constituted by a rectangular parallelepiped whose internal dimensions are 9.75 m for the length, 1.70 m for the width and 4.85 m for the height.
  • a cracking tube of refractory steel based on nickel and chromium having an average internal diameter of 140 mm, a thickness of 8 mm and, taking into account the capacity of the enclosure, is placed.
  • the relationship between lon and the internal mean diameter of the tube is 457.
  • This cracking tube is arranged in the form of a serpentine, comprising eight straight horizontal sections, of equal length each, connected to each other by elbows.
  • the internal diameter of the sections (2) and (3) located towards the entrance to the thermal enclosure is 172 mm; the following sections (4) and (5) have an internal diameter of 150 mm; then sections (6) and (7) have an internal diameter of 129 mm; the internal diameter of the sections (8) and (9) located towards the outlet of the thermal enclosure is 108 mm.
  • the internal diameters of the cracking tube at the inlet (10) and at the outlet (11) of the enclosure (1) being 172 mm and 108 mm respectively, the ratio between the internal diameters of the tube to entry and exit is therefore 1.6.
  • the reaction volume of the first half of the length of the cracking tube, corresponding to the straight sections (2), (3), (4) and (5) is 1.84 times greater than the reaction volume of the second half the length of the cracking tube, corresponding to the straight sections (6), (7), (8) and (9).
  • the thermal radiation enclosure of the steam cracking furnace is provided with burners arranged on the walls of the enclosure, in five horizontal rows, located at equal distance from each other. The thermal power of all of these burners is evenly distributed between these five rows.
  • the liquid hydrocarbons consist of a naphtha with a density of 0.718, having a distillation range of ASTM 45/180 ° C. and weight contents of 35% in linear paraffins, 29.4% in branched paraffins, 28.3% in compounds cyclic and 7.3% aromatic compounds.
  • the composition of the mixture of naphtha and water vapor used is such that the weight ratio of the quantity of naphtha to the quantity of water vapor is 4.
  • the naphtha is thus introduced into the cracking tube according to a flow rate of 3500 kg / h and water vapor at a flow rate of 875 kg / h.
  • the cracking temperature of the mixture of naphtha and steam rises from 470 ° C at the entrance to the oven radiation zone up to 775 ° C at the exit from this zone.
  • the evolution of the cracking temperature of the mixture along the cracking tube is described by the curve (a) of FIG. 4, representing on the abscissa the reaction volume (in liters) crossed by the mixture and on the ordinate the cracking temperature (in ° C) of the mixture.
  • Curve (a) shows that the cracking temperature of the mixture increases in its initial part relatively slowly as a function of the reaction volume passed through.
  • the pressure of the mixture is at the outlet of the oven of 170 kPa.
  • the average residence time of the mixture of naphtha and water vapor circulating in the cracking tube between the inlet and the outlet of the radiation zone of the furnace is 1030 milliseconds. Furthermore, the average residence time of this mixture circulating in the first half of the length of the cracking tube is 2.3 times greater than that in the second half of the length of the tube.
  • Example 1 The operation is carried out in a steam cracking furnace identical to that of Example 1.
  • a mixture of naphtha and steam is circulated in the cracking tube of this furnace identical to that used in Example 1.
  • the flow rates of naphtha and water vapor circulating in the tube are respectively 4800 and 1200 kg / h, this increase in flow rates compared to those of Example 1 can be easily achieved thanks to the fact that the cracking tube used has a relatively low pressure drop.
  • the cracking temperature of the mixture of naphtha and water vapor rises from 480 ° C. at the entrance to the radiation zone of the furnace to 775 ° C. at the exit from this zone.
  • the pressure of the mixture is 170 kPa at the outlet of the oven.
  • the average residence time of the mixture of naphtha and water vapor circulating in the cracking tube between the inlet and the outlet of the radiation zone of the furnace is 900 milliseconds. Furthermore, the average residence time of this mixture circulating in the first half of the length of the cracked tube is 2.3 times greater than that in the second half of the length of the tube.
  • Per hour 640 kg of ethylene, 612 kg of propylene, 122 kg of isobutene, 200 kg of butadiene and 170 kg of ethane are thus produced.
  • the ethane thus produced in this furnace is then subjected to a secondary stage of steam cracking making it possible to transform it into ethylene according to a weight yield of 85% and thereby improving the overall production of ethylene from the steam cracking installation.
  • the productions of olefins and of diolefins are higher than those of Example 1, because of the gain on the flow rates of raw materials which makes it possible to accomplish the steam cracking furnace of the present invention.
  • the productions of higher olefins and of butadiene are relatively high compared to the production of ethylene.
  • the production of propylene, isobutene and butadiene are 780 kg, 155 kg and 255 kg respectively.
  • a steam cracking oven comprises a thermal radiation enclosure, identical in shape and size to that of Example 1.
  • a cracking tube of refractory steel based on nickel and chromium, of a weight is placed. total substantially identical to that of Example 1, having an internal diameter of 108 mm, a thickness of 8 mm and, taking into account the capacity of the enclosure and the mechanical and thermal stresses of the oven, a total length of 80 meters between the entrance and the exit of the enclosure.
  • the ratio between the length and the internal diameter of the tube is 740.
  • This cracking tube is arranged in the form of a coil comprising eight straight horizontal sections, of equal length each, connected to each other by elbows. The internal diameter of these straight sections is constant and equal to 108 mm.
  • the internal diameters of the tube at the inlet and at the outlet of the enclosure are identical.
  • the reaction volume of the first half of the length of the cracking tube, corresponding to the first four straight sections is identical to the reaction volume of the second half of the length of the cracking tube, corresponding to the last four straight sections.
  • the thermal radiation enclosure of the steam cracking furnace is provided with burners arranged on the walls of the enclosure, in five horizontal rows, located at equal distance from each other. The thermal power of all of these burners is evenly distributed between these five rows.
  • the cracking temperature of the mixture of naphtha and steam is 490 ° C at the entrance to the oven radiation zone and 775 ° C at the exit from this zone.
  • the evolution of the cracking temperature of the mixture along the cracking tube is described by curve (b) of FIG. 4, representing on the abscissa the reaction volume (in liters) crossed by the mixture and on the ordinate the cracking temperature (in ° C) of the mixture.
  • Curve (b) shows that the cracking temperature of the mixture increases in its initial part relatively rapidly as a function of the reaction volume passed through.
  • the pressure of the mixture is at the outlet of the oven of 170 kPa.
  • the average residence time of the mixture of naphtha and water vapor circulating in the cracking tube between the inlet and the outlet of the radiation zone of the furnace is 830 milliseconds.
  • the maximum capacity loss of such a steam cracking furnace is approximately 35%, for an unchanged volume of the thermal radiation enclosure and for substantially identical mechanical and thermal stresses of the furnace, in comparison with the furnace. described in Example 1.
  • a steam cracking oven comprises a thermal radiation enclosure, identical in shape and size to that of Example 1.
  • a cracking tube of refractory steel based on nickel and chromium, of a weight is placed. total substantially identical to that of Example 1, having an internal diameter of 140 mm, a thickness of 8 mm and, taking into account the capacity of the enclosure and the mechanical and thermal stresses of the oven, a total length of 64 meters between the entry and exit of the enclosure.
  • the ratio between the length and the internal diameter of the tube is 457.
  • This cracking tube is arranged in the form of a coil comprising eight horizontal straight sections, of equal length each, connected to each other by elbows. The internal diameter of these straight sections is constant and equal to 140 mm.
  • the internal diameters of the tube at the inlet and at the outlet of the enclosure are identical.
  • the reaction volume of the first half of the length of the cracking tube, corresponding to the first four straight sections is identical to the reaction volume of the second half of the length of the cracking tube, corresponding to the last four straight sections.
  • the thermal radiation enclosure of the steam cracking furnace is provided with burners arranged on the walls of the enclosure, in five horizontal rows, located at equal distance from each other. The thermal power of all of these burners is evenly distributed between these five rows.
  • a mixture of naphtha and water vapor is circulated, identical to that used in Example 1.
  • the naphtha is introduced therein at a rate of 3500 kg / h and the vapor of water at a flow rate of 875 kg / h.
  • the cracking temperature of the mixture of naphtha and water vapor rises from 500 ° C at the entrance to the radiation zone of the furnace up to 775 ° C at the exit from this zone.
  • the pressure of the mixture is at the outlet of the oven of 170 kPa.
  • the average residence time of the mixture of naphtha and water vapor circulating in the cracking tube between the inlet and the outlet of the radiation zone of the furnace is 900 milliseconds.
  • the heat flux table measured inside the thermal radiation enclosure of the furnace is, under these conditions, represented in FIG. 2 by the surface inscribed in the three-dimensional graph connecting by the three coordinate axes, the length L of the thermal enclosure, the height H of this enclosure and the thermal flux F.
  • FIG. 2 shows, in particular, that the maximum of the thermal flux of radiation is located in the lower part of the thermal enclosure, corresponding to the second half the length of the cracking tube located towards the outlet of the radiation thermal enclosure.
  • the liquid hydrocarbons consist of a naphtha of density 0.690, having a distillation range ASTM 45/180 ° C and weight contents of 38.2% in linear paraffins, of 36.9% in branched paraffins, of 17.1% in cyclanic compounds and 7.8% in aromatic compounds.
  • the composition of the mixture of naphtha and water vapor used is such that the weight ratio of the quantity of naphtha to the quantity of water vapor is 4.
  • the naphtha is thus introduced into the cracking tube according to a flow rate of 3500 kg / h and water vapor at a flow rate of 875 kg / h.
  • the cracking temperature of the mixture of naphtha and water vapor rises from 435 ° C at the entrance to the radiation zone of the furnace up to 775 ° C at the exit from this zone.
  • the evolution of the temperature of the mixture along the cracking tube is described by the curve (a) of FIG. 5 representing on the abscissa the average residence time (in milliseconds) of the mixture circulating in the cracking tube from the inlet up to the exit from the radiation area of the oven and on the ordinate the cracking temperature (in ° C) of the mixture.
  • Curve (a) shows that the cracking temperature of the mixture increases in its initial part relatively slowly as a function of the average residence time of the mixture in the cracking tube and that in particular most of the residence time of the mixture is performed at a relatively low cracking temperature, in particular at a temperature below 700 ° C.
  • the pressure of the mixture is at the outlet of the oven of 170 kPa.
  • the average residence time of the mixture of naphtha and water vapor circulating in the cracking tube between the inlet and the outlet of the radiation zone of the furnace is 1180 milliseconds. Furthermore, the average residence time of this mixture circulating in the first half of the length of the cracking tube is 2.6 times greater than that in the second half of the length of the tube.
  • Example 5 The operation is carried out in a steam cracking oven identical to that of Example 5.
  • a mixture of naphtha and steam identical to that used in Example 5 is circulated in the cracking tube of this oven.
  • flow rates of naphtha and water vapor circulating in the tube are respectively 4800 kg / h and 1200 kg / h, this increase in flow rates compared to those of Example 5 can be easily achieved thanks to the fact that the tube cracking agent used has a relatively low pressure drop.
  • Curve (b) shows that the cracking temperature of the mixture increases in its initial part relatively slowly as a function of the average residence time of the mixture in the cracking tube and that in particular most of the residence time of the mixture is performed at a relatively low cracking temperature, in particular at a temperature below 700 ° C.
  • the pressure of the mixture is 170 kPa at the outlet of the oven.
  • the average residence time of the mixture of naphtha and water vapor circulating in the cracking tube between the inlet and the outlet of the radiation zone of the furnace is 1020 milliseconds. Furthermore, the average residence time of this mixture circulating in the first half of the length of the cracking tube is 2.6 times greater than that in the second half of the length of the tube. 750 kg of ethylene, 770 kg of propylene, 110 kg of isobutene, 180 kg of butadiene and 200 kg of ethane are thus produced per hour.
  • the ethane thus produced in this furnace is then subjected to a secondary stage of steam cracking making it possible to transform it into ethylene at a weight yield of 85% and thereby improving the overall production of ethylene from the steam cracking installation.
  • the productions of olefins and of diolefin are higher than those of Example 5, due to the gain on the flow rates of raw materials which the steam cracking furnace of the present invention makes it possible to achieve.
  • the productions of higher olefins and of butadiene are relatively high compared to the production of ethylene.
  • the production of propylene, isobutene and butadiene are 837 kg, 158 kg and 260 kg respectively.
  • Example 3 The operation is carried out in a steam cracking oven comprising a thermal enclosure, a cracking tube and burners, identical to those of Example 3 (comparative).
  • the thermal power of all the burners is also as in Example 3 (comparative), distributed homogeneously between the five rows.
  • the thermal flux table measured inside the thermal radiation enclosure of the furnace is, under these conditions, represented in FIG. 3 by the surface inscribed in the three-dimensional graph connecting by the three coordinate axes, the length L of the thermal enclosure, the height H of this enclosure and the thermal flux F.
  • FIG. 3 shows, in particular, that the maximum of the thermal flux of radiation is located in the upper part of the thermal enclosure, corresponding to the first half the length of the cracking tube located towards the entrance to the thermal enclosure.
  • the cracking temperature of the mixture of naphtha and water vapor rises from 495 ° C at the entrance to the radiation zone of the furnace up to 775 ° C at the exit from this zone.
  • the evolution of the cracking temperature of the mixture along the cracking tube is described by curve (c) of FIG. 5, representing on the abscissa the average residence time (in milliseconds) of the mixture circulating in the cracking tube from the inlet to the outlet of the radiation area of the oven and on the ordinate the cracking temperature (in ° C) of the mixture.
  • Curve (c) clearly shows that the cracking temperature of the mixture increases in its initial part rapidly as a function of the residence time of the mixture in the cracking tube, and that in particular a significant part of the residence time of the mixture is achieved at a relatively high cracking temperature, in particular at a temperature above 700 ° C.
  • the pressure of the mixture is at the outlet of the oven of 170 kPa. Given the distribution of the heat flux in the enclosure, the thermal power applied to the second half of the length of the cracking tube is identical to that applied to the first half of the length of the tube.
  • the average residence time of the mixture of naphtha and water vapor circulating in the cracking tube between the inlet and the outlet of the radiation zone of the furnace is 840 milliseconds.
  • the maximum capacity loss of such a steam cracking furnace is approximately 35%, for an unchanged volume of the thermal radiation enclosure and for substantially identical mechanical and thermal stresses of the furnace, in comparison with the furnace. in example 5.
  • a steam cracking furnace as shown diagrammatically in FIG. 1, comprises a thermal radiation enclosure (1) identical to that described in Example 1.
  • a cracking tube of refractory steel based on nickel is placed. and of chromium, of dimensions different from that described in Example 1; it has an average internal diameter of 108 mm, a thickness of 8 mm and, taking into account the capacity of the enclosure (1), a total length of 80 meters, comprised between the inlet (10) and the outlet (11 ).
  • This cracking tube is arranged in the form of a serpentine, comprising eight horizontal straight sections, of equal length each, connected to each other by elbows.
  • the internal diameter of the sections (2) and (3) located towards the entrance to the thermal enclosure is 135 mm; the following sections (4) and (5) have an internal diameter of 117 mm; then sections (6) and (7) have an internal diameter of 99 mm; the internal diameter of the sections (8) and (9) located towards the outlet of the thermal enclosure is 81 mm.
  • the internal diameters of the cracking tube at the inlet (10) and at the outlet (11) of the enclosure (1) being 135 mm and 81 mm respectively
  • the ratio between the internal diameters of the tube to entry and exit is 1.7.
  • the reaction volume of the first half of the length of the cracking tube, corresponding to the straight sections (2), (3), (4), and (5) is 1.95 times greater than the reaction volume of the second half of the length of the cracking tube, corresponding to the straight sections (6), (7), (8) and (9).
  • a mixture of ethane and water vapor is circulated.
  • the composition of the mixture of ethane and water vapor used is such that the weight ratio of the amount of ethane to the amount of water vapor is 2.25.
  • Ethane is thus introduced into the cracking tube at a rate of 1800 kg / h and water vapor at a rate of 800 kg / h.
  • the cracking temperature of the mixture of ethane and water vapor rises from 585 ° C at the entrance to the radiation zone of the furnace up to 846 ° C at the exit from this zone.
  • the pressure of the mixture leaving the oven is 170 kPa.
  • the average residence time of the mixture of ethane and water vapor circulating in the cracking tube between the inlet and the outlet of the radiation zone of the furnace is 640 milliseconds.
  • Example 3 The operation is carried out in a steam cracking oven comprising a thermal enclosure, a cracking tube and burners, identical to those of Example 3 (comparative).
  • the thermal power of all the burners is, as in Example 3 (comparative), evenly distributed between the five rows.
  • a mixture of ethane and water vapor is circulated, identical to that used in Example 8.
  • the ethane is introduced therein at a rate of 1800 kg / h and the vapor water at a flow rate of 800 kg / h.
  • the cracking temperature of the mixture of ethane and water vapor rises from 636 ° C at the entrance to the radiation zone of the furnace up to 846 ° C at the exit from this zone.
  • the pressure of the mixture leaving the oven is 170 kPa.
  • the average residence time of the mixture of ethane and water vapor circulating in the cracking tube between the inlet and the outlet of the radiation zone of the furnace is 585 milliseconds.
  • Example 8 The procedure is exactly as in Example 8, except that instead of using ethane, a mixture of gaseous hydro carbides is used comprising 76% by weight of ethane, 19% by weight of propane and 5% by weight of propylene.
  • the pressure at the outlet of the oven is 175 kPa instead of 170 kPa.
  • the cracking temperature of the mixture is at the entry of the radiation zone of 575 ° C instead of 585 ° C, and at the exit of this zone of 848 ° C instead of 846 ° C.
  • the average residence time the mixture of gaseous hydrocarbons and water vapor circulating in the cracking tube between the entry and the exit of the radiation zone is 665 milliseconds instead of 640 milliseconds.
  • Example 9 The procedure is exactly as in Example 9 (comparative), except that instead of using ethane, a mixture of gaseous hydrocarbons is used identical to that used in Example 10.
  • the pressure the mixture at the outlet of the oven is 175 kPa, instead of 170 kPa.
  • the cracking temperature of the mixture is at the entry of the radiation zone of 610 ° C instead of 636 ° C and at the exit of this zone of 848 ° C instead of 846 ° C.
  • the residence time of the mixture of gaseous hydrocarbons and water vapor circulating in the cracking tube between the entry and the exit of the radiation zone is 610 milliseconds instead of 585 milliseconds.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)

Claims (10)

1. Verfahren zur Herstellung von Olefinen und Diolefinen durch Kracken von flüssigen oder gasförmigen Kohlenwasserstoffen in Gegenwart von Wasserdampf, das darin besteht, durch eine Strahlungszone eines Ofens ein Gemisch von Kohlenwasserstoffen und Wasserdampf, das in einem im Inneren dieser Zone angeordneten Krackrohr zirkuliert, bei einem Ofenausgangsdruck im Bereich von 120 bis 240 kPa strömen zu lassen, wobei die Kracktemperatur des Gemisches am Eingang der Strahlungszone im Bereich von 400 bis 700°C und am Ausgang dieser Zone im Bereich von 720 bis 800°C ist, dadurch gekennzeichnet, daß
(a) die mittlere Verweilsdauer des im Krackrohr zirkulierenden Gemisches von Kohlenwasserstoffen und Wasserdampf zwischen dem Eingang und dem Ausgang der Strahlungszone im Bereich von 300 bis 1800 Millisekunden ist und
(b) das Reaktionsvolumen der ersten, zum Eingang der Strahlungszone liegenden Hälfte der Länge des Krackrohres 1, 3- bis 4-mal größer als das der zweiten, zum Ausgang dieser Zone liegenden Hälfte der Länge des Rohres ist.
2. Verfahren nach dem Anspruch 1, dadurch gekennzeichnet, daß die Erhöhung der Kracktemperatur des Gemisches von Kohlenwasserstoffen und Wasserdampf mit einer nicht homogenen Verteilung der längs des Krackrohres einwirkenden Wärmeleistung des Ofens verknüpft ist, welche Verteilung derart ist, daß die auf die zweite, zum Ausgang der Strahlungszone liegende Hälfte der Länge des Rohres einwirkende Wärmeleistung 1, 5- bis 5-mal größer als die auf die erste, zum Eingang dieser Zone liegende Hälfte der Länge des Rohres einwirkende ist.
3. Verfahren nach dem Anspruch 2, dadurch gekennzeichnet, daß die auf die zweite Hälfte der Länge des Rohres einwirkende Wärmeleistung 2- bis 4-mal größer als die auf die erste Hälfte der Länge des Rohres einwirkende ist.
4. Verfahren nach dem Anspruch 1, dadurch gekennzeichnet, daß die mittlere Verweilsdauer des im Krackrohr zirkulierenden Gemisches von Kohlenwasserstoffen und Wasserdampf zwischen dem Eingang und dem Ausgang der Strahlungszone im Bereich von 850 bis 1800 Millisekunden ist, wenn man flüssige Kohlenwasserstoffe einsetzt.
5. Verfahren nach dem Anspruch 1, dadurch gekennzeichnet, daß die mittlere Verweilsdauer des im Krackrohr zirkulierenden Gemisches von Kohlenwasserstoffen und Wasserdampf zwischen dem Eingang und dem Ausgang der Strahlungszone im Bereich von 400 bis 1400 Millisekunden ist, wenn man gasförmige Kohlenwasserstoffe einsetzt.
6. Verfahren nach dem Anspruch 1, dadurch gekennzeichnet, daß die Zusammensetzung des eingesetzten Gemisches von Kohlenwasserstoffen und Wasserdampf derart ist, daß das Gewichtsverhältnis der Kohlenwasserstoffmenge zur Wasserdampfmenge im Bereich von 1 bis 10 ist.
7. Verfahren nach dem Anspruch 1, dadurch gekennzeichnet, daß die eingesetzten Kohlenwasserstoffe flüssige Kohlenwasserstoffe, die unter dem Naphta, den Leichtbenzinen, dem Gasöl sowie ihren Mischungen mit den gesättigten Kohlenwasserstoffen mit 3 bis 6 Kohlenstoffatomen gewählt sind, oder auch gasförmige Kohlenwasserstoffe sind, die aus Alkanen mit 2 bis 4 Kohlenstoffatomen oder aus ihren Mischungen bestehen, welche Alkane eventuell als Mischung mit Alkenen mit 2 bis 6 Kohlenstoffatomen und/oder Methan und/oder Alkanen mit 5 bis 6 Kohlenstoffatomen eingesetzt werden.
8. Vorrichtung, die aus einem Ofen zum Kracken von Kohlenwasserstoffen in Gegenwart von Wasserdampf gebildet ist, der einen mit Heizmitteln ausgestatteten Wärmestrahlungsbehälter aufweist, den wenigstens ein Krackrohr durchsetzt, in dem das Gemisch von Wasserdampf und zu krackenden Kohlenwasserstoffen zirkuliert, dadurch gekennzeichnet, daß
(a) das Verhältnis zwischen der Länge und dem mittleren Innendurchmesser des den Wärmestrahlungsbehälter durchsetzenden Krackrohres im Bereich von 200 bis 600 ist und
(b) der Innendurchmesser des Krackrohres in einer kontinuierlichen oder diskontinuierlichen Weise vom Eingang bis zum Ausgang des Wärmestrahlungsbehälters derart abnimmt, daß das Verhältnis zwischen den Innendurchmessem des Rohres am Eingang und am Ausgang dieses Behälters im Bereich von 1,2 bis 3 ist.
9. Vorrichtung nach dem Anspruch 8, dadurch gekennzeichnet, daß die Heizmittel aus Brennern bestehen, deren Wärmeleistung längs des Krackrohres vom Eingang bis zum Ausgang des Wärmestrahlungsbehälters derart wächst, daß das Verhältnis zwischen der auf die erste, zum Eingang des Wärmestrahlungsbehälters liegende Hälfte der Länge des Krackrohres einwirkenden Wärmeleistung und der auf die zweite, zum Ausgang dieses Behälters liegende Hälfte der Länge des Rohres einwirkenden im Bereich von 40/60 bis 15/85 liegt.
10. Vorrichtung nach dem Anspruch 8, dadurch gekennzeichnet, daß das Krackrohr aus einer Folge von Rohren mit vom Eingang bis zum Ausgang des Wärmestrahlungsbehälters abnehmendem Innendurchmesser gebildet ist.
EP87108911A 1986-06-25 1987-06-22 Verfahren und Ofen für das Dampfkracken von Kohlenwasserstoffen für die Zubereitung von Olefinen und Diolefinen Expired - Lifetime EP0252355B1 (de)

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
FR8609218A FR2600666B1 (fr) 1986-06-25 1986-06-25 Procede et four de vapocraquage d'hydrocarbures liquides destines a la fabrication d'olefines et de diolefines
FR8609217 1986-06-25
FR8609220 1986-06-25
FR8609217A FR2600665B1 (fr) 1986-06-25 1986-06-25 Procede et four de vapocraquage d'hydrocarbures liquides destines a la fabrication d'olefines et de diolefines
FR8609218 1986-06-25
FR8609220A FR2600641B1 (fr) 1986-06-25 1986-06-25 Procede et four de vapocraquage d'hydrocarbures gazeux destines a la fabrication d'olefines et de diolefines

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EP0252355A1 EP0252355A1 (de) 1988-01-13
EP0252355B1 true EP0252355B1 (de) 1990-10-03

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ES (1) ES2018664B3 (de)

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FR2796078B1 (fr) 1999-07-07 2002-06-14 Bp Chemicals Snc Procede et dispositif de vapocraquage d'hydrocarbures
FR2834515B1 (fr) * 2002-01-10 2006-03-10 Atofina Vapocraquage de naphta modifie
EP1561796A1 (de) * 2004-02-05 2005-08-10 Technip France Spaltofen
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CN116496137A (zh) * 2023-02-24 2023-07-28 香港中文大学（深圳） 一种通过热辐射催化天然气产烯烃的方法

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DE10000889C2 (de) * 2000-01-12 2002-12-19 Mg Technologies Ag Verfahren zum Erzeugen von C¶2¶- und C¶3¶-Olefinen aus Kohlenwasserstoffen

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DE3765324D1 (de) 1990-11-08
ES2018664B3 (es) 1991-05-01
JPS6366289A (ja) 1988-03-24
US5124003A (en) 1992-06-23
CA1256456A (en) 1989-06-27
JPH0813972B2 (ja) 1996-02-14

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