Process for cracking hydrocarbons

Abstract

The present invention relates to a process for cracking a hydrocarbon feed, and in particular provides a process for cracking a hydrocarbon feed, the process comprising a) passing the hydrocarbon feed to a reactant tube comprising a first zone and a second zone downstream of the first zone, each zone comprising one or more electrical heating sections, b) heating the hydrocarbon feed in the one or more electrical heating sections in the first zone to vaporize the hydrocarbon feed, and c) heating the vaporized hydrocarbon feed in the one or more electrical heating sections in the second zone to crack the hydrocarbon feed, characterized in that the hydrocarbon feed is analyzed, and controlling electrical energy provided to the one or more electrical heating sections in the first zone and / or electrical energy provided to the one or more electrical heating sections in the second zone based on a result of the analysis.

Description

[0001] The present invention relates to a method for cracking hydrocarbon feeds, and in particular in an electrically heated furnace.

[0002] The cracking of hydrocarbons typically occurs in a furnace. For example, in steam cracking, the hydrocarbon feed to be steam cracked is typically passed through the reaction tubes in the furnace, which are heated. In a conventional furnace, the heat is provided by burners located inside the furnace, which generate the heat for cracking by the combustion of fuel.

[0003] The commercial cracking of hydrocarbons typically occurs at temperatures above 750 °C. Before cracking at such temperatures, the hydrocarbon to be cracked is vaporized, and for this purpose, the hydrocarbon is typically heated and vaporized in the convection section of the furnace and then passed to the burner section where cracking occurs.

[0004] In many conventional designs, the heating and vaporization are carried out in the so-called "convection section" of the furnace, which is the section located above the section where cracking occurs. (The latter is typically referred to as the "radiation section".) The hydrocarbon feed to be cracked is passed through tubes located in the convection section, and the combustion gases from the burners in the radiation section (which are still hot after leaving the radiation section) are used to heat and vaporize the hydrocarbon to be cracked.

[0005] Steam cracking can be carried out on different hydrocarbon feeds. These different hydrocarbon feeds include "light" hydrocarbon feeds such as ethane, "medium" feeds such as naphtha, and "heavy" feeds such as pyrolysis oil.

[0006] Typically, the cracking of different feeds occurs at similar temperatures, typically above 750 °C as already noted, although for lighter feeds, the optimum temperature tends to be slightly higher than for heavier feeds, and for lighter feeds, the optimum residence time also tends to be longer. In contrast, more energy is required to heat and vaporize medium and heavy feeds compared to light feeds.

[0007] For these reasons, furnaces designed to vaporize and crack naphtha feeds are typically not the optimum design for vaporizing and cracking ethane-containing feeds. For example, the number of tubes in the convection section required to completely vaporize naphtha tends to be greater than the number of tubes required to completely vaporize ethane, but is not sufficient to completely vaporize heavier feeds.

[0008] Steam cracking furnaces based on electric heating rather than burners have been proposed. In such designs, both the vaporization step and the cracking step can use electric heating.

[0009] A particular advantage of electric heating is that it can provide more control over the temperature of individual sections of the furnace / reactant tubes.

[0010] US 7288690 describes a method and apparatus for steam cracking hydrocarbons, in which a combined heat and power using fuel combustion is used to simultaneously generate both thermal energy and mechanical work convertible into electricity, and in which the mixture is initially subjected to heating using the thermal energy supplied by the combined heat and power, and subsequently heated to the desired cracking temperature by electrical heating using the electricity supplied by the combined heat and power.

[0011] WO 2022 / 094455 discloses an electrically heated cracking furnace. According to this document, different reactant coils can be fed with different hydrocarbons or mixtures of hydrocarbon feeds, and the heating can vary according to the feed to be cracked. This document also discloses that preheating can be provided outside the main reactor to provide preheating for each feed.

[0012] We have now found a method which enables the same reactant tube (or parallel tube bundle) to be used for different hydrocarbon feeds, and in particular in which both vaporization and cracking of each feed can be carried out in the same reactant tube. This enables a change from cracking of one feed to cracking of a different feed in the same reactant tube in a manner which provides optimized cracking.

[0013] Accordingly, in a first aspect, there is provided a method for cracking a hydrocarbon feed, the method comprising

[0014] a) conveying the hydrocarbon feed to a reactant tube, the reactant tube comprising a first zone and a second zone downstream of the first zone, each zone comprising one or more electrically heated sections,

[0015] b) heating the hydrocarbon feed in the one or more electrically heated sections in the first zone to vaporize the hydrocarbon feed, and

[0016] c) heating the vaporized hydrocarbon feed in the one or more electrically heated sections in the second zone to crack the hydrocarbon feed,

[0017] characterized in that the hydrocarbon feed is analyzed and the electrical energy supplied to the one or more electrically heated sections in the first zone and / or the electrical energy supplied to the one or more electrically heated sections in the second zone is controlled based on the result of the analysis.

[0018] A particular feature of this first aspect is the control of the heating in the first and second zones based on an analysis of the hydrocarbon feed.

[0019] In one embodiment, the hydrocarbon feed is analyzed before it enters the first zone. The analysis in this embodiment preferably provides information about the boiling point range of the hydrocarbon feed. This can be the actual boiling point range or other information indicative thereof such as density measurements.

[0020] Alternative embodiments involve, for example, analyzing a hydrocarbon feed between a first zone and a second zone with an ultrasonic sensor to measure the presence of a liquid phase. Heating in the first zone can then be adjusted accordingly, for example increasing the heating if liquid is observed. Heating in the second zone, such as in an earlier section of the second zone, can also be adjusted based on such a measurement. (In the absence of any other changes, an increase in the liquid present in the hydrocarbons leaving the first zone generally indicates an increase in the boiling point of the hydrocarbon feed, so this is an example of a method of providing information indicative of the boiling point range of the hydrocarbon feed.)

[0021] In any of the embodiments, the analysis can be performed on-line or off-line, and any suitable analysis can be used. In the present invention, the electrical energy supplied to one or more electrically heated sections is controlled based on the results of the analysis. Clearly, the most precise control of the cracking reaction is obtained when the results of an analysis that is updated frequently are used to control the electrical energy supplied to one or more electrically heated sections in the first and / or second zones. Preferably, the hydrocarbon feed is analyzed at least once every 12 hours, and the results are used to control the electrical energy supplied to one or more electrically heated sections in the first zone and / or the electrical energy supplied to one or more electrically heated sections in the second zone. Generally, this means providing the updated analysis results to a control system, through which the electrical energy supplied is controlled at least once every 12 hours. If necessary, the control system then adjusts the electrical energy supplied based on the updated analysis results. (It may also not be necessary to adjust.) Preferably, the hydrocarbon feed is analyzed at least once every 3 hours, such as at least once every hour, and most preferably not less than once every 10 minutes, and the results are used to control the electrical energy supplied to one or more electrically heated sections in the first zone and / or the electrical energy supplied to one or more electrically heated sections in the second zone.

[0022] The analyzer itself can be run to provide continuous or regular analysis.

[0023] In the case of running the analyzer to provide continuous analysis, the results of the analysis can be used to continuously control the electrical energy supplied or can be used discontinuously. In the latter case, the analysis results are suitably obtained from the continuous analyzer and used for said control at least once every 12 hours as already indicated, for example at least once every 3 hours, such as at least once every hour, and most preferably not less than once every 10 minutes.

[0024] In the case where the analyzer / analysis is discontinuous, the analysis is suitably performed at least at the frequency required for said control, i.e., at least once every 12 hours. Not every analysis performed needs to be used to control the electrical energy supplied to one or more electrically heated sections, although typically it is desirable to do so. Preferably, the analysis is performed at least once every 3 hours, such as at least once every hour. In the most preferred embodiment, the analysis can be performed not less than once every 10 minutes.

[0025] Generally, it is preferred to have an analysis method that can provide relatively quick results as this then enables the heating to be adjusted quickly and frequently in response to any changes in the detected feed composition. The analyzer can be located upstream or downstream of the first zone (for the first and second embodiments respectively) and is operated to provide a continuous or regular analysis of the hydrocarbon feed and the analysis can then be used to control the electrical heating sections in the first and / or second zones. Suitable analysis methods (particularly for the first embodiment) include GC, near IR analysis and density measurement.

[0026] A suitable process control system is used to regulate the control of the electrical energy to the electrical heating sections in the first and / or second zones, i.e., the results of the analysis are transmitted to the process control system of the cracking reaction and this will adjust the energy input accordingly.

[0027] Typically, if the boiling range of the hydrocarbon feed increases, the electrical energy supplied to the first zone is increased to provide increased heating and ensure vaporization. The electrical energy supplied to the second zone can be reduced.

[0028] (Obviously, process parameters other than heating can also be adjusted. For example, the hydrocarbon feed rate can also be adjusted according to the hydrocarbon feed and thus the residence time in the first and second zones can be adjusted.)

[0029] The method of the first aspect of the present invention exploits the increased controllability of electrical heating compared to a combustion (burner-based) furnace. In particular, the amount of heating from individual electrical heaters can be finely controlled between zero and the maximum rated value of the heater. Typically, in practice, each heating section in the zone can be heated by a number of electrical heaters. Either way, the heat supplied to each zone can be "finely" adjusted so that cracking can be optimized even if the feed composition changes by only a relatively small amount.

[0030] (As a simple example, if there are four heaters and it is desired to reduce the heat supplied by 25%, you can reduce the electrical energy supplied to each heater to reduce the total heat by 25% or you can switch off one of the heaters.)

[0031] As used herein, "electrical heating section" means a section of the reactant tube that is heated directly or indirectly by electrical energy. "Direct" heating can include, for example, applying electrical energy directly to the reactant tube. "Indirect" heating can include, for example, using one or more heating elements that heat the reactant tube by one or more of radiation, convection and induction.

[0032] Typically, the heating applied to each electrically heated zone and thus the temperature of each electrically heated zone is controllable separately. Typically, each electrically heated zone will have one or more electric heaters associated with the zone. As used herein, this means that each heating zone has one or more specific electric heaters which are adjusted when it is desired to control the temperature of the zone, and at least some of the electric heaters associated with a particular zone are different from and distinct from the electric heaters on different zones.

[0033] The heating applied to any heated zone of the cracking zone can generally be defined based on the electrical energy applied to the heated zone and is most conveniently defined by the power of one or more electric heaters heating the zone. Typically, the applied heating is reduced by reducing the electrical power supplied to one or more electric heaters of a particular heated zone and vice versa.

[0034] As has been noted, it is apparent that the most precise control of the cracking reaction is obtained when more frequent analysis results are provided and used to control the electrical energy supplied to one or more electrically heated zones in the first and / or second zones. However, it is also true that more frequent analysis may be more beneficial for a particular hydrocarbon feed type or operation.

[0035] For example, relatively simple feeds of relatively high purity such as ethane or propane generally may vary relatively little over time and high frequency analysis may not be necessary during the cracking of such feeds. (Control based on analysis provided once every 3 hours or once per hour may be sufficient to precisely control the electrical energy even if more frequent analysis is not harmful.)

[0036] In contrast, more complex feeds such as naphtha or gas oil can vary more significantly and potentially within a relatively short time period. This is especially the case if the hydrocarbon feed can be from different sources or from a single source such as a refinery which itself processes a range of different feedstocks to provide the hydrocarbon feed for cracking. (For example, naphtha feeds obtained from different sources are generally not the same.) In these cases, the hydrocarbon feed may exhibit "natural" variations over time which can be identified and adjusted based on the analysis of the present invention.

[0037] In a preferred aspect, the method of the first aspect of the present invention is applied to the cracking of naphtha, gas oil, pyrolysis oil or other complex hydrocarbon feeds (defined herein as hydrocarbon feeds comprising a mixture of at least two hydrocarbons, each hydrocarbon being present in an amount of at least 10 wt%).

[0038] In another preferred aspect, the method of the first aspect of the present invention is applied where the hydrocarbon feed is intentionally changed from one hydrocarbon feed to another.

[0039] The present invention is most advantageous when there are rather large variations in the hydrocarbon feed to be cracked. This can occur due to a change in the feed to a feed from elsewhere, as already discussed, or by a specific change to a different type of feed, for example between naphtha and ethane-containing feeds, or for example between naphtha and pyrolysis oil.)

[0040] Accordingly, in a second aspect, the present invention provides a method for transitioning from a first process of cracking a first hydrocarbon feed to a second process of cracking a second hydrocarbon feed, wherein:

[0041] a) The first process comprises

[0042] a. feeding the first hydrocarbon feed to a reaction tube, the reaction tube comprising a first zone and a second zone downstream of the first zone, each zone comprising one or more electrically heated sections,

[0043] b. heating the first hydrocarbon feed in the one or more electrically heated sections in the first zone to vaporize the hydrocarbon feed, and

[0044] c. heating the vaporized first hydrocarbon feed in the one or more electrically heated sections in the second zone to crack the hydrocarbon feed,

[0045] b) The transition comprises stopping the feeding of the first hydrocarbon feed to the reaction tube and starting the feeding of the second hydrocarbon feed to the same reaction tube,

[0046] characterized in that the second hydrocarbon feed is analyzed and, during the transition, the electrical energy supplied to the one or more electrically heated sections in the first zone and the electrical energy supplied to the one or more electrically heated sections in the second zone are adjusted based on the results of the analysis.

[0047] Typically, the preferred features of this second aspect, such as the preferred features of the analysis performed and the frequency at which the results of the analysis are used to adjust (control) the electrical energy supplied to the one or more electrically heated sections in the first and second zones, are as described for the first aspect.

[0048] The method referred to as "transition" generally means that the second hydrocarbon feed has a significantly different composition and / or boiling range from the first hydrocarbon feed, thereby causing a change in the heated section in which the feed is completely vaporized. Preferably, the average final boiling point of the boiling range of the second hydrocarbon feed differs (higher or lower) by at least 20 °C from the average boiling point of the boiling range of the first hydrocarbon feed. The second hydrocarbon feed can be of a different type from the first hydrocarbon feed. For example, cracking feeds can typically be characterized as "ethane-based", "propane-based", "butane-based", "naphtha-based" or "pyrolysis-based", such as pyrolysis oil obtained from plastic recycling, so a change from one of these to another would be a transition.

[0049] More generally (in both the first and second aspects), in the first zone, the hydrocarbon feed is heated in one or more electrically heated sections to vaporize the hydrocarbon feed. Typically, the hydrocarbon feed is heated to a temperature sufficient to vaporize the feed but not sufficient to cause cracking or at least not to cause a significant level of cracking. The most preferred temperature will vary depending on the hydrocarbon feed, but the temperature of the hydrocarbon feed at the outlet of the first zone is typically less than 600 °C.

[0050] In the second zone, the vaporized hydrocarbon feed is further heated to crack the hydrocarbon feed. The most preferred temperature for cracking will vary depending on the hydrocarbon feed, but the temperature of the cracked hydrocarbon product at the outlet of the second zone is typically at least 700 °C, and more typically (and preferably) at least 750 °C.

[0051] Generally, each of the first and second zones includes one or more electrically heated sections. Typically, at least one of the first and second zones includes more than one heating section. For example, there can be a total of at least four heating sections.

[0052] In some embodiments, particularly if there is a relatively large variation in the hydrocarbon feed composition / boiling point range, the number of heating sections provided for each of the first and second zones can be adjusted according to the hydrocarbon feed. For example, for one feed composition, the first zone can include "n1" heating sections and the second zone can include "n2" heating sections, where "n1 + n2" equals "n", and "n" is the total number of heating sections present. But for a different feed, the first zone can include "m1" heating sections and the second zone can include "m2" heating sections, where "m1 + m2" again equals "n" (i.e., the same total number of sections), but m1 ≠ n1 and m2 ≠ n2.

[0053] This can be achieved by adjusting the temperature in the heating sections as needed.

[0054] For example, if during a change in the hydrocarbon feed it is desired to increase the number of heating sections in the first zone, the electrical energy input can be adjusted such that the temperature of the first heating section, which was previously in the second zone, is reduced from a temperature sufficient to crack the feed to a temperature sufficient only to vaporize the feed.

[0055] This can be particularly advantageous during a transition or more generally if changing from a first hydrocarbon feed to a second hydrocarbon feed, where the latter is a relatively heavier feed, i.e., has a higher boiling point range.

[0056] In the present invention (first or second aspect), the first zone can be considered the "vaporization zone", while the second zone can be considered the "cracking zone". The individual heating sections in the second / cracking zone can be considered "cracking sections".

[0057] The first / vaporization zone can perform preheating and vaporization, and the heating section therein can be regarded as a preheating and / or vaporization section.

[0058] In a preferred embodiment suitable for the first or second aspect, a quench zone is provided downstream of the second / cracking zone, in which the product stream from the cracking reaction is cooled.

[0059] In one embodiment, the cooling in the quench zone can be carried out by indirect heat exchange, such as indirect heat exchange with water to generate steam.

[0060] In a preferred embodiment, the cracked product stream is cooled in the quench zone by indirect heat exchange with the introduced (fresh) hydrocarbon feed. This provides preliminary preheating of the hydrocarbon feed before the first and second zones and reduces the amount of energy required for vaporization in the first zone.

[0061] More generally, the method of the present invention can be applied to crack any hydrocarbon feed that can be cracked in similar processes and methods. These include, for example, those discussed in US 7288690 and WO 2022 / 094455 as already pointed out. The present invention can be used to crack halogenated hydrocarbons, including cracking dichloroethane. A preferred cracking method that can be applied is a method for cracking hydrocarbons to produce olefins. Suitable hydrocarbon feeds for cracking and especially for producing olefins include ethane, propane, butane, naphtha, gas oil, gas condensate, pyrolysis oil, and mixtures thereof.

[0062] A particularly preferred cracking method that can be applied is the steam cracking of hydrocarbons and especially the steam cracking of the hydrocarbon feeds as pointed out above.

[0063] Except for the requirements defined in the present invention, general method conditions such as feed flow rate, ratio of reactants (such as steam), residence time, and cracking temperature are largely the same as those of conventional methods. Similarly, a feed system and downstream systems such as a quench system and / or heat exchange of reactants with the feed stream can all be present and applied as in conventional cracking methods.

[0064] As already pointed out, the "electric heating section" can be heated directly or indirectly by electric energy. Typically, the reactant tube / its heating section is disposed inside a furnace or a heating chamber. A gas, preferably an inert gas, can be provided inside the chamber. Examples of suitable electric heating furnaces can be found in WO 2022 / 094455 or WO 2020 / 002326 as already pointed out. Examples

[0065] Example 1

[0066] This example illustrates the analysis of a hydrocarbon feed and, in particular, the control of the electrical energy supplied to one or more heating zones during a transition.

[0067] Cracking takes place in a reaction tube. The tube has a length of 15 m, an inner diameter of 47 mm, and an outer diameter of 53 mm. Heating is provided by a set of independently controlled electrical heaters, one heater per meter of tube. The tube metal temperature is measured by thermocouples.

[0068] Analysis of the feedstock is carried out in real time by an on-line near-infrared analyzer associated with an ASTM D86 laboratory analyzer to provide a distillation temperature profile, and the feedstock density is measured using a densitometer.

[0069] In the first cracking process, the feedstock is naphtha. Analysis determines that the feedstock has a density of 0.715 g / cm 3 and a distillation temperature profile as follows:

[0070]

[0071]

[0072] This naphtha at a flow rate of 250 kg / h is mixed with 75 kg / h of steam and fed into the reaction tube. The feedstock temperature at the inlet is 128 °C and the pressure is 530 kPaa. It is determined from the analysis that the feedstock can be completely vaporized by providing 30.9 kW of electrical power, and this energy can be provided by the first heater in the reaction tube. Thus, in the first process, the first 1 m of the reaction tube is the vaporization zone (first zone), where the naphtha is completely vaporized. The gas temperature at the end of the vaporization zone is 136 °C. The remaining 14 m is the cracking zone (second zone). The cracking gas temperature at the end of the cracking zone / the end of the reaction tube is 820 °C, which is a typical cracking temperature for naphtha. The average heat transfer to the reaction tube is 150 kW / m 2 .

[0073] It is desired to transition to a second cracking process, where the feedstock is gas oil. Analysis of the gas oil is carried out and it is found to have a density of 0.8233 g / cm 3 and a distillation temperature profile as follows:

[0074]

[0075]

[0076] This gas oil with a flow rate of 250 kg / h is mixed with 75 kg / h of steam and fed into the reactant pipe. The feedstock temperature at the inlet is 120 °C and the pressure is 530 kPaa. It is determined from the analysis that the feedstock can be completely vaporized by providing 102.5 kW of electric power, and in this process, it is decided to use the first 6 meters of the reactant pipe as the vaporization zone (the first zone), where the gas oil is completely vaporized. The feedstock is completely vaporized in the vaporization zone, and the gas temperature at the end of the vaporization zone is 301 °C. The remaining 9 meters is the cracking zone (the second zone). The cracking gas temperature at the end of the cracking zone / the end of the reactant pipe is 770 °C, which is the typical cracking temperature of gas oil.

[0077] During the transition, the feed of naphtha is stopped and the feed of gas oil is started. When starting to feed gas oil into the reactant pipe, the electric heating energy applied to the 2 - 6 m long section of the reactant pipe from the inlet is reduced.

Claims

1. A method for cracking a hydrocarbon feedstock, the method comprising a) conveying the hydrocarbon feedstock to a reaction tube, the reaction tube comprising a first zone and a second zone downstream of the first zone, each zone comprising one or more electrically heated sections, b) heating the hydrocarbon feedstock in the one or more electrically heated sections in the first zone to vaporize the hydrocarbon feedstock, and c) heating the vaporized hydrocarbon feedstock in the one or more electrically heated sections in the second zone to crack the hydrocarbon feedstock, Characterized in that analyzing the hydrocarbon feedstock and controlling the electrical energy supplied to the one or more electrically heated sections in the first zone and / or the electrical energy supplied to the one or more electrically heated sections in the second zone based on the results of the analysis.

2. The method according to claim 1, wherein the hydrocarbon feedstock is analyzed before entering the first zone, and the analysis provides information on the boiling point range of the hydrocarbon feedstock.

3. The method according to claim 1 or claim 2, wherein the hydrocarbon feedstock is analyzed to measure the presence of a liquid phase between the first zone and the second zone.

4. The method according to any one of the preceding claims, wherein the hydrocarbon feedstock to be cracked changes, including changing the feedstock to a different but same type of feedstock, or changing to a different type of feedstock.

5. A method for transitioning from a first process of cracking a first hydrocarbon feedstock to a second process of cracking a second hydrocarbon feedstock, wherein: a) the first process comprises a. conveying the first hydrocarbon feedstock to a reaction tube, the reaction tube comprising a first zone and a second zone downstream of the first zone, each zone comprising one or more electrically heated sections, b. heating the first hydrocarbon feedstock in the one or more electrically heated sections in the first zone to vaporize the hydrocarbon feedstock, and c. heating the vaporized first hydrocarbon feedstock in the one or more electrically heated sections in the second zone to crack the hydrocarbon feedstock, b) the transition comprises stopping the feeding of the first hydrocarbon feedstock to the reaction tube and starting the feeding of the second hydrocarbon feedstock to the same reaction tube, characterized in that the second hydrocarbon feedstock is analyzed and the electrical energy supplied to the one or more electrically heated sections in the first zone and the electrical energy supplied to the one or more electrically heated sections in the second zone are adjusted during the transition based on the results of the analysis.

6. The method according to claim 5, wherein the second hydrocarbon feedstock is analyzed before entering the first zone, and the analysis provides information on the boiling point range of the hydrocarbon feedstock.

7. The method according to claim 5 or claim 6, wherein the second hydrocarbon feedstock is analyzed to measure the presence of a liquid phase between the first zone and the second zone.

8. The method according to any one of claims 5 to 7, wherein the average final boiling point of the boiling point range of the second hydrocarbon feedstock differs (higher or lower) by at least 20 °C from the average boiling point of the boiling point range of the first hydrocarbon feedstock.

9. The method according to any one of claims 5 to 8, wherein the second hydrocarbon feedstock is of a different type from the first hydrocarbon feedstock.

10. The method according to any one of the preceding claims, wherein the hydrocarbon feed is analyzed at least once every 12 hours, and the result of the analysis is used to control the electrical energy supplied to the one or more electrically heated zones.

11. The method according to any one of the preceding claims, wherein the analysis is carried out by an on-line analyzer and is operated to provide a continuous or regular analysis of the hydrocarbon feed, preferably not less than once every 10 minutes.

12. The method according to any one of the preceding claims, wherein the analysis is selected from GC, near-IR analysis and density measurement.

13. The method according to any one of the preceding claims, wherein the hydrocarbon feed is heated in the first zone such that the temperature at the outlet of the first zone is less than 600 °C.

14. The method according to any one of the preceding claims, wherein the vaporized hydrocarbon feed is heated in the second zone such that the temperature at the outlet of the second zone is generally at least 700 °C, and preferably at least 800 °C.

15. The method according to any one of the preceding claims, wherein a quench zone is provided downstream of the second zone, in which the product stream from the cracking reaction is cooled by indirect heat exchange with the (fresh) hydrocarbon feed introduced before the feed is transferred to the first and second zones.

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