Process and plant for steam cracking

Abstract

A steam cracking process is proposed, wherein a feed mixture (5) containing one or more hydrocarbons and steam is fed to a cracking furnace (10, 80), wherein cracking gas (8) is extracted from the cracking furnace (10, 80), and wherein the cracking gas (8) or a portion thereof is subjected to cracking gas cooling (16), the cracking gas cooling (16) being carried out using a primary cracking gas cooler (161), a secondary cracking gas cooler (162), and a tertiary cracking gas cooler (163), and wherein the secondary cracking gas cooler (162) is arranged downstream of the primary cracking gas cooler (161) and the tertiary cracking gas cooler (163) is arranged downstream of the secondary cracking gas cooler (162). It is provided that the feed mixture (5) or a portion thereof is heated by means of the secondary cracking gas cooler (162). A corresponding facility (100-800) is also included.

Description

[0001] The invention relates to a process and a plant for steam cracking. background

[0002] Processes and plants for steam cracking hydrocarbons are described, for example, in the article "Ethylene" in Ullmann's Encyclopedia of Industrial Chemistry, online edition, April 15, 2009, DOI: 10.1002 / 14356007.a10_045.pub2. Steam cracking is primarily used to produce short-chain olefins such as ethylene and propylene, diolefins such as butadiene, or aromatics, but is not limited to the production of such compounds.

[0003] Steam cracking systems with cracking furnaces are used for steam cracking. These cracking furnaces can also be deployed in one or more groups and operated under different conditions or loaded with different feeds. Conventional cracking furnaces typically have a convection section and a radiant section. The radiant section is fired by burners arranged at least at the bottom. Flue gases from the radiant zone flow out through the convection zone.

[0004] The convection zone is typically used to preheat boiler feedwater, generate or further heat steam, and / or preheat the reaction feed or further heat a mixture of reaction feed and steam. For this purpose, appropriate tube bundles are passed through the convection zone. The mixture of reaction feed and steam is passed through the radiant zone for conversion in so-called coils. The coils can be provided in various configurations and arrangements described in the technical literature.

[0005] The cracked gas, which is discharged from the radiation zone via the aforementioned cracking tubes and is initially at a temperature typically between 750 and 875 °C, must be cooled as quickly as possible to bring the ongoing reactions to a halt as quickly as possible and thus prevent the excessive formation of undesirable byproducts. Quench heat exchangers, which are also referred to below as "cracked gas coolers," are used to cool the cracked gas. Various designs are described in the specialist literature.

[0006] EP 3 415 587 A1 proposes a modified design of the convection zone and the quench heat exchanger for fired furnaces with air preheating, in which a mixture of hydrocarbons and process steam is heated in the radiation zone directly before being fed into the reaction tubes against cracked gas directly after being removed from the reaction tubes in a cracked gas cooler.

[0007] There is still a need for improvements in steam cracking processes and plants that overcome certain disadvantages of conventional processes and, in particular, provide energy benefits. Short description

[0008] Against this background, a method and a system for steam cracking with the features of the independent patent claims are proposed. Embodiments of the present invention are the subject of the dependent patent claims and the following description.

[0009] The present invention and its embodiments propose variants of a process control in a fired cracking furnace, which enable a significant minimization of the fuel gas consumption or the underfiring power (and associated emissions, in particular of carbon dioxide) of more than 30%, compared to a conventional cracking furnace.

[0010] Combined with carbon-free fuel gas (blue or green hydrogen or ammonia) and compensation for the reduced steam production by means of electric instead of steam turbine drives (green electricity), a partially to largely carbon dioxide emission-free and sustainable production of ethylene and optionally other olefins can be achieved.

[0011] Within the scope of the present invention and its embodiments, combustion air preheating and cracked gas cooling against a reaction feed mixture (i.e., the use of a feed-effluent heat exchanger, FEHE or FEX) are proposed. Particular improvements in embodiments of the invention include the realization of very high air preheating temperatures (approximately 400 to 700°C) during combustion air preheating, whereby in corresponding embodiments, in particular, (indirect) cracked gas heat integration and flue gas utilization via conventional bundles (tube bundles) directly at the cracking furnace, i.e., within the convection zone, are possible.

[0012] The proposed cracked gas cooling system makes it possible to avoid and minimize obvious and expected disadvantages, difficulties, costs, and risks of existing processes and systems. This allows for increased flexibility and a broader range of applications while maximizing fuel gas savings.

[0013] The invention and its embodiments encompass the avoidance of new and additional process risks, particularly with regard to selectivity losses, precracking (i.e., undesirable premature cracking processes), coking, furnace operating time, and design and flexibility limitations. The invention and its embodiments can encompass conventional or only slightly modified process parameters (feed pressure, process steam pressure, process-side pressure drop). The term "conventional" is intended to refer in particular to operation within typical, particularly known, process parameter ranges.

[0014] In embodiments of the invention, a conventional furnace design can be used, with corresponding cracking furnaces having, in particular, a conventional convection zone with flue gas bundles (hereinafter also referred to simply as "tube bundles" or "bundles") in the convection zone. Cracking gas cooling can be achieved in conventional heat exchangers (linear coolers or straight-tube heat exchangers). Minimizing the structural complexity for additional equipment, control and instrumentation, and for the equipment itself, particularly with regard to the heat exchanger surfaces, is possible in embodiments of the invention. Furthermore, the use of additional, external heat sources can be avoided, thus maintaining furnace autonomy.

[0015] Furthermore, embodiments of the invention avoid conventional (large, complex) combustion air preheaters for heating fresh air with flue gas, as well as an unconventional and thus complex cracked gas cooler design. However, they still enable significant (additional) savings and high air preheating temperatures.

[0016] For electrically heated cracking furnaces whose feed preheating must be carried out without flue gas waste heat, the proposed three-stage cracking gas cooling system can achieve a favorable balance of heat integration between benefit, effort, and risk, particularly despite the conventional design of the coolers. In electrically heated cracking furnaces, a high degree of heat integration with regard to the cracked gas is advantageous because, due to the lack of flue gas, this is the only remaining internal heat source with the (required) high temperature level. This approach enables the integration of the available cracked gas heat of up to 80% of the maximum integration achievable with the maximum possible effort for feed preheating. This is therefore a so-called 80% solution, in which 80% benefit is achieved with 20% effort.

[0017] In addition, an elegant, simple circuit for using the cracked gas heat for air preheating in fired cracking furnaces with gas feed is proposed (indirectly via feed water, up to approx. 300 °C).

[0018] In addition to the advantageous use of cracked gas waste heat, this achieves a particularly compact design and flexible installation compared to conventional air preheating using flue gas.

[0019] These advantages are achieved in a steam cracking process, wherein a feed mixture containing one or more hydrocarbons and steam is fed to a cracking furnace, a cracking gas is withdrawn from the cracking furnace, and the cracking gas, or a portion thereof, is subjected to cracking gas cooling. The cracking gas cooling is carried out using a primary cracking gas cooler, a secondary cracking gas cooler, and a tertiary cracking gas cooler. The secondary cracking gas cooler is arranged downstream of the primary cracking gas cooler, and the tertiary cracking gas cooler is arranged downstream of the secondary cracking gas cooler. In the following, this is also referred to as a secondary cracking gas cooler, a feed-effluent heat exchanger, or a feed-effluent heat exchanger, arranged "sandwich-like" between the primary and tertiary cracking gas coolers.

[0020] In the proposed process, the feed mixture or a part thereof is heated by means of the secondary cracked gas cooler.

[0021] The invention combines, in particular, the following elements for a fired cracking furnace in the aspects and corresponding embodiments described below: A multi-stage air preheating system with at least one air preheater external to the convection zone and in particular indirectly against the cracked gas cooling (via saturated steam or hot boiler feed water, in particular from the tertiary cracked gas cooler or a steam drum) can be provided. A further air preheater can be provided, in particular, as a conventional bundle in the convection zone and heated by means of flue gas. In further embodiments, additional preheating stages and media (if necessary also external media, heat sources and the like) can be combined with this.

[0022] Furthermore, in this or other embodiments, a multi-stage cracked gas cooling system for fired and electrically heated cracking furnaces with at least one intermediate feed-effluent heat exchanger (in the aforementioned sandwich arrangement) can be provided. An upstream steam generator, a downstream steam generator, a boiler feedwater heater, or other means can be provided. The intermediate feed-effluent heat exchanger, i.e., the second cracked gas cooler, can be configured, in particular, for the temperature ranges specified below for cracked gas or feed.

[0023] The feed-effluent heat exchanger, and thus the secondary quenched gas cooler, can be designed in particular as a conventional heat exchanger, for example, as a straight-tube heat exchanger, particularly according to or based on the TEMA standard. Double-tube types (with or without longitudinal fins) can also be used, as can well-known special designs (e.g., hairpin heat exchangers).

[0024] In embodiments of the invention, in particular a combination and interconnection of the above-mentioned aspects (multi-stage air preheating, of which at least one air preheater is arranged as a bundle in the convection zone and multi-stage cracked gas cooling with feed-effluent heat exchanger) can be provided for different furnace types with further variants / additions.

[0025] In alternative configurations, a single-stage air preheating system against feedwater (particularly for a cracking furnace for gas feed) can also be provided, particularly in the process path from the furnace boundary (or a boiler feedwater pump) to the steam drum. This path includes at least the final cracked gas cooler (typically the tertiary cracked gas cooler).

[0026] In further embodiments of the invention, upstream and / or downstream preheater bundles (economizer bundles) can be provided in the convection zone. The sequence can include, in particular (starting, for example, from a boiler feedwater pump), the economizer bundle, then the tertiary cracked gas cooler, the air preheater, and another economizer bundle.

[0027] In embodiments of the invention, heating gas preheating is also possible, either in parallel with the first stage of air preheating (against saturated steam or boiler feed water) or as a convection zone bundle.

[0028] To summarize, a three-stage cracked gas cooler system with primary, secondary, and tertiary coolers is proposed, with the secondary cooler serving to superheat the feed and steam. The sandwich arrangement of the secondary cooler between the upstream and downstream primary and tertiary coolers enables the use of a conventional upstream primary cooler (linear or straight-tube steam generator) and avoids selectivity losses and runtime losses due to excessively rapid coking. A conventional downstream tertiary cooler can be used (as a straight-tube exchanger for steam generation or as a boiler feedwater preheater). This allows for proven, efficient cooling options at the cold cracked gas end with a flexible temperature window of the secondary cooler. This results in a direct reduction in steam production for fired furnaces and better utilization of the high cracked gas temperature level compared to steam generation.A process-critical total pressure drop (e.g., 150 to 200 mbar) in the cracked gas cooling system is not increased, or only slightly increased, by appropriate design in embodiments of the invention. A feed-side preheating section can be implemented in such a way that the pressure drops are no higher than in conventional systems. On the feed side, the pressure drop of the exchanger (including piping) corresponds approximately to that required for an equivalent bundle (in a range of, for example, 300 to 1000 mbar).

[0029] An adjustable temperature window can also be provided through appropriate upstream and downstream cooling, allowing the heat quantity to be adapted to the framework conditions or process requirements. Coking on the cracked gas side is minimized by selecting the temperature window. This can also prevent precracking. Furthermore, increased flexibility and advantages in the structural design (heat exchanger surface, material selection) result from the selection of the temperature window. The proposed wiring and the resulting temperature windows enable a significant reduction in the overall length, which would not be possible without a downstream tertiary cooler. Typical examples are 6 to 8 m overall length compared to 14 to 20 m overall length.

[0030] In embodiments of the present invention, the behavior over the runtime can be comparable to conventional convection zone bundles due to the positive coking behavior. No control is required.

[0031] In embodiments of the invention, the hydrocarbons in the feed mixture can have a boiling range of 35 to 400 °C to a proportion of more than 90%, i.e. originate in particular from naphtha or gas oil or correspond to corresponding cuts, wherein the secondary cracked gas cooler is operated with a cracked gas inlet temperature of 550 to 650 °C, in particular approximately 610 °C, a cracked gas outlet temperature of 420 to 520 °C, in particular approximately 460 °C, a feed mixture inlet temperature of 270 to 330 °C, in particular approximately 310 °C, and a feed mixture outlet temperature of 400 to 535 °C, in particular approximately 460 °C.

[0032] In other embodiments of the invention, the hydrocarbons in the feed mixture can have a boiling range of less than 35 °C to a proportion of more than 90% and in particular comprise ethane or propane, wherein the secondary cracked gas cooler is operated with a cracked gas inlet temperature of 580 to 650 °C, in particular approximately 610 °C or else 580 to 680 °C, in particular approximately 630 °C, a cracked gas outlet temperature of 300 to 450 °C, in particular approximately 370 °C or else 300 to 550 °C, in particular approximately 360 °C, a feed mixture inlet temperature of 180 to 240 °C, in particular approximately 215 °C, and a feed mixture outlet temperature of 400 to 535 °C, in particular approximately 485 °C.

[0033] The mentioned ranges represent the temperature ranges used during runtime in consideration of the desired performance (20 to 50%) and can be selected or adjusted accordingly.

[0034] In the proposed process, a straight-tube heat exchanger with tube-side cracked gas routing can be used as the secondary cracked gas cooler. The secondary cracked gas cooler tubes can have an outer diameter of 40 to 50 mm and a tube length of up to 12 m, and / or the secondary cracked gas cooler can be operated with a pressure drop of 10 to 60 mbar and / or at up to 80% of the speed of sound.

[0035] In appropriate designs, a particularly efficient counterflow exchanger is created. A heat exchanger according to the TEMA standard (Tubular Exchanger Manufacturers Association) in the so-called no-tube-in-window design with advantageous cross-longitudinal flow, avoidance of hotspots / pre-cracking, and favorable behavior with regard to vibrations is possible, as is the use of inlet and outlet cones to prevent blockages of the cracked gas tubes due to deposits of coke particles. In a heat exchanger with a no-tube-in-window design, the tubes are arranged in the baffles so that they always experience only a pure cross-flow of the cooling medium. In this way, heat exchange in stagnation zones and swirling areas, and thus also fouling or pre-cracking, can be avoided. For expert understanding, reference can be made to relevant specialist books, for example, by RK Shah and DPSekulic, "Fundamentals of Heat Exchanger Design", John Wiley & Sons, 2003, pages 18 and 19.

[0036] A low process-side pressure (shell space) allows for compensators to prevent thermal stresses. The main advantage over a primary feed-effluent gas cooler is that there is no increased pressure drop, because a high cooling rate is no longer required (which, in gas-to-gas exchangers, can only be achieved through pressure-loss-intensive measures). A (linear) double-tube design or other well-known configurations are also possible. This allows for single or multiple configurations depending on the requirements (process, mechanics, installation, etc.).

[0037] In the process, the cracking furnace can be operated using a fuel gas which is combusted with combustion air, wherein the combustion air or a part thereof is subjected to combustion air preheating.

[0038] In the radiant zone, the heat for the cracking reaction is supplied to the cracking tubes via direct heating. The heat balance of the furnace's radiant zone is determined by the heat demand for the desired cracking reaction and the radiant zone efficiency. The radiant zone efficiency is primarily determined by the air preheating temperature and fuel gas quality (with a typical excess air of 10%, selected geometry, and firing concept).

[0039] Typically, cracking furnaces are primarily underfired with residual gas. For liquid feedstock, this is usually a methane-rich fraction, while for gas feedstock, it is a methane / hydrogen fraction. With regard to decarbonization efforts, the example calculations are based on hydrogen-rich or exclusively hydrogen fuel gas. This is accompanied by an (additional) increase in the radiant zone efficiency. This is conservative in terms of considering the convection zone and the secondary cracking gas cooler and is associated with lower air preheating temperatures (in terms of savings). The addition of ammonia to the fuel gas is also feasible.

[0040] In embodiments of the invention, the combustion air preheating can be carried out using an air preheater located outside a convection zone of the cracking furnace and subsequently heated using an air preheater in the convection zone. Further details and advantages are given above.

[0041] The combustion air preheating can be carried out using the air preheater in the convection zone to a temperature of more than 400 °C, in particular up to 600 °C or up to 700, 750 or 800 °C.

[0042] In embodiments of the invention, the air preheater located outside the convection zone can be operated using boiler feedwater, which is heated using the tertiary cracked gas cooler. The fuel gas, or a portion thereof, can also be preheated using boiler feedwater, which in turn is then heated using the tertiary cracked gas cooler.

[0043] The fuel gas can have a hydrogen content of more than 90% or, as mentioned, it can be pure hydrogen. 70 to 80% of the fuel gas, for example, 77%, can be combusted by bottom burners, with the remaining portion being combusted by sidewall burners. The potentially high air preheating temperature in the air preheater in the convection zone eliminates the need for complex air supply to numerous / small sidewall burners. In the designs proposed here, the combustion air of the sidewall burners is typically used unheated, whereas at least partial air preheating is performed for the bottom burners. New systems, in particular, are increasingly being implemented with pure bottom firing, but many existing furnaces have mixed firing with 30 to 40% sidewall burner capacity. The concept proposed here therefore also enables significant savings potential during retrofitting with reasonable conversion costs.

[0044] Examples include a mixed firing system with a ratio of 77 / 23 from floor to wall. Preheated forced air can only be supplied to floor burners (within a temperature range of around 555 °C). A supply of (unheated) fresh air to the side wall burners results in an average air preheating temperature of around 430 °C in the example. Savings of 30 to 40% of fuel gas or

[0045] Underfiring performance is achieved through a radiant zone efficiency of 50 to 55% and air preheating to 400 to 600 or 700 °C.

[0046] The proposed concept and its configurations enable flexible furnace design to reduce underfiring for a typical fuel gas quality (from primarily hydrocarbons (methane) to primarily / exclusively hydrogen) and common firing variants (bottom firing, mixed firing), as well as common cracked tube types. A correspondingly optimized combination of efficiency and air preheating temperature can be found, subject to the constraints of the heat balance around the convection zone / cracked gas cooling.

[0047] In embodiments of the present invention, the cracking furnace can also be heated using electric current, as discussed in particular in connection with the description of the figures.

[0048] Operating the secondary cracked gas cooler in the proposed manner also enables the utilization of the cracked gas heat for feed heating in corresponding electric cracking furnaces, achieving direct heat integration at the highest possible temperature level. This minimizes preheating with electric current, while minimizing process risks (regarding loss of selectivity, increased coking, or precracking), and using conventional heat exchangers.

[0049] Steam generation occurs in the primary and tertiary cracked gas coolers (the primary cracked gas cooler being designed here, in particular, as a linear cooler). In the embodiments illustrated in the figures, the saturated steam produced can be used in a feed preheater, a dilution steam superheater, and a high-temperature bundle for preheating feed and, if necessary, process steam (up to approximately 300°C).

[0050] If the heat balance of the convection zone is not adequate (especially during conversion / retrofit), this can be compensated for with external heat exchangers using saturated steam as the heating medium. Due to the temperature limitation of the steam at approximately 330 °C, this is possible upstream of the dilution steam superheater. The resulting increased process steam temperature is beneficial for feed evaporation.

[0051] Between a feed preheater and a high-temperature bundle, a liquid feed may still be present in two phases, so combining it with steam at the aforementioned 330 °C may be unfavorable. Downstream of the high-temperature bundle, a boost with appropriate steam may be possible if temperatures are significantly below 300 °C. This is unproblematic, since the feed is in a purely gaseous state.

[0052] Taken together, a large part of the required feed heat is provided via saturated steam utilization: This means that 70-80% of the available cracked gas heat can be used for feed and process steam preheating with a moderate / acceptable FEX heating surface. This corresponds to approximately 80-90% of what is achievable with a single, technically complex primary FEX (assuming that high wall temperatures of >650-700°C on the process side are to be avoided at all costs (due to pre-cracking and possible coking). Compared to a very complex multi-stage primary FEX, this still corresponds to 75-80%. Note for example: With appropriate installation (FPH, DSS and HTC above the steam drum), the condensate collection tank and the condensate return pump can be omitted (gravitational condensate return).

[0053] The proposed steam cracking plant is designed to feed a feed mixture containing one or more hydrocarbons and steam to a cracking furnace, withdraw a cracked gas from the cracking furnace, subject the cracked gas or a portion thereof to cracked gas cooling, and carry out the cracked gas cooling using a primary cracked gas cooler, a secondary cracked gas cooler, and a tertiary cracked gas cooler. The secondary cracked gas cooler is arranged downstream of the primary cracked gas cooler and the tertiary cracked gas cooler is arranged downstream of the secondary cracked gas cooler. The plant is designed to heat the feed mixture or a portion thereof using the secondary cracked gas cooler.

[0054] For further features and advantages of a corresponding system and embodiments thereof, reference is expressly made to the above explanations concerning the method proposed according to the invention and its embodiments, since these apply equally to this.

[0055] The same applies to a system which, according to an embodiment of the invention, is designed to carry out a method according to any embodiment of the present invention. Short description of the drawing

[0056] Embodiments of the invention are described below purely by way of example with reference to the accompanying drawings and explanation of the technical background.

[0057] Figures 1 to 8 illustrate methods according to embodiments of the invention and an embodiment not according to the invention. Embodiments of the invention

[0058] The embodiments described below are described solely for the purpose of assisting the reader in understanding the claimed and previously discussed features. They are merely representative examples and are not intended to be exhaustive and / or limiting with regard to the features of the invention. It is to be understood that the advantages, embodiments, examples, functions, features, structures, and / or other aspects described above and below are not to be considered as limitations on the scope of the invention as defined in the claims or as limitations on equivalents to the claims, and that other embodiments may be utilized and changes may be made without departing from the scope of the claimed invention.

[0059] Different embodiments of the invention may include, comprise, consist of, or consist essentially of other useful combinations of the described elements, components, features, parts, steps, means, etc., even if such combinations are not specifically described herein. Furthermore, the disclosure may encompass other inventions that are not currently claimed but that may be claimed in the future, particularly if they are encompassed within the scope of the independent claims.

[0060] Explanations relating to devices, apparatus, arrangements, systems, etc. according to embodiments of the present invention may also apply to methods, processes, methods, etc. according to the embodiments of the present invention, and vice versa. Elements, method steps, etc. that are identical, have the same effect, are functionally equivalent, are structurally identical, or are comparable may be identified by identical reference numerals.

[0061] The figures illustrate systems according to embodiments of the present invention and are generally provided with the reference numerals indicated below. These systems each comprise a cracking furnace 10 with a radiation zone 11 and a convection zone 12.

[0062] In the radiation zone 11, reaction tubes 111 of a known type are arranged, in which a mixture of a reaction feedstock (specified in more detail below) and steam is heated. Heat exchangers and other devices, particularly of a known form, i.e., in the form of tube bundles, are arranged in the convection zone 11, which are also explained below with reference to specific embodiments. A flue gas is passed through the convection zone 12, from bottom to top in the plane of the drawing. This flue gas is discharged from the radiation zone 11 and cooled in the convection zone 12.

[0063] One in Figure 1The plant 100 illustrated is designed for processing liquid feedstocks such as naphtha. A feed stream 1 is heated in a feed preheater 121 from a temperature of, in particular, approximately 110 °C (or more generally, in a range from 50 to 130 °C, possibly also approximately 70 °C) to a temperature of, in particular, approximately 152 °C, with the flue gas downstream of the feed preheater 121 being at a temperature of, in particular, approximately 139 °C.

[0064] A denitrification device 122 is arranged in the flue gas stream upstream of the preheater 121. The temperature of the flue gas upstream of the denitrification device 122 is at a temperature of approximately 306°C in particular. The temperatures specifically mentioned here are examples that result from the specific design conditions, e.g., tube rows. A process temperature of approximately 250 to 400°C, in particular 300 to 350°C, should be targeted here. Corresponding temperatures may also depend on the manufacturer. At temperatures that are too low, more catalyst is required due to the lower activity; beyond 400°C, limitations due to "sintering" come into effect, particularly because the design temperature usually has a significant increase. A return line with a fan is provided to recirculate flue gas from downstream of the denitrification device 122 to upstream of the denitrification device 122. This is not specifically designated.

[0065] A first high-temperature bundle 123 is arranged in the flue gas stream upstream of the denitrification device 122, wherein the temperature of the flue gas upstream of the first high-temperature bundle 123 is at a temperature of, in particular, approximately 438°C. A dilution steam superheater 124 is located in the flue gas stream upstream of the first high-temperature bundle 123, wherein the temperature of the flue gas upstream of the dilution steam superheater 124 is at a temperature of, in particular, approximately 510°C.

[0066] Dilution steam 2 is optionally preheated by means of a steam preheater 13 from a temperature of, in particular, approximately 185 °C to a temperature of, in particular, approximately 311 °C, then superheated in the dilution steam superheater 124 to a temperature of, in particular, approximately 456 °C, then combined with the feed 1 preheated in the feed preheater 121, and passed through the first high-temperature bundle 123. Further heat exchangers, which are not specifically designated here, can optionally be provided upstream and / or downstream of the high-temperature bundle 123.

[0067] Components of a steam system include a first steam superheater 125 and a second steam superheater 126. Saturated steam 3 from a steam drum 14 is passed through the first steam superheater 125 at a temperature of, in particular, approximately 322 °C and heated to a temperature of, in particular, approximately 462 °C. After the addition of boiler feedwater 4, the temperature is reduced to, in particular, approximately 451 °C, and the corresponding steam is superheated in the second steam superheater 126 to a temperature of, in particular, approximately 505 °C. It is then available for any application.

[0068] The mixture of feed 1 and steam 2, in Figure 1designated 5, is present after heating in the first high-temperature bundle 123 at a temperature of in particular approximately 307 °C. In conventional steam cracking plants, a corresponding mixture 5 would then be passed through a second high-temperature bundle, which is also arranged in the convection zone 12. This is not the case in the plant 100. A device corresponding to such a second high-temperature bundle is nevertheless present in the form of an air preheater 127, wherein the temperature of the flue gas upstream of the air preheater 127 is in particular approximately 803 °C and downstream thereof, and thus upstream of the second steam superheater 126, is at a temperature of in particular approximately 655 °C.

[0069] Combustion air 6 is heated in a further air preheater 15 arranged externally of the convection zone 12 with saturated steam 9 from the steam drum 14 from a temperature of in particular approximately 15 °C to a temperature of in particular approximately 302 °C and then further heated by means of the air preheater 127 in the convection zone 12 to a temperature of in particular approximately 555 °C. The correspondingly heated combustion air 6 can then be supplied to the burners that heat the radiation zone 11 and which are not separately illustrated here.

[0070] The heating of the mixture 5 comprising feed 1 and dilution steam 2 takes place against the cracked gas flow, as explained below, and only then in a further high-temperature bundle 128, which is referred to here as the third high-temperature bundle 128 to simplify comparability with conventional systems, even though in the embodiment illustrated here there is no conventional second high-temperature bundle for heating the mixture 5. The temperature of the flue gas in the convection zone 12 upstream of the third high-temperature bundle 128 is in particular approximately 1099 °C. The temperature of the flue gas in the convection zone 12 downstream of the third high-temperature bundle 128 and upstream of the air preheater 127 is in particular approximately 803 °C.

[0071] In the third high-temperature bundle 128, the mixture 5 is heated from a temperature of, in particular, approximately 461 °C to a temperature of, in particular, approximately 621 °C and then passed through the reaction tubes 111 in the radiation zone 11. As illustrated, the heated combustion air 6 and fresh air 7 are used in the radiation zone 11. A cracked gas 8 is taken from the reaction tubes 111 in the radiation zone 11 and cooled in a cracked gas cooling system 16.

[0072] The cracked gas cooling system 16 comprises a primary cracked gas cooler 161, a secondary cracked gas cooler 162 and a tertiary cracked gas cooler 163, wherein the cracked gas 8 is present upstream of the primary cracked gas cooler 161 at a temperature of in particular approximately 861 °C, downstream of the primary cracked gas cooler 161 and upstream of the secondary cracked gas cooler 162 at a temperature of in particular approximately 600 °C, downstream of the secondary cracked gas cooler 162 and upstream of the tertiary cracked gas cooler 163 at a temperature of in particular approximately 455 °C, and downstream of the tertiary cracked gas cooler 163 at a temperature of in particular approximately 390 °C.

[0073] The cooling capacity of the primary cracked gas cooler 161 is in particular approximately 16.9 MW, that of the secondary cracked gas cooler 162 is in particular approximately 8.3 MW, and that of the tertiary cracked gas cooler 163 is in particular approximately 3.5 MW. The primary cracked gas cooler 161 and the tertiary cracked gas cooler 163 can be operated in particular with boiler feed water 9 from the steam drum 14. In contrast, the mixture 5 is passed through the secondary cracked gas cooler 162, which is heated from a temperature of in particular approximately 307 °C to the aforementioned temperature of in particular approximately 461 °C.

[0074] As mentioned, plant 100 is designed for liquid use. As previously explained, a two-stage air preheating process takes place: first external to convection zone 12 against saturated steam 9 and then in air preheater 127 in convection zone 12. Secondary cracked gas cooling in secondary cracked gas cooler 162 takes place against the preheated mixture 5, embedded between the primary and tertiary cracked gas coolers 161 and 163, which operate as conventional high-pressure steam generators.

[0075] For more complex cases (flexibility of use and mixed firing), the steam preheater 13 and the alternative or additional preheating of the mixture feed (e.g. against saturated steam) in the mentioned optional heat exchangers upstream and downstream of the first high-temperature bundle 123 can be provided as additional possible elements.

[0076] The Figure 1The arrangement of the elements in the convection zone shown is particularly optimized for an air preheater 17 for a high preheating temperature. The arrangement is not mandatory; in particular, the dilution steam superheater 124, the first and second steam superheaters 125 and 126, the air preheater 17, and the third high-temperature bundle 128 can also be arranged in a different order with corresponding advantages. Thus, in a first example, the entire combustion air can be preheated. The air preheater 17 is arranged in particular at 400 to 450 °C in the flue gas, i.e., further up. In a second example, when the air is preheated to more than 600 °C or for mechanical and / or material-related reasons, the air preheater 17 can be partially or completely arranged as the lowest bundle (see also Figure 5 ).

[0077] A division of the bundles (as is the case with the high-pressure steam superheaters 125 and 126, for example) and the type of flow (countercurrent or cocurrent), which result from detailed considerations, and the associated nesting, may be possible and advantageous under certain circumstances, but is not shown here.

[0078] An economizer bundle (for feedwater preheating) is neither required nor possible in the proposed concept of plant 100, since there is no longer any excess heat. For lower radiant zone efficiency or lower air preheating, such a bundle can be used effectively (typically before and / or after feed preheater 11, not shown).

[0079] For heavier and more severe applications, at least one additional mixing point for superheated process steam is typically required. This can be located, for example, between the parts of a split first high-pressure bundle or downstream of the secondary cracked gas cooler 162 (not shown).

[0080] Operating parameters of the plant 100 may include, in particular, operation with naphtha as feedstock in a mixed firing in a ratio of, in particular, approximately 77 to 23 (percentage shares based on the lower calorific value), a radiation zone efficiency of 54% with 78 mol percent hydrogen in the fuel gas, a total underfiring of 73 MW, of which 10 MW is attributable to sensible heat (in the combustion air 6), a utilized heat quantity of 40 MW in the radiation zone 11 and 29 MW in the convection zone 12.

[0081] The air preheating, in particular to approximately 555 °C, affects the combustion air 6, which is supplied to the bottom burners in the radiant zone 11. On average, the combustion air temperature is approximately 430 °C. For example, feedstock 1 can be processed in a quantity of 48 t / h with a propylene to ethylene ratio of 0.45. Steam can be provided in a quantity of 22 t / h, in particular at approximately 115 bar and a temperature of approximately 505 °C.

[0082] Compared to conventional plants, plant 100 results in a reduction in the underfiring capacity of 33% (based on the lower calorific value) and a 64% reduction in the amount of high-pressure steam.

[0083] One in Figure 2 The plant 200 illustrated is designed for processing gaseous feedstocks such as ethane and other mixtures, although such a feedstock is still designated 1 here.

[0084] An economizer bundle 129 is arranged in the convection zone 12 upstream of the feed preheater 121 and downstream of the denitrification device 122. However, a dilution steam superheater 124 is missing. The temperatures of the flue gas in the convection zone 12 are upstream of the third high-temperature bundle 128 at in particular approximately 1141 °C, downstream thereof and upstream of the air preheater 127 at in particular approximately 853 °C, downstream thereof and upstream of the second steam superheater 126 at in particular approximately 624 °C, downstream of the first steam superheater 125 and upstream of the denitrification device 122 at in particular approximately 376 °C, downstream of the economizer bundle 129 and upstream of the feed preheater 121 at in particular approximately 259 °C, and downstream of the feed preheater 121 at in particular approximately 100 °C.

[0085] The feed 1 is heated in the feed preheater 121 from a temperature of, in particular, approximately 70 °C to a temperature of, in particular, approximately 210 °C, before dilution steam 2 is added to obtain a mixture, which is also designated 5 here. Further heating of the mixture 5 also takes place here in the secondary cracked gas cooler 162, specifically from a temperature of, in particular, approximately 203 °C to a temperature of, in particular, approximately 483 °C. The subsequent heating in the third high-temperature bundle 128 takes place to a temperature of, in particular, approximately 642 °C.

[0086] The cracked gas 8 is withdrawn from the reaction tubes 111 in the radiation zone 11 at a temperature of, in particular, approximately 842 °C. In the primary cracked gas cooler 161, cooling takes place to, in particular, approximately 600 °C, in the secondary cracked gas cooler 162 to a temperature of, in particular, approximately 355 °C, and in the tertiary cracked gas cooler 163 to a temperature of, in particular, approximately 180 °C. The cooling capacity of the primary cracked gas cooler 161 is, in particular, approximately 15.1 MW, that of the secondary cracked gas cooler 162 is, in particular, approximately 14.6 MW, and that of the tertiary cracked gas cooler 163 is, in particular, approximately 8.8 MW. The primary cracked gas cooler 161 can, in particular, be operated with boiler feedwater 9 from the steam drum 14. The mixture 5 is passed through the secondary cracked gas cooler 162 as before.

[0087] The tertiary cracked gas cooler 163 is operated with boiler feedwater 4, in particular from the plant boundary, which is heated in the tertiary cracked gas cooler 163 from a temperature of in particular approximately 114 °C to a temperature of in particular approximately 311 °C. Subsequent cooling takes place in the further air preheater 15 arranged externally of the convection zone 12 to a temperature of in particular approximately 175 °C, before the boiler feedwater 4 is heated in the economizer bundle 129 to a temperature of in particular approximately 255 °C and can then be fed into the steam drum 14. The steam drum 14 is operated at a pressure of in particular approximately 120 bar and a temperature of in particular approximately 325 °C.

[0088] The saturated steam 3 from the steam drum 14 is fed to the first steam superheater 125 at a temperature of, in particular, approximately 325 °C, and heated there to a temperature of, in particular, approximately 470 °C. After the addition of boiler feed water 4, the temperature is reduced to, in particular, approximately 435 °C, and the corresponding steam is superheated in the second steam superheater 126 to a temperature of, in particular, approximately 515 °C.

[0089] The combustion air 6 is heated in the additional air preheater 15 arranged externally of the convection zone 12 from a temperature of, in particular, approximately 15 °C to a temperature of, in particular, approximately 291 °C, in particular against condensing saturated steam from the steam drum 14, and then further heated by the air preheater 127 in the convection zone 12 to a temperature of, in particular, approximately 600 °C. The correspondingly heated combustion air 6 can then be supplied to the burners that heat the radiation zone 11 and which are not separately illustrated here.

[0090] In other words, the process control for gas feed implemented in plant 200 comprises a first stage of combustion air preheating in the air preheater 15 arranged externally of the convection zone 12 with feedwater that was heated in the tertiary cracked gas cooler 163, followed by combustion air preheating in the air preheater 127 in the convection zone 12. The cracked gas cooling in the secondary cracked gas cooler 162 is carried out against the correspondingly heated mixture 5 of feed 1 and dilution steam 2, again embedded between the primary and tertiary cracked gas coolers 161 and 163 operated in the form of conventional high-pressure steam generators. The desired high air preheating temperature of 600 °C in the example is advantageously supplemented by pure bottom firing (large, few burners with little piping effort).

[0091] This example already achieves considerable savings of approximately 35% in fuel gas, and is not critical at any of the usual points. Sufficient high-pressure steam superheating occurs in high-pressure steam superheaters 125 and 126, and non-critical (tube wall) temperatures are present in the cracked gas coolers 161, 162, and 163, with a sufficient temperature difference for a compact design. This also applies to the other equipment in the convection zone.

[0092] Operating parameters of plant 200 may include, in particular, operation with ethane as the feedstock in a pure bottom firing system, air preheating to 600 °C, and a radiant zone efficiency of 57% with 100 mol percent hydrogen as the fuel gas. For example, feedstock 1 may be processed at a rate of 51 t / h with a conversion of 60%.

[0093] Compared to conventional plants, plant 200 results in a reduction in the underfiring capacity of, as mentioned, 35% (based on the lower calorific value) and a 53% reduction in the amount of high-pressure steam.

[0094] One in Figure 3 The plant 300 illustrated is designed for processing gaseous feedstocks such as propane and other mixtures, with a corresponding feedstock still being designated 1 here.

[0095] In this case, a first economizer bundle 129a and a second economizer bundle 129b are arranged in the convection zone 12 upstream of the feed preheater 121 and downstream of the denitrification device 122. A dilution steam superheater 124 is omitted, as in plant 200. The flue gas temperatures in the convection zone 12 partially correspond to those of plant 200, whereby a temperature between the first economizer bundle 129a and the second economizer bundle 129b can be, in particular, approximately 307 °C, and a temperature upstream of the denitrification device 122 and downstream of the first high-pressure steam superheater 125 can be, in particular, approximately 394 °C.

[0096] The feed 1 is heated in the feed preheater 121 as described for plant 200, before dilution steam 2 is added to obtain a mixture, which is also designated 5 here. Further heating of the mixture 5 also takes place in the secondary cracked gas cooler 162, and then in the third high-temperature bundle 128. The temperatures correspond in particular to those already explained for plant 200.

[0097] The fission gas 8 is withdrawn from the reaction tubes 111 in the radiation zone 11 at a temperature that can, in particular, correspond to the temperatures according to Annex 200. This also applies to the cooling in the primary fission gas cooler 161 and the secondary fission gas cooler 162. In the tertiary fission gas cooler 163, however, a temperature of approximately 230 °C is reached, resulting in a cooling capacity of approximately 6.9 MW. The specific performance data given here and below are examples and are to be understood in particular with reference to a total fission gas cooling capacity of just under 29 MW in the example.

[0098] The tertiary cracked gas cooler 163 is operated here with boiler feed water 4, in particular from the plant boundary, which, however, is previously heated in the first economizer bundle 129a from a temperature of in particular approximately 114 °C to a temperature of in particular approximately 150 °C. The further heating takes place in particular as in plant 200 to a temperature of in particular approximately 311 °C. The subsequent temperatures of the boiler feed water 4 and the resulting temperatures for the combustion air 6 correspond to those in plant 200, whereby the aforementioned temperature of in particular approximately 255 °C is reached in the second economizer bundle 129b.

[0099] The temperatures resulting for saturated steam 3 in the first steam superheater 125 and the second steam superheater also correspond to those already explained for plant 200. One difference is the smaller amount of steam produced in plant 300.

[0100] Plant 300 is specifically designed for gas feed with a significant propane content. The increasing propane-related shifting tendencies due to propane cracking are addressed by increased tube wall temperatures in the tertiary cracked gas cooler 163, particularly in the form of feedwater preheating in the first economizer bundle 129a upstream of the tertiary cracked gas cooler 163 and the increased cracked gas outlet temperature. The high-pressure steam production is therefore naturally somewhat lower with the same fuel gas savings and the other aforementioned boundary conditions.

[0101] It would be desirable to avoid the division shown here into the first and second economizer bundles 129a, 129b in the feedwater path due to the associated complexity, thus omitting the second economizer bundle 129b. However, to ensure comparability with the process data shown for system 200, this was not attempted or demonstrated here for system 300.

[0102] Operating parameters of plant 300 may, in particular, include operation with ethane as the feedstock in a pure bottom firing system, air and fuel gas preheating to 595 and 290 °C, respectively, and a radiant zone efficiency of 58% with 100 mol percent hydrogen as the fuel gas. For example, feedstock 1 may be processed at a rate of 51 t / h with a conversion of 60%.

[0103] Compared to conventional plants, plant 300 results in a reduction in the underfiring capacity of 35% (based on the lower calorific value) and a 58% reduction in the amount of high-pressure steam.

[0104] One in Figure 4 The plant 400 illustrated is designed for processing gaseous feedstocks such as ethane and other mixtures, with a corresponding feedstock still designated 1 here. Furthermore, plant 400 provides for heating gas preheating, which is explained further below.

[0105] The temperatures of the flue gas in the convection zone 12 of plant 400 are upstream of the third high-temperature bundle 128 in particular at approximately 1139 °C, downstream of this and upstream of the air preheater 127 in particular at approximately 839 °C, downstream of this and upstream of the second high-pressure steam superheater 126 in particular at 616 °C, downstream of the first high-pressure steam superheater 125 and upstream of the denitrification device 122 in particular at approximately 383 °C, downstream of the here again only one economizer bundle 129 and upstream of the feed preheater 121 in particular at approximately 266 °C and downstream of this in particular at approximately 100 °C.

[0106] The fission gas 8 is withdrawn from the reaction tubes 111 in the radiation zone 11 at a temperature that can correspond, in particular, to the temperatures according to systems 200 and 300. This also applies to the cooling in the primary fission gas cooler 161. In the secondary fission gas cooler 162, however, a temperature of approximately 365 °C is reached, with the same cooling capacity. In the tertiary fission gas cooler 163, a temperature of approximately 180 °C is reached, resulting in a cooling capacity of approximately 8.8 MW.

[0107] The saturated steam 3 from the steam drum 14 is fed to the first steam superheater 125 at a temperature of, in particular, approximately 325 °C, and heated there to a temperature of, in particular, approximately 480 °C. After the addition of boiler feed water 4, the temperature is reduced to, in particular, approximately 445 °C, and the corresponding steam is superheated in the second steam superheater 126 to a temperature of, in particular, approximately 515 °C.

[0108] The tertiary cracked gas cooler 163 is also operated here with boiler feedwater 4, in particular from the plant boundary, which is heated therein without preheating in the convection zone 12 from a temperature of, as above, in particular approximately 114 °C to a temperature of, in particular, approximately 325 °C. Subsequent cooling takes place in parallel in sections 4a and 4b in the further air preheater 15 arranged externally of the convection zone 12, on the one hand, and a fuel gas preheater 21, on the other hand. After the corresponding sections are recombined, a temperature of, in particular, approximately 134 °C is present before heating to a temperature of, in particular, approximately 221 °C can take place in the economizer bundle 129 and then feeding into the steam drum 14. The steam drum 14 is also operated here at a pressure of, in particular, approximately 120 bar and a temperature of, in particular, approximately 325 °C.

[0109] Heating gas 22 is heated in the heating gas preheater 21 from a temperature of, in particular, approximately 50°C to a temperature of, in particular, approximately 290°C and used at this temperature in the burners of the radiation zone 11. The combustion air 6 is heated in the further air preheater 15 arranged externally of the convection zone 12 from a temperature of, in particular, approximately 15°C to a temperature of, in particular, approximately 295°C and then further heated by the air preheater 127 in the convection zone 12 to a temperature of, in particular, approximately 595°C before it is also fed to the burners.

[0110] In plant 400, a process control system with heating gas preheating against feedwater 4b is thus implemented in parallel with the first stage of air preheating. With the same temperature and power requirements at the secondary cracked gas cooler 162, heating gas savings can be further increased.

[0111] Operating parameters of plant 400 may, in particular, include operation with ethane as the feedstock in a pure bottom firing system, air and fuel gas preheating to 595 and 290 °C, respectively, and a radiant zone efficiency of 58% with 100 mol percent hydrogen as the fuel gas. For example, feedstock 1 may be processed at a rate of 51 t / h with a conversion of 60%.

[0112] Compared to conventional plants, plant 400 results in a reduction in the underfiring capacity of 37% (based on the lower calorific value) and a 58% reduction in the amount of high-pressure steam.

[0113] One in Figure 5The system 500 illustrated is designed for processing gaseous feedstocks such as ethane and other mixtures, with a corresponding feedstock still being designated 1 here. Furthermore, the system 500 provides for a heating gas preheater, which is explained further below and is integrated into the convection zone 12.

[0114] The temperatures of the flue gas in the convection zone 12 of plant 500 are upstream of the third high-temperature bundle 128 in particular at approximately 1137 °C, downstream of this and upstream of the air preheater 127 in particular at approximately 869 °C, downstream of this and upstream of the second high-pressure steam superheater 126 in particular at 597 °C, downstream of the first high-pressure steam superheater 125 and upstream of the denitrification device 122 in particular at approximately 376 °C, downstream of a heating gas preheater integrated here in the convection zone 12, which is designated as 21 in plant 4, and upstream of the here again only one economizer bundle 129 in particular at approximately 299 °C, downstream of this and upstream of the feed preheater 121 in particular at approximately 246 °C, and downstream of this especially at about 100 °C.

[0115] The cracked gas 8 is withdrawn from the reaction tubes 111 in the radiation zone 11 at a temperature that can correspond in particular to the temperatures according to systems 200, 300, and 400. In the primary cracked gas cooler 161, cooling takes place to, in particular, approximately 620 °C, with a cooling capacity of, in particular, approximately 13.8 MW. In the secondary cracked gas cooler 162, a temperature of, in particular, approximately 340 °C is reached, with a cooling capacity of, in particular, approximately 16.7 MW. In the tertiary cracked gas cooler 163, a temperature of, in particular, approximately 180 °C is achieved, with a cooling capacity of, in particular, approximately 8 MW.

[0116] The saturated steam 3 from the steam drum 14 is fed to the first steam superheater 125 at a temperature of approximately 316 °C. The other temperatures correspond in particular to those explained for system 400.

[0117] The tertiary cracked gas cooler 163 is also operated here with boiler feedwater 4, in particular from the plant boundary, which is heated therein to the extent explained for plant 400. Subsequent cooling takes place in the additional air preheater 15 arranged externally of the convection zone 12 to a temperature of in particular approximately 176 °C, before heating to a temperature of in particular approximately 217 °C can take place in the economizer bundle 129 and then feeding into the steam drum 14. The steam drum 14 is operated at a pressure of in particular approximately 120 bar and a temperature of in particular approximately 325 °C, as already explained for previous plants.

[0118] Heating gas 22 is heated in the heating gas preheater 21 in the convection zone 12 from a temperature of, in particular, approximately 50 °C to a temperature of, in particular, approximately 322 °C and used at this temperature in the burners of the radiation zone 11. The combustion air 6 is heated in the further air preheater 15 arranged externally of the convection zone 12 to the extent explained for system 400 and is then further heated by the air preheater 127 in the convection zone 12 to a temperature of, in particular, approximately 660 °C before it is also fed to the burners in the radiation zone 11.

[0119] The process control implemented in plant 500 with heating gas preheating in the convection zone 12 can make it possible to further increase the heating gas savings compared to the heating gas preheating explained for plant 400, while simultaneously increasing the temperature and power requirements on the secondary cracked gas cooler 162 and similar requirements on the other heat exchangers.

[0120] Operating parameters of plant 500 may, in particular, include operation with ethane as the feedstock in a pure bottom firing system, air and feedstock preheating to 660 and 322 °C, respectively, and a radiant zone efficiency of 59% with 100 mol percent hydrogen as the fuel gas. For example, feedstock 1 may be processed at a rate of 51 t / h with a conversion of 60%.

[0121] Compared to conventional plants, plant 500 results in a reduction in the underfiring capacity of 40% (based on the lower calorific value) and a 62% reduction in the amount of high-pressure steam.

[0122] One in Figure 6The system 600 illustrated is designed for processing gaseous feedstocks such as ethane and other mixtures, with a corresponding feedstock still being designated 1 here. No heating gas preheating is provided; the combustion air preheating comprises a total of three stages using the air preheater 15 arranged externally of the convection zone 12 and two air preheaters 127a and 127b in the convection zone.

[0123] The temperatures of the flue gas in the convection zone 12 of plant 600 are, upstream of the second air preheater 127b, in particular at approximately 1137 °C, downstream thereof and upstream of the third high-temperature bundle 128, in particular at approximately 1006 °C, downstream thereof and upstream of the first air preheater 127a, in particular at approximately 777 °C, downstream thereof and upstream of the second high-pressure steam superheater 126, in particular at approximately 571 °C, downstream of the first high-pressure steam superheater 125 and upstream of the denitrification device 122, in particular at approximately 348 °C, downstream of the economizer bundle 129 and upstream of the feed preheater 121, in particular at approximately 272 °C, and downstream thereof, in particular at approximately 100 °C.

[0124] The fission gas 8 is withdrawn from the reaction tubes 111 in the radiation zone 11, as before, at a temperature of, in particular, approximately 824 °C. Cooling in the primary fission gas cooler 161 takes place to a temperature of, in particular, approximately 630 °C, with a cooling capacity of, in particular, approximately 13.1 MW. In the secondary fission gas cooler 162, a temperature of, in particular, approximately 340 °C is reached, with a cooling capacity of, in particular, approximately 17.3 MW. In the tertiary fission gas cooler 163, a temperature of, in particular, approximately 180 °C is achieved; the cooling capacity in the tertiary fission gas cooler 163 is, in particular, approximately 8 MW.

[0125] The saturated steam 3 from the steam drum 14 is fed to the first steam superheater 125 at a temperature of, in particular, approximately 325 °C. The other temperatures correspond to those explained for systems 400 and 500. Here, too, the steam drum 14 is operated at a pressure of, in particular, approximately 120 bar and a temperature of, in particular, approximately 325 °C.

[0126] The tertiary cracked gas cooler 163 is also operated here with boiler feed water 4, in particular from the plant boundary, which is heated therein from a temperature of in particular approximately 114°C to a temperature of in particular approximately 326°C. Subsequent cooling takes place in the further air preheater 15 arranged externally of the convection zone 12 to a temperature of in particular approximately 176°C, before heating to a temperature of in particular approximately 235°C in the economizer bundle 129 and subsequently feeding into the steam drum 14.

[0127] The combustion air 6 is heated in the further air preheater 15 arranged externally of the convection zone 12 from a temperature of in particular approximately 15 °C to a temperature of in particular approximately 296 °C and then further heated by means of the first air preheater 127a in the convection zone 12 to a temperature of in particular approximately 570 °C and by means of the second air preheater 127b in the convection zone 12 to a temperature of in particular approximately 750 °C before it is also fed to the burners in the radiation zone 11.

[0128] Operating parameters of plant 600 may, in particular, include operation with ethane as the feedstock in a pure bottom firing system, air preheating to 750 °C, and a radiant zone efficiency of 59% with 100 mol percent hydrogen as the fuel gas. For example, feedstock 1 can be processed at a rate of 51 t / h with a conversion of 60%.

[0129] Compared to conventional plants, plant 600 results in a reduction in the underfiring capacity of 40% (based on the lower calorific value) and a 62% reduction in the amount of high-pressure steam.

[0130] With System 600, the same high fuel gas savings as System 500 can be achieved, but without fuel gas preheating. Instead, a two-stage combustion air preheating is implemented in the convection zone to accommodate the very high air temperature.

[0131] One in Figure 7 The plant 700 illustrated is designed for processing gaseous feeds such as ethane or propane and other mixtures, with a corresponding feed still being designated 1 here. Combustion air preheating is carried out using boiler feed water; furthermore, a two-stage feed preheating is provided in feed preheaters 121a and 121b before combining with the dilution steam 2.

[0132] The temperatures of the flue gas in the convection zone 12 of plant 600 are upstream of the third high-temperature bundle 128 in particular at approximately 1127 °C, downstream thereof and upstream of the second high-pressure steam superheater 126 in particular at approximately 624 °C, downstream of the first high-pressure steam superheater 125 and upstream of the first high-temperature bundle 123 arranged here in particular at approximately 438 °C, downstream thereof and upstream of the denitrification device 122 in particular at approximately 305 °C, downstream of a second feed preheater 121b and upstream of the economizer bundle 129 in particular at approximately 218 °C, downstream of and upstream of a first feed preheater 121a in particular at approximately 161 °C, and downstream of this in particular at approximately 116 °C.

[0133] The fission gas 8 is withdrawn from the reaction tubes 111 in the radiation zone 11 at a temperature of, in particular, approximately 833 °C. Cooling in the primary fission gas cooler 161 takes place to a temperature of, in particular, approximately 525 °C, with a cooling capacity of, in particular, approximately 14.5 MW. In the secondary fission gas cooler 162, a temperature of, in particular, approximately 400 °C is reached, with a cooling capacity of, in particular, approximately 5.3 MW. In the tertiary fission gas cooler 163, a temperature of, in particular, approximately 200 °C is achieved; the cooling capacity in the tertiary fission gas cooler 163 is, in particular, approximately 7.5 MW.

[0134] The saturated steam 3 from the steam drum 14 is fed to the first steam superheater 125 at a temperature of, in particular, approximately 317 °C. At its outlet, the temperature is, in particular, approximately 447 °C. At the inlet of the second steam superheater 126, the temperature is, in particular, approximately 396 °C, and at the outlet, the temperature is, in particular, approximately 510 °C.

[0135] The tertiary cracked gas cooler 163 is also operated here with boiler feedwater 4, in particular from the plant boundary, which, however, is first preheated in the economizer bundle 129 to a temperature of, in particular, approximately 153 °C. The boiler feedwater 4 is heated in the tertiary cracked gas cooler 163 to a temperature of, in particular, approximately 301 °C. Subsequent cooling takes place in the additional air preheater 15 arranged externally of the convection zone 12 to a temperature of, in particular, approximately 197 °C, at which temperature it can then be fed into the steam drum 14. The secondary cracked gas cooler 162 is also operated here with boiler feedwater 9 from the steam drum 14, which is fed into the secondary cracked gas cooler 162 at a temperature of, in particular, approximately 187 °C. The steam drum 14 is operated at a pressure of in particular approximately 108 bar and a temperature of in particular approximately 317 °C.

[0136] The combustion air 6 is heated in the further air preheater 15 arranged externally of the convection zone 12 from a temperature of in particular approximately 15 °C to a temperature of in particular approximately 250 °C before it is fed at this temperature to the burners in the radiation zone 11.

[0137] Operating parameters of plant 700 may, in particular, include operation with ethane as the feedstock in a pure bottom firing system, air preheating to 250 °C, and a radiant zone efficiency of 49% when using hydrogen-rich (79 mol%) fuel gas. For example, feedstock 1 may be processed at a rate of 36 t / h with a conversion of 65%.

[0138] Compared to conventional plants, plant 700 results in a reduction in the underfiring capacity of 18% (based on the lower calorific value) and a 30% reduction in the amount of high-pressure steam.

[0139] Compared to a system with conventional air preheating by flue gas (flue gas utilization below approximately 300 °C combined with feed or steam heating in the tertiary cracked gas cooler 163), the system 700 offers significant advantages. These include the absence of a risk of condensation in the flue gas and the elimination of a complex air preheating stage or reduced flue gas utilization. A more compact design of the air preheater 17 is possible compared to an air preheater 127 in the flue gas duct. Complex and large flue gas ducts are eliminated, and a flexible installation location is possible. A simple feedwater bypass at the air preheater 17 achieves flexibility with regard to air preheating temperature, steam production, and fuel gas consumption. This results in lower power and better heat transfer at the tertiary cracked gas cooler 163 compared to feed or steam heating.The upstream economizer bundle 129 and a cracked gas cooling system limited to 200 to 220 °C minimize the risk of blockages on the cracked gas side of the tertiary cracked gas cooler 163 due to (too) low tube wall temperatures.

[0140] For pure ethane use (which results in a low tendency for the cracked gas to block), a downstream economizer can be used effectively, whereby a sequence of plant boundary - tertiary cracked gas cooler 163 - air preheater 17 - economizer - steam drum 14 can be provided. This results in a higher temperature difference at the tertiary cracked gas cooler 163 (less space required) even when the cracked gas is cooled to up to approximately 180°C (cf. Figure 2 ).

[0141] In Figure 8Illustrated is a plant 800 according to a further embodiment of the invention, in which a cracking furnace is electrically heated and is therefore designated 80. Here, too, a cracking gas is withdrawn from the cracking furnace 80, wherein the cracking gas 8 or a portion thereof is subjected to cracking gas cooling. This also comprises a primary cracking gas cooler 161 (in particular as a linear cooler), a secondary cracking gas cooler 162, and a tertiary cracking gas cooler 163. As before, the secondary cracking gas cooler 162 is arranged downstream of the primary cracking gas cooler 161, and the tertiary cracking gas cooler 163 is arranged downstream of the secondary cracking gas cooler 162, and a feed mixture 5 into the cracking furnace 80 is heated by means of the secondary cracking gas cooler 162.

[0142] To prepare the feed mixture 5, a feed stream 1 heated in a steam-operated feed preheater 121 and a dilution steam 2 heated in a steam-operated steam preheater 13, more precisely a process steam preheater or, more correctly, a process steam superheater, are combined. The feed mixture 5 is then heated in a heat exchanger that functionally corresponds to the previously explained high-temperature bundle 123 and is therefore designated as such here, but is operated with steam. A steam drum is designated 14; it also supplies the primary and tertiary cracked gas coolers 161 and 163, respectively, with steam 9.

[0143] A large portion of the steam generation can take place in the primary and tertiary cracked gas coolers 161, 163 (here, in particular, the primary cracked gas cooler 161 is provided as a linear cooler). The steam is used to preheat feed 1 and, if necessary, process steam 2 (up to approximately 300°C). Taken together, a large portion of the required feed heating is provided via saturated steam utilization and the secondary cracked gas cooler 162. This amounts to 70 to 80% with moderate / acceptable space requirements. This corresponds to approximately 80 to 90% of what is achievable with a single, complex primary cracked gas cooler 161, which would be used accordingly, i.e., as a feed-effluent heat exchanger (assuming that, in this case too, very high wall temperatures of more than 650 to 700°C on the process side are to be avoided at all costs (due to precracking and possible coking).In principle, a linear cooler with impingement or a similar design can be used here, which can be operated in cocurrent or countercurrent flow. Compared to a very complex multi-stage primary cracked gas cooler as a feed-effluent heat exchanger, this still corresponds to 75 to 80%. The final feed warming to the inlet temperature into the coils is carried out primarily with an electrically heated heat exchanger 81 (650 to 690 °C for gas feed such as ethane and propane, 580 to 620 °C for liquid feed such as naphtha). Condensed steam is collected in a condensate collector 82 and returned to the steam drum 14.

[0144] Below, aspects of the present invention will be explained again, particularly with regard to the effects, requirements, and design of the apparatus and bundles used, partially repeating what has been said previously. The explanations may relate to some or all embodiments.

[0145] A three-stage quench cooler or cracked gas cooler system with primary, secondary, and tertiary coolers is proposed, with the secondary cooler serving to superheat the feed and steam, i.e., as feed-effluent heat transfer. The sandwich arrangement of the upstream and downstream primary and tertiary coolers, as previously explained several times, enables / includes, among other things, the following configurations and aspects and leads to the advantages listed below.

[0146] A conventional upstream primary cooler (especially a linear or straight-tube steam generator) prevents selectivity losses as well as premature coking and fouling. A conventional downstream tertiary cooler (a straight-tube exchanger for steam generation or a condensate preheater) enables proven, efficient cooling at the cold cracked gas end with a flexible temperature window. This results in a necessary, direct reduction in steam production for fired furnaces. Better utilization of the high cracked gas temperature level compared to conventional steam generation is possible.

[0147] A process-critical total pressure drop (e.g., 150 to 200 mbar) in the cracked gas cooling system is not increased or only minimally increased by appropriate design. In particular, the temperature window for secondary cooling can be adjusted by appropriate upstream and downstream primary and tertiary cooling. In particular, the heat quantity can be adapted to the underlying conditions / process requirements. Coking (on the cracked gas side) is minimized by selecting the temperature window, as is precracking.

[0148] In certain embodiments, flexibility and optimization of the structural design (area, material, etc.) are also enabled by selecting the temperature window. Behavior over the operating time can be comparable to bundles in the convection zone, particularly due to positive coking behavior. In embodiments of the invention, no control is required. Should control be necessary (e.g., for different cracking operations and / or applications), this can be achieved via a (typical, known) air bypass, or possibly also via a steam-side control (condensate cover, less space required).

[0149] The secondary cracked gas cooler can be designed, in particular, as an efficient counterflow exchanger, for example, as a conventional straight-tube heat exchanger, with the cracked gas being conducted within the tube. Examples of dimensions and other aspects and advantages, particularly in comparison to a corresponding feed-effluent heat exchanger as the primary cracked gas cooler, are shown.

[0150] Aspects of the radiation zone and its design have also been explained with reference to corresponding embodiments of the invention. A correspondingly optimized "efficiency / air preheating temperature" pairing can be selected by the person skilled in the art, taking into account the constraints of the heat balance around the convection zone / gap gas cooling.

[0151] In the classic convection zone of an underfired furnace, the heat remaining in the flue gas is utilized to its full potential, with the overall thermal efficiency being determined primarily from the flue gas outlet temperature. Without air preheating, a heat surplus typically results (after meeting the process heat demand and high-pressure steam superheating), which is fed into steam generation by feedwater preheating (in an economizer bundle). The proposed interconnections, incorporating the cracked gas cooler heat as described above and an air preheating bundle, enable balancing even with a significantly reduced heat supply (due to high air preheating temperatures). Designs for dual air preheating have already been explained, whereby corresponding staged air preheating with steam up to a maximum of 320 °C and subsequent preheating by a bundle in the convection zone can be achieved.

[0152] Air preheating using tube bundles in the convection zone enables the realization of high air preheating temperatures of over 300 to approximately 700 °C and reduced heat dissipation in the convection zone to only approximately 30 to 50% of the heat transferred in the secondary cracked gas cooler. Further advantages include a moderate pressure drop on the air side (around 50 mbar) and a compact design thanks to a correspondingly wide flue gas temperature window.

[0153] The use of high-temperature-resistant materials is minimized due to the minimal internal pressure (air at significantly less than 1 bar overpressure), resulting in only a small required wall thickness. The air medium is non-critical, and a leak into the flue gas does not pose a safety risk. The performance over the operating time with a slightly increasing preheating temperature is positive. This can partially compensate for the loss of radiant zone efficiency (due to coking of the cans / reduced heat transfer). Control is not required.

[0154] The first stage of air preheating enables indirect use of quench heat, thus achieving the necessary reduction in steam production. Saturated steam utilization from the steam drum is possible, resulting in various designs / installations. A design above the steam drum with gravitational condensate return is possible. Alternatively or additionally, operation in the circulation of a steam generator (primary / tertiary cooler) is also possible. Flexible condensate return to the drum via a receiver and booster pump can be provided, as can condensate subcooling and operation with an external boiler feedwater treatment system.

[0155] Feedwater utilization from the tertiary cracked gas cooler is possible in a gas furnace, and is particularly simple and elegant. It is also conceivable from a steam drum (forced circulation pump) in a liquid furnace. This can be achieved with flexible heat provision and the required air preheating to 250 to 310 °C, as well as with a low pressure drop on the air side (typically less than 30 mbar). 250 °C is a sensible lower limit for efficiency reasons, but a range of 200 to 310 °C can also be used. Below this range, medium-pressure steam can also be used effectively, typically achieving temperatures of 160 to 180 °C. A compact design with hot medium in finned tubes is possible, with very good heat transfer from the steam or boiler feedwater in the tube. The finning results in good heat transfer to the air. In particular, a significantly more compact design is possible than with typical fresh air counter flue gas heaters.Control is not required; air preheating is limited by the condensate or boiler feedwater temperature. However, control is possible (condensate cover or steam pressure control; air bypass), e.g., for additional flexibility for different operating conditions / applications.

[0156] Decommissioning for special applications is easily possible (e.g., shut-off valve with minimum flow if heat retention is required). This can be combined with an upstream air heater to protect against external media (e.g., quench water, medium- or low-pressure steam).

[0157] In a gas furnace without air preheating, a charge preheater is typically only possible as the topmost bundle (at the cold flue gas end). The gaseous charge heats up significantly faster than the flue gas cools ("pinch," clamping due to temperature equalization). With air preheating, the radiant zone efficiency increases, while the underfiring and flue gas volume decrease. The temperature profiles of the charge and flue gas equalize or eventually reverse (e.g., at a radiant zone efficiency of 55%). In addition, with such reduced underfiring, the furnace can be operated only with residual gas (sulfur-free; methane and hydrogen, alternatively pure hydrogen fraction), thus, in particular, without sulfur-containing imported fuel gas. The typical sulfuric acid dew point as a limitation at the topmost bundle is eliminated.This allows a preheater as the top bundle to achieve a low flue gas outlet temperature (significantly less than 130 °C), thus achieving a high thermal furnace efficiency (up to over 95%).

[0158] A very flexible preheating system is possible in a single bundle: for example, from 70 °C to 150 to 300 °C. This provides a control variable for the secondary cracked gas cooler with regard to its heat output and space requirements.

[0159] A combination with (known) concepts in the form of heating gas preheating is also possible. This, comparable to air preheating, represents a way to introduce heat into the radiant zone and thus reduce heating gas consumption directly and indirectly (through increased efficiency). This equivalence means that air preheating can be partially replaced by heating gas preheating, up to approximately 30% with pure hydrogen combustion, and less so with increasing methane content. The fundamental advantage is the heat supply at a lower temperature level, thus being more efficient. The overall process advantage depends on where and how the heating gas preheating is implemented. The disadvantage is the potentially considerable (structural, process-related) effort.

[0160] To weigh up the cost / benefit, three cases are considered: a. Heating gas preheating analogous to two-stage air preheating. The cost is disproportionate to the benefit of slightly reduced heating surfaces. b. Heating gas preheating analogous to the first air preheating stage. This allows for greater utilization of quench heat or more efficient flue gas utilization, with less heat in the air preheater bundle in the convection zone. The convection zone can be relieved in the critical flue gas window (600 to 350°C, "pinch" range). In the gas furnace example, the savings in heating gas / underfiring can be increased slightly (by up to approximately 3%) while still delivering high-pressure steam according to specifications.The embodiments of the invention include the installation of a hot gas preheater parallel to the first stage of air preheating with an additional device or a hot gas preheater in the convection zone, specifically (i) below an economizer bundle as an additional bundle, or (ii) instead of the economizer bundle with minimal effort, but with a loss of feed preheating flexibility and thus some design flexibility for the secondary cooler in the cracked gas. c. Hot gas preheating outside the furnace. .

[0161] This can be achieved by an external heat source (e.g., plant steam). This is generally inexpensive and possible, but the contribution would be rather small (lower preheating temperatures) or the effort / complexity would be increased.

[0162] Depending on the general conditions and the savings target, it may be particularly useful to use heating gas preheating, e.g. according to b.

[0163] With the desired, necessary increase in combustion chamber temperature, an increase in nitrogen oxide emissions cannot be technically avoided. Therefore, in embodiments of the invention, a denitrification device is used within the usual flue gas temperature range (approximately 300 to 350 or 400 °C).

[0164] Typical special furnace operations (decoking, holding, changeover / emergency) should be possible without additional effort, if possible. Typical and potentially critical conditions include reduced radiation zone efficiencies, increased excess air, and elevated temperature levels in the convection zone bundles.

[0165] The proposed concepts demonstrate primarily favorable performance in this regard. The secondary cooler, used as a feed-effluent heat exchanger, generates comparatively little heat input compared to a high-temperature bundle in the convection zone. A proposed second stage of air preheating absorbs significant amounts of heat. Forced air flow allows for easy reduction of the air volume (e.g., speed control of the fresh air fan). This reduces deviations from typical and potentially critical operating parameters. The radiant zone efficiency decreases to a lesser extent, and as an additional, simple intervention option, decommissioning the first air preheating stage and the saturated steam preheater is possible.

[0166] The goal of reducing fuel gas demand at the fired furnace inevitably entails a (disproportionate) reduction in steam production. This makes it necessary for a typical cracker to provide alternatives to the existing steam turbine drives, and possibly also alternatives to steam heating. In terms of decarbonization, green electricity, electric drives, and heat pumps, for example, are expedient. The examples are based on a typical steam level (over 500 °C and more than 110 bar), which still ensures the most efficient use in turbines. A low steam pressure and temperature level can be useful in an overall assessment, as this creates some flexibility in the convection zone for further fuel gas savings.

[0167] The overall goal is to achieve a 30 to 40% reduction in fuel gas consumption in fired cracking furnaces (for olefin production). This is achieved by enabling very high air preheating temperatures (approximately 400 to 700 °C), heat integration directly at the furnace itself, and integration of cracking gas heat for (indirect) air preheating and process heating.

[0168] Thermodynamically, an optimization of the waste heat integration is achieved, which achieves or includes a more efficient use of the existing temperature levels of fission gas, a more efficient use of the existing temperature levels of flue gas, a more efficient use of the underfiring for the process task (fission reaction) and a reduction of steam as a waste heat product.

[0169] On the process side, no / few restrictions are achieved and additional risks are expected, neither with regard to the selectivity of the cracking, with regard to the flexibility of use, nor with regard to coking and the operating time of the furnace.

[0170] In terms of equipment technology, this allows for the use of well-known and proven equipment types / bundles, as well as a compact design and flexible installation of the equipment / bundles. This allows for a comparatively classic, compact design for the entire furnace.

[0171] There are no or few operational restrictions. Start-up and standby operating modes can be implemented similarly to those of a conventional cracking furnace, resulting in a comparable, minimal control effort compared to a conventional cracking furnace.

[0172] Overall, flexibility is maintained (e.g., with regard to fission, feed, load, fuel gas), resulting in comparable, and possibly even more favorable, operating times. For a gas-fired cracking furnace, fuel gas savings of 10 to 20% can be achieved simply by using air preheating (approximately 150 to 300 °C) using waste heat from the fission gas.

[0173] Boiler feedwater from the tertiary cracked gas cooler can be fed to the air preheater as a heat transfer medium. Only an additional, compact air preheater and the (always required) air preheating to the burners are required. This can be achieved by using hot boiler feedwater from low-temperature cracked gas cooling (conventional tertiary cracked gas cooler). This also results in a compact design and flexible installation, as well as little or no additional work on the furnace.

[0174] For the fission gas heat integration of an electrically heated fission, for example as in Figure 8 As shown, the sandwich cracked gas cooler allows 75 to 85% of the total, useful heat recovery to be utilized for process purposes. This occurs, as also mentioned, without process-related restrictions or additional risks (selectivity, coking, flexibility). Again, minimized effort for cracked gas heat integration with known and proven equipment types, as well as a compact design and flexible installation in appropriate configurations, are possible.

[0175] By definition, all-electric feed heating corresponds to 100%. Partially electric feed heating with indirect use of the cracked gas heat for feed heating via saturated steam then corresponds to 60%. If the heat exchanger described here is also used, a combination of indirect and direct heat integration can reduce the electrical power requirement for feed heating to 30% of all-electric heating.

Claims

1. A process for steam cracking, wherein a feed mixture (5) containing one or more hydrocarbons and steam is fed to a cracking furnace (10, 80), wherein a cracking gas (8) is withdrawn from the cracking furnace (10, 80), wherein the cracking gas (8) or a portion thereof is subjected to cracking gas cooling (16), wherein the cracking gas cooling (16) is carried out using a primary cracking gas cooler (161), a secondary cracking gas cooler (162) and a tertiary cracking gas cooler (163), and wherein the secondary cracking gas cooler (162) is arranged downstream of the primary cracking gas cooler (161) and the tertiary cracking gas cooler (163) is arranged downstream of the secondary cracking gas cooler (162), characterized in that the feed mixture (5) or a part thereof is heated by means of the secondary cracked gas cooler (162).

2. Process according to claim 1, in which the hydrocarbons in the feed mixture (5) have a boiling range of 35 to 400 °C to a proportion of more than 90%, wherein the secondary cracked gas cooler (162) is operated with a cracked gas inlet temperature of 550 to 650 °C, a cracked gas outlet temperature of 420 to 520 °C, a feed mixture inlet temperature of 270 to 330 °C and a feed mixture outlet temperature of 400 to 535 °C.

3. Process according to claim 1, in which the hydrocarbons in the feed mixture (5) have a boiling range of less than 35 °C to a proportion of more than 90%, wherein the secondary cracked gas cooler (162) is operated with a cracked gas inlet temperature of 580 to 650 °C, a cracked gas outlet temperature of 300 to 450 °C, a feed mixture inlet temperature of 180 to 240 °C and a feed mixture outlet temperature of 400 to 535 °C.

4. Method according to one of the preceding claims, in which a straight tube heat exchanger with tube-side cracked gas guidance is used as the secondary cracked gas cooler (162).

5. The method according to claim 4, wherein tubes of the secondary cracked gas cooler (162) have an outer diameter of 40 to 50 mm and a tube length of up to 12 m and / or the secondary cracked gas cooler (162) is operated with a pressure loss of 10 to 60 mbar and / or at up to 80% of the speed of sound.

6. Method according to one of the preceding claims, in which the cracking furnace (10) is operated using a fuel gas which is combusted with combustion air (6), the combustion air (6) or a part thereof being subjected to combustion air preheating.

7. The method according to claim 6, wherein the combustion air preheating is carried out using an air preheater (15) arranged outside a convection zone (12) of the cracking furnace (10) and then using an air preheater (127) in the convection zone (12).

8. The method according to claim 7, wherein the combustion air preheating is carried out using the air preheater (127) in the convection zone (12) to a temperature of more than 400 °C.

9. A process according to any one of claims 6 to 8, wherein the air preheater (15) arranged outside the convection zone (12) is operated using boiler feed water which is heated using the tertiary cracked gas cooler (162).

10. A method according to any one of claims 6 to 9, wherein the fuel gas or a portion thereof is preheated using boiler feed water heated using the tertiary cracked gas cooler (162).

11. A process according to any one of claims 6 to 10, wherein the fuel gas has a hydrogen content of more than 90%.

12. A process according to any one of claims 6 to 11, wherein 70 to 80% of the fuel gas is burned by means of bottom burners and the remaining portion is burned by means of side wall burners.

13. The method according to any one of claims 1 to 5, wherein the cracking furnace (80) is heated using electric current.

14. A steam cracking plant (100-800) configured to feed a feed mixture (5) containing one or more hydrocarbons and steam to a cracking furnace (10, 80), withdraw a cracked gas (8) from the cracking furnace (10, 80), subject the cracked gas (8) or a portion thereof to cracked gas cooling (16), and carry out the cracked gas cooling (16) using a primary cracked gas cooler (161), a secondary cracked gas cooler (162), and a tertiary cracked gas cooler (163), wherein the secondary cracked gas cooler (162) is arranged downstream of the primary cracked gas cooler (161) and the tertiary cracked gas cooler (163) is arranged downstream of the secondary cracked gas cooler (162), characterized in that the plant (100-800) is designed to heat the feed mixture (5) or a part thereof by means of the secondary cracked gas cooler (162).

15. System (100-800) according to claim 14, which is arranged to carry out a method according to one of claims 1 to 13.

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