Method and apparatus for steam cracking

Abstract

The invention relates to a method for reacting one or more hydrocarbons by steam cracking, wherein one or more input streams (F) containing one or more hydrocarbons (H) are directed through one or more radiant zones (11) of one or more cracking furnaces (10), thereby obtaining one or more product streams (C), wherein the one or more radiant zones (11) are heated by combusting a heating gas (X) with combustion air (L), wherein at least a part of the combustion air (L) is subjected to combustion air preheating (75), wherein steam (S, T) is generated from feed water (W), and wherein the feed water (W) is subjected to feed water preheating in one or more convection zones (12) of the one or more cracking furnaces (10). The combustion air preheating (75) is at least partly and / or at least sometimes performed using heat extracted from at least a part of the feed water (W) upstream of the feed water preheating. The invention also relates to a corresponding system.

Description

Technical Field

[0001] This invention relates to methods and systems for steam cracking. Background Technology

[0002] This invention relates to steam cracking (steam decomposition, thermal decomposition, steam cracking, etc.) for the production of olefins and other basic chemicals, as described, for example, in the article "Ethylene" in Ulimann's Encyclopedia of Industrial Chemistry, published online on April 15, 2009, DOI: 10.1002 / 14356007.a10_045.pub2. The terminology used below also refers to relevant professional literature.

[0003] To initiate and sustain the endothermic reaction, the required heat energy in steam cracking is typically provided by the combustion of heated gases in a combustion chamber, which forms the radiant zone or cracking furnace of a so-called cracking furnace. The gas is guided through a coil (cracking tube) to obtain a product mixture, called feed gas or cracked gas. In the most common applications, the combustion air required for combustion is guided into the radiant zone (called evacuation) without preheating and combusts there with the heated gases. Figure 1 The diagram is simplified and will be explained below using the corresponding reference numerals.

[0004] Figure 1 The pyrolysis furnace 10 shown or the corresponding furnace unit (also referred to herein as a pyrolysis furnace or furnace) includes a radiation zone 11 and a convection zone 12. A system for steam pyrolysis may contain multiple corresponding pyrolysis furnaces 10. In the following, multiple pyrolysis furnaces 10 may be referred to as system components or units, indicated by a central unit, while peripheral units are provided separately for each pyrolysis furnace 10.

[0005] The hydrocarbon input H is heated by a central input preheater 20 (shown by way of example) and process steam P is supplied by a central process steam generator 30, which is further heated in the convection zone 12 in a manner known per se (see in particular). Figure 4 These components combine to form a feed stream F, which is then supplied to the radiation zone 11. As described above, Figure 1 The illustrations are greatly simplified and are for illustrative purposes only. Thus, for example, in so-called adaptive control, the corresponding feed flow can be divided into multiple partial flows in the region of convection zone 12, which are then preheated separately from each other and can ultimately be introduced into radiation zone 11 by, for example, six or eight pyrolysis tube assemblies. Here and below, the central unit can be replaced by peripheral units at any time, and vice versa.

[0006] The cracked gas C originates from radiation zone 11 and can be cooled by one or more cracked gas coolers before being supplied to the central cracked gas separation and cracked gas preparation 90. This cracked gas cooler may be specifically configured as a known quench cooler or may include such a quench cooler, and may also function as a steam generator 13. Further details of the corresponding quench cooler are explained below; this quench cooler may be specifically designed as a conventional quench cooler or a so-called linear quench exchanger (LQE). The invention is not limited to the specific embodiments described.

[0007] Feedwater W is supplied via a central feedwater system 40. In the example shown, the feedwater is also heated in convection zone 12, then further heated, and finally evaporated through one or more cracked gas coolers to obtain high-pressure or ultra-high-pressure steam S (hereinafter also referred to as saturated steam). In the example shown, the saturated steam S is superheated in convection zone 12 to obtain superheated high-pressure steam or superheated ultra-high-pressure steam T (hereinafter also referred to as superheated steam), which is then supplied to the central steam system 50.

[0008] The feed heating gas Y is heated to form a preheated heating gas X by means of a central heating gas system 60 connected downstream of a possible central heating gas preheating 65, wherein process agents or auxiliary agents, such as high-pressure, medium-pressure or low-pressure superheated steam, washing water and / or quenching oil, and electric current, are used as heating media or heat sources, and is supplied to the radiant zone 11 or a burner therein (not shown separately).

[0009] In the embodiment shown here, combustion air L is delivered through air inlet 79 into the radiant zone 11 or the burner therein. Flue gas Z is discharged from the radiant zone 11, delivered through the convection zone 12, and then discharged into the flue gas treatment or central or peripheral chimney 80 (with or without a blower), thereby being released into the atmosphere.

[0010] Figure 1 The central heating gas preheating 65 shown is optional. Peripheral heating gas preheating (i.e., individually for each cracking furnace 10 or furnace unit) is also possible. The same applies to input preheating and process steam generation, which can also be carried out peripherally as an alternative to the central design.

[0011] According to existing technology, preheating combustion air can be used as a measure to improve efficiency, save heating gas, and thus reduce energy consumption and carbon dioxide emissions. Figure 2 and Figure 3 Corresponding embodiments are shown. Figure 2 The central combustion air compression 70 and combustion air preheating 75 are shown. Figure 3 The peripheral combustion air compression 70 and combustion air preheating 75 are shown.

[0012] Generally speaking, the term "improved efficiency" here can be specifically understood as an improvement in so-called specific efficiency, which is understood as the portion of the energy of the introduced heated gas recovered in the products formed, in this case, the pyrolysis gas. This differs from known thermal efficiency, which refers to the portion of unburned gas recovered in the products and other media (pyrolysis gas or steam), or in other words, the portion not lost to the surrounding environment as heat loss (through chimneys, hot surfaces, leaks). Specific efficiency can be improved by preheating the air because less underburning is required for the same amount of pyrolysis gas. Conversely, thermal efficiency is not necessarily improved by the application of air preheating, as this may also be limited by the minimum flue gas delivery temperature (see below).

[0013] In the following text, units arranged in the center and units arranged on the periphery have the same reference numerals. The arrangement type follows the illustrated positioning inside or outside the respective cracking furnace 10 or furnace unit; in the case of positioning inside, there is a peripheral arrangement, and in the case of positioning outside, there is a central arrangement. For example, central combustion air compression 70 can also be performed in the case of peripheral combustion air preheating 75. Hereinafter, combustion air will also be simply referred to as air, and its preheating will also be simply referred to as air preheating.

[0014] In air preheating, superheated steam, or non-superheated steam of high, medium, or low pressure depending on the application, can be used, or washing water and / or quenching oil can be used as the heating medium, or electric current can be used as the heat source. Heat directly transferred from the exhaust gas flow Z can also be used as the heat source. The use of superheated high-pressure or ultra-high-pressure steam T shown in the figure is optional and depends on the selected preheating temperature.

[0015] In summary, preheating combustion air can be supplied centrally or peripherally. Depending on availability and the required preheating temperature, (superheated) ultra-high pressure steam, (superheated) high pressure steam, (superheated) medium pressure steam, (superheated) low pressure steam, saturated steam, wash water, or quenching oil can be used as the heating medium, such as the heating medium from the central cracked gas separation and cracked gas preparation, or the flue gas from the convection zone outlet, typically in the case of a peripheral air preheating arrangement.

[0016] Low-pressure steam is understood herein to generally refer to steam with a pressure level of 1 bar absolute to 10 bar absolute (especially 4 bar absolute to 8 bar absolute); medium-pressure steam is understood to refer to steam with a pressure level of 10 bar absolute to 30 bar absolute (especially 15 bar absolute to 25 bar absolute); high-pressure steam is understood to refer to steam with a pressure level of 30 bar absolute to 60 bar absolute (especially 35 bar absolute to 50 bar absolute); and ultra-high-pressure steam is understood to refer to steam with a pressure level of 60 bar absolute to 175 bar absolute (especially 80 bar absolute to 125 bar absolute). Where high-pressure steam is mentioned below, it should also be understood as ultra-high-pressure steam.

[0017] The term "ultra-high pressure level" refers to the pressure level specified for ultra-high pressure steam, whether or not it is specified for the steam itself, or for example, for the feedwater used to generate the steam. The same applies to the terms high pressure level, medium pressure level, and low pressure level.

[0018] To provide the required pressure level for the air preheater used in air preheating, or to compensate for any pressure loss, the air drawn in from the atmosphere can be centrally or peripherally compressed by a drive fan in an air compressor. Alternatively, a blower located downstream of the air preheater can be used to generate the corresponding suction.

[0019] For example, air preheating related to steam cracking is described in US3426733A, EP0229939B1 and EP3415587A1, and air preheating related to air preheating in boilers is described in DE102004020223A1 and WO2013 / 178446A1.

[0020] As described in US4321130A, combustion air can be preheated by means of bottom, top, and / or quench water streams discharged from the primary fractionation unit before being introduced into the cracking furnace in a system for hydrocarbon pyrolysis conversion and separation. This unit is externally connected to the pyrolysis reactor to optimize the thermal efficiency of the entire process.

[0021] US2020 / 172814A1 discloses a pyrolysis furnace system for converting hydrocarbon input material into pyrolysis gas. The pyrolysis furnace system includes a convection section, a radiation section, and a cooling section. The convection section includes multiple convection chambers configured to absorb and preheat the hydrocarbon feed. The radiation section includes a calcination space containing at least one radiation coil configured to heat the input material to a temperature that allows for a pyrolysis reaction. The cooling section includes at least one transmission line heat exchanger.

[0022] Air preheating typically improves heat transfer in the radiant zone and reduces furnace fuel requirements. Therefore, under the same furnace load (specifically, the same amount of hydrocarbons and the same cracking intensity, resulting in the same product stream), the overall combustion power required is lower, while a relatively larger portion of the exhaust gas energy is transferred to the process gas. On the one hand, this leads to a reduction in exhaust gas mass flow rate, thereby reducing combustion emissions and waste heat output from the chimney to the atmosphere. On the other hand, it is evident that the residual heat in the flue gas at the radiant zone outlet is significantly reduced compared to an unpreheated furnace.

[0023] However, increasing the preheating temperature leads to design and operational difficulties in the downstream convection zone. In the convection zone, the hydrocarbon input to be decomposed and the associated process steam are preheated to temperatures of 550°C to 700°C. Furthermore, boiler feedwater supplied to the furnace at high or ultra-high pressure levels is typically preheated in the convection zone at 100°C to 110°C, evaporates in the cracked gas cooler, and is finally superheated in the convection zone.

[0024] Due to the reduced availability of exhaust gas heat in the convection zone, difficulties arise because, under the same furnace load, the preheating capacity required for hydrocarbon input and process steam, as well as the superheating capacity required for the saturated steam flow generated in the cracked gas cooler, remains almost unchanged even at higher air preheating temperatures. Therefore, the lack of exhaust gas heat is particularly evident in feedwater preheating, which must be partially limited. Furthermore, with the upper convection tube bundle (i.e., the heat exchange unit arranged here) in the convection zone used to transfer flue gas heat to the medium to be heated, the flue gas inlet temperature is significantly lower compared to an unpreheated furnace. Due to the reduced temperature gradient, the required surface area of ​​the convection tube bundle is significantly increased, necessitating greater construction work.

[0025] In EP3415587A1, the problem was intended to be solved, for example, by a heat pump system or by supplying unheated feedwater into a steam drum. However, the proposed solution therein results in a significant amount of additional work in terms of equipment due to the required heat pump and / or due to the substantial changes in the embodiments for cooling cracked gas and generating steam, and in particular, no proof of permanent operability has been provided.

[0026] Therefore, the present invention aims to provide a solution that makes economical, efficient and practical operation of a system for steam cracking possible. Summary of the Invention

[0027] Against this backdrop, the present invention proposes methods and systems for steam cracking. Advantageous embodiments form the subject matter described below.

[0028] This invention enables an extremely compact design of the convection zone, which is considered as the sum of the heights of all convection tube bundles in the flue gas passage, a simple structure of the chimney line downstream of the convection zone, and maximum flue gas heat utilization, i.e., a lower flue gas outlet temperature at the chimney. Furthermore, it achieves minimal fuel requirements while maximizing the production of superheated high-pressure or ultra-high-pressure steam.

[0029] In this context, the core concept of the invention is to use feedwater (i.e., water subsequently used to generate (ultra) high-pressure steam) to preheat combustion air.

[0030] According to the measures proposed in this invention, feedwater can be intercooled, which contradicts the common practice of maximizing feedwater preheating in steam production of sintering equipment. In this case, in the context of this invention, maximum steam production is deliberately sacrificed to achieve maximum energy recovery from flue gas with minimal structural complexity. In this situation, the reduction in steam production is particularly advantageous given future embodiments of the steam cracking system, as it allows for increased use of what is preferably referred to as green electricity to drive the machinery. This further reduces overall system CO2 emissions. Sintering usage is minimized while maximizing energy production from residual fossil fuel sintering.

[0031] While in the case of a pure steam boiler, it is only necessary to optimize the fuel utilization rate for steam generation, the situation is much more difficult in a steam pyrolysis furnace. Here, after the feedstock undergoes chemical conversion, generating steam is only a secondary task or a requirement for utilizing the heat obtained. Therefore, using the measures according to the invention in a steam pyrolysis furnace not only affects the overall fuel utilization rate, but also particularly the distribution between chemical process use and steam generation. Therefore, the measures provided in a pure steam boiler cannot be easily applied to a steam pyrolysis system.

[0032] In other embodiments according to the present invention and not according to the present invention, alternatively or in addition to the measures proposed according to the present invention, furnace-specific (ultra) high-pressure steam may be used as the heating medium in air preheating, feedwater and (ultra) high-pressure steam may be used in combination as the heating medium in air and / or heating gas preheating, (ultra) high-pressure steam may be used as the heating medium for process steam superheating, (ultra) high-pressure saturated steam may be used as the heating medium for input preheating, or (ultra) high-pressure steam may be used in combination as the heating medium for process steam superheating and input preheating.

[0033] This invention originates from a method for reacting one or more hydrocarbons via steam cracking, wherein one or more input streams containing one or more hydrocarbons are guided through one or more radiant zones of one or more cracking furnaces to obtain one or more product streams, namely cracked gas streams or crude gas streams, wherein the one or more radiant zones are heated by burning a heating gas with combustion air, wherein at least a portion of the combustion air is preheated, wherein steam is generated by feedwater, and wherein the feedwater is preheated in one or more convection zones of one or more cracking furnaces. As previously described, the input streams can also be guided in parallel in one or more convection zones, for example, according to multiple groups of cracking tubes divided in the radiant zone.

[0034] According to the present invention, as described above, combustion air preheating is performed using heat extracted from at least a portion of the feedwater upstream of the feedwater preheating.

[0035] Therefore, the present invention includes supplying cooling feedwater to the convection zone of one or more furnaces, thereby achieving maximum possible cooling and thus energy utilization of the flue gas. There are many methods for supplying cooling feedwater, with particular consideration given to the quality of the heated gas to avoid corrosion of the exhaust duct. In addition to using the feedwater supplied to the furnace as a heating medium in central or peripheral air heating, as described below, the feedwater can additionally, or alternatively according to embodiments not in this invention, be used as a heating medium in the preheating of central or peripheral heated gas. Cooling can, alternatively, and according to embodiments not in this invention, be carried out outside the furnace process.

[0036] Feedwater preheating can be performed in such a manner that a first portion (particularly adjustable) of the feedwater in one or more combustion air preheaters is used for heat exchange with at least a portion of the combustion air to be heated, and optionally, in one or more heating gas preheaters, for heat exchange with at least a portion of the heating gas to be heated, and a second portion (particularly adjustable) of the feedwater is directed as a bypass flow around the combustion air preheater and the optional heating gas preheater. Subsequently, the first and second portions can be combined again and then supplied to the feedwater preheating zone in the convection zone.

[0037] Specifically, given the anticipated adjustability of the first and / or second sections of the feedwater system, the feedwater temperature entering the convection zone can be controlled in this manner. The latter can particularly be used during operation to control the outlet temperature of the flue gas in the chimney. The latter largely depends on the feedwater temperature within this methodological system.

[0038] Such temperature control, especially in cases of partial condensation of the flue gas, can mitigate the risk of corrosion due to variable heating gas composition. Therefore, the flue gas temperature can be temporarily increased during operation. In this situation, less air preheating is achieved via feedwater, and the corresponding power can be compensated for by subsequent air preheating stages or by increasing the fuel supply within the furnace. Under optimal operating conditions with preferred heating gas composition, maximum preheating capacity can be achieved via feedwater, thereby maximizing the utilization of flue gas heat.

[0039] In other words, the temperature of the flue gas can be set by configuring the feedwater for air preheating and optional heating gas preheating, and in particular, based on the flue gas temperature to be achieved or detected in the downstream convection zone of the feedwater preheating.

[0040] Generally, the present invention can be used in a method where steam generated from feedwater comprises superheated or non-superheated high-pressure or ultra-high-pressure steam, which is generated by preheating downstream feedwater. In this case, after feedwater preheating, at least a portion of the feedwater can be subjected to feedwater evaporation using heat extracted from at least a portion of one or more product streams, particularly in one or more cracked gas or quench coolers, to obtain high-pressure or ultra-high-pressure steam. Then, at least a portion of the high-pressure or ultra-high-pressure steam can be subjected to steam superheating in one or more convection zones to obtain (superheated) high-pressure or ultra-high-pressure steam. See further details. Figures 1 to 4 Related explanations.

[0041] Generally, in this context, within the background of the present invention, combustion air preheating is performed using heat extracted from a portion of (superheated) high-pressure or ultra-high-pressure steam. In embodiments according to the invention, it can also be performed using heat from feedwater, while in embodiments not according to the invention, heat from feedwater can be substituted.

[0042] As has been mentioned several times, the heating gas can be preheated, which can also be performed using heat extracted from at least a portion of the feedwater upstream of the feedwater preheater. In embodiments according to the invention, this can be performed in addition to combustion air preheating, while in embodiments not according to the invention, it can be used as an alternative to combustion air preheating.

[0043] In the context of this invention, feedwater preheating is carried out in one or more flue gas passages within one or more convection zones. This preheating is particularly conducted at a temperature lower than the temperature level used to maintain superheated high-pressure or ultra-high-pressure steam, to provide process steam for forming one or more input streams, and to provide substantial input heating for one or more input streams. Specifically, feedwater preheating is carried out near the end or furthest end of the flue gas passage, from which the correspondingly cooled flue gas exits. That is, further heat recovery of the flue gas occurs at most a point downstream (in the direction of flue gas flow). In this way, the outlet temperature of the flue gas from the convection zones can be advantageously controlled.

[0044] In the context of this invention, water can be supplied at temperature levels of 80°C to 140°C, particularly via a central or peripheral water supply system, and the water can be cooled to temperature levels of 40°C to 100°C, 40°C to 95°C, 40°C to 90°C, or 40°C to 85°C during combustion air preheating.

[0045] In the context of this invention, feedwater can be supplied to the combustion air preheating system at a pressure level of 30 to 60 bar absolute pressure (particularly 35 to 50 bar absolute pressure) or 60 to 175 bar absolute pressure (particularly 80 to 125 bar absolute pressure), and can undergo feedwater preheating at this pressure level without additional pressurization. Alternatively, feedwater can be supplied to the combustion air preheating system at a pressure level between 20 and 60 bar absolute pressure (particularly 25 to 50 bar absolute pressure) or 30 to 40 bar absolute pressure, and subsequently, after additional pressurization, undergo feedwater preheating at a pressure level of 30 to 60 bar absolute pressure (particularly 35 to 50 bar absolute pressure) or 60 to 175 bar absolute pressure (particularly 80 to 125 bar absolute pressure). In the latter case, the feedwater can advantageously be boosted to the corresponding pressure by one or more pumps after the combustion air preheating.

[0046] Therefore, air can be preheated directly using feedwater at (ultra) high pressure levels, allowing the intermediate-cooled feedwater to be subsequently supplied directly to the convection zone. Alternatively, as explained, air preheating can also be performed using feedwater at reduced pressure levels. The latter significantly reduces the design pressure of the associated air preheater, thereby lowering the operating costs of the unit.

[0047] In the context of this invention, as described above, multiple pyrolysis furnaces can be used, which are supplied with water through a central water supply system, wherein combustion air preheating can be performed individually on each of the multiple pyrolysis furnaces (peripheral combustion air preheating) or on the multiple pyrolysis furnaces together (central combustion air preheating).

[0048] The following is a special reference Figures 5 to 22 Further explanation is provided for embodiments based on the present invention and those not based on the present invention.

[0049] In all embodiments of the present invention, combustion air preheating can be carried out in multiple stages. For example, feedwater can be used as the heating medium in the first stage, medium-pressure steam can be used as the heating medium in the second stage, and saturated or superheated (ultra) high-pressure steam can be used as the heating medium in the third stage.

[0050] Other possible heating types or heating media (especially electric current) can also be used. Furthermore, more or less of the aforementioned preheating stages can be provided. In this case, the heating medium (especially the condensate formed) flowing out in the previous stage (i.e., at a lower temperature level) can be fully or partially reused, preferably by further cooling the previously formed condensate directly in a heat exchanger at the same pressure, or by further cooling it after partial expansion to a lower pressure level and the addition of superheated steam at that lower pressure level. Optionally, it is also advantageous to return the condensate to the steam generator by a suitable height arrangement (above the steam drum, i.e., natural circulation) or by increasing the pressure (e.g., using a pump).

[0051] Then, the corresponding cooling feedwater is supplied to the convection zone, but the temperature is significantly reduced.

[0052] The present invention also relates to a system for reacting one or more hydrocarbons by steam cracking, characterized as described above.

[0053] With regard to the systems and features provided according to the invention, explicit reference is made to the above explanation of the methods according to the invention, as these also relate to the corresponding systems. This is particularly applicable to embodiments of the corresponding systems that are advantageously configured to perform the corresponding methods in any embodiment.

[0054] The inventive and non-inventive measures described in the background of this application, applied individually or in preferred combination, can significantly improve the structural complexity and / or energy efficiency of steam pyrolysis furnaces with air preheating, as will be illustrated again below with reference to specific examples.

[0055] Table 1 lists the first results of the effects of each measure. A furnace subjected to the same hydrocarbon load without air preheating but with central heating gas preheating (Ref. A, 100% basis for relative comparison of evaluation variables) was used as the first comparison system. Furnaces subjected to the same hydrocarbon load with air preheating and those with central heating gas preheating but not featuring the characteristics of the invention were proposed as the second comparison system (Ref. B). All air preheating cases listed in Table 1 are based on a combustion air temperature of 248°C at the radiant zone inlet. Variations indicated by 1F, 2A, 3B, 4B, 5B, and 6B in the figures represent variations of the invention and non-inventions.

[0056] Table 1 - Comparison of effects when air preheating temperature is 248℃

[0057]

[0058] *: Examples of air preheating without water supply

[0059] **Example of using water supply in air preheating**

[0060] All variations marked with ** in Table 1 are designed according to the present invention, wherein water supply is used as the heating medium for air preheating.

[0061] A comparison of Reference A and Reference B demonstrates the fundamental advantage of air preheating, namely a 22% reduction in fuel consumption. The same comparison shows that, in the case of an air preheating furnace, further measures are needed to compensate for the increased structural complexity (in the form of total tube bundle height) and the reduced furnace efficiency (from the perspective of the aforementioned thermal efficiency) associated with the increased flue gas outlet temperature. The embodiments of the invention described below aim to compensate for both of these disadvantages simultaneously and as much as possible.

[0062] A comparison of Variant 1F with Reference B shows that preheating the air with feedwater and then infeeding it laterally into the convection zone at a reduced temperature (hereinafter referred to as Measure 1 according to the invention) significantly reduces the flue gas outlet temperature, thereby improving furnace efficiency. The required additional construction work is very low, increasing by only 5 percentage points, while the outlet temperature decreases by only 50 K. Similar findings are observed when comparing Variant 2A and 3B. These two comparisons clearly demonstrate the effectiveness of Measure 1, namely, that it significantly improves furnace efficiency with minimal additional construction work.

[0063] Another major advantage of Measure 1 is the simplicity of the flue gas guidance design after leaving the convection zone. This is very similar to a furnace without air preheating, and therefore much simpler than using a direct heat exchanger between the exhaust gas flow and the combustion air, in which a large volume of piping and heat exchange surfaces must be installed in the flue path of each individual furnace. Measure 1 produces a similar process effect, transferring exhaust gas heat to the combustion air, but indirectly through the heat transfer medium (feedwater) already present in the furnace area, requiring a much smaller piping cross-section due to its liquid accumulation state.

[0064] Another advantage is the ability to control the temperature via the described bypass, allowing for simple adjustment / change of the exhaust gas temperature during operation compared to systems where heat exchange occurs directly between combustion air and exhaust gas flow. This results in better handling of fluctuations in the quality of the heated gas; see the preceding description.

[0065] The effect of using (ultra)-high pressure saturated steam for air preheating (considered separately, not innovative measure 2) can be illustrated by comparing variations 1F and 2A. As a result of the discharge of (ultra)-high pressure steam upstream of the superheater tube bundle used for (ultra)-high pressure steam, the tube bundle located further downstream in the flue gas path receives proportionally more waste gas heat. The temperature difference in the tube bundle increases, thus the required surface area and the resulting convection zone height decrease sharply. Therefore, using measure 2 alone results in a considerable minimization of construction work, but the furnace efficiency will decrease due to the 100K increase in flue gas outlet temperature.

[0066] It is thus evident that measures 1 and 2 have almost opposite effects. However, by comparing reference B with example 3B, it becomes very clear that combining measures 1 and 2 (referred to as creative measure 3) can simultaneously improve both the structural complexity and energy efficiency of the furnace.

[0067] A comparison of variants 3B and 4B illustrates the effect of additional process steam superheating using (ultra) high-pressure saturated steam (considered separately, not an inventive measure 4). Similar to measure 2, this removal of saturated steam and its use for process steam superheating results in a reduction in construction work, leading to stable furnace efficiency in the given example, when combined with measures 1 (inventive) and 2 (considered separately, not inventive).

[0068] A comparison of variants 3B and 5B illustrates the effect of additional input preheating using (ultra)-high-pressure saturated steam (considered separately, non-creative measure 5). Similar to measures 2 and 4 (in each case, considered separately, non-creative), this removal of saturated steam and its use for input preheating results in a reduction in construction work, leading to a constant furnace efficiency in the given example 5B by simultaneously applying measures 1 (creative) and 2 (considered separately, non-creative).

[0069] A comparison of Variant 4B or Variant 5B with Variant 6B illustrates the effect of the combined application of process steam superheating and input preheating using (ultra) high-pressure saturated steam (considered separately, non-inventive measure 6). Maximizing the removal of saturated steam and its use for process steam superheating and input preheating minimizes construction work, resulting in constant furnace efficiency as in Variant 3B, Variant 4B, and Variant 5B, in the given example, by simultaneously applying measures 1 (inventive) and 2 (non-inventive).

[0070] The different embodiments of the variants using the air preheater sequence listed in Table 1 have three stages, using wash water, medium-pressure steam and / or superheated (ultra) high-pressure steam in addition to the explained use of feedwater and / or (ultra) high-pressure steam.

[0071] As additional explanation of the effectiveness of the claimed measures, Table 2 shows the results of various variant embodiments with further increases in air preheating (300°C) and correspondingly further reductions in fuel consumption. In this case, the effect of the described measures remains unchanged. A comparison of variant 4A* and variant 4B* demonstrates the positive impact of measure 2 on the construction work. A comparison of example 4B* and example 4B** shows the increase in furnace efficiency with the addition of measure 1.

[0072] Table 2 - Comparison of effects when air preheating temperature is 300°C

[0073]

[0074] *: Examples of air preheating without water supply

[0075] **Example of using water supply in air preheating**

[0076] All variations marked with ** in Table 2 are designed according to the present invention, wherein water supply is used as the heating medium for air preheating.

[0077] It is generally shown that at higher preheating temperatures, a combination of multiple measures provides relatively large added value. For example, in a comparison of variant 4B** and variant 6B** (i.e., after adding measure 6 to measures 1 and 2), the construction effort is reduced by 5 percentage points. As another maximum combination embodiment, variant 6C** shows that, compared to variant 6B**, with almost the same furnace efficiency, an increase in steam output can be achieved by increasing the construction effort. In this case, it can be achieved by connecting process steam superheating and input preheating in series on the heat transfer medium side, i.e., the condensate formed in the process steam superheating is used downstream as the heat transfer medium for input preheating.

[0078] The examples listed in Table 2 use different embodiments of air preheater sequences with 2, 3, or 4 stages, and use low-pressure steam and / or superheated (ultra) high-pressure steam in addition to the feedwater and / or (ultra) high-pressure steam as explained.

[0079] This invention is also particularly applicable to systems, for example, those described in EP3415587A1, in which direct cooling of the cracked gas is performed against the input stream, so that during the cooling of the cracked gas, only a portion of the heat output is used to generate (ultra)high-pressure steam. Specifically, the application of the measures described in this application also provides the same or at least substantially the same advantages to such systems.

[0080] This invention can also be applied to systems for separating carbon dioxide from flue gas. In particular, with the application of inventive measure 1, a particularly low outlet temperature of the flue gas at the end of the convection zone is achieved, which is beneficial for subsequent removal of carbon dioxide, for example by amine scrubbing (the typical operating temperature for amine scrubbing is 20°C to 60°C).

[0081] In one embodiment of the invention, oxygen enrichment of the combustion air can also be performed. In this case, no specific purity requirement / concentration is required; for example, byproducts of water electrolysis can be used, or any other technological source can be used, such as an air separation device. The effect of oxygen enrichment is approximately equivalent to air preheating, because the adiabatic combustion temperature increases in each case, thus increasing the efficiency of the radiant zone and reducing the flue gas volume. This effect is not (completely) equivalent to air preheating, because a relatively high oxygen content (at lower nitrogen content, etc.) can achieve the same effect with slightly different flue gas compositions. Specifically, a higher proportion of carbon dioxide and water is formed from combustion—for example, the former facilitates the recovery of carbon dioxide through amine scrubbing, and is even more so in the case of any flue gas recirculation. Furthermore, the advantage of the invention is that it can improve the efficiency of the radiant zone or reduce the flue gas volume, thereby saving fuel by a greater amount than that described when using (ultra)high-pressure steam for air preheating.

[0082] As previously mentioned, these measures can be applied to steam crackers with all possible hydrocarbon inputs. Examples include hydrocarbons (gaseous), naphtha (liquid), gas oil (liquid), and products (gaseous and liquid) from recycling methods such as plastic recycling.

[0083] In all cases, all or only a portion of the combustion air may be preheated. For example, in cases using both ground burners and side burners, partial air preheating may be selected, and preheated air may be supplied only to some burners (preferably ground burners). In the context of this application, the indicated air preheating temperature always refers to the final preheating temperature of the entire combustion air. Process streams from other systems (e.g., gas turbine exhaust gas) may also be used for furnace air preheating.

[0084] In variants 4 to 6, each describes the use of (ultra)high-pressure steam to heat a separated water or hydrocarbon stream. Similarly, a mixture of hydrocarbons and water can also be heated in this manner. This embodiment is particularly suitable for gas inputs, as the total amount of input in the convection zone does not change in this case.

[0085] The described uses of saturated steam relate to the typical technical use levels to date, up to about 175 bar absolute pressure. However, alternatively, it is conceivable to provide saturated steam at higher pressure and temperature levels (e.g., 175 bar absolute pressure and 355°C) in part for further preheating and / or superheating in the furnace area.

[0086] This invention is preferably used in conjunction with the electric drive of one or more compressors in the associated isolated section of the system. As a result, the reduction in the output of (ultra)high-pressure steam from the furnace caused by the air preheating according to the invention is preferably compensated. The increased electrification of the system also enables improved utilization of renewable energy sources through grid input. Maintenance of the steam boiler, which serves as a backup system for system startup, is also required to a lesser extent.

[0087] The described measures can be applied to both entirely new constructions of steam cracking furnaces and modernizations of existing furnaces. In the latter case, particularly if, for example, it is necessary to accommodate an improved tube bundle structure within an existing steel structure, the advantages regarding the overall tube bundle height are especially relevant.

[0088] The invention will be further explained below with reference to the accompanying drawings, which illustrate embodiments of the invention compared to the prior art. Attached Figure Description

[0089] Figures 1 to 4 An arrangement not based on the invention is shown.

[0090] Figures 5 to 22 Arrangements according to embodiments of the invention are shown, as well as arrangements not according to the invention mentioned in each.

[0091] Figure 23 The embodiments of the present invention and embodiments not based on the present invention are summarized with schematic diagrams.

[0092] In the further description above and below, systems and corresponding method steps not based on the invention, as well as systems and method steps based on embodiments of the invention, have been described or described. For simplicity and to avoid unnecessary repetition, the same reference numerals and descriptions are used herein for method steps and system components (e.g., cooling steps and heat exchangers for this purpose). In the drawings, the same reference numerals are used for the same or similar components, and for clarity, further explanation is not required. Detailed Implementation

[0093] The advantages of the present invention and corresponding embodiments will be described below, particularly those based on the above. Figure 1 and Figure 2 A comparison with the embodiments of the prior art shown (according to) Figure 1 No air preheating is required; it features centrally heated gas preheating. Figure 2 The air is preheated to, for example, about 248°C, and has the following properties: Figure 1 (The central heating gas preheating is shown). In this case, these considerations are based on a cracking furnace with naphtha as input. However, different aspects of the invention are equally applicable to furnaces with gas or heavier liquid inputs.

[0094] The specific topology of convection region 12 below is as follows: Figure 4 As shown. However, other process arrangements can also be used within the scope of this invention. This topology includes a first feedwater preheating heat exchanger 121, an input preheating heat exchanger 122, a second feedwater preheating heat exchanger 123, a first high-temperature tube bundle heat exchanger 124, a process steam superheating heat exchanger 125, a first (ultra) high-pressure steam superheating heat exchanger 126, a second (ultra) high-pressure steam superheating heat exchanger 127, and a second high-temperature tube bundle heat exchanger 128, which are opposite to the Z-direction of the outflow flue gas.

[0095] Feedwater W is conducted through a first feedwater preheating heat exchanger 121 and a second feedwater preheating heat exchanger 123, and then supplied to a corresponding (ultra)high-pressure steam generator 13, such as a cracked gas cooler. The resulting unsuperheated (ultra)high-pressure steam S is guided through a first (ultra)high-pressure steam superheating heat exchanger 126 and a second (ultra)high-pressure steam superheating heat exchanger 127 to obtain superheated (ultra)high-pressure steam T, through which feedwater injection can be performed. Hydrocarbon input H is heated in input preheating heat exchanger 122, and process steam P is heated in process steam superheating heat exchanger 125. The two are then combined to form feed stream F, which is further heated in a first high-temperature tube bundle heat exchanger 124 and a second high-temperature tube bundle heat exchanger 128.

[0096] and Figures 1 to 4 The relevant explanations also apply to the following figures, and Figures 1 to 4 The reference numerals used in the figures also apply to the following figures. For clarity, not all material flows are mentioned again in the figures below.

[0097] Figures 5 to 10 Variations of the system for steam cracking according to a first set of embodiments of the invention are shown, denoted as Variations 1A to 1F. A key feature connecting these is the use of cooled feedwater to maximize energy recovery. In this case, as previously described, the principle of all shown Variations 1A to 1F is to use feedwater already present in the cracking furnace 10 as a heating medium for preheating combustion air 75, and optionally for preheating heating gas 65 in a low-temperature range (i.e., a temperature range not exceeding 100°C). The cooled feedwater flowing out from the combustion air preheating 75 and the heating gas preheating 65 (if applicable) is then supplied to the convection zone 12, but as previously mentioned, the temperature is significantly lower compared to the prior art.

[0098] As mentioned, Figures 5 to 10 The preheating shown can consist of multiple stages, such as a first stage using feedwater as the heating medium, a second stage using medium-pressure steam as the heating medium, and a third stage using (ultra) high-pressure steam as the heating medium.

[0099] As mentioned, other possible heating types or heating media can also be used. Furthermore, as also mentioned, more or fewer preheating stages can be provided. The same explanation applies to using the outflow heating medium or recycling the condensate back into the steam generation process.

[0100] exist Figure 5In the variant 1A shown, a portion of the feedwater W is used as the corresponding heating flow WH in the central combustion air preheater 75. Another portion can be directed through the central combustion air preheater 75 as a bypass WB to achieve the explained control possibilities. The latter is also the case in variants 1B to 1F explained below.

[0101] exist Figure 6 In the variant 1B shown, a portion of the water supply W is used as heating streams WH1 and WH2 in the central combustion air preheating 75 and the central heating gas preheating 65.

[0102] exist Figure 7 In the variant 1C shown, the feedwater WH is used to heat the peripheral combustion air preheating 75, instead of preheating the heating gas.

[0103] exist Figure 8 In the variant 1D shown, feedwater WH1 is used to preheat the peripheral combustion air 75 and feedwater WH2 is used to preheat the peripheral heating gas 65.

[0104] exist Figure 9 In the variant 1E shown, heating water WH1 is used to heat the peripheral combustion air preheating 75, and heating water WH2 is used to heat the central heating gas preheating 65. This forms two bypasses, referred to as WB1 and WB2 respectively.

[0105] exist Figure 10 In the variant 1F shown, the peripheral combustion air preheating 75 is heated by feedwater WH, while the central heating gas preheating 65 is not heated by feedwater.

[0106] Figures 11 to 13 Variations of the system for steam cracking not according to the second set of embodiments of the invention are shown, denoted as Variations 2A to 2C. A key feature connecting these is the use of furnace-specific (ultra)-high-pressure saturated steam as the heating medium in the combustion air preheating 75. The principle of the shown variations is that a portion of the saturated steam S generated in the steam generator 13 of the same cracking furnace 10 is used as the heating medium for preheating the combustion air 75 in a medium-high temperature range (i.e., a temperature range of 150°C to 330°C). The first and second (ultra)-high-pressure steam superheated heat exchangers 126 and 127 in the convection zone 12 (see...) Figure 4 The amount of saturated steam is reduced accordingly, resulting in a proportionally greater amount of waste gas heat available to the heat exchangers 121 to 125 located downstream of the path of the flue gas Z in the convection zone 12.

[0107] exist Figure 11 and Figure 12 In the variants 2A and 2B shown, these measures are used in conjunction with peripheral combustion air preheating 75, while central combustion air preheating is additionally present. Figure 12In the variant 2B shown, for better distinction, the central combustion air preheating is indicated by 75'. However, Figure 13 The variant 2C shown only includes central air preheating. In all cases, the corresponding saturated steam flow used for heating is denoted by SH. The resulting condensate is designated SC. In the illustrated example, the condensate is returned to the central steam system 50.

[0108] like Figure 11 , Figure 12 and Figure 13 As shown in variants 2A, 2B, and 2C, the resulting (ultra)high-pressure condensate can be supplied to the central steam system of the equipment to continue utilizing the residual energy contained therein, and ultimately to a suitable condensate preparation apparatus. Here, all or part of the condensate formed in the previous preheating stage (i.e., at a lower temperature) can also be reused, preferably after partial expansion to a lower pressure level and the addition of superheated steam at this lower pressure level. However, the condensate can also be subcooled during preheating without prior expansion and the addition of superheated steam.

[0109] Figure 14 and Figure 15 Variations of the system for steam cracking according to a third set of embodiments of the invention are shown, denoted as Variations 3A and 3B. A key feature connecting these is the combined use of feedwater and (ultra)-high-pressure saturated steam S as heating media in combustion air preheating 75 and / or heating gas preheating 65. The principle of all the variations shown is to combine the measures previously explained for the first and second set of embodiments for application, namely, using feedwater W for combustion air preheating 75 and / or heating gas preheating 65 in a low-temperature range up to 100°C, and additionally using saturated steam for combustion air preheating 75 in a medium- or high-temperature range from 150°C to 330°C.

[0110] As mentioned, preheating can consist of multiple stages; for example, the first stage may use feedwater as the heating medium, the second stage may use medium-pressure steam as the heating medium, and the third stage may use ultra-high-pressure saturated steam as the heating medium. Other possible heating types or heating media can also be used, as mentioned. Furthermore, as also mentioned, more or fewer preheating stages can be provided. The above explanation also applies to using the outflowing heating medium or recycling the condensate back into the steam generation process.

[0111] exist Figure 14 In the variant 3A shown, these heating media are used together to preheat the peripheral combustion air 75, while Figure 15In the variant 3B shown, a central combustion air preheater is also provided, which is indicated as 75' for better distinction. The peripheral combustion air preheater 75 uses (ultra) high-pressure saturated steam S, and the central combustion air preheater 75' uses feedwater W.

[0112] Figure 16 and Figure 17 Variations of the system for steam cracking according to the fourth set of embodiments are shown, denoted as Variation 4A and Variation 4B. Figure 16 An embodiment not based on the invention is shown, and Figure 17 An embodiment according to the invention is shown. A key feature connecting these is the use of (ultra)high-pressure saturated steam S as the heating medium for the superheating of process steam P. The principle of all the variations shown is that a portion of the saturated steam S generated in the steam generator 13 of the same cracking furnace 10 is used as the heating medium for the superheating of process steam P in a medium-high temperature range (i.e., in the temperature range of 150°C to 330°C). First and second (ultra)high-pressure steam superheating heat exchangers 126 and 127 (see [reference]) supply the saturated steam S to the convection zone 12. Figure 4 The amount of saturated steam is reduced accordingly, resulting in heat exchangers 121 to 125 located downstream of the flue gas Z path in convection zone 12 being able to utilize a proportionally greater amount of waste gas heat at higher temperature levels. Furthermore, this also partially or completely reduces the load on the process steam superheating heat exchanger 125 in convection zone 12, thereby allowing heat exchangers 121 to 124 located downstream of the process steam superheating heat exchanger 125 along the flue gas Z flow path in convection zone 12 to utilize a greater amount of waste gas heat at higher temperature levels.

[0113] exist Figure 16 and Figure 17 In the variants 4A and 4B shown, peripheral process steam heating 35 is provided in each case. Figure 16 In the variant 4A shown, only the peripheral process steam heater 35 is heated, but conversely, in Figure 17 In the variant shown, the peripheral combustion air preheating 75' is also heated, using (ultra) high-pressure saturated steam S as the heating medium. According to an embodiment of the invention, Figure 17 The variant shown can also use the feedwater for air preheating, in which case the feedwater is used for upstream central combustion air preheating 75.

[0114] Figure 18 and Figure 19 This illustrates a variant of the system for steam cracking according to the fifth set of embodiments, previously indicated as variants 5A and 5B. Figure 18 An embodiment not based on the invention is shown. Figure 19An embodiment according to the invention is shown. The connection of these is characterized by the use of (ultra) high-pressure saturated steam S as the heating medium for preheating the hydrocarbon feed H. The principle of all variations is to use a portion of the saturated steam S generated in the steam generator 13 of the same cracking furnace 10 as the heating medium to preheat the hydrocarbon feed H (including partial evaporation that may occur when the feed is liquid) in a medium-high temperature range of 100°C to 330°C. In this case, single-phase preheating of the input stream occurs on the input side (liquid or gaseous). Furthermore, partial or complete phase change from liquid to gaseous can also be achieved (depending on the input and output temperatures). First and second (ultra) high-pressure steam superheated heat exchangers 126 and 127, supplying saturated steam S to the convection zone 12 (see...) Figure 4 The amount of saturated steam is reduced accordingly, resulting in the heat exchangers 121 to 125, located downstream of the flue gas Z-path in convection zone 12, being able to utilize a proportionally greater amount of waste gas heat at higher temperature levels. Furthermore, the load on the input preheating heat exchanger 122 in convection zone 12 is partially or completely reduced, allowing the downstream first feedwater preheating heat exchanger 121 to utilize even more waste gas heat at higher temperature levels.

[0115] However, in this case, Figure 18 and Figure 19 In both variants 5A and 5B shown, an external input heating process 25 is provided. Figure 18 In the variant 5A shown, only the peripheral input heating process 25 is heated; conversely, in Figure 19 In the variant shown, the peripheral combustion air preheating 75′ is also heated, using (ultra) high-pressure saturated steam S as the heating medium. According to an embodiment of the present invention, Figure 19 The variant shown also uses water for air preheating, in which case the water is used for upstream central combustion air preheating 75.

[0116] Figures 20 to 22 Variations of the system for steam cracking according to the sixth set of embodiments are shown (previously referred to as variations 6A to 6C), wherein, Figure 20 An embodiment not based on the invention is shown, and Figure 21 and Figure 22An embodiment according to the invention is shown. A key feature connecting these is the combined use of (ultra)high-pressure saturated steam S as a heating medium for both process steam superheating and input preheating. The principle of all the variations shown is to use a portion of the saturated steam S generated in the steam generator 13 of the same cracking furnace 10 as a heating medium, both for superheating process steam P in the medium-high temperature range of 150°C to 330°C and for preheating hydrocarbon input stream H in the medium-high temperature range of 100°C to 330°C (including possible partial evaporation of liquid inputs). The first and second (ultra)high-pressure steam superheating heat exchangers 126 and 127 in the convection zone 12 (see...) Figure 4 The amount of saturated steam in the (ultra)high-pressure saturated steam S is correspondingly reduced. As a result, heat exchangers 121 to 125, located downstream of the flue gas Z path in convection zone 12, can utilize a proportionally greater amount of waste gas heat at a higher temperature level. Furthermore, the load on the process steam superheated heat exchanger 125 in convection zone 12 for process steam P is also partially or completely reduced, allowing downstream heat exchangers 121 to 124 to utilize a greater amount of waste gas heat at a higher temperature level.

[0117] In this case, Figures 20 to 22 In the variations 6A to 6C shown, each case is provided with an external input heating treatment 25 and an external process steam superheating treatment 35. Figure 20 and Figure 21 In the variants 6A and 6B shown, these units are filled with saturated steam S in the manner illustrated. Figure 22 In the variant 6C shown, the process steam superheating treatment 35 and the input preheating 25 are connected in series on the heat transfer medium side. Figure 21 and Figure 22 In the variants 6B and 6C shown, the peripheral combustion air preheating 75°C is further filled with saturated steam S. As an embodiment of the invention, Figure 21 and Figure 22 The variant shown also features the use of water supply for air preheating, in this case, in the upstream central combustion air preheating 75.

[0118] Figure 23 The embodiments of the present invention and embodiments not based on the present invention are summarized with schematic diagrams, and the corresponding material flows are not specified separately. Figure 23 This illustrates the possibilities of central and peripheral arrangements for the aforementioned units.

Claims

1. A process for reacting one or more hydrocarbons by steam cracking, wherein, One or more input streams (F) containing the one or more hydrocarbons (H) are directed through one or more radiant zones (11) of one or more cracking furnaces (10) heated by combustion of a heating gas (X) with combustion air (L), at least a portion of which is subjected to combustion air preheating (75), steam (S, T) is generated from feed water (W), and the feed water (W) is subjected to feed water preheating in one or more convection zones (12) of the one or more cracking furnaces (10), characterized in that the combustion air preheating (75) is at least partially and / or at least sometimes performed using heat extracted from at least a portion of the feed water (W) upstream of the feed water preheating.

2. The method of claim 1, wherein, The steam generated from the feed water (W) includes superheated and / or non- superheated high- or super-high-pressure steam (T) formed from the feed water (W) after the feed water preheating.

3. The method of claim 2, wherein, At least a portion of the feed water (W), after the feed water preheating, is subjected to feed water evaporation using heat extracted from at least a portion of the one or more product streams (C) to obtain high- or super-high-pressure steam (S).

4. The method of claim 3, wherein, At least a portion of the high- or super-high-pressure steam (S) is subjected to steam superheating in the one or more convection zones (12) to obtain superheated high- or super-high-pressure steam (T).

5. The method of claim 2, wherein, The combustion air preheating (75) is also performed using heat extracted from a portion of the superheated high- or super-high-pressure steam (T).

6. The method of any one of claims 1 to 5, wherein, The heating gas (X) is subjected to heating gas preheating (65) likewise performed using heat extracted from at least a portion of the feed water (W) upstream of the feed water preheating.

7. The method of any one of claims 1 to 5, wherein, The feed water preheating is performed in one or more flue gas passages in the one or more convection zones (12), wherein the feed water preheating is performed at a temperature level lower than for steam superheating to obtain the superheated high- or super-high-pressure steam (T) and to provide adequately heated process steam for process steam superheating for forming the one or more input streams (F).

8. The method of any one of claims 1 to 5, wherein, The feed water (W) is provided at a temperature level of 80°C to 140°C and is cooled at the combustion air preheating (75) to a temperature level of 40°C to 100°C.

9. The method of any one of claims 1 to 5, wherein, The feed water (W) is supplied to the combustion air preheating (75) at a pressure level of 30 bar absolute to 60 bar absolute or 60 bar absolute to 175 bar absolute and is subjected to the feed water preheating at the pressure level.

10. The method of any one of claims 1 to 5, wherein, The feed water (W) is supplied to the combustion air preheating (75) at a pressure level of 20 bar absolute to 60 bar absolute and is subjected to the feed water preheating at a pressure level of 30 bar absolute to 60 bar absolute or 60 bar absolute to 175 bar absolute.

11. The method of any one of claims 1 to 5, wherein, The air preheating is performed using a plurality of cracking furnaces (10) which are supplied with the feed water (W) by means of a central feed water system (40), the combustion air preheating (75) being performed separately for each of the plurality of cracking furnaces (10) or together for the plurality of cracking furnaces (10).

12. The method of any one of claims 1 to 5, wherein, The air preheating is further performed using saturated steam and / or steam condensate formed from the saturated steam.

13. The method of any one of claims 1 to 5, wherein, The preheating of the one or more input streams (F) and / or of one or more streams of matter used to form the one or more input streams (F) is performed using saturated steam and / or steam condensate formed from the saturated steam.

14. A system for reacting one or more hydrocarbons by steam cracking, said system comprising one or more cracking furnaces (10) having one or more radiant zones (11) and being designed to direct one or more input streams (F) containing said one or more hydrocarbons (H) through said one or more radiant zones (11) of said one or more cracking furnaces (10) to obtain one or more product streams (C), said system comprising one or more burners for heating said one or more radiant zones (11) by combustion of a heating gas (X) with combustion air (L), said system having a combustion air preheating device and being designed to heat at least a portion of said combustion air (L) in said combustion air preheating device, said system having one or more steam generators designed to generate steam (S, T) from feed water (W) and being designed to perform feed water preheating of said feed water (W) in one or more convection zones (12) of said one or more cracking furnaces (10), characterized in that, The combustion air preheating device comprises a heat transfer device designed to transfer heat to the combustion air at least sometimes, the heat being extracted from at least a portion of the feed water (W) upstream of the feed water preheating.

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