Method and system for steam cracking

Abstract

The present application provides a method of steam cracking using a steam cracking system including one or more combustion radiant sections, wherein during steam cracking operations, a fuel is combusted with an oxidant gas to heat the one or more combustion radiant sections to form an exhaust gas, a process gas is formed using a hydrocarbon feedstock and process steam, the process gas is passed through one or more coils in the one or more combustion radiant sections to form a cracked gas, at least a portion of the exhaust gas is cooled in an exhaust gas heat recovery section, and at least a portion of the cracked gas is cooled in a cracked gas heat recovery section, and the exhaust gas heat recovery section and the cracked gas heat recovery section each include one or more multi-stream heat exchangers. The exhaust gas heat recovery section comprises a heat exchange structure provided in an amount and configuration such that a first proportion of the total amount of heat recovered from the exhaust gas in the one or more multi-stream heat exchangers of the exhaust gas heat recovery section, during at least a portion of the steam cracking operation, is used for preheating at least a portion of the oxidant gas, the first proportion being greater than 35% of the total amount of heat recovered in the one or more multi-stream heat exchangers of the cracked gas heat recovery section, during at least the same portion of the steam cracking operation. Corresponding systems are also part of the invention.

Description

[Technical Field]

[0001] The present invention relates to a method and a system for steam cracking according to the preambles of the independent claims. [Background technology]

[0002] The present invention is based on steam cracking technology for the production of olefins and other basic chemicals, as described, for example, in the "Ethylene" section of Non-Patent Document 1.

[0003] Currently, in steam cracking, the thermal energy required to initiate and sustain the endothermic cracking reaction is provided by the combustion of fuel gas in a refractory furnace. The process gas, initially containing steam and the hydrocarbons to be cracked, is passed through a so-called cracking coil, located within a refractory box also known as the radiant zone or section. In this flow path, the process gas is continuously heated, enabling the desired cracking reactions to occur within the cracking coil, and thus the process gas is continuously concentrated in the cracked product. Typical inlet temperatures of the process gas to the cracking coil are 550-750°C, and outlet temperatures are typically in the range of 800-900°C.

[0004] In addition to the radiant zone, a combustion cracking furnace also includes a so-called convection zone or section and a so-called quench zone or section. The convection zone is typically located above the radiant zone and consists of various tube bundles that intersect the flue gas duct from the radiant zone. Its primary function is to recover as much energy as possible from the hot flue gases exiting the radiant zone. In practice, typically only 35-50% of the total combustion duty is transferred in the radiant zone to the process gases passing through the cracking coil. The convection zone therefore plays a central role in steam cracking energy management, providing effective utilization of approximately 40-60% of the heat input to the furnace (i.e., the combustion duty). In practice, combining the radiant and convection zones, modern steam cracking plants utilize 90-95% of the total combustion duty (based on the lower or net heating value of the fuel). In the convection section, the flue gases are cooled to a temperature level of 60-140°C, after which they exit the convection section and are discharged into the atmosphere via a chimney.

[0005] The exhaust gas heat recovered in the convection zone is typically used for process loads such as preheating boiler feedwater and / or hydrocarbon feed, (partial) vaporization of liquid hydrocarbon feed (with or without pretreatment or dilution steam injection), and superheating process steam and high-pressure steam.

[0006] The quench zone is located downstream of the radiant zone along the main process gas path. It consists of one or more heat exchanger units whose primary function is to rapidly cool the process gas below the maximum temperature level to stop the cracking reaction, further cool the process gas for downstream processing, and efficiently recover sensible heat from the process gas for further energy use. Further cooling or quenching can be achieved by injection of liquids, for example, by oil quenching during steam cracking of liquid feedstocks.

[0007] The heat from the process gas recovered in the quench section is typically used to vaporize high-pressure (HP) or super-high-pressure (SHP) boiler feedwater (typically in the pressure range of 30-130 bar absolute) and to preheat the same boiler feedwater before it is fed to the steam drum. The saturated high-pressure or super-high-pressure steam thus produced can be superheated in the convection zone (see above) to form superheated high-pressure or super-high-pressure steam, from which it can be distributed to the plant's central steam system to provide heat and power to heat exchangers and steam turbines or other rotating equipment. The typical degree of steam superheat achieved in the furnace convection zone is 150-250 K above the saturation temperature (dew point margin). In general, steam cracking furnaces can operate with high-pressure steam (typically 30-60 bar) or super-high-pressure steam (typically 60-130 bar). For purposes of clarity in describing the present invention, "high pressure steam" is used to refer to the entire pressure range of 30-130 bar, as well as pressure ranges above this upper limit, since the present invention may in some embodiments include the use of pressures up to 175 bar.

[0008] Patent Document 1 discloses a method for quenching cracked gas and recovering heat therefrom by cooling the gas through heat exchange with steam, thereby increasing the superheat level of the steam, and then recovering heat from the superheated steam. According to Patent Document 2, the combustion air of a steam cracking furnace is preheated by indirect heat exchange with medium- and low-pressure steam expanded through a steam turbine from high-pressure steam generated in the high-temperature section of an ethylene production plant.

[0009] Such air preheating is a known method for reducing fuel use in furnaces and is gaining increasing attention amid increased efforts to reduce carbon dioxide emissions. Due to reduced flue gas heat availability and additional air preheating requirements, air preheating in steam crackers can have a significant impact on heat balancing and recovery. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent No. 4,107,226 [Patent Document 2] U.S. Patent No. 4,617,109 [Non-patent literature]

[0011] [Non-Patent Document 1] Ullmann's Encyclopedia of Industrial Chemistry, published online April 15, 2009, DOI: 10.1002 / 14356007.a10_045.pub2 Summary of the Invention [Problem to be solved by the invention]

[0012] The object of the present invention is to further improve known steam cracking plants in terms of efficiency and resource utilization, especially in scenarios where the components of said plants are partly or fully electrified and more advantageous air preheating can be performed. [Means for solving the problem]

[0013] Against this background, the invention proposes a method and a system for steam cracking having the features of the independent claims, embodiments of which are the subject of the dependent claims and the following description.

[0014] Before further describing the features and advantages of the present invention, some terminology used in describing the invention will be further explained.

[0015] The terms "flue gas heat recovery section" and "convection section" may be used synonymously herein. The flue gas heat recovery section or convection section may also include an air preheat stage for the flue gas, which is typically not included in conventional furnace convection zone designs without air preheat, as further described in connection with FIG. 1 below.

[0016] Similarly, the terms "cracked gas heat recovery section" and "quench section" may be used synonymously herein. The cracked gas heat recovery section, or quench section, may include all multi-stream heat exchangers used to cool the cracked gas downstream of the cracking coil, but as understood herein does not include direct contact cooling stages (i.e., cooling by injection of a liquid stream into the cracked gas stream in an attemperator and / or quench column).

[0017] In this regard, the terms "section(s)" and "zone(s)", and combinations thereof, are also used synonymously herein.

[0018] A "multistream heat exchanger" is a heat exchanger configured to exchange heat between two or more medium streams, which are in indirect contact and separated by heat exchange surfaces such as the walls of one or more chambers or tubes. Such a multistream exchanger may be, for example, a quench exchanger, as mentioned in the opening paragraph of the paper, or a tube bundle exchanger arranged in the exhaust gas channel, as typically implemented in the convection zone.

[0019] The term "feed" is intended to include liquid or gaseous hydrocarbons that can be vaporized if necessary and that are diluted or mixed with a process or dilution stream to form the "process gas" that is fed to the cracking furnace or radiant zone during a steam cracking operation. When referring to one of the above streams being preheated, this can also include the first partial stream being preheated and the second partial stream not being preheated, especially when these partial streams are later recombined to form a combined stream that is at a higher temperature than the temperature before the partial streams were formed.

[0020] The term "firing efficiency" is used synonymously with the term "fuel-based radiant zone efficiency" and refers to the relative percentage or ratio of heat absorbed by the coils in the radiant section divided by the chemical energy converted to heat during combustion of fuel in the radiant section, typically calculated for the lower heating value.

[0021] The prior art generally discloses means and methods for improving the energy efficiency of cracking furnaces by predicting the preheating of combustion air. This is typically achieved by utilizing internal heat from the furnace's exhaust gas system using preheated air, or by utilizing external heat from other sources (e.g., superheated or saturated steam, electricity, quench oil, etc.). Higher air preheat temperatures are generally targeted to further minimize fuel gas consumption and thereby the furnace's carbon dioxide emissions.

[0022] WO 2018 / 229267 and WO 2021 / 052642 propose a modified convection zone and quench section setup, preferably used in combustion furnaces with increased efficiency in the radiant zone (by air preheating or oxygen enrichment), in which the mixed hydrocarbon feed / process steam stream is preheated at least directly against the cracked gas in a quench exchanger. According to the above-mentioned documents, the respective embodiments only comprise a single-stage air preheating system in which the air preheater is arranged at the downstream end of the convection section, thereby limiting the air preheating to a moderate temperature level. The air preheating temperature is not specifically mentioned, but for technical reasons it can be assumed to be at most 300-350°C.

[0023] Even simpler options for air preheating in a combustion furnace are external air preheating using an external heating medium other than combustion exhaust gases, such as boiler feedwater, steam, quench water, quench oil, thermo oil, etc., or the inclusion of a single air preheat stage at the downstream end of the convection section, but for the sake of brevity, these will not be described herein.

[0024] EP 0 229 939 and U.S. Pat. No. 3,426,733 also disclose air preheating in steam crackers. Electrified steam crackers equipped with electric or fired furnaces are also known, as disclosed, for example, in WO 2020 / 150244, WO 2020 / 150248 and WO 2020 / 150249.

[0025] Although U.S. Patent Application Publication No. 2014 / 0212823 mentions air preheat temperatures of up to approximately 482°C (900°F) that can be reached by internal air preheating of exhaust gases, it does not disclose a comprehensive concept for heat recovery and energy balancing of such furnaces. In fact, when employing conventional convection zone topologies such as those shown in WO 2018 / 229267 or WO 2021 / 052642, achieving balanced energy integration for internal air preheating at temperatures above 400°C is difficult. This is primarily because these topologies include numerous heat-consuming elements that cannot be supplied with sufficient heat at such high air preheat temperatures. This is because high air preheat temperatures and high radiant box efficiencies reduce the heat available in the convection zone, which further decreases when internal air preheating is anticipated.

[0026] Furthermore, in the case of external air preheating, the unavailability of suitable heating media above 300°C (the condensation temperature of ultra-high pressure steam is approximately 325°C at a typical pressure of 120 barg (measured in bar above atmospheric pressure)) prevents further increases in the preheating temperature. Thus, typical maximum air preheating temperatures found in the literature for steam cracking furnaces are up to approximately 300°C when using an external heat source; see, for example, EP 0 229 939. Also in the case of electrical air preheating, exceeding this range is usually not preferred, as it leads to very high power inputs with significantly lower efficiencies compared to fully electrified furnaces.

[0027] In this regard, the present invention and its embodiments provide a combustion cracking furnace heat recovery concept and corresponding process topology that is particularly suited to higher air preheat temperatures, thereby providing maximum combustion efficiency / minimum fuel usage while selectively recovering waste heat for the essential purpose of processing in the heat recovery section of the furnace.

[0028] The present invention and its embodiments provide advantageous solutions to these challenges, and the main idea or philosophy underlying embodiments of the present invention can be understood as maximizing the efficiency of the combustion furnace by (i) prioritizing the use of exhaust gas heat for maximum air preheat in the convection section, and (ii) simultaneously prioritizing the use of cracked gas heat for maximum preheat of the process gas in the quench section and / or the feedstock and / or steam used to form the process gas.

[0029] The approach of embodiments of the present invention can in principle drive furnace design towards two separate feed-waste cycles: (i) a combustion air / exhaust gas cycle and (ii) a process feed / cracked gas cycle. This means that a gradual reduction in fuel gas usage in a cracking furnace according to the present invention is achieved by simultaneously increasing the relative proportion of exhaust gas heat usage for air preheating and the relative proportion of cracked gas heat usage for preheating the process gas and / or the feed and / or steam used to form the process gas.

[0030] In this regard, the present invention proposes a method of steam cracking using a steam cracking system comprising one or more combustion radiant sections, wherein during the steam cracking operation, fuel is combusted with an oxygen-containing oxidant gas, e.g., combustion air, to heat the one or more combustion radiant sections and form exhaust gases. The oxidant gas may be oxygen-enriched air, or an oxygen-rich gas or gas mixture, such as "technical" oxygen. For purposes of brevity only, the following description focuses on combustion air, but is not so limited.

[0031] a process gas formed from a (gaseous or liquid) hydrocarbon feedstock and (dilution or process) steam; the process gas is passed through one or more cracking coils in the one or more combustion radiant sections to form a cracked gas; at least a portion of the exhaust gas is cooled in an exhaust gas heat recovery section; at least a portion of the cracked gas is cooled in a cracked gas heat recovery section; the exhaust gas heat recovery section and the cracked gas heat recovery section each comprise one or more heat exchangers; the exhaust gas heat recovery section comprises a heat exchange structure; and the heat exchange structure comprises at least The cracked gas heat recovery section is provided in an amount and configured such that during a portion of the steam cracking operation, a first proportion of greater than 35% of the total amount of heat recovered from the exhaust gas in the one or more heat exchangers of the exhaust gas heat recovery section is used for preheating the oxidant gas, and the cracked gas heat recovery section is configured such that during at least the same portion of the steam cracking operation, a second proportion of greater than 35% of the total amount of heat recovered in the one or more heat exchangers of the cracked gas heat recovery section is used for preheating the process gas and / or the hydrocarbon feedstock and / or steam used to form the process gas.

[0032] The term "heat exchange structure" may include any technical means configured to enable or promote heat transfer between different media, such as, for example, straight or wound coils, and the "configuration" of a heat exchange structure may in particular include heat exchange surfaces and / or technical modifications such as fins on the outer surface of the heat exchanger coil and / or grooved or finned channels on the inner surface of the heat exchanger coil, and / or any other features that increase the surface area of ​​the inner or outer surface of the heat exchanger coil.

[0033] The heat exchangers of the exhaust gas heat recovery section and the cracked gas heat recovery section are in particular multi-stream heat exchangers as described above, and in particular at least a significant proportion of the total amount of heat transferred in the exhaust gas heat recovery section and the cracked gas heat recovery section is transferred in such multi-stream heat exchangers. That is, the above proportions generally do not relate to or include heat recovered by other means, such as injection or direct contact cooling, even though in embodiments of the present invention, such injection or direct contact cooling may also be performed in the exhaust gas heat recovery section and the cracked gas heat recovery section. However, in the latter case, only a small amount of fluid compared to the exhaust gas or cracked gas, for example less than 10%, 5%, 0.5%, 1%, or 0.1% compared to the exhaust gas or cracked gas, is injected into the exhaust gas heat recovery section and the cracked gas heat recovery section.

[0034] In either case, preheating the oxidant gas may involve passing the entire oxidant gas stream through a heat exchanger, but may also involve heating a partial stream of the oxidant gas and recombining said partial stream with the remainder to form a combined stream at the resulting temperature. Heating in the exhaust gas heat recovery section and the cracked gas heat recovery section may be carried out in series or in parallel.

[0035] An advantage of the present invention is that it allows for high air preheat levels and therefore high radiant zone efficiencies for both gas and liquid feedstock crackers, resulting in lower overall fuel gas usage, which is particularly beneficial from a carbon dioxide emissions perspective, as discussed below with respect to "Scope 1" through "Scope 3" emissions.

[0036] This reduces the energy requirements of the cracking furnace or the system itself. Because this benefit is independent of the fuel supply technique applied, the present invention, in multiple embodiments, can be combined with any currently available or future combustion technology. The hot combustion air or alternative oxidant gas heated by the exhaust gases is itself the energy carrier within the furnace, recycling energy from the convection section to the cracking furnace firebox. The invention presented here therefore optimizes any furnace combustion system, regardless of the fuel / oxidant mixture delivered to the burner. This includes oxygen-enriched air, hydrogen-enriched or pure hydrogen fuel, ammonia fuel, and others. The present invention optimizes heat exchange between thermodynamically "similar" material streams with similar specific heat capacity curves versus temperature and similar flow rates (exhaust gas versus combustion air, and cracked gas versus process gas, i.e., feedstock and / or steam). Embodiments of the present invention are highly compatible with highly electrified separation train designs, which require significantly less steam and reduce superheat due to the absence of large steam turbines. Inherent safety is provided because heat is exchanged between "compatible" media without risk of explosion / deflagration if a tube ruptures (e.g., by avoiding air preheating for cracked gases, as well as minimizing / avoiding preheating of process gases or feedstock for exhaust gases).

[0037] The solution proposed according to the present invention differs significantly from the prior art, such as that presented in WO 2018 / 229267 and WO 2021052642, since these documents propose process configurations primarily aimed at increasing the proportion of cracked gas waste heat utilization for process gas preheating alone. Indeed, these documents disclose embodiments with and without air preheating, the process sequence for process gas preheating being arranged independently of the air preheating proposal in each of these two documents. The solutions proposed in both WO 2018 / 229267 and WO 2021 / 052642 are built around the core feature of carrying out initial cracked gas cooling in a feed-waste exchanger on a process gas stream that is already preheated in the convection section and may be further preheated in the convection zone of the furnace. The prior art presented in these documents is clearly aimed at combining the proposed process gas preheating sequence with very low levels of air preheating, as is clearly stated in, for example, these documents, and therefore does not propose a strict correlation between the waste heat utilization in the convection section and the waste heat utilization in the quench section.

[0038] According to embodiments of the present invention, the first ratio and the second ratio may be, independently of one another, ratios greater than 35%, greater than 40%, greater than 45%, or greater than 50%, and thus in such embodiments, the advantages of the present invention can be selected to be more or less pronounced by using lower or higher ratios.

[0039] In embodiments of the present invention, the oxidant gas may be preheated to temperatures above 400°C, above 500°C, above 600°C, or above 700°C, temperature levels that far exceed those known in the art.

[0040] In an embodiment of the invention, the oxidant gas or a portion thereof is at least partially heated against the exhaust gas of the exhaust gas heat recovery section in at least two separate oxidant gas preheating stages, and the exhaust gas can be used to superheat high pressure steam at a pressure level of 30 to 175 bar absolute between said two oxidant gas preheating stages.

[0041] Placing a second oxidant gas preheating stage upstream of the high-pressure steam superheating bundle in the convection section significantly changes the thermal balance of the convection section, so oxidant gas preheating is prioritized over export steam generation, and as a result is placed in an upstream portion of the exhaust gas path.

[0042] In embodiments of the invention, steam can be superheated in the exhaust gas heat recovery section, where such superheating of steam in the exhaust gas heat recovery section is limited to a maximum temperature of 450°C, 400°C, or 350°C, and / or a maximum temperature that provides a dew point margin of up to 150K, 120K, 80K, or 60K, where no further superheating of the steam is performed prior to delivery from the exhaust gas heat recovery section or steam cracking system, and where less than 25%, 23%, or 21% of the heat recovered in the exhaust gas heat recovery section is used to generate high-pressure delivery steam. By reducing the steam superheat level and / or maximum temperature, such embodiments allow steam superheat to be more easily located in the exhaust gas path downstream of the high-temperature oxidant gas preheat section.

[0043] In an embodiment of the present invention, the steam discharged from the exhaust gas heat recovery section or the steam cracking system, with or without prior attenuation, passes via conduits, pressure reducing valves and / or nozzles to one or more steam condensing heat exchangers at a ratio of more than 60%, more than 70%, or more than 80%. In particular, for the aforementioned majority of the discharged steam stream, any type of pressure reduction is achieved upstream of the heat exchangers without extracting usable mechanical work, as opposed to, for example, a turbine. At the same time, for the remaining minor portion of the discharged steam stream, an optional first pressure reduction, for example, from a very high pressure level to a high pressure level via a valve, can be achieved, resulting in a steam stream at a relatively low pressure but at a high superheat level, followed by the extraction of mechanical work from the steam stream, for example, by using a back-pressure turbine. The expanded steam stream thus obtained is then preferably sent to a steam condensing heat exchanger operating at a correspondingly lower pressure level. The purpose of only moderately superheated steam being discharged from the furnace is to provide energy primarily for heating the consumers without extracting significant mechanical work from the discharged steam, thus reducing the total amount and specific enthalpy of steam in this configuration.

[0044] In an embodiment of the invention, steam exported from the exhaust gas heat recovery section or steam cracking system is not used in steam turbine drivers delivering shaft powers of more than 5 MW, more than 3 MW, or more than 1 MW. Thus, the large rotating machinery in the downstream separation section is preferably driven by electric motors, "electrifying" such a setup, thereby reducing steam requirements and (local) emissions from the combustion steam generating device.

[0045] The process gas and / or the hydrocarbon feedstock and / or process steam used to form the process gas can be heated at least in part with the recovered cracked gas using a feed-waste exchanger, which in embodiments of the present invention may in particular be located in the flow path of the cracked gas downstream of the steam-producing quench exchanger. In general, heat recovery from the cracked gas for preheating the process gas and / or the hydrocarbon feedstock and / or process steam used to form the process gas can be carried out using various topologies and process sequences. In most embodiments shown herein, the initial cracked gas cooling is performed by a conventional steam-producing primary quench exchanger. Alternatively, embodiments of the present invention can also be provided that include a feed-waste primary quench exchanger.

[0046] The saturated steam produced in the quench exchanger can be used to preheat the process gas and / or the steam and / or hydrocarbon feed used to form the process gas, and the steam condensate recovered from such preheating can be used to further preheat the same medium at a lower temperature level. The indirect use of cracked gas heat for preheating process gas, steam, and / or feedstock via intermediate steam generation is a very suitable design option to ensure fast and reliable cracked gas cooling in state-of-the-art steam generators, thereby avoiding potential challenges in the design and operation of direct feed-waste exchangers. The present invention allows for the flexible use of indirect cracked gas heat recovery for feedstock preheating, which is particularly advantageous, for example, in the context of flexible feed steam cracking systems.

[0047] The use of saturated steam and condensate from this steam further limits the demand for heated delivery steam in the convection section, thereby facilitating the achievement of high oxidant gas preheating loads in the exhaust gas section. Furthermore, such indirect heat recovery is well suited to retrofitting existing plants, where increased utilization of cracked gas heat for preheating process gas, steam, and / or feedstock can be achieved without significant modifications to existing quench coolers and steam drums.

[0048] In some embodiments of the invention, preheating of the process gas and / or the process steam and / or hydrocarbon feedstock used to form the process gas is not performed in the exhaust gas heat recovery section. Thus, the hot exhaust gas leaving the radiant section is used in such embodiments directly to preheat the oxidant gas without prior heat transfer to the feedstock preheating bundles in the convection zone.

[0049] Final preheating of the mixture of steam and hydrocarbon feedstock, i.e., the process gas, or a portion thereof, can be accomplished in some embodiments using an electric superheater before the mixture enters one or more cracking coils of one or more fired radiant sections.

[0050] Fuel gas usage in systems according to embodiments of the present invention is reduced by at least 30%, or 35%, or 40%, or 45% compared to conventional combustion furnaces that do not use oxidant gas preheat and operate using a conventional tail gas and natural gas fuel mixture input.

[0051] In an embodiment of the present invention, a control system adapted to control the characteristics of one or more further flows may be provided. For example, such a control system may be used to avoid cooling the exhaust gas below the condensation temperature and the resulting corrosion problems. In terms of equipment, a backup oxidant gas preheater may be installed upstream of one or more oxidant gas preheaters in the convection section, which may be operated only in special circumstances where any kind of waste heat or low-temperature heat from the process plant is present. For example, a bypass controller or any additional equipment may be provided on the oxidant gas or exhaust gas side.

[0052] In embodiments of the present invention, saturated steam produced in the quench exchanger may be further used to preheat fuel gas, and steam condensate recovered from this or other preheating steps may be used to further preheat fuel gas at lower temperature levels. This use of saturated steam as a heat source may be used for any other heating application of a process stream, but particularly near sections of a furnace to avoid long transfer lines carrying the saturated steam stream (risk of liquid buildup in the piping and / or steam hammer).

[0053] In embodiments of the present invention, heat from the exhaust gas is not used to generate steam in the "boiler" bundle. Furthermore, when air is used as the oxidant gas, the air may be further enriched by adding an oxidant stream having an oxygen content above atmospheric from an external source, such as an electrolyzer, a cryogenic air separation unit, or a (vacuum) pressure swing adsorption unit.

[0054] In an embodiment of the present invention, the steam cracking system can be operated in an energy-flexible manner, i.e., by varying the air preheat temperature, for example, by using an air bypass line around one or both of the air preheat stages, a given chemical production load of the furnace can be accommodated with various total fuel gas consumptions. In an embodiment of the present invention, no boiler feedwater preheating is performed on the exhaust gas from the furnace. The fuel gas consumed in the radiant zone may include fossil-based and / or synthetic and / or biofuel-based hydrocarbons, fossil-based (gray / blue / turquoise) and / or renewable energy-based (green) hydrogen, and / or ammonia. The consumption of the supplied fuel gas may be varied during furnace operation along with other critical furnace operating parameters. In particular, increasing the content of carbon-neutral fuels (e.g., hydrogen, ammonia) in combination with measures to maximize the air preheat temperature can minimize the consumption of such valuable clean fuels. Adjustments to fuel consumption can be made by modifying hydrogen separation in the tail gas processing and / or by changing the amount of external fuel input.

[0055] Also provided is a steam cracking system comprising one or more combustion radiant sections and means configured to combust a fuel with an oxidant gas during a steam cracking operation to heat the one or more combustion radiant sections and form an exhaust gas; means configured to form a process gas from a hydrocarbon feedstock and process steam; means configured to pass the process gas through one or more cracking coils in the one or more combustion radiant sections to form a cracked gas; an exhaust gas heat recovery section configured to cool at least a portion of the exhaust gas; and a cracked gas heat recovery section configured to cool at least a portion of the cracked gas. The exhaust gas heat recovery section and the cracked gas heat recovery section each comprise one or more multi-stream heat exchangers, the exhaust gas heat recovery section comprising a heat exchange structure provided in an amount and configuration such that a first proportion of the total amount of heat recovered from the exhaust gas in the one or more multi-stream heat exchangers of the exhaust gas heat recovery section is used for preheating the oxidant gas during at least a portion of the steam cracking operation, the first proportion being greater than 35% of the total amount of heat recovered in the one or more multi-stream heat exchangers of the cracked gas heat recovery section, and the cracked gas heat recovery section is configured such that a second proportion of the total amount of heat recovered in the one or more multi-stream heat exchangers of the cracked gas heat recovery section is used for preheating the process gas and / or the hydrocarbon feedstock and / or steam used to form the process gas, during at least the same portion of the steam cracking operation.

[0056] For further details relating to the steam cracking system provided according to the invention and its preferred embodiments, reference is made to the above description of the method of the invention and its preferred embodiments. Advantageously, the device proposed here is adapted to carry out the method in at least one of the embodiments described in more detail above.

[0057] To summarize and partially repeat what has been said above, the present invention in particular enables high air preheat levels and therefore high radiation zone efficiencies for both gaseous and liquid feedstock crackers, which results in lower fuel gas usage, which is particularly beneficial in terms of carbon dioxide emissions: reductions in so-called "scope 1" emissions, for example, by reducing the combustion of carbonaceous fuels, and / or reductions in "scope 2" emissions, for example, by using less hydrogen from on-site electrolyzers and consequently less electricity consumption, and / or reductions in "scope 3" emissions, for example, by increasing the delivery of unused hydrogen fuel gas.

[0058] This reduces the energy requirements of the cracking furnace itself. This benefit is independent of the fuel supply technique applied, so the invention presented here can be combined with any currently available or future combustion technology.

[0059] The present invention allows for the use of gaseous hydrocarbon feedstocks, such as ethane, propane, or butane, as well as liquid hydrocarbon feedstocks, such as naphtha, diesel, or plastic waste pyrolysis oil. Embodiments of the present invention may be used to process exclusively one preferred type of hydrocarbon feedstock, such as ethane or naphtha, in a given furnace. Other embodiments of the present invention may use gaseous hydrocarbon feedstocks, such as (various) mixtures of ethane and propane, or liquid hydrocarbon feedstocks, such as (various) mixtures of naphtha and plastic waste pyrolysis oil. In further embodiments, the cracking operation may include multiple distinct operating periods alternating between liquid and gaseous hydrocarbon feedstocks in a single, feedstock-flexible furnace. Furthermore, the present invention is applicable to furnaces in which simultaneous cracking of gaseous and liquid hydrocarbon feedstreams is performed, at least temporarily.

[0060] The present invention can also be combined with any type of additional treatment step, which is used to (further) reduce the concentration of environmentally relevant components in the exhaust gas, for example to reduce the carbon dioxide content in a carbon capture process unit using amine scrubbing or equivalent treatment technology, and / or to reduce nitrous oxide emissions in a nitrous oxide removal unit using selective catalytic reduction or equivalent treatment technology. The implementation of such additional exhaust gas treatment steps is facilitated by the present invention through the reduction in fuel gas usage and the resulting reduction in exhaust gas volume.

[0061] According to embodiments of the present invention, high temperatures are achieved for the combustion air or alternative oxidant gas heated by the exhaust gas, which itself is an energy carrier in the furnace, which recycles energy from the convection section to the firebox of the cracking furnace. Thus, the invention presented here optimizes any furnace combustion system, regardless of the fuel / oxidant mixture sent to the burner. According to embodiments of the present invention, this includes oxygen-enriched air or oxidant gas consisting of pure oxygen, diluted or not with recycled fuel gas, hydrogen-enriched fuel or pure hydrogen fuel, ammonia fuel, and others.

[0062] Embodiments of the present invention provide optimized heat exchange between thermodynamically "similar" material streams with similar specific heat capacity curves versus temperature and similar flow rates (exhaust gas versus combustion air, and cracked gas versus feedstock). Embodiments of the present invention also achieve high compatibility with highly electrified separation train designs, which require significantly less steam and reduce superheat due to the absence of large steam turbines.

[0063] By avoiding, for example, air preheating on the cracked gas, as well as minimizing / avoiding preheating of process gas or feedstock on the exhaust gas, embodiments of the present invention are inherently safe, as heat exchange occurs between "compatible" media without risk of explosion / deflagration in the event of a tube rupture. The flexible use of indirect cracked gas heat recovery for preheating feedstock, process gas, or process steam is advantageous, for example, in the context of a flexible feedstock cracker.

[0064] Embodiments of the present invention may include the use of electric heaters in locations other than the final process gas preheat stage. Electric heaters may be used, inter alia, to superheat process steam prior to mixing with the hydrocarbon feed stream, and / or preheat oxidant gas, and / or superheat high-pressure delivery steam. Such electric heaters may be configured for temporary or flexible use to compensate for fluctuating preheat load requirements, for example, associated with fouling / coking of multi-stream heat exchangers and / or varying feedstock conditions. Electrically powered oxidant gas preheaters may also be operated, preferably in situations where there is a renewable electricity surplus on the grid, to temporarily reduce fuel gas requirements and increase fuel gas storage levels within the plant.

[0065] The invention can furthermore be combined with dedicated energy storage systems, such as latent heat storage systems, etc. In particular, a portion of the delivered high pressure steam can be temporarily routed to a suitable heat storage system.

[0066] A steam cracker plant equipped with a combustion furnace system according to the invention can further be integrated into a hybrid system architecture, in which the combustion furnace according to the invention operates in parallel with an electrically heated furnace (irrelevant to the electric coil heating principle: direct resistance coil heating, indirect radiant coil heating with electric heating elements, coil heating using inductive power transmission). The steam cracker plant may further comprise other units for steam generation from electrical energy (e.g. electric heat pump system, electric boiler, etc.).

[0067] The present invention is preferably combined with a separation train in which at least a majority, greater than 50%, greater than 70%, greater than 90%, or greater than 95%, of the molecular hydrogen contained in the cracked gas and possibly additional feed streams to the separation section of the plant is separated into a purified stream having a molar hydrogen content of greater than 95% for use in combustion in a furnace.

[0068] All features proposed herein for the embodiments of the present invention may be combined, individually or in any group, with the features proposed in International Patent Application No. PCT / EP2022 / 055877 and European Patent Application No. 21161768.3, which are incorporated herein by reference, to the extent possible, and with any combination of these features, and the skilled person should refer to these applications for any questions concerning the realization of these features.

[0069] The invention and its embodiments will be further explained in relation to the accompanying drawings.

[0070] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0071] [Figure 1] FIG. 1 illustrates an embodiment that does not form part of this invention. [Figure 2] FIG. 2 illustrates the basic principle of an embodiment of the present invention. [Figure 3] 3 to 8 show an embodiment of the present invention. [Figure 4] 3 to 8 show an embodiment of the present invention. [Figure 5] 3 to 8 show an embodiment of the present invention. [Figure 6] 3 to 8 show an embodiment of the present invention. [Figure 7] 3 to 8 show an embodiment of the present invention. [Figure 8] 3 to 8 show an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0072] In the figures, elements having identical, substantially identical, functionally equivalent, or technically equivalent functions and / or purposes may be identified with the same reference numerals, and repeated descriptions may be omitted for the sake of brevity. Descriptions herein of devices, apparatus, configurations, systems, etc. according to embodiments of the invention may also apply to methods, processes, procedures, etc. according to embodiments of the invention, and vice versa.

[0073] The various embodiments described herein are presented solely to aid in the understanding and teaching of the claimed features. These embodiments are merely a representative sample of embodiments and are not intended to be exhaustive and / or exclusive. It is understood that the advantages, embodiments, examples, functions, features, structures, and / or other aspects described herein should not be deemed limitations on the scope of the invention as defined by the claims or on the equivalents of the claims, and that other embodiments may be utilized and modifications may be made without departing from the scope of the claimed invention. The various embodiments of the invention may suitably comprise, consist of, or consist essentially of any suitable combination of the disclosed elements, components, features, parts, steps, means, etc., other than those specifically described herein. Furthermore, the present disclosure may include other inventions not currently claimed but which may be claimed in the future, particularly if they are encompassed within the scope of the independent claims.

[0074] In the figures, elements having identical, substantially identical, functionally equivalent, or technically equivalent functions and / or purposes may be identified with the same or similarly incremented reference numbers, and repeated descriptions may be omitted for the sake of brevity. Descriptions herein of devices, apparatus, configurations, systems, etc. according to embodiments of the invention may also apply to methods, processes, procedures, etc. according to embodiments of the invention, and vice versa.

[0075] When referring hereinafter to "combustion air," this is intended to encompass additional oxidant gases as described above as well.

[0076] Additionally, these figures do not show one or more air compression devices typically located upstream of the combustion air preheat section to compensate for the pressure drop across the combustion air preheat exchanger. The preferred pressure on the combustion side of the radiant section is typically in the slightly subatmospheric range, similar to conventional cracking furnaces without combustion air preheat. Therefore, it is most preferred to locate the flue gas blower / compression device downstream of the convection section outlet.

[0077] For reference and to further illustrate the background of the present invention, a combustion steam cracking apparatus not of the present invention is shown in a highly simplified schematic fragmentary view in FIG. 1 and is designated by the numeral 900.

[0078] The steam cracking system 900 shown in Figure 1 includes one or more cracking furnaces 90. For purposes of brevity only, the following refers to "one" cracking furnace 90, however, a typical steam cracking apparatus 900 may include multiple cracking furnaces 90 that may operate under the same or different conditions. Additionally, each cracking furnace 90 may include one or more of the components described below.

[0079] Cracking furnace 90 comprises a radiant zone 91 and a convection zone 92. In embodiments different from that shown in Figure 1, multiple radiant zones 91 can be associated with a single convection zone 92, and so on.

[0080] In the illustrated example, multiple heat exchangers 921-928 are disposed within the convection zone 92 in the number, arrangement, or order shown, or in a different number, arrangement, or order. These heat exchangers 921-928 are typically provided in the form of tube bundles passing through the convection zone 92 and positioned within the exhaust gas channel 911 from the radiation zone 91, indicated by the dash-dotted arrows.

[0081] In the illustrated example, the radiant zone 91 is heated by a plurality of burners, which are not shown for simplicity and may be disposed on the bed and / or wall sides of the refractory forming the radiant zone 91. As indicated by the two dash-dotted arrows, a fuel gas 901 and an oxygen-containing oxidant gas 902, such as air, oxygen-enriched air, etc., may be supplied to the burners in the radiant zone 91.

[0082] In the illustrated example, a gaseous or liquid hydrocarbon stream 903, indicated by a double arrow, is fed into the steam cracking system 900. Multiple hydrocarbon streams can be used, either in the illustrated manner or in a different manner. This hydrocarbon stream is first routed to a heat exchanger 927 in the convection zone 92, where it is preheated. Heat exchanger 927 is also referred to as a feed preheater. Process steam 904, also indicated by a double arrow, is fed and, in the illustrated example, passes through the convection zone 92, or more precisely, through a heat exchanger 924, where it is superheated. Heat exchanger 924 is therefore also referred to as a process steam superheater. Such process steam superheaters are typically used in cracking furnaces that operate, at least in part, with a liquid hydrocarbon feed stream, to facilitate vaporization of the feed by adding a highly superheated process stream. Cracking furnaces that operate solely with a gaseous hydrocarbon feed stream typically do not include such a process steam superheater.

[0083] The preheated hydrocarbon stream and the superheated process steam are combined to form a process gas stream 905, which passes through heat exchanger 925 and then heat exchanger 921, also indicated by the double arrows, and these heat exchangers 925, 921 are also called the first high temperature coil (heat exchanger 925) and the second high temperature coil (heat exchanger 921), and the process gas stream 905 then passes through one or more cracking coils in the radiant zone 91.

[0084] The product mixture 906 obtained in the radiation zone 91, also referred to as cracked gas or raw gas, exits the radiation zone 91 and passes through a primary quench exchanger 93, shown here as an ultra-high pressure steam generator, before being sent to subsequent processing and separation steps, not shown, which are commonly known in the art.

[0085] The steam generator 93 is associated with an extra-high pressure steam drum 94. Boiler feedwater 910 may be preheated in heat exchangers 928, 926 of the convection section 92, also referred to as a first economizer (heat exchanger 928) and a second economizer (heat exchanger 926), as indicated by solid arrows throughout, before being supplied to the extra-high pressure steam drum 94 and the extra-high pressure steam generator 93.

[0086] Saturated extra-high pressure steam 907 is taken from extra-high pressure steam generator 93, as indicated by the fine dotted arrow, passes through extra-high pressure steam drum 94, and is superheated in heat exchangers 923, 922 in convection zone 92, also referred to as a first extra-high pressure steam superheater (heat exchanger 923) and a second extra-high pressure steam superheater (heat exchanger 922), to form superheated extra-high pressure steam 908, as indicated by the coarse dotted arrow. Injection of boiler feedwater 910 may also be carried out at a location between heat exchanger 923 and heat exchanger 922.

[0087] In a non-inventive steam cracking system 900 configuration such as that shown in FIG. 1, heat recovered from cooling the cracked gas, such as in the primary quench exchanger 93 or elsewhere, is typically used only to generate very high pressure delivery steam, while heat recovered in the flue gas section, or convection zone 92, is used to preheat the feedstock as shown and to generate very high pressure delivery steam (by preheating boiler feedwater and superheating saturated ultra-high pressure steam).

[0088] The design philosophy underlying embodiments of the present invention, as described above and with respect to various embodiments below, involves maximizing furnace efficiency by (i) prioritizing the use of exhaust gas heat for maximum air preheat in the convection section, and (ii) simultaneously prioritizing the use of cracked gas heat for maximum process gas, feedstock, and / or process steam preheat in the quench section.

[0089] In FIG. 2 the basic principles of an embodiment of the present invention are illustrated diagrammatically in a strictly simplified diagram of a steam cracking system 100 .

[0090] The cracking furnace 10 shown in Figure 2 includes a radiant zone 11 and a convection zone 12. In embodiments other than that shown in Figure 1, multiple radiant zones 11 may be associated with a single convection zone 12, as described above for system 900 associated with Figure 1. The cracked gas heat recovery section is shown as 13.

[0091] In the illustrated example, multiple heat exchangers may be disposed in the convection zone 12, but are not shown in FIG. 2 for the sake of generality.

[0092] Similar to the heat exchangers 921-928 of the system 900 shown in FIG. 1, these heat exchangers are typically provided in the form of tube bundles passing through the convection zone 12 and positioned in the exhaust gas flow from the radiant zone 11. Alternative multi-stream heat exchanger designs may also be used, particularly for heat exchange between the exhaust gas and the oxidant gas. The convection zone 12 may comprise one or more straight exhaust gas channels and, if necessary, connecting ducts between or connecting the straight exhaust gas channels to a multi-stream heat exchanger with a separate shell, for example, via flange connections. In the present invention, such a separately arranged multi-stream heat exchanger that recovers heat from the exhaust gas flow also forms part of the exhaust gas heat recovery section.

[0093] As described with respect to system 900 shown in FIG. 1 , radiant zone 11 is heated using a plurality of burners, which are not shown for simplicity and may be disposed on the bed and / or wall sides of the refractory forming radiant zone 11. Fuel gas, not shown, and an oxygen-containing oxidant gas 102, such as air, shown by dash-dotted arrows, may be supplied to the burners in radiant zone 11. Exhaust gas 111, also shown by dash-dotted arrows, passes through convection zone 12, which is also referred to as an exhaust gas heat recovery unit. Oxygen-containing oxidant gas 102 is heated in exhaust gas heat recovery unit 12 and in optional further heating steps 1 and 2 that may be implemented in accordance with embodiments of the present invention.

[0094] In the illustrated example, a gaseous or liquid hydrocarbon feedstock 103, or a mixture of such feedstock and process steam 105, or process gas as the term is used herein, as depicted by the double arrow, is similarly fed to the steam cracking system 100. As described with respect to the system 900 shown in Figure 1, multiple hydrocarbon streams may also be used.

[0095] Such hydrocarbon feedstock 103 or process gas 105, in the illustrated example, is preheated in at least the cracked gas heat recovery section 13, and in optional further heating steps 3, 4 before and after, and passes through the radiant section 11 to form cracked gas 106, also indicated by the double arrow. In certain embodiments of the invention, the further heating steps 3, 4 may be performed in a multi-stream heat exchanger that is part of the convection zone 12.

[0096] The cracked gas 106 is then cooled in the cracked gas heat recovery section 13. One or more heat-consuming elements other than air or oxygen-containing oxidant gas may also pass through the convection section 12, as indicated at 199, and one or more heat-consuming elements other than a hydrocarbon feedstock may also pass through the cracked gas heat recovery section 13, although not specifically shown.

[0097] Figures 3-8 illustrate embodiments of the present invention for both gaseous feed steam cracking systems (Figures 3, 4, 5; also referred to as embodiments 1, 2, 3) and liquid feed steam cracking systems (Figures 6, 7, 8; also referred to as embodiments 4, 5, 6). Further process data is provided in Tables 1 and 2, and comparative data with prior art embodiments with and without conventional "low temperature" air preheating (APH) is also given. In these tables, "feed preheating" refers to the preheating of process gas and / or hydrocarbon feed and / or process steam; see Figures 3-8 for the concepts embodied.

[0098] As shown in Figures 3-8, in preferred embodiments, preheating of the combustion air is performed, at least in part, in at least two separate air preheating stages on the exhaust gas. Between the two air preheating stages, heat is recovered from the exhaust gas, preferably to superheat steam generated in a steam-producing quench exchanger. In some embodiments, additional heat may be recovered from the exhaust gas between the two air preheating stages to heat another stream, for example, to preheat a process gas stream as shown in Figure 6 for an embodiment with a liquid feed cracker setup.

[0099] Embodiments of the present invention can be applied in a similar manner to furnace systems operating with either gaseous or liquid feedstocks by using slightly different quench and convection section sequences while maintaining and specifically utilizing the features of the present invention. This is particularly worth mentioning when considering the following constraints that differentiate the processes of gaseous and liquid feedstock furnaces: the preheat load of a liquid feedstock furnace is much higher than that of a gaseous feedstock furnace due to the additional enthalpy of vaporization of the hydrocarbon feedstock. Furthermore, to avoid heavy hydrocarbon condensates, less heat can be recovered in the multi-stream exchangers of the quench section.

[0100] At the same time, there is an interest in maximizing air preheat in liquid-feed furnaces as well as gas-feed furnaces to reduce fuel gas consumption and exhaust gas emissions. Despite these additional / strict constraints, embodiments of the present invention are applicable to liquid-feed furnaces by making more extensive use of indirect cracked-gas heat recovery by cooling the cracked gas to generate steam and condensing at least a portion of said steam for preheating process gas (process steam and / or hydrocarbon feed) at lower temperatures. This is advantageous because preheating at temperatures below 300°C covers most of the additional vaporization enthalpy of the liquid feedstock.

[0101] All conservative embodiments of the present invention relating to liquid-feed furnaces can be characterized by a relatively greater use of indirect feed preheating using heat from the cracked gas compared to gaseous feed configurations. While one might think that the additional feed preheating load for feed vaporization in liquid furnaces limits the achievable air preheat level, the present invention proves the opposite, since the majority of the feed preheating load is required for vaporization of the liquid hydrocarbon feed, which can be achieved by condensing saturated, very high-pressure steam at temperatures well below 300°C. Furthermore, the multiphase nature of the coolant-side feed stream and its high content of fouling-prone components can further hinder the reliable design and operation of alternative direct feed-waste exchangers.

[0102] [Table 1] TIFF2025532505000003.tif250170 TIFF2025532505000004.tif178170

[0103] [Table 2] TIFF2025532505000006.tif251170TIFF2025532505000007.tif22170

[0104] This relatively large utilization of indirect process gas, hydrocarbon feedstock, and / or process steam preheating using heat from the cracked gas does not reduce the load available for air preheating, but rather leads to a reduction in the net delivered steam volume, which further reduces the relative heat load used in the convection section for steam superheating, thus actually increasing the load available to the internal air preheat segment.

[0105] In fact, as can be seen by comparing Tables 1 and 2, the liquid furnace embodiment (see Table 2) uses up to 10% of the recovered exhaust gas heat for superheating the outgoing steam, while the gas furnace embodiment (see Table 1) uses up to 21%. Therefore, differences in raw materials do not lead to changes in the achievable air preheat temperature, but only to variations in the outgoing, non-essential utility steam. The relevance of this minor drawback is further mitigated in the context of future, highly electrified plant designs, where steam demand will be significantly reduced compared to existing designs. Furnace designs with flexible raw material supply may offer further benefits.

[0106] In conventional configurations, initial process steam, hydrocarbon feed, and / or process steam preheating occurs solely in the convection section, with only preheating at higher temperatures above 350°C achieved using heat from the cracked gas (see WO 2021 / 052642). When combined with the downstream positioning of air preheat bundles within the convection zone as described above, application of such conventional designs for gas and liquid feed furnaces results in lower air preheat levels for the liquid feed furnace, since much of the residual exhaust gas heat is consumed in preheating the initial feed.

[0107] For completeness, it should be noted that the convection section of a liquid feed furnace typically comprises an additional process steam superheater, while the quench section does not include a tertiary quench exchanger, resulting in higher cracked gas temperatures at the outlet of the furnace under consideration, typically around 380°C compared to around 200°C in a gas feed furnace. This is necessary to avoid the condensation of heavy condensates if the cracked gas is cooled below this level. In liquid feed crackers, therefore, the cooling of the cracked gas to lower temperatures is carried out by direct contact cooling by injection of pyrolysis oil / gasoline and / or quench water (the related recovery of heat at these lower temperatures is outside the scope of this invention, see the terms introduced above).

[0108] According to embodiments 1, 2 and 3 shown in Figures 3, 4 and 5, a primary quench heat exchanger 131, a secondary quench heat exchanger 132 and a tertiary quench heat exchanger 133 are present in the cracked gas heat recovery section 13, through which the cracked gas 106 passes, while according to embodiment 4 shown in Figure 6, a single primary quench exchanger 134 is used in this connection. According to embodiments 5 and 6 shown in Figures 7 and 8, a primary quench exchanger 134 connected to a secondary exchanger 135 is used.

[0109] In all cases, the steam drum is designated 14. In embodiment 1 shown in Figure 3, the exhaust gas heat recovery unit is shown as a single unit 12, which can be divided into a (main) exhaust gas heat recovery subunit 121 and an auxiliary exhaust gas heat exchanger unit 129 according to embodiments 2 and 3 shown in Figures 4 and 5, and into partial units 121 and 122 according to embodiments 4, 5, and 6 shown in Figures 6, 7, and 8. In all embodiments, an ambient air stream is used as the oxidant gas 102. The hydrocarbon feedstock 103 can be, for example, ethane according to embodiments 1, 2, and 3 shown in Figures 3, 4, and 5, or naphtha according to embodiments 4, 5, and 6 shown in Figures 6, 7, and 8. In all cases, process steam is designated 104, and the mixture of feedstock 103 and process steam, i.e., "process gas" as the term is used herein, is designated 105. Further, the medium includes boiler feedwater 110 and exhaust gas 111.

[0110] Typical air preheat temperatures are 612°C according to embodiment 1 shown in FIG. 3, 907°C according to embodiment 2 shown in FIG. 4, 940°C according to embodiment 3 shown in FIG. 5, 475°C according to embodiment 4 shown in FIG. 6, 590°C according to embodiment 5 shown in FIG. 7, and 820°C according to embodiment 6 shown in FIG. 8.

[0111] Turning now to the embodiments relating to gaseous hydrocarbon feedstocks, i.e., embodiments 1, 2 and 3 shown in Figures 3, 4 and 5, we will discuss the common features and differences between these embodiments.

[0112] According to embodiment 1 shown in Figure 3, the feed 103 is preheated in a tertiary quench exchanger 133 before being combined with process steam 104. The diluted feed 105, i.e., process gas, is heated in a secondary quench exchanger 132. In contrast, according to embodiments 2 and 3 shown in Figures 4 and 5, there is a preheater 127 for the feed 103 and a heater 125 for the process gas 105, which operate using saturated steam 117 from the steam drum 14 to form steam condensate in the heater 125 and subcooled steam condensate 118 in the preheater 127. In embodiment 2 shown in Figure 4, the process gas 105 is further heated in the secondary quench exchanger 132 and auxiliary (electric) heater 136, while according to embodiment 3 shown in Figure 5, the primary quench exchanger 131 is used for this purpose.

[0113] In the first and second embodiments shown in Figures 3 and 4, the steam drum 14 operates using steam generated in a primary quench exchanger 131 using heat extracted from the cracked gas 106, while in the third embodiment shown in Figure 5, a secondary quench exchanger 132 is used for this purpose. In the embodiment shown in Figure 4, the boiler feedwater 110 is heated in a tertiary quench exchanger 133 before being sent to the steam drum 14. This is also done in the third embodiment shown in Figure 5, but in this embodiment, preheating of the boiler feedwater is also performed in the exhaust gas heat recovery unit. In the first, second and third embodiments shown in Figures 3, 4 and 5, the steam 107 from the steam drum 14 is also superheated in two steps in the exhaust gas heat recovery unit 12 (with optional injection of boiler feedwater between these two steps) and is discharged as superheated steam 119.

[0114] In embodiment 1 shown in Figure 3, preheating of the oxidant gas 102, for example combustion air, is carried out in two steps in the exhaust gas heat recovery unit 12, and bypasses are shown to bypass each of the two oxidant gas superheating steps in the exhaust gas heat recovery unit 12, which can be operated using a temperature controller TC that operates based on the exhaust gas temperature or the preheated air temperature.

[0115] In embodiments 2 and 3 shown in Figures 4 and 5, preheating of the oxidant gas 102, i.e., the combustion air, is carried out using an auxiliary exhaust gas heat exchanger unit 129, which is considered part of the exhaust gas heat recovery section 12 and may be arranged downstream of the (main) exhaust gas heat recovery subunit 121 in the exhaust gas path, and then in the main exhaust gas heat recovery subunit 121; in the embodiment shown in Figure 5, two heating steps are carried out in the main exhaust gas heat recovery subunit 121; in embodiment 2 shown in Figure 4, a bypass is shown that bypasses the auxiliary exhaust gas heat exchanger 129 and the heating in the main exhaust gas heat recovery subunit 121, which can be operated using a temperature controller TC that operates based on the exhaust gas temperature or the preheated air temperature.

[0116] Turning now to embodiments 4, 5 and 6, which relate to liquid or heavy hydrocarbon feedstocks, i.e., the embodiments shown in Figures 6, 7 and 8, we will discuss the common features and differences between these embodiments.

[0117] First, in embodiments 4, 5, and 6 shown in Figures 6, 7, and 8, the steam drum 14 operates using steam generated in quench exchanger 134 using heat extracted from the cracked gas stream 106. Further in embodiments 4, 5, and 6 shown in Figures 6, 7, and 8, the feedstock 103 is preheated in heat exchanger 151 and then further heated in heat exchanger 152 before being combined with the process steam 104. The process steam 104 is preheated in process steam preheater 161 before being combined with the feedstock 103.

[0118] In embodiment 4 shown in Figure 6, the process gas 105 is further heated in heat exchanger 153 and then heated in two stages in the heat recovery unit 12 or its sub-unit 121. In contrast, in embodiment 5 shown in Figure 7, the process gas 105 is not further heated in a heat exchanger corresponding to heat exchanger 153 shown in Figure 6, but is heated in a further heat exchanger 135 in the cracked gas heat recovery section 13 and then heated in one stage in the exhaust gas heat recovery unit 12 or its sub-unit 121. In a further alternative embodiment 6 shown in Figure 8, the process gas 105 is further heated in heat exchanger 153 as in embodiment 4 shown in Figure 6, but is then heated in a further heat exchanger 135 in the cracked gas heat recovery section 13 and also heated in one stage in the heat recovery unit 12 or its sub-unit 121 as in the embodiment shown in Figure 7.

[0119] In embodiments 4 and 5 shown in Figures 6 and 7, the boiler feedwater 110 is partially preheated in a boiler feedwater preheater 171 before being sent to the steam drum 14. In embodiment 6 shown in Figure 8, this boiler feedwater 110 is further heated in the heat recovery unit 12 or its subunit 121. A further portion of the boiler feedwater 110 is injected into the steam stream between the two heating stages in the recovery unit 12 or its subunit 121, essentially as shown in Figure 1.

[0120] In the latter case, heat exchangers 161, 152, 153, if present, operate in parallel with saturated steam 117 from steam drum 14, and the resulting steam condensate stream is then combined and used in boiler feedwater preheater 171 and subsequently in feed preheater 151, where the condensate is cooled to subcooled conditions before being delivered as subcooled steam condensate stream 108.

[0121] According to embodiments 4, 5 and 6 shown in Figures 6, 7 and 8, the combustion air 102, or oxidant gas flow, is first preheated in a downstream section of the heat recovery unit 12 or its subunit 122, and then preheated in an upstream section of the heat recovery unit 12 or its subunit 121.

[0122] Combustion air is at least partially preheated in the exhaust gas path using an air preheating system consisting of at least two multi-stream heat exchangers, with exhaust gas as the hot medium and air as the cold medium ("internal air preheating"). As shown in Figures 3-8, heat is preferably recovered from the exhaust gas between the two air preheating steps, preferably into superheated steam generated in a steam-generating quench exchanger. In some embodiments, heat can also be further recovered from the exhaust gas between the two air preheating steps to heat other streams, for example, to preheat a feed stream as shown in Figure 7 for a liquid feed cracker setup.

Claims

1. A method of steam cracking using a steam cracking system comprising one or more combustion radiant sections (11), comprising: During steam cracking operations, a fuel (101) is combusted with an oxygen-containing oxidant gas (102) to heat the one or more radiant sections (11) to form exhaust gases (111); The process gas (105) is formed from the hydrocarbon feedstock (103) and the process steam (104); passing the process gas (105) through one or more cracking coils in the one or more combustion radiant sections (11) to form cracked gas (106); At least a portion of the exhaust gas (111) is cooled in an exhaust gas heat recovery section (12); At least a portion of the cracked gas (106) is cooled in a cracked gas heat recovery section (13); the exhaust gas heat recovery section (12) comprises one or more heat exchangers; the cracked gas heat recovery section (13) comprises one or more heat exchangers (131, 132, 133, 134, 135); the exhaust gas heat recovery section (12) is configured to use a first proportion, greater than 35% of a total amount of heat recovered from the exhaust gas (111) in the one or more heat exchangers of the exhaust gas heat recovery section (12), for preheating the oxidant gas (102), at least during a portion of the steam cracking operation; the cracked gas heat recovery section (13) comprises a heat exchange structure, the heat exchange structure being provided in an amount and configuration such that a second proportion, greater than 35% of the total amount of heat recovered in the one or more heat exchangers (131, 132, 133, 134) of the cracked gas heat recovery section (13), at least during the same portion of the steam cracking operation, is used for preheating the process gas (105) and / or the hydrocarbon feedstock (103) and / or the process steam (104) used to form the process gas (105).

2. 2. The method of claim 1, wherein the first ratio and the second ratio are, independently of one another, greater than 35%, greater than 40%, greater than 45%, or greater than 50%.

3. The method of claim 1 or 2, wherein the oxidant gas (102) is preheated to a temperature greater than 400°C, greater than 500°C, greater than 600°C, or greater than 700°C.

4. the oxidant gas (102), or a portion thereof, is at least partially preheated against the exhaust gas of the exhaust gas heat recovery section (12) in at least two separate oxidant gas preheating stages; 4. The method according to claim 1, wherein the exhaust gas is used to superheat high-pressure steam between the two oxidant gas preheating stages at a pressure level of 30 to 175 bar absolute.

5. Steam is superheated in the exhaust gas heat recovery section (12); the superheating of steam in the exhaust gas heat recovery section (12) is limited to a maximum temperature of 450°C, 400°C, or 350°C and / or a maximum temperature that provides a dew point margin of at most 150K, 120K, 80K, or 60K; No further superheating of the steam is performed before the steam leaves the exhaust gas heat recovery section (12) or the steam cracking system; 5. The method of claim 1, wherein less than 25%, less than 23%, or less than 21% of the heat recovered in the exhaust gas heat recovery section (12) is used to generate high pressure delivery steam.

6. 6. The method according to any one of claims 1 to 5, wherein the steam leaving the exhaust gas heat recovery section (12) or the steam cracking system, with or without prior attenuation, passes via conduits, pressure reducing valves and / or nozzles to one or more steam condensing heat exchangers in a proportion of more than 60%, more than 70% or more than 80%.

7. 7. The method according to any one of claims 1 to 6, wherein the steam discharged from the exhaust gas heat recovery section (12) or the steam cracking system is not used in a steam turbine driver delivering a shaft power of more than 5 MW, more than 3 MW, or more than 1 MW.

8. 8. The method of any one of claims 1 to 7, wherein the process gas, and / or the hydrocarbon feedstock (103) and / or the process steam (104) used to form the process gas (105) are heated at least in part using heat from recovered cracked gas using a feed-to-waste exchanger.

9. 9. The method of claim 8, wherein the feed-waste exchanger is located in the flow path of the cracked gas downstream of a steam-producing quench exchanger.

10. the saturated steam produced in the quench exchanger is used to preheat the process gas (105) and / or the hydrocarbon feedstock (103) and / or the process steam (104) used to form the process gas (105); 10. The method of any one of claims 1 to 9, wherein the steam condensate recovered from the preheating is used to further preheat the process gas (105) and / or the hydrocarbon feedstock (103) and / or the process steam (104) used to form the process gas (105) at a lower temperature level.

11. 9. The method of claim 1, wherein preheating of the process gas (105) and / or the hydrocarbon feedstock (103) and / or the process steam (104) used to form the process gas (105) is not performed in the exhaust gas heat recovery section.

12. 12. The method according to any one of claims 1 to 11, wherein a final preheating of the process gas (105) or a portion thereof is performed using an electric superheater before the mixture enters one or more cracking coils of the one or more fired radiant sections.

13. One or more combustion radiant sections (11), and means configured to heat said one or more combustion radiant sections (11) by burning a fuel (101) with an oxidant gas (102) during steam cracking operations to form exhaust gases (111); means configured to form a process gas (105) from a hydrocarbon feedstock (103) and steam (104); means for passing said process gas (105) through one or more cracking coils in said one or more combustion radiant sections to form cracked gas (106); an exhaust gas heat recovery section (12) configured to cool at least a portion of the exhaust gas (111); a cracked gas heat recovery section (13) configured to cool at least a portion of said cracked gas (106); A steam cracking system comprising: the exhaust gas heat recovery section (12) and the cracked gas heat recovery section (13) each comprise one or more heat exchangers (131, 132, 133, 134); the exhaust gas heat recovery section (12) is configured to use a first proportion, greater than 35% of a total amount of heat recovered from the exhaust gas (111) in the one or more heat exchangers of the exhaust gas heat recovery section (12), for preheating the oxidant gas (102), at least during a portion of the steam cracking operation; a second proportion of the heat recovered in the one or more heat exchangers of the cracked gas heat recovery section (13) that is greater than 35% of the total amount of heat recovered in the one or more heat exchangers of the cracked gas heat recovery section (13), at least during a same portion of the steam cracking operation, for preheating the process gas (105) and / or the hydrocarbon feedstock (103) and / or the process steam (104) used to form the process gas (105), the second proportion being greater than 35% of the total amount of heat recovered in the one or more heat exchangers of the cracked gas heat recovery section (13 ... at least during a same portion of the steam cracking operation, the second proportion being greater than 35% of the total amount of heat recovered in the one or more heat exchangers of the cracked gas heat recovery section (13), the

14. A system according to claim 13, configured to carry out the method according to any one of claims 1 to 13.

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