Method and system for steam cracking

Abstract

There is provided a steam cracking process using a steam cracking system comprising one or more combustion radiation sections wherein during a steam cracking operation a fuel is combusted with an oxidant gas to heat the one or more combustion radiation sections to form a flue gas, a process gas formed from a hydrocarbon feed and a process steam, the process gas passes through one or more furnace tubes in one or more combustion radiation sections, thereby forming a pyrolysis gas, at least a portion of the flue gas is cooled in a flue gas heat recovery section, at least a portion of the pyrolysis gas is cooled in a pyrolysis gas heat recovery section, and the process gas passes through one or more furnace tubes in one or more combustion radiation sections. Wherein the flue gas heat recovery section and the pyrolysis gas heat recovery section respectively comprise one or more multi-flow heat exchangers. The flue gas heat recovery section includes heat exchange structures, the number and configuration of which are set to preheat at least a portion of the oxidant gas using a first proportion of greater than 35% of the total heat recovered from the flue gas within the one or more multi-flow heat exchangers of the flue gas heat recovery section, at least in a partial stage of the steam cracking operation, and to preheat at least a portion of the oxidant gas using a second proportion of greater than 35% of the total heat recovered from the flue gas within the one or more multi-flow heat exchangers of the flue gas heat recovery section. And wherein the pygas heat recovery section is configured to preheat at least a portion of the process gas, and / or the hydrocarbon feed, and / or the process steam using a second proportion of greater than 35% of the total heat recovered within the one or more multi-stream heat exchangers of the pygas heat recovery section at least during the same portion of the steam cracking operation. The corresponding system is also part of the invention.

Description

Technical Field

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

[0002] The invention is based on steam cracking technology for the production of olefins and other basic chemicals, as described, for example, in the article "Ethylene" in Ullmann's Encyclopedia of Industrial Chemistry, published online on April 15, 2009, DOI 10.1002 / 14356007.a10_045.pub2.

[0003] At present, the heat energy required to start and maintain the endothermic cracking reaction in steam cracking is provided by the combustion of fuel gas in a refractory furnace. The process gas, which initially contains steam and the hydrocarbons to be cracked, passes through the so-called cracking furnace tubes placed in a refractory box, also known as the radiant zone or radiant section. In this flow path, the process gas is continuously heated so that the required cracking reactions occur in the cracking furnace tubes, thereby continuously enriching the cracking products in the process gas. The typical inlet temperature of the process gas entering the cracking furnace tubes is between 550°C and 750°C, and the outlet temperature is usually between 800°C and 900°C.

[0004] In addition to the radiant zone, the combustion cracking furnace also includes a so-called convection zone or convection section and a so-called quench zone or quench section. The convection zone is usually located above the radiant zone and consists of various tube bundles that cross the flue gas pipe from the radiant zone. Its main function is to recover as much energy as possible from the hot flue gas leaving the radiant zone. In fact, usually only 35% to 50% of the total combustion load is transferred to the process gas passing through the cracking furnace tube in the radiant zone. Therefore, since the convection zone is responsible for the effective utilization of about 40% to 60% of the furnace heat input (i.e., combustion load), the convection zone plays a central role in the energy management of steam cracking. In fact, when the radiant zone and the convection zone are combined, modern steam cracking units utilize 90% to 95% of the total combustion load (based on the lower heating value or net heating value of the fuel). In the convection section, the flue gas is cooled to a temperature level between 60°C and 140°C before leaving the convection section and being released to the atmosphere via the chimney.

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

[0006] The quench zone is located downstream of the radiant zone along the main process gas path. The quench zone consists of one or more heat exchanger units and its main function is to quickly cool the process gas to below the maximum temperature level to stop the cracking reaction, thereby further cooling the process gas for downstream processing, and efficiently recovering sensible heat from the process gas for further energy use. In addition, further cooling or quenching can be achieved by injecting liquid, such as by oil quenching when steam cracking liquid feed.

[0007] The process gas heat recovered in the quench zone is usually used to vaporize high pressure (HP) or very high pressure (SHP) boiler feed water (pressure range is typically between 30 bar and 130 bar absolute) and to preheat the same boiler feed water before it is supplied to the steam drum. Accordingly, the saturated high pressure or very high pressure steam produced may be superheated in the convection zone (see above) to form superheated high pressure or very high pressure steam, and this superheated high pressure or very high pressure steam may be distributed from there to the central steam system of the plant to provide heat and power for heat exchangers and steam turbines or other rotating equipment. The typical steam superheat achieved in the convection zone of the furnace is between 150K and 250K above the saturation temperature (dew point margin). In general, steam cracking furnaces can be operated with high pressure steam (typically between 30 bar and 60 bar) or very high pressure steam (typically between 60 bar and 130 bar). For clarity of description of the present invention, high pressure steam will be used to cover the entire pressure range of 30 bar to 130 bar, but pressures above this upper limit are also included as the present invention may in certain embodiments include the use of steam at pressures up to 175 bar.

[0008] US 4,107,226 A discloses a method for quenching cracked gas and recovering heat from the cracked gas by cooling the gas in heat exchange with steam to increase the superheat level of the steam and then recovering heat from the superheated steam. According to US 4,617,109 A, the combustion air for the steam cracking furnace is preheated by indirect heat exchange with medium-pressure and low-pressure steam, wherein the medium-pressure and low-pressure steam are expanded from high-pressure steam generated in the hot section of the ethylene production plant by a steam turbine.

[0009] This air preheating is a well-known measure to reduce fuel use in furnaces and has gained increased attention in the context of increasing CO2 reduction efforts. Air preheating in steam crackers can have a significant impact on heat balance and recovery due to reduced flue gas heat availability and additional air preheating requirements.

[0010] The object of the present invention is to further improve the efficiency and resource utilization of known steam cracking plants, in particular if components of such plants are partially or fully powered and if a more advantageous air preheating is possible. Summary of the invention

[0011] Against this background, the invention proposes a method and a system for steam cracking having the features of the independent claims. Embodiments of the invention are subject matter of the dependent claims and the following description.

[0012] Before further describing the features and advantages of the present invention, some terms used in the description of the present invention will be further explained.

[0013] The terms "flue gas heat recovery section" and "convection section" are used synonymously herein. The flue gas heat recovery section or convection section may also include an air preheating stage for heat exchange with the flue gas, which is usually not included in conventional furnace convection zone designs without air preheating, such as further combined with the following Figure 1 shown.

[0014] Likewise, the terms "cracked gas heat recovery section" and "quench section" may be used as synonyms in the present invention. According to the understanding used herein, the cracked gas heat recovery section or quench section may include all multi-flow heat exchangers used to cool the cracked gas downstream of the cracking furnace tubes, but does not include a direct contact cooling stage (i.e., cooling by injecting a liquid stream into the cracked gas stream in a desuperheater and / or quench tower).

[0015] In this regard, the terms "segment" and "region" and combinations thereof may also be used synonymously herein.

[0016] A "multi-stream heat exchanger" is a heat exchanger configured to transfer heat between two or more media streams that are in indirect contact and separated by heat exchange surfaces such as the walls of one or more chambers or tubes. Such a multi-stream exchanger may be a quench exchanger such as described in the Ullmann article mentioned at the beginning, or a tube bundle exchanger placed in the flue gas channel, which is typical in the convection zone.

[0017] The term "feed" shall include liquid or gaseous hydrocarbons which may be vaporized, if necessary, and mixed or diluted with process steam or dilution steam to form the "process gas" which is fed to the cracking furnace or radiant zone during the steam cracking operation. If reference is made to preheating one of the streams, this may also include preheating the first partial stream without preheating the second partial stream, particularly if the partial streams are subsequently recombined to form a combined stream which is at a higher temperature than before the split streams were formed.

[0018] The term "combustion efficiency" is synonymous with the term "fuel-based radiant section efficiency" and refers to the relative fraction of the chemical energy converted to heat during combustion of the fuel in the radiant section divided by the heat absorbed by the furnace tubes in the radiant section, typically calculated as lower heating value.

[0019] The prior art generally discloses ways and methods to improve the energy efficiency of cracking furnaces by pre-setting combustion air preheating. This is generally achieved by utilizing internal heat of the furnace flue gas system using preheated air, or by utilizing external heat from other sources such as superheated or saturated steam, electricity, quench oil, etc. Higher air preheat temperatures are generally intended to further minimize fuel gas consumption, thereby reducing carbon dioxide emissions from the furnace.

[0020] WO2018 / 229267A1 and WO2021 / 052642A1 propose an improved convection zone and quench section arrangement, which is preferably used for a combustion furnace with improved radiant zone efficiency (by air preheating or oxygen enrichment), wherein the mixed hydrocarbon feed / process steam flow is at least directly preheated by heat exchange with the cracking gas in the quench exchanger. According to the document, individual embodiments only use a single-stage air preheating system, in which the air preheater is arranged at the downstream end of the convection section, which limits the air preheating to a medium temperature level. Although the air preheating temperature is not specifically mentioned, for technical reasons, it can be estimated that the maximum temperature is 300°C to 350°C.

[0021] A further direct option for air preheating in the combustion furnace is to use external air preheating using an external heating medium other than the flue gases from the combustion (e.g., boiler feed water, steam, quench water, quench oil, hot oil), or to provide a single stage of air preheating at the downstream end of the convection section, which is not shown here for simplicity.

[0022] EP0229939B1 and US3,426,733A also disclose air preheating in steam cracking plants. Electric steam cracking plants with electric furnaces or combustion furnaces are also well known and disclosed in, for example, WO2020 / 150244A1, WO2020 / 150248A1 and WO2020 / 150249A1.

[0023] US2014 / 0212823 A1 mentions that internal air preheating can be performed by heat exchange with flue gas, and the air preheating temperature can reach up to about 482°C (900°F), but does not disclose the comprehensive concept of heat recovery and energy balance of such furnaces. In fact, when a conventional convection zone layout as shown in WO2018 / 229267A1 or WO2021 / 052642A1 is adopted, it is difficult to achieve energy balance integration for internal air preheating at temperatures above 400°C. The main reason is that these layouts include a large number of heat consumers, which cannot be fully supplied with heat at such high air preheating temperatures. This is because, for higher air preheating temperatures and higher radiation box efficiencies, the available heat in the convection zone will decrease, and if internal air preheating is adopted, the available heat will decrease even more.

[0024] Furthermore, for external air preheating, further increases in preheating temperatures are hampered by the unavailability of suitable heating media at temperatures above 300°C (the condensation temperature of ultra-high pressure steam at a typical pressure of 120 barg (bars above atmospheric pressure) is about 325°C). As a result, typical maximum air preheating temperatures for steam cracking furnaces found in the literature rise to about 300°C when using an external heat source, see for example EP 0 229 939 B1. Furthermore, for electric air preheating, it is conventionally not preferred to exceed this range, as this results in very high electrical input at a relatively low efficiency compared to all-electric furnaces.

[0025] In this regard, the present invention and its embodiments provide a concept and corresponding process layout for heat recovery in a combustion cracking furnace that is particularly suitable for higher air preheat temperatures, thereby providing maximum combustion efficiency / minimum fuel usage while selectively recovering waste heat in the heat recovery section of the furnace for use in critical processes.

[0026] The present invention and its embodiments provide advantageous solutions to these problems, wherein the main idea or principle of the embodiments of the present invention can be seen as maximizing the efficiency of the combustion furnace by: (i) preferentially utilizing the flue gas heat in the convection section to maximize the preheating of the air, and (ii) simultaneously preferentially utilizing the cracking gas heat in the quench section to maximize the preheating of the process gas, and / or the feed, and / or the steam forming the process gas.

[0027] The method of the embodiment of the present invention can in principle push the furnace design towards two separate feed-discharge cycles, namely (i) combustion air / flue gas cycle; and (ii) process feed / cracking gas cycle. This means that according to the present invention, by simultaneously increasing the proportion of flue gas heat used for air preheating and the proportion of cracking gas heat used for preheating process gas, and / or feed, and / or forming steam used for process gas, the amount of fuel gas used in the cracking furnace can be gradually reduced.

[0028] To this end, the present invention provides a steam cracking method using a steam cracking system, the steam cracking system comprising one or more combustion radiant sections, wherein during the steam cracking operation, a fuel is combusted with an oxygen-containing oxidant gas such as combustion air to heat the one or more combustion radiant sections, thereby forming flue gas. The oxidant gas may also be oxygen-enriched air, or a gas or gas mixture enriched with oxygen, such as "industrial" oxygen. For simplicity only and not limitation, the subsequent explanation focuses on combustion air.

[0029] The process gas is formed by (gaseous or liquid) hydrocarbon feed and (dilution or process) steam, and the process gas passes through one or more cracking furnace tubes in the one or more combustion radiation sections to form cracking gas, wherein at least a portion of the flue gas is cooled in the flue gas heat recovery section, wherein at least a portion of the cracking gas is cooled in the cracking gas heat recovery section, wherein the flue gas heat recovery section and the cracking gas heat recovery section respectively include one or more heat exchangers, wherein the flue gas heat recovery section includes heat exchange structures, the number and configuration of the heat exchange structures are set to: at least in part of the stage of the steam cracking operation, use a first proportion of more than 35% of the total heat recovered from the flue gas in the one or more heat exchangers in the flue gas heat recovery section to preheat the oxidant gas, and wherein the cracking gas heat recovery section is configured to use a second proportion of more than 35% of the total heat recovered in the one or more heat exchangers in the cracking gas heat recovery section to preheat the process gas, and / or the hydrocarbon feed, and / or the steam used to form the process gas, at least in the same part of the stage of the steam cracking operation.

[0030] The term "heat exchange structure" may include any technical means configured to enable or promote heat transfer between different media, such as straight furnace tubes or spiral furnace tubes, and the "configuration" of the heat exchange structure may specifically include heat exchange surfaces and / or technical improvements, such as fins on the outer surface of the heat exchanger furnace tubes and / or grooves or fin channels on the inner surface of the heat exchanger furnace tubes and / or any other surface enhancement features on the inner or outer surface of the heat exchanger coil.

[0031] The heat exchangers in the flue gas heat recovery section and the cracking gas heat recovery section are specifically multi-flow heat exchangers as described above, and in particular, at least most of the total heat transferred in the flue gas heat recovery section and the cracking gas heat recovery section is transferred in such a multi-flow heat exchanger. That is to say, the aforementioned ratios generally do not involve or include heat recovered in other ways, such as by injecting a medium or direct contact cooling, even though in the embodiments of the present invention, such injection or direct contact cooling can also be performed in the flue gas heat recovery section and the cracking gas heat recovery section. However, if such a method is adopted, generally only a small amount of fluid compared to the flue gas or cracking gas is injected into the flue gas heat recovery section and the cracking gas heat recovery section, for example, less than 10%, 5%, 0.5%, 1% or 0.1% compared to the flue gas or cracking gas.

[0032] In various cases, preheating the oxidant gas may include passing the entire oxidant gas stream through a heat exchanger, or may include heating a portion of the oxidant gas stream and recombining the portion with the remainder to form a combined stream having a mixed temperature. The heating of the flue gas heat recovery section and the cracked gas heat recovery section may be performed in series or in parallel.

[0033] Advantages of the invention include that both gas and liquid feedstock cracking can achieve high preheat air levels and thus high radiant zone efficiencies according to the invention. The result is an overall reduction in fuel gas usage, which is particularly beneficial for carbon dioxide emissions, as described below for "scope 1" to "scope 3" emissions.

[0034] This results in a significantly reduced energy requirement for the cracking furnace or system itself. This advantage is independent of the fuel technology used, so the present invention can be combined with any currently available or upcoming combustion technology in embodiments. The high temperature combustion air or alternative oxidant gas heated by flue gas is itself an in-furnace energy carrier that circulates energy from the convection section to the combustion chamber of the cracking furnace. Therefore, the present invention optimizes any furnace combustion system and is independent of the fuel / oxidant mixture delivered to the burner. This also includes oxygen-enriched air, hydrogen-rich or pure hydrogen fuel, ammonia fuel, etc. According to the present invention, heat exchange between thermodynamically "similar" material flows having similar specific heat capacity versus temperature curves and similar flow rates (between flue gas and combustion air, cracking gas and process gas, i.e., feed and / or steam) can be optimized. Embodiments of the present invention are highly compatible with highly electrified separation device designs, and since there is no large steam turbine, the required steam is significantly reduced and the superheat is reduced. Intrinsic safety is provided as heat is exchanged between “compatible” media without risk of explosion / deflagration even in case of a pipe rupture (e.g. by avoiding air preheating with cracking gases and minimizing / avoiding preheating of process gases or feed with flue gases).

[0035] The solution proposed according to the present invention is significantly different from the prior art represented by WO2018 / 229267A1 and WO2021052642A1, because the process settings proposed in these documents are mainly intended to increase the share of the utilization of the cracking gas waste heat for process gas preheating only. In fact, these documents disclose embodiments with and without air preheating, wherein in these two documents, the arrangement of the process sequence for process gas preheating is independent of whether air preheating is performed. The solutions proposed in documents WO2018 / 229267A1 and WO2021 / 052642A1 are based on the following core features: in the feed-discharge exchanger, the initial cracking gas is cooled by heat exchange with the process gas stream, which has previously been preheated in the convection section and may be further preheated in the convection zone of the furnace. Obviously, the prior art represented by these documents is intended to combine the process gas preheating sequence proposed by them with a low level of air preheating. For example, this is explicitly mentioned in these documents. Therefore, the prior art suggests that there is no strict correlation between the waste heat utilization in the convection section and the quench section.

[0036] According to an embodiment of the present invention, the first ratio and the second ratio are independently greater than 35%, greater than 40%, greater than 45% or greater than 50%, so that in such an embodiment, the advantages of the present invention can be made more obvious or less obvious by selecting to use a lower or higher ratio.

[0037] In embodiments of the present invention, the oxidant gas may be preheated to a temperature exceeding 400° C., 500° C., 600° C. or 700° C., which are significantly higher than those known in the prior art.

[0038] In an embodiment of the present invention, the oxidant gas or a part of the oxidant gas is at least partially preheated by heat exchange with the flue gas in the flue gas heat recovery section in at least two separate oxidant gas preheating stages, and the flue gas can be used between the two oxidant gas preheating stages to superheat high-pressure steam with an absolute pressure level between 30 bar and 175 bar.

[0039] Placing the second oxidant gas preheating stage upstream of the high pressure steam superheating bundle in the convection section results in a significant change in the heat balance of the convection section, so that preheating of the oxidant gas takes precedence over external steam generation and is therefore placed in the upstream portion of the flue gas path.

[0040] In an embodiment of the present invention, steam can be superheated in the flue gas heat recovery section, wherein the maximum temperature of the steam superheated in the flue gas heat recovery section is limited to 450°C, 400°C or 350°C, and / or the dew point margin is made to be a maximum of 150K, 120K, 80K or 60K, and no further steam superheating is performed before the steam is output from the flue gas heat recovery section or the steam cracking system; and wherein the proportion of the recovered heat in the flue gas heat recovery section used to generate high-pressure output steam is less than 25%, 23% or 21%. By reducing the steam superheat level and / or the maximum temperature, in such an embodiment, the steam superheating can be more easily placed downstream of the high-temperature oxidant gas preheating section in the flue gas path.

[0041] In an embodiment of the present invention, the steam output from the flue gas heat recovery section or the steam cracking system passes through a conduit, a pressure reducing valve and / or a nozzle at a ratio of more than 60%, 70% or 80%, and enters one or more steam condensing heat exchangers with or without pre-superheating and desuperheating. In particular, for most of the output steam flow, any type of pressure reduction upstream of the heat exchanger is carried out without extracting usable mechanical work, which is different from the situation in, for example, a turbine. At the same time, for the remaining small part of the output steam flow, after an optional first pressure reduction, for example, by reducing the extremely high pressure level to a high pressure level through a valve, thereby producing a steam flow at a lower pressure but at a higher superheat level, further pressure reduction can be achieved, such as by using a back-pressure turbine and extracting mechanical work from the steam flow. The resulting expanded steam flow is then preferably directed to a steam condensing heat exchanger operating at a correspondingly lower pressure level. The purpose of only outputting the intermediate superheated steam from the furnace is to mainly provide energy to the heat consumer, and no mechanical work is extracted from the output steam in large quantities. Therefore, in this arrangement, the total steam volume and specific enthalpy are reduced.

[0042] In an embodiment of the invention, the steam output from the flue gas heat recovery section or the steam cracking system is not used in the steam turbine drive delivering shaft power greater than 5 MW, 3 MW or 1 MW. Therefore, the large rotating machinery in the downstream separation section is preferably driven by electric motors, thereby achieving "electrification" of such an installation and thus reducing the steam demand and (local) emissions from the combustion steam generation installation.

[0043] The process gas, and / or hydrocarbon feed, and / or the process steam used to form the process gas can be at least partially heated using a feed-discharge exchanger using the recovered cracking gas, and in an embodiment of the present invention, the feed-discharge exchanger can be located downstream of a steam-generating quench exchanger in the flow path of the cracking gas. Generally, different topologies and process sequences can be used to recover heat from the cracking gas to preheat the process gas, and / or hydrocarbon feed, and / or the process steam used to form the process gas. In most of the embodiments shown in the present invention, the initial cracking gas cooling is accomplished by a conventional steam-generating primary quench exchanger. Optionally, according to an embodiment of the present invention, an embodiment with a feed-discharge primary quench exchanger can also be provided.

[0044] The saturated steam generated in the quench exchanger is used to preheat the process gas, and / or the steam, and / or the hydrocarbon feed used to form the process gas, and the steam condensate collected from this preheating can be used for additional preheating of the same medium at a lower temperature level. Indirect use of the cracked gas heat to preheat the process gas, steam and / or feed by generating intermediate steam is a very suitable design option to ensure fast and reliable cooling of the cracked gas in the steam generator of the prior art, thereby avoiding the potential challenges in design and operation of the direct feed-discharge exchanger design. According to the present invention, indirect cracked gas heat recovery can be flexibly used for feed preheating, which is particularly advantageous in scenarios such as flexible feed steam cracking systems.

[0045] The use of saturated steam and its condensate further limits the need for superheated export steam in the convection section and thus helps achieve high oxidant gas preheating duties in the flue gas section. In addition, this indirect heat recovery is very suitable for the retrofit of existing plants, where the utilization of cracked gas heat for process gas, steam and / or feed preheating can be improved without significant modification of existing quench coolers and steam drums.

[0046] In one embodiment of the present invention, the process gas, and / or process steam, and / or hydrocarbon feed used to form the process gas is not preheated in the flue gas heat recovery section. Thus, in such an embodiment, the hot flue gas leaving the radiation section is directly used for oxidant gas preheating without first transferring heat to the feed preheating tube bundle in the convection zone.

[0047] In one embodiment, the mixture of steam and the hydrocarbon feed (ie, process gas) or a portion thereof may be finally preheated using an electric superheater before entering the one or more cracking furnace tubes in the one or more radiant combustion sections.

[0048] Compared with conventional combustion furnaces, the fuel gas usage of the system according to an embodiment of the present invention can be reduced by a minimum of 30% or 35% or 40% or 45%, while conventional combustion furnaces do not perform oxidant gas preheating during operation and use a conventional fuel mixture of exhaust gas and imported natural gas.

[0049] In embodiments of the invention, a control system may be provided which is adapted to control the properties of one or more other streams. For example, using such a control system, flue gas cooling below the condensing temperature and the attendant corrosion problems may be avoided. In terms of equipment, a backup oxidant gas preheater may be installed upstream of the oxidant gas preheater(s) in the convection section and operated only in special cases utilizing any type of waste heat or low temperature heat from the process unit. For example, a bypass controller on the oxidant gas or flue gas side may be provided, or any other additional equipment.

[0050] In embodiments of the present invention, the saturated steam generated in the quench exchanger can be further used to preheat the fuel gas, and the steam condensate collected from this preheating step or other preheating steps can be used to additionally preheat the fuel gas at a lower temperature level. This use of saturated steam as a heat provider can also be used in any other process stream heating applications, but is particularly suitable near the furnace section to avoid long delivery lines for the saturated steam flow (risk of liquid deposition in the pipe and / or steam hammering).

[0051] In embodiments of the invention, heat from the flue gases is not used to generate steam in the "boiler" tube bundle. Furthermore, when air is used as the oxidant gas, the oxygen content of the air can be further increased by adding an oxidant stream with a high oxygen content from an external source such as an electrolyser, a cryogenic air separation unit or a (vacuum) pressure swing adsorption unit.

[0052] In an embodiment of the present invention, the steam cracking system can be operated in an energy-flexible manner, that is, a given furnace chemical production load can be provided at different total fuel gas consumption rates, for example, the air preheating temperature can be changed by using an air bypass line in one or two air preheating stages. In an embodiment of the present invention, boiler feed water preheating is not performed by heat exchange with flue gas from the furnace. The fuel gas consumed in the radiation zone can contain fossil-based and / or synthetic and / or bio-based hydrocarbons, fossil-based (gray / blue / turquoise) and / or renewable (green) hydrogen and / or ammonia. The composition of the supplied fuel gas can be changed during the operation of the furnace along with other key melting operation parameters. Specifically, in order to minimize the consumption of such high-value clean fuels, the content of carbon-neutral fuels (e.g., hydrogen, ammonia) can be increased, and measures can be taken to maximize the air preheating temperature. Adjustment of the fuel composition can be achieved by changing the separation and degree of hydrogen in the tail gas treatment and / or changing the amount of external fuel imports.

[0053] A steam cracking system comprises one or more combustion radiant sections, a device configured to combust a fuel with an oxidant gas to heat the one or more combustion radiant sections to form flue gas during a steam cracking operation, a device configured to form a process gas from a hydrocarbon feed and process steam, a device configured to pass the process gas through one or more cracking furnace tubes in the one or more combustion radiant sections to form a cracked gas, a flue gas heat recovery section configured to cool at least a portion of the flue gas, and a cracked gas heat recovery section configured to cool at least a portion of the cracked gas. The flue gas heat recovery section and the cracking gas heat recovery section respectively include one or more multi-flow heat exchangers, wherein the flue gas heat recovery section includes a heat exchange structure, the number and configuration of the heat exchange structure enable the oxidant gas to be preheated using a first proportion of greater than 35% of the total heat recovered from the flue gas in the one or more multi-flow heat exchangers in the flue gas heat recovery section, at least in a portion of the steam cracking operation, and wherein the cracking gas heat recovery section is configured to: enable the process gas, and / or the hydrocarbon feed, and / or the steam used to form the process gas to be preheated using a second proportion of greater than 35% of the total heat recovered in the one or more multi-flow heat exchangers in the cracking gas heat recovery section, at least in the same portion of the steam cracking operation.

[0054] For more details about the steam cracking system provided according to the invention and its preferred embodiments, please refer to the above description of the method of the invention and its preferred embodiments. Advantageously, the proposed device is suitable for carrying out the method of at least one embodiment explained in more detail above.

[0055] To summarize and partially reiterate the above, the present invention allows in particular to achieve high air preheating levels and therefore high radiant zone efficiencies for gas and liquid feedstock cracking furnaces. This allows low fuel gas usage, which is particularly beneficial for CO2 emissions: so-called "scope 1" emissions can be achieved by, for example, reducing the combustion of carbon fuels, and / or a reduction in "scope 2" emissions can be achieved by, for example, using less hydrogen in the on-site electrolyzer, thereby reducing electricity consumption, and / or a reduction in "scope 3" emissions can be achieved by, for example, increasing the export of unused hydrogen fuel gas.

[0056] This reduces the energy requirements of the cracking furnace itself. This advantage is independent of the applied fuel technology, making the invention combinable with any currently available or upcoming combustion technology.

[0057] The present invention allows the use of gaseous hydrocarbon feeds such as ethane, propane or butane, as well as the use of liquid hydrocarbon feeds such as naphtha, gas oil or plastic waste pyrolysis oil. Embodiments of the present invention can be used to process mainly one preferred hydrocarbon feed type in a given furnace, such as ethane or naphtha. Other embodiments of the present invention may also use a (variable) mixture of gaseous hydrocarbon feeds such as ethane and propane, or a (variable) mixture of liquid hydrocarbon feeds such as naphtha and plastic waste pyrolysis oil. In a further embodiment, the cracking operation may include different operating stages of alternating liquid and gaseous hydrocarbon feeds in a single feed flexible furnace. In addition, the present invention can also be applied to furnaces that at least temporarily carry out co-cracking of gaseous and liquid hydrocarbon feed streams simultaneously.

[0058] The present invention can also be combined with any type of additional flue gas treatment step for (further) reducing the concentration of environmentally relevant components in the flue gas, for example, reducing the carbon dioxide content in a carbon capture process unit using amine scrubbing or equivalent treatment technology, and / or reducing nitrous oxide emissions in a nitrous oxide removal unit using selective catalytic reduction or equivalent treatment technology. The present invention facilitates the implementation of such additional flue gas treatment steps by reducing the amount of fuel gas used and thus reducing the amount of flue gas.

[0059] According to embodiments of the invention, high temperatures are achieved by using combustion air heated by flue gases or alternative oxidant gas, which are themselves energy carriers in the furnace, thereby recovering energy from the convection section to the combustion chamber of the cracking furnace. Thus, the invention optimizes any furnace combustion system, independent of the fuel / oxidant mixture fed to the burner. According to embodiments of the invention, this also includes oxygen-enriched air or oxidant gas made of pure oxygen, diluted or not diluted with recycled flue gases, hydrogen-enriched or pure hydrogen fuel, ammonia fuel, etc.

[0060] Embodiments of the present invention optimize heat exchange between thermodynamically "similar" material streams having similar specific heat capacity versus temperature curves and similar flow rates (e.g., flue gas to combustion air, and cracked gas to feed). In embodiments of the present invention, a high degree of compatibility with highly electrified separation device designs can also be achieved, as the need for superheated steam is significantly reduced due to the absence of large steam turbines.

[0061] Embodiments of the present invention are inherently safe because by avoiding, for example, air preheating with cracking gases, and also by minimizing / avoiding process gas or feed preheating with flue gases, the heat exchange is between "compatible" media and there is no risk of explosion / deflagration in the event of a pipe rupture. Flexible use of indirect cracking gas heat recovery for preheating feed, process gas or process steam is advantageous, such as in the context of a flexible feed cracking furnace.

[0062] Embodiments of the present invention may also include the use of electric heaters at other locations other than the final preheating stage of the process gas. The electric heaters may be particularly useful for superheating process steam prior to mixing with the hydrocarbon feed stream, and / or for preheating oxidant gas, and / or for superheating high pressure output steam. Such electric heaters may also be configured for temporary or flexible use to compensate for fluctuating preheating load requirements associated with multi-stream heat exchanger fouling / coking and / or variable feed supply conditions. In situations where there is excess grid renewable electricity, it may also be preferred to operate the electric oxidant gas preheater to temporarily reduce fuel gas demand and increase fuel gas storage levels within the plant.

[0063] The present invention can also be combined with a dedicated energy storage system, such as a latent heat storage system or the like. Specifically, at least a portion of the output high pressure steam can be temporarily delivered to a suitable heat storage system.

[0064] A steam cracking plant featuring a burner system according to the invention can be further integrated into a hybrid system architecture in which the burner according to the invention is operated together with an electric heating furnace (independent of the electric coil heating principle: direct resistive coil heating, indirect radiant coil heating through electric heating elements, inductive power transmission coil heating). The steam cracking plant can further include other units for generating steam from electrical energy (e.g. electric heat pump systems, electric boilers, etc.).

[0065] The invention is preferably combined with a separation device in which at least more than 50%, 70%, 90% or 95% of the molecular hydrogen contained in the cracked gas and possible additional feed streams is separated as a purified stream with a molar hydrogen content of more than 95% and used for combustion in the furnace.

[0066] All features proposed herein for the embodiments of the present invention may be combined individually or in any combination with features proposed in International Patent Application PCT / EP2022 / 055877 and European Patent Application 21161768.3, and these features and any combination of these features are incorporated herein by reference to the extent possible. The skilled person will solve any problems associated with implementing these features through these applications.

[0067] The present invention and its embodiments will be further explained with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0069] Figure 1 An embodiment is shown which does not form part of the present invention;

[0070] Figure 2The basic principle of an embodiment according to the present invention is shown; and

[0071] Figures 3 to 8 An embodiment of the present invention is shown. DETAILED DESCRIPTION

[0072] In the accompanying drawings, elements having the same, substantially the same, functionally equivalent or technically compatible functions and / or purposes may be identified with the same reference numerals, and repeated explanations may be omitted for brevity. The explanations of the apparatus, equipment, arrangement, system, etc. according to the embodiments of the present invention in the present invention may also be applicable to the methods, processes, procedures, etc. according to the embodiments of the present invention, and vice versa.

[0073] The various embodiments described in the present invention are intended only to aid in understanding and teaching the claimed features. These embodiments are provided only as representative samples of embodiments and are not exhaustive and / or exclusive. It should be understood that the advantages, embodiments, examples, functions, features, structures and / or other aspects described in the present invention should not be regarded as limitations on the scope of the invention defined by the claims or limitations on the equivalents of the claims, and other embodiments may be used and modified without departing from the scope of the claimed invention. The various embodiments of the present invention may appropriately include, consist of or consist essentially of appropriate combinations of disclosed elements, components, features, parts, steps, devices, etc., rather than those specifically described in the present invention. In addition, the content of the present disclosure may include other inventions that are not currently claimed but may be claimed in the future, particularly when these inventions are included within the scope of the independent claims.

[0074] In the accompanying drawings, elements having the same, substantially the same, functionally equivalent or technically compatible functions and / or purposes may be identified with the same or commonly increasing reference signs, and repeated explanations may be omitted for the sake of brevity. The explanations of the apparatus, equipment, arrangement, system, etc. according to the embodiments of the present invention in the present invention may also be applicable to the methods, processes, procedures, etc. according to the embodiments of the present invention, and vice versa.

[0075] When reference is made hereinafter to "combustion air", this is intended to encompass the injection of the other oxidant gases mentioned above.

[0076] Also not shown in the drawings are one or more air compression devices typically located upstream of the combustion air preheating section, which compensate for the pressure drop across the combustion air preheat exchanger. The preferred pressure on the combustion side of the radiant section is in the typical slightly subatmospheric range, as in conventional cracking furnaces without combustion air preheating. Therefore, the flue gas blower / compression device is most preferably located downstream of the convection section outlet.

[0077] For reference and further explanation of the background of the present invention, Figure 1 A conventional fired steam cracking plant is shown in a highly simplified partial schematic diagram and is generally indicated by reference numeral 900 .

[0078] Figure 1 The steam cracking system 900 shown includes one or more cracking furnaces 90. For simplicity, reference is made hereinafter to "one" cracking furnace 90, while a typical steam cracking unit 900 may include multiple cracking furnaces 90 that may operate under the same or different conditions. In addition, each cracking furnace 90 may include one or more components described below.

[0079] Cracking furnace 90 includes a radiation zone 91 and a convection zone 92. Figure 1 In embodiments different from the one shown, multiple radiation zones 91 may be associated with a single convection zone 92, and so on.

[0080] In the example shown, the heat exchangers 921 to 928 are arranged in the convection zone 92 in the number, arrangement or order shown, or in a different number, arrangement or order. These heat exchangers 921 to 928 are generally provided in the form of a tube bundle passing through the convection zone 92 and are located in the flue gas channel 911 from the radiation zone 91, wherein the flue gas channel 911 is indicated by a dotted arrow.

[0081] In the example shown, the radiation zone 91 is heated by a plurality of burners, which are not shown in the figure for simplicity, and which may be arranged on the bottom and / or wall side of the refractory material forming the radiation zone 91. As shown by two dotted arrows, a fuel gas 901 and an oxygen-containing oxidant gas 902 (e.g., air, oxygen, oxygen-enriched air, etc.) may be provided to the burners within the radiation zone 91.

[0082] In the example shown, a gaseous or liquid hydrocarbon stream 903, represented by a double arrow, is provided to the steam cracking system 900. A variety of hydrocarbon streams may also be used in the manner shown or in a different manner. The hydrocarbon stream is initially transferred to a heat exchanger 927 in the convection zone 92 and preheated therein. The heat exchanger 927 is also referred to as a feed preheater. A process steam 904, also represented by a double arrow, is provided, and in the example shown, the process steam 904 passes through the convection zone 92, or more precisely, passes through the heat exchanger 924 and is superheated therein. Therefore, the heat exchanger 924 is also referred to as a process steam superheater. Such a process steam superheater is typically used in cracking furnaces that are at least partially operated with a liquid hydrocarbon feed stream to promote feed evaporation by adding an over-superheated process stream. Cracking furnaces that are operated only 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 (as still indicated by the double arrows), and the process gas stream 905 passes through a heat exchanger 925, then through a heat exchanger 921, and subsequently through one or more cracking furnace tubes in the radiation zone 91, wherein the heat exchanger 925 and the heat exchanger 921 are also referred to as a first high-temperature coil (heat exchanger 925) and a second high-temperature coil (heat exchanger 921).

[0084] The product mixture 906 (also referred to as cracked gas or raw gas) obtained in the radiation zone 91 flows out of the radiation zone 91 and passes through the first-stage quench exchanger 93 (shown here as an ultra-high pressure steam generator), and then enters subsequent processing and separation steps, which are generally known in the art and are not shown here.

[0085] The steam generating device 93 is associated with the ultra-high pressure drum 94. As shown by the solid arrows throughout the figure, the boiler feed water 910 can be preheated in the heat exchangers 928 and 926 (also referred to as the first economizer (heat exchanger 928) and the second economizer (heat exchanger 926)) in the convection section 92, and then enter the ultra-high pressure drum 94 and the ultra-high pressure steam generating device 93.

[0086] As shown by the thin dashed arrow, saturated ultra-high pressure steam 907 is extracted from the ultra-high pressure steam generator 93, passes through the ultra-high pressure drum 94, and is superheated in the heat exchangers 923 and 922 in the convection zone 92, thereby forming superheated ultra-high pressure steam 908, as shown by the thick dashed arrow, wherein the heat exchangers 923 and 922 are also referred to as the first ultra-high pressure steam superheater (heat exchanger 923) and the second ultra-high pressure steam superheater (heat exchanger 922). At the position between the heat exchangers 923 and 922, the boiler feed water 910 can also be injected.

[0087] In such Figure 1 In a conventional arrangement of the steam cracking system 900 shown, heat recovered from cooling of the cracked gas, such as in the primary quench exchanger 93 or other locations, is typically used only to produce ultra-high pressure output steam, while heat recovered in the flue gas section (i.e., in the convection zone 92) is used to preheat the feed (as shown) and to produce ultra-high pressure output steam (by preheating boiler feed water and superheating saturated ultra-high pressure steam).

[0088] As described above, and as will be explained below in conjunction with various embodiments, the basic design concept of the embodiments of the present invention includes maximizing the efficiency of the combustion furnace by: (i) preferentially using the flue gas heat in the convection section to maximize the preheating of the air, and (ii) simultaneously in the quench section, preferentially using the cracking gas heat to maximize the preheating of the process gas, feed and / or process steam.

[0089] exist Figure 2 In FIG. 1 , the basic principles of an embodiment of the present invention are schematically illustrated in a highly simplified view of a steam cracking system 100 .

[0090] Figure 2 The cracking furnace 10 shown includes a radiant zone 11 and a convection zone 12. Figure 1 In other embodiments of the embodiment shown in FIG. 1 , multiple radiation zones 11 may also be associated with a single convection zone 12, and so on, which is described above in conjunction with Figure 1 This has already been mentioned in the description of the system 900. The cracked gas heat recovery section is indicated at 13.

[0091] In the example shown, a plurality of heat exchangers may be arranged in the convection zone 12, but for general reasons only one heat exchanger is arranged in the convection zone 12. Figure 2 Not shown.

[0092] and Figure 1 The heat exchangers 921 to 928 in the illustrated system 900 are similar and are typically provided in the form of a tube bundle passing through the convection zone 12 and located in the flue gas flow from the radiation zone 11. Alternative designs of multi-flow heat exchangers may also be used, particularly for heat exchange between flue gases and oxidant gases. The convection zone 12 may include one or more straight flue gas channels and, if applicable, connecting ducts between a plurality of straight flue gas channels or connecting the straight flue gas channels to a multi-flow heat exchanger having a separate housing by, for example, flange connections. According to the present invention, such an independently arranged multi-flow heat exchanger for recovering heat from the flue gas flow also forms part of the flue gas heat recovery section.

[0093] and Figure 1 Similar to the system 900 shown, the radiation zone 11 is heated by a plurality of burners, which are not shown for clarity and which may be arranged on the bottom and / or wall sides of the refractory material forming the radiation zone 11. The burners in the radiation zone 11 may be provided with a fuel gas not shown in the figure and an oxygen-containing oxidant gas 102 such as air, as indicated by dashed arrows. The flue gas 111, also shown by dashed arrows, passes through the convection zone 12, which is therefore also referred to as a flue gas heat recovery unit. The oxygen-containing oxidant gas 102 is heated in the flue gas heat recovery unit 12 and in optional further heating steps 1 and 2 that may be implemented according to embodiments of the present invention.

[0094] In the example shown, a gaseous or liquid hydrocarbon feed 103, or a mixture of the feed and process steam 105 (ie, process gas as referred to herein), as indicated by the double arrows, is also provided to the steam cracking system 100. Figure 1 The system 900 is shown as depicted in relation to various hydrocarbon streams.

[0095] In the example shown, this hydrocarbon feed 103 or process gas 105 is preheated at least in the cracked gas heat recovery section 13, and optionally in the additional heating steps 3 and 4 before and after it, and passes through the radiation section 11 to form the cracked gas 106 (also shown by double arrows). In certain embodiments of the present invention, the additional heating steps 3 and 4 can also be carried out in a multi-flow heat exchanger as part of the convection zone 12.

[0096] Subsequently, the cracked gas 106 is cooled in the cracked gas heat recovery section 13. As shown by reference numeral 199, one or more heat consumers other than air or oxygen-containing oxidant gas may also pass through the convection section 12, and one or more heat consumers other than hydrocarbon feed may also pass through the cracked gas heat recovery section 13 (not specifically shown).

[0097] Figures 3 to 8 An embodiment of the present invention is shown for a gaseous feed steam cracking system ( Figure 3 , Figure 4 and Figure 5 , also referred to as Example 1, Example 2 and Example 3) and a liquid feed steam cracking system ( Figure 6 , Figure 7 and Figure 8 , also referred to as Example 4, Example 5 and Example 6). Tables 1 and 2 provide additional process data, which also provide comparative data for prior art examples with and without conventional "cold" air preheating (APH). In the tables, "feed preheating" may refer to process gas, and / or hydrocarbon feed, and / or process steam preheating, and the relevant implementation principles can be referred to Figures 3 to 8 .

[0098] like Figures 3 to 8 As shown, in a preferred embodiment, the combustion air preheating is at least partially carried out by heat exchange with the flue gas in at least two separate air preheating stages. Between the two air preheating stages, heat is preferably recovered from the flue gas to superheat steam, wherein the steam is preferably generated in a steam generating quench exchanger. In some embodiments, between the two air preheating stages, heat can also be additionally recovered from the flue gas to heat other streams, such as preheating a process gas stream, such as Figure 6 The embodiment shown in FIG. 1 includes a liquid feed cracking furnace apparatus.

[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 sequences of quench cooling and convection sections, while retaining and fully utilizing the features of the present invention. Given the different process constraints in gaseous and liquid-fed furnaces, it is particularly noteworthy that the preheat duty ratio in a liquid-fed furnace is much higher than in a gaseous-fed furnace due to the additional vaporization enthalpy of the hydrocarbon feed. In addition, less heat can be recovered in the multi-stream exchanger in the quench section to avoid heavy hydrocarbon condensates.

[0100] At the same time, in order to reduce fuel gas consumption and flue gas emissions, it is equally important to maximize air preheating for both liquid-fed furnaces and gas-fed furnaces. Despite these additional / tighter constraints, embodiments of the present invention are still applicable to liquid-fed furnaces, particularly by further enhancing indirect cracking gas heat recovery, i.e., by generating steam through cracking gas cooling and condensing at least a portion of the steam for preheating process gases (process steam and / or hydrocarbon feed) at lower temperatures. Preheating at temperatures below 300°C is advantageous in that it covers most of the additional vaporization enthalpy of the liquid feedstock.

[0101] Robust embodiments of the liquid feed furnace of the present invention can all have a higher utilization of the cracked gas heat for indirect feed preheating compared to gaseous feed furnace arrangements. While one might think that the additional feed preheating duty for feed vaporization would limit the level of air preheating achievable in the liquid furnace, the present invention demonstrates that this is not the case, since a large portion of the feed preheating duty is used to vaporize the liquid hydrocarbon feed, which can be achieved by condensing saturated high pressure steam at temperatures well below 300°C. Furthermore, if the feed stream on the coolant side is multiphase and also contains significant amounts of fouling prone components, this can further hinder the reliable design and operation of alternative direct feed-discharge exchangers.

[0102] Table 1: Performance data of selected embodiments and prior art (gas feed cracking furnace)

[0103]

[0104] * = Example 2 includes an additional electric preheater with 8.9 MW load (see also Figure 4 ) Table 1: Performance data of selected embodiments and prior art (liquid feed cracking furnace)

[0105]

[0106] This practice of using a relatively high proportion of the heat of the cracked gas for indirect preheating of the process gas, hydrocarbon feed and / or process steam does not reduce the available load for air preheating, but instead results in a reduction in the net production of net exported steam, which in addition reduces the relative heat load for steam superheating in the convection section, thereby actually increasing the available load of the internal air preheating section.

[0107] In fact, as can be seen in a comparison of Tables 1 and 2, the liquid furnace embodiment (see Table 2) uses at most 10% of the recovered flue gas heat for superheating of the export steam, while the gaseous furnace embodiment (see Table 1) uses up to 21%. Therefore, differences in feedstock do not result in changes in the achievable air preheat temperature, but only in changes in the exported non-critical utility steam. The relevance of this small drawback will be further alleviated in future highly electrified plant designs, since the steam demand will be significantly reduced compared to existing designs. Further benefits can also be achieved for furnace designs with flexible feed supply.

[0108] In conventional arrangements, the initial preheating of process steam, hydrocarbon feed and / or process steam is performed only in the convection section, and the preheating is performed using the heat of the cracked gas only at high temperatures above 350°C (see WO 2021 / 052642 A1). Combined with the downstream positioning of the air preheating tube bundle in the convection zone, it can be seen that applying this conventional design to gaseous and liquid feed furnaces will result in a lower level of air preheating in the liquid feed furnace, because more residual flue gas heat is consumed for initial feed preheating.

[0109] For the sake of completeness, the convection section in the liquid-fed furnace usually has an additional process steam superheater, while the quench section does not include a three-stage quench exchanger, which results in a higher cracked gas temperature at the outlet of the furnace under consideration, usually about 380°C, compared to about 200°C for the gaseous-fed furnace. This is to avoid the condensation of heavy condensates when cooling the cracked gas below said level. Therefore, in the liquid-fed cracking furnace, the cooling of the cracked gas to lower temperatures is done by direct contact cooling by injecting pyrolysis oil / gasoline and / or quench water (the associated heat recovery at these lower temperatures is not within the scope of the present invention, see the above terminology for details).

[0110] according to Figure 3 , Figure 4 and Figure 5 In the embodiments 1, 2 and 3 shown in the figure, there are a primary quench heat exchanger 131, a secondary quench heat exchanger 132 and a tertiary quench heat exchanger 133 in the cracking gas heat recovery section 13 through which the cracking gas 106 passes. Figure 6 In the embodiment 4 shown, a single primary quench exchanger 134 is used. Figure 7 and Figure 8 In the illustrated embodiments 5 and 6, a primary quench exchanger 134 connected to a secondary exchanger 135 is used.

[0111] In all cases, the steam drum is indicated by the reference numeral 14. Figure 3 In the embodiment 1 shown, the flue gas heat recovery unit is shown as a single unit 12, and according to Figure 4 and Figure 5 In the embodiment 2 and the embodiment 3 shown in the figure, the unit can be divided into a (main) flue gas heat recovery subunit 121 and an auxiliary flue gas heat exchanger unit 129, and according to Figure 6 , Figure 7 and Figure 8 In the illustrated embodiments 4, 5 and 6, the unit can be divided into partial units 121 and 122. In all embodiments, an ambient air flow is used as the oxidant gas 102. Figure 3 , Figure 4 and Figure 5 In the examples 1, 2 and 3 shown, the hydrocarbon feed 103 is, for example, ethane. Figure 6 , Figure 7 and Figure 8 In the illustrated examples 4, 5 and 6, the hydrocarbon feed 103 may be, for example, naphtha. In all cases, the process steam is indicated by reference numeral 104, and the mixture of the feed 103 and the process steam (i.e., the "process gas" of the present invention) is indicated by reference numeral 105. Other media include boiler feed water 110 and flue gas 111.

[0112] Typical air preheat temperatures are as follows: Figure 3 Example 1 shown is 612°C, according to Figure 4 Example 2 shown is 907°C, according to Figure 5 Example 3 shown is 940°C, according to Figure 6 Example 4 shown is 475°C, according to Figure 7 Example 5 shown is 590°C, and according to Figure 8 Example 6 is shown at 820°C.

[0113] Let's look at the examples related to gaseous hydrocarbon feed, namely Figure 3 , Figure 4 and Figure 5 Embodiment 1, embodiment 2 and embodiment 3 are shown in the figures, and the common features and differences of these embodiments will be described below.

[0114] according to Figure 3In the embodiment 1 shown, the feed 103 is preheated in the three-stage quench exchanger 133 and then combined with the process steam 104. The diluted feed 105 (i.e., process gas) is heated in the two-stage quench exchanger 132. In contrast, according to Figure 4 and Figure 5 In the illustrated embodiments 2 and 3, there is a preheater 127 for the feed 103 and a heater 125 for the process gas 105, both of which are operated with saturated steam 117 from the drum 14, thereby forming steam condensate in the heater 125 and subcooled steam condensate 118 in the preheater 127. Figure 4 In the embodiment 2 shown, the process gas 105 is further heated in the secondary quench exchanger 132 and the auxiliary (electric) heater 136, and according to Figure 5 In the illustrated embodiment 3, a primary quench exchanger 131 is used for this purpose.

[0115] exist Figure 3 and Figure 4 In the illustrated embodiments 1 and 2, the drum 14 is operated by generating steam in the primary quench exchanger 131 using heat recovered from the cracked gas 106, and Figure 5 In the illustrated embodiment 3, a secondary quench exchanger 132 is used for this purpose. Figure 4 In the illustrated embodiment, the boiler feed water 110 is heated in a three-stage quench exchanger 133 before entering the steam drum 14. Figure 5 The embodiment 3 shown also has this operation, but in this embodiment, the preheating of boiler feed water is also carried out in the flue gas heat recovery unit. Figure 3 , Figure 4 and Figure 5 In the illustrated embodiments 1, 2 and 3, the steam 107 from the steam drum 14 is also superheated in two steps in the flue gas heat recovery unit 12 , and boiler feed water is optionally injected between the two steps and output as superheated steam 119 .

[0116] exist Figure 3 In the illustrated embodiment 1, preheating of an oxidant gas 102 such as combustion air is performed in two steps within a flue gas heat recovery unit 12, wherein bypasses for each of the two oxidant gas heating steps in the flue gas heat recovery unit 12 are shown, which bypasses can be operated using a temperature controller TC operating based on the flue gas temperature or the preheated air temperature.

[0117] exist Figure 4 and Figure 5In the illustrated embodiments 2 and 3, the auxiliary flue gas heat exchanger unit 129 is used to preheat the oxidant gas 102, i.e., the combustion air. The auxiliary flue gas heat exchanger unit 129 is regarded as a part of the flue gas heat recovery section 12 and can be arranged downstream of the (main) flue gas heat recovery subunit 121 in the flue gas path and then arranged in the main flue gas heat recovery subunit 121, wherein Figure 5 In the embodiment shown, two heating steps are performed in the main flue gas heat recovery subunit 121, and wherein Figure 4 In the illustrated embodiment 2, a bypass around the auxiliary flue gas heat exchanger 129 is shown and heating in the main flue gas heat recovery subunit 121 is shown, which can be operated using a temperature controller TC operating based on the flue gas temperature or the preheated air temperature.

[0118] Next, let's look at Examples 4, 5, and 6 related to liquid or heavy hydrocarbon feeds, namely Figure 6 , Figure 7 and Figure 8 The embodiments shown in the drawings will be described below with reference to the common features and differences of these embodiments.

[0119] First, in Figure 6 , Figure 7 and Figure 8 In the illustrated embodiments 4, 5 and 6, the steam drum 14 is operated by steam generated in the quench exchanger 134 using heat recovered from the cracked gas stream 106. Figure 6 , Figure 7 and Figure 8 In the illustrated examples 4, 5 and 6, the feed 103 is preheated in heat exchanger 151 before being combined with the process steam 104 and then further heated in heat exchanger 152. The process steam 104 is preheated in process steam preheater 161 before being combined with the feed 103.

[0120] exist Figure 6 In the embodiment 4 shown, the process gas 105 is further heated in the heat exchanger 153 and subsequently in two stages in the heat recovery unit 12 or its subunit 121. Figure 7 In the embodiment 5 shown, the process gas 105 is not Figure 6 The heat exchanger 153 shown is not further heated in a heat exchanger corresponding to the heat exchanger 153, but is heated in another heat exchanger 135 in the cracking gas heat recovery section 13, and then heated in a stage in the flue gas heat recovery unit 12 or its subunit 121. Figure 8 In another alternative embodiment 6 shown, Figure 6 Similar to the embodiment 4 shown, the process gas 105 is further heated in the heat exchanger 153, but then, Figure 7 Analogously to the exemplary embodiment shown, the process gas 105 is heated in a further heat exchanger 135 in the cracked gas heat recovery section 13 and in a stage in the heat recovery unit 12 or in a subunit 121 thereof.

[0121] A portion of the boiler feed water 110 is preheated in the boiler feed water preheater 171 and then Figure 6 and Figure 7 In the embodiments 4 and 5 shown, the steam is fed to the steam drum 14. Figure 8 In the embodiment 6 shown, the boiler feed water 110 is further heated in the heat recovery unit 12 or its subunit 121. Another part of the boiler feed water 110 is injected into the steam flow between two heating stages of the recovery unit 12 or its subunit 121, essentially as Figure 1 shown.

[0122] Heat exchanger 161, heat exchanger 152 and heat exchanger 153, where present, are operated in parallel using saturated steam 117 from drum 14, and the resulting steam condensate streams are subsequently combined and used in boiler feedwater preheater 171 and then in feed preheater 151 where the condensate is subcooled and output as subcooled steam condensate stream 108.

[0123] according to Figure 6 , Figure 7 and Figure 8 In the illustrated embodiments 4, 5 and 6, the combustion air 102 or the 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 .

[0124] Using an air preheating system consisting of at least two multi-flow heat exchangers, with flue gas as the heat medium and air as the cool medium, the combustion air is at least partially preheated in the flue gas channel ("internal air preheating"). Figures 3 to 8 As shown, between the two air preheating steps, heat is preferably recovered from the flue gas for steam superheating, which steam is preferably generated in a steam generating quench exchanger. In some embodiments, between the two air preheating steps, additional heat can also be recovered from the flue gas to heat other streams, such as preheating a feed stream, such as Figure 7 The one shown is for a liquid feed cracking furnace apparatus.

Claims

1. A steam cracking method using a steam cracking system, the steam cracking system comprising one or more combustion radiation sections (11), wherein: During a steam cracking operation, a fuel (101) is combusted with an oxygen-containing oxidant gas (102) to heat the one or more combustion radiant sections (11) to form a flue gas (111), wherein a process gas (105) is formed from a hydrocarbon feed (103) and a process steam (104), wherein the process gas (105) passes through one or more cracking furnace tubes in the one or more combustion radiant sections (11) to form a cracked gas (106), wherein at least a portion of the flue gas (111) is cooled in a flue gas heat recovery section (12), wherein at least a portion of the cracked gas (106) is cooled in a cracked gas heat recovery section (13), wherein the flue gas heat recovery section (12) includes one or more heat exchangers, wherein the cracked gas heat recovery section (13) includes one or more heat exchangers (131, 132, 133, 134) , 135), wherein the flue gas heat recovery section (12) is configured to: at least in part of the steam cracking operation, use a first proportion of greater than 35% of the total heat recovered from the flue gas (111) in the one or more heat exchangers of the flue gas heat recovery section (12) to preheat the oxidant gas (102), and wherein the cracking gas heat recovery section (13) includes heat exchange structures, the number and configuration of which are set to: at least in the same part of the steam cracking operation, use a second proportion of greater than 35% of the total heat recovered in the one or more heat exchangers (131, 132, 133, 134) of the cracking gas heat recovery section (13) to preheat the process gas (105), and / or the hydrocarbon feed (103), and / or the process steam (104) used to form the process gas (105).

2. The method according to claim 1, wherein: The first ratio and the second ratio are independently greater than 35%, greater than 40%, greater than 45% or greater than 50%.

3. The method according to claim 1 or 2, wherein: The oxidant gas (102) is preheated to a temperature exceeding 400°C, 500°C, 600°C or 700°C.

4. A method according to any one of the preceding claims, wherein: The oxidant gas (102) or a portion of the oxidant gas (102) is at least partially preheated in the flue gas heat recovery section (12) by heat exchange with the flue gas in at least two separate oxidant gas preheating stages, and wherein the flue gas is used between the two oxidant gas preheating stages to superheat high-pressure steam having an absolute pressure level between 30 bar and 175 bar.

5. A method according to any one of the preceding claims, wherein: superheating steam in the flue gas heat recovery section (12); Superheating of the steam in the flue gas heat recovery section (12) is limited to a maximum temperature of 450°C, 400°C or 350°C, and / or the superheating results in a dew point margin of a maximum of 150K, 120K, 80K or 60K; No further steam superheating is performed before the steam is output from the flue gas heat recovery section (12) or the steam cracking system; and Less than 25%, 23% or 21% of the heat recovered in the flue gas heat recovery section (12) is used to generate high pressure export steam.

6. A method according to any one of the preceding claims, wherein: The steam output from the flue gas heat recovery section (12) or the steam cracking system, with or without prior superheating and / or without prior extraction of available mechanical work, reaches one or more steam condensing heat exchangers through conduits, pressure reducing valves and / or nozzles in a proportion of more than 60%, 70% or 80%.

7. A method according to any one of the preceding claims, wherein: The steam output from the flue gas heat recovery section (12) or the steam cracking system is not used in a steam turbine drive delivering a shaft power greater than 5 MW, 3 MW or 1 MW.

8. A method according to any one of the preceding claims, wherein: The process gas, and / or the hydrocarbon feed (103), and / or the process steam (104) used to form the process gas (105) are at least partially heated by means of a feed-discharge exchanger using recovered cracked gas heat.

9. The method according to claim 8, wherein: The feed-discharge exchanger is located downstream of the steam generating quench exchanger in the flow path of the cracked gas.

10. A method according to any one of the preceding claims, wherein: The saturated steam generated in the quench exchanger is used to preheat the process gas (105), and / or the hydrocarbon feed (103), and / or the process steam (104) used to form the process gas (105); and The steam condensate collected from the preheating is used for additional preheating of the process gas (105), and / or the hydrocarbon feed (103), and / or the process steam (104) used to form the process gas (105) at a low temperature level.

11. The method according to any one of claims 1 to 8, wherein: In the flue gas heat recovery section, the process gas (105), and / or the hydrocarbon feed (103), and / or the process steam (104) used to form the process gas (105) are not preheated.

12. A method according to any one of the preceding claims, wherein: The process gas (105) or a portion of the process gas (105) is finally preheated using an electric superheater before the mixture enters the one or more cracking furnace tubes in the one or more radiant combustion sections.

13. A steam cracking system comprising: one or more combustion radiation sections (11); means configured to combust a fuel (101) with an oxidant gas (102) to heat the one or more combustion radiant sections (11) to form a flue gas (111) during a steam cracking operation; an apparatus configured to form a process gas (105) from a hydrocarbon feed (103) and steam (104); means configured to pass the process gas (105) through one or more cracking furnace tubes in the one or more combustion radiant sections to form cracked gas (106); a flue gas heat recovery section (12), the flue gas heat recovery section (12) being configured to cool at least a portion of the flue gas (111); and A cracked gas heat recovery section (13), the cracked gas heat recovery section (13) being configured to cool at least a portion of the cracked gas (106), wherein: The flue gas heat recovery section (12) and the cracked gas heat recovery section (13) respectively include one or more heat exchangers (131, 132, 133, 134); The flue gas heat recovery section (12) is configured to: preheat the oxidant gas (102) using a first proportion greater than 35% of the total heat recovered from the flue gas (111) in the one or more heat exchangers of the flue gas heat recovery section (12) during at least part of the steam cracking operation; and The cracking gas heat recovery section (13) includes heat exchange structures, the number and configuration of which are arranged so as to: at least in the same part of the stage of the steam cracking operation, use a second proportion greater than 35% of the total heat recovered in the one or more heat exchangers (131, 132, 133, 134) of the cracking gas heat recovery section (13) to preheat the process gas (105), and / or the hydrocarbon feed (103), and / or the process steam (104) used to form the process gas (105).

14. The system according to claim 14, wherein: The system is configured to perform a method according to any one of the preceding claims.

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