Method and system for steam cracking

Abstract

A method for steam cracking using a steam cracking apparatus (2100-2800) comprising an electric cracking furnace (10) without a convection section (12) and further comprising a quench cooling train (20) is presented, wherein a process gas stream is at least passed through the electric cracking furnace (10) and the quench cooling train (20). The operation of the quench cooling train (20) comprises at least two different cooling steps arranged in any order. In a first step at least a part of the process gas stream withdrawn from the electric cracking furnace (10) is cooled by boiler feed water vaporization at an absolute pressure level between 30 bar and 175 bar. In a second cooling step at least a part of the process gas stream withdrawn from the electric cracking furnace (10) is cooled by a superheated mixture of feed hydrocarbons used to form the process gas stream and process steam, thereby heating the process gas stream to a temperature level between 350 °C and 750 °C. A corresponding apparatus (2100-2800) is also part of the invention.

Description

Technical Field

[0001] The present invention relates to the methods and systems for steam cracking as described in the preamble of the independent claims. Background Technology

[0002] This invention is based on steam cracking technology for the production of olefins and other basic chemicals, such as that described in the article on "Ethylene" in the Ullman Encyclopedia of Industrial Chemistry (published online on April 15, 2009, DOI: 10.1002 / 14356007.a10_045.pub2).

[0003] US 2006 / 116543A1 discloses a method and apparatus for steam cracking hydrocarbons. The method includes heating a mixture of hydrocarbons and steam to a desired temperature, which is sufficiently high to crack the hydrocarbons and convert them into olefins. The method is characterized in that the energy required to heat the mixture is substantially provided by a combined heat and power (CHP) system, which utilizes the combustion of fuel to simultaneously generate heat and mechanical work, which are converted into electricity by an alternating current generator; and the mixture is initially preheated using the heat energy provided by the CHP system, and subsequently heated to the desired cracking temperature by electric heating using the electricity provided by the CHP system.

[0004] In US 2020 / 172814A1, a cracking furnace system for converting hydrocarbon feedstock into cracked gas includes a convection section, a radiant section, and a cooling section. The convection section includes a plurality of convection tube bundles configured to receive and preheat the hydrocarbon feedstock. The radiant section includes a combustion chamber comprising at least one radiant coil configured to heat the feedstock to a temperature permissible for pyrolysis. The cooling section includes at least one transfer line exchanger.

[0005] 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 the refractory furnace. The process gas, initially containing steam and hydrocarbons to be cracked, passes through a cracking coil, also known as the radiant zone or radiant section, placed within the refractory box. Along this flow path, the process gas is continuously heated, allowing the desired cracking reaction to occur within the cracking coil, thereby continuously enriching the process gas in the cracking products. The inlet temperature of the process gas entering the cracking coil is typically between 550°C and 750°C, and the outlet temperature is typically between 800°C and 900°C.

[0006] In addition to the radiant zone, a combustion pyrolysis furnace also includes what is commonly referred to as a convection zone or convection section and a quenching zone or quenching section. The convection zone, typically located above the radiant zone, consists of various tube bundles that pass through the flue gas duct from the radiant zone. The primary function of the convection zone is to recover as much energy as possible from the hot flue gas leaving the radiant zone. In fact, typically only 35% to 50% of the total combustion load is transferred to the process gas passing through the pyrolysis coils within the radiant zone. Therefore, the convection zone plays a central role in the energy management of steam pyrolysis, as it is responsible for effectively utilizing approximately 40% to 60% of the heat input into the furnace (i.e., the combustion load). In fact, when the radiant and convection zones are combined, modern steam pyrolysis equipment utilizes 90% to 95% of the total combustion load (based on the lower calorific value or net calorific 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 into the atmosphere through the chimney.

[0007] The heat recovered from the flue gas in the convection zone is typically used for process loads, such as preheating of boiler feedwater and / or hydrocarbon feed, (partial) evaporation of liquid hydrocarbon feed (regardless of whether process steam was previously injected), and superheating of process steam and high-pressure steam.

[0008] The quenching zone is located downstream of the radiant zone along the main process gas path. The radiant zone consists of one or more heat exchanger units, whose main functions are to rapidly cool the process gas below its maximum temperature level to stop the pyrolysis reaction, further cool the process gas for downstream processing, and effectively recover the sensible heat of the process gas for further energy use. Furthermore, further cooling or quenching can be achieved by injecting liquid, for example, by oil quenching when steam pyrolysis liquid feed is used.

[0009] The heat recovered from the process gases in the quenching section is typically used to evaporate high-pressure (HP) or ultra-high-pressure (SHP) boiler feedwater (typically in the pressure range between 30 bar and 130 bar absolute pressure) and to preheat the same boiler feedwater before it is supplied to the steam drum. The resulting saturated high-pressure or ultra-high-pressure steam can be superheated in the convection zone (see above) to form superheated high-pressure or superheated ultra-high-pressure steam, which can be distributed from the convection zone to the central steam system of the facility to provide heat and power to heat exchangers, steam turbines, or other rotating equipment. The superheat of the steam obtained in the furnace convection zone is typically 150 K to 250 K higher than the saturation temperature (dew point boundary). Generally, steam cracking furnaces can be operated using high-pressure steam (typically between 30 bar and 60 bar) or ultra-high-pressure steam (typically between 60 bar and 130 bar). In the description of this invention, for clarity, high-pressure steam will be used throughout the pressure range between 30 bar and 130 bar, but it can also exceed this upper limit, as this invention includes the use of steam at pressures up to 175 bar.

[0010] A crucial part of process gas handling after quenching and cooling is compression, which typically occurs after further processing (e.g., removal of heavy hydrocarbons and process water) to condition the process gas for separation. This compression, also known as process gas compression or cracked gas compression, is usually carried out by a multi-stage compressor driven by a steam turbine. In the steam turbine, steam at appropriate pressure from the central steam system of the facility can be used; this steam therefore includes steam generated using heat from the convection section and from the quenching and cooling process. Typically, in prior art steam cracking facilities, the heat of the flue gas (in the convection zone) and the process gas (in the quenching zone) is well balanced with the heat required to generate the majority of the steam needed to heat and drive the steam turbine. In other words, waste heat can be more or less adequately used to generate the steam required in the facility. Additional heat for generating steam can be provided in a (combustion) steam boiler.

[0011] For reference, and to further illustrate the background technology of the present invention, Figure 1 A conventional combustion steam cracker is shown in a highly simplified partial schematic diagram, and is labeled as 900.

[0012] Figure 1 The steam pyrolysis unit 900 shown includes one or more pyrolysis furnaces 90, as indicated by the heavy line. For simplicity, the term "one" pyrolysis furnace 90 is used hereinafter, while a typical steam pyrolysis unit 90 may include multiple pyrolysis furnaces 90, which may operate under the same or different conditions. Furthermore, the pyrolysis furnace 90 may include one or more of the components described below.

[0013] The pyrolysis furnace 90 includes a radiation zone 91 and a convection zone 92. In addition to... Figure 1 In other embodiments besides the illustrated embodiment, multiple radiation zones 91 may also be associated with a single convection zone 92, etc.

[0014] In the example described, multiple heat exchangers 921 to 925 are arranged in the convection zone 92, either in the arrangement or sequence shown, or in a different arrangement or sequence. These heat exchangers 921 to 925 are typically configured to pass through the convection zone 92 in the form of a tube bundle and are positioned within the flue gas flow from the radiation zone 91.

[0015] In the example described, the radiant zone 91 is heated by a plurality of burners 911 arranged on the bottom and wall sides of the refractory material forming the radiant zone 91; these burners are only partially specified. In other embodiments, the burners 911 may also be arranged only on the wall side or only on the bottom side. For example, the latter may be preferred when using pure hydrogen for combustion.

[0016] In the example described, a gaseous or liquid feed stream 901 containing hydrocarbons is provided to the steam cracking unit 900. Multiple feed streams 901 may also be used in the manner shown or in different ways. The feed stream 901 is preheated in a heat exchanger 921 within the convection zone 92.

[0017] Furthermore, the boiler feedwater flow 902 passes through the convection zone 92, or more precisely, through the heat exchanger 922, and is preheated in the heat exchanger 922. The boiler feedwater flow 902 is then introduced into the steam drum 93. In the heat exchanger 923 in the convection zone 92, the process steam flow 903, typically provided by a process steam generation system located outside the furnace system of the steam cracking unit 900, is further heated, and... Figure 1 In the example shown, process steam flow 903 is then combined with feed flow 901.

[0018] The resulting feed flow and steam flow 904 pass through an additional heat exchanger 925 in the convection zone 92, and then through the radiation zone 91 in the common multiple cracking coils 912 to form a cracked gas flow 905. Figure 1 The illustrations are highly simplified. Typically, the corresponding flow 904 is uniformly distributed in multiple cracking coils 912, and the cracked gas formed in the cracking coils 912 is collected to form the cracked gas flow 905.

[0019] like Figure 1 As further shown, steam stream 906 can be drawn from steam drum 93 and can be (over)heated in a separate heat exchanger 924 in convection zone 92 to produce high-pressure steam stream 907. High-pressure steam stream 907 can be used in any suitable location within the steam cracking unit 900 and for any suitable purpose, which will not be specifically described here.

[0020] The cracked gas flow 905 from the radiation zone 12 or the cracking coil 912 is conveyed to the quenching exchanger 94 via one or more transmission lines, where it is rapidly cooled for the reasons described above. The quenching exchanger 94 referred to herein represents a primary quenching (heat) exchanger. Other quenching exchangers may also be present besides this primary quenching exchanger 94.

[0021] The cooled pyrolysis gas stream 907 is conveyed to other processing units 95, which are shown only schematically here. Specifically, these other processing units 95 may be processing units for washing, compressing and fractionating the pyrolysis gas, as well as compressor units including steam turbines that can be operated using steam from steam boiler drum 93 and are indicated by 96.

[0022] In the example shown, the quenching exchanger 94 is operated using a water flow 908 from the steam drum 93. The steam flow 909 formed in the quenching exchanger 94 is returned to the steam drum 93.

[0023] Ongoing efforts to reduce CO2 emissions from at least local industrial processes also extend to the operation of steam cracking equipment. As with all technological fields, reductions in local CO2 emissions can be specifically achieved through the electrification of some or all of the possible processing units.

[0024] As described in EP 3075704A1 concerning reformers, in addition to burners, a voltage source connected to the reaction tube can be used to heat the feed with the resulting current. For example, steam cracking equipment using electrically heated steam cracking furnaces is proposed in WO 2020 / 150244A1, WO2020 / 150248A1, and WO 2020 / 150249A1. Electric furnace technologies in other or broader contexts are disclosed, for example, in WO 2020 / 035575A1, WO 2015 / 197181A1, EP3249028A1, EP 3249027A1 and WO 2014 / 090914A1, or in earlier documents such as DE2362628A1, DE 1615278A1, DE710185C and DE 3334334A1.

[0025] US 2006 / 116543A1 discloses a method and apparatus for steam cracking hydrocarbons. The method includes heating a mixture of hydrocarbons and steam to a desired temperature sufficiently high to crack the hydrocarbons and convert them into olefins. The method is characterized in that the energy required to heat the mixture is substantially provided by using a combined heat and power (CHP) system, which utilizes the combustion of fuel to simultaneously generate heat and mechanical work, which are converted into electricity by an alternating current generator; and the mixture is initially preheated using the heat provided by the CHP system, and subsequently heated to the desired cracking temperature by electric heating using the electricity provided by the CHP system.

[0026] In US 2020 / 172814A1, a cracking furnace system for converting hydrocarbon feedstock into cracked gas includes a convection section, a radiant section, and a cooling section. The convection section includes a plurality of convection tube bundles configured to receive and preheat the hydrocarbon feedstock. The radiant section includes a combustion chamber comprising at least one radiant coil configured to heat the feedstock to a temperature permissible for pyrolysis. The cooling section includes at least one transfer line exchanger.

[0027] Completely or partially altering the heating concept of a steam cracking plant—that is, using heat generated entirely or partially from electricity to replace heat generated from fuel combustion—is a significant intervention. As an alternative, less invasive redesigns are typically required, especially when retrofitting existing units. For example, this could include at least partially replacing the steam turbine driving the process gas compressor or other compressors with an electric drive. While such a steam turbine can be operated partially using steam generated from waste heat recovered in the convection section of the cracking furnace, as described above, a separate combustion boiler is usually required to supply sufficient steam. Therefore, replacing the steam turbine driving the aforementioned compressors with an electric drive, at least partially, can reduce or eliminate the load on the combustion boiler, thereby reducing local CO2 emissions.

[0028] However, as will be further explained below, specifically, the electrification of components of such equipment will have a significant impact on the overall thermal balance of the equipment. That is, if the steam turbine used to drive the compressor is replaced with an electric drive, the waste heat generated in the equipment (previously used to drive the steam turbine) can no longer be fully utilized. On the other hand, if the combustion furnace is replaced with an electric furnace, the waste heat of the flue gas previously used to provide steam, heat the feed, etc., will no longer be available.

[0029] In other words, replacing any carbon dioxide-emitting component in a steam cracker unit has a significant impact on the operation of the entire plant, and is not simply a matter of replacing one component with another. Therefore, the full and efficient integration of these components in the steam cracker unit is crucial for the overall plant design, especially energy management. This is the purpose of this invention.

[0030] In this regard, the present invention particularly relates to a situation in which a combustion-type steam pyrolysis furnace is replaced by an electrically heated steam pyrolysis furnace, resulting in a significant reduction or absence of steam available for steam-consuming equipment (e.g., steam turbines or other rotating equipment). The present invention particularly relates to a situation where the steam pyrolysis equipment is "fully electrified." In this case, as previously mentioned, a suitable operating mode must be found because the traditional steam production and consumption balance is almost completely altered. Summary of the Invention

[0031] Against this backdrop, the present invention proposes a method and system for steam cracking, having the features of the independent claims. Embodiments of the invention are the subject of the dependent claims and the description herein.

[0032] Before further explaining the features and advantages of the present invention, some terms used in the description of the present invention will be further explained.

[0033] The term "process steam" refers to steam added to a hydrocarbon feed prior to its steam cracking. In other words, process steam is part of the corresponding feed. Therefore, process steam participates in commonly known steam cracking reactions. Process steam can specifically include steam produced by the evaporation of "process water," i.e., water previously separated from the mixed hydrocarbon / water stream, such as water separated from process gases or their fractions extracted from a steam cracking furnace, particularly water separated by gravity separation in a vessel / condenser, deaerator, or using a filter.

[0034] "Process gas" refers to a gas mixture that passes through a steam cracking furnace and subsequently undergoes processing steps such as quenching, compression, cooling, and separation. When supplied to the steam cracking furnace, process gas comprises steam and hydrocarbons that have undergone steam cracking; that is, the "feed stream" that has undergone steam cracking is also referred to herein as process gas. If a distinction is necessary, it can be expressed as "process gas introduced into the steam cracking furnace" and "process gas effluent" or similar terms. When leaving the steam cracking furnace, process gas is rich in cracking products, particularly containing very few precipitated hydrocarbons. In subsequent processing steps, the composition of the process gas may be further altered, for example, due to the separation of distillates.

[0035] Unlike process steam, the term "high-purity steam" refers to steam produced by the evaporation of purified boiler feedwater. High-purity steam is typically defined according to standards customary in the field, such as VGB-S-010-T-00 or similar standards. High-purity steam generally does not include steam produced from process water, as the latter usually contains some other components from process gases.

[0036] The term "feed hydrocarbon" refers to at least one hydrocarbon that undergoes steam cracking in a process gas in a steam cracking furnace. When using the term "gas feed," the feed hydrocarbon mainly or solely comprises hydrocarbons containing 2 to 4 carbon atoms per molecule. In contrast, the term "liquid feed" should refer to feed hydrocarbons mainly or solely comprised of hydrocarbons containing 4 to 40 carbon atoms per molecule, with "heavy feed" at the upper end of this range.

[0037] The term "electric furnace" is generally used for steam cracking furnaces, in which the heat required to heat the process gas in the cracking coil is primarily or entirely provided by electricity. Such a furnace may include one or more electric heater units connected to an electrical supply system via wired connections and / or inductive power transmission. Within the heater unit material, the applied current generates a volumetric heat source through Joule heating. If the cracking coil itself is used as the electric heating unit, the released heat is directly transferred to the process gas via convective-conductive heat transfer. If a separate electric heating unit is used, the heat released by Joule heating is indirectly transferred from the heating unit to the process gas, preferably first by radiation and to a lesser extent by convection from the heating unit to the cracking coil, and then from the cracking coil to the process gas via convective-conductive heat transfer. The process gas can be preheated in various ways before being supplied to the cracking furnace.

[0038] In contrast, a "combustion furnace" is typically a steam cracking furnace, in which the heat required to heat the process gas in the cracking coil is provided primarily or entirely by burning fuel using one or more burners. The process gas can be preheated in various ways before being supplied to the cracking furnace.

[0039] When a combination of electric furnace and combustion furnace is used in steam cracking, the term "hybrid heating concept" is often used. In the context of this invention, it is preferable to strictly classify individual cracking coils as either combustion furnaces or electric furnaces, i.e., each cracking coil is either entirely heated by electricity or entirely heated by combustion.

[0040] The term "major" in this article may refer to a proportion or content of at least 50%, 60%, 70%, 80%, 90%, or 95%.

[0041] As used herein, the term "rotating equipment" may refer to one or more components selected from compressors, blowers, pumps, and generators, which are driven by a mechanical energy source such as an electric motor, steam turbine, or gas turbine.

[0042] A “multi-flow heat exchanger” is a type of heat exchanger in which the medium to be cooled passes through multiple channels, such as the “transmission line exchanger” mentioned in the article by Ullman mentioned at the beginning.

[0043] Advantages of the present invention

[0044] To the best of the inventors' knowledge, existing literature on electrically heated pyrolysis furnaces is limited to the design and operation of the electric coil heating section itself. Information regarding the integration of concepts into the overall furnace structure (including preheating and quenching sections) is scarce, as is information regarding integration into a broader pyrolysis unit structure. This is also true in addition to the aforementioned most recent publications (i.e., WO 2020 / 150244A1, WO 2020 / 150248A1, and WO 2020 / 150249A1).

[0045] The full and efficient integration of the electric furnace in the steam pyrolysis unit (hereinafter referred to as the "steam pyrolysis unit") is crucial to the overall design of the plant, especially energy management. As mentioned earlier, the lack of a convection zone in the electric furnace poses a significant challenge. This is important because, as previously stated, in combustion pyrolysis furnaces, 40% to 60% of the total heat input is recovered in the convection zone and can be used for various purposes.

[0046] The concepts and solutions provided by the present invention are specifically designed and suited to meet the following duties or requirements necessary for steam cracking units including electric furnace systems.

[0047] The process gas stream, premixed with feed hydrocarbons and steam, in the cracking coil is electrically heated from an inlet temperature between 550°C and 750°C to an outlet temperature between 800°C and 900°C, thereby achieving a cracking yield similar to or better than that obtained in a combustion cracking furnace.

[0048] Preheating of the feed hydrocarbons, if liquid, involves vaporizing them from a normal supply temperature between 20°C and 150°C to the aforementioned coil inlet temperature between 550°C and 750°C. Preheating and vaporization of the feed hydrocarbons are carried out with or without the addition of process steam, which is typically supplied to the steam cracking unit at a temperature level between 130°C and 200°C.

[0049] In one or more multi-flow heat exchangers, the process gas downstream of the cracking coil is effectively and very rapidly cooled to a temperature level between 300°C and 450°C (for liquid feed) or between 150°C and 300°C (for gas feed) to allow heat to be recovered from the process gas.

[0050] The energy flow between the balance furnace system and other steam cracking equipment is controlled to ensure safe, reliable and efficient operation of the equipment.

[0051] This invention proposes novel process solutions for the design, layout, and operation of the furnace in the aforementioned equipment. In short, this invention provides a solution to the problem of "how to balance and distribute heat in a low-emission to zero-emission steam cracking unit, wherein some, most, or all of the heat is generated by an electric furnace?"

[0052] The existing technology does not include examples of how to solve these problems because all combustion furnace integration concepts rely heavily on the presence of a convection zone in which heat is recovered from the hot flue gas flow.

[0053] While existing literature may indicate that heat from the process gas stream can be recovered and utilized, for example, for feed preheating or process steam generation, no solutions are provided for how to supply usable process heat to the numerous other process heat-consuming components in the steam cracking unit and adjacent chemical complexes. Although some have suggested abandoning steam as the primary energy carrier, the aforementioned heating problem remains unresolved unless all heating tasks within the unit are powered by electricity. This latter, less desirable solution is far from optimal, as using electricity for heating at cryogenic temperatures results in significant energy losses. In other embodiments of the prior art, the generated steam is strongly superheated, intended for power generation via a steam turbine combined with a generator system. This is also a debatable solution, as generating electricity using steam initially generated by electrically heating the reactor system similarly leads to very high energy losses and suboptimal resource management.

[0054] According to the present invention, a method for performing steam pyrolysis using a steam pyrolysis apparatus is provided, the steam pyrolysis apparatus comprising an electropyrolysis furnace without a convection zone, and further comprising a quenching and cooling unit, wherein the process gas flow passes through at least the electropyrolysis furnace and the quenching and cooling unit. It should be noted that although arrangements, apparatus, flows, etc., are referred to in the singular in the following description, the invention can also include embodiments in which each of these items may be provided in multiple forms. In this regard, flows can be combined from different components or can be distributed to different components as needed.

[0055] When referring to an electrocracking furnace without a convection zone, it means that there is no region from which a significant amount of process heat, typically exceeding 500 kW, is continuously recovered from the flue gas stream. In other words, an electrocracking furnace without a convection zone is a pyrolysis furnace that does not emit carbon dioxide from the flue gas stream, which is intentionally cooled to continuously recover a significant amount of process heat, typically exceeding 500 kW. However, the furnace system may have carbon dioxide emission sources for non-process purposes, such as safety-related igniters at the gas exhaust chimney outlet. These emission sources, however, provide a small amount of heat that is typically not recoverable.

[0056] Therefore, generally, during hydrocarbon cracking operations, it is preferable to transfer no more than 1000 kW of heat as sensible heat in the electrocracking furnace to a stream other than the process gas stream passing through or exiting one or more electrocracking furnace coil boxes according to the invention. For example, these other gas streams may be high-purity steam streams. In other words, the heat transferred in the electrocracking furnace to streams other than the process gas may also be no more than 5% or no more than 3% of the heat transferred to the process gas.

[0057] According to the invention, the quenching cooling unit preferably includes at least two different cooling steps, wherein in the first cooling step, at least a portion of the process gas stream extracted from the electrocracking furnace is cooled by evaporative boiler feedwater at an absolute pressure level between 30 bar and 175 bar (particularly between 60 bar and 140 bar, more particularly between 80 bar and 125 bar), and in the second cooling step, at least a portion of the process gas stream extracted from the electrocracking furnace is cooled relative to a superheated mixture of feed hydrocarbons and process steam used to form the process gas stream, said mixture being heated to a temperature level between 350°C and 750°C, particularly between 400°C and 720°C, more particularly between 450°C and 700°C.

[0058] According to a particularly preferred embodiment of the invention, the steam generating unit is operated in a thermally associated manner with the steam cracking unit and can be formed as part of the steam cracking unit. One or more steam generating units are used to generate superheated high-pressure steam at a first pressure level between 30 bar and 175 bar absolute pressure and at a first temperature level, without generating steam at a temperature level higher than the first temperature level. Here, the term "substantially no steam" specifically means that the amount of steam is less than 10% of the total amount of steam generated by the steam generating unit.

[0059] Furthermore, according to this embodiment, the superheated high-pressure steam at the first pressure level and the first temperature level expands at least partially adiabatic and isenthalpically to a second pressure level below the first pressure level. This second pressure level is specifically higher than, but not necessarily higher than, 20 bar absolute pressure, such that the temperature level of the superheated high-pressure steam decreases to the second temperature level only through adiabatic and isenthalpic expansion. The first temperature level is selected such that each intermediate temperature level reached during the adiabatic and isenthalpic expansion at intermediate pressure levels greater than 20 bar is 5 K to 120 K higher, particularly 10 K to 100 K higher, and further particularly 20 K to 80 K higher than the steam dew point at the corresponding intermediate pressure level during the adiabatic and isothermal expansion. In other words, according to the invention, the expanding steam is maintained at a moderate level of superheat through the first temperature level, while maintaining a sufficient distance from the boiling point profile for all intermediate pressure levels exceeding 20 bar throughout the expansion process. The latter is particularly relevant when expansion begins from a first pressure level greater than 40 bar, as in this case, a two-phase region can be reached or at least temporarily traversed. This situation can be avoided according to the present invention.

[0060] If the steam stream output from the furnace system is used solely to provide process heat to the consumer, then limiting the steam superheat level within the furnace system, i.e., moderate superheating, is highly appropriate according to this embodiment. The term "output" here refers to extraction from the steam generator, and not necessarily from the entire system. This steam can also be called "dry" steam, as its degree of superheating is chosen primarily to prevent condensation, which could lead to wear, for example, during steam transport. Through adiabatic and isotropic expansion, the steam pressure can be reduced to the pressure and temperature levels required by the radiator (if the temperature level meets the aforementioned requirements) without a phase change, either after or during expansion. For any possible adiabatic and isotropic expansion to the minimum pressure, i.e., the second pressure level, and for any intermediate pressure levels above 20 bar during expansion, the dew point margin of the steam stream remains within the aforementioned range.

[0061] According to embodiments of the invention, by avoiding strong steam superheating, the quenching heat can be maximized for feed preheating at higher temperature levels (typically exceeding 300°C). In embodiments including an electric steam superheater, as further explained below, the electrical energy input to the electrocracking furnace can be minimized.

[0062] This invention differs from all known integrated combustion furnace systems in that, due to the absence of a convection zone, it neither preheats the flue gas feed nor superheats it with steam. Unlike previously proposed electric furnace integration concepts, this invention explicitly uses steam as the primary energy carrier, and more specifically as a heat carrier, to handle heat consumers at different temperature levels. The steam generation and output conditions are specifically designed to meet the intended purpose of heat distribution within the steam cracking unit and adjacent chemical complex units.

[0063] Furthermore, the topology used in embodiments of the invention preheats the feed hydrocarbons, process steam, and boiler feedwater to a temperature level of approximately 300°C using only saturated and / or moderately superheated high-pressure steam and its resulting condensate. This topology represents an inventive solution for performing these process tasks in an electric furnace, where there is no additional flue gas waste heat, unlike in a combustion furnace. The advantages of these solutions are the use of a heat medium directly supplied by the electric furnace, thereby reducing piping requirements, and the minimization of available energy loss by maintaining a small temperature difference in the heat exchanger and, preferably, subcooling the formed condensate to maximize heat recovery.

[0064] By limiting the amount of steam used solely for process heat and setting steam parameters accordingly, the steam system can operate flexibly (related to pressure and temperature) and can further be used as a temporary energy buffer, for example, by changing the steam superheat level and / or pressure level during operation. Since steam turbines are less tolerant of changes in steam conditions than steam-based heat exchangers, the generated steam is not used for power generation in the turbine, which facilitates the operation of the steam system. In different embodiments, variations in electrical input can be achieved in different ways, for example, by modifying the setpoint of the controlled outlet temperature of a particular heat exchanger. Figure 2 In the embodiments shown, as further explained below, this change can be achieved by reducing the outlet temperature of the heat exchanger X2 supplying the steam. To maintain the same chemical production load on the furnace, this would result in an increase in the total electrical energy input for heating other heat exchangers and / or coils. In embodiments employing electric steam superheating, this change can be achieved directly by altering the load.

[0065] Therefore, according to the invention, preferably, steam generated by one or more steam generating units is not used in turbine drives that transmit shaft power greater than 1 MW, and preferably not in turbines or other rotating equipment as defined above. In other words, according to the invention, turbines that supply steam from one or more steam generating units are not used, and at least turbines that transmit shaft power exceeding 1 MW are not used.

[0066] The superheated high-pressure steam at the first pressure and first temperature levels preferably does not include steam generated from process water, and preferably only includes steam generated from boiler feedwater. Therefore, the superheated high-pressure steam is preferably high-purity steam as defined above. The superheated high-pressure steam is preferably not used to form one or more process gas streams, i.e., it does not participate in steam cracking reactions.

[0067] In other words, according to the present invention, as described above, only moderately superheated high-purity steam streams are generated and output at the corresponding pressure level (i.e., the first pressure level), and for any adiabatic and isenthalpic expansion down to the minimum pressure (i.e., the second pressure level), the dew point margin of the resulting expanded steam stream is within the range already mentioned.

[0068] According to the present invention, a quenching and cooling unit comprising a primary quenching exchanger and a secondary quenching exchanger is preferably used as the quenching and cooling unit. The primary quenching exchanger is used to perform at least a portion of the first step in the cooling process, and the secondary quenching exchanger is used to perform at least a portion of the second step in the cooling process, or the primary quenching exchanger is used to perform at least a portion of the second step in the cooling process, and the secondary quenching exchanger is used to perform at least a portion of the first step in the cooling process. The corresponding embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0069] According to the present invention, a multi-flow heat exchanger can be used in a steam generating unit, in which heat from the process gas stream extracted from an electrocracking furnace is transferred to the boiler feedwater stream and / or the steam stream used to form superheated high-pressure steam and / or an electric steam superheater. Furthermore, at least a portion of the feed hydrocarbons used to form the superheated mixture of feed hydrocarbons and process steam, i.e., the process stream to be subsequently cracked, can be preheated in a multi-flow heat exchanger using at least a portion of the process gas stream extracted from the electrocracking furnace, which is subsequently referred to as a feed-discharge exchanger.

[0070] According to the present invention, as a quenching cooling system, a quenching cooling system comprising a structure having three or four quenching exchangers connected in series in the process gas flow can be used, wherein at least one quenching exchanger can be provided as the multi-flow heat exchanger just mentioned. In this series, the first and second quenching heat exchangers can be the primary and secondary quenching heat exchangers described above. Heat can be transferred to the boiler feedwater flow and / or the steam flow used to form superheated high-pressure steam in the third (if any) and fourth quenching heat exchangers. Optionally, the last quenching exchanger in the series of three or four quenching exchangers can be used to preheat at least a portion of the feed hydrocarbons used to form a superheated mixture of feed hydrocarbons and process steam, particularly in mixtures that already include process steam, especially in embodiments of the invention where an electric steam superheater is provided. Hereinafter, the last quenching heat exchanger in the series of three or four quenching heat exchangers is also referred to as a “tertiary” quenching heat exchanger, and the penultimate quenching heat exchanger in the series of four quenching heat exchangers is referred to as an “intermediate” quenching heat exchanger. Note that the specific designations herein are for ease of reference only.

[0071] To partially repeat the above, the superheated high-pressure steam at the first pressure level and first temperature level preferably excludes steam generated from process water and / or includes only steam generated from boiler feedwater, such that the superheated high-pressure steam at the first pressure level and first temperature level is provided as high-purity superheated high-pressure steam. Furthermore, also as mentioned above, preferably, in steam turbine drives that transmit shaft power greater than 1 MW, steam generated by one or more steam generators is not used.

[0072] As described above, according to a particularly preferred embodiment of the invention, the steam pyrolysis unit can operate in different operating modes using different electrical energy sources, which is made possible by the flexibility in the generation and use of steam according to the invention. Thus, the invention can also be used to stabilize the power grid.

[0073] For further details regarding the steam cracking system and its preferred embodiments provided according to the present invention, please refer to the above description of the method and its preferred embodiments. Advantageously, the proposed apparatus is adapted to perform the method in at least one of the embodiments described in more detail above.

[0074] In summary, this invention presents a novel concept that ensures that the steam pyrolysis furnace can meet all of the aforementioned duties or requirements in the design of a highly electrified steam pyrolysis unit.

[0075] The solution for limiting the overheating of high-pressure steam provided by embodiments of the present invention breaks through the existing technological level in current steam cracking unit designs, which are entirely based on large rotating machinery driven by a combustion furnace and turbines. This technological choice is a highly effective solution in the design of highly electrified steam cracking units.

[0076] In fact, the current practice of producing high-superheated, high-pressure steam in the furnace section (with a dew point margin typically above 150 K at the furnace outlet) is due to the large amount of waste heat energy present in the convection section of the furnace, which can be used to power the turbine to drive the compressor and pumps. Furthermore, depressurized steam extracted from the turbine or from the turbine outlet is used to provide different levels of process heat.

[0077] In the separator units of highly electrified pyrolysis plants, using electric compressor drives instead of steam turbines can reduce the loss of available energy in the steam pyrolysis equipment. Furthermore, the highly superheated, high-pressure steam in the separator units is not being utilized more efficiently. Therefore, by reducing the superheat level, this invention allows most of the heat energy recovered in the quenching section to be used for the necessary preheating of the feed hydrocarbon / process steam mixture. This preheating can be carried out directly in the feed-discharge heat exchanger or indirectly by generating superheated, high-pressure steam and using that steam in the feed preheating step.

[0078] By maximizing the use of quenching heat for feed preheating, the total electrical energy input of the electric furnace is reduced, thereby lowering the operating cost of the electric furnace. This facilitates the integration of the electric furnace into the power grid and reduces the overall available energy loss in the furnace section.

[0079] In the illustrated embodiments, the variant of using the primary quenching exchanger for steam production has the advantages of the fastest cooling and reaction quenching speeds for cracked gas (due to the high heat transfer coefficient of boiling water), while the variant of designing the primary quenching exchanger as a feed-discharge exchanger has the advantage of the lowest input electrical energy.

[0080] According to embodiments of the invention, moderate superheating within a given range can further provide direct and flexible heat to process heat consumers because heat can be distributed to consumers at different temperature levels simply by performing single-phase, adiabatic and isotropic expansion of the moderately superheated steam output from the furnace, without the need for a pressure-reducing station for the entire steam level or for injecting additional boiler feedwater for de-heating and / or turbine stages.

[0081] As mentioned above, preheating at a lower temperature can reduce pipe volume and achieve maximum heat recovery through subcooled steam condensate.

[0082] In terms of dynamic behavior, the ability to balance and buffer changes in power input through the steam system helps to integrate such furnace systems into industrial complexes that are preferably supplied with renewable electricity.

[0083] Other features and embodiments of the invention are listed below. All these features and embodiments can be combined without limitation with those described in the context, provided they are within the scope of the claims and are technically feasible or reasonable.

[0084] The present invention is preferably combined with a separator unit, in which all gas compressors or pumps with a power load exceeding 1 MW are driven by electric motors.

[0085] The output superheated, high-pressure steam is most advantageously distributed to different steam pressure levels via adiabatic and isenthalpic expansion elements. Individual heat consumers (e.g., with critical scaling services) may also include an additional cooling step, which can be performed by direct water injection or by using a saturated boiler drum.

[0086] Steam pyrolysis apparatus incorporating features according to the invention can operate according to any possible electric heating principle, such as direct resistance coil heating, indirect radiant coil heating via an electric heating element, and coil heating using induction transmission. The steam pyrolysis apparatus may include other units for generating steam from electrical energy, such as electric heat pump systems and electric boilers.

[0087] The output superheated steam can be expanded to a pressure steam level below 20 bar absolute pressure, for example, to supply medium- and low-pressure steam consumers. The second pressure level is chosen to be 20 bar absolute pressure to facilitate defining the envelope of the initial steam superheat curve. Without limiting the scope of the invention, a higher dew point margin may be possible when expanding to a pressure below 20 bar absolute pressure.

[0088] In addition to the inherent energy storage that can be obtained through steam superheating / pressure changes, the present invention can also be further combined with dedicated energy storage systems (e.g., latent heat storage systems or similar systems). Attached Figure Description

[0089] The present invention and its embodiments will be further described below with reference to the accompanying drawings, in which:

[0090] Figure 1 The embodiments shown are not part of this invention;

[0091] Figures 2 to 9 Embodiments of the present invention are shown; and

[0092] Figures 10 to 12 The advantages of embodiments of the present invention are shown. Detailed Implementation

[0093] Figure 1 As explained at the beginning.

[0094] exist Figure 2 The accompanying drawings illustrate a steam pyrolysis apparatus 2100 according to an embodiment of the present invention, for implementing a steam pyrolysis method according to an embodiment of the present invention, and optionally as part of a system according to the present invention. In the following drawings illustrating the steam pyrolysis apparatus, the method steps can be implemented using corresponding processing units or devices, and therefore the descriptions relating to the method steps are also related to these processing units and devices, and vice versa. For brevity, repeated explanations are omitted, and for clarity, mixed language is used to describe the apparatus or system and method in the embodiments of the present invention. If a component is described in the singular, it does not preclude that these components are provided in multiple forms. The steam pyrolysis apparatus 2100, such as other steam pyrolysis apparatuses shown below, can be part of a system 200 according to an embodiment of the present invention, which may include multiple other components, and the possible system boundaries of the system are limited only within… Figure 2 It is shown very schematically in the middle.

[0095] exist Figures 2 to 9 In the diagram, thick solid arrows represent hydrocarbon feedstock, process steam, process gas, or cracked gas streams, and the resulting streams, such as hydrocarbon fractions. Thin dotted arrows represent liquid boiler feedwater streams, dashed arrows represent saturated high-purity steam streams, and dotted-dashed arrows represent superheated high-purity steam streams. Condensate streams are represented by double dashed arrows.

[0096] The steam pyrolysis unit 2100 includes an electric steam pyrolysis furnace 210 (generally as described above), also referred to as an "electric coil box". There is no convection zone.

[0097] Process steam PS, particularly at a temperature level of approximately 185°C, is mixed in a mixing nozzle M with a feed hydrocarbon stream HC preheated in heat exchanger X1. The resulting process stream PR is further heated in heat exchanger X2 to a temperature level of approximately 300°C. Heat exchangers X1 and X2 can also be combined, particularly when process steam PS is added upstream of heat exchanger X1.

[0098] Four quenching exchangers 21, 22, 22a, and 23 are arranged in series in the process gas path downstream of the electric steam cracking furnace 210, forming the quenching cooling unit 20 of the steam cracking unit 2100. As described above, and for reference only, the first and second quenching exchangers 21 and 22 in this series can be the primary and secondary quenching exchangers described previously. The last quenching exchanger 23 in this series can also be referred to as a tertiary quenching exchanger, and the penultimate quenching exchanger 22a in this series can also be referred to as an intermediate quenching exchanger. Optionally, both quenching exchangers 21 and 22a can be referred to as secondary quenching exchangers.

[0099] The process stream PR is further heated to a temperature level of approximately 660°C in electric heater E1 and preheated in quenching exchanger 22 before being supplied as feed stream to electro-steam cracking furnace 210. The process stream, as cracked gas (hereinafter referred to as PE for clarity), is extracted from cracking furnace 210 and passes through quenching exchangers 21, 22, 22a, and 23. The process stream PE effluent from electro-steam cracking furnace 210 is extracted from electro-steam cracking furnace 210 at a temperature level of approximately 840°C, from quenching exchanger 21 at a temperature level of approximately 550°C, from quenching exchanger 22a at a temperature level of approximately 340°C, and from quenching exchanger 23 at a temperature level of approximately 200°C.

[0100] Afterwards, if only Figure 2 As shown, the process flow PE can be subjected to any type of processing. According to an embodiment of the invention, the processing includes compression in a compressor 60, particularly a process gas compressor driven by an electric motor M. For further details, please refer to the description above. In particular, a separation unit is provided in which all or substantially all of the compressors are electrically driven.

[0101] A steam generating unit 30 is provided, which includes a steam boiler drum 31 and other components for generating steam. Generally, if a component is mentioned throughout the description as belonging to a device or group of components that primarily perform a certain function, this does not preclude the component from belonging to a different device or group of components with additional or different functions; this is typical for equipment including interconnected components. For example, quenching exchangers 21, 22, and 23 are described herein as part of the cooling unit 20, but could also be integrated into the steam generating unit 30.

[0102] Boiler feedwater BF (also indicated by dashed arrows) is heated to a temperature level of approximately 180°C in heat exchanger X3 and to a temperature level of approximately 290°C in quenching exchanger 23. Boiler feedwater BF is then supplied to steam drum 31, and the flow of boiler feedwater BF is also conveyed from steam drum 31 to quenching exchanger 21 for evaporation. Saturated steam SS (as indicated by dashed arrows) is formed in the steam drum and is supplied at a temperature of approximately 325°C and a pressure of approximately 122 bar absolute pressure. Saturated steam SS can be partially used to operate heat exchangers X2, X3, and X1, where condensate CO is formed in heat exchanger X2, which is then subcooled in heat exchangers X3 and X1.

[0103] The remaining portion of the saturated steam SS is superheated in the quenching exchanger 22a to form (moderately) superheated high-pressure steam SU, as indicated by the dashed arrow in the figure. The parameters of the superheated high-pressure steam SU have been extensively described previously. In the illustrated embodiment, the temperature of the superheated high-pressure steam SU is approximately 375°C, and the absolute pressure is approximately 121 bar. In the steam utilization device designated 50 for reference only, the superheated high-pressure steam SU is used for heating purposes, but preferably not substantially for driving rotating equipment. Here, the superheated high-pressure steam SU undergoes adiabatic and isenthalpic expansion using expansion units 51, 52, and 53 to form high-pressure steam HP, medium-pressure steam MP, and low-pressure steam LP, which are supplied to heat consumers 54, 55, and 56. Steam (high-pressure or ultra-high-pressure steam) output from all furnaces can be collected into the corresponding steam headers, i.e., a large-capacity piping system that distributes steam to the different consumers throughout the equipment. The supply connection to the low-pressure steam header begins from this highest-pressure header. In conventional equipment, this steam header operates at approximately a constant pressure for turbine operation, slightly below the steam outlet pressure at the furnace outlet. According to embodiments of the invention, the pressure level of the highest-pressure steam header can vary more significantly to achieve a favorable buffering effect.

[0104] Summary of Figure 2 As illustrated in the description of the steam cracking unit 2100, the process gas PE is rapidly and efficiently cooled in the first step (in the quenching exchanger 21) by the vaporization of boiler feedwater BF, similar to existing technologies for combustion furnaces. In the second step (in the quenching exchanger 22), the process gas PE is cooled by the process gas PR in the feed-discharge exchanger, the process gas PR being preheated before being supplied to the electric steam cracking furnace 210. Figure 2 In the illustrated embodiment, a quenching exchanger 22a can be provided to cool the process gas PE, while moderately overheating a portion of the saturated vapor SS generated in the quenching exchanger 21.

[0105] Figure 3 An additional steam cracking apparatus 2200 according to an embodiment of the present invention is shown. Generally, with Figure 1 The descriptions related to the steam pyrolysis unit 2100 shown also apply to... Figure 3 The steam cracking unit 2200 shown below will only be described in terms of differences.

[0106] exist Figure 3 In the steam cracking unit 2200 shown, the quenching exchanger 22a is omitted, and instead an electric steam superheater E2 is provided. Here, the process gas PE is extracted from the quenching exchanger 22 at a temperature level of approximately 340°C.

[0107] exist Figure 4The image shows another steam cracking apparatus 2300 according to an embodiment of the present invention. Generally, based on the... Figure 2 Description of the steam cracking unit 2100, and Figure 3 The instructions related to the 2200 steam cracking unit also apply to Figure 4 The steam cracking unit 2300 will be described below only for the differences.

[0108] exist Figure 4 In the steam cracking unit 2300 shown, there is also no quenching exchanger 22a; instead, an electric steam superheater E2 is installed. Figure 4 The electric heater E1 is omitted from the steam cracking unit 2300 shown. In addition, the process gas flow PR heated in the heat exchanger X2 is further heated in the quenching exchanger 21, and the steam boiler drum 31 is connected to the quenching exchanger 22.

[0109] The process gas PE effluent from the electric steam cracking furnace 210 is extracted from the quenching exchanger 22 at a temperature of approximately 340°C. The process stream PE is extracted from the quenching exchanger 21 at a temperature of approximately 525°C.

[0110] Therefore, in Figure 4 In the illustrated embodiment, the first two quenching steps are reversed, meaning that the outflowing process gas PE is first cooled by the feed process gas PR to be preheated, and then by the boiler feedwater BF. In such an embodiment, an electric feed preheater is not required because a sufficiently high preheating temperature can be achieved in the quenching exchanger 21. The high-pressure steam to be output is then moderately superheated, wherein… Figure 2 and Figure 3 Both variants can be used for superheated steam.

[0111] Figures 2 to 4 All three embodiments shown are specifically designed for an electric steam cracking furnace 210 operating with light (gaseous) feedstocks (most preferably composed primarily of ethane). Therefore, all of these embodiments include a quenching exchanger 23, which, in accordance with current industrial practice, further cools the cracked gas to a temperature level as low as 200°C while specifically preheating the boiler feedwater supplied to the steam drum 31.

[0112] Furthermore, the initial preheating (at a temperature level below 300°C) of the hydrocarbon feed HC and process steam PS after mixing to form the process stream is accomplished by using saturated steam in heat exchanger X2. The resulting high-pressure condensate CO can be further used for the other preheating steps described above.

[0113] Figure 5 An additional steam cracking apparatus 2400 according to an embodiment of the present invention is shown. Generally, based on the... Figure 2 Description of the steam cracking unit 2100, and Figure 3 The instructions regarding the steam cracking unit 2200 also apply to... Figure 5 The steam cracking unit 2400 will be described below only for the differences.

[0114] exist Figure 5 In the steam cracking unit 2400 shown, the quenching exchanger 22a is also not used; instead, an electric steam superheater E2 is provided. A portion of the superheated steam SU is now supplied to the heat exchanger X3 instead of a portion of the saturated steam SS. Therefore, the process stream PR can be heated in the heat exchanger X2 to a temperature level of approximately 330°C, resulting in less heat being extracted in the quenching exchanger 22, while the process stream PE effluent cooled therein is extracted at a temperature level of approximately 370°C.

[0115] Figure 5 The embodiments specifically illustrate that, as an alternative to the previously shown embodiments, moderately superheated steam SU can also be used for initial preheating of the hydrocarbon feed HC and process steam PS after the formation of the process flow PR.

[0116] Figure 6 Another steam cracking apparatus 2500 according to an embodiment of the present invention is shown. Generally, with Figure 2 The descriptions of the main components of the steam cracking unit 2100 shown also apply to... Figure 6 The steam cracking unit 2500 shown is different, but there are some differences, which will be explained below.

[0117] exist Figure 6 In the steam cracking unit 2500, as described above, process steam PS at a temperature level of approximately 185°C is mixed with feed hydrocarbon HC in a mixing nozzle M to form process stream PR at a temperature level of approximately 120°C. Process stream PR is further heated to a temperature level of approximately 280°C in quencher 23, and further heated to a temperature level of approximately 660°C in quencher 21, as described above, before being supplied to electric steam cracking furnace 210. Process gas PE effluent is extracted from electric steam cracking furnace 210 at a temperature level of approximately 840°C, from quencher 21 at a temperature level of approximately 510°C, from quencher 22 (without a separate quencher 22a) at a temperature level of approximately 340°C, and from quencher 23 at a temperature level of approximately 200°C.

[0118] Boiler feedwater BF is supplied to the steam drum 31 connected to the quenching exchanger 22. Saturated steam SS can be generated at a pressure level of approximately 122 bar absolute pressure and a temperature level of approximately 325°C. It is superheated in the electric heater E2 to form superheated steam SU with the parameters given above.

[0119] Figure 6 The illustrated embodiment also includes another option: ensuring initial preheating of the hydrocarbon feed HC and process steam PS after the formation of the process flow PR, wherein the quenching exchanger 23 is designed as a feed-to-discharge exchanger. This possibility can also be combined with, for example... Figure 2 , Figure 3 and Figure 5 The examples shown are combined.

[0120] Figure 7 An additional steam cracking apparatus 2600 according to an embodiment of the present invention is shown. Generally, based on the... Figure 2 Description of the steam cracking unit 2100, and Figure 3 The instructions regarding the steam cracking unit 2200 also apply to... Figure 7 The steam cracking unit 2600 will be described below only for the differences.

[0121] exist Figure 7 In the steam cracking unit 2600 shown, there is no quenching exchanger 23; instead, an oil quencher 25 is used. Therefore, the boiler feedwater BF is heated only in heat exchanger X3 before being transferred to the steam drum 31, specifically to a temperature level of approximately 260°C. An additional heat exchanger X4 provides for further heating of the feed hydrocarbons, which are then mixed with the process steam PS in a mixing nozzle M. The process steam PS is also heated in another heat exchanger X5. Heat exchangers X2, X4, and X5 operate using saturated steam SS and collect the condensate stream, which is then used in heat exchangers X1 and X3 as previously described.

[0122] exist Figure 7In the steam cracking unit 2600 shown, the initial temperature level of the process steam PS is approximately 180°C. The temperature level of the process stream PR downstream of heat exchanger X2 is approximately 300°C. Heating in electric heater E1 is specifically to reach a temperature level of approximately 630°C. The process gas PE effluent is extracted from the electric steam cracking furnace 210 at a temperature level of approximately 870°C, from the quenching exchanger 21 at a temperature level of approximately 600°C, from the first quenching exchanger 22 at a temperature level of approximately 390°C, from the quenching exchanger 22a at a temperature level of approximately 380°C, and from the oil quencher 25 at a further suitable temperature level. The saturated steam generated in the steam drum 21 is provided at a pressure level of approximately 122 bar absolute pressure and a temperature level of approximately 325°C. The superheated high-pressure steam SU downstream of the quenching exchanger 22a is provided at a pressure level of approximately 121 bar absolute pressure and a temperature level of approximately 380°C.

[0123] exist Figure 8 The image shows another steam cracking apparatus 2700 according to an embodiment of the present invention. Generally, based on the... Figure 2 Description of the steam cracking unit 2100, and Figure 7 The instructions related to the 2600 steam cracking unit also apply to Figure 8 The steam cracking unit 2700 will be described below only for the differences.

[0124] exist Figure 8 In the steam cracking unit 2700 shown, process steam PS is sequentially mixed with feed hydrocarbon HC in first and second mixing nozzles M1 and M2, wherein the process steam PS mixed in the second mixing nozzle M2 is further heated in a separate electric heater E3.

[0125] As an alternative process variation Figure 7 and Figure 8 Exemplary embodiments of the invention are shown respectively, applied to an electric furnace 210 operating with liquid feedstock and heavy liquid feedstock. In these embodiments, similar to a furnace burning liquid feedstock, there is no quenching exchanger 23. The feed preheating section is generally more complex, characterized by, for example, having an additional feed preheating step (see...). Figure 7 and Figure 8 This includes one or more process steam superheating steps in an electric process steam superheater (for heavy liquid feedstocks) and / or a multi-flow heat exchanger. However, Figure 7 and Figure 8 The embodiments shown are... Figure 2 A direct modification of the illustrated embodiment. Therefore, Figures 3 to 5 The variations presented in the illustrated embodiments can be similarly applied to... Figure 7 and Figure 8 The liquid feed furnace shown is as applied to Figure 2 It is the same as a gas feed furnace.

[0126] Figure 9 Another steam cracking apparatus 2800 according to an embodiment of the present invention is shown. Generally, based on the... Figure 2 Description of the steam cracking unit 2100, and Figure 8 The instructions related to the 2700 steam cracking unit also apply to Figure 9 The steam cracking unit 2800 will be described below only for the differences.

[0127] and Figure 3 The steam cracking unit 2200 shown is similar, except that the quenching exchanger 22a is omitted, and instead an electric steam superheater E2 is provided. As an exemplary variant, Figure 9 This illustrates a process variation for a heavy liquid feed furnace, similar to... Figure 4 The gas feed variant shown (where the quenching exchanger 21 is designed as a feed-discharge exchanger).

[0128] Figure 10 The Morrillon (enthalpy / entropy) plot of water is shown, where the horizontal axis displays entropy *s* in kJ / (K*kg) and the vertical axis displays enthalpy *h* in kJ / kg. Point 71 indicates moderate superheating used in embodiments of the invention, while point 72 indicates high superheating used in the prior art. Adiabatic and isenthalpic expansion according to the invention and its embodiments, i.e., the characteristic change in the state of the valve or pressure regulator when steam is used only for heating, is indicated by arrows starting from point 71, while polytropic expansion according to the prior art rather than the invention, i.e., the characteristic change in the state of the turbine when steam is first used for mechanical purposes before being used for heating, is indicated by arrows starting from point 72.

[0129] According to the present invention, the pressure can be reduced to the pressure and temperature level required by the heat consumer simply by isenthalpic expansion without phase change. Figure 11 The temperature change curve 81 for this isenthalpic state change is shown (support point at 380°C and 120 bar absolute pressure), with a pressure range between 20 bar and 160 bar absolute pressure, and corresponding optimal curve envelopes 82 and 83 (dew point margins of +20 K and +80 K, respectively). Figure 8 In the diagram, the horizontal axis represents absolute pressure in bar, and the vertical axis represents temperature in °C.

[0130] Figure 12 This shows the corresponding dew point margin for the same example isenthalpy curve 81 within the same pressure range. Figure 8 In the middle, the horizontal axis again shows the absolute pressure in bar, while the vertical axis shows the temperature difference in K.

Claims

1. A method for steam cracking using a steam cracking apparatus, the steam cracking apparatus comprising an electric steam cracking furnace (210) without a convection zone (92), and further comprising a quenching and cooling unit (20), wherein the process gas flow passes at least through the electric steam cracking furnace (210) and the quenching and cooling unit (20), characterized in that: The quenching and cooling unit (20) is operated to include at least two different cooling steps arranged in any order, wherein in the first cooling step of the cooling steps, at least a portion of the process gas stream extracted from the electric steam cracking furnace (210) is cooled by vaporized boiler feedwater at an absolute pressure level between 30 bar and 175 bar, and wherein in the second cooling step of the cooling steps, at least a portion of the process gas stream extracted from the electric steam cracking furnace (210) is used to cool a superheated mixture of feed hydrocarbons and process steam forming the process gas stream, the superheated mixture being heated to a temperature level between 350°C and 750°C.

2. The method according to claim 1, wherein, During hydrocarbon cracking operations, no more than 1000 kW of heat is transferred as sensible heat in the electric steam cracking furnace (210) to a stream other than the process gas stream passing through or extracted from the electric steam cracking furnace (210).

3. The method according to claim 1 or 2, wherein, A quenching and cooling unit (20) is used, comprising a primary quenching exchanger (21) and a secondary quenching exchanger (22), wherein the primary quenching exchanger (21) is used to perform at least a portion of the first cooling step in the cooling process, and the secondary quenching exchanger (22) is used to perform at least a portion of the second cooling step in the cooling process, or the primary quenching exchanger (21) is used to perform at least a portion of the second cooling step in the cooling process, and the secondary quenching exchanger (22) is used to perform at least a portion of the first cooling step in the cooling process.

4. The method according to claim 3, wherein, The steam generator (30) is operated in a manner thermally associated with the steam cracking unit; Using one or more of the steam generating devices (30), superheated high-pressure steam at a first pressure level between 30 bar absolute pressure and 175 bar absolute pressure and at a first temperature level is generated, and steam at a temperature level higher than the first temperature level is not generated. as well as The superheated high-pressure steam at the first pressure level expands at least partially in an adiabatic and isenthalpic manner to a second pressure level below the first pressure level, such that the temperature level of the superheated high-pressure steam decreases to a second temperature level, wherein the first temperature level is selected such that the second temperature level is 5 K to 120 K higher than the dew point of the steam at the second pressure level.

5. The method according to claim 4, wherein, A multi-flow heat exchanger is used in the steam generating unit (30), and / or an electric steam superheater is used in the steam generating unit (30). In the multi-flow heat exchanger, the heat transferred from the process gas flow extracted from the electric steam cracking furnace (210) is transferred to the boiler feedwater and / or to the steam flow used to form the superheated high-pressure steam.

6. The method according to claim 4 or 5, wherein, At least a portion of the feed hydrocarbons used to form the superheated mixture of feed hydrocarbons and process steam are preheated in a multi-flow heat exchanger using at least a portion of the process gas stream extracted from the electric steam cracking furnace (210).

7. The method according to claim 5 or 6, wherein, A quenching and cooling unit (20) is used, comprising an additional secondary quenching exchanger (22a) and / or a tertiary quenching exchanger (23), wherein the additional secondary quenching exchanger (22a) and / or the tertiary quenching exchanger (23) are provided as the multi-flow heat exchanger.

8. The method according to any one of claims 4 to 7, wherein, The superheated high-pressure steam at the first pressure level and the first temperature level does not include steam generated from process water, and / or only includes steam generated from boiler feedwater, such that the superheated high-pressure steam at the first pressure level and the first temperature level is provided as high-purity superheated high-pressure steam.

9. The method according to any one of claims 1 to 8, wherein, The steam cracking unit, or at least one of the steam cracking units, is operated with different energy consumption rates in different operating modes while maintaining a constant total output of cracked products.

10. The method according to any one of claims 1 to 9, wherein, At least a portion of the feed hydrocarbons, and / or the process steam, and / or the boiler feedwater used to form the superheated mixture of feed hydrocarbons and process steam are preheated using saturated steam generated in one or more steam generators (30), which are operated in a manner thermally associated with the steam cracking unit.

11. The method according to any one of claims 1 to 10, wherein at least a portion of the feed hydrocarbons, and / or the process steam, and / or the boiler feedwater for forming the superheated mixture of feed hydrocarbons and process steam are preheated using a saturated or subcooled condensate stream.

12. A system (200) for performing a method of steam cracking, the system (200) comprising a steam cracking apparatus including an electric steam cracking furnace (210) without a convection zone (92) and a quenching and cooling unit (20), wherein the system (200) is adapted to allow the process gas flow to pass at least through the electric steam cracking furnace (210) and the quenching and cooling unit (20), characterized in that: The quenching and cooling unit (20) includes means for performing at least two different cooling steps arranged in any order, wherein a first cooling step is adapted to cool at least a portion of the process gas stream extracted from the electric steam cracking furnace (210) with vaporized boiler feedwater at an absolute pressure level between 30 bar and 175 bar, and wherein a second cooling step is adapted to use at least a portion of the process gas stream extracted from the electric steam cracking furnace (210) to cool a superheated mixture of feed hydrocarbons and process steam forming the process gas stream, the superheated mixture being heated to a temperature level between 350°C and 750°C.

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