Tubular reactor (steam cracker) with direct electrical heating

Abstract

Heater systems for performing chemical reactions include a housing containing a reaction coil having a plurality of inlet tubes, a manifold, and an outlet tube. Each inlet tube includes an inlet receiving a reactant mixture and an outlet discharging a heated reactant mixture. The manifold combines the heated reactant mixture discharged from each inlet tube, producing a combined heated mixture, and conveys the combined heated mixture to an outlet tube. The outlet tube receives the combined heated mixture from the manifold and conveys the heated mixture to a coil outlet. Circuitry configured for providing an electric current directly electrically heats a portion or an entirety of each of the inlet tubes. Further, the heater system includes indirect electrical heating elements, inductive heating, or fired heating configured to provide a heat flux to the inlet tubes and the outlet tube. Also disclosed are processes for conducting reactions using such heaters.

Description

TUBULAR REACTOR (STEAM CRACKER) WITH DIRECT ELECTRICAL HEATINGFIELD OF THE DISCLOSURE

[0001] Embodiments of the present disclosure generally relate to heaters for use in the cracking of hydrocarbons.BACKGROUND

[0002] In the refining and petrochemical industries, heaters are predominantly fuel fired. The current fired heaters generate carbon dioxide when combusting hydrocarbon fuels, which is a source of greenhouse gases that lead to global warming. Thus, there is a general desire to move away from hydrocarbon fuel-fired heaters.SUMMARY OF THE CLAIMED EMBODIMENTS

[0003] Embodiments herein are directed toward heaters that are used in for the cracking of hydrocarbons to produce olefins, such as ethylene, propylene, butenes, and butadienes. Such heaters may additionally be used to produce aromatics. The heaters used in embodiments herein are at least partially electrically heated, thus reducing the production of greenhouse gases associated with the production of the olefins or olefins and aromatics.

[0004] In one aspect, embodiments disclosed herein relate to a heater system for performing chemical reactions, such as steam cracking of hydrocarbons or steam reforming of hydrocarbons. The heater system includes an insulated housing containing a reaction coil. The reaction coil includes a plurality of inlet tubes each including an inlet for receiving a preheated reactant mixture and an outlet for discharging a heated reactant mixture. A manifold is provided to combine the heated reactant mixture discharged from each inlet tube, producing a combined heated mixture, and to convey the combined heated mixture to one or more outlet tubes, the one or more outlet tubes configured to receive the combined heated mixture from the manifold and convey the heated mixture to a coil outlet. Circuitry7configured for providing an electric current directly electrically heats a portion or an entirety of each of the inlet tubes.

[0005] The heater system of some embodiments further includes circuitry configured for providing an electric current to directly electrically heat a portion or an entirety of the one or more outlet tubes. In other embodiments, heat is provided by the directelectrical heating of the inlet tubes supplemented with heat provided by one or more of indirect electrical heating elements, inductive heating, or fired heating. In other embodiments, heat is provided by the direct electrical heating of the inlet tubes supplemented with heat provided by one or more of indirect electrical heating or fired heating of the inlet and outlet tube(s).

[0006] In another aspect, embodiments disclosed herein relate to processes for performing chemical reactions using the above-described heater systems.

[0007] In some embodiments, the process may be a process for thermally cracking hydrocarbons in a heater comprising a tubular reactor (coil) having a plurality of inlet tubes, a manifold, and an outlet tube. The process includes feeding a mixture of hydrocarbons and steam to each of the plurality of inlet tubes at a coil inlet temperature and heating the mixture of hydrocarbons and steam in each inlet tube from the coil inlet temperature to a second temperature, initiating a cracking reaction and producing a heated mixture. Heating of the mixture of hydrocarbons and steam in each inlet tube is conducted, in part or wholly, by providing an electric cunent to directly electrically heat at least a portion of each of the inlet tubes. The heated mixture from each inlet tube is then fed to the manifold, producing a combined heated mixture. In the manifold, the combined heated mixture is conveyed, while continuing the cracking reaction, through the manifold to the one or more outlet tubes. The combined heated mixture is conveyed, while continuing the cracking reaction, in the one or more outlet tubes to recover a cracked hydrocarbon-steam mixture at a coil outlet temperature. In some embodiments, heat for performing the cracking reactions is provided by the direct electrical heating of the inlet and outlet tubes. In other embodiments, heat for performing the cracking reactions is provided by the direct electrical heating of the inlet tubes supplemented with heat provided by one or more of indirect electrical heating elements, inductive heating, or fired heating. In other embodiments, heat is provided by the direct electrical heating of the inlet tubes supplemented with heat provided by one or more of indirect electrical heating or fired heating of the inlet and outlet tube(s).

[0008] Other aspects and advantages will be apparent from the following description and the appended claims.BRIEF DESCRIPTION OF DRAWINGS

[0009] Fig. 1 and IB illustrate heating systems useful in processes for the conversion of reactants, such as for the cracking of hydrocarbons, according to one or more embodiments disclosed herein.

[0010] Figs. 2-4 illustrate tubular reactors useful in heater systems according to embodiments herein.

[0011] Fig 5 illustrates a heater system useful in processes for conversion of reactants, such as the cracking of hydrocarbons, according to one or more embodiments disclosed herein.

[0012] Fig. 6 illustrates a system for cracking of hydrocarbons using heater systems according to one or more embodiments herein.DETAILED DESCRIPTION

[0013] Embodiments herein relate to heaters and heater arrangements configured for providing heat to one or more tubular reactors (process coils) used for the conversion of reactants to desired products. In particular aspects, embodiments herein relate to heaters and heater arrangements configured for providing heat to one or more process coils that are used to crack higher molecular weight hydrocarbons to form lower molecular weight hydrocarbons, including olefins such as ethylene, propylene, butenes, and butadienes, and other optional products such as aromatics. Embodiments herein further relate to processes for cracking hydrocarbons using such heaters and heater arrangements. The process coils are heated, at least in part, by direct electrical heating. Direct electrical heating refers to the direct resistive heating of the walls of the tubular reactor according to the “Joule effect” to provide at least a portion of the heat necessary to drive an endothermic reaction within the tubular reactor. The power of heating generated by an electrical resistor is proportional to the product of its resistance and the square of the cunent.

[0014] Process coils useful in embodiments herein may include serpentine coils, such as Short Residence Time (SRT) coils available from Lummus Technology LLC. As illustrated in Figures 1 and 2, a SRT coil may be disposed within an enclosure 6, which may be insulated and contain refractory along the floors, walls, and / or ceilings. The process coils may include a plurality of inlet tubes 10 (seven as illustrated in the Figures) and one or more outlet tubes 12. The reactant feed mixture 2 is distributed, such as through venturis (not illustrated), to each of the inlet tubes 10. The reactantmixture is then heated in each of the tubes 10, combined in a manifold 14, and then fed through a larger diameter outlet tube or tubes 12, producing a reaction effluent 4.

[0015] While illustrated in Figures 1 and 2 as a 7: 1 coil (seven inlet tubes connected to one outlet tube, any number of inlet tubes and outlet tubes may be used. For example, two or more inlet tubes, such as 2 to 16 inlet tubes, may be connected to a single outlet tube, such as a 4:1 arrangement, a 6:1 arrangement, an 8:1 arrangement, or a 12:1 arrangement, for example. Other examples of such coils include SRT-VII, which may include a 32:4 arrangement (32 inlet tubes and 4 outlet tubes). SRT II, SRT III, SRT IV, SRT V, and SRT VI, available from Lummus Technology LLC, have other exemplary coil arrangements that may be used according to embodiments herein.

[0016] In other embodiments, the arrangement of coils may include a multi-pass coil (not illustrated), which includes a plurality of inlet tubes, two to four of which may be connected via y-connectors (first manifold) or similar arrangements to a second pass tube, which are in turn connected via a second manifold to a single outlet tube. For example, a 4:2:1 coil has four inlet tubes, two of which are connected to each of two tubes, such as by Y-connectors of a two tube second pass, then to a single outlet tube. Other various arrangements of a multi-pass coil may also be used, and embodiments herein may include 2 to 12 passes.

[0017] Heating of process coils within the heater systems according to some embodiments herein is provided solely by direct electrical heating. Heating of process coils within the heater systems according to other embodiments herein is provided by multiple heating methods, and such multi-heat source heater systems may be considered as "hybrid" type heaters. Heating of process coils in the hybrid heaters is provided partially by direct electrical heating, in all embodiments, along with heating provided by one or more additional heat sources, including indirect electrical heating (inductive heating or radiant heating using an electrical resistance heating element, for example) or fired heating (radiant or radiant and convective) using conventional burners. In some embodiments, each of direct electrical, indirect electrical, and fired heating are used. Heating of the process coils, and thus heating of the reactants traversing therethrough, is provided at least in part by direct electrical heating in all embodiments.

[0018] In particular embodiments, the inlet tubes are heated by direct electrical heating.In some embodiments, the inlet tubes are heated solely by direct electrical heating. Insome embodiments, the inlet tubes are only partially heated by direct electrical heating, such as 5% to 49%, for example 20% to 30%, by direct electrical heating, with a majority' of the heat provided to the inlet tubes by indirect electrical heating or fired heating, or both. In other embodiments, the inlet tubes are heated primarily (greater than 50%) by direct electrical heating, with a portion of the heat provided by indirect electrical heating or fired heating, or both.

[0019] The indirect electrical heating and fired heating may be provided to different sections or zone of the process coils. For example, direct electrical heating of a first (e.g., upper) section of the inlet tubes and indirect electrical heating or fired heating of a second (e.g., lower) section or zone of the inlet tubes may be used. Similarly, heating of a first (e.g., upper) section of the one or more outlet tubes may be by a different method or combination of methods than a second (e.g., lower) section or zone of the one or more outlet tubes.

[0020] In some embodiments, the inlet tubes are isolated from the one or more outlet tubes, such as in different compartments within the heater. Preferably, the heating arrangements are configures such that the hybrid heating may supply heat to both the inlet and outlet tubes, thus simplifying heater design and permitting partial heating of the tubes, even those being heated by direct electrical heating, by indirect electrical and / or fired heating. Regardless of the design configuration being used, embodiments herein aim to provide a homogeneous heat input to each of the inlet tubes.

[0021] The outlet tube or outlet tubes, in some embodiments, are also heated by direct electrically heat. In other embodiments, the one or more outlet tubes may be heated by indirect electrical heating (inductive heating or radiant heating using an electrical resistance heating element, for example) or fired heating (radiant or radiant and convective) using conventional burners. Thus, heaters according to embodiments herein may include one or more of circuitry and control systems for directly electrically heating the inlet tubes, circuitry and control systems for directly electrically heating the outlet tubes, circuitry' and control systems for indirectly electrically heating the outlet tubes, circuitry and control systems for inductively heating the outlet tubes, and a fired heater and associated controls to indirectly heat at least the outlet tubes.

[0022] Where fired heating is used, the fired heating may include combustion of one or more of tail gas derived from reaction byproducts, hydrogen, natural gas, ethane,ammonia, light hydrocarbon fuel gas. Fired heating, when used, may be provided by floor burners, wall burners, or both floor burners and wall burners. Other fuels, such as ethane, propane, or other carbon based or hydrocarbon based fuels may also be used, but it is preferred to use fuels that produce no carbon oxides, such as hydrogen or ammonia, or fuels that produce limited carbon oxides, such as methane. In some embodiments, the fired heating is performed using an oxy-fuel combustion process, burning the fuel with essentially pure oxygen, no nitrogen, to enable direct recovery7and / or sequestration of any carbon oxides produced.

[0023] The circuitry for the direct electrical heating of the inlet tubes may be separate from the circuitry used for the direct electrical heating of the outlet tubes, as well as the circuitry used for the indirect electrical heating within the heater enclosure. The inlet tubes, for example, may be electrically isolated from the remainder of the process coil, including the manifold, the outlet tubes, as well as any upstream piping or process unit operations. Similarly, where direct electrical heating of the outlet tube(s) is used, the outlet tube(s) is(are) electrically isolated from the remainder of the process coil, including the manifold, the inlet tubes, as well as any downstream piping or process unit operations. Electrical isolation may be achieved, for example, by appropriate selection of the materials of construction of the inlet tubes, manifold, and outlet tubes, or in the mechanism / materials connecting the inlet tubes, manifold, and outlet tubes.

[0024] Upstream unit operations may include, for example, mixers configured to mix reactants (such as hydrocarbons and steam for cracking heaters), heaters used to preheat the reactants (such as hydrocarbons or hydrocarbon-steam mixtures) upstream of the inlet tube, as well as the distribution system (venturis) used to apportion the reactants (such as a hydrocarbon-steam mixture) to each of the inlet tubes. The upstream heaters may include, for example, heaters (direct electrical, indirect electrical, inductive) or heat exchangers (indirect thermal, such as convective coils disposed in a flue of the heater, or external heat exchangers not directly connected or forming part of the heater system). Downstream unit operations may include, for example, feed-effluent exchangers, transfer line exchangers, quench units, separation units, and other equipment used to recover heat from the process coil effluent and to separate the reaction effluent into various product and recycle fractions.

[0025] Referring again to Figure 1, a simplified diagram of a heater according to embodiments herein is illustrated. The feed mixture 2 is distributed through venturis (not illustrated) to each of the inlet tubes 10. The feed mixture is then heated in each of the tubes 10, combined in a manifold 14, and then fed through a larger diameter outlet tube 12 following which the reaction effluent is recovered via effluent outlet 4 and fed for downstream processing, such as to a transfer line exchanger (not illustrated).

[0026] As illustrated in Figure 1, the system includes circuitry 18 and a power supply system 20 for direct electrical heating of the inlet tubes 10. The power supply, and its associated control system (not illustrated) may be located externally to enclosure 6. The manifold 14 is electrically isolated from the inlet tubes 10. An inlet end 16 of each of the inlet tubes is electrically isolated from the rest of the coil and upstream piping, such as that associated with the distribution system. Although the circuitry may be configured in a number of ways, for instance parallel and series or in a delta or Wye type circuit, for simplicity only a single inlet tube circuit connection is shown on the diagram.

[0027] As also illustrated in Figure 1, the system may include circuitry 22 and a power supply system 24 for direct electrical heating of the outlet tubes. The power supply, and its associated control system (not illustrated) may be located externally to enclosure 6. When direct electrical heating of the outlet tube is used, manifold 14 is electrically isolated from the outlet tube 12. An outlet end 26 of the outlet tube is electrically insulated from the rest of the coil and downstream piping and unit operations.

[0028] As further illustrated in Figure 1, the system may include electrical heating elements 30, disposed within enclosure 6, for indirectly electrically heating the outlet tube, the inlet tubes, or both. The electrical heating elements are illustrated as vertically arranged, but may be arranged horizontally (Fig. 5) or in other manners so as to efficiently heat the outlet tube. Electrical heating elements may be disposed, as illustrated in Figs. 2 and 5, along an entire height of the process coil, or may be disposed along only a select section of the process coil, such as to heat an upper portion or a lower portion of the inlet tubes and outlet tube. The system may include circuitry and a power supply system 25 for providing power to the electrical heating elements 30. The power supply, and its associated control system (not illustrated) may be located externally to enclosure 6.

[0029] In operation, the reactant mixture (such as a hydrocarbon-steam mixture) is fed to the inlet tubes at an inlet temperature and passes downward, as represented by directional arrow 32. The reactant mixture (e.g., hydrocarbon-steam mixture) traversing the inlet tubes is provided a heat input QI as it is directly electrically heated from the first temperature to a second temperature, producing a heated mixture. In some embodiments, the heating of the inlet tubes may be sufficient to initiate reaction (e.g., a cracking reaction).

[0030] The heated mixture from each inlet tube is then fed to a common manifold 14, mixing the feeds received from each inlet tube, producing a combined heated mixture. As the combined heated mixture is conveyed through the manifold, an already initiated reaction may continue.

[0031] The combined heated mixture is then fed to and conveyed through outlet tube 12. The reactant mixture traversing the outlet tube is provided additional heat inputs (Q2, Q3). facilitating the continued reaction and producing a reaction effluent 4 (e.g., a cracked hydrocarbon-steam mixture) recovered from outlet end 26 at a coil outlet temperature. In embodiments where direct electrical heating of the outlet tube is used, the outlet tube is provided a heat input Q2 as it is directly electrically heated. The optional indirect electrical heat input is also illustrated as Q3, which may supply heat to both the outlet tube and inlet tubes. Fired heaters may optionally be used, as noted above, and are illustrated in Figure IB, where the fired heaters may include one or more floor burners 27, one or more wall burners 29, or both floor and wall burners.

[0032] Referring now to Figure 2, embodiments herein may include separate direct electrical heating of the inlet and outlet tubes. In such embodiments, the inlet tubes 10 may include an adiabatic inlet end 16 that is electrically isolated from upstream equipment (not illustrated) and the rest of the coil. Inlet tubes 10 also include an outlet end 40 that is electrically isolated from manifold 14. The outlet tubes may similarly include an inlet end 42 that is electrically isolated from manifold 14 and an outlet end 26 that is electrically isolated from downstream equipment (not illustrated) and the rest of the coil.

[0033] As illustrated in Figure 2, electrical isolation of the manifold, without any additional external heat inputs, results in an essentially adiabatic manifold (someconductive heat may be transferred from the inlet and outlet tubes, convective heat from the surrounding atmosphere, as well as radiation from the surrounding environment). In some embodiments, the manifold may be disposed within a trough or other structure within the enclosure so as to minimize the radiant and convective heat to which the trough is exposed. The reactant mixture may thus be conveyed through the manifold essentially adiabatically, and any reaction occurring within the manifold may be considered an adiabatic reaction as the reaction mixture passes from the inlet tubes through the manifold to the outlet tubes. Depending upon the extent of the radiant, convective, and conductive heat to which the manifold is exposed, an endothermic reaction, while consuming heat, may not result in any appreciable decrease in temperature along the adiabatic manifold.

[0034] Where a multi-pass coil is used, such as where a 4:2:1 coil is used, the second pass may be heated by direct electrical heat, indirect electrical heat, or fired heating. Where direct electrical heating is used, the manifolding between passes is electrically isolated and essentially adiabatic, as described above.

[0035] In various embodiments, for example, the heater system may be used to crack a hydrocarbon to form ethylene, propylene, butenes, and butadienes, among other products. The hydrocarbon-steam mixture is introduced to the inlet tubes at a first temperature in a range from 500°C to 700°C. The hydrocarbon-steam mixture is then directly electrically heated in the inlet tubes to a second temperature, such as in a range from 700°C to 1150°C, initiating a cracking reaction. The hydrocarbon-steam mixture recovered from the inlet tubes at the second temperature then passes through the manifold and is introduced to one or more outlet tubes at a third temperature. The third temperature is in a range from 650°C to 1150°C, for example. The combined heated mixture introduced to the one or more outlet tubes at the third temperature is then heated within the outlet tube(s) to continue the cracking reaction and the cracked hydrocarbon- steam mixture is recovered from the one or more outlet tubes at a coil outlet temperature in a range from 750°C to 1150°C.

[0036] A majority of the heat input to the system is provided by the heating of the inlet tubes, at least a portion of which is provided by direct electrical heating. For example, in some embodiments, a heat input to the plurality of inlet tubes is 50% to 90% of a total heat input to the plurality of inlet tubes and the outlet tube(s). In otherembodiments, a heat input to the plurality of inlet tubes is 60% to 88% of a total heat input to the plurality of inlet tubes and the outlet tube(s). In yet other embodiments, a heat input to the plurality of inlet tubes is 65% to 86% of a total heat input to the plurality of inlet tubes and the outlet tube(s).

[0037] Front loading the heat flux toward the inlet tubes, facilitated by using the direct electrical heating, while maintaining the total heat input to the coil required for the desired reaction may provide an ethylene yield advantage. It has been found that a heat input of 50% to inlet tubes and 50% to outlet tubes would produce less ethylene than 70% heat input to inlet tubes and 30% heat input to the outlet tubes. With a higher heat flux to the inlet tubes, ethylene yield increases, and severity is reduced along the entire coil. Further, while reaction heat (endothermic) increases, coil outlet temperature may decrease. Further, the maximum tube metal temperature may shift from the top section of the outlet tube (typical for fired heaters) to a lower section of the inlet tubes. While adjusting the heat inputs in this manner increases ethylene production, too much heat input to the inlet tubes may result in coking, which may increase pressure drop, which may reduce yield or run length) or increasing the required tube metal temperature to provide the desired extent of conversion, which may also reduce run length and further promote coking. Thus, it has been found that a balance in the distribution of heat input to the inlet tubes and heat input to the outlet tubes provides advantages in both ethylene yield and run length.

[0038] Embodiments herein include direct electrical heating of the inlet tubes. Such direct electrical heating of the inlet tubes may be supplemented by one or more of inductive heating, indirect electrical heating, and fired heating of the inlet tubes. When hybrid heating of the inlet tubes is used, direct electrical heating may provide 10% to 90% of a total heat input to the plurality of inlet tubes. In various embodiments, direct electrical heating may provide from a lower limit of 20%, 30%, 40% or 50% to an upper limit of 30%, 50%, 65%, or 80% of the total heat input to the plurality of inlet tubes, where any lower limit may be combined with any upper limit.

[0039] In some embodiments, only a section or sections of an inlet tube may be heated by direct electrical heating. The inlet tubes 10 may include a first section that is heated by supplemented direct electrical heating and a second section that is not heated by direct electrical heating. For example, as illustrated in Fig. 3, relative to an inlet end 16of inlet tubes 10 may include a proximal section 1 OP and a distal section 1 OD. In some embodiments, proximal section 10P of each inlet tube is heated by supplemented direct electrical heating while distal section 10D is heated by indirect electrical or fired heating, for example. In other embodiments, distal section 10D of each inlet tube is heated by supplemented direct electrical heating while proximal section 10P is heated by indirect electrical or fired heating.

[0040] Depending upon the type and arrangement of supplemental heat, a total heat input to a proximal section of each inlet tube is less than a total heat input to a distal section of each inlet tube in some embodiments. In other embodiments, a total heat input to a proximal section of each inlet tube is greater than a total heat input to a distal section of each inlet tube.

[0041] In some embodiments, both proximal section 10P and distal section 10D may be heated by supplemented direct electrical heating, each section being electrically isolated and including circuitry for providing an electric current for direct electrical heating. The proximal section and distal section may be on separate circuits thereby allowing individual control of the heat flux along the inlet tubes.

[0042] To effect the desired isolation of the proximal and distal sections, or to provide for the desired heating profile along the length of the inlet tubes, proximal section 10P may be made from a different material of construction, where the metal, ceramic, or alloy used to make the tube or tube section differs in one or more of electrical properties, magnetic properties, or thermal properties. For example, a high chrome alloy may provide for different electrical resistance than a low chrome alloy. Electrical isolation of the manifold may similarly be provided by proper selection of the material of construction, such as by using a low conductive alloy or an electrically insulating material.

[0043] In addition to material of construction, the proximal and distal sections may vary in design. For example, as illustrated in Fig. 4, inlet tube proximal section 10P may include tubes having a wall thickness that is greater than a wall thickness of tubes in distal section 10D. The tubes may have a similar outer diameter, differing in inner diameter, for example. The metal thickness differences may be used to provide a difference in total resistance along the length of the tube, thereby impacting the effectiveness in any circuit used for direct electrical heating of the respective sections.

[0044] Similarly, as illustrated in Figs. 3 and 4, the outlet tube may be divided into sections to implement a desired heating profile. Relative to an inlet end 42 of the outlet tube, the outlet tube 12 may include a proximal section 12P and a distal section 12D. As with the inlet tubes, proximal and distal sections 12P and 12D of the outlet tube may vary in dimension (length, inner diameter, etc.) as well as material of constructions (high conductivity, low conductivity, etc.), to implement the desired heat transfer profile and the required circuitry or electrical isolation.

[0045] While Figs. 3 and 4 are illustrated and described with respect to two inlet sections and two outlet sections, proximal and distal, embodiments having three or more sections, such as three to 6 sections, are contemplated.

[0046] Referring again to Fig. 5, embodiments herein may include a plurality of electric heating elements 30, which may be arranged within the enclosure horizontally or vertically. The circuitry associated with the plurality of heating elements may be divided, for example, into unit cells 50, or blocks, of two to thirty- electrical heating elements. In this manner, the power supply may be of a commercially feasible size, and more importantly, the unit cells may be individually controllable such that the heat input across the height and / or width of the heater system provided by the electrical heating elements may be tailored to provide a desired heating profile of the inlet and outlet tubes. Although the circuitry may be configured in a number of ways, for instance parallel and series or in a delta or Wye type circuit, for simplicity only a couple circuit connection are shown connecting power supply 25 to the multiple electrical heating elements on the diagram.

[0047] Tailoring of the heating profile may be further effected by the type and amount of heating provided along a length of the process coil. Control systems are used to control or vary the power provided to different sections of the heater, such as the indirect electric heating elements or the direct electrical heating circuits of embodiments herein. Control systems may also be provided to control or vary the heat input (firing rate) of any fired heaters used in the heater system. Overall, control circuits may be provided and configured for controlling one or more of: a power (current) provided to each of the inlet tubes or sections thereof for direct electrical heating; a power (current) provided to the outlet tube(s) or sections thereof for direct electrical heating; an amount and location of heat flux provided by direct electrical heating; anamount and location of heat flux provided by indirect electrical heating; an amount and location of heat flux provided by inductive heating; an amount and location of heat flux provided by fired heating; and amount of heat flux provided to the outlet tube(s) relative to a total heat flux provided to the inlet tubes.

[0048] An exemplary’ control scheme may include a power controller used to control a power for direct electrical heating of one or more coils, and a controller to control firing of one or more burners within the heater. The controller for the direct electrical heating may be fully decoupled from the controller used to control firing of the burners, so as to effect individual control, while a main control system may be used to determine inputs to the respective control systems so as to effect the desired heating profile.

[0049] The power going to different sections / zones within the heater and the coils need not be equal and can vary vertically or horizontally. For example, a top section of the cracking coil may be at higher temp or higher heat flux as compared to the lower section.

[0050] The distribution between the direct and indirect electrical heating (percentage wise) as well as any fired heating, may be based on application requirements, such as to obtain a desired heating profile for a given reactant feed (e.g., cracking of heavy vs. medium or light hydrocarbons). The distribution of heating may also be determined based on external requirements, such as price or availability of an energy' source (e.g., renew able energy sources used may have a lower price or a higher availability at a given time of day).

[0051] Referring now to Fig. 6, a system for cracking hydrocarbons using heater systems according to embodiments herein is illustrated. A preheated hydrocarbon- steam stream 60 is further heated in a feed-effluent exchanger 62 (secondary transfer line exchanger 62) and then fed to a feed preheater 64, a heater system 66 (such as described in one or more of Figs. 1-5). and a quench system 68. The preheated hydrocarbon-steam mixture 60 may be heated from an inlet temperature in a range from 200°C to about 350°C to a temperature in a range from 550°C to 650°C, for example, forming a heated feed stream 70. The heated feed stream 70 may then be further heated in feed preheater 64. which may be an electric heater (direct, indirect, or inductive), producing a reactor feed stream 72 that me be fed to a reaction coil of a heater system 66 as described in Figs. 1-5. The reactor effluent 74 recovered from the coil outlettube(s) is then quenched in quench system 68 from the coil outlet temperature, such as a temperature from 750°C to 1100°C, to a temperature of less than about 700°C to stop the cracking reaction. The quenched reactor effluent 76 may then be fed to the secondary’ transfer line exchanger to recover additional heat, cooling the reaction effluent to a temperature in a range from about 250°C to about 400°C, recovering a cracked gas stream 78 that may be forwarded to downstream heat and product recovery systems.

[0052] Preheater 64, heater system 66, and quench unit 68 may be considered a “unit cell” 80, and cracking complexes according to embodiments herein may include multiple unit cells 80. In some embodiments, multiple unit cells 80 may be fluidly connected to a lesser number of secondary transfer heat exchanger(s), thereby producing a single, or a few, cracked effluents that may be fed to dow nstream product recovery units.

[0053] As described above, embodiments herein provide heater systems that include direct electrical heating of process coils. In some embodiments, the direct electrical heating of the inlet tubes of the process coils may provide an advantageous yield of ethylene. The use of direct electrical heating, or a combination of direct and indirect electrical heating according to embodiments herein may reduce or even eliminate the production of carbon dioxides commonly associated with commercial cracking furnaces. In embodiments where fuel-fired burners are used, carbon-free fuels like hydrogen (H2) or ammonia (NH3) can be used, and there will not be any greenhouse gas emissions from the flue gas stack.

[0054] Unless defined otherwise, all technical and scientific terms used have the same meaning as commonly understood by one of ordinary skill in the art to which these systems, apparatuses, methods, processes and compositions belong.

[0055] The singular forms “a,” “an,” and “the” include plural referents, unless the context clearly dictates otherwise.

[0056] As used here and in the appended claims, the words “comprise,” “has,” and “include” and all grammatical variations thereof are each intended to have an open, non-limiting meaning that does not exclude additional elements or steps.

[0057] '‘Optionally” means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0058] When the word “approximately” or “about” are used, this term may mean that there can be a variance in value of up to ±10%, of up to 5%, of up to 2%. of up to 1%, of up to 0.5%, of up to 0.1%, or up to 0.01%.

[0059] Ranges may be expressed as from about one particular value to about another particular value, inclusive. When such a range is expressed, it is to be understood that another embodiment is from the one particular value to the other particular value, along with all particular values and combinations thereof within the range.

[0060] While the disclosure includes a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the present disclosure. Accordingly, the scope should be limited only by the attached claims.

Claims

1. CLAIMSWhat is claimed as new and desired to be protected by Letters Patent is:

1. A process for thermally cracking hydrocarbons in a heater comprising a reaction coil having a plurality of inlet tubes, a manifold, and one or more outlet tubes, the process comprising:feeding a preheated mixture of hydrocarbons and steam to each of the plurality of inlet tubes at a coil inlet temperature;heating the mixture of hydrocarbons and steam in each inlet tube from the coil inlet temperature to a second temperature, initiating a cracking reaction and producing a heated mixture, wherein the heating of the mixture of hydrocarbons and steam in each inlet tube comprises, in part or wholly, providing an electric current to directly electrically heat at least a portion of each of the inlet tubes; feeding the heated mixture from each inlet tube to the manifold, producing a combined heated mixture;conveying the combined heated mixture, while continuing the cracking reaction, through the manifold to the one or more outlet tubes;heating the combined heated mixture, while continuing the cracking reaction, in the one or more outlet tubes to recover a cracked hydrocarbon-steam mixture at a coil outlet temperature.

2. The process of claim 1, wherein the combined heated mixture is conveyed essentially adiabatically through the manifold.

3. The process of claim 1, wherein heating of the combined heated mixture in the one or more outlet tubes comprises one or more of direct electrical heating and inductive heating4. The process of claim 1, wherein supplemental heating of the inlet tubes and heating of the combined heated mixture in the one or more outlet tubes comprises one or more of indirect electrical heating and fired heating.

5. The process of claim 3, when fired heating is used, the fired heating comprising combustion of one or more of tail gas derived from reaction byproducts, hydrogen, natural gas, ethane, ammonia, light hydrocarbon fuel gas.

6. The process of claim 5, wherein the fired heating comprises an oxy-fuel combustion process.

7. The process of claim 1, further comprising partially heating each inlet tube by one or more of indirect electrical heating and fired heating.

8. The process of claim 7, wherein, relative to an inlet end of the inlet tube, a proximal section of each inlet tube is heated by direct electrical heating.

9. The process of claim 7, wherein, relative to an inlet end of the inlet tube, a distal section of each inlet tube is heated by direct electrical heating.

10. The process of claim 7, wherein, relative to an inlet end of the inlet tube, a total heat input to a proximal section of each inlet tube is less than a total heat input to a distal section of each inlet tube.

11. The process of claim 7, wherein, relative to an inlet end of the inlet tube, a total heat input to a proximal section of each inlet tube is greater than a total heat input to a distal section of each inlet tube.

12. The process of claim 7, wherein the direct electrical heating provides 10% to 90% of a total heat input to the plurality of inlet tubes.

13. The process of claim 7, wherein the direct electrical heating provides 50% to 80% of a total heat input to the plurality of inlet tubes.

14. The process of claim 7, further comprising controlling an amount of direct electrical heating based on one or more of a time of day, cost of electricity relative tocost of fuel, hydrocarbon feed composition, and desired ethylene yield.

15. The process of claim 1, wherein a heat input to the plurality of inlet tubes is 50% to 90% of a total heat input to the plurality of inlet tubes and the one or more outlet tubes.

16. The process of claim 1, wherein a heat input to the plurality of inlet tubes is 60% to 88% of a total heat input to the plurality of inlet tubes and the one or more outlet tubes.

17. The process of claim 1, wherein a heat input to the plurality of inlet tubes is 65% to 86% of a total heat input to the plurality of inlet tubes and the one or more outlet tubes.

18. The process of claim 1, wherein:the coil inlet temperature is in a range from 500°C to 700°C;the coil outlet temperature is in a range from 700°C to 1150°C.

19. A heater system for performing chemical reactions, such as steam cracking of hydrocarbons or steam reforming of hydrocarbons, the heater system comprising: an insulated housing containing a reaction coil, the reaction coil comprising: a plurality of inlet tubes each including an inlet for receiving a reactant mixture and an outlet for discharging a heated reactant mixture;a manifold configured to combine the heated reactant mixture discharged from each inlet tube, produce a combined heated mixture and to convey the combined heated mixture to one or more outlet tubes;the one or more outlet tubes configured to receive the combined heated mixture from the manifold and convey the heated mixture to a coil outlet;circuitry configured for providing an electric current to directly electrically heat a portion or an entirety of each of the inlet tubes;a heater configured to provide a heat flux to one or more outlet tubes.

20. The heater system of claim 18, wherein the manifold is electrically isolated from each of the inlet tubes, the one or more outlet tubes, or both of each of the one or more outlet tubes and each of the inlet tubes.

21. The heater system of claim 18, wherein the heater is configured to provide a heat flux to the one or more outlet tubes and a heat flux to each of the inlet tubes.

22. The heater system of claim 18, wherein the heater comprises one or more of the following disposed within the housing:circuitry to directly electrically heat a portion or an entirely of the one or more outlet tubes;circuitry to inductively heat a portion or an entirety of the one or more outlet tubes; a fired heater to indirectly heat the outlet tube, each of the inlet tubes, or both of the one or more outlet tubes and each of the inlet tubes; andelectrical heating elements to indirectly heat the outlet tube, each of the inlet tubes, or both the outlet tube and each of the inlet tubes.

23. The heater system of claim 18, further comprising a preheater or a series of preheaters configured to directly or indirectly heat the reactant mixture or a portion thereof.

24. The heater system of claim 18, wherein, relative to an inlet end of the inlet tube, an inner diameter of a proximal end of each inlet tube is less than an inner diameter of a distal end of each inlet tube.

25. The heater system of claim 18, wherein, relative to an inlet end of the inlet tube, a material of construction of a proximal end of each inlet tube is different than a material of construction of a distal end of each inlet tube.

26. The heater system of claim 18, whereina material of construction of each of the inlet tubes is different than a material of construction of the manifold;a material of construction of each of the inlet tubes is different than a material of construction of the outlet tube; and / ora material of construction of the manifold is different than a material of construction of the one or more outlet tubes.

27. The heater system of claim 18, further comprising a power source, disposed outside the enclosure, for the electric current to the circuitry.

28. The heater system of claim 21, further comprising one or more control circuits configured for controlling one or more of:a power (current) provided to each of the inlet tubes for direct electrical heating; a power provided to different portions of each of the inlet tubes for direct electrical heating;an amount of heat flux provided by the direct electrical heating;an amount of heat flux provided by the heater;an amount of heat flux provided to the one or more outlet tubes relative to a total heat flux provided to the inlet tubes;an amount of heat flux provided to different portions of each of the inlet tubes; an amount of heat flux provided to different portions of the one or more outlet tubes.

29. The heater system of claim 18, wherein the heater comprises a plurality' of electric heating elements, and wherein the plurality' of electric heating elements are provided as individually controllable heating blocks or units comprising two to thirty electrical heating element circuits.

30. The heater system of claim 18, wherein the inlet tubes have a smaller inner diameter than the inner diameter of the outlet tubes.

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