Electric furnace to produce olefins

Abstract

To provide a reactor for decomposing a hydrocarbon feed and a method of thermally cracking the hydrocarbon feed.SOLUTION: A method of thermally cracking a hydrocarbon feed (105) includes feeding the hydrocarbon feed (105) into at least one coil (130) in a reaction section (112) of an electric heater (110), using electrical energy to heat the hydrocarbon feed (105) in the electric heater (110) to a reaction temperature, and directing a reaction output from the electric heater (110) to at least one exchanger (150) to cool the reaction output.SELECTED DRAWING: Figure 1

Description

Background Art

[0001] Furnaces used in thermal decomposition are generally fired heaters that use high-temperature combustion gases (flue gases) or gaseous and liquid fuels to generate heat and supply reaction duty. The heat raises the temperature of the fluid flowing through coils configured inside the fired heater. The thermal cracking reaction occurs in the radiant section of the fired heater. These are highly endothermic reactions, and heat is applied to sustain the reaction. Generally, 30% to 50% of the combustion duty is used to carry out the reaction in the radiant section of the heater. The remaining duty in the flue gas is recovered in the convection section of the heater and can be used to preheat the feed and / or for steam generation.

Summary of the Invention

Means for Solving the Problems

[0002] In one aspect, embodiments of the present disclosure relate to a reactor for decomposing a hydrocarbon feed, comprising a heater chamber defining a reaction section of an electric heater, a plurality of electric heating elements disposed around the heater chamber, the electric heating elements being operated by electricity, at least one coil extending from a feed inlet through the reaction section, and a primary exchanger having an inlet fluidly connected to the at least one coil and an effluent outlet.

[0003] In another aspect, embodiments of the present disclosure relate to a method for thermally decomposing a hydrocarbon feed, comprising supplying the hydrocarbon feed into at least one coil in a reaction section of an electric heater, using electrical energy to heat the hydrocarbon feed in the electric heater to a reaction temperature, and directing the reaction output from the electric heater to at least one exchanger to cool the reaction output.

[0004] In another aspect, embodiments of the present disclosure relate to a method of designing a pyrolysis plant comprising an electric heater for pyrolyzing a feed and a recovery section, determining the amount of steam generated and the amount of steam consumed by the pyrolysis plant, determining the amount of power used by the pyrolysis plant to pyrolyze the feed, and adjusting at least one parameter of the pyrolysis plant to reduce the amount of power used by the pyrolysis plant.

[0005] The configuration diagrams shown in the attached sketches can be slightly modified for specific crude oils, hydrocarbon feeds, and product slates. Other aspects and advantages will become apparent from the following description and the appended claims.

Brief Description of the Drawings

[0006]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0007] Embodiments disclosed herein generally relate to the decomposition of hydrocarbons to produce light olefins such as ethylene and propylene using an electric heater to heat a hydrocarbon feed to a reaction temperature. The electric heater may also be referred to as an electric furnace. Hydrocarbon feeds useful in the embodiments herein can be obtained from light hydrocarbons (ethane, propane, butane) and hydrocarbons in the naphtha range (C5 - C12) to heavier hydrocarbon gases and mixtures thereof, including whole crude oil.

[0008] The thermal decomposition of hydrocarbons is generally used to produce light olefins. For example, when ethane is decomposed, it mainly produces ethylene. When naphtha is decomposed, it can produce ethylene, propylene, butene, butadiene, and benzene as useful products. The thermal decomposition reaction is highly endothermic, and heat is supplied to sustain the reaction. To obtain a substantial feed conversion, the reactor temperature is preferably above 700 °C and can exceed, for example, 800 °C.

[0009] In some cracking processes, a catalyst can be employed to lower the operating temperature, but as a result, the ethylene yield can be lower than that of thermal decomposition. The heat of reaction in the case of thermal decomposition and catalytic cracking per unit weight of the olefins produced is approximately the same, but the combustion duty in the case of thermal decomposition is extremely high. To sufficiently heat the feed (for example, to a temperature higher than 800 °C) for ethylene production, a higher proportion of sensible heat (the energy required to change the temperature of a substance without a phase change) to the reaction duty can be used. The sensible heat can be recovered by exchanging it with other process fluids, and thus, the ethylene heater can be designed to efficiently preheat the feed and generate additional steam. When using the electric heater according to the present disclosure, since there is no flue gas containing high thermal energy, the electric heater can be designed to preheat the feed and carry out the reaction, or other more efficient methods of preheating the feed can be used.

[0010] The cracking reaction can produce a small amount of coke as a by-product, and the coke can accumulate and deposit in the reactor. To minimize coke deposition and improve olefin production, steam can be added to the hydrocarbon feed and decomposed.

[0011] In a combustion heater, a feed mixture (hydrocarbon and dilution steam (DS)) is typically preheated in the convection section of the combustion heater, enters the radiation section of the heater, where the reaction occurs. Since these are high-temperature reactions, high-temperature flue gas is generated from the reactions in the combustion heater. Generally, only 30 - 50% of the combustion duty from the combustion heater goes to the reaction section, and the remaining amount of the combustion duty can exit the radiation section as flue gas. The energy in the flue gas can be recovered in the convection section of the combustion heater, which may include coils suitably configured therein to recover heat from the flue gas. In the convection section of the combustion heater, the feed and dilution steam are preheated and can be superheated to a desired temperature before entering the radiation section. Even after heating the feed mixture surplus, thermal energy is present in the flue gas. If this energy is not recovered, the energy is wasted and the cost of olefin production goes up. In contrast, when using an electric heater according to an embodiment of the present disclosure, 90 - 98% of the electrical energy used by the electric heater can go to the reactions in the reaction section of the heater. Thus, the electric heaters disclosed herein can generate only enough energy for the reactions and little or no excess heat is generated. Since little or no excess heat is generated, the electric heaters disclosed herein may not have a convection section.

[0012] To preserve the olefins formed in the reactor, the reaction output (also called the effluent) can be rapidly quenched. Older quenching methods used the injection of oil or water at the reactor outlet. More recently, quenching methods have come to use indirect cooling. In some methods, the effluent can be cooled by generating high-pressure (or ultra-high-pressure) steam before sending the effluent to the recovery section. This high-pressure steam was traditionally superheated in the convection section of the combustion heater. However, when using an electric heater according to an embodiment of the present disclosure that does not have a convection section, the steam can be generated in other parts of the process (e.g., in an exchanger or in the recovery section where the effluent is cooled, such as using a secondary electric heater).

[0013] According to embodiments of the present disclosure, a reactor for decomposing a hydrocarbon feed may include an electric heater and at least one exchanger that can be used to cool the reaction output from the electric heater and / or preheat the feed entering the electric heater. The electric heater may include a heater chamber that defines a reaction section of the heater, a plurality of electric heating elements disposed around the heater chamber, where the electric heating elements are operated by electricity, and a plurality of coils extending from a feed inlet of the reaction section to an outlet of the reaction section. In some embodiments, a primary exchanger may be used to first cool the reaction output from the electric heater, and the primary exchanger may have an inlet fluidly connected to the plurality of coils and an effluent outlet. In some embodiments, a secondary exchanger may be used to further cool the primary exchanger effluent, and the secondary exchanger may have an inlet fluidly connected to the effluent outlet of the primary exchanger. In some embodiments, a tertiary exchanger may be used to further cool the secondary exchanger effluent, and the tertiary exchanger may have an inlet fluidly connected to the effluent outlet of the secondary exchanger.

[0014] The exchanger may further include a vapor outlet and / or a vapor flow path that can direct the heated vapor to one or more areas of the reactor and / or to a preheat section. For example, the heated vapor from the exchanger may be directed towards the feed inlet of the electric heater to preheat the feed before entering the electric heater. The preheat section may be provided separately from the reaction section of the electric heater or may be provided together with the reaction section as a single unit. For example, the preheat section of the reactor may be downstream of the feed inlet of the electric heater and spaced apart from the reaction section. In some embodiments, the preheat section may include one or more exchangers. The feed inlet to the electric heater may be fluidly connected to a plurality of feed sources.

[0015] According to embodiments of the present disclosure, the main reaction section of an electric heater may have different configurations of one or more coils extending through the reaction section of the electric heater. The coils may be heated by different heating elements in a single electric heater, or the coils in the reaction section may be heated using a single heating element in the electric heater. Both preheat and reaction heat may be supplied by a single electric heater.

[0016] FIG. 1 shows an example of a reactor 100 using an electric heater 110 according to an embodiment of the present disclosure. The electric heater 110 includes a main reaction section of the reactor, where a hydrocarbon feed 105 can be heated to a reaction temperature to decompose the hydrocarbon feed. The hydrocarbon feed 105 can be heated by a secondary exchanger 160, pass through a flow path 120, and flow to one or more coils 130 extending through the reaction section 112 of the electric heater 110. The reactor 100 may not include a convection section (such as found in a combustion heater), but instead may include a flow path 120 fluidly connected to coils 130 disposed in the electric heater 110 (for supplying one or more feeds to the electric heater) and one or more electric heating elements 140 disposed around the coils 130 in the electric heater 110. The reactor 100 may further include feed exchangers (such as a primary exchanger 150 and a secondary exchanger 160) and a common flow path (such as through a header) from the feed exchangers for supplying feeds to various coils in the reaction section 112 of the reactor 100. Thus, in contrast to a combustion heater, the electric heater 110 may not include a convection section. Instead, the feed exchangers and the common flow path (such as a header) may direct the feed to the coils 130.

[0017] A reactor using the electric heater 110 according to an embodiment of the present disclosure may utilize a coil concept to decompose a feed passing through the coil 130. In the illustrated embodiment, four radiant coils 131, 132, 133, 134 (collectively referred to as 130) may be configured in the electric heater 110 to extend through the reaction section 112 of the electric heater 110. However, more or fewer than four coils may be configured to extend through the reaction section of the electric heater 110. The reaction section 112 of the electric heater 110 may have one or more electric heating elements 140 disposed around a wall forming the reaction chamber of the electric heater 110, and the heating element 140 may be directed to heat the reaction section 112. When the feed is flowed through the coil 130, the electric heating element 140 around the coil 130 may be used to heat the feed flowing through the coil 130 to the decomposition reaction temperature.

[0018] According to an embodiment of the present disclosure, each coil 130 may be controlled independently, including the amount of feed flowing through the coil, if any, and the temperature of the coil. For example, if a radiant coil 130 is connected to different feed manifolds, that coil 130 can decompose the fluid-connected feeds as each feed flows through the coil 130. By providing a reaction section of the reactor 100 that can receive multiple feeds, equipment for the decomposition process can be compressed (e.g., multiple feeds can be directed to a single electric heater 110 instead of using multiple heaters for multiple feeds), which can save plot space in the overall plant design.

[0019] The amount of feed to the coil 130 can be controlled via the control valve 122. In embodiments where two or more different feeds are fluidly connected to the coil 130, the control valve 122 disposed along the flow path 120 from the feed source to the coil 130 can be controlled to allow the amount of feed to flow through the coil 130. Further, a flow rate venturi 124 can be associated with each coil to provide flow rate control of the feed flowing into the coil 130. The feed can be heated to the reaction temperature in order to decompose the feed using the heat electrically provided from the electrical heating element 140 in the electric heater 110 as it flows through the coil 130. For example, the same coils (e.g., 131, 132, 133, or 134) provided in the electric heater 110 according to embodiments of the present disclosure can be used to decompose ethane in one run and naphtha in another run, or in another case, the coil can be in a decoking mode. Thus, by using the coil concept where the feed is flowed through a coil disposed inside the reaction section 112 of the reactor 100 to decompose the feed, the specific processing conditions for each coil can be controlled to decompose regardless of which feed is flowing through the coil.

[0020] One or more additional flow paths 121 and valves 123 (e.g., isolation valves or diverter valves) are fluidly connected to the flow path 120 and can be used to direct steam, or a mixture of steam and air, through the coil 130 for decoking of the radiation coil (periodically removing coke deposits on the inner surface of the radiant tubes). For decoking purposes, components in the electric heater can be configured similarly to like components in a conventional combustion heater, with the exception that instead of using flame heating, the electric heater can use one or more electric heating elements. By configuring components such as coils in the electric heater in a similar manner to like components in the combustion heater, a transfer line valve can be installed to separate the decoking effluent from the cracker effluent. Further, a high-temperature isolation valve can be used for a simpler decoking procedure (e.g., an isolation valve can be used to isolate one or more coils for decoking). When a high-temperature isolation valve is not used, the effluent can be cooled sufficiently such that the coil and exchanger can be decoked by steam only. When steam or air is used for decoking, a high-temperature isolation valve can be used to divert the effluent to a decoke drum. The decoking effluent can also be directed to the recovery section of the reactor along with the cracker effluent.

[0021] The electric heater 100 may include one or more heating elements 140 distributed around the coil 130 such that the electric heating is evenly distributed around the coil 130 in the reaction section 112. In contrast to the electric heater 110, the burner in a combustion heater releases intense heat into a small volume (flame shape). Thus, in a combustion heater, the coil surface facing the burner can reach extremely high temperatures, while the coil surface perpendicular to the burner can reach relatively very low temperatures at a given length of the heater. The temperature gradient formed by the directional radiation of heat in a combustion heater from the flame is sometimes referred to as the shadow effect. Due to the shadow effect, the peak temperature in a combustion heater can be different from the average temperature. In such a scenario, the combustion heater tube design can be defined by the peak temperature. For example, the refractory bricks used to form the combustion heater are designed to withstand the higher peak temperatures in the heater. Further, since the heat from the flame is transferred by conduction, the conductivity is designed to be high to transfer the heat more quickly.

[0022] In the electric heaters of the present disclosure, the electric heating is controlled at a constant heat flux and can be directed to all sides of the coil (e.g., around the entire circumference of the coil). Further, in the case of a combustion heater, it is difficult to control the heat input to any section of the coil (e.g., the lower 20% of the coil or the upper 20% of the coil), but the electric heating according to embodiments of the present disclosure can include segmenting the heater such that the heating elements heat multiple different sections of the coil so that the entire tube can be evenly heated. In some embodiments, a control system can be used to control the temperature of individual coils and / or individual segments of individual coils to provide a specific heating profile of the coil for a particular decomposition process. By using the electric heaters according to embodiments of the present disclosure, a more controlled and even heating profile can be provided to the coils in the heater, thereby significantly improving the heat transfer performance, reducing the peak tube temperature, and improving the selectivity to olefins.

[0023] Figure 4 shows a graphical comparison of the heating performance with respect to the coil metal temperature when heated by a combustion heater (from a burner) and when heated by a constant heat flux from an electric heater. As shown in Figure 4, when using electric heating, the radial temperature gradient can be minimized (since there is no difference between the peak temperature and the average temperature), and thus a lower heating temperature can be used to reach the desired metal temperature.

[0024] Furthermore, since the amount of heat to a single coil or group of coils can be supplied by individual heating elements 140, the amount of heat can be individually controlled in the electric heater 110. In a conventional combustion heater, the entire firebox is heated from a burner. Adjusting one or more burners directed at a single coil will affect the adjacent coil heat distribution unless each coil is stored in a separate cell. With electric heating, heating and insulation can be switched off without affecting other coils. Thus, when the electric heater has many coils, each coil can be controlled independently. Furthermore, the heat input along different sections of the coil can be controlled. For example, a high heat flux at the inlet section of the coil and a low heat flux towards the end of the coil can be achieved by adjusting the heater parameters of one or more electric heating elements. By varying the heat profile along the coil, the reaction in the coil can be controlled and / or the coking rate can be controlled. Depending on the furnace design, a temperature and / or flux distribution can be imposed. Based on the performance of individually controlled coils in the decomposition process, the temperature control of individual coils can be optimized to improve the performance of the coils.

[0025] With an electric heater, the heat load can be varied from 0 to 100%, and thus adjusting the turndown or heat severity (or coil outlet temperature (COT)) may no longer be a problem. With a combustion heater, very low turndown is not possible due to the possibility of extinguishing the flame. Furthermore, at low loads in a combustion heater, carbon monoxide, nitrogen oxides, and nitrogen dioxide increase.

[0026] Compared with combustion heaters, extremely high fluid temperatures can be achieved with electric heaters. However, coil metallurgy can still limit the design. Therefore, ceramic tube coils can be used with electric heaters to achieve higher temperatures. Additionally, other types of coils can be used, including single-pass coils or multi-pass coils configured in one or more rows. Since the severity of each coil can be controlled individually, differential splitting of different feeds through different coils can be easily achieved. Further, co-cracking of different feeds can be performed by mixing different feed streams and supplying the combined feed to a radiant coil.

[0027] After the feed in coil 130 is heated to the reaction temperature, the reactants can be directed from the reaction section 112 to a primary exchanger, such as transfer line exchanger (TLE) 150, to be rapidly cooled to the outlet temperature. When the reaction output is cooled in the primary TLE 150, high-pressure, high-temperature steam can be generated. In some embodiments, the high-pressure, high-temperature steam can be directed to the preheat section of reactor 100 to preheat the feed before it enters the reaction section 112. In some embodiments, the high-temperature steam can be mixed with the feed and directed into the reaction section 112 to facilitate heating of the feed for cracking.

[0028] The effluent from the primary TLE 150 can be directed to a secondary exchanger, such as TLE 160. In the secondary TLE 160, the effluent can be further cooled and steam can be generated. The steam generated from the secondary TLE 160 can be directed to the preheat section of the reactor and used to preheat the feed 105. In some embodiments, the steam generated from the secondary TLE 160 can be directed into the reaction section 112 to facilitate heating of the reaction section 112. In some embodiments, additional exchangers (e.g., tertiary or higher TLEs) can be used in addition to the first and second exchangers (e.g., primary TLE 150 and secondary TLE 160).

[0029] In some embodiments, a separate electric heating element may be used with the primary TLE 150 and / or the secondary TLE 160 to superheat the steam generated by the TLE. By not generating much steam in the TLE, additional heat in the effluent can be directed to preheating the reaction mixture. Thus, the maximum heat input to the reaction system 112 can go to the heat of decomposition (e.g., more than 90% of the heat), and only a small amount can go to heating the steam (the minimum amount of heat can be lost through the walls of the reaction section 112). In contrast, 10 - 40% of the heat of combustion in a combustion heater can go to heating the steam and the boiler feed water.

[0030] The preheating section of the reactor 100 can be formed integrally with the main reaction section in a single reactor unit, or the preheating section of the reactor can be provided separately from the main reaction section. According to embodiments of the present disclosure, all preheating of the feed to the reactor can be done electrically. In some embodiments, a common preheated and mixed feed with the dilution steam header can be employed. The preheating section can include one or more exchangers. In some embodiments, different feed types can be preheated in separate individual exchangers. For example, if the reactor 100 is for cracking ethane, naphtha, and gas oil, separate exchangers in the preheating section can be used to preheat each feed.

[0031] (For example, a common feed exchanger (e.g., TLE150) can be used with reactor 100 such that different feeds can be received through different coils in the reaction section, so the crossover temperature (or the inlet temperature to the reaction section) can be well controlled and substantially constant from start of run (SOR) to end of run (EOR). This is different from combustion heaters. Due to coking in the radiant coils of a combustion heater, the crossover temperature increases with time and affects process performance. Thus, a low crossover temperature is typically used at SOR so as not to exceed metallurgical limits at EOR. In a conventional combustion heater, a feed / effluent exchanger and / or a spare electric heater are used to preheat the feed so that a constant temperature can always be achieved. When using an electric heater, a high crossover temperature can be used from the start to reduce the electrical energy for the reaction section and to reduce the cost of the heater (with fewer radiant coils for a given ethylene capacity).

[0032] When only a feed / effluent exchanger is used and no additional preheater for the feed is installed, additional heat can also be supplied by a primary (reactor) electric heater 110. Heater 110 can be designed and configured to supply heat for the preheating operation.

[0033] Merely to provide a better understanding of the embodiments disclosed herein, examples of different possible parameters for a reactor according to embodiments of the present disclosure, such as those shown in FIG. 1, are presented below. However, other parameters can be used within the scope of the present disclosure.

[0034] The first example of reactor 100 can have an inner diameter (ID) ranging from about 1 inch to 3 inches for the inlet pipe, an inner diameter ranging from about 2 inches to 4 inches for the outlet pipe of the multi-pass coil, a length between 20 ft and 50 ft, and a radiant coil containing between 100 and 200 tubes, and can include a linear TLE having an ID ranging from about 2 inches to 8 inches, a length between about 20 ft and 30 ft, and having between 40 and 50 tubes. In the case of the multi-pass coil, the inlet pipe diameter and the outlet pipe diameter can be up to 8 inches or more, and the overall length can be up to 500 ft or more.

[0035] The first exemplary reactor 100 can have the following operating conditions.

[0036] Naphtha feed: S.G = 0.703, P / N / A, COP (coil outlet pressure): 30 psia, S / O = 0.5, feed rate = 95026 lb / h at 8000 operating hours, C2H4 = 29.0 wt%, C3H6 = 13.5 wt%, COT (coil outlet temperature) = 1596°F (869°C), and TLE outlet = 1100°F (593°C).

[0037] Four radiant coil tubes are combined (as shown, for example, in FIG. 1) in a linear TLE and can be quenched. To maintain the yield of the reaction, the reaction output is rapidly quenched and steam generation can be used. Saturated super high pressure (SHP) steam can be generated. By designing the TLE to give a conventionally low TLE outlet temperature, the amount of duty for preheating the feed can be reduced. Thus, instead of a very low TLE outlet temperature, a higher outlet temperature (e.g., 1000 - 1200°F) may be preferred. Even at a higher outlet temperature, the reaction can still be essentially quenched. The heat available in the effluent may still be high but may not be sufficient to heat the feed to a crossover condition that is also relatively high (1000 - 1200°F). For process optimization, the TLE effluent may not be used for this service unless the heater effluent is cooled to a higher temperature (e.g., above 1200°F) that can affect the yield, or the crossover temperature is set to a lower temperature that can increase the radiant coil duty. In some embodiments, an additional electric heater can be used to preheat the feed to the crossover temperature without process optimization.

[0038] The reactor configuration can include a radiant electric heater that supplies reaction heat and a subsequent TLE that generates SHP saturated steam. The energy remaining in the effluent can be used to preheat the feed (e.g., naphtha feed) and / or dilution steam and / or mixed feed (e.g., naphtha + dilution steam) in a shell and tube exchanger. To maintain the temperature profile, an additional electric heater can be used to preheat the feed to the crossover temperature. Instead of a naphtha feed header or a hydrocarbon feed header, another hydrocarbon (HC) + dilution steam (DS) mixed stream header (high temperature) can be used. A high temperature valve can be used to control the flow rate to the group of coils (or electric heater). The flow rate to the individual tubes can be distributed via flow rate venturis (e.g., 124 shown in FIG. 1). Exchangers can be used for different feeds. For example, one exchanger for naphtha and one exchanger for gas feed may be sufficient for the entire plant.

[0039] The effluent from the exchanger (e.g., secondary TLE 160) can be further quenched to about 200 °C using quench oil before entering the gasoline separator 170.

[0040] Operating Option - 1 A low crossover temperature (about 1000°F) with a high TLE outlet temperature (about 1100°F). When a secondary TLE 160 is used to heat the feed mixture (HC + DS), there can be a difference of at least 100°F, enabling a shell and tube exchanger design. There may be approximately equal flows on the tube side and the shell side in the secondary TLE 160, and thus the temperature drop on the effluent side can be approximately equal to the temperature reached on the shell side. The effluent can be cooled to 350°C (662°F). Thus, the naphtha + DS feed mixture can be heated to 300°C (572°F) using only external means. A common feed preheater can be used instead of a separate electric preheater for each electric heater 110. By optimizing the primary TLE 150 outlet temperature, a separate electric preheater can be eliminated. Superheat dilution by other means can also be used to preheat the naphtha + DS mixture. The main heat load on the naphtha feed is the naphtha vaporization duty. Using other sources such as quench oil or low or medium pressure steam to vaporize the naphtha can avoid a separate electric heater.

[0041] Operating Option - 2 The reactor 100 can operate at a high crossover temperature and a low TLE outlet temperature, and the radiant duty can be the lowest compared to other operating options. The low TLE outlet temperature can be achieved in one stage (e.g., using the primary TLE 150) or in two stages (e.g., using the primary and secondary TLEs 150, 160). In both stages, SHP steam can be generated. In some embodiments, only the primary TLE 150 can be used for steam generation (in the case of high speed quench). In some embodiments, a secondary TLE 160 can be used to preheat the HC + DS mixture (which can operate similarly to a lower mixed preheat (LMP) coil in a combustion heater convection section that heats using effluent instead of flue gas).

[0042] Operating Option - 3 In combination with other additions, the combination of operating option 1 and operating option 2 can be used. For example, the dilution steam can be superheated in different electric heaters, and the superheated dilution steam can be used to preheat the hydrocarbon (and partial steam) to the crossover temperature.

[0043] It is possible to carry out the decomposition reaction in a single electric heater, but the heat balance may not work well for different feeds. When using a single electric heater for the decomposition process, a part of the electric heater can be dedicated to preheating the feed. The flow control can be based on the high-temperature stream, for example, using valve 122 and flow venturi 124. Therefore, the temperature can be selected to improve reliability and cost-effectiveness. Preheating is a low-speed process and can use more flow path surface area to be heated. Instead of using a separate electric heater for preheating, a shell-and-tube exchanger can be used to recover the energy in the effluent for use in preheating. For example, the feed can enter the electric heater at about 140°F and the effluent can exit the reaction section at about 650°F (before the oil quench). At such temperatures, two or more electric heaters can be used with a common feed preheater (when no energy from other sources is included).

[0044]

Table 1

[0045] When electricity is generated from natural sources of generation (such as sunlight or wind) and the efficiency of generation is not important, the electric heater can be 50% more efficient than a conventional combustion heater. However, when electricity has to be generated using natural gas / fuel oil for the heat source, electric heating may not be economical.

[0046] Power grid The decomposition process using an electric heater according to an embodiment of the present disclosure may consume a large amount of power, so it may be advantageous to reduce electrical losses as much as possible. For example, assuming that electricity is available at the site at a high voltage with minimal losses from the power plant, there may still be limitations in the manufacture of equipment using high voltages. Most countries use 66KV transmission lines for long distances (e.g., from substation to substation), but power of 3000V - 11000V may be available to consumers. In the ethylene industry, ID fans consume a great deal of electricity. Most countries use 6000 - 6600V (e.g., PTTPE in Thailand, Petronas in Malaysia). When higher than 11KV, corona discharge should be considered. The above calculations show that about 50MW of power may be the minimum consumption, but for 100MW, the following calculations are shown. For higher capacity electric heaters or multiple electric heaters, higher amounts may be considered.

[0047]

Table 2

[0048] Low voltages of about 250 - 440V may not be used without excessive power losses in the conductor (cable). The current requirements can be very high, and it is preferable to use 6000V or more. Assuming the cable is 50m from the transformer and 20mm thick, the resistance can be extremely small, for example, less than 0.001 ohm.

[0049] Control Compared with a combustion heater, electric heating can be accurately controlled by adjusting the power. A voltage regulator can be used to adjust the power. However, at high power, the power loss may be large and may not be practical. In such cases, individual coil control may be preferred over overall electric heater control. That is, the power to each coil (or group of tubes) can be controlled. Also, by segmenting the power, the temperature distribution can be maintained. For example, a 45 ft long coil can be segmented into five sections. The power to each section can be controlled (on or off), which can enable different severities in different coils, simultaneous cracking and decoking in different coils of the same heater, etc.

[0050] Other aspects Generally, in a conventional ethylene plant, a liquid feed header and a gas header are provided where the liquid feed is vaporized. It is possible to find some low-temperature heat sources available in the recovery section, such as a naphtha + DS (0.2 w / w) feed. In this scenario, if an electric heater is used, one electric heater can be used for the entire plant. Similarly, the dilution steam can be superheated and supplied to all the electric heaters in the plant. A technique similar to this can reduce the total number of electric heaters required for cracking.

[0051] In the above example, a single-pass coil configuration is considered, but other types of coil configurations can be used. Other coil configurations can include multi-pass coils such as SRT-1 (serpentine coil), SRT III (4-pass coil), SRT V, VI, or VII (2-pass coil with multiple inlets and multiple outlets), U coil (one inlet with one outlet), Y coil (two inlets with one outlet), and other configurations. In contrast to conventional combustion heaters where different types of heater coil designs may not be installed or operated within the radiation box, the electric heaters according to embodiments of the present disclosure can include multiple different heater coil designs, including SRT-1 and SRT VI heater coil designs.

[0052] The coil can be manufactured from a metal material including a ceramic material, or an alloy such as carbon steel, austenitic stainless steel, Cr-Mo steel, other alloy steels, and nickel-based alloys. When using a ceramic tube, a relatively short residence time can be used (for example, when using a metal tube, a gas temperature higher than 950 °C can be difficult). Figure 3 shows a graph of the expected ethylene yield and COT versus residence time.

[0053] Since high temperatures are possible using the electric heater of the present disclosure, only steam decoking can be used. Individual coils can also be decoked. Periodic decoking with steam / air can also be used to improve reliability.

[0054] According to an embodiment of the present disclosure, a single header can be used to supply different feeds to the electric heater. A liquid header (e.g., a naphtha header), a gas header (e.g., an ethane header), and / or a mixed stream header (e.g., a hot naphtha + dilution steam header or an ethane + dilution steam header) can be used to supply feeds to one or more electric heaters. By using a mixed stream header, the maximum amount of electrical energy can be used for feed preheating and the minimum amount of electrical energy can be used for steam generation.

[0055] An electric heater may have a number of coils, which may be grouped into different groups or configured together in a single reaction section of the electric heater. The coil outlet temperature can be controlled to optimize olefin production and achieve a desired run length. Such control can be implemented at least in part by providing groups of coils with their own feed control valves. A single electric heater may have one group or multiple groups of coils. Unlike in the case of a combustion heater, an electric heater can be divided into a number of subsections by arranging insulators and / or diverting electrical energy to specific coils in the physical configuration. The power consumption for an electric heater can be high (e.g., ranging from dozens of megawatts to hundreds of megawatts). Thus, the power grid can be divided to supply each individual group of coils or some groups of coils. To control the temperature in a group of coils, the power grid can be segmented to supply power to each group of coils. In some embodiments, the heating coils can be intertwined.

[0056] For example, using a three-group system configured vertically (e.g., l-2-3, l-2-3, l-2-3), the maximum heat can be released when all three groups obtain full power from the power grid. When any one of groups 1 or 2 or is active, the power is 1 / 3 of the total power. When using a partial amount of power, even heating across the coils can be maintained. The groups can be configured vertically, and the lower 1 / 3 or 1 / 2 can have different power from the rest. In some embodiments, the groups of coils can be configured horizontally. The duty for complete decomposition up to complete decoking can be precisely controlled. Further, split decomposition can be achieved using an electric heater. Two adjacent groups of coils can have different power supplied to each group.

[0057] The effluent in the reactor with an electric heater can be rapidly cooled by generating steam. The effluent outlet temperature can be selected to reduce steam generation while still being able to quench the reaction. Excess energy in the effluent can be used to preheat a high-temperature feed mixture (e.g., a mixed hydrocarbon and dilution steam feed) so that no additional heater is required to preheat the feed. For a low-temperature feed, the steam already generated can be used. In this way, a higher portion of the supplied electrical energy can be used for the cracking process.

[0058] Method In the cracking process, the feed mixture can be heated to a certain temperature level (reaction temperature) so that the reaction occurs. In a conventional combustion heater, the energy in the flue gas can be used, and additional energy can be used to generate high-pressure steam. However, in an electric heater, the feed can be preheated by exchanging thermal energy with the effluent from the reaction. (When all compressors are powered by electricity, it can be used in the recovery section, or electricity can be generated back, or used to preheat other process streams) To generate high-pressure steam, a minimum amount of energy can be used with an electric heater reactor. The effluent from the electric heater can be rapidly quenched to a sufficient level to decelerate the pyrolysis reaction. The quench / outlet temperature can be determined according to the type of feed. For example, when cracking ethane, the outlet temperature can be approximately 700 - 750 °C (e.g., by generating steam, the reactor effluent is cooled to about 700 °C). Further cooling of the effluent can be achieved by exchanging heat with a feed stream (e.g., ethane and dilution steam) in a tubular exchanger. In the case of a naphtha cracker, the outlet temperature can be between 600 °C and 700 °C, which is higher than the outlet temperature when using a combustion heater.

[0059] In some embodiments, the outlet temperature can be lowered to generate more steam that can be used in other areas of the reactor. For example, in the case of ethane, an outlet temperature between 350°C and 450°C can be selected to generate high-pressure steam in the transfer line exchanger (TLE) section of the reactor. In the case of naphtha cracking, an outlet temperature between 350°C and 525°C can be selected to generate steam. In the case of the electric heater according to embodiments of the present disclosure, a relatively small transfer line exchanger (high-pressure exchanger) can be used to generate high-pressure steam. When using a relatively small TLE, a linear exchanger can be used, and the effluent can be integrated for further cooling. Instead of a linear exchanger, a conventional exchanger can also be used.

[0060] Other exchangers (secondary and / or tertiary) can be used with the electric heater of the present disclosure, and the feed can be exchanged with the effluent using a low-pressure exchanger. In a combustion heater, after generating steam using a primary exchanger, a secondary exchanger can be used only for some feeds (such as ethane and propane with low fouling tendency). However, when using the electric heater according to embodiments of the present disclosure, all feeds (gas feeds and liquid feeds) can use the secondary exchanger. These secondary exchangers can be installed with individual reactors to correspond to the electric heater, or can be installed according to the overall plant design to correspond to each type of feed.

[0061] For example, a plant can have an ethane feed and a naphtha feed that are directed to a plurality of conventional combustion heaters, where, for illustrative purposes, two of the combustion heaters can crack ethane, five of the combustion heaters crack naphtha, and one spare combustion heater can crack either one. In such an example, each ethane combustion heater can have one secondary TLE, but the naphtha (and spare) combustion heaters may not have a secondary TLE. In the case of the reactors in the comparative plant, when using the electric heaters according to embodiments of the present disclosure, all the ethane electric heaters can be grouped, and ethane can be sent (optionally with dilution steam) to one or more secondary exchangers that heat an ethane (+ dilution steam) feed for the ethane electric heaters. All the naphtha electric heaters can be grouped and can exchange heat with a naphtha (optionally mixed dilution steam) feed. The secondary exchangers can be configured on a per individual heater basis (e.g., a number of small exchangers) or on a per feed basis (e.g., a few large exchangers for each feed type). In some embodiments, when designing on a per individual heater basis, a spare secondary exchanger may not be provided due to cost, but when designing on a per feed basis, a single spare secondary exchanger can service the entire plant, so a spare secondary exchanger can be provided.

[0062] Furthermore, using the electric heaters disclosed herein can achieve simplification of the design, and after integrating the effluents from all primary TLEs (e.g., high-temperature (above 600 °C) TLEs for ethane cracking heaters or naphtha cracking heaters) in the plant, the mixed effluent can be used to preheat the feed mixture. In this case, the overall integrated effluent can be split into one or two or more streams. One effluent stream can go to preheat ethane, and another effluent stream can go to preheat the naphtha feed. The secondary exchanger can also be designed to preheat both the ethane feed and the naphtha feed separately in a single exchanger. Under these conditions, providing a spare secondary exchanger may not significantly increase the cost but may significantly increase the on-stream time. Currently, only the primary TLE can be cleaned during operation with the radiant coil in the combustion heater, while the secondary exchanger is mechanically cleaned (longer time and thus losses in production). By providing a spare secondary exchanger, the on-stream time increases (the effluent stream can continue to be directed to where it is needed while other stream lines can be cleaned).

[0063] The electric heaters according to embodiments of the present disclosure can be used for different types of hydrocarbon cracking processes. For example, the electric heaters disclosed herein can be used for pyrolysis processes for olefin production. Further, in addition to olefin production, the electric heaters as described herein can be used for catalytic reactors, for example, for methane reformers or dehydrogenation reactors such as propane dehydrogenation.

[0064] For cracking, different hydrocarbon feeds can be supplied into the electric heaters of the present disclosure. For example, the hydrocarbon feed can include hydrocarbons from C2, C3, C4, C5, …, up to residual oil, and all crude oils and any of their parts / fractions or mixtures, condensates, and hydrocarbons with a wide boiling curve and an end point above 500 °C. Such hydrocarbon mixtures include, inter alia, all crude oils, virgin crude oils, hydrotreated crude oils, light oils, vacuum gas oils, kerosene, jet fuels, diesel, kerosene, gasoline, synthetic naphtha, raffinate reformate oils, Fischer-Tropsch liquids, Fischer-Tropsch gases, natural gasoline, distillates, virgin naphtha, natural gas condensates, atmospheric pipe still bottoms, vacuum pipe still streams including bottoms, naphthas in a wide boiling range up to light oil condensates, heavy non-virgin hydrocarbon streams from refineries, vacuum gas oils, heavy light oils, atmospheric residues, hydrocracker waxes, and Fischer-Tropsch waxes. In some embodiments, the hydrocarbon mixture can include hydrocarbons boiling from the naphtha region or lighter to the vacuum gas oil region or heavier. If necessary, these feeds can be pretreated upstream of the processes disclosed herein to remove portions of sulfur, nitrogen, metals, and Conradson Carbon.

[0065] Figure 2 shows a block flow diagram of a process 200 that can be used to thermally crack a hydrocarbon feed using an electric heater according to an embodiment disclosed herein. As shown, a dilution stream 214, such as steam, can be added to the hydrocarbon feed 210 and preheated using the effluent 212 in an exchanger 220. This can be done in one or more exchangers. Additional preheating can be done in a separate heater or can be combined with the main electric heater. The exchangers and preheaters can be designed, in particular, for a single heater or, generally, to operate uniformly throughout the plant. Further, the exchangers and heaters can be designed to operate together, which can be considered in the overall economics.

[0066] When the feed mixture 216 is preheated to a desired inlet temperature, also known as the crossover temperature (TXO), the preheated feed mixture 216 can then enter the electric heater 230. The electric heater can superheat the feed mixture 216 to the reaction temperature, and the decomposition reaction can proceed in the coils of the electric heater 230 (e.g., short residence time (SRT) coils). The flow to each coil can be distributed by a control valve (e.g., a high-temperature valve) and a venturi. The heat input into the electric heater 230 can be operated by adjusting the electrical input.

[0067] In the reaction section of the electric heater (in the coils), the process performance of the decomposition can be the same as when the reaction occurs in a conventional combustion heater. In other words, in the reaction section of a conventional combustion heater and an electric heater according to an embodiment of the present disclosure, a significant difference in process performance may not be detected. Thus, the electric heater of the present disclosure can have a reaction section that provides the same or similar level of pyrolysis performance as a combustion heater. In some embodiments, such as embodiments that provide uniform circumferential heating of individual coils, the performance and selectivity can be improved, some by reducing the number or temperature of hot spots associated with combustion heating.

[0068] Depending on the electric heater design, the coil design can be modified. For example, a single-pass design or a multi-pass series-parallel configuration can be used. In some embodiments, the coil design in the electric heater can be the same as the coil design in a combustion heater (e.g., the same coil design as in an SRT® furnace by Lummus Technology, including SRT-I, SRT-II, SRT-III, SRT-V, SRT-VI, and SRT-VII combustion heaters). In some embodiments, different coil configurations can be used in a single electric heater. For example, serpentine coils and multi-pass split design coils can be configured and operated in the reaction section of a single electric heater.

[0069] The severity of pyrolysis can be adjusted by monitoring the outlet temperature of the output 218 from the electric heater 230 and by adjusting the heat input to the electric heater 230. Further, the skin temperature of the coil in the electric heater 230 can be measured and / or predicted using the devices and methods used in combustion heaters. For example, to monitor the skin temperature of the electric heater coil, which can be used to determine, for example, the first stage of coking, corrosion, excessive and insufficient equilibrium heat loads in the heater, and prediction of the coil life, a scanning infrared camera, high-resolution imaging using a focal plane array detector, thermocouples, and selection of temperature measurement points can be used.

[0070] The output 218 from the electric heater 230 can be directed to an exchanger (e.g., TLE) 240 where the output 218 can be rapidly cooled (quenched) after exiting the reaction section of the electric heater 230. Quenching the output 218 can be done to prevent secondary reactions and to stabilize the gas composition from the output. The same type of TLE used with conventional combustion heaters can be used with the electric heater 230 of the present disclosure. For example, the cooling of the decomposed gas output 218 in the TLE 240 can be carried out by the vaporization of high-pressure boiler feed water (BFW) 242, which can be brought around the TLE tubes to cool the decomposed gas output 218 and vaporize to generate high-pressure steam 244. A direct injection quench point can be provided to suppress the high-speed fouling that can occur in the TLE cooling tubes when the decomposed gas is cooled below the dew point of the heavy ends of the decomposed gas when decomposing a liquid feed (e.g., when processing a heavy gas oil feed).

[0071] The effluent 212 exiting the TLE240 can be analyzed and directed to different paths for different uses depending on the type of effluent. For example, the effluent 212 can be heated and undergo additional decomposition. In some embodiments, the effluent can be hydrotreated to reduce at least one component of nitrogen, sulfur, metals, and Conradson carbon in the hydrocarbon mixture. The same types of equipment and processes used with a conventional combustion heater for combined effluent analysis can be used with the electric heater 230 according to embodiments of the present disclosure.

[0072] In some embodiments, when using the electric heater of the present disclosure, the effluent can be cooled to a relatively high TLE outlet temperature compared to when using a conventional combustion heater. For example, when using a conventional combustion heater, the effluent is cooled to 350°C - 400°C (at the start of the cracking cycle) and high-pressure steam (e.g., 115 bar) can be generated by cooling from a coil outlet temperature of 800 - 850°C. When minimal steam is required, such as when using the electric heater of the present disclosure, the TLE240 outlet temperature can be raised to 600 - 650°C. At lower TLE outlet temperatures, the rate of the pyrolysis reaction may slow down, thereby potentially reducing the energy used to preheat the feed. Thus, a lower TLE outlet temperature can reduce the electricity consumption in the electric heater but also reduce steam generation. Optimal outlet temperatures / steam generation can be determined for different pyrolysis processes. For illustrative purposes below, examples of using different TLE outlet temperatures are considered.

[0073] When considering the minimum steam, it is possible to eliminate feed preheating and heat the feed to the reaction temperature in a separate heater. Generally, in a gas combustion heater, the heater crossover temperature for naphtha is 1100 - 1175°F (593 - 635°C), and the heater crossover temperature for ethane is 1250 - 1300°F (677 - 704°C). This level of preheating the feed cannot be achieved with only effluent heating. By reducing the crossover temperature to 900°F (482°C) for naphtha and 1000°F (538°C) for ethane, a separate electric preheater may not be required. Unfortunately, in order to reduce the crossover temperature, the skin temperature of the tubes in the radiant coil may increase and the run length may be shortened. For a reasonable run length, more coils are required. In the case of a liquid feed, it is difficult to eliminate the electric preheater. Naphtha effluent may condense and foul the lines, so naphtha effluent may not be cooled below 350°C or 300°C. However, ethane effluent can be cooled to 200°C, and its enthalpy can be used to preheat ethane feed or ethane / dilution steam mixed feed. This process can be carried out using a secondary TLE, and the secondary TLE can be used together with a conventional combustion heater or an electric heater. Further, conventional decoking and feed switching can be used together with the electric heater according to the embodiments of the present disclosure. For example, steam can be used to decoke the coils in the electric heater disclosed herein.

[0074] Unlike conventional combustion heaters, the electric heaters according to the embodiments of the present disclosure do not have a convection section. In an electric heater, for example, a group of 1 - 10 or 20 (or actually achievable numbers) of coils can form an electric heater. The size of the coils and the electric heater can be defined by the decoking ability.

[0075] One or more electric heaters may be used in an ethylene production plant. The ethylene production plant may have an ethylene production capacity of more than 1800 KTA, and an average ethylene production capacity greater than 1500 KTA. To achieve such production, multiple electric heaters (e.g., six or seven operable electric heaters and a spare electric heater) may be used in the plant. Each electric heater in the plant may be designed to optimize ethylene production. For example, in the case of a plant capable of producing 1000 KTA (kilotons per year) of ethylene, five groups of coils + one spare group form electric heaters respectively (each group of coils / electric heater may have a 200 KTA size). As another example, a 2000 KTA plant may include five groups of coils + one spare group that form electric heaters respectively (each electric heater may have a 400 KTA size). A single electric heater may produce ethylene of 200 KTA or more, for example, between 250 KTA and 300 KTA. In some embodiments, an electric heater that produces 200 KTA of ethylene may have a power consumption of between 65 MW and 130 MW. In some embodiments, an electric heater that produces 1800 KTA of ethylene may consume a total power of 1170 MW.

[0076] Depending on the electric heating system (e.g., resistive, inductive, and / or capacitive), heating can be supplied to each coil or each group of coils and can depend, for example, on the electric heater manufacturer. For example, in some embodiments, an electric heater (e.g., an electric heater including coils configured as in an SRT-VI® heater) can have a common pipe for a plurality of feeds such as Feed-1, Feed-2, etc. (e.g., Feed-1 can be naphtha, Feed-2 can be liquefied petroleum gas (LPG), Feed-3 can be ethane, etc.). The feeds can be preheated outside the electric heater where the pyrolysis reaction is carried out. A group of coils (generating steam) and the TLE can form an electric heater according to embodiments of the present disclosure and can be separated for decoking or repair.

[0077] In a combustion heater, a large-capacity heater may use a twin-cell radiant box design, which may include two radiant cells in a common convection section. A combustion heater with a single-cell design may be used to build a 200 KTA capacity. Since an electric heater does not have a convection section as in a conventional combustion heater, 200 KTA ethylene production may be used as a basis for comparison between the electric heater and the combustion heater. However, ethylene production from the electric heater may be less than or more than 200 KTA (e.g., from about 170 KTA to over 400 KTA). Examples of electric heater designs for naphtha cracking and ethane cracking based on 200 KTA of ethylene are given herein. For simplicity, full-range naphtha at high severity and pure ethane at 65% conversion are considered. Further, different coil configurations (e.g., coil configurations used in SRT-I, SRT-II, SRT-III, SRT-V, SRT-VI, or SRT-VII by Lummus Technology, or a single-pass coil configuration) may be used in the electric heater, but the example of the electric heater design is presented using a coil configuration that matches the coil configuration in an SRT-VI combustion heater by Lummus Technology, which is a high-selectivity two-pass coil with a long run length. An electric heater with this coil configuration can be used for both naphtha cracking and ethane cracking to produce ethylene. A standard coil outlet pressure of 25 psia may be used. A steam-to-oil ratio (S / O) of 0.1 - 1.5 w / w may be used for various feeds, e.g., 0.5 w / w may be used for naphtha cracking and 0.3 w / w may be used for ethane cracking. The electric heater can operate for at least 45 days.

[0078] The naphtha properties include a specific gravity (SG) of 0.707, an initial boiling point (IBP) of 91°F (33°C), a 50 v% of 189, a final boiling point (FBP) of 348°F (176°C), 74.6 wt% paraffin, 16.65 wt% naphthene, 8.75 wt% aromatic compounds, and an interference-to-noise power ratio (P I / N ratio) of 0.83. 100% pure ethane may be used to pyrolyze ethane in the electric heater.

[0079] Table 3 given below provides exemplary design and operating parameters for an electric heater capable of pyrolyzing naphtha and ethane to produce ethylene. Case 1 corresponds to the naphtha heater design and Case 2 corresponds to the ethane heater design.

[0080] [Table 3]

[0081] Cases 1A and 2A correspond to conditions with high crossover temperature and low TLE outlet temperature (to maximize steam generation), and all duty can be supplied by the electric heater. This produces the maximum amount of steam. Cases 1B and 2B produce a lower amount of steam. The available heat in the effluent can be used to preheat the feed to the maximum extent. For some feeds, maximum preheating up to the crossover temperature of the reaction mixture is possible without using a separate electric heater. In some embodiments, a separate electric heater may be used to superheat the steam (up to about 500 °C).

[0082] Using a high crossover temperature (or preheat temperature) can reduce the radiant coil surface area, thereby enabling the electric heater to operate for at least 45 days. For example, as shown in Cases 1A and 2A, an electric heater with eight coils configured in an SRT-VI configuration can achieve a 200 KTA capacity. Using a lower crossover temperature may require more coils to achieve the same capacity. For example, to achieve the same capacity, eight coils are used in Cases 1A and 2A, and nine coils are used in Cases 1B and 2B. When more coils are added, a lower crossover temperature can be used without using a separate electric heater for the feed.

[0083] In the case of ethane cracking, the heat transfer coefficient is low because the hydrocarbon feed rate is low (due to the high ethylene yield). To obtain the maximum profit, a slightly different SRT-VI design can be considered for ethane cracking. However, in case A, any coil design can be considered, and case B can be designed similarly using one more coil than case A.

[0084] Table 4 given below provides another example of design and operating parameters for an electric heater capable of pyrolyzing naphtha and ethane.

[0085]

Table 4

[0086] The naphtha heater can utilize more power than the power of the ethane cracking heater. For example, the reaction section in the naphtha heater can have a minimum power consumption of about 70 MW / heater, while the reaction section of the ethane heater can have a minimum power consumption of about 52 MW / heater. When preheating is carried out before cracking, the total power used can be 10 - 20% more than the power consumption of the reaction section alone. In this calculation, an efficiency of 90% can be assumed for the electric heater, but an efficiency of over 95% can be possible. For example, in electric heating, 90 - 98% of the electrical energy can be used for the reaction. Therefore, there may be little or no recovery of the heat not used for the reaction. Since only an amount of energy sufficient for the reaction can be supplied by the electric heater, there is substantially no excessive or wasted energy use.

[0087] Furthermore, since the electric heater of the present disclosure has no convection section and burner, the electric heater of the present disclosure can be configured differently from the conventional combustion heater layout. Therefore, the plot space of the reactor using the electric heater of the present disclosure can be reduced compared to the combustion heater.

[0088] The electric heater may have power requirements ranging from 2600 KW to 5200 KW per ton of ethylene. When producing 1800 KTA of ethylene, the electric heater uses approximately 580 MW to pyrolyze ethane and can use up to 1170 MW when pyrolyzing naphtha. Additional energy can be used to superheat the steam used in the cracking process and for the recovery section. For example, for the entire plant (including the electric heater, preheating components, and recovery components), approximately 600 MW of power can be used for an ethane cracker and approximately 1300 MW of power can be used for a naphtha cracker. The energy source used to supply power to the electric heater (and / or auxiliary components for preheating and recovery) can be, for example, nuclear, hydro, solar, wind, or a renewable method. In some embodiments, fossil fuels can be used to generate electricity for the electric heater plant. However, the use of fossil fuels for power generation can nullify the environmental benefits of using the electric heater. Additionally, when surplus electricity is used in the electric heater or elsewhere, the resulting surplus heat energy can be converted (e.g., using a generator) and returned to electricity.

[0089] The specific energy of the electric heater when pyrolyzing naphtha to produce ethylene can be up to about 57,000 KW / T (kilowatts per ton) of ethylene, and the specific energy of the electric heater when pyrolyzing ethane to produce ethylene can be up to about 42,000 KW / T of ethylene. When not generating steam in the heater, additional energy may be required to power the recovery section. Thus, according to embodiments of the present disclosure, the power usage across the entire plant, including preheating components, the electric heater, and recovery components, can be pre-planned to account for different cracking processes that can be used in the plant and / or different feeds that can be thermally cracked.

[0090] According to embodiments of the present disclosure, the plant design can also include considerations of the starting state. Further, the plan can include determining the generation and consumption of steam caused by pyrolysis, for example, determining which steam level should be generated to reduce the total energy consumption to less than a certain amount, and also including considerations of the generation of dilution steam from heat exchange using process streams. For example, through the full electrification of the plant, external steam can be reduced to a minimum, and when the plant is properly configured, the starting boiler can sometimes be eliminated. The complete steam balance can be determined before determining the amount of power for the electric heater. For example, the dilution steam can be superheated so that the energy balance of the decomposition heater does not significantly affect the severity of the decomposition. The dilution steam can be superheated in the same heater where the feed is decomposed, or the dilution steam can be superheated in a separate heater. The choice of an integrated or separate dilution steam heater can depend on the available energy.

[0091] A method for designing a pyrolysis plant (including an electric heater for pyrolyzing the feed, a recovery section, and optionally a preheating section) can include determining the amount of steam generated and the amount of steam consumed by the pyrolysis plant, determining the amount of power used by the pyrolysis plant to pyrolyze the feed, and adjusting at least one parameter of the pyrolysis plant to reduce the amount of power used by the pyrolysis plant. The parameters that can be adjusted to change the amount of energy used by the pyrolysis plant can be selected from at least one of reducing the crossover temperature of the feed to the electric heater, designing the electric heater to have at least one additional coil to reduce the crossover temperature of the feed, increasing the outlet temperature from the recovery section, reducing the amount of steam consumed by the recovery section, increasing the amount of steam consumed by the preheating section, and other things described above.

[0092] Using an electric heater for pyrolysis can require more power for pyrolysis than when the electric heater is used in other industries (e.g., for melting iron ore). For example, an electric heater in other industries may have a maximum power consumption of about several kilowatts, while the power consumption of the electric heaters disclosed herein used to decompose hydrocarbon feeds can be about several megawatts. Thus, the method of the present disclosure can include designing a pyrolysis plant that uses a minimal amount of power while still being able to pyrolyze a selected feed. In some embodiments, the electric heater can be modular, thereby allowing for design adjustments according to the pyrolysis process and feed. Other separation techniques such as adsorption / absorption can be considered when designing the plant. When alternatives to cryogenic separation are available, small-scale chemical olefins can be very attractive via this route.

[0093] In contrast to combustion heaters, electric heaters can maintain a constant crossover temperature throughout the pyrolysis process run. Further, unlike combustion heaters, electric heaters can maintain a constant crossover temperature for a range of severities from low to high and throughputs from low to high.

[0094] Furthermore, the electric heater of the present disclosure does not generate flue gas and thus may only include a radiation section and an effluent cooling section. Therefore, the efficiency of electric heating can far exceed the efficiency of combustion heating, where generally 35 - 45% of the radiation duty is absorbed during gas fuel heating. By controlling heat loss (when the electric heater has no radiation duty absorbed during gas fuel heating), more than 95% of the electrical energy used to generate heat can be absorbed in the process. Therefore, the reaction section duty in the electric heater can be relatively small compared to a combustion heater. However, while the flue gas generated in a combustion heater can be used to preheat the reaction mixture to the required reaction inlet temperature (crossover temperature, TXO), the electric heater has no flue gas for preheating. The overall fuel efficiency (thermal efficiency) including preheated flue gas can be about 94%. When using a combustion heater, heating the reaction mixture from the battery, even when limiting the conditions to reaction conditions, additional energy is available in the flue gas. The flue gas can be used to generate and superheat high-pressure steam, and the high-pressure steam can be used in the recovery section to drive a compressor. Although the radiation efficiency is low, the thermodynamic utilization rate of fuel energy is much higher.

[0095] In electric heating, since there is no flue gas, most of the heat used in the process can go into the reaction. Therefore, the amount of steam generated during the process can be significantly reduced. Steam generation can be used in the cracking process as a way to recycle heat (for example, to preheat the feed before it enters the reaction section of the heater), and thus, when steam generation is reduced, other heating options can be used to compensate for the reduced amount of steam. For example, additional preheating of the feed can be carried out using a second electric heater. When the entire pyrolysis plant (such as one or more main reaction heaters, one or more recovery sections (such as exchangers), one or more preheating sections (such as preheat heaters), and / or post-treatment equipment) is using electrical energy, optimization of preheating and reaction heating can be done in a more efficient way. For example, the heat generated from one plant equipment unit (such as from the main reaction electric heater) can be recycled to another plant equipment unit (such as to the preheating section). Optimization of preheating can also be done for a single electric heater where thermal energy (high temperature) from the reactor effluent can be used to preheat the feed and / or generate steam.

[0096] Currently, an ethane cracker can produce a significant amount of steam compared to the feed (about 2 kgSHP of superheated steam per Kg of ethane feed). The ethane heater also uses a certain type of preheating (secondary TLE). In the case of gas cracking using an electric heater, the electricity demand can be reduced by preheating the feed with the effluent as much as possible. A certain level of external reaction mixture preheating can be done when using an electric heater, and this can be done by additional electric heating. In some situations, this can be included in the main reaction heater or a separate preheater. The size and / or cost of the electric heater can be considered according to the electricity demand to optimize the design for sourcing preheater energy (such as from the main reaction heater or a separate preheater).

[0097] With electrical heating, the heating rate can be made uniform, and by manipulating the electrical input, the heat flux input can be adjusted. The maximum metal temperature can occur close to the end of the coil. In some heater designs, there is no shadow factor. Thus, the predicted maximum tube metal temperature (TMT) can be significantly lower in an electrical heater than that observed in a combustion heater. This can reduce the cost of the electrical heater. Other benefits of using an electrical heater can include, for example, control principles, plot space modularization, etc.

[0098] As described herein, an electrical heater can offer advantages over conventional combustion heaters. For example, in an electrical heater, only the duty required for the reaction can be supplied while taking into account only minor losses (in a combustion heater, most of the combustion duty can be lost in the flue gas). Further, the reactor effluent from the electrical heater can be used to preheat the feed, thereby reducing the total duty supplied to the reactor. An electrical heater can also be more compact compared to a combustion heater (including both a radiant section and a convection section).

[0099] Furthermore, an electrical heater can provide more controlled heating than a combustion heater. For example, electrical heating can be more uniform than heating by a combustion heater, and the heating rate can be better controlled in an electrical heater compared to a combustion heater. Further, selected coils in the electrical heater can be selectively controlled (e.g., controlled heating of a single coil or a group of coils) so that olefins can be produced much more selectively.

[0100] Using an electric heater can also improve safety. Most heater accidents often occur during startup and shutdown due to improper handling of fuel safety standards. Since no fuel is used in an electric heater, accidents related to the safety of fuel types can be eliminated or reduced. Furthermore, compared to conventional heaters, the structure of the electric heater according to the embodiments disclosed herein can be simplified, so safety may not be as much of a concern in earthquake-prone areas and under strong wind loads (e.g., due to low structural height and non-use of fuel).

[0101] Although the present disclosure has been described with respect to a limited number of embodiments, those of ordinary skill in the art who benefit from the present disclosure will recognize that other embodiments can be devised without departing from the scope of the present disclosure as described herein. Accordingly, the scope of the present disclosure should be limited only by the appended claims.

Claims

1. A reactor for decomposing a hydrocarbon feed, comprising: a heater chamber defining a reaction section of a heater; a plurality of electric heating elements disposed within the heater chamber, the electric heating elements being operated by electric power; at least one coil extending from a feed inlet through the reaction section; a primary exchanger having an inlet fluidly connected to the at least one coil and an effluent outlet; and a reactor for decomposing a hydrocarbon feed.

2. The reactor according to claim 1, further comprising a secondary exchanger having an inlet fluidly connected to the effluent outlet of the primary exchanger.

3. The reactor according to claim 1 or 2, wherein the primary exchanger further comprises a steam outlet and a steam flow path directed towards the feed inlet.

4. The reactor according to claim 1 or 2, further comprising a preheating section downstream of the feed inlet and spaced apart from the reaction section, the preheating section comprising at least one exchanger.

5. The reactor according to claim 1 or 2, wherein the feed inlet is fluidly connected to a plurality of feed sources.

6. A method for thermally decomposing a hydrocarbon feed, comprising: feeding the hydrocarbon feed into at least one coil in a reaction section of an electric heater; using electrical energy to heat the hydrocarbon feed in the electric heater to a reaction temperature; and directing the reaction output from the electric heater to at least one exchanger to cool the reaction output. and a method for thermally decomposing a hydrocarbon feed.

7. The method according to claim 6, further comprising recovering heat from the reaction output using the at least one exchanger and using the recovered heat to preheat the hydrocarbon feed before feeding the hydrocarbon feed into the electric heater.

8. The method according to claim 6 or 7, further comprising selectively heating different sections of the at least one coil to a selected temperature using a plurality of electric heating elements disposed around the at least one coil in the electric heater.

9. The method according to claim 6 or 7, further comprising supplying a plurality of different types of feeds to different coils in the reaction section and collectively separating the reaction output from the plurality of feeds.

10. The method according to claim 6 or 7, further comprising supplying a second hydrocarbon feed into the electric heater, the second hydrocarbon feed having a composition different from that of the hydrocarbon feed.

11. Using a valve to isolate one of the at least one coil; Decoking the isolated coil The method according to claim 6 or 7, further comprising.

12. Designing a pyrolysis plant comprising an electric heater for pyrolyzing a feed and a recovery section; Determining the amount of steam generated and the amount of steam consumed by the pyrolysis plant; Determining the amount of power used by the pyrolysis plant to pyrolyze the feed; Adjusting at least one parameter of the pyrolysis plant to reduce the amount of power used by the pyrolysis plant. Including, the method.

13. The method according to claim 12, wherein adjusting the at least one parameter includes reducing the crossover temperature of the feed to the electric heater.

14. The method according to claim 13, further comprising designing the electric heater to have at least one additional coil to reduce the crossover temperature of the feed.

15. The method according to any one of claims 12 to 14, wherein the pyrolysis plant further comprises a preheating section, and adjusting the at least one parameter includes increasing the outlet temperature from the recovery section, reducing the amount of steam consumed by the recovery section, and increasing the amount of steam consumed by the preheating section. ​ ​

Images