Hybrid reactors using fuel and / or electricity

Abstract

An apparatus for heating petroleum, petrochemicals, chemical process fluids, and boiler feedwater, or for generating steam, using a combination of electric elements and combustion burners, or by operating them separately. The apparatus includes a radiant heating section and an exhaust gas stack for exhausting combustion gases to the atmosphere. The radiant section includes one or more process coils, one or more fuel-fired burners for combusting fuel and generating combustion gases, the one or more fuel-fired burners being arranged to provide radiant energy to a first section of the one or more process coils, and one or more electric heating elements arranged to provide radiant energy to a second section of the one or more process coils. The one or more electric heating elements are configured to provide 5% or more of the maximum energy output of the combined fuel-fired burners and electric heating elements.

Description

[Background technology]

[0001] In the refining and petrochemical industries, heaters are primarily fuel-fired. Current combustion heaters produce carbon dioxide when burning hydrocarbon fuels, a greenhouse gas that contributes to global warming. Therefore, there is a general desire to move away from hydrocarbon fuel-fired heaters.

[0002] However, electric heaters are currently limited to relatively small volumes and are currently under development for larger volume applications. However, none of the heaters are designed to have a hybrid energy input, with both fuel-fired burners and electric heating elements coexisting, or with both fuel-fired and electric power.

[0003] Transitioning to solely electric heating presents several challenges. When both electric heating elements and fuel burners are installed in a heater, concentrated combustion from the burners tends to damage the electric heating elements due to overheating or carburization. Furthermore, because electric heaters do not directly burn fuel, they do not produce exhaust gases. Electric heaters do not have convection sections, which are traditionally used for additional heat recovery for steam generation and preheating. If power is lost, the electric heaters must be shut down, disrupting plant operations or potentially damaging equipment due to sudden changes in operating conditions.

[0004] Therefore, there is a need in the art for a heater that reduces greenhouse gas production while providing continuity of operation. Summary of the Invention

[0005] This Summary introduces various concepts that are described in more detail below in the Detailed Description. This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0006] In one aspect, embodiments disclosed herein relate to an apparatus for heating petroleum, petrochemicals, chemical process fluids, and boiler feedwater, or for generating steam using a combination of electric elements and combustion burners, or by operating them separately. The apparatus includes a radiant heating section and an exhaust gas stack for exhausting combustion gases to the atmosphere. The radiant section includes one or more process coils; one or more fuel-fired burners for combusting fuel and generating combustion gases, the one or more fuel-fired burners being arranged to provide radiant energy to a first section of the one or more process coils; and one or more electric heating elements arranged to provide radiant energy to a second section of the one or more process coils. The one or more electric heating elements are configured to provide 5% or more of the maximum energy output of the combined one or more fuel-fired burners and the one or more electric heating elements.

[0007] In another aspect, embodiments disclosed herein relate to an apparatus for heating petroleum, petrochemicals, chemical process fluids, and boiler feedwater, or for generating steam using a combination of electric elements and combustion burners, or by operating them separately. The apparatus includes a radiant heating section and an exhaust gas stack for exhausting combustion gases to the atmosphere. The radiant section includes one or more process coils; one or more fuel-fired burners for combusting fuel and generating combustion gases, the one or more fuel-fired burners arranged to provide radiant energy to a first side of the one or more process coils; and one or more electric heating elements arranged to provide radiant energy to a second side of the one or more process coils, the second side being opposite the first side. The one or more electric heating elements are configured to provide 5% or more of the maximum energy output of the combined one or more fuel-fired burners and the one or more electric heating elements.

[0008] In yet another aspect, embodiments disclosed herein relate to an apparatus for heating petroleum, petrochemicals, chemical process fluids, and boiler feedwater, or for generating steam using a combination of electric elements and combustion burners, or by operating them separately. The apparatus includes a radiant heating section, a convective heating section configured to receive combustion gases from the radiant heating section, and an exhaust gas stack for exhausting the combustion gases to the atmosphere. The radiant section includes one or more process coils and one or more fuel-fired burners for combusting fuel to generate combustion gases, the one or more fuel-fired burners arranged to provide radiant energy to a first side of the one or more process coils, and one or more electric heating elements positioned adjacent to a refractory material in a wall of the radiant heating section horizontally between the one or more fuel-fired burners and the one or more electric heating elements and arranged to provide radiant energy to a first side of the one or more process coils, the second side being opposite the first side. The one or more electric heating elements are configured to provide 5% or more of the maximum energy output of the one or more fuel-fired burners and the one or more electric heating elements combined.

[0009] Other aspects and advantages of the claimed subject matter will be apparent from the following description and appended claims. [Brief explanation of the drawings]

[0010] [Figure 1A] 1 illustrates various heater designs according to embodiments herein. [Figure 1B] 1 illustrates various heater designs according to embodiments herein. [Figure 2A] 1 illustrates various heater designs according to embodiments herein. [Figure 2B] 1 illustrates various heater designs according to embodiments herein. [Figure 3A] 1 illustrates various heater designs according to embodiments herein. [Figure 3B] 1 illustrates various heater designs according to embodiments herein. [Figure 4A]1 illustrates various heater designs according to embodiments herein. [Figure 4B] 1 illustrates various heater designs according to embodiments herein. [Figure 5A] 1 illustrates various heater designs according to embodiments herein. [Figure 5B] 1 illustrates various heater designs according to embodiments herein. [Figure 6A] 1 illustrates various heater designs according to embodiments herein. [Figure 6B] 1 illustrates various heater designs according to embodiments herein. [Figure 7A] 1 illustrates various heater designs according to embodiments herein. [Figure 7B] 1 illustrates various heater designs according to embodiments herein. [Figure 8] 1 illustrates various heater designs according to embodiments herein. [Figure 9A] 1 illustrates various heater designs according to embodiments herein. [Figure 9B] 1 illustrates various heater designs according to embodiments herein. [Figure 9C] 1 illustrates various heater designs according to embodiments herein. [Figure 10A] 1 illustrates various heater designs according to embodiments herein. [Figure 10B] 1 illustrates various heater designs according to embodiments herein. [Figure 10C] 1 illustrates various heater designs according to embodiments herein. [Figure 10D] 1 illustrates various heater designs according to embodiments herein. DETAILED DESCRIPTION OF THE INVENTION

[0011] In one aspect, embodiments disclosed herein relate to heaters that provide a combination of both a fuel-fired burner and an electric heating element. Embodiments herein have a fuel-fired burner and an electric heating element in the same chamber, and the heater can operate the fuel burner, the heating element, or both simultaneously.

[0012] According to some embodiments herein, a heater for heating petroleum, petrochemicals, chemical process fluids, and boiler feedwater, or for steam generation / superheating using a combination of electric heating elements and fuel-fired burners or their separate operation, includes a radiant heating section, a convection heating section, and an exhaust gas stack. The radiant section includes one or more fuel-fired burners, such as wall burners and / or floor burners, and one or more electric heating elements, which can be metallic, non-metallic, or a combination of metallic and non-metallic, each of the burners and electric heating elements arranged and configured to provide radiant heat to one or more process or utility streams (heating coils, radiant coils, or process coils) located within the radiant section of the heater. The convection section of the heater is configured to receive combustion gases generated by the fuel-fired burners and, in some embodiments, is further configured to provide convective heat to one or more process or utility streams (convection coils) located and arranged within the convection section of the heater. The exhaust stack is configured similarly to a typical furnace, receiving the (heat-depleted) combustion gases from the convection heating section and venting the combustion gases to the atmosphere.

[0013] In some embodiments, one or more fuel-fired burners are arranged to provide radiant energy to a first portion or a first section of one or more process coils. Additionally, one or more electric heating elements disposed within the radiant heating section are arranged to provide radiant energy to a second portion or a second section of one or more process coils. For example, in various embodiments, the fuel-fired burners and electric heating elements may be arranged to provide heat to different coils, may be arranged vertically within the heater to provide radiant heat to different elevations of the same or different coils, or may be arranged horizontally within the heater to provide radiant heat to different coils or different sections of the coils.

[0014] Heating at different elevations can be provided, for example, by placing electric heating elements at a lower elevation within the heater and vertically positioning fuel-fired burners above the electric heating elements. In this way, combustion products that preferentially exhaust upward may not result in soot or buildup of combustion products on the electric heating elements. Similarly, as discussed further below, design considerations can be provided to prevent undesirable interactions between horizontally aligned burners and heating elements.

[0015] In other embodiments, one or more fuel-fired burners are arranged to provide radiant energy to a first side of one or more process coils. Additionally, one or more electric heating elements disposed within the radiant heating section are arranged to provide radiant energy to a second side of one or more process coils. For example, a process coil may be disposed intermediate (between) one or more fuel-fired burners and the electric heating elements. Thus, radiant energy from the fuel-fired burners may impinge upon and heat the side of the process coil facing the burners, while radiant energy from the electric heating elements may impinge upon and heat the side of the process coil facing the electric heating elements.

[0016] In other embodiments, one or more fuel-fired burners and one or more electric heating elements may be positioned in a radiant heating section arranged to provide radiant energy to the same side of one or more process coils. For example, a fuel-fired burner may be positioned intermediate (between) one or more electric heating elements and a process coil.

[0017] Thus, embodiments herein are configured and arranged to provide radiant energy to the process coil via radiant energy from a fuel-fired burner, an electric heating element, or both a burner and a heating element. Such a configuration allows the heater to be operated with fuel combustion, partial fuel combustion supplemented by electric heating, or fully electric heating. Greenhouse gas emissions can be reduced, and waste heat from the combustion exhaust can be recovered via a convection section for feed preheat or an auxiliary stream. If a carbon-free fuel such as H2 or NH3 is used, there are no greenhouse gas emissions from the exhaust stack. More importantly, the heater and associated equipment can continue to operate during power outages by operating the fuel-fired burner, or during fuel shortages by operating the electric heating element.

[0018] As outlined above, embodiments herein may include providing radiant energy directly from the electric heating element to the process coil. Appropriate heater design may limit or prevent undesirable overheating or carburization of the electric heating element. Exposure of the electric heating element to radiant energy from the burner, as well as exposure of the electric heating element to combustion products, may be limited by design considerations such as, for example, disposal of the process coil intermediate the electric heating element and the burner, appropriate exhaust stack (relative alignment of the burner with the convection section and exhaust stack, flow directing features, etc.), vertical alignment of the heating element with the burner, partial or complete shielding of the electric heating element via shielding walls, tiles, or tubes, or various combinations of two or more of these design considerations.

[0019] In some embodiments, the heater may not include a convection section and may exhaust the combustion gases directly through an exhaust stack, hi other embodiments, the hot exhaust gases may be sent to an external gas-to-fluid heat exchanger or other heat recovery unit such as a waste heat boiler.

[0020] For example, in some embodiments, the burner and heating element are separated by a heating surface where fuel combustion is completed before the combustion exhaust can reach the heating surface. As another example, in other embodiments, the heating element is shielded by a high-temperature material that prevents combustion and its exhaust from direct contact with the heating element. As another example, electric heating elements may be configured to provide varying amounts of heat from one element or group of elements to another. In such examples, the heat profile of the heating elements may be non-uniform across either the width or height of the furnace, or both. The heating elements may provide a uniform heat flux or may be arranged to provide heat in a heat flux pattern selected to meet process requirements. Heating elements located throughout zones within the heater (e.g., floor, lower wall, or upper wall) may have the same or different mechanical configurations. The heating elements may be installed evenly throughout the heater or in a selected pattern. Thus, embodiments herein provide unique and advantageous arrangements of fuel-fired burners and electric heating elements, which may provide excellent flexibility in heating operations with electrical energy, combustion, or both.

[0021] Referring now to the figures, there are shown exemplary embodiments of various configurations of hybrid heaters including electric heating elements and fuel-fired burners, where like numbers represent like parts.

[0022] 1A (side view) and 1B (top view) illustrate a hybrid vertical cylindrical (VC) heater 10 design according to an embodiment of the present disclosure. In this embodiment, the heater 10 includes a radiant section 12, a convection section 14, and an exhaust gas stack (not shown). Within the radiant section 12, a process coil 16 is positioned intermediate a floor burner 18 and an electric heating element 20. The process coil maintains clearance (at a distance) from a refractory wall 22 of the combustion box (radiant section 12). The electric heating element 20 is located next to or above the refractory wall 22. The fuel-fired burner 18 may include multiple burners, e.g., 1, 2, 3, 4, or more burners, up to 10, 12, or 16 burners, located in a central region of the combustion box. The process coil 16 separates the electric heating element 20 from the burner 18.

[0023] In a typical fuel-fired-only VC heater, the process coil is adjacent to the internal insulating material. Combustion energy is transferred by direct radiation to the process coil and the refractory material behind the coil. The energy accepted by the refractory material is then re-radiated to the side of the coil opposite the burner. The heat transfer intensity due to re-radiation is less than that due to direct radiation from the flame. Thus, the front side (flame side) of the coil may reach the maximum allowable tube metal temperature or process fluid film temperature, while the back side is at a much lower temperature.

[0024] In contrast, embodiments herein may provide radiant energy from an electric heating element to balance the heat input to the process coil, so that both the front and back sides can be under close process and mechanical conditions. In other words, the electric heating element may provide sufficient energy so that the front and back sides of the process coil can have similar temperatures, increasing the average heat flux to the coil. This means that for a given process efficiency, the maximum tube metal temperature can be reduced, increasing the amount of heat absorbed by the coil if the heater is operated near the maximum tube metal temperature. Furthermore, for the same process efficiency, less heating surface is required for optimized heat distribution to the coil. The reduced heating surface area requirement may also reduce the pressure drop on the process side. This means the heater may allow for a higher capacity compared to a typical VC heater.

[0025] Similar arrangements may be provided for hybrid box or cabin heaters according to embodiments herein, as illustrated in Figures 2A and 2B. Figure 2A is a single-combustion box heater with a vertically arranged coil 16, and Figure 2B is a single-combustion cabin heater with a horizontally arranged coil 16. As with the embodiment of Figures 1A and 1B, the process coil 16 is positioned intermediate the floor burner 18 and the electric heating element 20. The process coil maintains clearance (at a distance) from the refractory wall 22 of the combustion box (radiant section 12). The electric heating element 20 is located next to or above the refractory wall 22. Similar advantages in coil heating (front and rear), reduced surface area requirements, and reduced pressure drop may be achieved for box and cabin heaters according to embodiments herein.

[0026] 3A and 3B illustrate a hybrid box or cabin heater according to an embodiment herein, in which the hybrid heater includes a partition wall 24. The burner 18 can be installed next to the partition wall 24. The partition wall 24 allows heat transfer to be performed differently on different sides of the wall. That is, combustion can be different on each side of the wall without significantly affecting the process. Similar to the hybrid designs of FIGS. 1A / B and 2A / B, in the hybrid design, the electric heating element 20 is installed on the opposite side of the coil so that it can provide energy as needed. Similar advantages in coil heating (front and rear), reduced surface area required, and reduced pressure drop can also be achieved for the box heater and cabin heater according to FIGS. 3A and 3B.

[0027] While the configurations of Figures 1A-3B provide for the use of a central floor burner, embodiments herein may also use a combination of floor and wall burners, or wall burners alone, as illustrated in Figures 4A-7B. Figures 4A and 4B each show a hybrid design in which one side of the coil is heated by fuel combustion and the other side by electrical heating. Figures 5A and 5B each show a box or cabin design with an offset convection section. The radiant coils can be arranged either vertically (Figure 5A) or horizontally (Figure 5B). Similar advantages in coil heating (front and rear), reduced surface area required, and reduced pressure drop can be achieved for the embodiments of Figures 4A-5B.

[0028] 6A and 6B are dual-combustion hybrid designs. If it is necessary to have heat input with hybrid heating from both sides (both electric and combustion heating on both sides of the coil), one or more burners 18 may be installed at a higher elevation and one or more electric heating elements 20 at a lower elevation to minimize the possibility of flame impingement on the one or more electric heating elements 20. One or more burners 18, as well as one or more electric heating elements 20, are arranged on both sides of the process coil 16. As illustrated in FIGS. 7A (side view) and 7B (top view), a VC heater may also be provided with a similar vertical electric heater-burner arrangement, where an inner arrangement of electric heating elements 20 and burners 18 may be arranged around an inner heater casing 28 and an outer arrangement of electric heating elements 20 and burners 18 may be arranged within an outer heater casing 30. While the burners 18 and heating elements 20 are illustrated at similar distances from the process coil 16, embodiments herein may have casings associated with the electric heating elements closer to the process coil than the burners.

[0029] Embodiments herein may also include locating the electric heater and burner on the same side of the process coil, as illustrated, for example, for the dual-fired heater in Figure 8. The burner 18 and electric heating element 20 are separated by a mechanical barrier 32, such as a partition wall, tile, or an enclosure within which the heating element resides. Such a mechanical barrier 32 prevents flame impingement on the electric heating element 20.

[0030] Furthermore, the electric heating element and the burner can be on the same side of the heater wall, as shown in Figures 9A-9C (top view), but separated by a partition wall. As illustrated in Figures 9A-9C, the heater may include one or more sections with the electric heating element 20 and one or more sections with the burner 18, where one or both of the electric heating element 20 and the burner 18 may be located adjacent to the wall on the same side of the heater. The section with the electric heating element and the section with the burner can vary from one section to multiple sections, at different locations on the same side. A partition wall 32 may be provided between the electric heating element section and the burner section. The partition wall 32 may extend partially into the heating chamber or from one side to the opposite side, physically separating the heating element and the burner. The separate chambers may or may not have openings in the partition wall to allow atmosphere exchange within the furnace and balance pressure between the chambers. Additionally, the burners can be installed on only one side (FIG. 9C). Similar designs as shown in FIGS. 9A-9C can be applied to any other type of dual combustion design, including VC heaters as shown in FIGS. 1A and 1B.

[0031] FIGS. 10A-10D illustrate several ways in which the electric heating element can be isolated from the burner and burner flame. As illustrated in FIG. 10A, a protective tile 32A can be provided intermediate the burner (not shown) and the heating element 20. The protective tile 32A can be attached using tile supports 34A, which can be connected to the refractory insulation 36 or the casing (heater shell) 38, or both. As illustrated in FIG. 10B, in contrast to individual protective tiles associated with each heating element, a shielding wall 32B can be provided intermediate the burner (not shown) and the heating element 20, and the shielding wall 32B can be held in place by one or more shielding wall supports 34B, for example, located on the heater's top and bottom walls (not shown). FIGS. 10C and 10D illustrate a similar concept, with the heating element 20 positioned within a shielding tube 32C (FIG. 10C) or a split shielding tube 32D (FIG. 10D).

[0032] The hybrid heaters described herein can be operated with electric power while the burners are off, with the power off and the burners firing, or with both electric and burner elements operating simultaneously. Additionally, embodiments herein that include multiple burners or multiple electric heating elements can operate with less than the total number of burners fired, less than the total number of electric heating elements powered, or both burners and heating elements operating in a reduced number. In various embodiments, the burners can be fired at design capacity or at a reduced capacity. Burners can also be selectively fired, i.e., different burners can be fired separately or some burners can be turned off. Additionally, the heating elements can be fully on, partially on, or powered differently for optimal heat balance.

[0033] Electric heating elements, as previously described, may be used to supplement and provide additional heat to the back side of the process coil. Because some energy may still be re-radiated by the refractory material, the number, size, spacing, and location of the electric heating elements may be appropriately designed depending on the particular heater and process coil arrangement to provide the intended effect of enhanced heating using the hybrid heater.

[0034] Hybrid heaters according to embodiments herein may provide heating of the process fluid via electric heat, fuel-fired heat, or both, as previously described. The amount of heat input via each source may depend on operating conditions; during an upset, slowdown, or maintenance event, 100% of the heating may be provided via combustion, or 100% of the heating may be provided via electricity. However, during normal operation, the total heat input is provided by a combination of electric heating elements and fuel-fired burners. For such hybrid heating, the electric heating elements of the hybrid heaters herein are designed to provide 5% or more of the maximum energy output of the combined fuel-fired burners and heating elements. For example, the electric heating elements of the hybrid heaters herein may provide 5% or more, 8% or more, 10% or more, 15% or more, 20% or more, 30% or more, 40% or more, or even 50% or more of the maximum combined energy output, and may provide up to 15%, 20% or less, 25% or less, 30% or less, 40% or less, 50% or less, 60% or less, 70% or less, or 80% or less of the maximum combined energy output, any lower limit may be combined with any mathematically compatible upper limit.

[0035] Tables 1 and 2 compare conventional heaters with hybrid designs according to embodiments herein. [Table 1] [Table 2]

[0036] As illustrated by the comparison in Tables 1 and 2, the radiant heat surface can be reduced by about 20-30%, with CO2 reductions averaging about 42%. The more power supplied to the heater, the greater the CO2 reduction. With a larger amount of electrical energy input and reduced fuel combustion requirements, the associated operating plant may also meet its needs with non-carbon-containing fuels, allowing the heater to operate with zero CO2 emissions.

[0037] Embodiments herein also contemplate retrofitting existing heaters to provide hybrid heating capabilities. For example, in heaters where the coil is located adjacent to the refractory material, the electric heating element may be located intermediate the process coil and the refractory material. The process coil may be moved as needed to provide space for the electric heating element.

[0038] As previously described, embodiments herein provide hybrid heaters that enable hybrid heating with fuel and power. Embodiments herein may also provide operational flexibility to operate independently on fuel or power. Accordingly, embodiments of the present disclosure may provide one or more of the following advantages: increased heater capacity, reduced heater surface area, reduced process fluid pressure drop, reduced CO2 emissions, and process continuity during fuel or power outages, among other benefits. Furthermore, embodiments herein may provide adaptability to operate more effectively in slowdown conditions.

[0039] While only a few exemplary embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without substantially departing from the invention, and all such modifications are therefore intended to be included within the scope of this disclosure as defined in the following claims.

Claims

1. 1. An apparatus for heating petroleum, petrochemical products, chemical process fluids, and boiler feed water or for generating steam using a combination of electric elements and combustion burners or their separate operation, comprising: a radiant heating section and an exhaust gas stack for exhausting combustion gases to the atmosphere; one or more process coils disposed within the radiant heating section; one or more fuel-fired burners disposed within the radiant heating section, the one or more fuel-fired burners configured to combust fuel and generate the combustion gases, the one or more fuel-fired burners arranged to provide first radiant energy to a first region of the one or more process coils; one or more electric heating elements disposed within the radiant heating section, the one or more electric heating elements arranged to provide second radiant energy to second sections of the one or more process coils; The apparatus, wherein the one or more electric heating elements are configured to provide 5% or more of a maximum energy output of the one or more fuel-fired burners and the one or more electric heating elements combined.

2. The apparatus of claim 1 , wherein the one or more fuel-fired burners comprise one or more floor burners, one or more wall burners, or a combination of floor and wall burners.

3. The apparatus of claim 1 , wherein the one or more fuel-fired burners are wall burners positioned vertically above the one or more electric heating elements.

4. The apparatus of claim 1 , further comprising a shielding wall disposed intermediate the one or more fuel-fired burners and the one or more electric heating elements.

5. The apparatus of claim 4 , wherein the shielding wall comprises one or more shielding walls disposed intermediate a portion of one or more fuel-fired burners and a portion of one or more electric heating elements.

6. The apparatus of claim 5 , wherein the one or more shielding walls are disposed on one side of the radiant heating section and extend partially from an outer wall of the radiant heating section toward the interior of the radiant heating section.

7. The apparatus of claim 5 , wherein the one or more shielding walls are disposed on both sides of the radiant heating section and extend partially from an outer wall of the radiant heating section toward the interior of the radiant heating section.

8. 6. The apparatus of claim 5, wherein the one or more shielding walls are disposed on both sides of the radiant heating section and extend from a first side of the outer wall of the radiant heating section to a second side of the outer wall of the radiant heating section, and the one or more shielding walls include a plurality of holes extending through the one or more shielding walls.

9. 1. An apparatus for heating petroleum, petrochemical products, chemical process fluids, and boiler feed water or for generating steam using a combination of electric elements and combustion burners or their separate operation, comprising: a radiant heating section and an exhaust gas stack for exhausting combustion gases to the atmosphere; one or more process coils disposed within the radiant heating section; one or more fuel-fired burners disposed within the radiant heating section, the one or more fuel-fired burners configured to combust fuel and generate the combustion gases, the one or more fuel-fired burners arranged to provide first radiant energy to a first side of the one or more process coils; one or more electric heating elements disposed within the radiant heating section, the one or more electric heating elements arranged to provide second radiant energy to a second side of the one or more process coils; the second side is opposite the first side, and the second radiant energy is greater than or equal to 5% of a maximum combined energy output of the one or more fuel-fired burners and the one or more electric heating elements.

10. The apparatus of claim 9 , wherein the one or more fuel-fired burners comprise one or more floor burners, one or more wall burners, or a combination of floor and wall burners.

11. 10. The apparatus of claim 9, wherein the one or more fuel-fired burners are wall burners positioned vertically above the one or more electric heating elements.

12. The apparatus of claim 11 , further comprising a shielding wall disposed intermediate the one or more fuel-fired burners and the one or more electric heating elements.

13. 10. The apparatus of claim 9, wherein the one or more process coils are arranged in a circular array within the radiant heating section, the one or more electric heating elements are positioned between the one or more process coils and a refractory wall of the radiant heating section, and the one or more fuel-fired burners are positioned proximate a center of the radiant heating section.

14. The apparatus of claim 13 , wherein the one or more process coils are oriented vertically within the radiant heating section.

15. The apparatus of claim 13 , wherein the one or more process coils are oriented horizontally within the radiant heating section.

16. 14. The apparatus of claim 13, further comprising a divider wall disposed proximate a center of the radiant heating section, and the one or more fuel-fired burners disposed circumferentially around the divider wall.

17. 1. An apparatus for heating petroleum, petrochemical products, chemical process fluids, and boiler feed water or for generating steam using a combination of electric elements and combustion burners or their separate operation, comprising: a radiant heating section and an exhaust gas stack for exhausting combustion gases to the atmosphere; one or more process coils positioned proximate the center of the radiant heating section; one or more fuel-fired burners disposed within the radiant heating section and circumferentially around the one or more process coils, the one or more fuel-fired burners configured to combust fuel and generate the combustion gases, the one or more fuel-fired burners arranged to provide first radiant energy to a first side of the one or more process coils; the one or more electric heating elements disposed within the radiant heating section and proximate to a refractory material of a wall of the radiant heating section located horizontally between the one or more fuel-fired burners and the one or more electric heating elements, the one or more electric heating elements arranged to provide second radiant energy to the first side of the one or more process coils, the second side being opposite the first side; The apparatus, wherein the one or more electric heating elements are configured to provide 5% or more of a maximum energy output of the one or more fuel-fired burners and the one or more electric heating elements combined.

18. 18. The apparatus of claim 17, further comprising a shielding wall disposed intermediate the one or more fuel-fired burners and the one or more electric heating elements.

19. 18. The apparatus of claim 17, wherein the one or more process coils are oriented vertically within the radiant heating section.

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