Patent Application
20240352338
In the refining and petrochemical industries, heaters are predominantly fuel fired. The current fired heaters generate carbon dioxide when firing hydrocarbon fuels, which is a source of greenhouse gases that lead to global warming. Thus, there is a general desire to move away from hydrocarbon fuel-fired heaters.
Electric heaters, however, are presently limited to relatively small capacity, and only now under development for large capacity application. However, none of the heaters are designed to have co-existence of fuel fired burners and electric heating elements, a hybrid energy input with both fuel combustion and electricity. When the electric heating elements and fuel burners are both installed in a heater, the intensive combustion from the burners tends to damage the electrical heating elements due to overheating or carburization.
Several challenges exist when shifting to solely electrical heating. Further, the electric heaters do not directly combust any fuels and will not have any flue gas. The electric heater will not have convection sections, which are traditionally used to capture additional heat for steam generation and feed pre-heating, among other uses. When the electric power is lost, the electric heater will have to be shut down and the plant operation will be interrupted, or equipment damaged, due to sudden operating condition changes.
Accordingly, there exists a need in the art for heaters that provide operational continuity while also reducing greenhouse gas production.
This summary is provided to introduce a selection of concepts that are further described 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.
In one aspect, embodiments disclosed herein relate to an apparatus for heating petroleum, petrochemical, chemical process fluids, and boiler feed water or steam generation with a combination, or individual operation, of electrical elements and fired burner. The apparatus further includes a radiant heating section and a flue gas stack for exhausting a combustion gas 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 for combusting a fuel and producing the combustion gas, wherein the one or more fuel-fired burners are arranged to provide a first radiant energy to an upper elevation of the one or more process coils; one or more electrical heating elements disposed within the radiant heating section, the one or more electrical heating elements arranged to provide a second radiant energy to a lower elevation of the one or more process coils; and an internal baffle located at an elevation between the upper elevation and the lower elevation, the internal baffle arranged to provide shielding of the one or more electrical heating elements from flame and combustion gases from the one or more fuel-fired burners. The one or more electrical heating elements are configured to provide 5% or more of a combined maximum energy output of the one or more fuel-fired burners and the one or more electrical heating elements.
In other aspects, embodiments disclosed herein relate to a process for retrofitting a fuel-fired heater, having a radiant heating section, one or more process coils in the radiant heating section, and a flue gas stack, for heating petroleum, petrochemical, chemical process fluids, and boiler feed water or steam generation to include a combination of electrical heating elements and fuel-fired burners. The process includes removing one or more fuel-fired burners disposed at a lower elevation in the radiant heating section; retaining one or more fuel-fired burners disposed at an upper elevation in the radiant heating section; disposing one or more layers of refractory material in the lower elevation in the radiant heating section; disposing one or more electrical heating elements in the lower elevation in the radiant heating section proximate a surface of the one or more layers of refractory material, wherein the one or more electrical heating elements are disposed at a distance of 12 to 18 inches from the one or more process coils; and disposing an internal baffle between the upper elevation and the lower elevation, the internal baffle configured to provide shielding of the one or more electrical heating elements from flame and combustion gases from the one or more fuel-fired burners.
In yet another aspect, embodiment disclosed herein relate to a method of retrofitting a cracking heater comprising a radiant heating zone and a convective heating zone, wherein the radiant heating zone comprises a floor, floor burners disposed in the floor, a refractory wall including a first wall opposite a second wall, wall burners disposed along a height of the first wall and the second wall, and a radiant coil disposed within the radiant heating zone intermediate the first wall and the second wall. The method includes installing an intermediate floor at an elevation below a wall burner; installing a second refractory wall from the floor to the intermediate floor; moving a floor burner from the floor to the intermediate floor; and installing one or more electrical heating elements along a height of the second refractory wall.
Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.
In one aspect, embodiments disclosed herein relate to heaters providing a combination of both fuel-fired burners and electrical heating elements. Embodiments herein will have a fuel-fired burner and electrical heating elements in the same chamber and the heater can be operated with the fuel burner, heating elements, or both at the same time.
A heater for heating petroleum, petrochemical, chemical process fluids, and boiler feed water or steam generation/superheat with a combination, or individual operation, of electrical heating elements and fuel-fired burners according to some embodiments herein include a radiant heating section, a convective heating section, and a flue gas stack. The radiant section includes one or more fuel-fired burners, such as including one or both of wall and floor burners, and one or more electrical heating elements, which can be metallic, non-metallic or a combination of metallic and non-metallic, where each of the burners and electric heating elements are arranged and configured to provide radiant heat to one or more process or utility streams (heating coils, radiant coils, or process coils herein) disposed within the radiant section of the heater. The convective section of the heater is configured to receive a combustion gas produced by the fuel-fired burners and, in some embodiments, is further configured to provide convective heat to one or more process or utility streams (convective coils) disposed and arranged within the convective section of the heater. The flue gas stack is configured similar to typical furnaces and receives the (heat-depleted) combustion gas from the convective heating section and for exhausting the combustion gas to the atmosphere.
In some embodiments, the one or more fuel-fired burners are arranged to provide radiant energy to a first portion or first area of the one or more process coils. Further, the one or more electrical heating elements disposed within the radiant heating section are arranged to provide radiant energy to a second portion or second area of the one or more process coils. For example, in various embodiments the fuel fired burners and electrical 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 portions of a coil.
Heating at different elevations may be provided, for example, by disposing electrical heating elements at a lower elevation within the heater and disposing fuel-fired burners vertically above the electrical heating elements. In this manner, the combustion products, which preferentially exhaust upward, may not result in soot or deposition of combustion products on the electrical heating elements.
In other embodiments, the one or more fuel-fired burners are arranged to provide radiant energy to a first elevation of the one or more process coils. Further, the one or more electrical heating elements disposed within the radiant heating section are arranged to provide radiant energy to a second elevation of the one or more process coils. For example, a process coil may be disposed intermediate (between) both one or more fuel-fired burner and one or more electrical heating elements. Radiant energy from the fuel-fired burners may thus impact and heat the first elevation of the process coils, while radiant energy from the electrical heating elements may impact and heat the second elevation of the process coils.
Embodiments herein are thus configured and arranged to provide radiant energy to process coils via radiant energy from fuel-fired burners, electrical heating elements, or both burners and heating elements. Such configurations will allow the heater to be operated with fuel firing, or partial fuel firing supplemented by electric heating, or completely with electric heating. The greenhouse gas emission can be reduced and the waste heat from combustion exhaust can be recovered by feedstock preheat of auxiliary streams via the convection section. In embodiments where carbon-free fuels like H2 or NH3 are used, there will not be any greenhouse gas emissions from the flue gas stack. More importantly, the heater and associated equipment can stay in operation in the event of a power failure, by operating the fuel-fire burners, or fuel supply shortage, by operating the electrical heating elements.
As outlined above, embodiments herein may include providing radiant energy directly from an electrical heating element to a process coil. Proper design of a heater may limit or prevent undesired overheating or carburization of the electrical heating elements. Exposure of the electrical heating elements to radiant energy from the burners, as well as exposure of the electrical heating elements to combustion products, may be limited, for example, by design considerations such as: vertical arrangement of heating elements and burners; partial or total shielding of the electrical heating elements via shield walls, shield tiles, or shield tubes; or various combinations of two or more of these design considerations.
In some embodiments, the heater may not be equipped with a convection section and may just exhaust combustion gas directly through the flue gas stack. In other embodiments, the hot flue gas may be routed to other heat recovery units such as external gas-fluid heat exchangers or waste heat boilers.
For example, in some embodiments, the electrical heating elements are shielded by a high temperature material where the combustion of fuel and the exhaust gas will not be in direct contact with the electrical heating elements. As another example, the electrical heating elements may be configured to provide varying amounts of heating from one element, or group of elements, to another. In such examples, the heat profile of the electrical heating elements may be non-uniform across either or both the width or height of the furnace at the elevations where the electrical heating elements are disposed. The electrical heating elements may provide uniform heat flux or may be arranged to provide heat in a selected heat flux pattern to meet process requirements. The heating elements, both fuel fired and electrical, are disposed throughout areas (floor, lower wall, or upper wall, for example) in a heater that may have the same or different mechanical configurations. The heating elements may be installed evenly or in a selected pattern throughout the heater. Embodiments herein may thus provide unique and advantageous arrangements of the fuel-fired burners and electrical heating elements, providing for excellent flexibility in operation of heating by electrical energy, combustion, or both.
In some embodiments, the electrical heating elements may be useful for retrofit of an existing heater to convert from 100% fuel fired to at least partially electrically heated. This can be accomplished by installing an electric heating section below the combustion section and may result in improved heat flux distribution, increased coil life, and improved overall performance.
Referring now to the Figures, exemplary embodiments of various configurations of hybrid heaters, including electrical heating elements and fuel-fired burners, are illustrated. In the Figures, like numerals represent like parts.
In a typical fuel-fired only heater, the process coils are next to the internal insulating material. The combustion energy is transferred to the process coil and the refractory material behind the coil by direct radiation. The energy received by the refractory material is then re-radiated to the side of the coil opposite the burner. The heat transfer intensity by re-radiation is less than the direct radiation from the flame. The front side (flame side) of the coil may thus reach a maximum acceptable tube metal temperature or process fluid film temperature, while the back side is at a much lower temperature.
In contrast, embodiments of
With respect to the embodiments of the hybrid heating designs as illustrated in
Other embodiments may be designed to minimize the effects of the combustion zone on the electrical heating elements. As illustrated in
The general configuration illustrated in
The electrical heating element 20 can include a first power connection 21 and a second power connection 22. The second power connection 22 is installed outside the heater 10 and is cooled by ambient air. The first power connection 21 may also be installed outside the heater 10, but may be located in a recessed cavity created by a bull nose, or internal baffle 24. Being located in such an area may limit the ability for ambient air to properly cool the first power connection 21. However, in some embodiments, the fuel fired burner 18 may introduce combustion air 26 through a channel created by external baffle 28. The combustion air will travel over the first power connection 21 providing adequate cooling. At the same time, the heat removed from the first connection point 21 by the combustion air 26 will pre-heat the combustion air utilized for combustion in fuel fired burner 18 to improve the overall fuel efficiency.
The internal baffle 24 may define an opening between the lower electrical heating zone and the upper fuel fired zone to equalize the pressure between the lower electrical heating zone and the upper fuel fired zone. While not illustrated, the opening may also be closed to minimize the combustion flue gas entering the electrical heating section, with provision of pressure relief in case any potential pressure buildup in the electrical heating section.
In some embodiments, one or more purge connections 30 are provided in the radiant section 12. The purge connection can be used to set an environment within the heater prior to the heater startup or can be used to remove any hazardous gas from the heater during shut down. When necessary, a purge gas may be provided through the purge connection to maintain the radiant section with a required working environment, such as to prevent moisture from accumulating in the electrical heating zone, such as due to combustion in the upper zone, which may cause damage to the heating elements. The purge can be continuously or intermittently operated as needed. In some embodiments, one or more sensors may be located with or proximate the purge connection to monitor temperature, pressure, humidity, flow rate, etc. The purge gas can be air, nitrogen, or other types of gas which may be required to meet the requirements of the selected heating elements. In some embodiments, a small amount of oxygen may be introduced with non-air purge gases to ensure that the heating elements maintain an oxide layer or are not exposed to a reducing atmosphere.
For the upper fuel fired section, the fuel fired burners 18 can be installed through the floor of the fired section as hearth burners (
Retrofitting of an existing heater to arrive at the embodiments of
In other embodiments, a shielding baffle or refractory may be installed to retrofit an existing heater to provide for the hybrid heating. This may be accomplished by installing layers of refractory material in the lower portion of the heater as illustrated in
Further, as illustrated in
The electrical heating elements can be completely with metallic heating elements or non-metallic heating elements or combination of metallic and non-metallic, in any form, style or material. Non-metallic SiC elements or MoSi2 elements offer high heat flux at temperatures>1000 C. However, with the placement of the electrical heating elements as described in
In some embodiments, the process conditions in hybrid heaters are kept unchanged, including the steam production, while the fuel firing can be reduced by about 15%, i.e., 15% CO2 reduction, up to about 35% reduction. By adjusting the excess air to the burners only a small reduction in SHP steam production can be expected. With higher excess air, higher steam production is possible, but that will increase fuel consumption and reduce the % CO2 reduction.
With hybrid heating, the heat flux in the radiant section will be improved due to even heat output by the electrical heating element over the surface area of the process coils. The hybrid heating can improve the heat flux and reduce the maximum tube metal temperature which may improve the heater run length or the coil service life.
Further, in some embodiments, the fuel firing and amount of electrical heating elements can vary along the length of the heater. As illustrated in
In one or more embodiments, the fuel firing and the electrical heating may be separated by one or more partition plates. As illustrated in
In some embodiments, it may be desired to allow purge gas to flow through the gaps between the partition plates 46 and the radiant coil 16 and/or the gaps between the partition plates 46 and the refractory material 40 of the exterior wall. The purge gas flowing through the gaps in the partition plates 46 between the electrical heating elements 20 and the fuel firing hearth burner 18 may reduce restriction in heat flux, prevent any pressure buildup in the electrical heating section, and promote upward flow of exhaust so as to avoid soot or combustion gas impingements, maintaining an environment favorable to the electrical heating element operation.
In one or more embodiments, the partition plates 46 may be composed of any high temperature material. In some embodiments, the partition plate 46 may be in the physical form of flat plates, bellowed plates, and fabric, in any combination thereof.
The hybrid heaters described herein can be operated with electric power while the burners are in off status, while the electric power is turned off and the burners are fired, or where both the electric and burners are operated at the same time. Further, embodiments herein including multiple burners or multiple electrical heating sections can be operated with less than a total amount of the burners fired, less than a total amount of the electrical heating sections powered, or both burners and heating elements operating at a reduced number. In various embodiments, the burners can be fired at the design capacity or reduced capacity. The burners can also be fired selectively, i.e., different burners are fired differently, or some burners are in off conditions. Further, the heating elements can all be on, or partially on, or powered differently, for optimum heat balance.
The electrical heating elements may be used, as described above, to supplement and provide additional heat to the back side of process coils. As some energy may still be re-radiated by the refractory material, the number, size, spacing and location of the electrical heating elements may be appropriately designed for a particular heater and process coil arrangement to provide the intended effect of enhanced heating using the hybrid heater.
Hybrid heaters according to embodiments herein may, as noted above, provide for heating of the process fluid via electrical heat, fuel-fired heat, or both. The amount of heat input via each source may depend upon operating conditions, where during upset, turndown, or maintenance conditions, 100% of heating may be provided via combustion, or 100% of the heating may be provided via electric. During normal operations, however, the total heat input will be provided by a combination of electrical heating elements and fuel fired burners. For such hybrid heating, the electrical heating elements of hybrid heaters herein are designed to provide 5% or more of the combined maximum energy output of the fuel fired burners and heating elements. For example, the electrical heating elements of 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 combined maximum energy output, and up to 15% or less, 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 combined maximum energy output, where any lower limit may be combined with any mathematically compatible upper limit.
As described above, embodiments herein provide hybrid heaters, allowing for hybrid heating by fuel and electricity. Embodiments herein may also provide for operational flexibility for operating with fuel or electricity independently. Embodiments of the present disclosure may thus provide advantages in one or more of increased heater capacity, reduced heater surface area, reduced process fluid pressure drop, reduced CO2 emissions, process continuity during fuel or electricity upsets, among other advantages. Further, embodiments herein may provide adaptability to operate more effectively at turndown conditions.
Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.
| Number | Date | Country | |
|---|---|---|---|
| 63497775 | Apr 2023 | US |
