WO2025166115A1

WO2025166115A1 - Converted gas-fired furnace

Info

Publication number: WO2025166115A1
Application number: PCT/US2025/013959
Authority: WO
Inventors: Rolando JULIANO; Dyson CABAHUG
Original assignee: Watlow Electric Manufacturing Co
Current assignee: Watlow Electric Manufacturing Co
Priority date: 2024-02-01
Filing date: 2025-01-31
Publication date: 2025-08-07
Anticipated expiration: 2026-08-01

Abstract

A converted gas-fired furnace includes at least one lower radiant heating zone, an upper convective heating zone, electric ceramic fiber heaters, and duct heaters. The lower radiant heating zone includes a plurality of lower tubes configured to carry a fluid to be heated. The upper convective heating zone includes a plurality of upper tubes configured to carry the fluid to be heated. The electric ceramic fiber heaters are disposed within the lower radiant heating zone and are configured to heat the fluid in the lower tubes. The duct heaters are configured to heat the fluid in the upper tubes.

Description

CONVERTED GAS-FIRED FURNACE

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. provisional application number 63/548,740 filed February 1 , 2024. The disclosure of the above application is incorporated herein by reference in its entirety.

FIELD

[0002] The present disclosure relates to gas-fired furnaces, and more specifically to industrial gas-fired furnaces for heating fluids such as hydrocarbon oils for pyrolytic conversion.

BACKGROUND

[0003] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0004] Conventional gas-fired furnaces include a lower radiant heating area, an upper convective heating area, a plurality of lower tubes disposed within the lower radiant heating area, and a plurality of upper tubes disposed within the upper convective heating are. The tubes are configured to carry a fluid to be heated, such as hydrocarbon oils for subsequent refining. Gas nozzles are typically located at the bottom of the lower radiant heating area, and the gas nozzles supply combustible fuel and air to the lower radiant heating area. The hot combustion gases heat the fluid in the lower tubes by radiation and heat the fluid in the upper tubes by convection. The partially cooled gases from the upper and lower heating areas pass through a flue to a stack.

[0005] Heating the fluid in the lower and upper tubes using the hot combustion gases generates exhaust gases (e.g., carbon dioxide), which may be detrimental to the environment. Additional equipment is often used to remove harmful substances from the combustion gases, however, the additional equipment can be expensive and reduce the overall efficiency of the furnace.

[0006] These and other issues related to gas-fired furnaces is addressed by the present disclosure.

SUMMARY

[0007] This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all of its features.

[0008] In one form, the present disclosure provides a converted gas-fired furnace that includes at least one lower radiant heating zone, an upper convective heating zone, a plurality of electric ceramic fiber heaters, and a plurality of duct heaters. The lower radiant heating zone comprises a plurality of lower tubes configured to carry a fluid to be heated. The upper convective heating zone comprises a plurality of upper tubes configured to carry the fluid to be heated. The electric ceramic fiber heaters are disposed within the lower radiant heating zone and are configured to heat the fluid in the lower tubes. The plurality of duct heaters are configured to heat the fluid in the upper tubes.

[0009] In variations of the converted gas-fired furnace of the above paragraph, which can be implemented individually or in any combination: the electric ceramic fiber heaters comprise cylindrical shells surrounding the plurality of lower tubes within the lower radiant heating zone; the cylindrical shells comprise two halves; a plurality of structural supports are secured around the cylindrical shells; the cylindrical shells are a single unitized piece; the electric ceramic fiber heaters comprise flat panels secured to side walls of the lower radiant heating zone; the electric ceramic fiber heaters comprise power leads, the power leads extend through the side walls of the lower radiant heating zone; the electric ceramic fiber heaters comprise power leads, the power leads extend through preexisting apertures disposed along a bottom wall of the lower radiant heating zone; a fluid circuit comprises a plurality of ducts, a blower and a return duct, the ducts extending from the plurality of duct heaters to the upper convective heating zone, the blower in fluid communication with the plurality of duct heaters and the ducts, the return duct extending from an outlet of the upper convective zone to the blower, heated fluid from the duct heaters is recirculated through the fluid circuit; a distribution manifold is in communication with the duct heaters and extend along a lower portion of the upper convective zone; the duct heaters are arranged in series; the electric ceramic fiber heaters comprise a first set of electric ceramic fiber heaters and a second set of electric ceramic fiber heaters, the first set of electric ceramic fiber heaters comprises cylindrical shells surrounding at least some of the plurality of lower tubes within the lower radiative heating zone and the second set of electric ceramic fiber heaters comprises flat panels secured to internal side walls of the lower radiant heating zone; the duct heaters are arranged below the lower radiant heating zone; and a plurality of ducts extending from the plurality of duct heaters to the upper convective heating zone, the ducts extending through and fluidly isolated from the lower radiant heating zone.

[0010] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

[0011] In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

[0012] FIG. 1 A is a side schematic view of a converted gas-fired furnace comprising ceramic fiber heaters according to the principles of the present disclosure;

[0013] FIG. 1 B is another side schematic view of the converted gas-fired furnace of FIG. 1A;

[0014] FIG. 2A is a side view of the converted gas-fired furnace of FIG. 1A comprising electric heaters;

[0015] FIG. 2B is a close-up view of converted gas-fired furnace at the area encircled in FIG. 2A;

[0016] FIG. 2C is a perspective view of a half-shell of one electric heater of FIG. 2B;

[0017] FIG. 3A is a perspective view of a portion of the electric heater according to one form;

[0018] FIG. 3B is a side view of the portion of the electric heater of FIG. 3A;

[0019] FIG. 3C is an end view of the electric heater of FIG. 3A;

[0020] FIG. 4A is an end view of an electric hear according to another form;

[0021] FIG. 4B is a perspective view of the electric heater of FIG. 4A;

[0022] FIG. 5A is a side schematic view of another converted gas-fired furnace comprising electric heaters according to the principles of the present disclosure;

[0023] FIG. 5B is a perspective view a portion of one electric heater of the electric heaters of FIG. 5A; [0024] FIG. 5C is a perspective view of a portion of one electric heater of FIG. 5A;

[0025] FIG. 5D is a perspective view of another electric heater of the electric heaters of FIG. 5A;

[0026] FIG. 6A is a side view of another converted gas-fired furnace comprising electric heaters according to the principles of the present disclosure;

[0027] FIG. 6B is a close-up view of converted gas-fired furnace at the area encircled in FIG. 6A;

[0028] FIG. 7 is a side view of a portion of another converted gas-fired furnace comprising electric heaters according to the principles of the present disclosure; and

[0029] FIG. 8 is a side view of another converted gas-fired furnace comprising electric heaters according to the principles of the present disclosure.

[0030] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

[0031] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

[0032] With reference to FIGS. 1A, 1B, and 2A-2C, one form of a converted gas-fired furnace according to the teachings of the present disclosure is illustrated and generally indicated by reference numeral 10. The converted gas-fired furnace 10 is generally configured to heat a fluid flowing therethrough, such as by way of example hydrocarbon oil. It should be understood, however, that other types of fluid may be heated according to the teachings herein, such as by way of example, water or various chemical compositions, among others. Further, the term "fluid" as used herein should be construed to include liquid, gas, and/or plasma. Advantageously, rather than using conventional combustion gases, the fluid is heated using electric heaters (described in greater detail below) and includes a lower heating zone 12, an upper heating zone 14, sets of lower tubes 16a, 16b, upper tube banks 17, 18, 20 and a plurality of electric heaters 22. Accordingly, the term "converted" should be construed to mean a preexisting gas-fired furnace that is modified to use electric heat rather than gas heat, while maintaining its preexisting structure (set forth in greater detail below) that has previously been designed specifically for gas heat. Thus, the teachings of the present disclosure are directed to modifying a gas-fired furnace with electric heat rather than gas heat, which may be entirely electric heat as illustrated and described herein, or a combination of electric heat and gas heat (a "hybrid"). Much of the existing structure of a gas-fired furnace is maintained for a low cost and efficient alternative to an entirely redesigned electric furnace, thereby providing a low cost alternative to meet changing environmental standards and regulations for gas-fired furnace operators.

[0033] In the example illustrated, the lower heating zone 12 is a radiant heating zone formed by side walls 24 and a bottom wall 26. The side walls 24 extend from the bottom wall 26 to the upper heating zone 14. In the example illustrated, the bottom wall 26 includes preexisting apertures 25 extending therethrough. The preexisting apertures are configured to receives gas nozzle fittings (not shown) that supply combustible fuel and air to the lower heating zone 12 of conventional gas fired furnaces.

[0034] In some forms, one or more bridge walls (not shown) may extend vertically upward from the bottom wall 26, for example, to divide a lower portion of the converted gas-fired furnace 10 into two or more separate radiant lower heating zones configured to heat tubes disposed therein. In other forms, a partition wall 27 is disposed at an upper portion of the lower heating zone 12 and extends in a horizontal direction to separate the lower heating zone 12 from the upper heating zone 14. This partition wall 27 does not extend across the heating area within the zones and instead functions to transition from a wider lower heating zone 12 to a more narrow upper heating zone 14.

[0035] In the example illustrated, the upper heating zone 14 is a convective heating zone located above the lower heating zone 12 and contains a volume that is less than the volume of the lower heating zone 12. The upper convective heating zone 14 is formed by side walls 34 and an upper wall 36. The side walls 34 extend in a vertical direction from the side walls 24 to the upper wall 36. The upper wall 36 generally extends in a horizontal direction and has at least one aperture 37 at an upper portion to allow fluid flowing through the upper heating zone 14 to flow out of, or be exhausted from, the converted gas-fired furnace 10. The exhausted gas is further circulated as set forth in greater detail below. [0036] The sets of lower tubes 16a, 16b are in fluid communication with each other and are configured to carry the fluid to be heated. The set of tubes 16a are horizontally disposed within the lower heating zone 12 adjacent one of the side walls 24 and extend substantially an entire width of the side wall 24. Each tube 38 in the set of tubes 16a are fluidly connected to each other by elbows 40, which connect ends of adjacent tubes 16a as shown. In the example illustrated, a subset of tubes is spaced apart from the side wall 24 and are vertically aligned with each other within the lower heating zone 12 so as to generally form a column (FIG. 1B). The distance between adjacent tubes 38 may vary along the column. For example, adjacent tubes 38 located near a lower portion of the column may include a greater distance therebetween than adjacent tubes 38 located near an upper portion of the column. In other forms, the tubes 38 located in the column may have equal spacing therebetween. These and other spacing configurations should be construed as being within the scope of the present disclosure.

[0037] Similarly, the set of tubes 16b are horizontally disposed within the lower heating zone 12 adjacent the other side wall 24 and extend substantially an entire width of the side wall 24. Each tube 42 of the set of the tubes 16b are also connected to each other by elbows as set forth above, which connect ends of adjacent tubes 42. In the example illustrated, a subset of tubes 42 are spaced apart from the side wall 24 and are vertically aligned with each other within the lower heating zone 12 so as to form a column (FIG. 1 B). As set forth above, the distance between adjacent tubes 42 may vary along the column. For example, adjacent tubes 42 located near a lower portion of the column may include a greater distance therebetween than adjacent tubes 42 located near an upper portion of the column. In other forms, the tubes 42 located in the column may have equal spacing therebetween. These and other spacing configurations should be construed as being within the scope of the present disclosure. Further, in this form, the tubes 42 also extend parallel to the tubes 38.

[0038] The upper tube banks 17, 18, 20 are horizontally disposed within the upper heating zone 14 between side walls 34 and are in fluid communication with each other to carry the fluid to be heated. That is, fluid flowing through the sets of tubes 16a, 16b subsequently flows through the upper tube banks 17, 18, 20 where the fluid is heated further before exiting the converted gas-fired furnace 10. In the example illustrated, the upper tube bank 17 is located closer to the lower heating zone 12 than the upper tube banks 18, 20. Each of the tube banks 17, 18, and 20 comprises a plurality of rows of tubes. In one form, adjacent rows of tubes are vertically offset from each other (FIG. 1 B). In another form, adjacent rows of tubes may be vertically aligned with each other (not shown). In one form, the spacing between the rows of tubes may be equal to each other or may vary along the tube bank 17. These and other configurations of the tube banks 17, 18, and 20 should be construed as falling within the scope of the present disclosure.

[0039] The upper tube bank 18 is located closer to the upper wall 36 of the upper heating zone 14 than the tube banks 17, 20 and comprises a row of tubes. The structure and function of the upper tube bank 18 is generally similar or identical to that of upper tube bank 17, therefore, will not be described again in detail. The upper tube bank 20 is located between the upper tube banks 17, 18 in the upper heating zone 14 and comprises a row of tubes. The structure and function of the upper tube bank 20 is again generally similar or identical to that of upper tube banks 17, 18, therefore, will not be described again in detail.

[0040] With reference to FIGS. 2A-2C and 3A-3C, the plurality of electric heaters 22 comprises a plurality heaters disposed within the lower radiant heating zone 12. As described in greater detail below, the plurality of electric heaters 22 are disposed around (in one form) or disposed adjacent to (in another form) respective tubes 38, 42 of the sets of lower tubes 16a, 16b. In this way, fluid flowing through the tubes 38, 42 is heated by the electric heaters 22. In one form of the present disclosure, the electric heaters are an electric ceramic fiber heater 23, which as described in greater detail below, generally includes a ceramic body with electrical heating elements disposed within the ceramic body, along with power leads electrically connected to the electrical heating elements and extending outside the ceramic body for connection to a power supply. Such ceramic fiber heaters are provided by Watlow Electric Manufacturing Company and are available in a variety of shapes, sizes, and electrical configurations. Further information on this type of heater construction can be found at: https://www.watlow.com/products/heaters/high-temperature- heaters/ceramic-fiber-heaters. It should be understood, however, that other forms of heaters may be employed while remaining within the scope of the present disclosure, such as by way of example, layered heaters, heat trace, and flexible heaters (e.g., silicone rubber), among others. Accordingly, the electric ceramic fiber heaters 23 should not be construed as limiting the scope of the present disclosure. [0041] In one form, each electric ceramic fiber heater 23 includes a shell 54 and a heating element 56 embedded within the shell. In the example illustrated, the shell 54 is in two pieces, or halves, and has a cylindrical shape to surround and conform to a respective tube 38, 42. In this way, heat generated by the electric ceramic fiber heaters 23 is directed or radiated to the tube 38, 42 to heat the fluid flowing through therethrough. In another form, the shell 54 is made of a single unitized cylindrical body that surrounds the tubes 38, 42, which is described in greater detail below.

[0042] A plurality of structural supports 58 (FIGS. 3A-3C) are secured to the walls 24 of the converted gas-fired furnace 10 and are configured to support the electric ceramic fiber heaters 23. In the example illustrated, sets of structural supports 58 are arranged in rows in the lower heating zone 12 and include a pair of legs 58a, 58b that form a V-shape or U-shape. Distal ends of the legs 58a, 58b may be secured to the wall 24 via welding, mechanical fasteners, or any other suitable attachment means. Each of the electric ceramic fiber heaters 23 is generally supported on the leg 58a of the structural supports 58, thereby supporting the electric ceramic fiber heaters 23 along their entire length. In one form not shown, the structural supports may be secured around the cylindrical shell 54 and then secured to the walls 24 of the converted gas-fired furnace 10.

[0043] The heating element 56 (FIG. 3C) is embedded within the shell 54 and is configured to generate heat that is transferred to the tube 38, 42 by radiation. The heating element 56 is embedded within and extends substantially along the entire length of the shell 54 in a predetermined configuration. In one form, the heating element 56 is embedded within and extends along the length of the shell 54 in a spiral configuration. In another form, the heating element 56 is embedded within and may extend along the length of the shell 54 in a straight line or linear configuration. In yet another form, the heating element 56 is embedded within and may extend along the length of the shell 54 in a sinuated configuration. The heating element 56 is generally a resistive heating element.

[0044] Power leads 60 are connected to a power source (not shown) and to the respective heating elements 56 and are configured to provide power to the heating elements 56 such that the heating elements 56 generate heat. The power leads 60 generally extend from the shell 54 of the electric ceramic fiber heater 23 in a radial direction as shown. In another form, the power leads 60 may extend from the shell 54 of the electric ceramic fiber heater 23 in an axial, or other direction.

[0045] In one form of the present disclosure, each electric ceramic fiber heater 23 includes a plurality of heating zones (not shown) that may include additional power leads and busing arrangements depending on the zone configuration. For example, each heating zone is operable independent of the other heating zones. A plurality of power leads may be connected to respective heating zones of the radiant electric heater 22 and may be independently controlled using a switch, for example, to heat the respective heating zones based on requirements of the fluid flowing through the tube 38, 42. Examples of such heating zones is disclosed in U.S. Patent No. 10,247,445, which is commonly owned with the present application and the contents of which are incorporated herein by reference in their entirety.

[0046] Referring now to FIGS. 4A and 4B, another form of the electric ceramic fiber heaters is illustrated and generally indicated by reference numeral 122. The ceramic fiber heater 122 includes a shell 154 and a plurality of heating elements 156 embedded within the shell 154, similar to the heating elements 56 as described above. In the example illustrated, the shell 154 is a single unitized piece comprising a plurality of cylindrical sections 157 that surround and conform to the respective tubes 138. In this way, heat generated by the ceramic fiber heater 122 is directed, or radiated to the tubes 138 to heat the fluid flowing therethrough. The heating elements 156 and their power leads 160 are similar to the heating elements 56 described above, and thus further details and variations are not described here for purposes of clarity.

[0047] A plurality of structural supports 158 are secured to the walls (not shown) of the converted gas-fired furnace 10 and are configured to support the ceramic fiber heater 122. In the example illustrated, the structural supports 158 may be secured around the cylindrical sections 157 of the shell 154 and may be secured to the walls of the converted gas-fired furnace 10 via welding, mechanical fasteners, or any other suitable attachment means.

[0048] Referring to FIGS. 5A-5C, another form of a converted gas-fired furnace according to the teachings of the present disclosure is illustrated and generally indicated by reference numeral 210. The converted gas-fired furnace 210 is similarly configured to heat a processing fluid flowing therethrough using electric heaters as set forth above. Accordingly, the converted gas-fired furnace 210 includes a lower heating zone 212, an upper heating zone 214, sets of lower tubes 216, upper tube banks 217, 218, 220 and a plurality of electric heaters 222.

[0049] The structure and function of the lower heating zone 212, the upper heating zone 214, the lower tubes 216 and the upper tube banks 217, 218, 220 are similar or identical to that of the lower heating zone 12, the upper heating zone 14, the lower tubes 16a, and the upper tube banks 17, 18, 20, respectively, described above, and therefore, will not be described again in detail.

[0050] The plurality of electric heaters 222 in this form are also ceramic fiber heaters but are in the form of flat panels (described in greater detail below) rather than the cylindrical shells illustrated and described above. Accordingly, the electric heaters 222 comprise a plurality of ceramic fiber heaters 224 and a plurality of duct heaters 226. The ceramic fiber heaters 224 are disposed within the lower heating zone 212 and disposed proximate or adjacent to the respective tubes 216, which is illustrated and described in greater detail below. In this way, fluid flowing through the tubes 216 is heated by the ceramic fiber heaters 224. The duct heaters 226 are also electric in this form, and are provided by Watlow Electric Manufacturing Company. Further specifics of the duct heaters, which may be LDH Series or D Series can be found at the following links: https://www.watlow.com/Products/Heaters/Air- Heaters/LDH-Series-Duct-Heaters and https://www.watlow.com/Products/Heaters/Air-Heaters/D-Series-Duct-Heaters. Additionally, the duct heaters 226 may be employed with the electric ceramic fiber heaters set forth above that include the cylindrical shapes. Further, it should be understood that the duct heaters heat the upper heating zone and the electric ceramic fiber heaters heat the lower heating zone in all of the various forms of the present disclosure illustrated and described herein.

[0051] As further shown, each electric ceramic fiber heater 224 is in the form of a panel 254 (FIG. 5B) with embedded heating elements 256. In the example illustrated, the panel 254 is flat and has a rectangular shape. In other forms, the panel 254 may include a square shape, or any other suitable size and shape while remaining within the scope of the present disclosure. The flat panel 254 is removably secured to an inner surface of a wall 236 of the converted gas-fired furnace 210 using mechanical fasteners such as bolts, screw, or rivets, for example. In some forms, the flat panel 254 may be welded to the wall 236 of the converted gas-fired furnace 210 or may be secured to the wall 236 using any other suitable attachment means. The flat panel 254 is also positioned adjacent to the tubes 216 such that a gap exists between the panel 254 and the tubes 216. In this way, heat generated by the electric ceramic fiber heaters 224 is directed or radiated to the tubes 216 to heat the fluid flowing therethrough. The gap between the panel 254 and the tubes 216 also facilitates removal of the panel 254 from the wall 236 for servicing, for example. The panels 254 generally cooperate with each other to substantially cover the entire wall 236 of the converted gas-fired furnace 210.

[0052] With specific reference to FIG. 5B, the heating element 256 is embedded within the panel 254 and is configured to generate heat that is transferred to the tubes 216 by radiation. The heating elements 256 and their power leads 260 are similar to the heating elements 56 described above, and thus further details and variations are not described here for purposes of clarity.

[0053] With reference to FIGS. 5B and 5C, the power leads 260 (only one shown in the figures) are connected to a power source (not shown) and the heating element 256 and is configured to provide power to the heating element 256 such that the heating element 256 generates heat. The power leads 260 in one form exit the panel 254 via a pocket 262 formed in the panel 254 of the electric ceramic fiber heater 224. In the example illustrated, the pocket 262 is formed in a corner section of the panel 254 though the pocket 262 may be formed in other areas of the panel 254 (e.g., the pocket 262 may be formed in a center area of the panel 254 or along an edge of the panel 254). Further, the pocket 262 may also be provided with other forms of the electric ceramic fiber heater as illustrated and described herein while remaining within the scope of the present disclosure. Further, the power leads 260 may exit the panel 254 in any number of directions and configurations while remaining within the scope of the present disclosure.

[0054] With reference to FIGS. 5A and 5D, the duct heaters 226 are disposed below the lower heating zone 212 and are spaced apart from each other as shown. The duct heaters 226 are also in fluid communication with the upper heating zone 214 by ducts 237 (shown in phantom lines in FIG. 5A), which in one form are fluidly isolated from and extending along the lower heating zone 212. That is, a respective duct 237 extends from a respective duct heater 226 along the lower heating zone 212 to the upper heating zone 214. In this way, fluid (e.g., air) heated by the duct heater 226 flows through the respective duct 237 to the upper heating zone 214 where the heated air is transferred to the fluid flowing through the upper tube banks 217, 218, 220 (i.e., heating the fluid flowing through the upper tube banks 217, 218, 220) before exiting the converted gas-fired furnace 210. In one form, the ducts 237 extend from respective duct heaters 226 to the upper heating zone 214 without going through the lower heating zone 212. That is, the ducts 237 extend from the respective duct heaters 226 along the outside of the converted gas-fired furnace 210 (i.e., external to the converted gas-fired furnace 210) and into the upper heating zone 214, thereby remaining fluidly isolated from the lower heating zone 212. However, in another form, the ducts 237 may extend along the inside the lower heating zone 212 (not shown) while remaining within the scope of the present disclosure. It should be noted that though the duct heaters 226 are shown located below the lower heating zone 212, the duct heaters 226 can be located anywhere in the proximity of the converted gas-fired furnaces disclosed herein, provided the heated fluid from the duct heaters 226 flows to the upper heating zone 214. In general, the duct heaters 226 are located to be in fluid communication with the upper heating zone 214 via one or more ducts. In another example, the duct heaters 226 are located proximate the lower heating zone (e.g., at a side of the lower heating zone). In yet another example, the duct heaters 226 are located proximate the upper heating zone 214 (e.g., at a side of the lower heating zone). These and other locations should be construed as falling within the scope of the present disclosure.

[0055] Each duct heater 226 includes a housing 270 and a heating module 272. The housing 270 in one form is secured to a bottom wall 271 of the lower heating zone 212 and/or another structural element, thereby securing the housing 270 in a fixed position. The heating module 272 is generally removably disposed within the housing 270 and includes a plurality of heating bundles 274. In this way, the heating module 272 may be conveniently removed from the housing 270 to service the heating module 272. Each heating bundle 274 includes one or more heating elements, such as by way of example tubular heaters, configured to heat the fluid passing therethrough. That is, a duct manifold 278 is in fluid communication with the duct heaters 226 and carries fluid flowing through the duct manifold 278 to the duct heaters 226 where the fluid is heated before entering the upper heating zone 214. A blower 280 receives fluid from a return duct 279, or from the ambient environment in another form, and forces the fluid through the duct manifold 278, through the duct heaters 226, through the ducts 237 and into the upper heating zone 214. In one form as shown, the duct heaters 226, the duct manifold 278, the upper heating zone 214, the return duct 279 and the blower 280 form a closed fluid circuit within which fluid flows. In one form, the fluid circuit may include a heat exchanger (not shown; e.g., a condenser) disposed between the blower 280 and an outlet of the upper heating zone 214. The heat exchanger receives fluid from the upper heating zone 214 via the return duct 279, and then transfers heat from the fluid to ambient air that may be forced over the heat exchanger by a fan (not shown). In some configurations, the heat exchanger transfers heat from the fluid to a stream of liquid such as water, for example.

[0056] With reference to FIGS. 6A and 6B, flat panels 354 (FIG. 6B) of the electric ceramic fiber heaters 324 are removably secured to an inner surface of a vertical wall 336 of a converted gas-fired furnace 310. The power leads 360 extend from heating elements (not shown) of the electric ceramic fiber heaters 324 and through the wall 336 to a power source (not shown) externally located. Further details of the electrical connections and cables running to the power supply are set forth in greater detail below.

[0057] With reference to FIG. 7, panels 454 of electric ceramic fiber heaters 424 are removably secured to an inner surface of a vertical wall of a converted gas-fired furnace 410 such that power cables 460 extend from the power leads (illustrated above) and through apertures 434 formed in a bottom wall 438 of the converted gas-fired furnace 410 and to a power source (not shown), which is externally located. The power cables 460 in one form extend through preexisting apertures 434 formed from the gas nozzles (not shown), thereby making use of a preexisting feature but now with a new function (power cable routing).

[0058] With reference to FIG. 8, another form of a converted gas-fired furnace according to the teachings of the present disclosure is illustrated and generally indicated by reference numeral 510. The converted gas-fired furnace 510 in this form is configured to heat a fluid flowing therethrough using electric heaters as illustrated and described herein. The converted gas-fired furnace 510 similarly includes a lower heating zone 512, an upper heating zone 514, sets of lower tubes 516 (only one shown in the figures), upper tube banks 517, 518, 520 and a plurality of electric ceramic fiber heaters 522.

[0059] The structure and function of the lower heating zone 512, the upper heating zone 514, the lower tubes 516 and the upper tube banks 517, 518, 520 are similar or identical to that of the lower heating zone 12, the upper heating zone 14, the lower tubes 16a, and the upper tube banks 17, 18, 20, respectively, described above, and therefore, will not be described again in detail.

[0060] The plurality of electric heaters 522 comprises a plurality of electric ceramic fiber heaters 524 and a plurality of duct heaters 526. The structure and function of the electric ceramic fiber heaters 524 and the duct heaters 526 are similar or identical to those described above, along with their respective variants, and therefore, will not be described again in detail.

[0061] The duct heaters 526 are arranged in series and are in fluid communication with the upper heating zone 514 by a duct 537 that is fluidly isolated from the lower heating zone 512. That is, the duct 537 extends from the last duct heater 526 in the series of duct heaters 526 to a distribution manifold 527 in fluid communication with the upper heating zone 514. In this way, fluid (e.g., air) heated by the duct heaters 526 flows through the distribution manifold 527 (via the duct 537) and into the upper heating zone 514 via openings 529 in the distribution manifold 527. The heated fluid is then transferred to the fluid flowing through the upper tube banks 517, 518, 520. Fluid exiting the upper heating zone 514 flows through a duct 558 and to a blower 560, where the fluid is forced through the duct heaters 526 to be heated and directed back into the upper heating zone 514 of the converted gas-fired furnace 510. It should be understood that fluid exiting the upper heating zone 514 may be cooler than fluid entering the upper heating zone 514. The duct electric heaters 526, the duct 537, the distribution manifold 527, the upper heating zone 514, the duct 558 and the blower 560 form a closed fluid circuit where fluid flows. In one form, the fluid circuit includes a heat exchanger (not shown; e.g., a condenser) disposed between the blower 560 and an outlet of the upper heating zone 514, as set forth above.

[0062] The duct heaters 526 is this form are supported by a structural member 540 located external to the converted gas-fired furnace 510 as shown. This structural member 540 may include, by way of example, a platform or a truss structure, among others. The structure of the duct heaters 526 are similar or identical to that of the duct heaters, and therefore, will not be described again in detail. In this variation of the present disclosure, the lower heating zone 512 is heated by the electric ceramic fiber heaters as described herein, while the upper heating zone 514 is heated by the duct heaters that are disposed closer to the upper heating zone 514, thereby providing less heat loss than other variants described herein. [0063] Unless otherwise expressly indicated herein, all numerical values indicating mechanical/thermal properties, compositional percentages, dimensions and/or tolerances, or other characteristics are to be understood as modified by the word “about” or "approximately" in describing the scope of the present disclosure. This modification is desired for various reasons including industrial practice, material, manufacturing, and assembly tolerances, and testing capability.

[0064] As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.”

[0065] The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.

Claims

CLAIMS What is claimed is:

1 . A converted gas-fired furnace comprising: at least one lower radiant heating zone comprising a plurality of lower tubes configured to carry a fluid to be heated; an upper convective heating zone comprising a plurality of upper tubes configured to carry the fluid to be heated; a plurality of electric ceramic fiber heaters disposed within the lower radiant heating zone and configured to heat the fluid in the lower tubes; and a plurality of duct heaters configured to heat the fluid in the upper tubes.

2. The converted gas-fired furnace according to Claim 1, wherein the electric ceramic fiber heaters comprise cylindrical shells surrounding the plurality of lower tubes within the lower radiant heating zone.

3. The converted gas-fired furnace according to Claim 2, wherein the cylindrical shells comprise two halves.

4. The converted gas-fired furnace according to Claim 2, further comprising a plurality of structural supports secured around the cylindrical shells.

5. The converted gas-fired furnace according to Claim 2, wherein the cylindrical shells are a single unitized piece.

6. The converted gas-fired furnace according to Claim 1, wherein the electric ceramic fiber heaters comprise flat panels secured to side walls of the lower radiant heating zone.

7. The converted gas-fired furnace according to Claim 6, wherein the electric ceramic fiber heaters comprise power leads, and the power leads extend through the side walls of the lower radiant heating zone.

8. The converted gas-fired furnace according to Claim 1, wherein the electric ceramic fiber heaters comprise power leads, and the power leads extend through preexisting apertures disposed along a bottom wall of the lower radiant heating zone.

9. The converted gas-fired furnace according to Claim 1 , further comprising: a fluid circuit comprising a plurality of ducts, a blower and a return duct, the ducts extending from the plurality of duct heaters to the upper convective heating zone, the blower in fluid communication with the plurality of duct heaters and the ducts, the return duct extending from an outlet of the upper convective zone to the blower, wherein heated fluid from the duct heaters is recirculated through the fluid circuit.

10. The converted gas-fired furnace according to Claim 1 , further comprising a distribution manifold in communication with the duct heaters and extending along a lower portion of the upper convective zone.

11 . The converted gas-fired furnace according to Claim 10, wherein the duct heaters are arranged in series.

12. The converted gas-fired furnace according to Claim 1 , wherein the electric ceramic fiber heaters comprise: a first set of electric ceramic fiber heaters comprising cylindrical shells surrounding at least some of the plurality of lower tubes within the lower radiative heating zone; and a second set of electric ceramic fiber heaters comprising flat panels secured to internal side walls of the lower radiant heating zone.

13. The converted gas-fired furnace according to Claim 1 , wherein the duct heaters are arranged below the lower radiant heating zone.

14. The converted gas-fired furnace according to Claim 12, further comprising a plurality of ducts extending from the plurality of duct heaters to the upper convective heating zone, the ducts extending through and fluidly isolated from the lower radiant heating zone.