US2797297A - High pressure heaters - Google Patents

Description

.June 25, 1957 A. c. K. NIHLEIN 2,797,297

HIGH PRESSURE HEATERS Filed Nov. 18, 1954 5 Sheets-Sheet 1 FIG. I

FIG. 2

. 7 INVENTOR. ARVID C. K. NIHLEN ATTORNEYS June 25, 1957 A. c. K. NlHLEN 2,797,297

- HIGH PRESSURE HEATERS Filed Nov. 18, 1954 v 3 Sheets-Sheet 2 1'; i INVENTOR. 74 f ARVID c. K. NIHLEN A'-Sr./ w w 7 if p: i 1/ 84 NM 212? ATTORNEYS mon'rnnssunn nnarrns Arvid C. K. Nihlen, @herlin, fihio, assignor to Brown Fintube Company, Elyria, Uhio, a corporation of this Application November 18, 1954, Serial No. 469,797

10 Claims. (Cl. ZE -3 This invention relates to heaters for air and other gases, and more particularly to heaters that are adapted to heat gases to high temperatures at high pressures.

The general object of the invention is the provision of efiicient electric heaters for air and other gases that will function tto deliver gas at'high temperatures of the order of 1500 to 2000 F. or more and at relatively high pressures of the order of 100 to 300 pounds persquare inch or more. Another object is the provision of such heaters in which the highly heated parts are not subjected to destructive forces by the pressure of the gas within the heater. Another object is the provision of such heaters that can be constructed of relatively economical materials. A further object is the provision of such heaters in which heat losses to the exterior are minimized, and the temperature of the outside shell of the heaters kept reasonably low.

Further objects and advantages of the invention will become apparent from the following description of preferred forms thereof, reference being made to the accompanying drawings in which- Figure 1 is a vertical, axial section through one form of heater embodying the invention.

Figure 2 is a transverse section through the heater shown in Figure l, the section being taken along the line 22 of Figure 1.

Figure 3 is a vertical, axial section through a modified form of heater.

Figure 4 is a transverse section through the heater of Figure 3, taken along the line 4-4 of Figure 3.

FigureS is a transverse section taken along the line 5-5 of Figure 3.

Figure 6 is a vertical axial section through another modified form of heater.

Figure 7 is a transverse section through the heater of Figure 6 taken along line '7-7 of Figure 6, and

Figure 8 is a transverse section taken along the line 88 of Figure 6.

The heating of relatively large volumes of air or other gas to high temperatures at substantial pressures involves serious diificulties from an engineering standpoint because the heaters must be reasonably large in order to have the required heating capacity and with large heaters the internal gas pressures are difficult to withstand because ordinary materials are seriously weakened at the temperatures at which the heaters must operate. Accordingly, in the past it has been necessary to construct the pressure retaining portions of such heaters from heat resistant alloys and to make them of'heavy wall thickness to enable them to withstand the operating temperatures and pressures. This has resultedin expensive and heavy heaters of limited capacity.

According to the present invention, difiiculties with prior types of heaters are eliminated, and heaters are provided which are capable of heating large quantities of air or other gases to high temperatures at substantial pressures without requiring extremely heavy wall construc- 2,797,297 Patented June 25, 1%57 tions or special heat resistantalloys in the pressure withstanding portions of the heater. This is accomplished by employing the incoming cool air to maintain the external shells of the heaters, which must withstand the internal pressure, at reasonable low temperatures,-and by so designing the heaters that the major parts thereof that are subjected to the highest temperatures are subjected to substantially equal pressures on both sides by the gases flowing through the heaters and therefore not subjected to substantial expansive forces.

Referring to Figures 1 and 2 of the drawings, one preferred form of heater made according to my invention may comprise an external pressure vessel or shell tube 10 having end flanges 11 and 12, to which suitable end clo sure plates 14 and 15 may be bolted. Air, or other gas to be heated, is admitted to the interior of the shell 10 through an inlet 17 extending through the side wall of "the shell and preferably welded thereto as shown, while the heated air or other gas is discharged through an outllet tube 18 which extends through the end plate or closure 14.

border to heat the gas passing through the shell tube from the inlet 17 to the outlet 18, electric heating eleare bent at their ends, as shown at 30, to provide a support for a bottom ceramic plate 31. The lower ends of tubes 22 project through the bottom plate 31, which functions to hold them in proper spaced relationship. The resistance wire 21 is wound on tubes 22 between plates 25 and 31, and the leads for the electric heaters are carried to the exterior of the heater through an appropriate fitting 33.

Inasmuch as the straps 2.6, the outlet tube 18 and the 'fitting 33 are subjected to high temperatures, they are preferably composed of a heat resisting alloy such as .Inconel (which is a corrosion and heat resistant chromenickel steel made by International Nickel Company); and for further protection against radiant heat and erosion, they may be sprayed with a heat resisting ceramic material.

'In order to increase the rate of heat transfer between the electric heating coils and the gases passing through the heater, to prevent the shell 10 from becoming excessively hot and to reduce heat losses through shell It), theheating elements 28 are surrounded by a finned tube 35 which has longitudinally extending external fins 36 thereon. Pinned tube 35 is secured at its upper end to a flange or plate '37, which is clamped between the flange 11 and the closure plate 14, the fins on-the tube extending radially outward toward the inner surface 39 of the shell 10. The upper portion of the tube 35 is without fins, as shown, to a point below the point of connection of inlet tube 17 to provide an annular distribution zone through which the cool incoming gas is distributed around the finned tubed so that it can flow along the several fins 36. In this region, however, studs 38 are preferably welded to the tube 35 to increase the heat transfer rate while permitting distribution of the incoming gas. At the bottom of the heater the fin tube is stopped short of the bottornxclosure plate 15 to provide a passage for the gas to flowaround the end of the tube and into the interior thereof.

:Gas flowing through the interior of the tube passes 9 through and around the heating elements 20 and in contact with the heated wall of the tube 35; the hot gas is discharged through the outlet pipe 18. The top plate 14 and the bottom plate 15 are prevented from overheating by disc 41 and 42, respectively, which are composed of insulating material and protect the inner surfaces of closure plates 14 and 15 from direct contact with the heated gas.

In operation, heat from the heating elements heats the gas flowing over the elements and through the ceramic tubes 22, while radiation from the elements heats the gas and the inner surface of the tube 35. This surface heats the gas coming in contact therewith, and also heat is transmitted through the wall of the tube to the fins 36. Cool gas entering the heater through the inlet 17 is heated by contact with the tube 35 and the fins 36; the entering gas, in flowing downwardly along the outside of the tube 35 in contact with the fins, abstracts suflicient heat from the tube and the fins to prevent these elements from becoming unduly heated. Furthermore, the cool gas flowing in the inner wall 39 of the shell 10 prevents the shell from being overheated and makes it possible to construct the shell from comparatively inexpensive materials, ordinary steel being suitable for many installation purposes. For other installations where high temperatures and pressures are involved, a heat-resisting steel is preferred. In either event, the shell, while it is subjected to the entire pressure within the heater, is not subjected to excessively high temperatures; this eliminates weakening of the shell by heat, also reduces heat losses from the heater, and makes it unnecessary to insulate the shell.

The gas which has been preheated to some degree as it flows downwardly along the exterior of the finned tube 35 turns around the lower edge of the finned tube and flows upwardly through the interior of the finned tube and through and around the ceramic tubes 22 on which the heating coils 21 are wound. In passing through and around the heating tubes the gas becomes heated to the desired degree and is discharged through the discharge pipe 18. Although the pipe 18 is subjected to the elevated temperatures of the outgoing gas, it is of smaller diameter and can be constructed to withstand readily the temperatures and pressures involved. A heater of the general type disclosed having a length of four feet and a shell diameter of ten inches may be constructed with the ability to deliver 150 standard cubic feet of air per minute at a temperature of 1600 F. and a pressure of 300 pounds per square inch.

A modified form of the invention is shown in Figures 3, 4 and 5. The heater shown in these figures of the drawing is adapted to heat comparatively large volumes of air to temperatures as high as 2,000 F. at pressures up to 300 lbs. per square inch. In this form of the invention the outer or shell tube is shown at 45, the shell tube being supported at its lower end by a square base member indicated in general at 46. Member 46 is built up of a base plate 47, four side plates 48 (see Figure 4), and an upper flange 49 which is bolted to the end flange 51 of the shell tube. A supporting plate 52 of a ceramic or suitable heat-resistant insulating material is interposed between the flanges 49 and 51 and functions to support and guide the longitudinally extending heating elements 53 and 54. Cover plate 48' is removable to give access to the interior of the base member 46.

A finned tube 55 having longitudinally extending fins 56 is disposed within the shell tube and around the heating elements 53 and 54. The lower end of the finned tube terminates above the plate 52, leaving a space 57 within the shell tube as shown. The upper end of the finned tube is provided with a flange 59 that is bolted to the upper end flange 60 of the shell tube 45. The inlet 61 for the heater is connected laterally to the shell tube 45 a short distance below the flange 60 and above upper ends 62 of the fins 56. As in the previous form of the invention,

the finned tube is provided with studs 58 in the region above the fins. The outlet 63 from the heater extends laterally from the portion 64 of the finned tube 55 that projects above the flange 59. Outlet 63 is preferably lined with aluminum oxide or other refractory insulating material 63a. The finned tube terminates in an end flange 65, which is bolted to the flange 66 of upper housing member 67, a ceramic or other heat-resistant insulating plate 68, through which the upper ends of the heating elements 53 and 54 project, being interposed between the flanges 65 and 66. Preferably, the under side of plate 68 is protected by aluminum oxide or other suitable heat-insulating material shown at 69.

Connections to the heating elements 53 are made in the base member 46, as shown particularly in Figure 5. In the form of the invention illustrated in the drawings, there are three heating elements 53 and three heating elements 54 preferably in the form of silicon carbide bars. In the embodiment shown, three-phase current is supplied to the heating elements 53 through suitable conductors 70 extending through the plates 48, brackets 71 and clamps or contact rings 72. At their upper ends adjacent heating elements 53 and 54 are connected together by connectors 73 disposed within the upper housing 67. The lower ends of elements 54 are connected together, as shown in Figure 5, by clamps 74, bars 75 and central connection 76, thus providing a Y-conuected, three-phase circuit. Obviously other circuit arrangements can be employed. The connectors within the lower housing 46 are protected from the heated air by the plate 52, while the connectors within the upper housing 67 are protected by the plate 68 and aluminum oxide insulation 69.

In order to provide for more effective heat transfer, a vertically extending central member 77 is centered within the heating elements 53 and 54, as shown particularly in Figure 4. Member 77 preferably is made up of a central tubular portion 78 having longitudinally extending fins 79 welded thereto; fins 79 extend longitudinally from a zone adjacent the lower edge of outlet 63 to a zone adjacent the lower edge of the finned tube 55 and project radially outwardly toward the spaces between adjacent heating elements 53 and 54. The member 77 receives heat radiated from the heating elements 53 and 54 and transfers it by convection to the gas passing through the heater; it also guards the heating elements from backradiation which might otherwise cause them to overheat.

In order to support the member 77, the tube 78 is provided with a shoulder 80, as shown in the lower portion of Figure 3, which rests on the plate 52; at its upper end the tube 78 is guided by a plug 81 that is supported by the plate 68; plug 81 carries a pin 82 that prevents rotation of the tube 78, the tube being slotted as at 83 to receive the pin. Thus, expansion and contraction of the tube 78 is provided for. The lower ends of the resistors 53 and 54 are supported by the clamps 72 and 74, and also rest upon a block 84 of aluminum oxide or other suitable insulating material. The resistors extend through openings in the plates 52 and 68 and since they are only supported at their lower ends, there are no difliculties due to expansion and contraction under temperature changes.

The generation of heat in the resistors is localized by spraying their external surfaces above and below the fins 79, i. e., in the areas indicated by reference characters 85 and 86, with a conductive metal such as copper. The sprayed metal coatings reduce the resistance of the elements and localize the heating in the regions between the with the heating elements and incontact with-the central member 77 and its fins 79. The heated gas is discharged through the outlet 63.

In this .apparatus the shell tube 45 is preferably composed of stainless steel. The finned tube .55 and fins 56 are preferably composed of a heat resistant alloy such as Inconel, with the interior of the finned tube being coated with-a heat resistant ceramic coating. The central finned member 77 and fins 79 are also .preferablycomposed of Inconel and provided with heat resistant ceramic coatings. The portion of the finned tube that extends above the flange 59 is preferably surrounded by heat insulating material as shown at 87.

As in the case of the previous modification, the incoming gas cools the finned tube and prevents it from reaching excessively high temperatures. Also, the portion of the finned tube below the flange 59 is subjected to substantially the samepressures on'the inside and on the outside and hence, is'not subjectedto any great forces due to the pressure of the air or other gas being heated. The short section of the finned tube above the flange 59 becomes heated to substantially the temperature of the outflowing gas, but this section is short and may be reinforced externally as by a reinforcing tube 88 if necessary.

Another modified form of heater is shown in Figures 6, 7 and 8 of the drawings. In this form of heater the-air or other gas to be heated travels the length of theheater three times, making it possible to design a heater of lesser length than the other forms for the same heating cylindrical section 93, which is insulated as at 94, and a bottom .plate 95. Gas to be heated is admitted to the interior of the shell through the intake conduit 96 disposed just above closure plate 91.

Closure plate 91 for the shell tube 90 supports the finned tube 97, which is provided with longitudinally extending external fins 98 as before. In this modification of the invention, the fins are shown as being of lesser depth than in the previous modifications, and the annular space between the finned tube 97 and the interior of the shell tube 90 is smaller to give a comparatively high velocity of gas flow in this zone. Obviously, the proportions of the fins and the spacing between the finned tube and the shell tube can be varied in this modification of the invention as well as in the previously described forms.

The upper end of the finned tube 97 is closed by an upper closure plate 99. ' Plates 99 and 91 function to support the heating elements, which may comprise ceramic tubes 101 with coils 102 of resistance wire'wound around them. The lower ends of ceramic tubes 101 are supported by flanges 104 welded to tubes 105, which, in turn, are welded to the plate 91, and the upper ends of the ceramic tubes are guided by metal tubes 106 which extend downwardly from and are welded to plate 99. The upper ends of the tubes 101 are slidable on the tubes 106 so as to permit differences in expansion of the heating tubes and the finned tube in operation. Electric power may be supplied through leads 107, the lower'ends of the coils 102 being connected to complete the circuit.

The outlet from the interior of the finned tube 97 is through a short outlet tube 108 which projects upwardly through a central opening 109 in the top closure plate 110 andinto the outlet conduit 111. Conduit 111 preferably is welded to plate 110 and may be enclosed in insulating material 112.

In this form of the invention air or other gas to be heated is admitted to the interior of the shell tube through the inlet 96 and flows upwardly, as indicated by the arrows, along the exterior of the finned tube 97 and fins 98 and withintheannular space between the finned tube 'and the interior ofithe shell tube. At the upper end of ences in external and internal gas pressures. :pressures on both inside and outside of the shell tube 97 'thesheater the gas is constrained to turn downwardly into theopen ends of the heating tubes 101; the gas flows downwardly through the interior of the heating tubes, being discharged into the hollow base member92. Here the direction of flow is reversed again, the gas flowing upwardly from the hollow bottom 92 through the openings 115 in the plate 91 and around the exterior of the tubes 101 in contact with the heating coils 102. In this passage the gas is brought to the desired high temperature by radiation as well as by convection. In some installationsit may be desirable to include within the shell tube 97 baflie members 117 to obtain high velocity and to direct the gas flowing upwardly through the shell'tube into close proximity to the exterior of the heating elements.

After passing over the exterior of the heating tubes, the gas is discharged through the discharge pipe 108 and into the discharge conduit 111.

It will be evident that in this form of the invention none of the highly heated parts, with the exception of the discharge conduit 112, are subject to substantial differ- The gas are substantially'identical. The same is true of the ceramic heatng tubes 101, the plate 99, and the discharge tube 108. The-outer shell is kept at a reasonably low tempearture by the incoming gas, and this is also true of the closure plate 91. The base member 92 and the top plate are not'subject to gas at the highest discharge temperature, but only to gas that has been partially heated inits passage through the apparatus. As in the previously described forms of invention, those parts of the apparatus subjected to high temperatures may be constructed of appropriate heat-resisting alloys.

From the foregoing'description it will be seen that the invention provides an efficient electric heater for air and other gases which has the ability to deliver gas at high temperatures under relatively high pressures. The construction of the heater with the incoming gas cooling the exterior of the finned tube and the interior of the shell tube reduces heat losses and prevents undue heating of the shell tube, while the finned tube is not subjected to any substantial bursting pressures. Thus, the heaters can be constructed of relatively light materials without danger of failure.

Those skilled in the art will appreciate that various changes and modifications can be made in the preferred forms of the invention disclosed herein without departing from the spirit and scope thereof. The essential characteristics of the invention are defined in the appended claims.

I claim:

1. A heater for air and other gases comprising an elongated pressure vessel, a laterally extending inlet and an outlet, both communicating with the interior of said pressure vessel adjacent one end thereof, a heating element within the pressure vessel, and an externally finned tube within said pressure vessel and surrounding said heating element, the interior and the exterior of said finned tube both being subjected to the pressure within the pressure vessel and said inlet to said pressure vessel leading to the exterior of said finned tube and said outlet from said pressure vessel leading directly from the interior of said finned tube.

2. A heater for air and other gases comprising a shell tube, a finned tube within the shell tube and concentric therewith, said finned tube having longitudinally extending external fins thereon, means blocking the annular space between said shell and finned tubes adjacent one end of said shell tube, a closure for the other end of said shell tube, said finned tube stopping short of said closure, an inlet extending into said shell tube adjacent said blocking means, the fins on said finned tube stopping short of the zone adjacent said inlet and said finned tube being provided with outwardly projecting 7 studs in said zone, an outlet leading from the interior of said finned tube adjacent said blocking means, and heating means disposed within said finned tube. and spaced from the inner wall thereof.

3. A heater for air and other gases comprising a shell tube, a finned tube within the shell tube and concentric therewith, said finned tube having longitudinally extending external fins thereon, closures for the ends of said shell tube, said finned tube stopping short of one of said closures and being secured in leakproof relation to the other closure, an inlet extending laterally into said shell tube adjacent said other closure, the fins on said finned tube stopping short of the zone adjacent said inlet and said finned tube being provided with outwardly projecting studs in said zone, an outlet leading from the interior of said finned tube through said other closure and heating means disposed within said finned tube and spaced from the inner wall thereof.

4. A heater for fluids comprising an elongated pressure vessel, an inlet extending laterally into said pressure vessel adjacent one end thereof, an elongated electric heating element within the pressure vessel and extending parallel to the axis thereof, a tube within said pressure vessel, said tube extending parallel to the axis of said pressure vessel and surrounding said heating element and providing a space between the interior of said pressure vessel and the exterior of said tube, said inlet to said pressure vessel leading to said space, said tube having longitudinally extending external fins thereon, said fins being disposed in said space, said tube stopping short of the end of said pressure vessel remote from said inlet to provide a passage for fluid to flow from said space to the interior of said tube, and means at the other end of said pressure vessel blocking communication between said space and the interior of said finned tube, said tube projecting beyond said other end of said pressure vessel and said blocking means and an outlet from said pressure vessel leading from the portion of said tube projecting beyond said blocking means.

5. A heater for fluids comprising an elongated pressure vessel, an inlet and an outlet both communicating with the interior of said pressure vessel, a plurality of elongated electric heating elements within the pressure vessel, said heating elements extending parallel to and being circumferentially spaced around the axis thereof, a heat transfer member disposed within the heating elements, a tube within said pressure vessel, said tube extending parallel to the axis of said pressure vessel and surrounding said heating elements and providing a space between the interior of said pressure Vessel and the exterior of said tube, said tube stopping short of the end of said pressure vessel remote from said inlet to provide a passage for fluid to flow from said space to the interior of said tube, said tube being open to permit fluid to flow along said heating elements and along said heat transfer member, and means at the other end of said pressure vessel blocking communication between said space and the interior of said finned tube, said inlet to said pressure vessel leading to said space and said outlet from said pressure vessel leading from the interior of said tube.

6. A heater for fluids comprising an elongated pres sure vessel, an inlet and an outlet both communicating with the interior of said pressure vessel, a plurality of elongated electric heating elements within the pressure vessel, said heating elements extending parallel to and being circumferentially spaced around the axis thereof, a central tubular heat transfer member disposed within the heating elements and having fins extending outwardly therefrom parallel to said heating elements, a tube within said pressure vessel, said tube extending parallel to the axis of said pressure vessel and surrounding said heating elements and providing a space between the interior of said pressure vessel and the exterior of said tube, said tube stopping short of the end of said pressure vessel remote from said inlet to provide a passage for fluid to flow from said space to the interior of said tube, said tube being open to permit fluid to flow along said heating elementsand along said heat transfer member, and means at the other end of said pressure vessel blocking communication betwen said space and the interior of said finned tube, said inlet to said pressure vessel leading to said space and said outlet from said pressure vessel leading from the interior of said tube.

7. A heater for fluids comprising an elongated pressure vessel, an inlet and an outlet both communicating with the interior of said pressure vessel adjacent one end thereof, a plurality of elongated electric heating elements within the pressure vessel, said heating elements extending parallel to and being circumferentially spaced around the axis thereof, a central tubular heat transfer member disposed within the heating elements and having fins erqtending outwardly therefrom parallel to said heating elements and directed radially outwardly into the spaces betwen adjacent heating elements, a tube within said pressure vessel, said tube extending parallel to the axis of said pressure vessel and surrounding said heating elements and providing a space between the interior of said pressure vessel and the exterior of said tube, said tube having longitudinally extending external fins thereon, said fins being disposed in said space, said tube stopping short of the end of said pressure vessel remote from said inlet to provide a passage for fluid to flow from said space to the interior of said tube, and means at the other end of said pressure vessel blocking communication between said space and the interior of said finned tube, said inlet to said pressure vessel leading to said space and said outlet from said pressure vessel leading from the interior of said finned tube.

8. A heater for fluids comprising an elongated pressure vessel, an inlet extending into said pressure vessel adjacent one end thereof, a plurality of elongated tubular electric heating elements within the pressure vessel and extending parallel to the axis thereof, said heating elements each comprising a ceramic tube having resistance wire wound on the exterior thereof, a tube having longitudinally extending external fins thereon disposed within said pressure vessel, said finned tube extending parallel to the axis of said pressure vessel and surrounding said heating elements and providing a space between the interior of said pressure vessel and the exterior of said finned tube, said inlet to said pressure vessel leading to said space, plates closing the ends of said finned tube, said plates supporting said tubular heating elements and having openings therein providing communication with the interiors of said tubular heating elements, said tube stopping short of the end of said pressure vessel remote from said inlet to provide a passage for fluid to flow from said space to the interior of said heating element, means at the end of said pressure vessel adjacent said inlet blocking communication between said space and the interior of said finned tube, a chamber at the end of said finned tube adjacent said inlet providing a communicating passageway between the interiors of said heating elements and the space of said finned tube surrounding said heating elements, and a discharge conduit extending from the said space within said finned tube to the exterior of said pressure vessel at the end thereof opposite said inlet.

9. A heater for fluids comprising an elongated pressure vessel, an inlet extending into said pressure vessel adjacent one end thereof, an elongated tubular electric heating element within the pressure vessel, an externally finned tube within said pressure vessel, said finned tube surrounding said heating element and providing a space between the interior of said pressure vessel and the exterior of said finned tube, said inlet to said pressure vessel leading to said space, closure means at the ends of said finned tube, said closure means having openings therein providing communication with the interior of said tubular heating element, means atthe end of said pressure vessel remote from said inlet providing passage for fluid to flow from said space to the interior of said tubular heating element, means at the end of said pressure vessel adjacent said inlet blocking communication between said space and the interior of said finned tube, means at the end of said finned tube adjacent said inlet providing a passageway between the interior of said heating element and the space within said finned tube surrounding said heating element, and a discharge conduit extending from the said space within said finnedtube to the exterior of said pressure vessel.

10. A heater for fluids comprising a shell tube, a finned tube within the shell tube and concentric therewith, said finned tube and said shell tube defining an annular space between them, said finned tube having longitudinally extending external fins thereon disposed in projecting studs in said zone, and means for supplying.

heat to the interior of said finned tube.

References Cited in the file of this patent UNITED STATES PATENTS 1,439,340 St. Clair Dec. 19, 1922 1,519,395 Clench Dec. 16, 1924 1,624,843 McQuinn Apr. 12, 1927 1,754,232 Fisher Apr. 15, 1930 2,527,013 Kjelgaard Oct. 24, 1950 2,619,579 Cartinhour Nov. 25, 1952 2,623,154 Suhr Dec. 23, 1952

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