US3422811A - High temperature surface-combustion radiant heater - Google Patents

Description

Jan. 21, 1969 E. E. STRAND 3,422,811

HIGH TEMPERATURE SURFACE-COMBUSTION RADIANT HEATER Filed Feb. 8. 1968 Sheet of 5 INVENTOR: ELMER E. STRAND.

ATTORNEY Ji 2 .969 E- E. STRAND 3,422,811

HIGH TEMPERATURE SURFACE-COMBUSTION RADIANT HEATER Filed Feb. 8, 1968 Sheet 2 of 5 -INVENTOR.' ELMER E. STRAND :z QLMM 29 u ATTORNEY Jan. 21; 1969 E. E. STRAND 3,422,811

HIGH TEMPERATURE SURFACE-COMBUSTION RADIANT HEATER Filed Feb. 8, 1968 Sheet 3 of 5 EE-312i? INVENTOR; ELMER E. STRAND- ATTORNEY.

E. E. STRAND Jan. 21, 1969 HIGH TEMPERATURE SURFACE-COMBUSTION RADIANT HEATER Filed Feb. 8, 1968 Sheet 4 INVENTOR: ELMER E. STRAND,

ATTORNEY.

E. E. STRAND Jan. 21 1969 HIGH TEMPERATURE SURFACE-COMBUSTION RADIANT HEATER Filed Feb. 8. 1968 Sheet INVENTOR. ELMER E. STRAND ATTORNEY,

United States Patent 3,422,811 HIGH TEMPERATURE SURFACE-COMBUSTION RADIANT HEATER Elmer E. Strand, 59 E. Sunset Ave., Salt Lake City, Utah 84115 Continuation-impart of application Ser. No. 555,570, June 6, 1966. This application Feb. 8, 1968, Ser. No. 704,018 U.S. Cl. 126-92 13 Claims Int. Cl. F33d 11/44; F24c 3/04; F23d 13/12 ABSTRACT OF THE DISCLOSURE A surface combustion type, radiant gas heater, having a burner and reverberatory screen assembly, is provided with a reflector that is spaced backwardly from the screen assembly. The reflector is backed by a cooling jacket through which a cool-ant is forced. Higher than usual burner screen temperatures can be obtained, and the screen assembly is fabricated of materials capable of withstanding such high temperatures. In the industrial treatment of materials, an impermeable, but thermal energy absorbing and radiating member is spaced forwardly of the screen assembly to seal the material being treated from the products of combustion generated by the heater. A plurality of the heaters can be combined in mutually spaced side-by-side relationship to provide progressive heating of the material being heated or heating of a larger expanse of material. Olftake ducts formed between the heaters can then form passages through which the products of combustion can be removed.

This application is a continuation-in-part of my application Ser. No. 555,570, filed June 6, 1966, now abandoned.

This invention is concerned with the generation of heat of exceptionally high temperature (e.g. in the neighborhood of 3000 F.) and with the application of such heat to useful purpose. It provides a gas-fired radiant heater that can be constructed and operated economically to produce the desired heat and to apply such heat to a variety of purposes, especially the treatment of materials industrially.

Use is made of various concepts and features shown by the Mentel et a1. U.S. Patent 3,084,736 granted Apr. 9, 1963, entitled Gas-Fueled Infrared Generator, but considerably higher temperatures are achieved with correspondingly increased intensity of radiated energy and without contamination of the materials being treated by the accompanying products of combustion. Moreover, a series of the heaters can be advantageously utilized for the overall treatment of a broad surface area or for progressive heating of a material. Danger of flame flash back into the fuel feed system is greatly minimized if not completely eliminated.

The Mentel et al. infrared generator is known as a surface combustion type of gas burner. It utilizes a fine mesh burner screen unit, through which the fuel gas is forced from a plenum chamber for combustion at the outer face of such screen in a manner that heats the screen to incandescense. A reverberator screen of relatively course mesh is spaced outwardly from the burner screen unit, so as to act as a damper to prevent hot gases from being wiped away too rapidly and also as a reflector to reverberate infrared rays back onto the burner screen, thereby building up its temperature to incandescence. A reflective, safety screen may be spaced in back of the burner screen to help prevent flash back of flame into the plenum chamber and combustion of fuel gas therewithin at the relatively low temperature specified, i.e. 900 F. to 1800" F.

Features of the present invention are the utilization of ice a reflector of radiant energy rays, as the back of the plenum chamber, the provision of a forced cooling system for such reflector, the provision of an impermeable and imperforate thermal energy absorptive and radiating plate spaced forwardly of the reverberator screen, and the provision for leading off and venting products of combustion from between the burner screen and the impermeable radiating plate.

For the extremely high temperatures that are preferred with heaters of the invention, although not necessarily employed, the screens and radiating plate must be of a material, such as silicon-carbide or ceramic coated Fiberchrome, manufactured by the Johns-Manville Corporation, capable of withstanding the extremely high temperatures involved, but the reflector can be of any heatconductive material having a reflective surface, e.g. polished stainless steel or polished aluminum.

One highly useful application of the radiant heaters of this invention is in connection with the method and apparatus of Storrs U.S. Patent No. 2,809,154, granted Oct. 8, 1957, entitled, Heat Treatment of Substances for the Recovery of Decomposition Products. As so applied, high intensity radiant energy is projected downwardly onto material passing therebeneath from a radiating plate shared in common by a series of the heaters. Other uses will become apparent. For example, the heaters of the invention can be used to dry materials, in calcined operations, or in the roasting of metallurgical ores in accordance with methods other than that taught by the said Storrs patent.

Some representative applications of the invention are shown in the accompanying drawings, which illustrate the best modes presently contemplated of practicing the invention. Further objects and features of the invention will become apparent from the accompanying drawings and detailed description that follows:

The drawings FIG. 1 represents a fragmentary top plan view, partly in horizontal section, taken from the standpoint of the line 11 of FIG. 4, and showing a series of the radiant heaters of this invention serving as the heating means for a material-processing retort;

FIG. 2, a corresponding bottom plan view taken from the standpoint of the line 2-2 of FIG. 5;

FIG. 3, a fragmentary perspective View, drawn to a. considerably larger scale, of supporting framework forming a component of one of the heaters of the series;

FIG. 4, a fragmentary end elevation drawn to a considerably larger scale than are FIGS. 1 and 2;

FIG. 5, a longitudinal vertical section taken on the line 55 of FIG. 4;

FIG. 6, a transverse vertical section taken on the line 66 of FIG. 5 and drawn to a still larger scale;

FIG. 7, an enlarged fragmentary view of that portion of FIG. 6 encircled by the line 7, an intermediate portion being broken out for convenience of illustration;

FIG. 8, a side elevation view of a thermal reactor utilizing another embodiment of the heater of the invention;

FIG. 9, a horizontal section, taken on the line 9-9 of FIG. 8;

FIG. 10, a fragmentary, enlarged vertical section, taken on the line 10-10 of FIG. 9;

FIG. 11, a fragmentary, vertical section, drawn to an even larger scale than is FIG. 10, and taken on the line 1111 of FIGS. 9 and 10;

FIG. 12, a horizontal section, taken on the line 1212 of FIG. 10;

FIG. 13, a vertical section, taken on the line 1313 of FIG. 12;

FIG. 14, a view like FIG. 12, but showing still another form of the invention; and

'3 FIGS. 15 and 16, vertical sections taken on the line 1515 and 16-16, respectively, of FIG. 14.

Detailed description Referring to the drawings: In the particular embodiment illustrated in FIGS. 1-7, a series of six radiant heater units 20, constructed in accordance with the invention, are arranged side-by-side any event is to subjecta material to be heat-treated to the radiant heating effect of the heater units 20. It is tobe understood, however, that one or more of. such heater units can be employed in other ways for various industrial, commercial, or domestic heating purposes.

Each heater unit comprises a dual assembly of respective sets of screens 24, 25, and 26, FIG. 7, and 27, FIG. 6, providing a surface-combustion type of gas burner, such as shown by the afore-referred-to Mentel et al. Patent No. 3,084,736. Screen 24 is a safety screen, screens 25 and 26 together form a burner or generator screen unit, and the screen 27 is a so-called reverberator screen, all in substantial accord with the infrared generator of such patent, the commercial form of which is manufactured by the C. A. Olsen Manufacturing Co., Elyn'a, Ohio, un-

der the trade designation Infralux. However, other surface-combustion types of burner screen construction can be employed. For example, where the excessively high temperatures noted above are involved, it will be necessary to utilize perforate cloth of graphite, silicon carbide, or ceramic coated Fiberchrome, instead of the customary metal screen. One satisfactory, fine mesh carbon cloth, is that produced by the Carboiundu-m Company under the trademark Carbotex.

The two sets of screens forming the dual assembly of each heater unit 20 are mounted in a supporting frame 28, see especially FIG. 3, and, for this purpose, each set is advantageously framed by stainless steel stripping 29 that encloses the edges of the screens 24, 25, and 26 together with an interposed spaced strip 30 of mild steel, and that has a depending flange 29a to which a longitudinal edge of screen 27 is secured.

The frame 28 has longitudinal side members 28a, FIG. 3, which seat and support outer longitudinal edge margins of adjoining sets of screens, and transverse end members 28b, which similarly seat and support ends of such sets of screens. Otherwise, the frame 28 has flue-forming side and end members 28c and 28d, respectively, joined to and upstanding from the outer lateral edges of the respective side members 28a and end members 2811, respectively, and has lower transverse end members 28c, joined at their opposite ends to depending portions of respective flueforming end members 28d.

The inner longitudinal edge margins of adjoining, sets of screens are secured to and serve to support an-openended conduit 53, FIGS. 5 and 6, that provides circulation for a coolant fluid in a cooling chamber 31.

Such cooling chamber 31 and a plenum chamber 32 for the distribution of a gaseous fuel, such as natural gas or packaged LPG, are formed above the sets of screens by means of and at opposite faces ofa reflector plate 33, which is concave and preferably curved as a parabolic reflector and has its longitudinal edges connected in fluidtight relationship with the side walls 34 of an inverted tank. The plate is preferably stainless steel, with its reflector surface highly polished. Connections with the mild steel tank walls 34 are preferably made by welding. Plates 35 close opposite ends of the plenum chamber 32, and the cooling tank has end walls 36 and a top wall 37, which,

4 together with sidewalls 34, completely enclose the cooling chamber 31.

A fuel gas and air mixture is introduced into plenum chamber 32 from any suitable source byway of a supply pipe 38 and perforate distributor header 39, which advantageously has a perforate divider plate 39a extending diagonally along its length. This makes for uniform burning conditions at the burner screens. A coolant fluid,.usually and preferably water, is introduced to cooling-cham ber 31 through a pipe 40 and discharged through a pipe 41. Although most of the heat energy is reflected by reflector 43, the provision for forced cooling, especially by a liquid coolant, enables operation at ultra-high temperatures. i The screen sets are anchored to respective flanges 44a 'of walls: 44 by means of bolts 42, with heat resistant gaskets 43 interposed. Following installation of'the assembled screens and tank in supporting frame28, heat insulation 44 is packed into the spaced b'etween'walls34 and flue-forming walls 28c.' Opposite margins of the framed screens are secured to the bottom of conduit 30 by screws 45, with heat resistant gaskets 46 interposed and an insulated, protective shield 47 applied therebelow for supporting inner longitudinal edges of the screens 27.

As is usual with surface combustion. types of gas burners, the gas from plenum chamber 32 burns on the outer surface of each of the screens 26. Spaced below the screens is a heat absorbing and radiating plate 48 that, with the reflector 33, has the effect of intensifying the radiant energy generated by the burner screens. Screens '24, 25, and 26 are preferably 40, 10, and 60 mesh, US. Standard, respectively, and screen 27 preferably has openings inch square.

Leading from the combustion chamber 49, formed between the screens and plate 48, are flues 50 for conducting gases of combustion to disposal through any suitable stack (not shown). Adjoining end members 28d of side-byside frames 28, see FIG. 1, provide for formation of the flues 50 between upstanding side wall members 28c of v such frame.

The combustion chambers 49, which are in communication side-by-side along the length of the retort served by the several heater units 20, are preferably sealed from, the

outside atmosphere by liquid trap seals SLFI G. 5', utilizing depending flanges 48a of plate 48. Plate 48 acts as a black body in absorbing, with great efiiciency, the radiant energy directed to it from the burner screens and reflector 33, until the plate 48, itself, becomes intensely hot. Since the plenum chamber is insulated and insulation is provided 'around the combustion chamber, the radiant energy absorbed by plate 48 can only be emitted downwardly from the plate 48 to thematerial 23. The retort chamber 52 containing the material 23 thus receives maximum. radiant heat energy frorn'the intensely hot plate 48, while being completely separated from gases of combustion which are conducted away without contacting such material. Because the gases of combustion are of low density, they are virtually unaffected by the reverberating thermal'energy and they are relatively cool as they are conducted away, in comparison to the more intense temperatures of the burner screen and plate 48.

In the embodiment of FIGS. 8-13, the heaters of' the invention are shown generallyat 55. They are wedgeshaped and are mounted like spokes beneath a central exhaust stack 56 of a thermal reactor, shown generally at 57. A reactor of this type is fully shown and described in my co-pending application for US. Patent, Ser. No. 704,067 filed Feb. 8, 1968.

Each heater includes a lower frame that includes a coolant circulating system made up of hollow side members 58 and 59, that converge to be connected at one of their ends by a hollow end member 60. The other ends of the side members are more widely spaced and are connected by a hollow member 61 that has a partition 61a intermediate its length.

Spaced between end members 60 and 61 and interconnecting the side members 58 and 59 are a series of intermediate, elongate, hollow members 62 of triangular crosssection. Each intermediate member has its ends welded to the side members 58 and 59 such that orifices 63v and 64, through the respective side members, interconnect the interiors of the side members with the interior of the intermediate member. The members 62 are arranged with their apexes downwardly and their bases spaced just slightly apart. The side walls of the triangular intermediate members thus form reflectors to reflect radiant energy towards and through a burner screen 65, that is stretched tautly below the apexes. The burner screen is cerarnically bonded to the bottoms of side members 58 and 59 and end members 60 and 61. Although other materials can be used, a fine mesh, ceramic coated, Fiberchrome screen has been found suitable for use as the burner screen.

A closed hood 66 is fixed to the side and end members and a fitting 67 in the large end of the hood overlying end member 61 is adapted to have a fuel line 68 connected thereto. A controlled ratio of gas and air can be supplied as a fuel gas through line 68 and fitting 6 7 to hood 66, in any convenient manner.

The fuel gas entering the hood moves downwardly through the small openings between the bases of intermediate members 62 and through the burner screen where it is ignited at the face of the burner screen and behind a reverberator screen 69. The reverberator screen is like that heretofore described and has larger openings therethrough than does the burner screen. As illustrated, the reverberator screen in clamped between an insulating member 70 that is affixed to the bottom of the burner screen beneath the end and side members, and an angle member 71. In a reactor such as that illustrated, and shown more in detail in my aforementioned co-pending application for patent, Ser. No. 555,570, the angle member 71, at the large end of the heater, rests on a ring of insulation 72, FIG. 10, that is supported by a ring member 73, having insulation 74 on the inside thereof and an outer ore guide 750 that serves as a facing.

A circular, impermeable and imperforate membrane member 76, corresponding to the plate 48 previously described, and made of a material or materials capable of absorbing and radiating heat energy but impervious to gases of combustion, is clamped at its outer edge between ring of insulation 72 and ring member 73 by bolts 77 that are passed through the ring of insulation to be threaded into a ring member 77a. Material to be heat treated, using the heaters of the invention, is spread on a screen 78 that is rotated beneath the impermeable membrane, and after it has been so treated the residue is removed. Screen 78 is stretched tautly over rods 78a that radiate out from and that rotate with a central plate 78b. The inner edge of impermeable membrane 76 is clamped between a ring of insulation 79, on which the small end of the heater rests, and an insulating ring member 80 that is positioned on a support plate 81, by bolts 82. An inner ore guide 75b depends from support plate 81 to a point just above screen 7 8, so that it holds material to be heat treated on the screen.

The details of the screen 78, the drive means therefor, the feed means for feeding material onto the screen, the means for removing residue from the screen, and the inner and outer ore guides are all shown in detail in my co-pending application for US. patent Ser. No. 704,067 filed February 8, 1968.

Gases of combustion formed by operation of the heaters cannot pass through the impermeable membrane and are discharged upwardly through flues or ducts defined by the outside walls of the hoods of adjacent heaters to be directed into exhaust stack 56 by a hood 83 that fits over the heaters and that is sealed to them and to the ring of insulation 72 throughout the space between the heaters. Because the gases are not very dense, they are not significantly affected by the radiant energy reverberation between the burner screen assembly, the reflector, and membrane 76 and since they are carried away quickly after combustion takes place they remain relatively cool. The hood 83 is sealingly connected to the lower end of the exhaust stack. The outer walls of the side members and hoods of adjacent heaters thus form flue-walls to direct the gases of combustion into the exhaust stack 56. If found necessary, to prevent heating of the coolant water, insulation 84, can be placed against the lower frame, adjacent to the side members. Brackets 84a, suspended from the hood holds support plate 81 and the heaters resting thereon.

In practice, fuel is supplied to the interior of hood 66 through fitting 67 and is thereafter distributed through the narrow spaces between the bases of intermediate members 62 and the burner screen to the combustion chamber formed between the front face of the burner screen and the reverberator screen. The adjacent, inclined faces of the intermediate members cooperate to form a reflective surface, corresponding to that previously described, and with the burner screen to form a plenum chamber at the back side of the burner screen. As the fuel is passed through the narrow openings formed between the intermediate members 62 it is cooled, or maintained cool, by the contact with the intermediate members through which water is being circulated as a coolant. Thus, there is very little, if any, danger of the fuel in the plenum chamber being hot enough to support flash back and the safety screen heretofore described is not necessarily required.

In FIGS. 1416, there is shown another type of coolant system that can be used in lieu of the coolant system of the lower frame shown in the embodiment of FIGS. 8-13. The coolant circulating system of the lower frame of FIGS. 14-16, is made up entirely of pipe members and, in some cases, may be more economical to construct than coolant circulating system of the lower frame heretofore described. As illustrated, pipes 85 and 86 serve as the side members of the frame and with pipes 87 and 88, connected at the ends thereof as the long and short end members, respectively. Intermediate, pipes 89 extend between the side members and are closely spaced so that fuel supplied through the hood will be evenly distributed as it passes between them. The intermediate pipes are made of a material that will carry the coolant water and that will provide good reflective surfaces that will cooperate with the reverberator screen 89 in heating the burner screen to incandescence and in radiating energy through the burner screen to the impermeable membrane 90. The mounting of the reverberator screen 89 and if impermeable membrane 90 are the same as previously described in connection with the heater of FIGS. 813.

Openings 91, through the wall of pipes 85 and 86, into each of the intermediate pipes 89, are designed to insure continuous flow of water as a coolant, through each intermediate pipe.

Water is supplied to pipe 87 at one side of a plug 92, and is passed through pipes 85, 88 and 86 and each of the intermediate pipes 89, before being returned to pipe 87 to be discharged at the opposite side of plug 92.

When the coolant system, shown in FIGS. 14-16, is used, the exterior surfaces of curved walls of adjacent intermediate pipes cooperate to form a reflective surface that functions to reflect heat energy in the same manner as do the reflective surfaces heretofore described.

Obviously, a lower frame utilizing a combination of pipes and other specially designed members, such as are shown in FIGS. 813, could also be used.

It should also be apparent that the overall shape of the heaters can be changed, as required for a heating operation. For example, they can be made rectangular or circular rather than wedge-shaped, as disclosed. Also, a plurality of heaters can be arranged other than as shown, so that material to be heat treated can be passed beneath them, or so that they can be moved into position to heat such material. If only one heater is required for an operation, it can be made of any desired size or shape.

Experience with the radiant heaters of this invention has shown that an exceptionally high conversion of available B.t.u. input to radiant energy output that can easily be put to useful purpose, is accomplished.

Although preferred forms of my apparatus have been herein disclosed, it is to be understood that the present disclosure is made by way of example and that variations are possible without departing from the hereinafter claimed subject matter I regard as my invention.

I claim:

1. A gas-fired, high temperature radiant heater, comprising an assembly of screens forming a surface combustion type of gas burner;

means including a reflector having a substantially concave forward face forming with said screens a plenum chamber behind and in operative communication with said assembly of screens;

means for introducing fuel gas into said plenum chamber, so fuel gas will pass into the screen for surface combustion forwardly and outside of said chamber; and

means including a chamber behind said reflector for forcing a coolant in intimate contact with the back of said reflector.

2. A radiant heater in accordance with claim 1, wherein the coolant is a liquid.

3. A radiant heater in accordance with claim 1, wherein the screens are of a highly heat resistant material, such as silicon carbide, for ultra high temperature operation.

4. A radiant heater in accordance with claim 1, wherein there is additionally provided an imperforate, heat-radiating member spaced forwardly of the assembly of screens, so as to separate the combustion area of the heater from an area of heat application.

5. A radiant heater in accordance with claim 4, wherein the heat-radiating member has an area substantially commensurate wth the screen area, so as to define a combustion chamber between it and the screens.

6. A radiant heater in accordance with claim 5, wherein fiues for products of combustion lead from the combustion chamber and said chamber is otherwise closed.

7. A radiant heater in accordance with claim 5, wherein there are additionally provided walls defining a retort chamber within the area of heat application, for the treatment of materials.

8. A Iradiant heater in accordance with claim 1, wherein a perforate tube is provided in the plenum chamber in communication with the means for introducing fuel gas thereinto, as a distributor for said fuel gas.

9. A gas-fired, high temperature radiant heater, comprising an assembly of screens forming a surface combustion type of gas burner; l

a reflector having at least one reflective surface spaced behind the assembly of screens and arranged to reflect energy back toward the said screens, said reflector surface forming with the screens a plenum chamber;

means for introducing fuel gas into said plenum chamber whereby fuel gas will pass into the screens for surface combustion forwardly and outside of said chamber; and

means for forcing a coolant into intimate contact with the back of said reflective surface.

10. A gas-fired, high temperature, radiant heater according to claim 9, further including an impermeable, heat-absorbing and radiating member spaced forwardly of the assembly of screens and forming with the said assembly of screens, at one side of the impermeable member, a combustion chamber wherein the fuel gas is burned, the opposite side of the impermeable member being adapted to have heat radiate therefrom to an area of heat application.

11. A gas-fired, high temperature, radiant heater according to claim 10, further including flue means connected into the combustion chamber to carry away gases of combustion formed during the burning of the fuel gas.

12. A gas-fired, high temperature, radiant heater, according to claim 1, wherein the reflector comprises closely spaced, hollow elements through which the coolant is adapted to be circulated, each said element having a reflective surface; and

means for circulating said coolant through the said hollow elements.

13. A gas-fired, high temperature, radiant heater according to claim 12, wherein the means for introducing fuel gas into the plenum chamber comprises a hood, extending over the hollow elements; and

conduit means for directing said fuel gas into the hood,

whereby it is distributed through the spaces between the hollow elements to the plenum chamber.

No references cited.

FREDERICK KETTERER, Primary Examiner.

U.S. Cl. X.R. 431-

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