CA1088412A - Radiant heating - Google Patents

Abstract

Abstract of the Disclosure Improved gas-fired radiant heater has porous re-fractory panel mounted by its edges on a support to define a gaseous combustion mixture plenum from which the mixture flows through the panel to burn at its outer face, and a conduit for non-combustible gas extends along the margin of the panel and discharges the non-combustible gas through the panel all along its margin to keep the combustion mixture from escaping through the panel edges where burning can damage the panel and to keep the panel support relatively cool. No further sealing of the panel margin is needed, but the sealing is effected with less of non-combustible gas if the panel edges are compressed so as to reduce their thickness about 10%. One or more of the margins of a rectangular panel can be arranged as a depending flange with its mounting at least partially recessed 90 that two or more panels can be juxtaposed at such margins to form an effect-ively continuous radiating surface of relatively large size.
The air seal construction also makes such heaters very practical for firing house heating furnaces.

Description

~88412 The present lnvention relates to gas-fired radian~
heaters and to equipment with which they are used. Such heaters are described in U.S. Patents 3,785,763; 3,248,099 and 3,824,064. ~
Such heaters are very efficient a~d very desirable for generating ~ ;
extremely large quantitles of concentrated infra-red energy. ~ -Such a heater utilizes a panel of interfelled ceramic fibers, a gaseous combustion mixture being continually passed through ~
the panel and ~urnt at the panel face from which it emerges. `
The combustion takes the form of a flame that extends over the entire area of the face from which the combustion mixture emerges, the flame length being very small so that the surface fibers at the flame are heated to red heat or hotter and form an essentially continuous wall of heat that makes a very effective heat radlator.
By increasing or decreasing the rate of flow and/or composition of the combustion mixture, the temperature of the heated ~ibers can be controlled.
Among the ob~ects of the present invention is the ~;
provision of novel heater structures that are simpler to construct or provide improved operation or both.
The foregoing as well as additional ob;ects of the present invention will be more fully understood from the follow-ing de cription of several of its exemplifications, reference belng made to the accompanying drawings in which:
Fig. 1 is a face view of an infra-red heater according to the present invention;
Fig. 2 1~ a sectional detail view of the heater of Fig. 1, taken along the line 2-2;
Fig. 3 is a plan view of a component that can be used in the making of the heater of Figs. 1 and 2;
Fig. 4 is a detail view similar to that of Fig. 1, . ~
showing some structure features suitable for the infra--red heaters ; -: ' of the present invention;
Fig. 5 is a view similar to that of Fig. 2 showlng an dnv/ ~

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optional method of constructing the heaters of the present invention;
Fig. 6 is a sectional view of a gas-fired radiant heater according to another aspect of the present invention;
Fig. 7 is a plan view of an assembly of heaters of the type illustrated in Fig. 6;
Fig. ~ is a sectional view similar to Fig. 6 of a modified heater construction pursuant to another aspect of the present invention;
Fig. 9 is a plan view of the heater of Fig. 8;
Fig. 9A, appearing on the same sheet as Fig. 10, is a plan view o a component of the structure of Figs. 8 and 9;
Fig. 10 is a broken-away plan view of a portion of a heater showing a detail feature suitable for use according to thc present invention;
Pig. 11 is a sectional view Oe the construction Oe Fig. 10, taken along line 6-6;
Fig. 12 is a sectional view of a different heater construction pursuant to a further aspect of the present invention;
~igs. 13 and 13A are sectional views of a heater construction typifying yet another aspect of the present invention;
Figs. 14, 15 and 17, all appearing on tho same sheet are views of still further embodiments of the present invention; and ;
~ig. 16 is a vertical sectional viow partly diagrammatic of a ;
heating arrangement pursuant to the present invention.
According to one aspect of the present invention in a gas-fired radiant heater having a combustion mixture plenum covered by a face of a porous refractory panel through the thickness of which combustion mixture passes from that plenum to burn on the opposite face of the panel, there is provided the improvement according to which the panel extends beyond the margins of that plenum, a second plenum encircles the combustion mixture plenum and has gas-discharge openings covered by extending portions of the first panel face, for discharging a non-combusting gas through the thickness of the panel from its first face to its exposed face all around the combustion mixture in the panel, to keep that combustion mixture from reaching the panel ;

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According to another aspect of the pTesent invention in the : .:.
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operation of a gas-fired radiant heater havi.ng a ~orous réfractory panel .
through the thickness of which a stream of combustion mixture is passed from one face of the panel to the opposite face where it burns to generate heat, there is provided the improvement according to which a thin stream of non-combusting gas encircling the combustion mixture stream is also passed through the panel thickness from said one face of the panel to said .
opposite ace to confine the combustion mixture stream and keep combustion 10 mixture .~rom reaching the edges of the panel. The ;~ .

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~ 89~12 porous refractory panel can be fla~, convex, concaveJ cup-shaped, hat-shaped,or have any other desired configuration.
This non-combustlble gas stream acts as a barrier which directs ~he combustible mixture ~hrough the refractory panel and minimizes leakage of combustible gases past the frame members that hold the panel. By acting as a combustible gas barrier, the non-combustible gas stream significantl~ reduces the importance of the seal shown in Patents 3,785,763 and 3,824,064, greatly reducing burner assembly time and parts tolerance. The non-combustible gas stream also greatly reduces contact of the hot -gaseous products, resulting from the combustion at the panel surface, on the frame members keeping them much cooler and reducing heat warpage.
The narrow stream of relatively cold gas is conveniently ;
provided by holding the porous panel on the ledge carried by the combustion mixture plenum for the porous panel, and a slot extends along the ledge and is connected to a supply of the non-combustible gas.
An even greater simplification of the oregoing heater construction and operation is effected by squeezing the panel margins to that they are compressed at least about 10% from their uncompressed thickness, inasmuch as this simple expedient also h~lps reduce the e~cape of combustion mixture through the panel ed~es. When combining a marginal gas stream seal with the edge compression, very effective edge sealing is accomplished with only a fraction of the ~low of non-combustible gas otherwise re-quired. With either arrangement however, no other assistance is needed to sesl against edge leakage of combustion mixture, and edge impregnation as well as edge wrapping of the panel is com-pletely dispensed with.

Turning now to the drawings, the basic radiant heaterof Flgs. 1 and 2 has the usual porous refractory panel 10 held at its margin~ ~y uppe~ frame mem~ers 21, 22, 23, 24, against a dnv/ ~
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1~1884~2 lower frame 30. Frame 30 has four lengths of tubular supports, two of which are shown in Fig. 2 at 31, 32, secured to the margins of a rçctangular back plate 40 by welding, brazing, cementing as wi~h epoxy or other cement, or otherwise joining in a gas-tight manner, indicated at 42. Back plate 40 and the four tubular supports thus define a plenum for the comhustion mixture fed to the panel lO. A pipe connection can be welded through an aperture in the back plate in the standard manner for receiving a com-bustion mixture supply conduit, and a baffle,a portion of which 0 i9 shown at 44, can be fitted to help equalize the combustion mixture flow toward all portions of panel 10.
One or more lengths of the tubular support frame can also have a connector 53 welded through an aperture Eor the supply of air from a pump or a storage tank or the like. A slot 55 i~ also provided along the top wall 57 of the support frame for discharge of the air from the interior of the tubular support lengths through the margin of the porous refractory panel. The ~ -individual tubular supports are mitered together at the corners of the frame with the mitered ~oint sealed as by welding, brazing, ;
cementing or otherwise securely ~oining, to keep combustion mix- ;
ture from leaking out of the plenum as well as from being non-uniformly diluted with the air moving through the tubular supports.
The upper frame members 21, 22, 23, 24 are shown as angles each having an upper flange 61 that overlies a margin of the outer face of panel 10, and a depending flange 62 that is secured to a low~er frame member, as ~y means of the screws 64.
The screws can ~e threadedly received in the outer walls of the tubular support members, and can pass through openings in the flsnge 62. Such openings can be elongated in the direction perpendicular to the wall 57 if adJustability is to be provided for the spacing between wall 57 and flange 61.
The porou3 panel 10 permlts the gaseous combustion mixture to freely pass through it so that pressures 1ll the plenum .

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10~8412 need only be about 2 to 7 lnches of water above the ambient atmosphere to provide very effective uniform combustion over the entire outer face of panel 10. A slmilar air pressure in the interior of the tubular support will cause streams of a~r to pass through the margin of porous panel 10 and emerge from ~ts outer face. The porous interfelted fibrous structure of the panel surprisingly does not permit much change in the width of the air stream moving through the panel, particularly when the pressure that propels the air stream from the tubular support is within an inch or two of water height with respect to the pressure that propels the gaseous combustion mixture from the plenum. This is readily noted when the burner is in operation inasmuch as the outer surface of the panel glows red hot over its entire area except for a narrow and ~harply defined band around its periphery and ad~acent the outer rame mem~ers.
The frame members are thus kept much cooler than they would be wlthout the marginal air stream, particularly where the -burners are operated with the outer surface of their panels 10 positioned in a generally vertical plane, or positioned facing downwardly. In those positions the very hot gaseous products resulting from the combustion at the panel's surface, rise and ~;
flow over the frame members of the burners of Patents 3,785,763 and 3,824,064 to heat them up to high temperatures that can reach dav/ ~

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jO0F in some cases. The marginal air stream of thc present in-vention, on the other hand, acts as a barrier layer against the hot combustion products, keeping those hot gases from directly , reaching the rame members in substantial volume. Marginal stream' ;
taXen from the air at ambient temperatures and passing throuyh a panel as much as 1 1/2 inch thick will generally keep the outer faces of 1/16 inch thick steel frame members several hundred ~egrees F below the temperatures corresponding ~rame members reach ~, ''', in the constructions of the above patents. The temperature o~ the '"' ~ ' rames of the present invention will be even lower where the heater ; ' is used to heat objects that do not cause ~uch re1ection of the ,;, burner'a radiating heat back to those ~rame members. ' A further benefit of the present invention is that by,, minimizing contact of the hot combustion gases with the ~rame members and thus keeping them much cooler, emission of radiation , '~
from the ~rame members themselves is greatly reduced, The heaters ; '.;
of the pxesent invention can be positioned much closer to their , ,targets, than prior art heaters and still permit minimizing damage to the target in the event o~ emergency shutdown~ The porous reractory panel itself cools down very sharply when the fuel gas ~low into the plenum is s~opped and the air flow is mai~tained but the ram_ me~bers of the ~rior art heaters take much longer to cool down. Thus when using such~heaters to ,heat a moving web of heat-sensitive'material, the heaters are preferably arranged to , ~, generate much more heat than the web can tolerate should the web Is~op moving. With the prior art heaters the rate o cool-down ¦Ifor the ~rame members can become a cr~tical factor that determines ~how ciose the prior art heater can be brought to ~he we'b without ~ .,' :.' "
l ' , . '' ' . ''. ~: -~ 8~1Z`' maging ~he web in the event the web suddenly stops'ana the h~ater ' cannot be mechanicall~ pulled away from it. The heat~rs of the '-pre.~ent invention don't have to be pulled away and can therefore be installed in a less expensive manner. Their closer proximity to the target makes the heat transfer to the target more efficien ,~;;
and enables the use of less fuel to achieve the desired xesu~ts. '~
~oreover in some treatments such as the volatilizing of ~, "
. water from a 'target web, the most effective wave-leng~hs are ,.,.
between about 3.2 to about 3.6 microns, a range ~hat is most ,.,.. ~ ~

eficien~1y produced at relatively low radiation temperatures~ ' ... .. .
By moving,the heaters of the present invention closer to their ta~ ~
gets, their radiation temperatuxes can be diminished to thus make ' , more.e~icient use o~ the fuel ,energy and with less uel, without , , , decreasing the treatment e~ectiveness. ,, "
~ eaters placed very close to targ.ets may be desirably ~' made to extend beyond the edges of the target to attain greater treatment uniformity. Each such e~tension can be approxima.ely equal to the distance from ~he heater to the target, for good ` ,, results. , , 2Q' ~ocating slot 55 immediately opposite the panel margins alongside the inner edges of the upper rame members 21,'22, 23, , 24 helps guide the protective streams to the desired location~ ~. -i This guiding action is further improved by sealing ~he edges of ~ .,:. .
the panel so that not much non-combustible gas can escape ,.".
laterally. Fig. 2 illustrates a prior art edge sealing te~hnique according'to which a ~hin foil of aluminum 70, about 2 mils thick .. ',~
~¦ is wrapped around each panel edge, and,the lower face of ~he foil ..
¦ is sealed against wall 57 by a ~arrow line o~ seala~t 7:2 such as ¦ a sll~cone rubber vulcanized in place.
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` Accordiny to the present invention, whcn edge se~ling of the panel is desircd, the sealant 72 can be of a ma~erial such as ~ordinary rubber or neoprene, that need not be resistant to high temperatures. However during normal operation of the burner con-struction o the present invention, only air from the interior of the tubular support will tend to leak out from the margins of the panel~ Such leakage is not dangerous nor is it extensive when sealant 72 is entirely omitted. Omitting the ~oil 70 can cause extensive air leakage unless the outer frame is a ver~-close fit against the support frame. The marginal air stream with or withou-leakage keeps the combustion mixture from leaking out the edges o~
the panel.
The slot 55 does a very e~ective job when it is about 1/4 inch wide, although it can be as little as 1/16 inch or as muc as 1/2 inch wide and still gi~e good results. The width of pro-tectiva gas stream emerging from the ~ace of the porous panel is generally a little larger than the width of the slot, and changes in gas pressure vary this broadening ef~ect. A desirable gas pressure in the tubular frame is one that approximatel~ e~uàls the ~20 pressure in the combustio~ mixture plenum. ;~
The cooling a~d combustion-mixture-leak-blocking e~fects of the marginal stream of ~he present invention are also obtained when the discharge slot 55 is located ~urther toward the outer ac of the frames so that the gas discharged thxough the slot is dir-;; ected partly o~ completely a~ frame flange 61. Most of the di-~-charged gas will then move along t~e interior of panel 10 and -escape just past the inner margin o f that ~rame flange.
' ~ ¦ It ~5 not essential to make the tubu~ar support me~bers~
gas-tight where they are threadedly en~aged by screws 64. Even !
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~ere relatively expensivc inert gas is used rathcr than air, the leakage through such threaded connections is minisculc as com- :
¦ parea with the discharge through slot 55~ The threaded engagement ~an be sealed however, as by applying pipe-~hread dope or the lik :~
to the mating threads before they are engaged. Alternatively the :
connection between the outer and inner ~rames can be made as shown in U. S. Patents 3,785,763 and 3,824,064. - :~
. Instead of making tubular frame 30 of our separate lengths, it can be made from a single piece of formed sheet metal, as illustrated in Fig. 3. An elongated strip of sheet metal . twent~ to fifty thousandths of an inch thick can be bent into the .
~orm illustrated by the sectional view in Fig. 2, or a standard . metal kube oE rectangular section can be milled to cuit the slot 55 through one wall, and the resulting ~hape then subjected to ~ ;
mitering cuts 81, 82, 83, 8~ and 85 as shown in Fig. 3. These cut - : .
leave wall 88 intact and the mitered length then bent to form a ¦ ~ -one-piece tubular ~rame a corner of which is shown in Fig. 4. The . inner edge of each corner is therl welded, brazed, cemented or o~herwise joined as at 89 to seal the en~ire height of that corne ~.
and the tubular frame is ready for similar joinir.g to the back . plate 40~
It is not necessary to seal ~he outer face 90 of the mitered joints, particularly if the joints are a close fito A ..
little extr~ leakage at those locations from the in~erior of the ......... .
tubular frame does no particular harm~ However, that outer face can be sealed, especially if lateral leakaige from the :Eram~ ~argin taXes place~
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The tubular frame need not extend inwardly of the slot `~55, although it helps to have that frame provide an additional flat support 73 for the porous panel 10. Such support can be reduced to the thickness of the metal from which the tubular frame is made, as by suitably shaping the tube from which it is sliced, or by milling the slot 55 alongside the inner wall of the tubular ,. ~ .
frame.
Figure 5 shows another tubular frame co~struction of the present invention which is simple to manufacture. ~ere a flat support 173 takes the place of support 73 and extends toward the center of the plenum. ;
It is also helpful to seal the outer margin of panel 10 as by dipping it in or brushing on a hardenable liquid resin that hardens to a temperature-resistant solid. Solutions of silicone rubber, colloidal s-llica, and sodium silicate are ex- ;;
amples of suitable hardenable materials. When this type o edge ~`
sealing is used, the aluminum foil is not needed.
In some installations the panel temperature is so hot and there i6 80 much reflection of heat from the surfaces being heated by the heater, that aluminum can be damaged. Other metals , such as stainless steel can then be used for the sealing foil. -`
Fig. 6 illu~trates a heater 100 w1th improved edge sealing. Heater 100 ha~ a cup shaped panel 102 of lnterfelted refractory fibers, clamped by its edges around a sllpport assemble 104 made of stainless steel or other metal members shaped from relati~ely thin stock, about 1/16 inch thick. A central dish 106 -, has a~floor 105 and inclined walls 107 with raised edges 108 a8ainst whlch the panel 102 is preased to deflne a combustion i mixture plenum L10. Outer face 103 of panel 102 is of rectangular-shape, and 90 i8 plenum 110.

Secured to the outer margin of the floor 105 of dlsh 106 is a series of angles two of which are shown at 112, 114, de-fining a rectangular frame against whlch the edges }20 of panel 102 are fitted. These angles are illustrated as having horizontal dav/~Vb - 10 -~ 4~2 I -¦~ ~s 122 welded or brazed to the floor of dish 106, and vertical webs -~¦124 that approach but do not quite reach the dish edges 108. The ¦frame angles define with dish walls 107 an outer plenum 130 that ¦encircles combustion mixture plenum 110 and 'has a discharge slot ¦132 that is engaged by the margin of panel 102. The rame members ¦are mitered or otherwise interfitted at the corners of the frame ¦to minimize,or completely seal the outer plenum against,leakage in those locations. Supply nipples 146, 148 are fitted'in opening ¦in the floor 105 and one or more of the frame angles 112, to - ';~
~0 ¦deliver, respectively, combustion mixture and non-combustible yas.
¦Baffles such as the U-shaped deflector 116 can also be provided ¦to help more uniformly distribute the incoming gases. Inasmuch ¦as air is generally the non-combustible gas that ~lows through ¦plenum 130, a little leakage doesn't do any particular harm other than consume a little excess air. '- ' I Anchoring of panel 102 in place is shown as effected wit ;
¦the help of a series of four or more clamping angles 136, 138, ~ ' ¦clamping the panel edges 120 against the frame angles, with the help of screws 140 that penetrate through aligned openings in the ;~
20 ¦ angles and are threaded ir.to self-locking nuts 142 mounted in webs l 124 as by securing clips or welding. The screws which need be no ¦ thicker than about 3/16 inch, are readily pushed through the edges of the panel without seriously damaging the panel, and any damage l that might promote gas leakage is more than compensated by drawing '' 'I up the clamps sufficiently to compress the panel edges. Standard -l panels have a wall thickness of about 1 1/8 inches and an inter-¦ ~iber spacing such that more than half that thickness is fiber I and binder, so that compressing the edges to reduce t'he overall ¦ thickness only about 10% sharply reduces the air space between 30 ¦ fibers and greatly limits leakage.
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However very effective panels of interfelted fibers ;
can be made by needling a mat of such fibers without the help of binder. Such needled panels can be extremely pliable, as com-pared to molded binder-containing mats that are stiff like boards and can have their edges compressed down to as little as about 30% of their uncompressed thickness. Even compressing such ~ ;
edges that are originally about one inch thick down to a~out 3/8 inch provides an extremely effective back-up for the air seal.
For such pliable panels it is preferred that the edge 0 compression be down to about half the original thickness, or less. If desired however a pliable panel can be stiffened over its edges alone, or over its entirely, as by impregnating it with a water solution of starch or the like. In such stiffened condition, the degree of edge compression can be reduced.

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To reduce any effect that the compression may have in breaking panel fibers that are binder-impregnated, the panel ;~;
edges to be compressed are first dipped in water or other solvent ~;
for the binder carried by the fibers. Such wetting makes the edges more readily deformable so that the compressing is easily effected without seriously stressing the clamping structures.
To assure uniformity of co~pression of board like panels, the screws 140 are no more than about 8 inches apart when the angles have the above-noted wall thickness. Where the heaters are operated in confined spaces so that the clamping angles are subjected to considerable reflected heat, it is helpful to cut slots about six lnches apart through the vertical webs of those angles, to allow for thermal expansion and contraction without distortion of the support. Such slots need only be about 20 mils wide, but can be omitted where the clamping angles do not engage each other at the corners of the frame so that expansion is possi -ble at those corners.
A feature of the heater construction of Fig. 6 is that a plurality of such heaters can be juxtaposed to make an effectiv ,_ ly continuous radiant heating assembly that covers an extended area. Thus individual heaters are conveniently made with rec-tangular heater faces about one foot by two feet in siæe, larger sizes of stiff board-like panels being somew~at awkward to manu-facture because the molding and handling is more difficult. How-ever by making the smaller sized panels so that their edges 120 are bent down at least about 90 degrees from the plane of the panel body, considering such edye as a flange ben~ clown from a f~at sheet, and loca~ing the edge mountings 30 they~are at least partially inboard of the outer face of that flange and not pro-~ecting beyond that ~ace more than about 5 m~liimeter3, theyjuxtapose in a very desirable manner as illustrated iIl Fig. 7.
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In Fig. 7 an assembly 200 of individual heaters 100 is made with the adjacent faces o their panel l_dges 120 about 3 millimeters apart as indicated at 202~ The margins of the panel faces 102 can be made so that they have an essentially zero radius of curvature where they bend into the edges 120, but it is some-times simpler to make them with a radius of about 1/8 inch, and the foregoing 3 millimeter spacing of such rounded corners does not significantly detract from an effectively continuous heater surace junction, particularly where the combustion mixture is .0 arranged to burn over the entire rounded corner. Increasing the spacing from about 3 millimeters to about 5 millimetexs does make a significant discontinuity in the radiation uniformity but this can generally be tolerated.
While the clamping screws 140 are shown as having round heads and thus project out the furthest from the outer faces of the refractory panel edges, such projection is not a problem so long as it i9 not over the 5 millimeter limit noted above, or the preferred 3 millimeter limit. These screws can be in unsymmetrica L
~ locations along each edge, so that the screws on one heater are !0 offset from the screws of an adjacently positioned heater, as also illustrated in Fig. 7. Indeed the round-head screws can be re-placed by socket-head screws which project a trifle more but are easier to install during manufacture. Flat-head screws can alternatively be used with the screw openings in the clamping angles countersunk 90 that the screw heads do not project beyond those angles, if minimum or zero spacing 202 is desired. ~-. . ' . ',',': . '' - 14 - ~ -.
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The burner construction of Fig. 6 can also have panels . :.
of the pliable needled type described above. Such a pliable ~
panel behaves very much like a blanket, and can have its edges ... :. .
fold,d and tucked in place between the side anch`orage members.
Because of their high pliability, the corners of such panels .~.. ..-.
will squeeze into shape, although it may be helpful to cut away all excess corner material, and to even notch out some of the -panel corners to make it easier to clamp these panels into place. It is preferred to confine any notching to portions ~ `
of the corners covered by the anchorage members so as to reduce : ` :
e leaKage of gas at ~he notch-s.

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1-- . , I ' , ¦ It is not necessary to have the entire margin of each ¦refractory panel lQ2 flanged over as at 120. Thus each of the ¦panels in Fig, 7 has at least one margin that is not juxtaposed Ito another panel, and some have two such non-juxtaposed margins.
¦Whexe only two panels are to be juxtaposed, each can have only one ¦margin provided with a flanged-over edge 120, in which event the ¦remaining three margins can have simpie constructions as shown in ¦the flat panel exemplifications of Fi~s. 1 to 5 as well ¦a5 in Figs, 8 and 9.
¦ Very close juxtaposition can also be provided by molding lor 9haping juxtaposed edges 120 so that they are bent down more ¦than 90 degrees from the horizontal as measured by the angle 150 ¦in Fig. 6. A panel can thus b~e molded around a suitably shaped ¦molding screen with as many as three of its four sides having ¦~lanyed edges bent as much as lOO or 110 degrees measured at angle ¦150, and the thus molded panel can then be slipped sidewat~s o~f ¦the mold in the direction away from its fourth side. Where only ¦one flanged edge margin i5 de~ired, it can be made when rnolding ¦the panel, or by ben~ing down the edge of a flat-molded panel, ¦after that edge is softened by wetting.
¦ The construction of Figs. 8 and 9 is one that is easily `
¦manufactured from readily available sheet metal, for flat heater ¦panels. It has a pane~ support which is a welded-together assembl~ ' 1f a rectangular plenum box 30~ and a hollow-centered rectangular ¦
¦encirclin~ plenum tube 304. Plenum box 302 is conveniently pre-¦pared by suitably notching out the corners o~ a rectangular sheet, ¦then bending up the ~our wings tnus formed, and welding the I . .
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resulting corners gas tight. A hole can then be punched in the floor of the box to receive a PTM half close nipple 306 also welded on gas tight A baffle 308 can also be spot welded over the hole to distribute the combustion mixture fed through it. If desired an extra tap 310 can also be provided at a second hole in the box floor, for a pressure gage or the like.
Tubular plenum 304 is easily made from sheet metal bent into the shape of a channel having a web 312, and unequal flanges 314, 316. The channel is cut into four lengths each of which is mitered and then welded together gas tight, if desired. The tubular plenum can then be affixed to the plenum box as by spot wclding the ~langes 316 to the floor of the box. A gas inlet 320 in the form of half a close nipple can be affixed to the tubular plenum, along with an extra tap 322 in the same manner as for the box plenum, and a baffle 324 can be fixed over inlet 320 by spot welding to either the outside of the box plenum or the inside of the tubular plenum. ;
A slot 330, preferabLy l/4 inch wide, encircles the top o~ the box plenum. ~he refractory matrix is clamped in place by a clamping frame 342 of angular section as illustrated in Fig. 8 and having slits 344 cut in the web overlying the face of the panel as shown in Fig. 9. The slits can be about 8 inches apart and preferably 1/16 inch wide to take care of the most severe ~ -thermal conditions. The clamping frame is secured by screws 346 as in the construction of Fig. 6, although sheet metal screws can be used instead in either construction,in which event the nuts can be omitted and if desired locking washers fitted under the screw heads.
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In severe thermal conditions, such as firing face down or when firing directly at opposing burners, it is desirable to insulate the clamping frame 342 from the radiated and convected :~
heat by over-wrapping with a high tempera~ure insulating material such as mineral fibers felted or needled in blanket form. Fig. 8 shows a fiber blanket 350, approximately 1/2-inch thick, clamped and compressed between clamping frame 342 and re~ractory matrix .
340 is wrapped around the clamping frame 342 and web 312 and .:.
secured to flange 316 by means of clamp 360 and sheet metal or .
other screws 362. The fiber blanket 350 insulates the clamping rame from convected heat and its pure white color reflects some ; :
radiated energy from opposing burners making the system more efficient. In very high ambient operating conditions it may be desirable to completely wrap the non-radiant surfaces of burner . ~:
300 with the fiber blanket. : .
Fig. gA shows the fiber blanket 350 as prepared for instat`lation, having a tuck-in margin 370 which is inserted under the face of clamping frame 342. . . . .
In less severe appl~cations it may be desirable justto :. :.
l20 cover the face o 342 and hold the blanket in place with the screws .; ..
3~6 and washers under their heads. . ;:.-The radiant heaters of the present invention can be -:
eguipped with automatic igniters such as electric spark igniters or pilot lights. Figs.lo andll show a particularly desirable . ;.:
automatic igniter construction fitted.into a heater of the type ;.
illustrated in Fig9. 8 and 9. A standard combination 500 o~ spark ~:.
rod 501, ground rod 502 and flame-checking rod 503 is mounted so ~:
that the rods are generally parallel to and about 1/16-inch above . ' . ~'' .
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the outer face 505 of t~e porous refractory panel 340. Below ¦the opposite face of the panel underneath the rod assembly, the box plenum is provided with a partition 507 that isolates a chamber 509 from the remaining space in the box plenum, an~ the .
chamber is fitted with its own supply connector 511 to receive a - .
separate combustion mixture. .;. .:
The spark rod 501 and *lame-checking rod 503 are each . .... .
housed in two identical insulators 550 which go through aligned ~. :
openings punched in the top flange 520 of the clamping frame 342 : :
~in~e 1anges 316 and 314 o plenum 304 as shown in Fig.ll. .
~round rod 502 i9 welded or brazed to 1ange S20. The ends of rods 501 and 503 by flange 316 are threaded to accept connector ;
542 ~hich holds them in place and provides a ready connection for ~ :
. necessary wiring. -. The construction of Figs 10 andll is operated to start .~
the burners using a safety check. A separate pilot combustion : . :
mixture is first started into cha~ber 509 and at the same time the .:`
spark rod is electrically energized to begin sparking. I~ the . .
. ~lame rod does not sense a flame withln a short period o~ time, such as lO to 30 seconds, the flow o combustion mixture can be automatically cut of~ and the starting sequence must then be :~
manually rec~cled, preferably after the combustion mixture flow .
. is checked as by purging chamber 509. When the starting sequence cause ignition o the separate combustion mixture, the 1ame-ecking rod 503 senses the ignition and opens the valve that *eed .:
the main combustion mixture into plenum 302 which i9 then ignited ~ -.
by the 1ame at chamber 509. .

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~y using a small chamber 509 with a low BTU~hour input for the automatic ignition test, the danger of explosion at ~' ignition is minimized. A chamber volume of about 100 cubic centimeters or less is very effective for this purpose. ,~,' , The pilot combus~ion on the radiating surface of the ~ ,' panel contribut,es to the overall radiation.
The spacing of the rod assembly from the refractory ~ ' panel is preferably kept very small so that the rods do not interfere with placing the radiating surface close to the materiai being radiated, such as a moving textile web that is being dried. '' "
Because the effectiveness of the heater increases when brought , c}ose t,o the material treated, the spacing o the panel from that matexial ls sometimes arranged to be as little as two inches or even less. ' , ' Pig.12 illustrates a radiant heater 700 of,the present invention particularly adapted for the sealing of metal tubes in , a metal sheet, Heater 700 has a dome-shaped holder 70~ welded gas-tight to a ~upport ring 704 that is shaped to fit'and receive the ~, brim 710 of a hat-shaped refracto;ry ceramic panel 720.,,The crown ,,, portion 712 of the panel is thus held in spaced relatlon to the dome-shaped holder 702~to define a plenum 730 for the combustion "
, mixture to be burned on the concave surface of the crown 712. An inlet 732 and pressure gauge tap 734 are shown as fitted to the '~
~' holder 702. ' ' ',~ ' The brlm of panel 720 is shown as clamped against , '' , support ring 704 by a clamping ring 706 which is bolted to an ~, extensi,on 708 of support ring 704 and is offset from it to form a cylindrical wall 740 that deines an an~ular plenum 750 for the ~," , . . '''- '''' :
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non-combustible gas. If deslred the offset can be made integral ^~- wlth the clamping ring so that support ring extension 708 can be in the general plane of the main portion of the support ring.
Alternatively wall 740 can be divided into upper and lower short cylinders separately integral with the separate rings. An inlet 760 and a pressure gauge tap 770 are also provided for the annular plenum.
Non-combustible gas pumped into plenum 750 of heater ~ -700 flows through the brim 710 of the porous refractory panel 720 -.
and keeps the combustion mixture fed through plenum 730 from reaching the lowest portion of the internal surface of the panel where it is aligned with plenum 750. No external cooling coil or ;~
~acket is needed for the heater 700, inasmuch as the non-combustible -gas emerging from the lower portion of the interior of the panel ~;
flows outwardly along the bottom of clamping ring 706 and keeps it a~ well as the a~ociated metal parts sufficiently cool. Holder 702 as well as the remaining members that hold panel 720 can all be made of aluminum about 60 mils thick.
Flg. 12A shows a modified sealing arrangement of the ~ust-described embodiment. Here a burner 1500 having a generally flat burner face 1520 is used. This extends the heat-up time somewhat as compared to the construction of Fig. 12, and as a result wide assemblies may take as much as 50~ more time to seal.
However the sealing time i9 still far less than obtainable from the prior art.
The burner 1500 of Fig. 12A can be constructed in~ the manner described above preferably along the lines of its Fig. 5 where the ceramic fiber mat has its margin merely fitted to a frame havlng an inert gas blow-through arrangement in which the inert -;~
gas thus blown through the margins of the mat acts as to seal --those marglnA against combustible mixture leakage. No other margin sealing i3 then needed.
Another feature of the present invention is that the '~

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heaters with the air seal construction are particularly sulted for use in house hot air and/or hot water heating furnaces. The air seal effectively prevents diffusion of the combustion mixture to edge locations where it can burn at a low feed rate and thus gsadually burn back deeply into the binder holding the refractory ~.
fibers, eventually creating a line of weakness at which an un- ~:
needled panel tends to readily break. Indeed the burn-back can ~:
sometimes burn back far enough to cause ignition within the mixture `.

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plenum itself, rendering the heater unsuited for continued opera-tion. The edge seal construction of the present invention accord-ingly provides a very long life ~or tha refractory panel, and is also so simple that it is inexpensively constructed and thus more attractive for relatively small home-type equipment.
Figs. 13and13A show a hot air heat exchanger constructior for house heating pursuant to the present invention. Here a cylindrical heat exchanger 800 has a hollow interior 802 in which is received a ibrous panel 804 also of generally cylindrical shape. The panel has an open end 806 clamped to a mounting plate 808 as by means of a rib 810 formed or welded on the plate and around which the panel end is squeeæed by a split sheet metal strap 812 w~.ose ends can be pulled together by a tightening screw 814. -Before the panel is fitted in place a partition disc 820, held on a tubular support 822 having an externally threaded extension, i9 mounted on mounting plats 808 which has a threaded aperture 826 that threadedly receives the threaded extension 824.
Partition disc 820 has its periphery located just above ;~
the edge of rib 810, to define a marginal slot 830 for discharge of a sealing gas stream through the marginal portion of the panel 804. An inlet nipple 832 provides for the delivery of the sealing as stream to the sealing plenum 840 below partition disc 820. ;-~
xtension 824 provides for the supply of combustion mixture to the -lenum 850 above the partition disc.
Strap 812 is also shown as carrying a ring of outwardly-extending ears 842 that heIp retain a mass of insulation packing 844 ~itted axound the open end of panel 804 when mounting plate ~ . .~ . , ,.
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808 is brought into engagement with the mouth 846 of heat exchangex 800. Some of those ears are also perforated to receive an ignition and test assembly 860 shown in the form of a series of ceramic tubes 862 each having an enlarged head 865 and threaded into aligned openings in the mounting plate. Through the pas- -sageway in each ceramic tube there penetrates a rod 867 having a `
disc-shaped inner end 870 and staXed as at 872 so that it is appropriately located with respect to the ceramic tube. A washer 874 can be slipped over each rod before it is inserted in the ceramic tube, to ~urnish better positional coaction with the tube and the staking. The outer edge of each rod can be threadedl engaged to a mounting tip 876.
The discs 870 of each rod are arranged so that they are in edge-to-edge opposition suitable for sparking and for flame detection, as described in connection with Figs 10 and 11.
The outside of hea~ exchanger 800 can be located in the circulating air plenum of a standard house heater, or if desired in a water tank containing water to be heated. This heat ex-changer can be made o metal or even of glass, borosilicate glass being particularly suited when the heat exchanger i9 used to heat water. Water to be heated in this way can be colored with dyes for example, to better absorb radiant energy transmitted through a transparent heat exchanger. Metal heat exchangers are desirably ~
ribbed to increase their effective surface area and thus increase ~-their heat transfer to surr0unding air or the like.
Another feature o~ the present invention is the ability to use an inert or reducing gas to seal the combustion mixture . , . ~.. '." ~
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on its way through the porous refractory panel. Thus ~he sealing gas can contribute to make the burnt combust:ion mixture provide an atmosphere of exceedingly low oxygen content, or even of strongly reducing ability as for example by reason o a signifi-cant hydrogen content.
Fig.l4 show~ an annealing tunnel furnace 900 having upper and lower radiant heaters 902, 904 facing each other and held in fixed relation by sid~ blocks 906 o~ thermal insulation.
A wire mesh conveyor 908 is arranged to slide through-the furnace interior to carry workpieces that are to be annealed or brazed.
A strip curtain 9lO closes off the entrance to the furnaceJ above the converyor, the portion of the entrance below the conveyor "
being closed by a one-piece wall 91~.
~ he heaters 902, 904 are operated in the manner des-cribed above, except that the sealing gas streams, indicated by arrows 920, can be cracked ammonia, or a propane-nitrogen mixturet or pure propane or the like. With such sealing gases, it is preferable to adjust the combustion mixtures so that they have little or no surplus oxygen. ~he urnace interior then becomes a very efective reducing atmosphere that will prevent oxidation of the workpieces and even reduce any oxidation present on those pieces when they are introduced into the furnace. ~otwithstanding the strongly reducing character of the furnace interior, the burning of the combustion mixture takes place very effectively to pr de radi-tion at temperatures at least as high as red heat.

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- Fig. 16 shows a partqcularly effective heating arrangement for heat treatment of a moving web 1200, such as textile drying and curing or paper processing, the directive of movement is shown by arrow 1202. In thls arrangement a series of burners 1210 face the moving web adjacent each other on opposite sides of the web. Immediately facing each burner 1210 is a re-radiator 1220 having a very thin layer of heat-absorbing material ~ ;
such as oxidized stainless steel 1222, backed by a high temperature insulator 1224 such as refractory felt. The re-radiators are preferably substantially wider than the burners and in use the heat absorbing layer 1222 absorbs substantial quantities of heat which penetrate web 1200 so that the layer becomes quite hot and re-radiates heat back to the web 1200. To improve the drying or gas-removing effect of the heat treatment process, intake and exhaust ducts 1230 and 1232, respectively introduce streams oE
poorly saturated air ad~acent the location where the web approaches the burner, and withdraw more saturated air ad~acent the locations where the web leaves the burner. To further improve the efficiency of this system, heat from the withdrawn air can be used to pre-heat the incoming poorly saturated air.

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The needled ceramic fiber panels described above are conveniently manufactured in very long lengths, as long as 25 feet or even longer. Such panels are particularly suited for use with very long radiant heaters, and a construction of this type is shown in Fig. 15.
Here a ceramic fiber panel lOlO about fifteen feet long and about one foot wide, has its edges clamped against the face of an air seal plenum 1020 surrounding a rectangular combustion mixture plenum 1030. Angles 1040 compress and clamp the panel edges, being drawn against the air seal plenum face by screws 1050 that can be fitted with shoulders 1052 against which they can be tightened at relatively high torque with a min:imum oE
attention.
A panel lOlO that is not stiffened with binder or the like, will belly out as shown at 1060, under the influence OL the pressure in plenum 1030. This is not particularly harmful, and is in some respects desirable because it reduces the heat ~ -radiation from the face of the panel to the clamping angles.
The bellying action can be reduced by pretensioning the panel when it is mounted.
Another technique for stiffening a pliable panel is ; to needle it around a stiffener as shown in Fig 16, for example.
In this construction a wide mesh metal screen 1102 is laid in between two layers 1108, 1110 of ceramic fibers, and a needling o ation then perform~d to Interfelt the two fiber layers.

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Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore,.to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. ~;

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Claims (16)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a gas-fired radiant heater having a combustion mixture plenum covered by a face of a porous refractory panel through the thickness of which combustion mixture passes from that plenum to burn on the opposite face of the panel, the improvement according to which the panel extends beyond the margins of that plenum, a second plenum encircles the combustion mixture plenum and has gas-discharge openings covered by ex-tending portions of the first panel face, for discharging a non-combusting gas through the thickness of the panel from its first face to its exposed face all around the combustion mixture in the panel, to keep that combustion mixture from reaching the panel edges.

2. The combination of claim 1 in which there is no additional impediment to the movement of combustion mixture from within the panel to the panel edges.

3. The combination of claim 1 in which the panel is a compressible ceramic fiber panel and the margins of the panel are squeezed sufficiently to reduce their thickness at least about 10% to reduce the escape of non-combusting gas out the panel edges.

4. The combination of claim 1 in which the panel is a felted ceramic fiber panel.

5. The combination of claim 1 in which the porous refractory panel is a needled mat of fibers.

6. The combination of claim 1 in which the second plenum is defined by a tubular conduit that extends around the combustion mixture plenum and has a panel-contacting face that is slotted to provide the gas-charge open-ings which that face covers.

7. The combination of claim 6 in which the tubular conduit has a rectangular cross section.

8. The combination of claim 7 in which the tubular conduit is a succession of lengths of channelling extending around the combustion mixture plenum, each channelling length having a web and two flanges defin-ing respectively three walls of the tubular conduit, one of the flanges being secured to the combustion mixture plenum to hold the conduit in place adjacent the side of said plenum and use that side as an additional wall of the tubular conduit.

9. The combination of claim 6 in which the tubular conduit is a succession of lengths of tubular conduit connected together, and a plate is secured across all the connected lengths to span the space enclosed by that conduit and define with those lengths the combustion mixture plenum.

10. The combination of claim 1 in which the plenums are defined by metal walls and the sides of the heater are covered with thermal insulation.

11. The combination of claim 10 in which the refractory panel is held against the plenums by a set of metal flanges clamping the panel margin against the face of the plenums, and the thermal insulation is a blanket having one edge gripped between the flanges and the panel, the blanket being folded outwardly over the flanges and the burner sides.

12. The combination of claim 1 in which the refractory panel is held against the plenums by a set of metal flanges clamping the panel margin against the face of the plenums, and a relatively thin thermal insulation blanket covers the outer faces of the flanges.

13. The combination of claim 8 in which the securing of the flanges to the combustion mixture plenum is by spot welding to the floor of that plenum.

14. In the operation of a gas-fired radiant heater having a unitary porous refractory panel through the thickness of which a stream of combus-tion mixture is passed from one face of the panel to the opposite face where it burns to generate heat, the improvement according to which a thin stream of non-combusting gas encircling the combustion mixture stream is also passed through the panel thickness from said one face of the panel to said opposite face to confine the combustion mixture stream and keep combustion mixture from reaching the edges of the panel.

15. The method of claim 14 in which the non-combusting gas is air.

16. The method of claim 14 in which the non-combusting gas is a reduc-ing gas.