US2215081A - Bell type furnace - Google Patents

Description

Sept. 17, 1940.

o. H Ess 2,215,081

BELL TYPE FURNAGE Filed Sept. 3, 1937 3 Sheets-'Sheet l INVENTOR sgat. 17, 1940. F. ol HEss 2,215,081

BELL :rYPE FURNACE Filed sept. 3, 195'. 3 sheets-sheet 2 BY VM L, fa/5K2@ ATTORNEY F. O. HESS BELL TYPE FURNACE Sept. 17, 1940.

3 Sheets-Sheet 5 Filed Sept. 3, 1937 Patented Sept. 17, 1940 UNITED 'STATES PATENT OFFICE BELL TY'PE FURNACE Frederic O. Hess, Philadelphia, Pa., assignoi- .to

The Selas Company, Philadelphia, Pa., a corporation of Pennsylvania Application September 3, 1937, Serial No. 162,263

10 Claims. (Cl. 266-5) heated, and for the removal of the material which has been heated.

Such bell type furnaces are-in extensive use for metal annealing and other heat treatment purposes. For the usual purposes for which such furnaces are employed, it is highly desirable that the heat supplied to the work be distributed thereto in a uniform manner, and be regulated to avoid'the risk of overheating either the work or the furnace, While at the same time avoiding;

l0 unnecessary waste of time in heating the work and furnace up and completing the heat treating operation.` For most purposes, for which suchv furnaces are used, it is also practically` essential' that the composition of the atmosphere'envelopl5 ing the work be closely controlled, and in many cases the work is enclosed by an inner hood or work cover, having side and roof walls parallel and spaced away from the inner walls of the outer bell. Such an inner hood also shields the work Z0 against contact with atmospheric air, and desirably retards the work cooling rate, when'slow cooling is desirable, and, when the outer bell is removed and in use in connection with another base or' hearth and inner hood if, as is not 35 unusual, a single outer bell is employed with two or more furnace bases vand inner `hoods to form two or more successively heated furnaces.

The heating means employed in such a bell furnace mustnot only satisfy the-furnace heat 40 distribution and temperature requirements but must meet the mechanical requirements incidental to the fact that the movable outer bell is a relatively massive structure which may weigh sevtioned type, with gas burning means incorporated in its walls and comprising combustion spaces facing and open to the work or the work enclosing hood heat and directly radiating to the work of its enclosing hood, and having said spaces so dis- 5 tributed, and subject to such ready control, as to insure the proper heat distribution and temperature control.

A more specific object of the present invention is tovprovide burner units adapted for removable l0 mounting in openings formed for the purpose in, and extending through the wall of the outer furnace bell, so that each burner unit can be withdrawn for inspection, repairs or replacement, while the furnace is in operation and without significant disturbance in the furnace operating conditions.

The burner units hereinafter described in detail herein, were especially devised for the purposes of, and comprise a part of the present invention, but in respect to the form and character of their coinbustion space and the manner in which fuel and air -jets are pressed into said spaces, the said units embody the essential features and principles of a burner in commercial use, and commercially known as a Duradiant burner, previously devised by me, and disclosed in my prior application Serial No.l 88,744, filed July 3, 1936.

A bell type furnace having heating means constructed and arranged in accordance'with the 80 present invention, has important practical advantages. With it high combustion efficiency is maintained, and the maximum operating economy of fuel burning furnaces over electrically heated furnaces is obtainable. Burners of the special type mentioned, constructed for efficient operation, with a relatively low rate of fuel combustion per individual furnace, and made with a small heat liberating, or burning capacity, and this coupled with the relatively 10W cost of constructing the burners and mounting them in the Wall of the outer bell, make it practically feasible *to employ as many individual burner units in a by its capacity for a more rapid heating up operation, since there are no metal burner parts to be heated up to heat radiating temperatures; and is characterized by its avoidance of the expense inherent in the use of relative large amounts of heat resisting metallic alloys, and by its avoidance of any such heavy maintenance expense as is inevitable with direct flame impingement against metallic parts at high temperatures.-

The various features of novelty which characterize myinvention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages, and specic objects attained with its use,

reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

Of the drawings:

Fig. 1 is a vertical section on a diametral plane of a bell type furnace, circular in horizontal cross section;

Fig. 2 is a plan view of a portion of the base member of the furnace shown in Fig. 1;

Fig. 3 is a partial section taken similarly to Fig. 1, but on a larger scale. l

Fig. 4 is an end-elevation of one of the burner units shown in Figs. 1 and 3;

Fig. 5 is a somewhat diagrammatic plan View of a bell furnace rectangular-in horizontal cross section; n

Fig. 6 is an elevation, partly in section on the line 6 6 of Fig. 5. l

In Figs. 1-4, I have illustrated the use of one form of the present invention in a bell type furnace, circular 'in horizontal4 cross section, and whlch may be, and as shown is, of conventional construction, except in respect to itsy heating provisions, including the gas burner parts incorporated in the vertical wall of the bell, dome or hood member A of the furnace,

'Y and the vent passages formed in the stationary shifted horizontally, in opening up the furnace base member B, on which the bell A is removably seated in the operative condition of the furnace. Inl accordance with the usual practicev of the art, the bell member A comprises an outermetallic armor or shell, andalrefractory shell lining, which may comprise an inner layer A' of insulating fire brick or like refractory material, and an outer layer of so-called heating insulating refractory material, The shell is supported on a horizontal flange portion A3 of the metallic shell. secured to the metallic shell of the bell A, extends upwardly from the center of the top portion of the shell, for engagement by the hoisting hook of a crane, not shown, by which such a bell is customarily lifted or lowered,l and for the removal of treated work, and for the vintroduction of the work to be treated. and in thereafter restoring thev furnace to its operative condition.

As shown, the work C rests upon a metalpart D, which may be of alloy steel, and forms the top or hearth portion of the base member B,

f the portion of the latter below the p'art D being formed of refractory material. 'In most cases, and as shown, the work C is normally enclosed by an inner metallic hood or cover member E,

.supported by the hearth D and having its side and roof walls respectively spaced away from the side and roof walls of the bell A, to provide A metallic bail or eye A4- a heating space EA between the hood E and bell A. Suitable sealing means are provided to make a gas tight joint between the loweredge ofthe hood E and the memberD. As shown for this sealing purpose, the member D is formed to provide an annular` troughD at lthe periphery of the member, the trough being open at itstop and being formed in what may be regarded as a depending peripheral flange portion D2 of the l member D. The lower edge of the member Eis I received in the trough space D' and rests upon the bottom wall of the latter, and the -joint between the member D and E is sealed by sand, or the like, in said trough space. It is also customary, though not universal practice,to provide special' means for sealing the joint between the lower edge of the bell A and the surface B 4of the base B on which the bell A is seated.`

discharge conduits,v such-as are formed by the f vertical metal tubes F andG, respectively, shown in Fig. 1 as extending up through the member D into the space within the hood E, and which in many cases, at least, should be formed of highly resistant metallic alloys. At their lower ends, the pipes or tubes F and Gr'communicate with the channels or pipesF and Gf formed or imbedded in the masonry portion of the base member B, and leading to the exterior of the furnace.

In respect to its features, specifically mentioned above, the furnace shown in Fig. 1 follows the usual practice of the art, and embodies no feature ofv construction and arrangement which is original with me, but is a typ1cal example of the sort of furnace with which my invention may be used with advantage.

In accordance'with the present invention, the

furnace collectively shown by Figs. 1 4, is heated by the combustion of a combustible mixture of air and gas in the combustion spaces ofburner elements or units-'incorporated in the vertical wall of the bell A. Each burner element orunjt in the formbest shown in Figs. .3 and 4, coml prises a burner assembly insertable in, and removable from the furnace wall, and a special refractory block h constituting a permanent portion of the inner refractory lining layer A', andformed with an outer conical passage h', into which the corresponding' burner assembly extends, and an inner expanding passage h3 co-vv axial, and communicating, with the passage h',

'Ihe burner assembly, as shown, comprises a metal casting H having a rectangular plate-like body portion adapted to overlap the outer metallic shell of the bell A at the margin of the opening A5 through which the burner assembly extends. As shown, each part H is secured in place by clamping bolts or screws I threaded into the metallic shell of the bell A. The casting H comprises an outer pipe elbow portion,l H', having a downwardly facing internally threaded, inlet H2, and a horizontal internally threaded outlet H3 opening at the furnace, side of the part H. A horizontal metal pipe H4 has its outer end threaded into the outlet H3, and has its inner end threaded into the outer end of a tubular part H5. The inner end portion of the latter is of larger diameter than its outer end portion and is internally threaded for threaded engagement with the externally threaded body of a'burner tip element J. The part H4 may be formed of heat resistant metallic alloy material and the part H5 may be formed of vsuch material or of refractory ceramic material.

The tube H4 passes axially through an outer refractory body K in conical frustum form, and into a refractory burnerbody element L shaped externally to form an extension of said conicalfrustum. The member L is formed with a cup shaped combustion space or cavity L extending into it from its inner end coaxial with a passage L2, which comprises an inner end portion large enough to snugly receive vthe metallic burner part H5, and an outer .end portion of smaller diameter receiving the corresponding portion of the metal pipe H4. The parts H4 and H5 thus form means for detachably clamping the parts H, K and L together. .Advantageously the part K is formed of heat insulating refractory material and the part L of refractory material having a relatively small coefficient of thermal expansion. l

The chamber h2 in the'blockJL is outwardly flared to form a symmetrical extension of the space L from which a large portion, ordinarily more than one half, of the heat generated by the burner is, radiated to the adjacent'portion of the hood E, and from which gaseous products of combustion pass into the space EA.

In the preferred form illustrated, the burner tip member J is of refractory ceramic material, and comprises a main cylindrical portion which extends into the bore of the larger inner end portion of the member H5, and an inner end portion -J which is shorter, and of larger diameter, than the first mentioned cylindrical portion, and is external to the member H5, and a conical intermediate portion J2, engaging the beveled end H5.l

of the member H.

A multiplicity of peripheral grooves J44 are formed in the outer surface of the' tip member J. Each groove J4 comprises a portion parallel to the axis of the tip` member and extending for the full length of the main cylindrical portion of the tip, and comprises aninclined discharge end ,portion J5 extending alongside the outer surface of the tapered intermediate section J2 of the tip member, to the periphery of the inner end cylindrical, burner tip portion J As is clearly shown in Fig. 3, each groove J4 thus forms a gas passage or orifice rectangular in cross section, and having three walls formed by the ceramic tip member J, and a fourth wall formed by the adjacent portion of the burner part H5. As shown, the tip member J is formed with a screw Athread J5 engaging the internal screw thread formed in the inner end portion of the member' H5, so that the tip member is firmly anchored in place in the burner assembly.

The portion of the Wall of the cavity L in the refractory part L at the inner side of the inner end of the metalli'- part H5, surrounds and defines a combustion space in which the fuelmixture delivered thereto through the lchannels J4, is wholly or largely burned. That space may be described as cup shaped, and the Wall of the cavity'L may be regarded as comprising a circular series of surface portions or sectors alongside the jets issuing from the respectively adjacent burner channels'J4. Each of said surface sectors has a portion adjacent the burner body which is inclined away from the axis of the burner at about the same angle as the adjacent burner channel portion J5, and which is laterally displaced from the axis of that channel portion. In other Words, the said portion of the cavity Wall may be regarded as a part of a conical surface with its apex in the axis kof the burner, at some distance outward from the point of thatv axis at which the inclined channel portions J5, if extended, would intercept said axis.

The inclination to the burner axis of each such sector portion of the Wall of the cavity L', diminishes as the distance from the discharge end of the corresponding channel J4 increases, so that the line of intersection with the cavity Wall of a plane radial to the burner axis, is concave toward said axis. The described shaping of the wall of the cavity L relativeto the inclination of the burner orice discharge J5, serves the purpose of so locating the corresponding sector portion relatively to each fiame or burning jet formed by .the combustion of the fuel mixture supplied by the adjacent orifice J4, that said surface will be heated to incandescence and with a desirably close approximation .to temperature uniformity of all portions of the Wall directly alongside the flames, regardless of the actual length of the latter.

The lengths of the flame jets will depend somewhat upon the composition of the combustible mixture, and with lany given fuel composition, will be longer or shorter, accordingly, as the gas pressure in the pipes H4, and consequently the rate of combustion and total heating eect are relatively great or relatively small.

The burner construction illustrated, in respect to its use of 'a burner tip member formed and shaped like the member J, to deliver combustiblev mixture jets into a combustion space surrounded by a refractory Wall, like the Wall of the cavity L', not claimed herein, but is claimed in my said prior application, Serial No. 88,744.

In the' intended operation of the form of the invention shown in Figs. 1 4, the combustion of the fuel mixture supplied to each pipe H4, is completely effected in the cavity L', or in that cavity and its extension h2. In consequence, the composition of the combustion gases passing into the space EA, will depend upon the composition of the combustible mixture. It is thus possible by varying theniixture composition to control the of the cavity L', and of lower, but still high,

temperatures by the wall of the conical space h2. In consequence, a large portion of the heat liberated is transmitted to the hood E by radiation.

rI'he form and character of the burners shown and described, make it practically feasible to incorporate a relatively large number of. closely spaced burners in the wall ofthe bell A, soy as to insure whatever heat distribution, and gradual tion in the rates at which heat is transmitted to the different unit areasof the work cover or hood E, may be desirable. As shown in Fig. 1

the burner elements are arranged in a number of superposed horizontal rows extending circularly about the axis of the furnace. As shown, the burners in each horizontal rowI receive fuel mixture through corresponding individual valved branches M of a circular manifold M serving the burners of that row. Each manifold M receives a combustible mixture through a corresponding valved branch N from one or more vertical bus pipes N, to which the mixture is supplied through a supply pipe Oincluding a regulating valve O', from a so-called mixing machine (not shown) or other means for supplying a combustible mixlture of gas and combustion air of suitable composition, andat a suitable pressure.

In the construction shown, the pro-ducts of combustion are discharged from the chamber EA through a vent system which, as shown, comprisesa horizontal channel P extending radially inward to the center of the base member B from the -exposed peripheral edge of the latter and communicating through a vertical channel portion P' with a space-beneath the hearth plate D. That space, as shown, is divided into sections by spaced apart radial'piers Q beneath the body of the hearth plate D and resting on an upper surface B2 of the masonry portion of the base member B within and somewhat smaller than the inside diameter of the flange D2. Communication is thus pro-vided between the space vabove the surface B2, and the spaces between the radially extending brick parts OA resting on the previously mentioned surface B' of the base B, and" directly supporting theflange portion D2 of the plate D. 'I'he last mentioned spaces open directly into the heating space EA. 'I'he channel P may open at its inner end directly into the atmosphere, or may open into a chimney connection, if the conditions of use are such as to make such disposition of the products of combustion desiri able. 'Ihe withdrawal of the products of combustio-n from the furnace through the baseas illustrated in Figs. 1 and 2, while convenient, es-

pecially in the case of .relatively small furnaces,

is not essential. On the contrary, the products of combustion may bedischarged through outlets formed in the vertical wall of the Vbell A, or through openings in the roof of the-bell shown in the construction shown in Figs. 5 and 6.

In Figs. 5 and 6, I have illustratedthe use of the-present invention in a furnace of the bell type which is rectangular in-horizontal cross section, anciv of a general design well adapted for use in relatively large capacity furnace units.

' The heating provisions ofthe furnace shown in Figs. 5 and 6, as shown, are identical in principle with those of the `furnace rst described, except that in the furnace of Figs. 5 and 6, the

products of combustion are discharged from the 604 space between the outer bell `"AA and inner bell or work cover.. EA, through outlet openings A10 in the roof ofthe bell AA. As shown, each outlet A1o is provided with a damper A11 which may be adjusted to insure theproper distribution of discharge among the different outlets A1, and also. if desired, to maintain a pressure in the space EA somewhat in excess of atmospheric.

pressure in the space'enclosed by the bell AA,

`and thus guard against inleakage of air into said space.

. In the rectangular form of furnace shown in Figs. 5 and 6, as Well as in the cylindrical form shown, in Fig. 1, burners may be incorporated in-.th'e' tcp or roof wall of the bell, as Well as in its'vilrticai wan or wens, if and when the spetinction of the burner ames.

For operation, the bus pipes N maybe connected through flexible hose pipes, or other connections customarily employedwith'gas' flred bell type furnaces, to stationary supply piping (not shown) adjacent the furnace base member.

When the supply pipe connection to the bus pipes I N include exible hose sections so that the conl nection may be established with the bell elevated above its base, the burner flames may be ignited by means of a torch extended into the bell through its then open bottom. To permit ignition to be initiated, electrical ignition devicessuch as are customarily employed with certain so-called radiant tube bell furnaces, or other expedients may be employed. 'In particular, the bell may be formed withk passages A12, normally closed by suitable refractory, plug closure parts R, through each of which, when open, a torch may be inserted into the space EA to ignite one or more burners. The passages A2 may be formed in either the vertical wall or the top wall or in both walls, as bell form dimensions and operating conditions make desirable.

' The ignition operation is less important with my improved furnace than it would be,I but for the unusually great turn down' capacity of the Duradiant type of burner, whichis adapted to operate with a rate of combustion varying between a practical maximum, and a rate which is extinction, except as a result of an abnormal reduction in,A or total failure of, the combustible `mixture supply pressure. A reduction in that pressure resulting from some temporary interference with, but not entirely stopping the operation of the mixture forming and `compressing apparatus, ordinarily will not result in the ex- After the heating up operation is wholly or largely completed,

' the refractory material at the inner side of the bell wall, and particularly the portions thereof formed by the burner body elements L, are hot enough to automatically reignite the ,burner flames when the latter are extinguished as a result ofan interruption, for a few seconds, or even a few minutes, in the supply of combustible mixture at an operative pressure.

In normal annealing operations in which the work is heated up to a temperature in the neighborhood of 1300 to 1450" F., or so, the entire' inner surface ofthe outer bell will be heated to incandescence. combustion spaces L' and their extensions h2 will be substantially higher, however, than the temperatures' of' the fiat portions of the inner surface of the bell between thedifferent recesses h2, while the work isbeing heated up. After the work has been fully heated up, and is being subjected to a fsoaking" treatment at constant temperature so that the only substantial need for heat results from the external radiation and 'I'he .wall temperatures of the i other furnace heatlosses, the difference in thetemperatures of adjacent portions of the inner side of the bell may become quite small.

The -burner spacing most suitable, from the practical standpoint, in'any particular furnace will depend upon the furnace form and dimensions and operating conditions. In' general, in suchA a furnace as is shown in Figs. and 6,`-hav ing all of its burners in its vertical walls and in which operating conditions make it desirable to supply heat at practically the same rate to all portions of the outer surface of the Work cover E, the burner spacing should be such that every point in said surface will receive radiant heat in significant amounts directly from each of a plurality of burners. In-general, the distance separating adjacent burners may be greater when the individual burners are relatively larger than when relatively small, -and in a furnace adapted for a relatively rapid heating up operation, the burners should be more closely spaced than in a furnace intended for a less rapid heating operation.

Merely by Way of illustration and example, and not by way of limitation, I note that in one rectangular furnace of the general form and character shown in Figs.l 5 and 6, devised by me, for use in heating'a metallic work charge of 35,000 pounds up to a temperature of 1450 F. in fourteen hours, and in which the space surrounded by the vertical walls of the outer bell is approximately twenty one feet long, six

and one-half feet high and five and one-half yfeet wide, one hundredl burners, all mountedI surface of the outer bell of said furnace, the

`diameter of the inner and larger end of the conical space h2 of each burner being four inches, and in said furnace, the average distance between the inner vertical Wall surface of the outer bell A, and the outer vertical wall surface of the Work cover, E, is approximately 12 inches. Each of said hundred vburners is adapted to lib-4 erate 20,000 B. t. u.s per hour, but the maximum rate of.heat liberation per burner required inI the intended use of the furnace is substantially lower.

While in accordance with the provisions of the statutes, I have illustrated and described the best forms of embodiment of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit ofmy invention'as set forth in the appended claims and thatin some cases certain features of`my invention may be used to advantage'without a'corresponding use of other features.

Having now described myinvention, what I claim as new and desire to secure by Letters Patent, is:

1. In heating a furnace-of the type specified having a removable cover member with an inner portion of its wall formed of refractory material, the method which consists in burning fuel wholly Within a multiplicity of combustion space recesses formed in said wall at the inner side of and distributed over said wall and thereby so heating the walls of said recesses that a large portion of the heat of combustion is radiated directly from said recesses inwardly away from.

the inner sideof said wall.. v

2. In heating a furnace of the type specifiedv portion of its wall formed of refractory material, the method which consists in burning fuel in regulated amounts wholiy within a multiplicity of combustion spaces recesses formed in said wall at the inner side of and distributed over said wall, and thereby so heating the walls of said recesses that a large portion of the' heat of combustion is radiated directly from said recesses inwardly away from the inner side of said wall, and Varying the relative amounts of fuel burned in the different recesses to thereby `vary`the relative amounts of heat liberated in at its inner side to provide a multiplicity of4 distributed combustion spaces, each adapted to `radiate heat inwardly away from the inner side of said wall and to discharge combustion gases into the space enclosed -by said cover member, and means comprising a passage leading from the outer side of the cover member through the wall ofthe latter toward each combustion space for supplying fluid fuel and air for its cornbustion to said space and burner means Within said wall through which each passage communicateswith the corresponding combustion space and which is adapted to deliver'said fuel and air thereto so as to eifect its complete combustion within said space.

4. A combination, as specified in claim 3, including means for adjusting the .amounts of fuel supplied to the different combustion spaces by the corresponding passages.

5. In a furnace of the kind specified., the combination with a base member, of a removable cover member having the inner portion of its Wall formed of refractory material and recessed at its inner side to provide a multiplicity of distributed cup shaped combustion spaces, each adapted to radiate heat inwardly away from the inner side of said wall and to discharge combustion gases into the space enclosed by said cover member, and means comprising a'passage leading from the outer side of the cover member through the wall of the latter toward each combustion space and burner means through which said passage communicates with the correspondin g combustion space for supplying a combustible mixture of fuel and air to each combustion space at its outer side in a multiplicity of jets extending alongside and closely adjacent to corresponding sector portions of the wall of the space.

6. In a furnace of the kind specified, the combination with a base member, of a removable cover member having the inner portion of its wall formed of refractory material and having a multiplicity of passages transverse toand extending between the inner and outer sides of said cover member and a separateuid fuel burner removably mounted in each passage and each-comprising an inner end portion of refractory material forming a'wall for a combustion space adapted to radiate heat inwardly away from the inner side of said wall and to discharge products of combustion at the inner side of said wall and means for supplying fluid fuel and air for its combustion to said combustion space in a multiplicity of jets in predetermined spaced relation with the wall of said space and so as to effect the complete combustion of the fuel within said space. v

'7. In a furnace of the kind specified, the lcombination with a base member, of a removable cover member having the inner portion of its wall formed of refractory material and having a multiplicity of passages transverse to and extending between the inner and outersides of said cover member and a separatefluid fuel burner removably mounted in each passage and each comprising an inner end portion' of refrac tory material forming'a wall for a combustion V space adapted to radiate heat inwardly away from the inner side of said wall and to discharge products of combustion at the inner side of said wall and a metallic outer portion adapted to engage the outer side of the wall at the margin of said opening and a tubular metallic portion mechanically connecting the said inner refractory and outer metallic burner portions and adapted to supply fiuid fuel and air for its cornbustion to said combustion space so as to effect complete combustion of the fuel within said space.

8. In a furnace of the kind specified, the combination with a base member, of a removable cover member having the inner portion of its wall formed of refractory material and having a multiplicity of passages transverse tol and `extending between the inner and outer sides of said cover member, each passage including a conical portion diminishing in cross section as the distance from the outer side of cover mem-V body portion and mechanically connecting the latter to said outer metallic burner portion and adapted to pass uid fuel and air for its vcombustion through said body portion'in said space and so as to effect the complete combustion of the fuel in said space.

9. In a furnace of the kind speci'ed, the commetallic burner portion.

bination with a base member, of a removable cover member having an inner portion of its vertical walls formed of refractory material, and recessed at its inner side to provide a multiplicity of distributed combustion spaces arranged in superposed horizontal rows and each adapted to Vradiate heat inwardly away from the inner side of said wall and to discharge combustion gases into the space enclosed by said. bell cover member, and means for ,deliveringA a regulable amount of a combustible mixture of fuel and air to each combustion' space in jets of such character as to effect the complete combustion-of the fuel within said spaces, said means comprising a passage leading from the outer Y side of the cover member through the wall of the latter to each combustion space, and horizontal manifold pipes each connected to the said passages leadingv to a plurality of combus tionspaces in the same horizontal row.

10. In a furnaceof the kind specified, the combination with a base member, of a removable cover member having an outer metallic shell and a lining formed of refractory material,

and having a multiplicity of passages transverse to, and extending between the inner and outer sides of said cover member, and a separate burner element removably mounted in each passagev and comprising a body portion of refractory'material received in said passage, with its inner end forming a heat radiating outer wall of a combustion space open' at its inner side and a metallic outer burner portion engaging the outer side of and` detachably secured to said shell, at the margin of `said passage, and'a tubular metallic portion mechanically connecting said body and outer metallic burner portions and adapted to supply fluid fuel and air forits combustion to said combustion space in jets of such character as to effect the complete combustion i of the fuel within said spaces, -and fuel supply piping external to, connected to and supported from said outer metallic burner portions.

through vertical branch pipes, each mechanically connected at one end to a corresponding outer metallic burner portion andv adapted to supply fuel to the outer end of the corresponding tubular FREDERIC o. nnss.

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