US2602440A - Combustion tube heating apparatus - Google Patents

Description

July 8, 1952 E. A. comes` l 2,602,440

. coMBUsTIoN TUBE HEATING APPARATUS Filed sept. 2o, 194s 2 SHEETS-SHEET 1 A JNVENTOR.

July 8, 1952 E. A. coRNs COMBUSTION TUBE HEATINGV APPARATUS 2 SHEETS-SHEET 2 Filed Sept. 20, 1948 INVNTOR bw/N A. Coe/vs ATTORNEYS.

Patented July 8, 1952 COIVIBUSTI'ON TUBE HEATING y.APPARATUS EdwinACorns; Lakewood, hioassigv nor'to Lee WilsonRocky River, Ohio Application September 20, 1948;,.Se1ia1'Nm 50,061

8 Claims'. (C1. 126-91) l f This'invention relates' to furnaces, particularly industrial 'furnaces of ajkind sometimes usedl for annealing, providedI withv heating elements Aof the'radiant-tube type'.

In'the'past", industrial`V furnaceshave-been proposed'V4 emplciying radiant-tube heating elements extending' transversely into; and even entirely acrossI the` interior' of the furnace, thereby correspondinglydecreasing the space-available for" the material to be, heat-treated; In' otherfinstances. elortshave been made to provide radiant-tube heatingelementsparalleling the side walls ofthe furnace. Inboth cases; difliculties'have.been'exu perien'ced in soarranging the parts; particularly theburner parts; as tof escape the; necessity for having' a plurality of4v openings' through the furnace'wallf.' one for each' end of the heating element; in additionto which it has been found necessary toA usev supporting. hangers: or"V costly alloy metals. or refractory supports interfering with heatltransier atthe supporting points. Also, expansion of the metal of. the heatingielement due to its changingA temperature has required special. provisions, such as sliding joints or seals,

to permit expansion without objectionable stress and distortionof the heating elements'.

' j The present invention resolves. these andzother difficulties by meansA ofa'novel .constructionin which a heating element ofthe. radiant-tube type is employed which i'sformed'into a.closedvertical loop, the same. cooperatingA wtha fittingv obv-i'- ating the. need'.for supporting.. means. located. insidethefurnace. and, requiring .bute single openf ing'in the furnace Wall; Accordingly, the invenn tion may besaid'tohave foritsprincipal objects .Y/ A

to provide simple, improved, more. efficient. in.n stallations -in which .closed-loop heating `elements ofthe. radiantftube .type are. employedv to decrease the number ofopenings in thefurnace walLand increase thespace available vwithinlthe furnace..

The invention lcomprehends. the constructions illustrated in Figures 1 `to-6 of the` accompanying drawings, in which Figuren 1 shows la. vertical lsection, withparts in elevatiomofone preferred-em bodiment. ofthe invention; Figure 2LA is. asec-`V tional plan-corresponding toFigure `1;. Figure 3 v isa-n.. elevation ofr the heating elementoff Figures 1 and2asY seen fromtherig-ht in Figure l; Figure lLis a verticalsection, with parts ineleva-tion,

along lined-4- of Figure l-,butonanenlarged Y.

scale; Figure 5 is-a'verticalsection corresponding. toFigure 1V but illustrating. afsecondpreferred embodiment of. the nature-of a modification; and Figure 6is an elevation'of the heatingv element of Figure 5as seenrfrom the left in Figure-5.v

The installation illustrated in Figureifl. makes use of an upright'peripheral portion-I' of. antan;- nealing furnace, which portionmayv bel either an end wall or a sidewall, having.therein an open;- ing 2 for a burner assemblyiwhich openingjis preferably slightly flaredv at the endther'eof adjacentthe interior of the furnace. Inside the furnace is a closediloop heating element. of: 4the radiantetube type, the same being` generallyf oval in shape,l extending. normally to opening 2,'lying in aplane paralleling theupright portion off the furnace, and conveniently comprising aplurality of parallel tubular membersinterconnected by elbows as shown-in Figure 3. While'the-arrangement and proportions may vary widely,l the heating element shown extends on oppositev sides`A of the burner assembly approximately equardistancesV above and-below opening 2, is narrow in width in proportion to its length, and diminishes in crossV section from a maximum in the zone where` it receives incoming4 gases to a minimum in the zonewhere it returns outgoing gases.

The ends. of the heating element 3 receiving incoming and returning outgoing. gasesv are ,respectively designated 3a vand. 3b.

At one side of the oval, heating. element 3is connected to a multiple-,Wall fitting.. comprising part of the. burnerassembly. TheV latter, lgenerally designatedlll, has portsat cacho-fthe. two ends of the fitting for incoming and., outgoing gases, the portsat the end ofthe fitting@ adjacent the interior of the furnace communicating with ends.3a and 3b. of heating element. and those at the opposite end ofthe fitting, thatis. to say at the end thereof that projects out of .the furnace, communicating with a discharge stackv 5, an airv inlet conduit 5,.and a gas inlet conduit. 1. The tting which, together with other elements, makes up burner assembly vcomprisesthree principal elements; viz., an inner cylindrical shell I I an outer cylindrical shellvIZ, the latterincluding an annular closure welded in place at the end of the fitting which projectsout of thefurnace, and, welded toeither or to both-of inner shell Il and outer shell I2', a. two-branch coupling member I3 that-may conveniently be cast as an integralA unit; Branch |l ofV coupling membery I3Viswelded to enda ofheating element 3f; branch |1319, to end 3b of the heating element.

vAs illustratednin Figures l and-3, coupling I3 is cutaway at anangle of about immediately below branch I3b, this in order to permit it-to receive `atubular connecting member. ltwhich; at its outer. end, constitutes branchA l3ar-.of,coupling position as seen from either end. Thus there is' formed between inner shell and outer shell] I2 a generally annular passage Il shown to best advantage in Figure 4 through which passage products of combustion received from` end 3bI of heating element 3 by branch I3b of coupling member I3 can pass on their way to discharge stack 5. projects an igniter I8 which, as shown, takes the form of a spark plug. The latter may be mounted at any suitable place but isvillustrated as located outwardly of the furnace between the furnace wallfand the port in outer shell I2 communicating withdischarge stack 5.

Projecting into inner shell II from the outer end thereof is a burner tube. 2| which is mounted in concentric relation to inner shell I I. The end of burner tube 2| carries a burner nozzle 22, the latter beingreceived within a supporting ring 23 retained in the desired concentric v:relation to inner shell Il by means of spacer 24 (Figure 4). In the periphery of burner nozzle 22 .is formed a series of air passages 25 which extend longitudinally of the nozzle within supporting ring 23. The function of these air passages is to admit air to the combustion zone.

Burner tube 2| is Welded to and carried by a flanged housing 3| which is removably mounted, as by bolts, on a registering flange at the outer end of inner shell II; preferably, a suitable packing material, such as an asbestos gasket, is interposed between the two flanges. An adjustable coupling 32 connected to gas inlet conduit 'I projects through housing SI into burner tube 2|, but is spaced therefrom to permit primary air to pass between them. A series of ports 33`is provided in the inner wall of housing 3| to admit secondary7 air into the generally annular spaceA I5 between burner tube 2| and inner shell Air linlet conduit 5 is coupled directly to housing 3| as indicated in Figure 1.

In placing the apparatus in use, gas is permitted to pass through gas inlet conduit I into burner tube 2|, thence into branch I 3a of coupling member I3, thence into heating element 3, thence into branch |319 of coupling member I3, and thence into the generally annular passage I1 between inner shell and outer shell I2. At this stage, the resulting mixture of air and gas is ignited by means of spark plug I8. The mixture burns back through heating element 3 to burner nozzle 22, to which additional air is supplied in the meanwhile through air inlet 6. Part of the air so supplied passes through burner tube V2| as-previously described; another part passes through generally annular passage I6 into air passages 25 in the periphery of burner nozzle 22; the remainder passes through generally annular passage I6, around supporting ring 23, and into branch |3a of coupling member I3, where it mixes with gas and air issuing from burner nozzle 22.

In operation,l air passing through generally annular passage lf3 is pre-heated by products 'of Into this generally annular passage combustion passing through generally annular passage I'| on their way to discharge stack 5.

The embodiment of the invention illustrated in Figures 5 and 6 contemplates the installation, in an opening 2 in the wall of an indus* trial furnace, of a somewhat differently constructed multiple-shell fitting which, together with other elements, makes up burner assembly '4. As before,'the tting has separate ports for incoming and outgoing gases communicating at the inner end of the fitting with heating element 3 and at the outer end thereof with air inlet conduit 6,. gas inlet conduit 'I and discharge stack 5; In the embodiment of the invention shown in Figures 5 and 6, unlike that shown in Figures 1 to 4, air inlet conduit 6 takes the form of an air intake stack concentric with 'and surrounded by discharge stack 5, thus permitting additional pre-heating of the incoming air.

The fitting, which, with other elements, goes to make upl burner assembly 4, comprises an inner shell 4| communicating directly with` airintake stack `6 and, surrounding'inner shell 4|, an outer shell 42, the latter carrying anl annular closure at the end thereof which projects from the furnace and terminating at its other end in a two-branch coupling member 43. Branch 43a of coupling member 43 communicates with end 3a of heating element 3; branch 43h, with end 3b of the heating element. Coupling member 43 is cut away as shown to permit it to receive an integral tubular connecting member 44 having elbow 45 communicating with a generally annular passage 46 within inner shell 4|. Between vinner shell 4| and outer shell 42, which, as

shown, are mounted in concentric relation` to each other, is a generally annular passage 47 through which products of combustion received from end 3b of heating element 3 through branch 43h of coupling member 43 are transmitted to the annular space 48 between air intake stack 6 and discharge stack 5.

If desired, a park plug (not shown) may be provided as in the installation illustrated in Figures l to ,4.,

ProjectingV into inner shell 4| from the outer end thereof is an open-ended burner tube 5| carrying a burner nozzle 52 provided' vwith longitudinally extending air passages 53. Arseriesl of ports 54 for admitting air from inner shell 4 v and air intake stack 6 is provided at theY open end of burner tube 5|, which is held in place in concentric relation to inner shell 4| by spacing elements 55. Inner shell Y4| is provided at its outer end with an upstanding flange registering with but separated by an asbestos gasket from closure 53, into which is threaded a coupling 5l which receives gas inlet conduit 1. A packing assembly 58 occupies the extreme outer end Yof inner shell 4|, the packing-assembly being so designed as to ,permitv gas linlet conduit 'l to project therethrough into the open end of burner tubeSI.

In operation, gas is admitted through gas inlet conduit I into burner tube 5| and thence through coupling member 43 into heating element 3. Air

yis admitted through' air intake stack 6 tothe This secondary airis pre'- Y element 3: these products are returned through end 3b of heating element 3 to branch 43h of coupling member 43, proceeding thence through the generally annular passage 41 in outer shell 42 to the annular space 48 within discharge stack 5.

In both embodiments of the invention, the heating element and fitting are welded or otherwise'sealed in gas-tight relation to each other and to the metal shell of the furnace. For example, an annular flange B0 Welded to burner assembly 4 may itself be welded to a collar 6I, the latter being welded to metal shell 62. In such case, central stiffening ribs 63a, and 63h may be welded to collar BI, thus assisting in preventing canting of burner assembly 4 under the bending moment imposed by the weight of the heating element at the opposite end of the fitting. The resulting structure obviates the need for alloy metal hangers or refractory sup ports located in the interior of the furnace, accomplishing the same end from the exterior, and at the same time effectively seals the furnace against escape of unburned g'as and products of combustion.

In both embodiments, those parts that are subjected to high temperatures; e. g., the burner tube, burner nozzle, inner shell, outer shell, coupling member and heating element, are made of heat-resistant alloy steels such as chrome-nickel steel containing about 25% chromium and about 12% nickel. As indicated, parts are preferably Welded together in gas-tight relation, especially at points where there is danger of escape of gas or products of combustion. However, these and like considerations are not necessarily of the nature of limiting factors, particularly in the event that some fuel other than gas is used; as a matter of fact, numerous modifications in composition, arrangement and proportions of these and other features may be made without departing from the spirit of the invention.

It is intended that the patent shall cover, by suitable expression in the appended claims, whatever features of patentable novelty reside in the invention.

I claim:

1. A heat-treating furnace having a peripheral wall; means defining an opening in the wall; a burner tube extending into the opening from a point outside the wall, said burner tube carrying a burner nozzle at the inner end thereof; a fitting mounted in the opening in surrounding relation to the burner tube and extending from a point outside the wall to a point inside the wall, said fitting comprising an outer shell that is substantially concentric with the opening in the wall, an inner shell that is substantially concentric with the burner tube, and an elbow located at the inner end of the inner shell to change the direction of travel of the eiilux from the burner tube immediately upon its discharge from the burner nozzle; and, supported by the fitting itself in close proximity and substantial parallelism to the wall, a radiant tube heating element taking the form of a generally oval loop having an inlet end on one side of said loop at a point between the ends of said side and connected in sealed relation to the said elbow located at the inner end of the inner shell and an outlet end adjacent said inlet end and connected in sealed relation to the inner end of said outer shell, the iiow in all portions of that side of the loop in which said inlet and outlet ends are disposed being in the same direction and the flow in all portions of the opposite side of the loop being in the opposite direction.

2. A heat-treating furnace as in claim 1 in which the inner shell is substantially concentric with the outer shell.

3. A heat-treating furnace as in claim 1 in which the inner shell is eccentric to the outer shell.

4. A heat-treating furnace as in claim 3 in which the inner shell is tangent to the outer shell.

5. A heat-treating furnace as in claim 4 in which the point of tangency betweeen the inner and outer shells is at the siX-oclock position.

6. A heating unit comprising a combustion tube member of generally elongated oval form having substantially parallel side sections and curved sections connecting said side sections, said combustion tube member having one of its side sections provided with adjacent inlet and outlet ends disposed between said curved sections; a tubular discharge member connected in sealed relation to and extending from said outlet end of said combustion tube member in a direction substantially perpendicular to the plane of said combustion tube; a tubular inlet member of smaller cross-sectional area than said discharge member and disposed within said tubular discharge member, said tubular inlet member being connected in sealed relation at one end. thereof to said inlet end of said combustion tube; and connecting members for holding said tubular discharge and inlet members in fixed relation to each other.

'7. A heating unit as in claim 6 in which kthe connecting members hold the discharge and inlet members in concentric relation to each other.

8. A heating unit as in claim 6 in which the connecting members hold the discharge and inlet members in eccentric relation to each other.

EDWIN A. CORNS.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 2,041,930 Houlis May 26, 1936 2,064,095 Wilson Dec. 15, 1936 2,200,731 Woodson May 14, 1940 2,220,582 Ruckstahl Nov. 5, 1940 2,232,272 Rieger Feb. 18, 1941 2,255,540 Dreifein Sept. 9, 1941 2,391,447 Edge Dec. 25, 1945

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