US2576988A - Steam generating apparatus - Google Patents

Description

Dec. 4, 1951 P. ARAN-r STEAM GENERATING APPARATUS 2 SHEETSI SHEET 1 Original Filed Aug. 6, 1946 0 6 0* 0. /4 6 d 6 i d. u Ku 0u ou 44 4 47 3 Ku 50 3 IM 4 A. 6 0

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i llllll llllt- |y mvENToR fez'zyz'wlai Q llvllll lllllll nlllllfllnl lill |I||IM Dec. 4, 1951 P. ARANT 2,576,588

STEAM GENERATING APPARATUS original Filed Aug. e, 194e 2 SHEETS- SHEET 2 ATTORNEYS Patented Dec. 4, 1951 astasss engineering APBARA'rus` terre fliegt eliieiiibre Calif e..SeieiieifV te. Clayton Manuf ctl'iig Company, l' .'Q'alirif?,

generatie"ereeiifome" .Original application August (i, 1951.6, Serial NIL. 688,720.- Dirided and this. applicatie@ August 6., 1.94.6, SerialNQ- 688,721

ie (e1- 12e-eea The present inveiiiien ieletee te steam eener: eiiiie eiereieius eed. ,in'ee 'iieiiieiileiir' ife nevel eeiibueiieri Chemiker iiiiegJ eniifiaekei eeeiiiie means forsuchappara'tus.

The prin 'f'pal object of the invention is to pro- Videfe eerbiiiieii .eheiiibei iiiiiiis'ieieteeiri 'gelierating apparatus which will satisfactorily with,- s'tand" exces'sivel'y7N highl operating temperatures, ier uiiu'eueliif ieiie Periode. ei tiiiie Another object'of the invention is to provide a eeiiib-i1etienehemee`i lining ineens ier Steam eeneieti'ie' eleper'etue Whieii -`'Will' eiimiiieie the usual great thickness oi insulating materialnorf mally 'required to satisfactorily'rese'ist the great heatgen'erated by the combustion olf'fu'el within the( combustion Acl'larnber,f thereby 'enabling the apparatus to be made more compact.

A'further object of the invention is to proyide Sieem eeiiereting eminente-e. ineiiisiiiie 'ineens for maintaining a low jalgzetternperature.

A still further objetpf the invention is to provide steam geniavtrg @.Dloaratus'whichV will riet eeuee undue he'eeing' ei the beiler teem. er, chamber in which it is installed.

other ebieeie ene features ei tile inventieii will be epperent from the ieilewiee dee'erietieii. teken in eenieneiiieri with the eeeemeeiiyiliie drawings, in which:

Fig. 1 is a longitudinal sectional View through a steam generating apparatus embodying the present novel heating coil, combustiony chamber lining, and jacket cooling construction Fig. 2 is a sectional View taken on the line 2--2 of Fig. 1;

Fig. 3 is a sectional view on theline 3-3 of Fig. l and particularly illustrating the construction of the hase of the' apparatus and the air deflecting means for maintaining` a law. jacket temperature;

Eig. 4 is an enlarged fragmentary sectional View taken on the line 4 4 'of Eig.` 3, and illustrating the manner in which the shell surrounding the heating coil is assembled with the 1case and one of the legs ofthe apparatus;

Fig. 5 is an enlarged `.fragmentary sectional View taken on the 1ine5--5 of Eig. 3, and illustrating the means Yemployed yfor supporting `the helical water wall coil perpendicular with respect to the vhase of the apparatus; and

Fig. e is an enlarged fragmentary sectional View taken on the line ,6r- `of Eig. 3, and illus- .tratine ,one .of the apertures .which establish. munieation between the annular airspa. bese and the Space in the ieeiiei, ier .feeiiiiatiiie feeeeeieei ef the` .ieeY-iiie ai? ire Pille @eee inte `ige ieeieei-.eiiseelee irl,-

2 Reierrirfig` now to Figs. 1 to 6, inclusive, of the drawings, thev numeral t generally identies. the ste rn generating apparatus which includes legs 2 pporting housing comprising a base v3, an

intermediate jacket section 4, and a top sectionI 5.

"Ihfevbfas'e 31 includes a lower horizontal, circular hotto'rn wall 6 having a peripheral flange 'I welded to the lower end of an outer ring 8( The pas' 3 further' includes an 'upper horizontal, circular wall'k provided with a flange* IQ at'itsouter per riphpery welded to the 'lower'end of an intermediat'e'r'ing I I arrangedv concentric with the ring S.` The'w'alls 6 'ande are spaced'apart to provide'an irfsp'ace'IZ thereloetwefen.'A A plurality of airde`` fleeting bafflesV ,I3 are spot welded'tlthe underside'f the w'a'll'il' and serve vas yspacing"rn'eansheprovided with a central airinlet opening I5 vcoin- Inunicating with the air supply duct I4. The duct I4 is' preferably designed to deliver airV to the opening moving at high velocity in a countrclockwise, spiral'or volute path and may be constructed, for example, in the manner dis# closed in Kerrick Patent 2,284,906. The wall 9 is provided withv an opening Il arranged concentric withthe opening I6 of the Walle, but of smaller diameter, and has a bushing l'mounted therein. The bushing I8 has apass'ageway I9 which estab# lishes communication between the air supply duct I4 and a combustion chamber 26 within the jacket 4 above the base 3. The passage in the bushing I8 is smaller than the opening IIS and therefore a portion of the air supplied through the duct I4. is deflected laterally or outwardly by the wall 9 into the space I2 between the walls .6 and 9 to maintain a low. jacket temperature, as will be `explained later.

It will he understood, of course, that a forced draft is maintained in the steam generating apparatus I and to .this end air is forced into the Supply duet I4 by the blower I5 which yis capable 9i Supplying e greater volume of air then is rev .quired ferv eempieie eemleustieri 0i the fuel. with Suiiieieni .excess ier diversion inte the eil' eneee I? fer ieeket eeeiine An inne'ring ',22 is preferably welded at its lower end to the upper side ofthe wall 9 and'v'is arranged concentric with the rings 8 and I I The ring 22 is".consideraloly smaller than the ring II pro` `ldingl a space 23 between the outerV periphery thereof and the inner periphery of the ring II. `Suitable refractoryy material 24 is disposed between the bushing I 8 and the ring 22 and is sup- 3 ported by the wall 9. The upper surface 25 of the refractory material 2li is inclined downwardly toward the bushing |8, as best shown in Fig. 1.

Thel air inlet duct Eil supports a burner device 25 including a pair of nozzles 2`| for atomizing the fuel introduced into the combustion chamber 2B. A pipe 23 is connected to the burner 26 for supplying fuel thereto, and electrode means 29 is arranged to initiate ignition of the fuel.

The steam generating apparatus includes a novel heating coil construction generally identified by the numeral 35. The heating coil 35 includes a preheater section 35, a water wall section 3l and a generating section 33, arranged in series flow, but with the generating section 3S disposed below the preheater section 36 and within the upper end portion of the water wall section 3l. The preheater section 3B has an inlet 3s and may include any suitable number of spirally wound pancake coil sections 4Q arranged in superposed relation. In one operative form of the invention, the preheater section 35 includes, for example, eight individually wound pancake coils Fill, as illustrated in Fig. 1, and the inner end or outlet i of the uppermost pancake coil 'tu is welded to the inner end or inlet 42 of the second pancake coil lli, and the outlet 53 of said second pancake coil is welded to Ahe inlet 44 of the third pancake coil lill, and so on, throughout the height of the preheater section 33, with the result that the pancake coils di] are interconnected in series and the outlet of the preheater section 35 is located at the outer end i5 of the lowermost pancake coil 43.

The water wall section 5l consists of a double wound helical coil preferably made of two predetermined lengths of pipe 56 and 5| interconnected at one end in the finished coil by a return bend 52. The method of winding the double coil 3l' is set out in full in my copending application, Serial No. 688,720, filed of even date herewith, and of which the present application is a division. The end 53 of the pipe 59, remote from the return bend 52, is welded to the outlet end l5 of the preheater section 35, and the corresponding end 5d of the pipe 5| is welded to the inlet 55 of the generating section 38. The double winding of the water wall section 3`| provides a construction in which the fluid flows downwardly for the full length of the pipe 5U, or in a direc-l l tion counter to that of the path of travel of the combustion gases, and then reverses flow at the return bend 52 and flows upwardly in the pipe 5| toward its end 5d in the same general direction as the travel of the combustion gases; the result being that the fluid flow in any two adjacent turns of the water wall section 31 occurs in opposite directions, as indicated by the arrows in Fig. l. In the present construction, the water wall 3l is illustrated as having, for example, about sixteen complete turns disposed vertically one above the other, with the upper half, or first eight turns, in substantially abutting relation and with the remaining eight turns spaced about 1/2 inch apart, and maintained ln such spaced relation by clips 55 welded to or inserted between adjacent turns. The object of the different spacing of the turns of the water wall section 37 will be explained later.

The generating section 38 is shown in Fig. l as consisting, for example, of ve individual pancake coils 5t arranged so that the inner end 6| of the uppermost or first pancake coil Ell is welded directly to the inner end 62 of the lowermost or fifth pancake coil 50. The outer end 53 of the lowermost pancake coil 50 is welded to the outer end 64 of the next adjacent, or fourth, pancake coil 5D, the inner end 65 of the fourth pancake coil is welded to the inner end of the third pancake coil, the outer end 6l of the third pancake coil is welded to the outer end of the second pancake coil, and the inner end 69 of the second pancake coil is welded to one end of the discharge pipe Thus, the fuid discharged from the upper end 54 of the water wall section 31 enters the first pancake coil 6i] of the generating section 33 and ows therefrom to the lowermcst pancake coil 6i! and then upwardly through the fourth, third and second pancake coils and into the discharge pipe I, by flowing in the same general direction as the travel of the combustion gases.

The pancake coils Eil are slightly spaced apart and are held in such spaced relation by clips l2 welded or otherwise secured to the outermost coils thereof. A baffle plate 3 is arranged in the generatnig section between the second and third pancake coils 6U, the fourth and fifth pancake coils ou and below the rth pancake coil 6U to prevent the direct passage of combustion gases through the core lll formed at the central porton of the generating section 38. Scot blowers (not shown) are preferably disposed between the pancake coils lu of the preheater section 35.

A shell llb', formed from a rolled sheet of metal, encloses the coil 3l and its longitudinal edges are in abutment, and a strip |18 (Fig. 2) is welded to the shell I Iii at the abutting portions thereof to hold the same in cylindrical form. A plurality of angle brackets H5 (lig. e) is welded to the shell I le adjacent the lower end thereof.

'he lowermost turn of the coil 3l, of course, is arranged on a helix and in order to support the same vertically, a plurality of strips or reet (Figs. 3 and b) of dinerent Vertical height are welded to the lower side of said turn.

rihe shell |16 is of insufficient length to enclose the preheater section 3u' and, hence, a second shell |20 (Fig. 1), having the mam inlet 39 and the discharge pipe 1| extending therethrough, is arranged in telescoping relation with the shell ||6 and is welded at its lower end |2| to the upper end of the shell H6.

A crossbar E22 (Fig. 2) extends across the upper portion of the shell |20 and the opposite ends thereof are secured to said shell by brackets |23 bolted to said crossbar and shell, respectively. A second bar |2fl arranged at right angles to the crossbar |22 has one end welded to the adjacent side of the crossbar |22 and its other end fastened to the shell |2 by a bracket |25 bolted t0 both said bar and shell. Another bar |2' has one end thereof welded to the opposite side of the crossbar |22 and its opposite end is secured by a bracket |28 and suitable bolts to the shell H5. A tie bar |29 (Fig. 1) bridges the crossbar |22 and overlies the adjacent end portions of the bars |24 and |2`| and is welded along its lower edges to all of said bars to stiffen the same and form a rigid bridge across the crossbar |22. A hook member |30 has a shank |3| disposed at the point of juncture of the bars |22 and |21 and is welded thereto and to the tie bar |29. The lower edges of the bars |22, |24 and |21 are preferably welded to the upper pancake coil section 40 0f the preheater section 36. The hook |30 thus provides a convenient device for handling the entire shell and coil assembly by means of a crane (not shown) After the assembly of the coil and shell has been completed, as above described, the same is subieoted to .a conventional beat treatment .to relieve all stresses and strains therein.

After the een assernoly has been heat treated., a stainless steel cylindrical sheet liner |32 l(Fig. l) is inserted within the lower portion of the water wall section 3|. The height of the liner |32 is preterably such that it extends upwardly into the region of the eener-ating coil section 38.- 'lille upper end of the liner |32 is Curved inwardly, indicated at |33, to facilitate suoli inser-tio.rle The liner |32 preferably made or" stainless steel, that a chrome-nickel steel. commercially known as lil-8 stainless steel, although other stainless steels of diiererit ratio or onreine to nickel have been found to be satisfactory Qrdie nary sheet iron may also be used in manine, the liner |32, but the life of .such a liner is relatively short andstainless. steel is preferred because it eliminates the replacement problem:

The thickness of the stainless `steel liner |32 is o f the order of .04 inch to ,.llineli ahdpreferably .06 inch. The heavier gauge 'material capable of slightly deforniine out of round '11:1- dividual turns of the water Wall section 3 1 so that goed heat transier Contact can be maintained between the outerfsurface of the liner |32 and the inner surface of Vall of the coil turns. The liner 32 is made by rolling a flat sheetof stainless steel into cylindrical form and then welcllllg or otherwise securing the Vertical edges together. Afterward, one end is rolled to turn the same inwardly to provide the rounded edge |33, Apreviously referred to,

The external diameter of the liner |32 is dependent upon the internal diameter of the water wall section 31 and their relative rates of thermal expansion. In this connection, the liner |32 is made of `such Aexternal diameter that it can be readily slipped into the water Wall section 31 with some slight clearance, the clearance being such that Vit will subsequently be `eliminated n nder normal combustion temperatures by expansion of the liner |32 into positive contact with the innermost surfaces of the water Wall section 31.

In one operative example of a 5o horsepower unit, the internal diameter of the turns of the water wall section 31 was. 231/8 illglles and. 'the outer diameter of :the liner |32 was 22% inches, thus allowing 1A of an inch total clearance for expansion. The internal diameter o the turns of the water wall section 3,1 is held to a desired dimension by the expedient v of employing the 4shell ||6 of predetermined internal diameter and the step of allowing the helical coils formed from the pipes 5 and'5l to only partially uhwind after the shell I'IB has been slipped thereover, as described herein in connection With the method of making said water wall section.

No special heat treatment is ygiver! to the stainless steel liner |32; itis simply inserted within the water wall section 31 after the coil assembly 35 has been stress-relieved. In operation, the liner |32 will expand vinto positive enfgagement with the surrounding turns o f the water wall section 31, and in some instances ymay bulge slightly outwardly between adjacent turns, as illustrated-to an exaggerated degree in Fig. 4. Normally, however, the liner |32 Will contract up.- on cooling, so that it can be readily removed from the coil 31. After the unit has been in operation for a period of time, the coil 31 andthe liner |32 take a more or less permanent set, 'in contact, as a result of the loss of elasticity due to repeated heating and cooling.

Continuing now with the description of the remainder or the steam generating unit L four inverted U-sliaped members |35 (Figs- 3 and e) aredisposed in the space 2.3 and their end edges.

are respectively welded tothe rines Il. and 22- s The U-shaped inernbers |35 arranged to serve as supports for the feet lll the lower enol oi the water Wall section 3l. The members lat `are, also vertically aligned with the brackets lill secured to the lower `end of the shell llt, VBolts tot protect .through the brackets H9., .the .hori- Zontal wall of the U -shapeol members |35, through openings-in the. bottom walls tand o and through an opening an inwardly extending ilahge oi thesupporting legs 2, asbest illustrated by way of example, in Fig. e, for scouring the shell lili in assembled relation with the `base 3 and legs 2-v The legs 2 are additionally secured to the base 3 by bolts .|63 which extend through. the ring t and into. a reinforcing strip 3a (Figlel) engaging theinner surface of the ring ,8.

Layers ldlland i4! of heat .insulating material surround the shellsl 4|||5 and lgll to minimize heat losses A eap member .|42 is disposed above the upper end of the shell llt and is secured thereto in. any suitable manner. The cap lila has a central flue .opening |43 and. a sleeve Ulli provided with openings |45. surrounds .the line opening Ille. i layer of .insulating material alto is disposed outwardly ,of the sleeve |451 andovere lies the upper vsurface oi the cap |42, as s The outer ring 8 of base, .3 has .an outwa Aly extending flange lol (Figs. :1- and 3) at itsupper end, and the intermediate ring has .an outav wardly projecting ilange W8 which loverlies and engages the flange |41. The lower end of .the jacket section e Vhas an k,outwardly extending flange MS that rests upon the harige |43. The llanges uit, let and les may be bolted or welded together, as desired. .The jacket e has lining of insulating material |50 which is all'allgedolltf tvardly of the insulating material lili to prode an annular air space |5| completely surroonding the insulated heating coil assembly.

The upper end of the jacket @has an ontwardly extending ange |52 (Fig, l) and the cap 5 has a similar harige |53 resting upon .the harige l5?, The flanges |52 and |53 may be v.bolted 0r Welded together, as desired. Thesleeve ille. proieotsinto an opening les in the can so that an lair `space |55, .communicating with the annular air space l5l, is formed between `the inner Silllc@ Oi Said capand the insulating material |46, the openings it providing communication between the air space |55 and the flue opening |43.

The flange Hllof the intermediate ring contains a plurality of oiroumferentially spaced apertures |56 which have their edges bent, as indicated in Fig. 6, to form air scoops acing in a counterclockwise direction. These apertures establish communication between the annular air space l5! `in the jacket 4 and an annular air space |58 between the Vrings 8 and Accordingly, air travelling in a countercloelrwise, spiral path and introduced through the opening I5 into the air space 2| in the base 3 iS deeoted outa Wardly by the overlying portion of the wall o and the baffles I2 into the air space |58, and is seooped by the leading edges of `the apertures |55, into the annular jacket air space |5| to remove any heat that has passed through the insulating layers lille-|42, whereby to maintain the temperature of the jacket!! at a minimum t0 prevent undue heating of the boiler room or chamber in which the steam generating unit vI is installed. The 75 heated air forced out of the air space |5| passes asvaes 7 through the air space |55. openings |45 and is exhausted into a stack |59 surrounding the opening |54 in the cover 5.

It will be noted from Fig. 1 that the lower end of the liner |32 rests upon the upper surface 25 of the refractory material 24. The object of such arrangement is to provide a seal at the lower end of the liner |32 that will keep the fuel confined within the combustion chamber so that it cannot leak into the space occupied by the water wall section 31 and the insulating material |43, lill and |56. The seal is particularly important when gaseous fuels are used inasmuch as under such conditions it would be highly undesirable to have combustible material leak out of the combustion chamber into the air space |51 surrounding the coil 35 in View of the re hazard which it would present. In the case of liquid fuels, such as oil, the same might also constitute a re hazard, but oil presents the further objection in that it would be absorbed by the insulating material and decrease the efficiency thereof.

In actual operation, operating temperatures in steam generating units of the character comprising the present invention range from 2500io F. to 2900 F. depending upon the size of the unit. The highest temperature which presentday refractory materials are capable of withstanding is about 2900 to 3000 F. maximum,

which does not leave any margin of temperature 1.

resistance to resist direct flame impingement causing heating above the maximum and which most generally causes refractory failure at the point of flame impingement. The present invention eliminates the use of refractory material in the side walls of the combustion chamber by incorporting a water wall section 31 and a stainless steel liner |32, which was unexpectedly found to satisfactorily solve the problem of resisting excessively high combustion chamber temperatures. In fact, the present liner has withstood operating temperatures of 3000 F. without failure. The stainless steel liner |32 serves not only to rapidly transfer heat therefrom to the water wall section 31 to thereby avoid excessive overheating of said liner, but transfers enough heat to the coil 31 to prevent condensation of liquid fuels and moisture thereon.

A further advantage of the sheet metal liner |32 and water wall arrangement 31 disclosed herein is that it greatly outlasts refractory walls, but what is more important, makes it possible to make the unit more compact by not occupying anywhere near as great a space as would normally be required for the thickness of refractory material necessary to withstand the same combustion chamber temperatures.

It is important to make the metal liner |32 of a dimension that will allow the liner to expand and make positive contact with the turns of the water wall 31 upon thermal expansion thereof. If insufficient clearance for expansion is allowed, the liner |32 will buckle upon expansion and burn or scale at the buckled points. On the other hand, if too much clearance is provided, the liner will not expand into heat-transferring contact with the water wall 31 and burn or scale because of improper cooling thereof.

Insofar as the operation of the heating coil itself is concerned, the liquid to be heated is introduced through the inlet 39 into the preheater section 36 so that the liquid is preheated before it enters the water wall section 31. Hence, too low temperatures in the water wall section 31 are avoided. and this eliminates condensation of fuel vapor which would cause carbon deposits. It also eliminates collection of and condensation of moisture from the air on the external surface of the water wall tubing, which would result in active corrosion. The Water wall section 31, as previously explained, is double wound so that the fluid flows downwardly in the water wall section in the helical coil portion formed by the pipe and upwardly in the water wall section 31 through the helical coil portion formed by the pipe 5 I, to be discharged into the uppermost pancake coil of the generating section 38. The iiuid passes through the first pancake coil Si! of the generating section 38 and then directly to the bottom pancake coil 60, and at this point changes from counterflow to direct flow and passes upwardly through the balance of the pancake coils 60 and is then discharged through the riser pipe 1| into a steam separator (not shown) or any other apparatus.

The upper turns of the water wall section 31 are arranged closely adjacent each other for the purpose of providing a combustion gas seal at the critical point or level of the combustion chamber 2), whereas, the lowermost turns of the water wall section 31 are spaced apart to facilitate absorption of the radiant heat of the liner E32, the surface of the water wall coils 31 directly in contact with the liner |32, of course, absorbing heat by direct conduction. The vertical spacing or pitch of the lower coils of the water wall section 31 is such that sufficient heat transfer will be effected by direct conduction and radiation to maintain the liner |32 suiciently cool to prevent overheating or burning out of the same.

The double wound water wall 31 provides a return pass for the uid without requiring the necessity of employing any external piping or tubing. At the saine time, the flow of the fluid through the water wall section 31 results in the absorption of heat from the combustion chamber and from the liner |32 so that the uid is discharged into the generating section 38 at a slightly elevated temperature above that at which it entered the water wall section 31.

The object of connecting the upper pancake coil Bill of the generating section 38 to the lower pancake coil of said section is to provide a construction in which some fluid is always present in the pancake coil 60 nearest to the combustion chamber 20, but which iiuid is not at the maximum temperature to which the unit is capable of heating the same. In other words, additional heat is absorbed in the generating section 38 by the fluid as it travels in a generally upward direction through the generating section 38. The principal advantage of such an arrangement is that excessive temperatures in the lowermost pancake coil 66 are avoided. The arrangement also creates a higher temperature differential between the temperature of the fluid in the coil and the temperature of the combustion lgases, which increases the effectiveness of the heating coil. In fact, thermal efliciencies as high as 82% are commonly attained in units embodying the coil assembly 35.

The present coil construction not only makes it possible to develop a given boiler horsepowei` with less heating surface than previous units designed to develop the same boiler horsepower, but has also resulted in a reduction in the feed pump pressure required to force the feed water into the coil. For example, previous 50 horsepower units supplying steam at a pressure of lbs. per square inch have required a feed pump 9 pressure of 280` to 290` lbs. per square inch as compared with a feed water pumpf pressure of 260 lbs. per square inch for the present unit. This indicates that less actual steam or vapor was formed in the heating coil 35 with a greater proportion of solid liquid than vapor, which resulted in less friction flow loss through said coil. In practice, it is desired to maintain a stream of fluid flowing through the heating coil 35 containlng a maximum ratio of' 251%V vapor to 75% liquid. In other words', the reduction in the back pressure indicates that a greater percentage of heat is absorbed by the-liquid and only a comparatively small amount ofthe liquid is converted to vapor during the passage of liquidi through the heating coil before it discharges from the outlet pipe 'Il into a steam separator or otherr apparatus (not shown).

While the heating coil, combustion chamber lining means, and the means for maintaining a low jacket temperature have been described in connection with a steam generating apparatus, it is to be understood that the invention is not limited to the useA of these features in` apparatus for generating steam, and that the invention contemplates. their usev wherever susceptible.

It will be` understood that various changes may be made in the materials and details of construction of the apparatus disclosed herein, without departing from the spirit of the invention or the scope of the annexed claims.

I claim.:

1. Steam generating apparatus, comprising: a shell; a coil in said shell including a plurality of superposed vertically spaced helical turns; and a cylindrical chrome-nickel steel liner within said heating coil, said liner having a` thickness in the range of .04 to. .14 and initially tting within said coil with a slight clearance but being thermally expansible into positive heat transfer encoil, said liner having a thickness of .04" to .14"

and initially .fitting within said coil with a slight clearance but being thermally expansible into positive heat transfer engagement with said coil upon heating thereof, the lower end o'f said liner resting upon said bottom wall of said combustion chamber.

3. Steam generating apparatus, comprising: a shell; a combustion chamber within said shell; means at the lower end of said shell forming a bottom wall for said combustion chamber; a coil within said shell including superposed helical turns with the turns at the upper endof said coil arranged close together and the turns at the lower end of said coil spaced apart a predetermined distance; and a cylindrical, chromenickel steel sheet metal liner within the lower portion of lsaid coil initially fitting Within said coil with a slight clearance but being thermally expansible into positive heat transfer engagement with the inner periphery of the turns of said coil upon heating thereof, said liner extending throughout the height of lsaid spaced apart turns with the lower end of said yliner resting upon said bottom wall of said combustion chamber.

4. Steam generating apparatus, comprising: a

lio

base including two substantially horizontal, circular walls. spaced apart to provide an air space therebetween, the upper ci said walls being smaller in diameter than the lower of said walls; a pair of spaced. apart concentric ring members having an air space disposed therebetween and having their lower ends connected with the periphery of said spaced horizontal walls to form an annular continuation of the air space between said horizontal walls; means for forcing air under pressure into the central portion of the air space between said horizontal walls; means interposed between said horizontal walls for delecting the air, thus introduced, outwardly into said annular air space between said concentric rings; a housing disposed above said base includ- Ving a shell having insulating material surrounding the same; a jacket lined with insulating material surrounding said shell, with an annular air space between said shell insulating material and said jacket insulating material; and means between said base and housing establishing communication between said annular air space in said base and said annular air space in said housing.

5. Steam generating apparatus, comprising: a shell; a heating coil Within said shell; a sheet metal liner within said heating coil, said liner initially fitting within said coil with a slight clearance but being thermally expansible into positive heat transfer vengagement with said coil upon heating thereof; heat insulating material surrounding the exterior of said shell; a jacket surrounding said heat insulating material; a liner of heat insulating material lining said jacket and being separated from said first-mentioned heat insulatingmaterial by an annular air space; a base at the lower end of said shell and jacket, the lower end of said liner resting upon said base and cooperating therewith to provide a combustion chamber, said base including a double wall with an air space therebetween communicating with said annular air space; and means for forcing air under pressure into said combustion chamber, and into the air space between said double walls of said 'base and thence into said annular air space.

6. Steam generating apparatus, comprising: a jacket; a shell within said jacket; an annular air space between said shell and jacket; a coil Within said shell; a sheet metal liner within said coil, said liner initially fitting within said coil with a slight clearance but being thermally expansible into positive heat transfer engagement with said coil upon heating thereof; a 'base member below said jacket, shell, coil and liner and including a bottom wall; refractory material supported by said bottom wall, the lower end of said liner resting upon said refractory material and `cooperating therewith to provide a combustion chamber; a second bottom wall disposed below said rstbottom wall to provide an air space between said two bottom Walls; means establishing communication between said annular air space and said air space between said bottom walls, each of said bottom Walls having an opening communieating with said combustion chamber; burner means aligned with said openings; and means for forcing air under pressure into the opening in said second bottom Wall.

7. Steam generating apparatus, comprising: a

jacket; a shell within said jacket; an annular air space between said shell and jacket; a coil within Ysaid shell; a sheet metal liner within said coil, said liner initially tting within said coil with a slight clearance but being thermally expansible into positive heat transfer engagement with said coil upon heating thereof; a base member below said jacket, shell, coil and liner and including `a bottom wall; refractory material supported by said bottom wall and cooperating with said liner to provide a combustion chamber; a second bottom wall disposed below said rst bottom wall to provide an air space between said two bottom walls; means establishing communication between said annular air space and said air space between said bottom walls, each of Ysaid bottom walls having an opening communicating with said combustion chamber, the opening in the rst bottom wall being smaller than the opening in the second bottom wall to effect deiiection of air into the space between said bottom walls; burner means aligned with said openings; and means for forcing air under pressure into the opening in said second bottom wall.

8. Steam generating apparatus, comprising: a jacket; a shell Within said jacket; an annular air space between said shell and jacket; a coil within said shell; a sheet metal liner within said coil, said liner initially fitting within said coil with a slght clearance but being thermally expansible into positive heat transfer engagement with said coil upon heating thereof; a base member below said jacket, shell, coil and liner and including a bottom wall; refractory material supported by said bottom wall, said liner cooperating with said bottom wall to provide a combustion chamber; a second bottom wall disposed below said first bottom wall to provide an air space between said two bottom walls; means establishing communication between said annular air space and said air space between said bottom walls, each of said bottom walls having an opening communicating with said combustion chamber, the opening in the rst bottom wall being smaller than the opening in the second bottom wall to effect deflection of air into the space between said bottom walls; burner means aligned with said openings; means for forcing air under pressure into the opening in said second bottom wall; and baffle members in the air space between said bottom walls extending outwardly from a point adjacent said openings in said bottom walls.

9. Steam generating apparatus, comprising: a jacket; a shell within said jacket; an annular air space between said shell and jacket; a coil within said shell; a sheet metal liner within said coil, said liner initially iitting within said coil with a slight clearance but being thermally expansible into positive heat transfer engagement with said coil upon heating thereof; a base below said jacket, shell, coil and liner, the lower end of said liner resting upon said base and cooperating therewith to provide a combustion chamber, said base including two substantially horizontal, circular bottom walls spaced apart to provide an air space therebetween, the upper of said walls being smaller in diameter than the lower of said walls and both of said walls having an air inlet opening; a pair of concentric rings having an air space formed therebetween and having their lower ends connected with the periphery of said spaced bottom walls to form an annular continuation of the air space between said horizontal walls, the annular air space of said base being aligned with the annular air space between said jacket and shell; a transverse wall separating said annular air spaces, said transverse wall having apertures establishing communication between said annular air spaces; and means for forcing air under pressure into said combustion chamber and the air space between said bottom walls through the air inlet openings in said bottom walls.

10. Steam generating apparatus, comprising: a base including two substantially horizontal, circular walls spaced apart to provide an air space therebetween, the upper of said walls being smaller in diameter than the lower of said walls; a pair of concentric rings having an air space formed therebetween and having their lower ends connected with the periphery of said spaced bottom walls to form an annular continuation of the air space between said horizontal walls; a housing disposed above said base member including a shell having insulating material surrounding the same; a jacket lined with insulating material, with an annular air space between said shell insulating material and said jacket insulating material; means establishing communication between said annular air space in said base and said annular air space in said housing; a helically wound heating coil within said shell above said base; a plurality of supporting elements positioned in said base in the annular air space between said concentric rings; and feet members secured to the lower turn of said helical coil and resting upon said supporting elements, said feet members varying in vertical height to support said coil perpendicularly relative to said base.

l1. Steam generating apparatus as defined in claim 10, including a liner disposed within said heating coil and having its lower end supported by the base.

12. Steam generating apparatus as dened in claim l0, including means for forcing air into the base in the space between the circular walls thereof, and baffle means in Said space for deecting the air outwardly into the annular space between the concentric rings, for flow upwardly through the annular space in the housing.

13. Steam generating apparatus, comprising: a base member; a plurality of radially extending inverted U-shaped supporting members carried by said base; a substantially cylindrical shell having its lower edge resting upon said supporting members; a body of refractory material supported by said base and disposed inwardly of said supporting members; bracket means carried by said shell member at a region adjacent to but spaced from the lower end thereof; a leg having a flange extending inwardly at a point below said base; and bolt means extending through said bracket means, one of said U-shaped supporting members, base and flange of said leg and securing said shell, base and leg in assembled relation.

PERRY ARANT.

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

UNITED STATES PATENTS Number Name Date 477,261 Miller June 21, 1892 708,066 Norris et al. Sept. 2, 1902 1,437,975 Hoffman et al. Dec. 5, 1922 1,629,921 Mansfield May 24, 1927 1,636,907 Hall July 26, 1927 1,685,804 Buerger Oct. 2, 1928 1,695,030 Scheminger Dec. 1l, 1928 1,737,202 Runnels Nov. 26, 1929 (Other references on following page) Number anims 13 UNITED STATES PATENTS Name Date Hamm et a1. Aug. 21, 1934 Warren July 16, 1935 Jones Nov. 9, 1937 Jackson Nov. 28, 1939 Price Dec. 19, 1939 Goerg Jan. 9, 1940 Emmet Jan. 14, 1941 Purtell July 1, 1941 Barnes Jan. 12, 1942 Kerrick June 2, 1942 Sterich Feb. 22, 1944 Number Name Date Breese et a1. Aug. 8, 1944 Livingood June 12, 1945 Doerner July 2, 1946 Roselund Sept. 2, 1947 FOREIGN PATENTS CountryV Date Great Britain Dec. 23, 1926 OTHER REFERENCES Handbook of Engineering Fundamentals, Eshbach, John Wiley 8: Sons. New York, 1936.

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