US2570630A

US2570630A - Heating coil

Info

Publication number: US2570630A
Application number: US688720A
Authority: US
Inventors: Arant Perry
Original assignee: Clayton Manufacturing Co
Current assignee: Clayton Manufacturing Co
Priority date: 1946-08-06
Filing date: 1946-08-06
Publication date: 1951-10-09
Anticipated expiration: 1968-10-09
Also published as: US2576988A

Description

P. ARANT HEATING COIL Oct. 9, 1951 E r1 lllll'l A mlnl E INVENTOR BY M* ATTORNEYS OCt. 9, P, ARAN-r.

HEATING COIL Filed'Aug.' e, 1946 5 sheets-sheet 2 v @da i" v i INVENTOR fel'lyl'mzi BY @man ATTORNEYS oct. 9, 1951 P. ARANT i 2,570,630

HEATING COIL Filed Aug.A 6, 1946 5 Sheets-Sheetl 5 oct.' 9,v 1951 P. ARANT` 42,570,630

HEATING COIL A Sheets-Sheet 4 Filed Aug. 6, 1946 lNvENToR ATTORNEYS atented ct. 9, i951 HEATING COIL Perry Arant, Alhambra, Calif., assi'gnor to Clayi ton Manufacturing Company, Alhambra, Calif., a corporation of California Application August 6, 1946, Serial No. 688,720

The present invention relates to a heating coil construction, particularly adapted for use 1n *steam generating apparatus, and to the method f making such coil.

More specifically, the invention relates to a heating coil construction including a preheater section, a water wall section and a generating section, arranged in series in the order mentioned, and to the method of making such coil.

One of the principal objects of the invention is to obtain compactness and reduction in size of the heating coil for developing a given rated horsepower without sacrificing eiciency and economy.

Another object of the invention is to provide a heating coil construction which has-great stability by virtue of the fact that it enables the uid to be kept in a substantially liquid state until it is dicharged into aV steam generator or other zone of low pressure.

Another object of the invention is to provide a heating coil construction which will have a greatly increased life.

Another object of the invention is to provide a heating coil including a Water wall arranged so that fluid can be returned from the water wall section to the main portion of the heating coil without the use of any external risers.

Another object of the invention is to provide a heating coil construction wherein liquid will always be present in the portion of the coil nearest the rebox to thereby assure that the radiant heat of the rebox will not evaporate the water therefrom so as to cause such portion ofthe coil to be empty when the burner is re-started.

Another object of the invention is to provide a combustion chamber lining means for steam generating apparatus which will eliminate the usual great thickness of insulating material normally required to satisfactorily resist the great heat generated by the combustion of fuel within the combustion chamber.

A further object of the invention is to provide a heating coil having a water wall section serving as a portion of the combustion chamber lining arranged so as to eliminate condensation of fuell 7 Claims. (Cl. LZ2- 250) substantially constant rate so that a forced draft is maintained through the heating coil for the products of combustion, with suicient excess air supplied under pressure for diversion and use to maintain low jacket temperatures.

Other objects and features of the invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which:

Fig. l is a longitudinal sectional view through a steam generating apparatus embodying the present novel heating coil, combustion 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 the line 3 3 of Fig. 1 and particularly illustrating the construction of the base of the apparatus and the air deflecting means for maintaining a low jacket temperature; Y

Fig. 4 is an enlarged fragmentary sectional view taken on the line 4 4 of Fig. 3, and illustrating the manner in which the shell surrounding the heating coil is assembled with the base and one of the legs of the apparatus;

Fig. 5 is an enlarged fragmentary sectional View taken on the line 5 5 of Fig. 3, and illustrating the means employed for supporting the helical water wall coil perpendicular with respect to the base of the apparatus;

Fig. 6 is an enlarged fragmentary sectional view l taken on the line 5 6 of Fig. 3, and illustrating one of the apertures which establish communicaticnbetween the annular air space in the base and the annular air space in the jacket, for facilitating scooping of the moving air from the base into the jacket air space;

Fig. 7 is a somewhat diagrammatic perspective view illustrating apparatus suitable for making the double wound water wall section of the heating coil;

Fig. 8 is an enlarged sectional View taken on the line 8 8 of Fig.r 7, through the clamping means for securing the ends of two pipe sections to the mandrel of the winding apparatus;

Fig. 9 is a diagrammatic plan view showing the relationship of the mandrel clamp and pipes at the starting of the winding operation;

Fig. 10 is a view similar to Fig. 9 showing a portion of the double coil wound upon the mandrel with the turns closely adjacent each other,

'and spacer elements positioned to effect winding of the remainder of the coil with the turns spaced a predetermined distance apart;

Fig. 11 is a sectional view taken on the line Il 'l I of Fig. 10;

Fig. 12 is a diagrammatic view illustrating the double wound coil in a substantially completely wound condition and with a shell slipped over the wound portion thereof;

Fig. 13 is a diagrammatic view illustrating the ends of the double wound coil interconnected by a return bend and with the shell completely enclosing the coil;

Fig. 14 is a diagrammatic view illustrating the manner in which two pipe sections pre-connected by a U-bend may be clamped to a mandrel to effect winding thereof;

Fig. 15 is an enlarged fragmentary sectional View on the line I-I5 of Fig., 14 illustrating the clamping means for securing the U-bend to the mandrel; and

Fig. 16 illustrates a length'y of; pipe pro-vided1 with a U-bend intermediate its ends and adapted to be wound upon the mandrel of Fig. 14.

Referring now to Figs.l l to 6, inclusive, of the drawings, the numeral. I generally identifies the steam generating apparatus which includes legs 2` supporting a housing comprising a base 3, an intermediate jacket section 4, and a top section 5.

The base 3 includesV a lower horizontal, circular bottom wall 5 having a peripheral flange 1 welded to the lower end of an outer ring 3. The base 3 further includes an upper horizontal, circular wall 9 provided with a flange I9 at its outer periphery welded to the lower end of an intermediate ring I I arranged concentric with the ring 8. lIhe walls 6 and 9 are spaced apart to provide an air space i2 therebetween. A plurality of air deflecting baffles I3 are spot welded to the underside of the Wall 9 and serve as spacing means between the walls 9 and 6. An air supply duct I4 is disposed below the wall 6 and secured thereto in any desired manner. A blower I5 forces air under pressure into the duct I4; The wall 5 is provided with a central air inlet opening I5 communicating with the air supply duct I4. The duct I4 is preferably designed to deliver air to the opening I6 moving at high velocity in a counterclockwise, spiral or volute path and may be constructed, for example, in the manner disclosed in Kerrick Patent 2,284,906. The wall 9 is provided with an opening I1 arranged concentric with the opening I5 of the wall 5, but of smaller diameter, and has a bushing I8 mounted therein. The bushing Idhas a passageway I 9 which establishes communication between the .air supply duct I4 and a combustion chamber 2i] within the jacket 4 above the base 3. The passage in the bushing i8 is smallerthan the opening I6 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 5 and 9 to maintain a low jacket temperature, as will be explained later.

It will be understood, of course, that aforced draft is maintained in the steam generating apparatus I and to this end air is forced into the supply duct I4 by the blower I5 which is capable of supplying a greater volume of air than is required for complete combustion of the fuel, with sufficient excess for diversion into the air space I2 for jacket cooling.

An inner ring 22 is preferably-welded at its lower end to the upper side of the wall 9 and is arranged concentric with the rings 8 and Il. The ring 22 is considerably smaller than the ring II providing a space 23 between the outer periphery thereof and the inner periphery of the ring II. Suitable refractory material 24 is disposed between the bushing I8 and the

ring

2,2 and is supported by the wall 9. The upper sur- 4 face 25 of the refractory material 24 is inclined downwardly toward the bushing I8, as best shown in Fig. 1.

The air inlet duct I4 supports a burner device 25 including a pair of nozzles 21 for atomizing the fuel introduced into the combustion chamber 20. A pipe 28 is connected to the burner 25 for supplying fuel thereto, and electrode means 29 is arranged to initiate ignition of the fuel.

The steam generating apparatus I includes a novel heating coil construction generally identied by the numeral 35. The heating coil 35 includes a preheater section 35, a water wall section 31 and a generating section 38, arranged in series flow, but with the generating section 38 disposed below the preheater section 36 and within the upper end portion of the water wall section 31. The preheater section 35 has an inlet 39 and may include any suitable number of spirally wound pancake coil sections 4E! arranged in superposed relation. In one operative form of the invention, the preheater section 36 includes, for example, eight individually wound pancake coils 4D, as illustrated in Fig. l, and the inner end or outlet 4I of the uppermost pancake coil 40 is welded to the inner end or inlet 42 of the second pancake coil 40, and the outlet 43 of said second pancake coil is welded to the inlet 44 of the third pancake coil 4U, and so on, throughout the height of the preheater section 36, with the result that the pancake coils 4i) vare interconnected in series and the outlet of the preheater section 36 is located at the outer end 45 of the lowermost pancake coil 45.v

The Water Wall section 3,1 consists of a double wound helical coil preferably made of two predetermined lengths of pipe 50 and 5I interconnected at one end in the finished coil by a return bend 52. The method of winding the double coil 31 is set out in full hereinafter. The end 53 of theY pipe 5D, remote from the return bend 52, is welded to the outlet end 45 of the preheater section 35, and the corresponding end 54 of the pipe 5I. is welded to the inlet -55 of the generating section 38. The double winding of the water wall section 31 provides a construction in which the fluid flows downwardly for the full length of the pipe 5 9, or in a direction 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 5I toward its end 54 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, thewater wall 31 is illustrated as having, for` example, about sixteen complete turns disposed vertically one above the other, with the upper half, or rst eight turns, in substantially abutting relation and with the remaining eight turns spaced about 1A; inch apart, and maintained insuch spaced relation by clips 56 welded to or inserted between adjacent turns. The object of the different spacing of the turns of the water walllsection 31 will be explained later.

The generating section 38 is shown in Fig. 1 as consisting, for exampleof five individual pancake coils 30 arranged so that the inner end 5I of the uppermost or first pancake coil 60 is welded directly to the inner end 52 of the lowermost or fifth pancake coil 6U. The outer end 53 of the lowermost pancake coil 60 is welded to the outer end 64 of the next adjacent, or fourth, pancake coilBU, the inner end of the Vfourth pancake c oiLis weldedto the inner end G ljofthel third pancake coil, theouter end 61 of the thirdpancake coil is welded to the outer end68 of the secondpancake coil, andthe inner end 89 ofthe second vpancake coil is welded to one end 1 0 of a discharge pipe 1|. Y

Thus, the fluid discharged from the upper end 540i thewater wall section 31 enters the iirstV pancake coil 60 of the generating section 38 and flows therefrom to the lowermost pancake coil andthen upwardly through the fourth, third andY second pancake coils and into the discharge pipe,1| by owing inthe samegeneral direction as tlie travel of the combustion gases. l n c,

The pancake ncoilslli are slightly spaced apart and are heldin such spaced relation by clips 12 welded or otherwisesecured to the Houtermost coils thereof. AV baiiie plate 13 is arranged in the generating sectionlbetween the second and third pancake coilsY 60, the fourth and fifth pancake coils 60 and belowV the fifth pancake coil 60 to prevent the direct passage of combustion gases through the corer14 formed at the central portion of the generating section 38. Soot blowers (not Shown) are preferably disposed between the pancake coils 40 of the preheater section 36.

vIt will be convenient, at this point, to describe the' apparatus and method employed in making the double wound water wall section 31, and reference will Vtherefore be made to Figs. '7 to 13, inclusive.

' In Fig..'7, the numeral 80y generally identifies the coil lwinding apparatus, and such apparatus includes a table 8| having a top 82 and legs 83 which are adustable vetrically to va1y the inclination'and/or height of the table top 82 relative to the coil windingrapparatus 80. The table top 82 serves as a 'support for the pipes 50 and 5| previously referredto. The winding apparatus '80 further includes a base' 84 having a pedestal l85 mounted at one end thereof, and a conventionallgear"reductionunit 85 mounted upon said pedestal. A shaft 81 driven by areversible motor 81?'cons'titutes a drive for the gear reduction unit'85, and a'shaftA 88 constitutes the driven shaft 'of the gear reduction unit 85. The shaft 88 drives a. shaft |38a having a hollow cylindrical mandrel 89 mounted thereon provided with a angev90 at the inner end thereof. Theouter end of the shaft 80a carries a bushing 9| (Fig. '7), which is Vsupported in a journal 92 comprising hinged sections Y93 and 94 which are releasably held engaged with the bushing 9| by the coaction of a ,bolt 95 pivotally mounted upon ears 96 on the bearing section 93 and projecting between ears 91 on the bearing section 94, the latter be- Yingengaged by a thumb screw 98 threaded onto the bolt 95. The journal 92 is carried by a triangular frame 99, which is detachably supported upon the base 84 upon studs |00 projecting longitudinallyrfrom one end |0| of said base. The frame 99 is removablyretained in position upon the studs |00 by pins |02. y The mandrel 89 carries a clamp |05 for securing the

ends

53 and 54 of the pipes 50 and 5| to the mandrel 89 to effect winding thereof. The clamp '|05 includes a plate |06 having a stud |01 (Fig. 8) projecting inwardly therefrom and normallyV disposed in the stem portion of a T-shaped slot I 08 formed inthe mandrel 89 at a point near the unanged end thereof. A washer |09 is disposed upon the stud |01 for engagement with the inner surface o f the mandrel 89 and a wing nut 0 is threaded onto the stud |01 Afor detachably sec-fing the degli.) '.05 t0. the mandrel 139-1 The,

plate |06 carries circumferentially projecting ngers and'll2 ofa diameter small enough to be snugly received in the

ends

53 and 54 of the pipes 50 and 5|, respectively. The opening |08 is suiciently large to enable the plate |06 and the fingers and ||2 carried thereby to pass therethrough for removal from the interior of the mandrel 89, as will be explained later.

Fig. 9 illustrates the coil winding apparatus 80 in the position it assumes at the beginning of a winding operation. Thus, it will be noted that the mandrel 89 has been rotated to a position where the clamp 05 is disposed at the lower side thereof, and the pipes 50 and 5| have been advanced by the machine operatoruntil the ends 53 and 54 thereof have the ends of the ngers ||2 and III, respectively, received therein. This provides a quick and simple way of securing the

ends

53 and 54 of the pipes 50 and 5| to the mandrel 89 to effect winding thereof. The motor 81a is' started to cause driving of the mandrel 89 in aclockwise direction, as viewed in Fig. 7, whereupon winding of the pipes 50 and 5| upon the mandrel 89 commences. The pipes 50 and 5| are guided during the winding operation by the operator to effect close winding of, say, the first eight turns of the coil. The motor 81a is then preferably stopped and a spacer element or plate I I4 (Fig. 10) is inserted between the pipe 50 and the last wound turn of the coil, and another spacer element or plate ||5 is inserted between the pipes 50 and 5|. The spacer elements ||4 and ||5 are supported upon the table top 82 and extend to a point well under the mandrel 89 as will be apparent from Fig. 11. The thickness of the plates I|4 and I5 will vary in accordance with the desired spacing of the turns of the lower end portion of the water wall section 31, and in the illustrative example shown, these plates are /z inch thick. The motor 81a is restarted to drive the mandrel 89 in the same direction as before to continue the winding of the coil. The winding of the coil is interrupted as the ends 53a and 54a (Fig. 12) of the pipes 50 and 5| approach the edge of the table top 82 nearest to the mandrel`89. The clips 56 are now preferably attached to or inserted between the spaced turns of the coils to maintain the same spaced apart.

The thumb screw 98 may be loosened to release the journal 92 from the bushing 9| and the pins |02 removed to permit detachment of the frame 99 from the base 84. A shell I|6 of predetermined internal diameter may then be slipped over the unsupported end of the mandrel 89 onto the wound portion of the double coil until it engages the unwound ends of ythe pipes 50 and 5I, as illustrated in Fig. 12. The driving torque on the mandrel 89 is then released by reversing the motor 81a and the two helical coils formed from the pipes 50 and 5| are allowed topartially unwind into engagement with the inner surface of the shell IIB. Ihe pipe ends 53a and 5,4a are evened up, if necessary, and the return bend 52 is then welded thereto. The ends 53a'and 54"l with the return bend 52 attached thereto are then bent around the mandrel 89, and the shell IIB is then pushed over the remainder of the coil into engagement with the flange 90, as shown in Fig. 13. The wing nut |I0 is then loosened, thereby releasing the clamp |05 and said clamp is then moved toward the head of the T-slot |08 so that it can be withdrawn through said slot to, Vparrait the double wound coil Bland the, shell 7 |6 to be removed simultaneously from the man drel 89. Y The shell |6 is formed from a rolled sheet of metal and its Vlongitudinal edges are placed lin abutment and. a strip IIB (Fig. 12) is welded to the shell llt at the abutting portions thereof to hold the same in cylindrical form. A plurality of anglebrackets H9 is welded to the shell H6 adjacent one end thereof.

The lowerrnost turn of the coil 31, cf course, is arranged on -a helix and in order to 'support the same vertically, a plurality of strips or feet V||1 (Figs. 3 and 5) of different vertical height are welded tothe lo'wer side of said turn.

After the feet I |1 have been welded to the water Wall-section 31, the shell VHt is slipped down and the end 54 of said section is welded to the inlet end 55 of the Ygenerating section 33, and 'the end 53-is welded YtoV the outlet end 45 fof the preheater section 36. The shell l i6 is restored/to its original position but is of insuiiicient length to enclose the preheater section 3E and, hence, a second shell |2e V(Fig. 1), having the main inlet 39 and the discharge pipe 1| extending therethrough, i-s arranged in telescoping rel-ation with the shellll and is Awelded at its lower end `|-2| to the 'upper end of the vshell H6.

A crossbar i272 (Fig. 12.) extends across the upper portion of the shell |29 and the opposite ends thereof are secured 'to said shell by brackets |23 bolted to said cross'bar and shell, respectively. A second bar |24 arranged at right angles to the crossbar |22 has one end welded to the adjacent side of the crossbar l 22 and its other end Yfastened to the shell i2@ by a bracket |25bolted to both said bar and shell. Another bar |21 has one end thereof welded to the opposite side of the crcssbar |22 and its opposite end is secured by a bracket |23 and suitable bolts to the 'shell l i6. A tie bar |29(Fig. l) bridges the crossbar |22 and `over-lies the adjacent end portions of the bars |24 and |121 and iis welded along its lower edges to all of said bars 'to stiften the same and form aV rigid bridge across the crossbar |22. A hook member |3543 has a shank |3| disposed at the point of juncture-of the bars |22 and E21 and is welded thereto and to the tie bar i297. rThe lower edges of the bars |22, |-2ii and |21 lare preferably welded to the upper pancake coil section Il@ of thepreheater section V36. venient device for handling the entire shell and coil assembly by means ef a crane (not shown). After the assembly of the coil and shell has been completed, as above described, the same is subjected to a conventional heat treatment to relieve l all stresses. and strains therein.

After the coil assembly has been heat treated, a stainless steel cylindrical sheet liner |32 (Fig. 1)4 is inserted within the lower portion of the water wall section 31. The height of the liner |32 is preferably such that it extends upwardly into the region of the generating coil section 38. The upper end of the liner |32 is curved inwardly, as indicated at |33, to facilitate such insertion. The liner |32 is preferably made of stainless steel, that is, a chrome-nickel steel, commercially known as 18-8 stainless steel, although other stainless steels of different ratio 'of chrme to nickel have been found to be satisfactory. Ordinary sheet iron may also be used in making the liner |32, but the life of such a liner is relatively short and stainless steel is preferred because i eliminates the replacement problem. 'i The thickness of the stainless steel liner-|3`2 is ofv the order of v'04 inch to -.14 incl-'i and-prefee' The hook |33 thus provides a cone ably .'06 inch. The heavier :gauge materialrs capable of slightly deforning Vout of round individual turns of the/water wall section 31 so that good heat transfer -contact can be maintained between the outer surface of the liner |32 and the inner surface of all of the coil turns. The liner |32 is made by rolling a flat sheet of stainless steel into cylindrical form and then welding or otherwise securing the vertical edges together. Afterward, one 'end is rolled to turn the same inwardly to provide the rounded edge |33, pre@- viously referred to. Y,

The external diameter of the liner |32 is dependent upon the internal diameter of the water wall section 31 andtheir relative rates of thermal expansion. -In this connection, the liner; |32'isv made of -such external diameter'that it canbe readily slipped into the water wall section V31 with some'slight clearance, the clearance being vsuch that it vwill subsequently be eliminated under 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 horsepower unit, the internal diameter of the turns of the water wall section 31 was 231A; inches andthe cuter diameter of the liner- V|32 was 22% inches, thus allowing 1/4 of an inch total clearance for expansion. The internal diameter of the turns of the water wall section 31 is held to a desired dimension by the expedient of employing the shell H6 of' predetermined internal diameter and the step of allowing the helical coils formed from the pipes '50 andV 5| to only partially unwind after the shell llt` has been slipped thereover, as de-7 scribed herein in connection with the method of making said water wall section;

No special heat treatment is given to the stainless' steel liner |32; it is simply `inserted within the water wall-section 31 after the `coil `assembly 35 has been stress-relieved. In operation, the liner '|32 will expand into positive yengagement withv the surrounding turns of the water wall section 31, and in some instances may bulge slightly outwardly betweenadjacent turns, as illustrated to an exaggerated degree in Fig. 4. Normally, however, the liner |32 will contract upon cooling, so that it can be readily removed from the coil 31. After the unit has been in operationfor a period of time, the coil 31 and the liner |32 take a more or less permanentset, in contact, as 'a result of the -loss of elasticity due to repeated heating 'and cooling. v

When the pipe being wound to form the water wall section 31 is smaller than one inch in external diameter, it is unnecessary torplace the shell ||6 Ythereover to limit the. extent Vof. un` winding thereof. The reasonfor this is that, with a smaller diameter pipe, the pipe takes a more or less permanent set as it is wound upon the mandrel 89,'and does not tend to unwind to any substantial degree, thus no vdiinculty arises in maintaining a nxed internal diameter. However, when pipe, such as the-pipes 50 and 5|, of an external diameter greater than one inch is Wound upon the mandrel 89, the inherent elasticity of the pipe would, 'unless constrained, cause the same to unwind to a considerable degree and result in coils'of varying'internal diameter. I To avoid this, the shell H6, of predetermined internal diameter, is* slipped over the Vcoil on the mandrel 89 to limit the extent of unwinding cf the helical coils 'when the driving torque 'on said mandrel isreleas'ed. In thisr'manner, it is possible to maintain the' internal diameter m'of the double wound coil 31 to a givenz'size so' that ai liner |32 of predetermined external diameter will properly vlit and expand into positive engagement with the inner surface of the coil during operation of the steam generating apparatus I.

v`While the aforedescribed method of winding the water wall section 31 contemplates joining the ends of the pipes 50 and 5| by a return bend 52, after said pipes have been wound upon the mandrel 89, Figs. 14 and 15 indicate the manner in which a double wound coil can be formed by first interconnecting the ends of two pipes by a return bend and clamping the returnbend to the winding mandrel. Thus, two lengths of pipe 50b and may be rst interconnected by a return bend '52 length of tubing may be bent substantially medially of its length'to provide a return bend 52c and substantially parallel portions 50c and 5|, as diagrammatically illustrated in Fig. 16. In either event, the tubular material to be wound is connected to a mandrel 89h, ofv a winding apparatus 80h similar to the apparatus 80; by a clamping device generally identiedby the numeral |05". The clamping device, |0511' includes a bracket |06b which is riveted' or otherwise permanently secured to the inner face ofthe mandrel 89b adjacent an opening |08". Clamping fingers |||b and ||2b extend through the opening |08b and grip the inner and'outer portions of the U-bend 52h, as best illustrated in Fig. l5. A wing bolt ||0b extends through the clamping lingers 7|||b and ||2b and is bracket |061.

After the U-bend 52D has been clamped tothe mandrel 89h, one turn'of the pipes 50| and 5|b is wound upon the mandrel 09h, and spacing elements, such as the elements 4 and ||5 shown in Fig. 10, are disposed between the pipes 50h and '5|b and between the pipe 50h and the adjacent wound turn of the coil, as will be readily understood, to eiect spacing of the turns adjacent the return bend 52b a predetermined distance apart. After the desired number of spaced turns'has been wound uponthe mandrel 89h, the spacing elements are removed and the remainder of the pipes 50b and 5|b is wound upon said mandrel with the turns in contact, under the guidanceof the operator.

It .will also be understood that when pipe in excess of 1" external diameter is wound upon the mandrel 89h, winding of the coil will be continued until the pipes 50|u and 5|b have been almost completely wound thereon Then a shell, similar to the shell H6, will be slipped over the wound portion of the coil. and the winding torque released slightly to permit the turns to partially unwind and expand into engagement with the inner surface of the shell. Of course, the shell will be slipped over the mandrel 891D in a manner opposite to that shown in Fig. 12, i. e., so that the brackets ||9 mounted upon the shell will be disposed adjacent the end of the coil having the return bend 52h. The unwound portions of the pipes 50h' and 5|b are'then bent against the mandrel 89b and the shell is slipped farther onto the mandrel to completely enclose the coil.

The removal of the wound coil from the mandrel 80h, irrespective of whether it is enclosed in As an alternative to this procedure, a single threaded into the a shell or not, can be effected by removing the Continuing now with the description'of the remainder of the' steam generating unit I, four inverted U-shaped members |35 (Figs. 3 and 4) are disposed in the space 23 and their end edges are respectively welded to the rings ll'and `22L The U-shaped members |35 are arranged to serve as supports for the feet ||1 at the lower end of the water wall section 31. The members |35 are also vertically aligned with the brackets H9 secured to the lower end ofthe shell ||6. Bolts |36 project through the bracketsr |19', the horizontal wall of the U-shaped members |35, through openings in the bottom walls 9 and" 6 and through an opening in the supporting legs 2, as best illustrated-in Fig. 4, for securingthe shell 6 in assembled relation with the base 3 and legs 2. The legs 2 are additionally secured to the base 3 by bolts |38 which extend through the ring 8 and into a reinforcing stripV |39 (Fig. 4)- engaging the inner surface of the ring 8.

The outer ring 8 of the base 3 has an outwardly extending flange |41 (Figs. 1 and 3) at-its upper end, and the intermediate ring has an outwardly projecting flange |48 which overlies and engages the flange |41. The lower endof the jacket section4has an outwardly extending iiange |49 that rests upon Vthe flange. |48. The flanges |41, |48 and |49 may be bolted or welded together, as desired. The jacket 4 has aliningvof insulating material |50 which is arranged outwardly of the insulating materialA |4| to provide an annular air space |5| completely surrounding the insulated heatingV coil assembly. f

The upper end of the jacket 4 has an outwardly extending flange |52 (Fig. '1) f and the-cap 5 has a similar ange |53 resting uponltheflange |52. The flanges |52 and |53may be bolted or welded together, as desired. The sleeve |44 projects into an opening |54 in the cap 5 so that an air space |55, communicating with-the annular air space V| 5|, is formedY between 4the inner surface of said cap and the insulating material |46, the openings |45 providing communication between the air space |55 and the ue openingv The ange |48 of the intermediate ring contains a plurality o-f circumferentially spaced apertures |56 which have their edges bent, as indicated in Fig. 6. to form air scoops facing in a counterclockwise direction. These apertures establish communication between'theannular air space |5| in the jacket 4 andanannular air space `|50-between thef'rings 8 and Accordingly, air travelling in a counterclockwise, spiral path and introduced `through the opening I6 into the air space 2 in the base 3 is deflected outwardly by the overlying portion of the wall 0 and the baflies I3 into the air space |58,` and is sc'ooped by the leading edges ofthe apertures |56; into the annular jacket air space |5| to remove any heat `that has passed through the insulating layers |4|-| 42, whereby to maintain theitem perature of the jacket 4 at a minimum to prevent undue heating of the lboilerroom or chamber in which` the steamA .generating unit isy installed. The: heated air forced out oiY the air space |51 passes through the air space l55, open ings |245 and is exhausted into a stack |59 surrounding the opening |54 in the cover 5T.

It will be notedfrom Fig. l that thelower end of the liner |32 rests upon the upper surface 25 of therefractory 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 conned within the combustion chamber 2li so that it cannot leak into the-space occupied by the water wall section 31 and the insulating material 14B, |41' and i150. The seal is particularly important when gaseous fuels arel used inasmuch as under such conditions it would be highly undesirable to-havecombustible-material leak out of the combustion chamberinto the air space [5l surrounding the coil 35 in View of the fire hazard which itwould present. In the case of liquid fuels, such as oil, the same might also, constitute a re hazard, but oil'presentsthe further objection in that it would be absorbed by the insulating material anddecrease the efciency thereof; Y

In actual' operation, operating temperatures in steam generating urn-itsVK ofthe character comprising the present invention range from 250()o FL to 2900F. dependingupon the size of the unit.V The highest temperaturev which present-day refractory materialsI are capable of withstanding is about 2900 to 3000 F. maximum, whichY does not leave any margin of temperature resistance to resist direct flame impingement causing heating above the maximum and which most generally` causes refractory failure at the point oi flame impingement. The present invention eliminates the use of refractory' material in the side walls of the combustion` chamber by incorporating a water wall section 31 and a stainless steel liner 132. which was unexpectedly found to satisfactori-ly solve the problem ofgresisting excessively bien comhnstion chamberv temperatures. In fact', the present liner has withstood operating temperatures of 200W F. without failure. The stainless steel liner |32 serves not only to rapidly transfer'heat therefrom to tbe water wall section 31' to thereby avoid' excessive over-heating of said linerhut transfers enough heat to the coil 31130 prevent condensation of liquid fuels and moisture thereon.

A further advantage.- nf thel sheet metal` liner f3! and water wall arrangement 3T disclosed herein is that` it greatly ontl'asts refractoryY Walls., but what is more important. makes it possible to make the unit more compact by not occu'oving anywhere near as great a @nace as would normally be reunir-ed for the thir-.lrness of refractory material necessary tn withstand the same combustion cb amber temperatures. Y

It is important to make the metal liner i732V of a. dimension that will allow the liner to expand and make positive contact with the turns of the water wall 31v upon thermal expansion thereof. Ifinsuilicient clearance for expansion is allowed, the liner {B2-'will' buckle upon expansion andburn or scale at thebuckled points. On the other hand', iftoo much clearance is provided, the liner will not expand intol heat-transferring contact with the water wall 31 and burn or scale because of improper cooling thereof.

Insoiar as the operation of the heatingf coil itselfj i-s concerned, the liquid to beV heated is introduced throughthe inlet 39 into the preheater section 36 so that the liquidv is preheated 'before itA entersy the water wall section 31. Hence, too low temperatures in the water wall section 31 are avoided", andi this eliminates condensation'yof fue-l vapor which: would' cause carbondeposits. It also eliminates collection of and condensation of moisture from the air on the externalsurface 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 uidflows downwardly in the water wall section in theV helical coil portion formed by the pipe 50 and upwardly in the Water wall sectiony 3-1 through the helical coil portion formed by the pipe 51|", to. be discharged' into the uppermost pancake coil EE of the generating section 38. The fluid passes through the firstA pancake coil'- 60 of the generating section 38 and then directly tothe bottom pancake coil 6U, and' at this point changes from counterflow to direct ilow and passes-np- WardlyV through the balanceof the pancake coils lill and is then discharged' through the riser pipe Il into afsteam separator (not shoW-n-)- orp any other apparatus. y Y

The upper turns of the water wall, section 31 are'arranged closely adjacent each otherA for` the purpose of providing a combustiongas sealfatfthe criti'calipoint or level ofthe combustion chamber 2G; Whereas; the lowermost turns of thewater wall sectionY 312 are spaced* apartl to facilitate absorption of theY radiant heatof the liner |32, the surface ofthe Water wall coils 31' directly in contact with the liner |32', of course, absorbing heat by direct conduction. The Vvertical spacing or pitch of the lower coilsv of the vs fater wall section 31' is such that' sucien-t' heat transfer will be eiiected by direct conductionand radiation to maintain the liner |32 sufficiently cool'to prevent overheating or burning out of the same.r

The Vdouble Wound water wal-I 31" Vprovides a return pass for the uid without requiring the necessity of employing any external piping or tubing.. At` the same time, the ow of the fluid through the water wall section 31v resultsv in the absorption of heat from the combustion chamber and from theY liner i372 so that the fluid is di'schargedr intothe generating section 38- at aslightl-yfelevated temperature above that at which it entered' the water wall' section 31. f f

The object of' connecting the upper pancake coil 89 ofthe generating Vsection 38 to the lower pancake coil of said section is to providea construction in which some fluid is always present in the pancakeV coil El! nearest tothe lconibustioli chamber 2E), but which fi-uidfisnot at the rmaximum temperature tov which the unit is capa-ble 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 60 are avoided. The arrangement also creates a higher temperature Ydifferei-itial between 'the temperature of the uidV inthe coil andthe temperature ofthe combustion gases, which increases the effectiveness of the. heating coil. In fact, thermal ellicienciesasr high as $270'. are commonly attained in units embodying the coil assembly 35. A Y

The present coil construction notA only` nia-kes it possible to develop a givenboiler horsepower with less heating' surface than previous units designed toy develop the same boiler horsepower, but has also resulted in a reduction the feed pump pressure required toY force themed-Water into' the coil. For' example, previous. 50 horsepower units supplying steam; atA a pressure of 1100 lbs'` per square inch have required a feed pump pressure of 280 to 290 lbs. per square inch as compared with a feed water pumppressure of 260 lbs.' per square inch for the-present unit; This indicates that less actual steam or vapor was formed in the heating coil 35v with'a greater'proportion of solid liquid than vapor, which resulted in less friction flow loss through said coil. 11n practice, itis desired to maintain a streamef fluid flowing through the heating coil '35 containing a maximum ratio of V25% 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 of the liquid is converted to vapor during the passage of liquid through the heating coilbefore it discharges from the outlet pipe 1I into a steam separator or other 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 use of these features in apparatus for generating steam, and that the invention contemplates their use wherever susceptible.

The details of the invention disclosed herein, other than the heating coil per se and the method of making the same, are -claimed in my copending application Serial No. 688,721, filed of even date, as a division hereof.

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

I claim:

1. A heating coil, comprising: a preheater section having an inlet and an outlet and including a plurality of pancake coils connected in series; a generating section having an inlet-and an outlet and comprising spaced coils of pipe; and a water wall section comprising a continuous coil having one end thereof connected with the outlet of the preheater section and the other end thereof connected with the inlet of said generating section, said preheater section being entirely above said water wall section and said generating section being'substantially completely within the upper portion of said water wall section.v

2. A heating coil, comprising: a preheater section having an inlet and an outlet and including a plurality of pancake coils connected in series; a generating section having an inlet and an outlet and including a plurality of pancake coils each' 3. A heating coil, comprising: a preheater section having an inlet and an outlet and includ- Ving a plurality of pancake coils connected in series; a generating section having an inlet and an outlet and including upper and lower pancake coils with at least one pancake coil disposed therebetween and including means interconvnecting the outlet of said upper pancake coil with the inlet of said lower pancake coil, and

means :connecting the outlet of 'said' lower pani cake coil with the inlet of saidintermediate pancake coil; and a water wall section compris-A ing a continuous coil having one end thereof connected with the outlet of said preheater section and the other end thereof connected with the inlet of lsaid upper pancake coil of said generating section.

4. A heating coil, comprising: a preheater section including a plurality of coils Vconnected in series so that flow occurs downwardly VVtherethrough; a water wall section comprising a continuous double Wound coil having one end there# of connected with the outlet of said preheater section so that flow continues downwardly through one portion of said double wound coil and upwardly through another portion of said double wound coil; and a generating section including vertically spaced coils with theinlet of the upper coil of the generating section connected with the other end of said water wall section and the outlet thereof connected directly with the inlet of the lower coil of said generating section so that flow again occurs downwardly, the outlet of the lower coil of said generating section being connected with the inlet of the coil next adjacent thereto and the intermediate coils of the generating section being connected in series so that flow through the intermediate coils of said generating section occurs in an upward direction.

5. A heating coil, comprising: a preheater section including a plurality of superposed pancake coils connected in series, the upper pancake coil having an inlet for the preheater section and the lower pancake section having an outlet for the preheater section; a water Wall section disposed below said preheater section and including a continuous coil having one end thereof connected with the outlet of said preheater section; and a generating section including a plurality of superimposed pancake coils disposed below said preheater section and within said generating section, the inlet of the upper pan cake coil of said generating section being connected with the other end of said water Wall section and having the outlet thereof connected with the inlet of the lowermost pancake coil of said generating section, the outlet of said lowermost pancake coil of said generating section being connected to the inlet of the next adjacent intermediate pancake section and said intermediate pancake sections being interconnected in series so that the pancake coil adjacent the uppermost pancake coil of the generating section is provided with an outlet serving as a discharge for the complete coil assembly.

6. A heating coil, comprising, a cylindrical shell, a `preheater coil in the upper portion of said shell, a water wall section below said preheater coil and including two interwound helical coils with their ends interconnected at the bottom by a return bend, said water Wall coils being in continuous firm contact with the inside of said shell, a generating coil having spaced apart tubes Within the upper portion of said Water Wall section, the upper ends of the said helical coils being connected to the outlet of said preheater coil and the inlet of said generating coil, respectively, the turns of said water wall section being axially spaced apart below said generator coil but in close contact with each other throughout that part of the Water wall section extending around said generating coil.

7. A heating coil, comprising, a cylindrical l5 shell, awaterwall section comprising a helically Wound coill in said shell with the turns. thereof infirm line contact with the inside of said shell, a generating section comprising a plurality of pancake. coils having spaced apart tubes, one above the other, arranged within and across the upper portion of said Water Wall section and defining a combustion chamber therebelow, the turns of said Water Wall section being in closeV contact with each other throughout that portion of the Water Wall section` extending around said generating section but being Vertically spaced apart below said generating section at the sides of said combustion chamber.

PERRY ARANT.

REFERENCES CITED Number Number 16 UNITED STA-TES- PAFI'ENTS- Name Date Baclizstrorn Feb. 27, 1917 Winslow Oct. 8, 1918 Quinnet' al Dec. 7, 1926 Hall July 26, 1927 Billow O ct. 22, 1929 Elze June 24, 1930 Bottoms- June 27, 1933 Hamm etal Aug. 21, 1934 Baumann Aug. 20, 1935 Sterricky July 13, 1937 Bailey et al. Aug. 22, 1939 Goergi Jan. 9, 1940 McCullough et al. Oct. 10, 1944 Livingood June 12, 1945 Arant May 9, 1950 FOREIGN PATENTS Country Date