US2686500A - Vapor generator - Google Patents

Description

Aug. 17, 1954 E- J. HAUCK VAPOR GENERATOR s Sheets-Sheet 1- Filed Sept. 1, 1949 PEIH INVENTOR Edwin JJ /auck BY ATTORNEY Aug. 17, 1954 E. J. HAUCK VAPOR GENERATOR Filed Sept. 1, 1949 3 Sheets-Sheet 2 WH N , INVENTOR Edwin J flauck Vllflf llfllllrlllll all 01M ATTO RN EY 0 O O O O 000 E. J. HAUC K VAPOR GENERATOR 3 Sheets-Sheet 3 o o o o 0 o o o o OO O O O O O O 0 OO O O O O O O O 00 000000000 INVENTOR ATTORNEY O O O O O O 000 O 0 OOO (g Q Q o O O O 0 O idwin J f/auck 0 00 O O O O O O C O O O O O O 00 Aug. 17, 1954 Filed Sept. 1, 1949 O O O O O O O K Patented Aug. 17, 1954 UNITED STATES PATENT OFFICE VAPOR GENERATOR Edwin J. Hauck, Fair Lawn, N. J assignor to The- Babcock & Wilcox Company, New York, N. Y.,. a corporation of New Jersey Application September 1, 1949, Serial No. 113,559.

6 Claims. 1.

The present invention relates in general to the construction and operation of fiuid heating apparatus of the class known as vapor generators and having provision for superheating the vapor generated therein. More particularly, my invention relates to steam generators of the type embodying tubular steam generating and steam superheating elements and deriving heat from the combustion of fuel in an associated furnace.

The vapor generator of my invention is adapted for various methods of firing including, for ex.- ample, firing by means of a traveling grate stoker located at the bottom of a fluid cooled combustion chamber, below the location; of convection heating surface components or sections, in and adjacent an upper portion of the chamber. The furnace chamber extends throughout the height of the setting and a bent tube boiler section is offset therefrom in a space adjacent the roof. A superheater is positioned forwardly of the boiler section and overlies a substantial area of the horizontal cross section of the combustion chamber. In accordance with certain objects of my invention, provision is made for accommodating a superheater of considerable depth in comparison with the depth of combustion chamber space available, and for protecting the tubular superheater elements from intense radiant heat, while permitting an appreciable amount of radiant heat to penetrate the superheater tube bank or banks so as to obtain a more nearly uniform superheat temperature throughout a relatively wide range of vapor output capacities. It is also my purpose to indicate the adaptability of my invention to vapor generators having different arrangements of gas flow paths therethrough, with provision for the effec-' tive trapping of solids discharged from the heating gases at one or more points along such paths of fiow.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its, use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of my invention.

Of the drawings:

Fig. 1 is a sectional side elevation of a vapor generator embodying various features of my invention;

Fig. 2 is a sectional front elevation of, one-half of the illustrated embodiment taken along line of Fi 1 p t y brok n. away along; lin v 2a-2a;

Fi s. 3 and 4 r par l s c i na P a i of the embodiment taken along lines. 39-3 and 44, respectively, of Fig. l; and

Figs. 5 and 6 are partial sectional side elevations showing modifications.

In more detail, Figs. l-xi illustrate an embodiment of my invention in the form, of a. vapor generator comprising a two-drum water-tube boiler l0 and its associated superheater l2 deriving heat in common from a fuel fired furnace or combustion chamber M. The vapor generator enclosure or setting is of substantially rectangular horizontal arrangement throughout its height and generally defined by fluid. cooled upright walls l5, It, and I! which constitute the iront, rear and opposing side walls, respectively, of chamber l4. Front wall I5 is extended over the combustion chamber to form an upper enclosing wall or roof it, while rear wall I6 includes a rearWa-rdly offset upper portion is to provide a boiler tube space 2| laterally adjoining the upper portion of combustion chamber 14. The lower portion of rearwall l6 may include, as shown, an inner wall section [6a directly adjacent chamber I4, and an outer casing wall section [6b spaced therefrom and forming an enclosure for circu latory connections later to be described. The lower-portions of front wall [5, and each side wall ll, may be similarly formed with spaced inner and outer portions [511, I51), and Ila, llb, substantially as shown. The complete vapor gener= ator assembly is suitably suspended from an overhead load supporting structure indicated at 22.

The boiler NJ is of a two drum. bent-tube type comprising horizontally disposed upper and lower drums 23 and 24 of which the upper drum 23 is of larger diameter than the lower drum 24, and the longitudinal drum axes are disposed in a com-s mon upright and substantially vertical plane. Upri ht boiler tubes 25 extend between drums 23 and 2A and are connected thereto at their opposite ends, the tubes 25 being arranged in transversely spaced banks, 25a and 25b and throughout each bank are spaced apart in longitudinal and transverse parallel rows, with the upper and lower end portions of the tubes being bent as shown for radial entry into the respective drums. Tubes 25, as shown, are suitably of 2" O. D. throughout, and in all transverse rows are arranged at alternate center-to-center spacings of 3"" and 4%" to facilitate tube removal. How ever, as. will be understood, tubes 25 of other,

3 diameters, at other spacings, may be utilized, such as tubes of 2 /2" 0. D. equally spaced on 13%" centers in each transverse row, for example, and swaged to 2" O. D. at their drum ends for adequate ligament strength. Other boiler tubes 25 connecting drums 23, 24, and of larger diameter than tubes 25, are arranged in rows adjacent the respective side walls 11.

In two intermediate rows, boiler tubes 21 and 28 are reversely bent intermediate their ends as indicated and thereby provide opposite end tube portions associated with separate banks. An upright gas directing baffle 29 extends downwardly between these rows of tubes 21, 28 from upper drum 23 to a point upwardly and vertically spaced from the lower drum 24 at a lesser distance than its vertical displacement from upper drum 23, the baiiie 28 having its shorter lower vertical portion forwardly offset from its longer upper vertical portion and connected thereto by an inclined intermediate portion 31. A gas outlet 32 is provided in rear wall l9 adjacent upper drum 23. Brackets 34 secured to upper drum 23, at opposite sides, may be utilized in conjunction with hangers 35 for supporting the weight of boiler section 15.

As herein illustrated, the combustion chamber I4 is fired by means of a spreader stoker delivering fuel to a traveling grate 35 located at the bottom of the chamber and providing top-run grate movement toward front wall l wherein the customary fuel delivery opening 31 is provided, the fuel feeding mechanism being indicated generally at 38. A fuel such as crushed coal is thus projected into the combustion chamber toward rear wall 55, in upwardly spaced relation to grate 36, and over substantially the entire grate area. With air supplied in the usual manner from beneath the grate, and through the grate, the finer fuel particles are burned in suspension while the coarser particles fall to the grate and are burned thereon. In the course of operation, combustion takes place at the highest rates adjacent rear wall It, opposite the wall through which fuel is introduced, and thus results in the creation of a zone of intense radiant heat, and maximum temperature conditions, in this part of the chamber. Residual ash is carried forwardly by the grate and discharged at a point 39 adjacent front wall 15. The walls of combustion chamber [4 are lined throughout with fluid cooling tubes which in the front, rear and side walls comprise the upright fluid cooling tubes 45, 46 and 41 respectively. In front wall 85, the tubes 45 are spaced apart, for example, and have their lower ends connected to header 48 which extends transversely of the setting at an elevation above fuel delivery opening 3'1, the tubes 45 being extended along the roof i8 and having their upper ends connected to upper drum 23.

In each side wall II, the tubes 41 are spaced apart, for example, and extend upwardly from a lower header 49, located adjacent the top run of grate 36, to an upper header 5| located adjacent the uppermost part of chamber 14. Other tubes associated with each side wall ll include a group of horizontally arranged tubes 52 disposed adjacent the furnace face of side wall header 49 to provide a heat barrier between the fuel bed and the header, the tubes 52 having fluid inlet end portions bent downwardly and connected to a transverse header 53 at the rear of grate 36, below top-run level, and having fluid 4 outlet end portions bent upwardly and connected to the front wall header 48, above top-run level.

In rear wall Hi, the tubes 46 are suitably more closely spaced than the tubes in other walls and are connected at their lower ends to the rear wall header 53. In the form shown, tubes 48 are tightly spaced throughout the width of rear wall 16 so as to place successive tubes of the row in contacting relationship, substantially as indicated in Fig. 4. From their lower end connections to header 53, tubes 46 extend upwardly along the lower rear wall portion 16a to approximately the centerline elevation of the lower boiler drum 24, at which elevation the tubes 46 are bent forwardly toward the front wall l5 to form an arch 54 extending forwardly and upwardly over the rear end of stoker grate 36. Selected tubes 46a, such as all alternate tubes of the tube row 45, for example, are continued forwardly and upwardly in vertically spaced rows 55 to a location forwardly of superheater l2 where they are extended vertically in horizontally spaced rows 51 to an elevation adjacent the root [8. From this elevated position, tubes 46a are extended over the superheater in a single upwardly inclined row 58 toward drum 23 to which the upper ends of tubes 45a are connected. The remaining alternate tubes 4% are bent upwardly and rearwardly to form a rounded nose 59 of arch 54 at a distance from rear wall 16 of approximately one-fourth to one-third of the total depth of combustion chamber 4 between the inner faces of front and rear walls 15 and 16. From the arch nose 59, the tubes 4% are continued upwardly and rearwardly below superheater 12 to a point adjacent the front boiler bank 25a where the tubes 46b are bent in the reverse direction as at 6| to a forward position adjacent superheater l2 where the tubes 46b continue upwardly in a single vertical row 62 and thereafter are extended rearwardly in an upwardly inclined direction toward upper drum 23 for connection thereto in a single row below the row 58 of tubes 46a.

A refractory backing 55 is applied to the rearward side of tubes 45 forming arch 54, while above the nose 59 the spaces between successive tubes 4% are closed by suitable known intertube space closure means so as to form a baffle 63 extending upwardly between the boiler and superheater and terminating at an elevation approximately half-way of the vertical distance separating the boiler drums 23 and 24. The baffle 63 thus includes a lower portion 64 inclined upwardly from the arch nose 59 toward boiler section l9, and a forwardly inclined upper terminal portion 65 disposed at substantially the same elevation as the oppositely inclined intermediate portion 35 of boiler baiile 29. The vertical space between the upper end of baiile portion 65 and the roof 58 provides a gas flow opening 5! connecting the superheater cavity 68 with the boiler tube space 21.

The circulatory connections for the furnace wall tubes include a group of downcomers 79 which extend downwardly from lower drum 24 between the inner and outer rear wall sections [Ba and [5b. Tubes H of this group are connected to rear wall header 53, while tubes 12 and tubes 13 extend forwardly between side wall sections Ila and llb and are connected at spaced intervals to the front wall header 48 and to a lower side wall header 49 respectively, Riser tubes 14 connect each upper side wall header 5! to the upper boiler drum 23.

A hopper 15, comprising a series of hoppersections. 16-, is provided beneath boiler section II] throughoutthe width of the setting between opposite sidewalls H, with each hopper section having its inclined front wall 18 extending from the juncture of the lower rear furnace wall section L60, with arch 54, and its inclined rear wal1.l9 forming a lower end continuation of the upper setting wall portion l9. The end walls of the hoppersections are suitably shaped, as indicated in Fig. 2,. to provide spaces enabling the downcomers 1:0 to. be connected to the lowermost part of drum 24, without passing through any part of the ash collecting space of the hopper. The hopper 15-is divided longitudinally of the drum by an upright partition 8| in each'section so as to separate the hopper into-front and rear compartments 82' and; 83 of which each is provided with a separate'lower end outlet 84.

The superheater I2 is positioned above arch 54 between the upright tube rows 51 and 62 which are formed by upper length portions of the rear furnace wall tubes 46. The divided, and substantially right-angled upwardly divergent arrangement of selected rear wall tubes 46a and lfibbeyond the arch thus provides a large superheater cavity 68 forwardly of the boiler section In and at the same time provides a staggered tube screen 56, 51 forwardly of the superheater and throughout the height of the cavity. The superheater is, of the pendant continuous-tube type having multiple loop coils or platens arranged in Parallel planes, equally spaced across the width of cavity 68 between, opposite side walls H. The entire, weight. of the superheater is transmitted to the overhead structure 22 through the superheater inlet and outlet headers 85 and 86. The superheater tubes, I3, suitably of, 2" O. D., are arranged in two spaced banks 43a and i312, and in transverse rows in which the tubes are more widely spaced in the front bank I3a than in rear bank [312, such as at center-to-center spacings of 6" and 3", in the respective banks. End tube lengths in the rearmost row of rear bank I3b are connected' to inlet header 85 to which inlet tubes 8'! from drum 23 are connected. End tube lengths in the two front rows of front bank l3a are connected to outlet header 85. Cross over connections are provided for connecting each pair of tube coils in two planes of inlet bank I317 to a pair of tube coils in a single plane of outlet bank Ma.

The superheater loops are for-med so as to provide the maximum amount of superheater surface which can reasonably be accommodated within the cavity 68. The upper portions of all loops are accordingly arranged vertically and thus parallel to-the screen tuberows 51 at the front and to the vertical row 62 of wall tube extensions 46b at the rear. The majority of the loops are provided with bends 89 intermediate their lengths, and at progressively higher elevations from front to rear ofthe banks, so as to position the lower end portions of such bent loops substantially parallel to the-inclined screen tube rows 56 at the front and to the inclined upper bafile portion 65 at the rear. The lower portions ofthe angularly formed, bent loopsthus extend substantially normal to the inclined lowerbaffle portion 64, with their lower return bends closely adjacent thereto and positioned rearwardly of a vertical plane tangent to the arch: nose 59 so as to be shielded from the intense radiant heat from the furnace zone below the arch. The remainder of the cavity space, rearwardly of the bent loops, is occupied by straight. vertical-loops 9 l ,of different lengths, directly adjacent the gas outlet 61 from. the cavity.

mitting limited longitudinal movement. of. one

loop relative to another. In bank l3b, the lower end portion 93 of each foremost loop is extended forwardly and downwardly across. the interbank space toward the rearmost loops of the frontbank I300 where other suitably short connecting ties 94 are provided.

Ample provision is made for maintaining the various heating surface componentsfree from excessive accumulations of fly ash and other solid products of combustion. For example, the arrangement of the total heating surface is such as to provide spaces between or adjacent heating surface sections for the advantageous application of access openings 95 and soot blowers 96.

In the operation of the unit illustrated in Figs. 1-4, the heating gases resulting from the com bustion of fuel in chamber I4 are directed through successive heating surface sections in three: successive passes, namely, a first pass generally transverse of tubes it throughout the height of superheater l2; a second, downward pass longitudinally throughout the first boiler bank 251a; and a third, upward pass longitudinally throughout the second boiler bank 25b, to gas outlet 32. In entering the superheater cavity 68, the gases in the uppermost part of chamber M follow a generally horizontal path into and through the upper portion of the cavity, while the gases at a lower elevation tend to follow a diagonally upward path into and through a lower portion of the cavity. Thus, with superheater loops, as disclosed, having upper portions in vertical planes and lower portions extending rearwardly at an angle to such planes, the resultant flow of all entering gases, at all elevations, is generally transverse 01 superheater loops throughout the height of the cavity. The direction of gas flow with respect to the superheater tube lengths thus traversed is therefore, from a practical standpoint, substantially uniform throughout the height of the cavity so as to provide a corresponding uniformity of gas flow resistance over the entire length of superheater loops adjacent the furnace and thus obviates bypassing of gases across lower portions of loops as would be expected if the customary completely vertieal loops were correspondingly suspended so as to position an equally large proportion of superheater surface forwardly of the arch nose 59.

The disclosed arrangement of superheater also enables a shorter overall depth of unit to be utilized for an equivalent amount of superheater surface, than if the screen tubes were extended in vertical planes substantially tangent to or adjacent the arch nose 59 with the entire superheater surface disposed to the rear of such planes. Thus, by extending the screen tubes Mia. to positions forwardly of the arch and close to the front furnace wall l5, the available size of superheater cavity is increased without increasing the horizontal depth of unit as measured from the front wall 5 to the first boiler bank 25a. Furthermore, by forming the superheater loops as described, with lower loop portions extending rearwardly at an angle to their upper loop portions, the lower return bends of the loops are brought into positions above arch 54 where they are adequately shielded from intense radiant heat from the furnace chamber M. An additional advantage in operation results from the wider transverse spacing of superheater tubes in the forward bank I3a than in the rearward bank I32), and also the provision of a widely spaced tube screen 56, 51 forwardly of both banks. In such an arrangement, an appreciable amount of radiant heat is allowed to penetrate into the superheater bank or banks and thus acts to flatten the curve of superheat temperatures at increasing vapor output capacities.

The modifications illustrated in Figs. 5 and 6 are to be understood as embodying a majority of the features described in connection with the embodiment of vapor generator shown in Figs. 1-4. For this reason, much of the detail construction has been omitted from the drawings so as to direct attention more particularly to the distinct modifications involved. Elements corresponding to elements of Figs. 1-4 are accordingly identified by the same reference characters in Figs. 5 and 6-. The burners 98, indicated in front wall [5, may be utilized separately as the sole firing means for chamber It or, if desired, may be utilized alternately with, or simultaneously with, a stoker firing means in a lower part of the chamber.

Referring to Fig. 5, the vapor generator is arranged for cross pass flow of heating gases throughout the boiler tube banks 25a and 252). In order to provide such an arrangement, the baflie HH associated with intermediate portions of selected rearwall tubes 4%, is extended as at 102 across the first boiler bank 25a and across the two intermediate rows of tubes 27 and 28 which have end portions associated with the respective banks. The bafile l! extends upwardly and rearwardly from the arch nose 59, in a plane adjacent the lower ends of the superheater loops and thus defines in part the superheater cavity 68 in addition to defining gas flow passes through the boiler. A short baffle section I03, forming a continuation of baffle HM, extends downwardly and rearwardly along the inclined intermediate portion of tubes 28. In this modification, the rear wall is is separated from the boiler tube bank 25b so as to provide additional space 196 for gases flowing around the end of bafile NH. A tube row of bank 251), or an additional row, is positioned adjacent rear wall E9, in spaced relation to the main body of tubes of the bank.

A hopper 468, having inclined front and rear walls [89 and HG, respectively, is positioned beneath both banks of boiler section 16, as in the previously described embodiment, and similarly divided into sections throughout the width of the setting, with downcomers it disposed between successive sections, as heretofore disclosed. The hopper is separated into front and rear compartments H2 and H3 by means of an inclined partition H4 extending from the lower drum 24 to the upper margin of the gas outlet 1 I5 which is provided in the hopper rear wall H0. Each compartment is formed with a bottom outlet H6, and the compartment H3 of each hopper section having a discharge spout i I! which extends across the gas outlet duct 1 E5.

The gases from combustion chamber I l thus pass to the upper side of baffle lfil to enter the superheater cavity 88 and then continue around the upper end of the baffle to provide two pass flow transversely of the front and rear boiler banks 25a and 25b and, upon arriving at space H9 rearwardly, of the arch nose 59, are directed between drum 2e and the front hopper wall 569 into the front hopper compartment H2 from whence they pass into the gas outlet H5. During the two-pass flow of gases over the second boiler bank 252), solid particles discharged from the gas stream'are directed into the rear hopper compartment H3, While particles remaining in the gas stream are discharged into the front compartment H2.

Fig. 6 illustrates the adaptability of the vapor generator to single pass gas flow throughout all heating surface sections. In this form, the inclined baffle [2! associated with intermediate portions of selected rear wall tubes 461), extends upwardly and rearwardly toward the boiler section [0 and terminates at a point directly in advance of the first row of tubes of the front bank 251:. In the absence of all boiler baffling, the gases are directed across both banks 25a and 25b in a single substantially horizontal pass and leave the setting through a gas outlet [22 which is formed in the upper rear wall portion IS, the outlet 122 being positioned opposite the space between the drums, and having a height practically equal to the vertical distance separating the drums.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form of my invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

Certain features disclosed herein are also disclosed, and are claimed, in the copending application of Charles L. Marquez, Jr., Serial No. 112,802, filed August 27, 1949.

I claim:

1. A vapor generator having walls defining a combustion chamber and a boiler space in laterally adjoining front and rear relation within a common setting, said walls including a front upright wall through which fuel is introduced into said chamber and opposite upright walls of which the first forms the rear outer wall of said chamber and a second forms the rear outer wall of said boiler space, a tubular boiler section in said space comprising an upper drum adjacent the upper boundary of said space and having up right tubes extending downwardly from said drum and connected thereto at their upper ends, an arch extending forwardly from said first rear wall above the elevation of fuel introduction into said chamber and providing an arch nose rearwardly spaced from said front wall, an upper arch portion extending upwardly from said nose in a plane intersecting all of said upright tubes in downwardly spaced relation to said upper drum to define a gas flow opening into said boiler space, the lower portion of said arch lying in a plane intersecting said front wall at an elevation lower than the uppermost end of said upper arch portion which continues to at least a position forwardly adjacent said boiler section tubes, a tubular superheater disposed above said arch and in part between said arch and said front wall, wall cooling tubes associated with said first rear wall having portions, associated with said arch and having other length portions extending upwardly clear of said arch and forming a tube screen between said superheater and the fuel introduction zone of said chamber therebelow; and other tubes associated with said first rear wall and said arch having portions extending up wardly between said superheater and said boiler section tubes.

2. A vapor generator as claimed in claim 1 wherein said boiler section tubes are arranged in front and rear banks and a bailie directly succeeding said arch is disposed throughout between the major portions of said banks and extends downwardly from said upper drum to an elevation below said gas flow opening.

3. A vapor generator as claimed in claim 2 comprising a lower boiler drum disposed at approximately the elevation of said arch and to which the lower ends of said banks of upright tubes are connected, and walls forming a separate hopper compartment beneath each of said banks, said arch having an outer wall surface defining an enlargement of said boiler space having direct communication with the hopper compartment beneath said front bank, said hopper compartment walls including a side wall inclined downwardly and rearwardly in continuation of an inclined outer surface portion of said arch and a wall extending downwardly from said lower drum and separating one compartment from another.

4. A vapor generator as defined in claim 1 and further comprising a stoker-fed grate in a lower portion of said combustion chamber onto which grate the introduced fuel is deposited, said boiler section including a lower drum adjacent the lower boundary of said space, to which lower drum the lower ends of said upright boiler tubes are connected, said boiler section tubes being arranged to form a front and a rear bank, said superheater above said arch comprising depending loops of angular formation having upright upper straight length portions positioned beyond said arch and rearwardly inclined lower return bend portions disposed adjacent said arch in overlying rela tion thereto, said upper arch portion continuing rearwardly to form a baffle extending across said front boiler bank in spaced relation to said upper and lower drums and defining therewith a twopass gas flow path across upper and lower portions of said front bank, and means including hopper walls below said lower drum for directing gases to a gas outlet at the rear of the setting.

5. A vapor generator having fluid cooled Walls defining a combustion chamber and a boiler space in laterally adjoining front and rear relation within a common setting, said walls including a front upright wall extending throughout the height of said chamber and opposite upright walls of which the first forms the rear wall of said chamber and a second forms the rear wall of said boiler space, said first rear wall providing a heating gas outlet from an upper part of said chamber and said second rear wall providing a gas outlet from said space, a tubular boiler section in said space comprising an upper drum adjacent the upper boundary of said space and a lower drum adjacent a lower boundary of said space at an elevation intermediate the height of said setting, upright boiler tubes arranged in front and rear banks within said space and extending between and connected at opposite ends to said drums, fuel firing means in a lower portion of said chamber creating a maximum temperature zone adjacent said rear wall, an arch extending forwardly from said first rear wall at an elevation above said firing means and said zone and providing an arch nose at a distance from said first rear wall less than one-half of the horizontal depth of said chamber, said arch having an inclined upper section formed as a baflie extending rearwardly and upwardly to a position forwardly adjacent said front bank of boiler tubes, said upper arch section lying in a plane intersecting the planes of said two rear walls at elevations below said upper drum and also intersecting said front wall at an elevation above said fuel firing means, means including said baffle for directing gases into said front tube bank in a pass including at least the upper portions of tubes forming said bank, a row of upright wall cooling tubes in said first rear wall having portions entering into the formation of said arch, selected tubes of said row entering into the formation of said bafile and other tubes of said row extending upwardly from said nose in widely divergent relation to said bafiie tubes and forming a tube screen having its lower portion inclined upwardly toward said front wall and its upper portion extended vertically in rearwardly spaced relation thereto, and a superheater disposed above said arch and having depending loops in each of a plurality of parallel upright planes arranged normal to said first rear wall, said loops being of angular formation in said planes corresponding to the formation of said screen and providing upper loop portions forwardly of said nose and lower loop portions directed toward said inclined baflle section at a steep angle and terminating in return bends c0n fined to the horizontally projected area of said arch.

6. A vapor generator as defined in claim 1 wherein said upper arch portion terminates at said position forwardly adjacent said boiler section tubes so as to direct gases transversely of said tubes in a single pass.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,878,908 Steinmuller Sept. 20, 1932 1,929,891 Jones Oct. 10, 1933 1,940,132 Kearns Dec. 19, 1933 2,107,022 Badenhausen Feb. 1, 1938 2,126,730 Bumstead Aug. 16, 1938 2,244,451 Falla June 3, 1941 2,313,251 Marshall Mar. 9, 1943 2,347,574 Mosshart Apr. 25, 1944 2,416,053 Grossman Feb. 18, 1947

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