US2939435A - Marine boiler - Google Patents

Description

June 7, 1960 Filed Feb. 6, 1957 G. W. KESSLER MARINE BOILER 8 Sheets-Sheet 1 Until L E &

INVENTOR. George W. Kessler ATTORNEY June 7, 1960 G. w. KESSLER MARINE BOILER 8 Sheets-Sheet 2 Filed Feb. 6, 1957 9 mmwmb B mm on INVENTOR. George W. Kessler ATTORNEY June 7, 1960 e. w. KESSLER 2,939,435

MARINE BOILER Filed Feb. 6, 1957 8 Sheets-Sheet 3 FIG.3-

OUTLET INVENTOR.

George W. Kessler ATTORNEY June 7, 1960 e. w. KESSLER MARINEBOILER 8 Sheets-Sheet 4 Filed Feb. 6, 1957 Y INVENTOR.

I George W. Kessler ATTORNEY.

June 7, 1960 e. w. KESSLER MARINE BOILER 8 Sheets-Sheet 5 Filed Feb. 6, 1957 ATTORNEY June 7, 1960 G. w. KESSLER 2,939,435

MARINE BOILER Filed Feb. 6, 1,957 8 Sheets-Sheet 6 FIG. 6

George W. Kessler ATTORNEY June 7, 1960 G. w. KESSLER 2,939,435

MARINE BOILER Filed Feb. 6, 1957 8 Sheets-Sheet 7 INVENTOR. George W. Kessler wow,

ATTORNEY MARINE BOILER 8 Sheets-Sheet. 8

Filed Feb. 6, 1957 INVENTOR. George W. Kessler ATTORNEY MARINE BOILER ""slei", EWe'StB iIrY KX, "a'sfs igiirh' to The Babcock a Wilcox Company, New Y-er'u, Nev,

'poration etNew Jersey Fir arms, 1.951, Serena-6385s! *18 Claims. c|.1'2'2==4'7s This invention relates to, a'fluid' heating apparatus 'and more-particularly to an improved construction and operation of a water tube steam boiler including a novel superheater' arrangement whichis particularly adapted for use in raemarinetinst-allation. r i

A's the'trend in marine installations is toward higher optimum superheat steamdemperature, it has been noted that in connection with the generation of high pressure and temperature steam in marine boilers fired by residual oiltype fuels, serious difficulties have been encountered in maintaining metal temperatures of the superheater parts below the high temperature corrosion limits thereof,

he; 'the temperature' at-which corrosion becomes excessive,

when-the same are customarily subjected to the high temperature -'combnstion gases for producing desired relatively very high temperature 'superh'eat steam. It has been discovered that the corrosive impurities present in the residual fuel oils fired react'with the metal super produced while maintaining the metal temperatures of the superheater parts at or below their high temperat e corrosion limit.

Heretofor'e, control superhe'at temperature overa wide range in a marine installation has been attained by means of a two-furnace, single uptake, control superheat boiler. As marine steam generating installations of this type are characterized by relatively'low spaceand head room limi- 'tatio'ns, it is a necessary requisite that these units be com} pact and lightweight in design, yet capable of adequately high thermal efiiciency requiring the minimum alteration of the surrounding ship structure. Because of the initial limitation ofavailable installation space, units of this type were limited to the amount of steam superheating surfaces capable of being located therein in a position for effective heat absorption, the limited amount of superheater absorption-surface being another factor which advers'ely' affects the desirability of maximum superheat temperaturewith'optimum permissible metal temperature ofthe 'supe'rheater parts; i

It is another object 'oflthis' invention to provide in a marine boiler unitofa predete'r'minate weight and size,

means for providing maximum. superheater absorption 'surfaceswithout materially altering'or enlarging the' acceptableor allowablesizea'nd weight of the marine-boiler which must of necessity be limited to thesurroundin'gl ship structure in which his to be'in'stalled. a r

It is anotherobje'ct or this invention to provide animp'rove'd superheater arrangement capable ofgreaters'efiec- 2,939,435 Patented June 7, 1960 tiveness, yet is rendered readily accessible and easily maintained so that the same can be sustained over a relamay long period of time. V V

The above objects and advantages of the instant invention are attained by providing in a marine boiler burning residual fuel oils, an improved superheater construction comprising of atleast-a pair of superheater sections which are serially connected whereby each section thereof is disposed in adjacent progressively'decreasing gas temper- .aturenones of agas convection pass. According to this invention, each section consists of a pair of verticaljuxtaposed headers of which at :leas t one is provided with means forpartitioningthe same into distinct chambers and a plurality of horizontally etxending, nested U-shaped, superheatertub es connecting the charnbers of one header in communication with itsassociated header. With this arrangement, each section is provided with a plurality of steam passes serially connected which are generally in counter and parallelheat transfer relationship to gas flow through the convection pass and which through any crosssectional plan or section of the entire superheater is provided with a stearri passwhich is in both counter and parallel heat transfer relationshipto the gas flow. V

In one form of the invention, each section of the, superheater isconnected in series. by airelatively large diameter crossover tube and in another forrn of the invention, each sectionis connectedinseries by a-plurality of additional ush d s e h at t v With eitheriof thesejarrangements, the relatively cool saturated steam accumulated the steam drum is first introduced into that .sectionof the superheater disposed in the hotportion of the gas convection zone. This relatively cool steam is then-passed through the first section serially-in several alternating passes which are generally in acounter and. parallel heat transfer relat-ionship tothe gas flow whereby the steam is heated to an intermediate superheat' steam temperature. Theintermedia'te superheated steam is then introduced into the second or next succeedingsuperheater section which is: disposed in the relatively cooler portion of the g'aspass whereby the intermediate" superheatedsteam is again successively or serially passed in; several alternating passes which are generally in counter and parallel heat transfer relationship relative to the gas flow so as to become highly superheated thereby. .In-this manner, efiective heat transfer isattained to produce the desired high temperature superheat steam while at the same time maintaining the tube temperatures of the various parts of the super-heater below that temperature at which corrosion becomes excessive.

V According to this invention, the superheater cavity is also extended to a extent without materially increasing the weight and size of the boiler as determined by the surrounding ships structure. This is attained by boundingthe superheater cavity by a group of spaced screen tubes which are connected to a pair .of spaced relatively small diameter water headers or drums rather than to'a single relatively large water drum as was heretofore customary in a comparable boiler arrangement as shown in the patent to Rooney 2,332,534. .With this novel arrangement, the' superheater cavity may extend downwardly an amount suilicient'to facilitate the addition of several more superheater tubes, thereby increasing the amount of available superheating surface over those of rior known-eenstructien havin the same vertical height between uppererm n and lowert'ubeheade r. i

Thisd'ual header arrangement is of further advantage in' that by spacing the same, a hopper-like bottom is provided for the superheater cavity' whereby the superheater tubes can be readily washed" down and otherwise maintained; thereby facilitating cleaning ofthe super- ;heat'er parts andconsequently' rendering the same more simple .in construction,

provision whereby highoptinium superheat steam tem-.

peratures are attainable while maintaining the metal temperature of the superheater parts within trouble-free temperature i A still further feature of this invention resides in-the provision whereby the superheater parts can be readily cleaned and washed down as required. Y

Other features and advantages will be readily apparent when considered in view of the following description and drawings in which:

Fig. 1 is a partly diagrammatic sectional elevation view of an improvedmarine boiler installation in'accordance with the instant invention. j

Fig. 2 is a plan section taken along line 2-2 of Fig. 1. Fig. 3 is a fragmentary, enlarged detail, elevation view of the improved superheater arrangement according to this invention. V i

Fig. 4 is a partly diagrammatic section in elevation of a modified form of the'invention;

Fig. 5 is a plan section'taken along line 5-5 of 'Fig. 4. Fig. 6 is a fragment y, nlargeddetail view of a modified superheater arrangement shown by Fig. 4.

Fig. 7 is a diagrammatic not to' scale perspective view of the superheater arrangement of Fig. 3.

Fig. 8 is a perspective not to-scale schematic view of the superheater arrangement 'o'f'Fig. 6.

In the form of the invention illustrated in Figs. 1 to 3, the improved marine boiler of this invention consists of a setting 10 comprising of a front 11, rear 12, and side walls 13 and 14 which are substantially rectangularly disposed enclosing a main furnace cavity 15, an auxiliary furnace cavity 16 and a gas convection pass 17 associated with the latter and disposed, between the auxiliary and supported the steam and water drum 18. Laterally offset and disposed adjacent the lower portion of the side wall 13 is a water drum 19 which is connected to the steam drum 18 by a bank of inclined steam generating tubes 20 which extend longitudinally of the drums 18 and 19 and transversely across the setting. On the outer side of the generating tube bank 20, the side wall 13 connects to the front and rear wall to form a common flue 21 for exhausting the combustion gases of both furnaces, the gases of the auxiliary furnace 16 flowing through the convection pass 17 across the main furnace to the flue. Immediately adjacent the inner side of the tube bank 20 is located the main furnace cavity which is adapted to be fired by fuel burners 22. If desired, a heat trap in the form of economizer tubes and/or air heater tubes 23 are advantageously located in the flue 21.

The auxiliary furnace 16 is separated from the main furnace 15 by the associated gas convection pass 17. As shown the side 16a, roof 16b and rear wall 16c of the auxiliary furnace cavity are lined with water-cooled wall tubes. The sidewall'water tubes 24'extend vertically from the lower side wall header 25 and the extensions thereof are, angularly inclined adjacent the roof to continue along the same to connect with the water and steam drum 18. The rear wall tubes 26 extend between the 4 34 located in the front wall independently fire the auxiliary furnace.

A distinctive feature of the instant invention resides in the provision of a pair of spaced relatively small water drums or headers 30 and 31 which extend transversely across the setting adjacent the bottom of the gas convection pass. Connecting each of the headers 30 and 31 to the steam and water drum 18 are a spaced group of water tubes 32 and 33 which extend transversely of the setting and form therebetween a superheater cavity, the tubes 32 and 33 forming a water cooled screen for protecting an improved superheater 35, as will be hereinafter described, disposed within the cavity from excessive radiantly transmitted heat from high temperature gases in furnaces 15 and 16.

In the embodiment of Figs. 1 to 3, the screen tubes 32 extend upwardly from the water header 30 and incline slightly toward the main furnace 15,'the lower half'por- 'tion of the screen tubes 32 comprising a shield of bare, tangent touching tubes to protect the superheater- 35 fr'om flame radiation. Alternate tubes 32 at the upper half portion thereof are bent inwardly toward the superheater cavity to 'form' spaces therebetween to provide passage openings for the combustion .gases flowing through the gas convection pass.

include a pluralityof downcomers disposed between the outer casing 36 and walls 11 and 12 of the'setting 10.

Referring to Figs. 1 and 2, drum 18.is connected to water drum 19 by downcomers 37. Downcomers 38 and 39 connectthe drum 18 to the spaced water headers 30 and 3L-respectively. Downcomer 40 connects the drum 18 to the rear wall header 27 and downcomer 41 connects the drum 18 to side wall header 25. The space formed by the walls 11 and 12 and casing 36 further provides a chamber through which combustion air is supplied to the burners 22 and 34.

. According to this invention, the improved superheater arrangement 35 has its heat absorbing surfaces positioned in the gas convection pass 17 whereby said surfaces can be independently heated by the firing of the burners 34 associated with the auxiliary furnace cavity and thereby rendering superheat steam temperatures controllable over a relatively wide range. Since the trend in marine boilers is toward higher superheat steam temperatures, it has been discovered that because of the corrosive impurities present in the residual fuel oils, the superheater tubes .rapidly corrode or deteriorate if heated to temperatures above 1150 F. Consequently for all practical purposes,

the temperature of superheat steam obtainable is limited perature zones A and B of the gas convection pass 17.

In the illustrated form of the invention, reference being had particularly to. Figs. 3 and 7'; the superheater 35' is lower and upper rear wall headers 27 and 28 respectively, v,

shown as comprising 'an inlet section 42 to' an outlet section 43. The inlet section 42 includes a pairof vertically disposed juxtaposed headers '45, 46 positioned between thecasin-g 36' and adjacent the 'rear wall 12,,one -of thegheaders having connectedtheretoa steam, inlet ,pipe 44 connecting with .the steam drum 1-8, and the :outlet .section .consistingof juxtaposed headers 51 and 52, header 51 being provided with an outlet connection 58 for delivering the .finally superheated steam to a .point of use (:not shown).

As shown, header 45 is divided by a diaphragm 47 which partitions header 45 into anupper. inlet and alower " outlet chamber 48 and 49 respectively. Chambers 48 and 49 of header 45 are connected .in communication with the associated header-46 by a plurality of .nested, vertically spaced, U-shapedheat receiving superheater tubes .50. In the illustrated form of the invention of "Fig. 3, the superheater tubes 5.0 are vertically stacked .in nested groups of three, the vertically stacked tubes 50 being divided into an upper group 50A connecting the .upper header chamber 48 to the associated intermediate header and-a lower group 50B connecting the associated header 46 to the lower chamber149 .of header 45.

Referring to Fig. '2, ;it will .be noted thatthenested, vertically stacked .tubes of .group 50A each comprises an inlet leg portion 50A extendinghorizontally across the convectionpass, a .cross-o'venportion .50A forming a continuation thereof which extends beyond the front wall of the unit and a return leg .50A which also extends across the convection ;pass upstream of the gas flow from that of the intake leg portion 5 A Each of the .nested and vertically stacked group of tubes 50B likewise comprises an =intake.leg portion 0B in communication with the interior of header 46 and which extends -horizontally across the convection pass, a crossover por-- tion 508 forming a continuation ofleg 503 extending through the front refractory .wall and return leg portion 50B spaced downstream of intake leg portion 5.0B

.leg 50B being in communication with chamber 49. In .Figs. 3 .and;7,.it will.be noted by the broken-arrowindicating the steam flow that the saturated steam from the steam dru-m'is introduced into header 45 through inlet 44 and flows through the inlet section 42in the following manner. The-steamintroduced into header 45 flows into chamber 48, then through the intake leg portion 50A, ofnestedtubetgroup 50A, through the cross-over portion 50A; .and through the return leg portion :50A wherein the steam is discharged into the associate header 46 .in-a steam flow path which is generally in a counterflow, heat transfer relationship to that of thevgas flow. The com- .bined delivery of steamfrom all of the tubes 50A then .moves down the associate header-46 and .into the lower group of superheater tubes 50B whereby the steam is directed from header 46 through .the intake leg portion 50B through the cross-over portion 503 thence through the return leg portion 5013 andfinally into lower header 52, the header 51 being divided by a diaphragm :53 into upper and lowercharnbers 54 and 55 respectively.

Vertical stacks o'fnested U-shape heat absorbing tubes 56 connect the chambers 54 and 55, header 51 to its associated header, the stack of tubes 56 being divided into a lower portion 56A connecting the lower chamber 55 to the associated header 52 and an upper group 563 connecting the associated header 52 to the upper chamber 54'.

. Referring to Fig. 7, each of the nested tubes vertical- 56A jcomrnunicating with chamber 55 and extending 'tion 56A form-ing a continuation of leg 56Aywhi'cli extends through the front re'fractory'wall 1-1 and a return 1y stacked in group 56A comprises "an intake leg portion:

across zone Bot the convectionpaiss, a cross-over porassets;

.leg .portion 56A spaced upstream of the intake leg ,portion 562. with respect to thefgas flow, 'the return 'leg portion '56A being in communication with the interior of theassociatedintermediate header'SZ. Thus, it will he noted that the intermediate superheated steam introduced into chamber '55 through the cross-over tube 57 Iilows through the intake leg portions 56A of the tube group 50A through the cross-over portion 56A and ithencethrough the return leg portion 56A; wherein the .steam is discharged into the associated header 52, the steam traversing allow path through tubes 56A which is generally in acounterflow heat transfer relationship Eto that of the gas 'flowfin the convection pass. The combined delivery of the steam from all of the tubes 156A then moves .up the associated header'SZ and flows outwardly therefrom through'the inta'ke leg portion 56B, through the cross-over portion 56B: forming'a continuation thereof and thence through the retur'ri leg' portion -56B .spaced downstream of leg portion 56B with respect to gasfiow wherein the steam is finally discharged .into the upper chamber "54 ofheader 51, the steam traversing .a flow ,path through tubes 56B which .is' generally in a parallel heat transfer relationship to that of the gasflow. Thus, it wiIl be noted that'the intermediate .superheat steam flowing through the outlet section 43 of the superheateruis raised to its finally superheated steam temperaturelinwhic'h state it is delivered through the 1 outlet pipe 58 at fits optimu'm' superheated tempera- .turetto a point of use. p

. -By this arrangement, it will be noted that the relative cool steam at saturated temperature is first intro- .duced .into section '42 of the superheater, the heat ab- :sorptiomsurfaces of which .are exposed to the hottest gas in zone A in the gas convection pass, and that by flowingthe steam serially inseveral alternating counter and parallel flow heat transfer \relationshhips between header 45 and 46 in the hotzone, the saturated steam is superheated to an intermediate temperature whereby the relative steam temperatures within the tubes 50 and thegas temperature heating the surfaces thereof are such that the superheatermetal temperatures are maintained below their high temperature corrosive limit. The intermediate superheated steam is then passed into the second section ofthesuperheater, disposed in the cooler zone Band the steam finally heated therein by means of flowing the steam .in through the second superheater section in ,generally an alternate counter and parallel heat transfer relationship to the gas flow. Thus, a highly heated 'superheat steam is attained in that portion ofthe superheater having its metal .heat absorption surfaces exposed to the relatively cooler combustion gases of zone B. In this manner, a more uniform balance is achieved between therelative temperatures of the steam, the combustion gases and theassociated metal superheaterparts in contact therewith. Consequently, this balance is maintained so that the optimum superheat steam temperatures of 1000 F. or above may be achieved without ,the metal parts of the superheater parts exceeding temperatures at which intolerable corrosion of the superheater tubes 50 and 56 occurs. 7

According, to this invention, it will be 'noted that the utilization of the spaced water header construction 30 and 31-as hereinbefore described enables the superheater 'cavityor section to' be extended downwardly a maximum extent. This 'is rendered possible over the priorknown construction because it has been discovered that by utilizing a pair of spaced smaller diameter water headers 30' and 31, the tube groups 32, 33 connecting into each of the water headers '30 and 31 respectively .klower ends thereof 32a, 33a.are bent for connecting the .same into its respective header. For this reason; additional-space is availed of without altering the overall size of .the'unit whereinseveral additional superheater tubes '50 and 56 may beaccommodated' and-thereby Itmay' extend downwardly a greater-amount before'the 'superheat steam temperature.

, spams v '7 creasing the overall amount of heat absorbing surface of the superheater.- Thus it will be noted that" for a given steam temperature withfthe greater the amount of superheater absorption surface available, lower resultant tube temperatures are attained and conversely,

for any .given tube temperature, the more superheater which is' adapted to be closed by a removable closure 61.

Because of this construction, the superheater tubes 50 and 56 may be readily washed down or otherwise maintained so that they can be kept comparatively clean thereby increasing the efiiciency thereof. As shown in Fig. 2, the U-shaped, vertically stackedisuperheater tubes 50 and 56, nested in groups of three are rendered readily accessible in that the space between the horizontally extending leg portions of theU -shaped tubes of each section 42, 43 provide sufficient walk-in area so that an operator may physically enter and physically clean tubes by hose and/or scraping or. the like to maintain the tubes reasonably clean for sustaining the effectiveness of the same. Thus, the instant supcrheater'arrangement herein described allowsfor optimum superheat steam temperatures while maintaining the metal temperatures thereof within safe operating limits and also the arrangernent thereof is such that greater accessibility and ease of maintenance may be had-without increasing or altering substantially the overall size and dimensions of the unit. I

It will be further noted that the tubes 50 and 56 extend through the front and rear walls and are supported thereby. If desired, a plurality of large diameter water tubes 62 connecting the drum 18 to headers 30 and 31 are disposed in pairs adjacent tubes 50 and 56 for supporting the intermediate portion of the horizontal legs of the nested tubes, each pair of tubes having secured thereto suitable superheater supporting plates 63.

A modified form of the invention is illustrated in Figs. 4 to 8. In this form of the invention the marine boiler unit is arranged generally in much the same manner as hereinbefore described, but utilizing a modified superheater arrangement. As shown the setting 110 comprises a front wall 111, rear wall 112, and side walls 113 and 114 which are rectangularly disposed and enclose a main furnace cavity 115, an auxiliary furnace cavity 116 and a gas convection pass 117 disposed the'rebetween, each of the furnace cavities 115 and 116 being independently fired by fuel burner means 118 and 119. The water and steam drum 120 is supported adjacent the upper portion of the unit and extends transversely of the setting in the vicinity'of the gas pass. Laterally offset and adjacent the bottom portion of the side wall 113, there is positioned a water drum 121 which is connected to the steam drum 120 by a bank of inclined generating tubes 122. As hereinbeforc described, on the outer side of the tube bank I The auxiliary furnace 116 in this form of the invention.

is likewise provided with water cooled side walls 116a, rear wall 116b, and roof 1160, the side wall tubes 125 extending vertically from the lower side wall header 126 and inclining adjacent the roof of the furnace to con- 8 tween the lower 128 and the upper 129 rear wall headers, the latter being connected to the main steamdrum 120 by riser tubes 130.

Positioned belowthe main water and steam drum 120 are a. pair of spaced relatively small diameter water headers 131 and 132 which extend transversely across the settingat the bottom of the gas convection pass 117, each of the water headers 131 and 132 being connected to the steam drum 120 by a group of spaced water tubes 133 and 134 respectively which extend transversely across the setting and form therebetween a superheater cavity.

,As hereinbefore described, the spaced group of tubes 133, ,134 form a water cooled screen for protecting the modified superheaterr135 in the superheater cavity from flame radiation.

As shown in Fig. 4, the screen tubes 133 extend upwardly from the water drum 131, the lower portion of the screen consisting of bare, tangent touching tubes to form'an imperforate shield, while the upper portion of the screen has alternate tubes inclined outwardly to provide spaces therebetween for permitting the gases to flow out from the gas pass and into the upper portion of the main furnace from whence they are exhausted through the flue 123. Screen tubes 134 are alternately staggered throughout the greater portion thereof. Thus, it will be noted that when the burners of the auxiliary furnace are "fired, the combustion gases tend to flow from the auxiliary furnace through screen tubes 134 and into the gas convection pass 117 whereby the gases are directed over the superheater after which the gas flows outwardly through the passages formed between tubes 133 at the upper portion of the screen.

The water supply connection from the drum 120 to the various drums and headers of the unit include a plurality of downcomers which are disposed in the spaces formed between the outer casing 136 and the front and rear wall of the setting. Referring to Fig. 5 downcomers 137 connect the drum 120 to the water drum 12 1 and downcomers 138 and 139 connect the steam drum to the spaced water header 131 and 132 respectively while downcomers 140 connect the steam drum 120 to the side wall header 126 and downcomer 141 connects the steam drum to the rear wall header 128.

The modified superheater arrangement 135 as illustrated in the embodiment of Figs. 4 to 6 and 8 comprisesan inlet section 142 and an outlet section 143. As shown in Fig. 6, the inlet section 142 includes an inlet header 144 and a juxtaposed associated header 145 vertically disposed between the casing 136 and the rear wall 112, each header being provided with a diaphragm means 146, 147, respectively for partitioning each into an upper and lower chamber. As shown in Figs. 6 and 8 it will be notedthat the diaphragm 146, 147, dividing their respective headers into upper and lower chambers, are

' located at different elevations whereby the inlet header drum 120. The rear furnace wall tubes 127 extend be- 144 is divided into an upper chamber 148 and a relatively shorter lower chamber 149 while the associated header is divided so as to have substantially equal lower and upper chambers 150 and 151 respectively which are approximately double the length of the lower inlet header chamber 149.

A group of horizontally, vertically stacked, nested,

hairpin tubes 152 extending through the rear wall and across the hot zone of the gas pass connect the chambers 148 and 149 of the inlet header 144 with the chambers 150 and 151 of the header 145. As indicated in Fig. 6, the vertically stacked, hairpin tubes 152 are divided into an upper portion 152a, an intermediate portion 152b, and a lower portion 1520. The lower portion 152:: of

V the tubes 152 connects the lower chamber 149 of the inlet header 144 to the lower half of chamber 150, the

f intermediate group 152b connects the upper half of chamber l'50 of the-associated header 45 with the lower portiorrof the upper inlet header chamber 148 and the upper group of tubes 152a connects the upper portion of the :and extending across the cooler portion gas pass'connects the chambers-157, 158 of the outlet header-153 With'the sehambers 159, 169 of the associated header 154, the verti- 1calstack of tubes 161 being divided into an -upper161a, intermediate 161i) and lower 161c portions. 1 Referring to Figs..6, and ;8 ,it will'be noted that-the upper portion .1611: of thetubes, 161;connects. the upper chamber 159 of The outlet section 143 includes an outlet-header 153 ,and a juxtaposed associated header 154 vertically disg'pOSQd between the casing 136 and the rear wall .and spaced from inlet section v142.. .T-he headersj153 and 154 of the outlet section 143 are likewisepartitioned by means of ,diaphragms 155, .156 wherein-the diaphragm divides the outletheader 153-into upper and lower chamqbersl57, 158,'respectively, which-are substantially equal {and correspond inlength to,therespectivechambers 148 ;-and 149 of the. inlet header 144: and v the associated header 154 is divided into upper and lower chambers 159-160 ,substantiallysimilar to that of the *associatedhea'der .145 of the inlet section.

vA group of horizontallyextending verticallysta'cked hairpintubes 161 extending throughthe rear Wall 112 associate header :154 to the-upper portion of the upper chamber; 157 of the outlet header. .The intermediate pors,tion;161b:ofgtheitubes ccnnectsthe lower portion -of.,.the mpper chamber157 i in connnunicationwiththe upper portion f :the lower; chamber 160 of the associated, header .:1'5,4.:and Y the bottom-portion161's of the tubes connect the lower portion of the lowerchamberlfifiincommuni cation with the.lower chamber :158 of the outlet header .1153. Thus it will be noted that the steam flowsthrough .lthesuperheater outlet section 143 in a plurality of. passes .in alternating parallel and countersteam flow heat trans- :fcrrelationship relative to the gas flow through the convcction pass.

According to this form of theinvention, the superheater inlet section 142 ,and outlet section 143 are con- :nected in series by means of a plurality of horizontally =.extending, vertically stacked, nestedtpairs of U-shaped, -crossover tubes 162 which extend across the convect on gas pass, the U-tubes connecting the upper chamber 151 of the header 145 to the upper chamber 159 of the header 154. In addition to the functioning as cross-over tubes,

'the group of U-shaped tubes 162 also increase the amount z-available of heat absorption surfaces of the superheater. :It will be further noted that the vertically arranged tubes 1610f the outlet sectionarenested in pairs. .velocity of the superheat steam in the outletsection is increased thereby functioning as an aid to maintain lower Thus the tube temperatures in that portion of the superheater in which'the'higher steam temperatures are attained.

In the modified form of the zsuperheater relatively co'ol saturated steam is introduced into the inlet section JIM-which is disposed in the hot zone A of the convec- ;tion pass 117 through pipe 163. Flowing the steam back and'forthbetween the headers144 and 1 35 of the inlet section through-tubes 152 in alternate passes of parallel and counter flow heat transfer relationship, as indicated Tby the arrows, the'saturated steam is etiectiv ely superheated to an intermediate temperature.

ate superheat steam is. then directed into the outlet seclliOn 142 through thecross-over superheater tubes 162,

The intermedi- =whereby the steam is iinallysuperheatedto maximum :temperatures by passing the same through a series of :parallel and counter-fiow heat.transfenrelationship bef tween headers 153 and l54'through tubes "161, the latter being disposed: in the tcooler;-.-por.tio n .B'- -ofs. the -gas;;pat's.

' Thus, the ;.arrangement;1is such ;that the hottest esteam temperature is attained in that portion of the superheater disposed in :the coolest portion oof the gas t convection :5 apass, ithe zarrangement 'being such that maximum steam -itemperatures are attained while maintainingtubetem- ,iperatureubelow theinh'igh temperature corrosive limit. ,The zfinallyzsuperheated steam is then discharged through :pipe'16 4. l

As :hereinbefore, described,; two spaced water headers 1131 and 132 enable the superheatercavity to extend downwardly-amaximum-extent. In addition, the conustmctionturther enables 1the=superheater cavity .to be eprovidedewith-a hopper-like bottom 165having an open- .15.ing;166;-disposed-;between the. headers 131 and 132,.the

opening 1166 :being provided' withta'. suitable closure 167. .Thus, .withathiseconstruction, maintaining and cleaning eat .the :tubes is z-greatly :facilitated as hereinbefore .de- :scribed. 1

In both forms of the invention illustrated, it will be :n'oted;that?.the:.-superheater tubes:50, '56, 152, 161rand 1'62 :exten'd ,through: both the refractory front and rear walls. and; arexsupported. thereby, thus, greatly facilitating .andcsimplifyingathe fabrication .and supporting means of ,1125 c-theasuperheater tubes.

.The operation-of-..-the boiler I .:scribedis as?follows:

..The:stearn generatingunit is started up with only the main furnace burners in use. Thenheating gasesgener- :atedlbythe-"fuelz'burning inssuspension in the main fursnac'e flow {transversely-of fthe generating tube bank to ;-thegas:-ontlet :flue, passing .over the air heater and/or neconomizertubes ,before leaving the unit, the water -.cooled screen' tubes forming :an effective radiantheat shield between the main .furnace cavity and the superheater. tubes. When: sufficient steam: is flowing .through :the isuperheater. tubes, theuauxiliary furnace burn'ers are :startedup andare regulablyxoperated as tonumber' and firing :rate to control the :superheat steam temperatures. The heating gases generated in the auxiliary furnace :ehambers flow substantially'horizontally across'the rows of screen tubes and. superheater-tubes throughout .their {length due to the :gasflow: equalization space formed by the arrangement of the screen tubes throughoutits extent in space relation 'withI-thesuperheater tubes. This construction further facilitates efiective convection .:heating of 'the entire isuperheating surface.

According to this invention the hottest gasesgenerated in the auxiliary furnace cavity flow through the rows-of ' staggeredscreen'tubes 33, 134 and across the superheater tubes '50, 1'52, thelatter thus being disposed in the hot-test portion of the gas convection pass. Flowingthe steam in a plurality of passes that are in substantial parallel and counter flow heat transfer to the gas flowing over tubes50, 152 of the inlet section of the superheaL- efiectively superheats thestearn therein to an intermediate temperature whereby hot combustion gas temperatures in contact therewith are proportionately cooled. Thus the'tubes subjected to the hottest 'gases are in contact with relative low temperature steam.

The intermediate superheat steam is then directed to vthe outlet section of the superheater. The relatively cooler combustiongases flowing over sections 42, 142 are then brought into contact with the outlet section 43, 143 of'the superheater wherein the intermediate superheat steam flowing through the outlet section in a'plurality of passes of alternating counter and parallel 'flo'w heat transfer relative to the combustion gas flow becomes highly superheated therein. Thus, it Will be noted that 70 the tubes exposed to the higher steam temperature'are externallyin contact with the lowergas temperatures in the gas pass. Consequently the arrangement is such that the balance of relative temperatures attainablebetween the combustion gases, metal parts of the- -super- 75 heater 7 and steam in contact therewith enables the attainarrangements herein de- "ment of maximum temperature of superheat steam without exceeding safe operating superheater tube temperature. a

After leaving the superheater tubes, the gases flow across the upper portion of screen tubes 32, 133 and through the passage opening thereof to the extreme upper portion of the main furnace cavity. Theconfinement of the auxiliary furnace products of combustion to the extreme upper portion of the main furnace cavity avoids the introduction of relatively cold and inert gases into the main combustion zone of the main furnace cavity so that combustion is completed therein with little or no interference by the heating gases'of the auxiliary furnace. 'The gases are then passed across the upper end of the tube bank to the outlet flue within which they contact the economizer and/or air heater tubes. The contact of these gases with the bank of tubes and air heater or economizer tubes further reduces their temperaturesto the desired value, thereby increasing the efficiency of the unit.

The fuel supply to the burners in either of the cavities can be regulated either manually or automatically to maintain any desired superheat temperatures over a relatively wide range. The described constructions are particularly advantageous in providing a heating gas flow path from the auxiliary furnace chamber which follows the natural flow path of the gases without any substantial change of direction of the same; consequently the. pressure .drop throughout is extremely low. I

From the foregoing description it will be noted that the two furnace, single uptake type, marine boiler of the instant invention is provided with a superheater having more heat absorptionarea effectively disposed'in a gas convection pass which is divided into progressively decreasing temperature zones wherein steam is effectively superheated in stages from a saturated steam temperature to an intermediate superheat temperature in the hot zone and from said intermediate temperature to a high optimum superheat temperature in the cooler zone. This is accomplished by flowing the steam in each zone in a plurality of alternating parallel and counter-flow steam heat transfer relationship relative to the gas flow through the convection pass. Thus the heating of the relatively cool saturated steam to an intermediate superheat temperature in the hot zone and highly superheating the intermediately heated superheat steam in the cooler zone as described provides the attainment of maximum superheat steam while maintaining superheater tube temperatures within their high temperature corrosion limit.

Further, the arrangement is such that superheater cavity is bottomed by a pair of space water headers to provide for the formation of a hopper bottom having a centrally disposed opening to facilitate maintenance, hosing and cleaning of the superheater tubes. Also the nesting of the superheater tubes into relative small groups further aids in rendering each tube individually accessible for cleaning.

While the instant invention is disclosed herein with 'particular references to specific embodiments thereof, it is to be appreciated that the invention is not to be taken as limited to all of the details thereof, as modifications and variations thereof may be made without departing from the spirit or scope of the invention.

a What is claimed is:

1. In combination with a two furnace, single uptake, controlled superheat boiler, the improvement of a gas convection pass disposed between said furnaces, said pass having progressively decreasing gas temperature zones, asuperheater arrangement having a pluralityof sections serially connected and including a first section disposed in the hottest gas zone and each succeeding section being located in successive lower temperature zones of said gas pass, said sections each including a pluralityof heat aborbing superheater tubes extending transversely of its .respe tive temperature zone, means for introducing saturated steam into said first section and means for serially flowing steam through each of said sections successively in a steam flow that is in an alternating counter and parallel flow heat transfer relationship to the gas flow whereby said steam is superheated in each section to suecessive increasing superheat temperature until said steam is superheated to an optimum high temperature, said high temperatures being readily available while said tube temperatures are maintained within tolerable corrosive temperature limits.

2. The invention as defined in claim 1 wherein a said steam flow through said superheater in a plan section thereof is in both counter and parallel flow heat transfer relationship to said gas flow.

3. In combination with a two furnace, single uptake, controlled superheat boiler, the improvement of a gas convection pass disposed between said furnaces, said pass having progressively decreasing gas temperature zones, 'a superheater arrangement including a first section and a second section serially connected, each section being located in succeeding temperature zones of said gas pass, said sections each including a plurality of heat absorbing superheater tubes extending transversely across its respective temperature zone and means for serially flowing steam through each of said sections in a steam flow that is in an alternating counter and parallel flow heat transfer relationship to the gas flow whereby said steam is superheated in each section to successive increasing superheat temperature until said steam is superheated to an optimum high temperature, said high temperatures being readily available while said tube temperatures are maintained within tolerable corrosive temperature limits.

4. In combination with a twofurnace, single uptake, controlled superheat boiler, the improvement of a gas convection pass disposed between said furnaces, said pass having progressively decreasing gas temperature zones,

a superheater arrangement including a first section and a second section serially connected, each section being located in succeeding temperature zones of said gas pass, said sections each including a plurality of vertically disposed heat absorbing superheater tubes extending horizontally across its respective temperature zone and means for serially flowing steam through each of said sections in a steam flow that is in an alternating counter and parallel flow heat transfer relationship to the gas flow whereby said steam is superheated in each section to successive increasing superheat temperature until said steam is superheated to an optimum high temperature, said high temperatures being readily available while said tube temperatures are maintained within tolerable corrosive temperature limits.

5. In combination with a two furnace, single uptake, controlled superheat boiler, the improvement of a gas convection pass disposed between said furnaces, said pass having progressively decreasing gas temperature zones, a superheater arrangement including a first section, said first section having a plurality of heat absorbing superheater tubes extending transversely of said convection pass in the hottest zone thereof, means for serially flowing relative cool, saturated steam through said tubes in a plurality of passes in alternating counter and parallel flow heat transfer relationship to the gas flow whereby said steam is heated to an intermediate superheat temperature, a second section, means connecting said sections in series, said second section including a plurality of superheater tube members extending transversely of the convection pass in the next succeeding lower gas zone, and means for serially flowing said intermediately heated steams through said tube members in a plurality of passes in alternating counter and parallel fiow heat transfer relationships to the gas flow whereby said intermediate steam is superheated to an optimum high temperature whereby said high steam temperature is obtainable while superheater tube temperatures are kept within tolerable corrosive temperature limits.

:6. A;marine boiler consisting of -a-setting, tanwupper steam and water drum, a laterally offset lower, water drum, a bank of inclined steamgenerating-tubes connectinggsaid upper and lower drums, a pair of spaced water headers arranged below said upper drum, spaced groups of vertically arranged water tubes connecting the upper drum to each of saidlower pair of water jheader-s, said spaced groups oftubes forming therebetween a superheating cavity and said pair of spaced waterheaderscooperating to extend the superheater cavity to a maximum extent and toform ahopper bottom of said superheater .cavityto facilitate cleaning of the same, a main furnace chamber between said tube bank and said tube group, means for firing said mainfurnace, a multi-steam-flow csuperheater disposed in said superheating cavity and screened by said spaced group of water tubes for super- :heating steam to a relatively high temperature while maintaining said superheatertemperature below its high tternperature'corrosionlimit, an auxiliary furnacecham- ;ber laterally adjoining .theouter side'of'said supcrheater tubes, means for independently firing said auxiliary furnace chamber, a singleheating gas outlet flue at the outer side .of said tube bank and arranged to receive :all of .the heating gases flowing from both of .said furnace chambers, said flue beingso located that the heat- :ing gases from said auxiliary furnace chamber ,tend ;to how over saidsuperheater, through themain furnace tchamber and across said tube bank before entering --said;flue, said steam flow in said superheater being in alternating counter and parallel flow heat transfer relationship with respect to the -.ga ses flowing from said auxiliary furnace.

' 7. Theinvention as defined in claim 16 wherein the lower :half of said groups of vertically arranged tubes disposed between the :main furnace and said ,muti-pass :superheater are contiguous tangent touching tubes to :shield said superheater from'flame' radiation.

-8. A' marine boiler consisting of setting, auuppersteam and .water drum, a laterally offset lower water drum, 'a bank of inclined steam generating tubes connecting said upper and lower drums, a pair of space water headers .sarranged below said upper'drum, a spaced group of veritically arranged water tubes connecting the upper drum :to each'of said lower pair of :waterheaders, said spaced group of tubes'formingitherebetween a superheater cavity and said pair of spaced water headers'cooperating'toex- 'tend the superheater to a maximum extent andto form a hopper bottom for said superheater cavity to facilitate cleaning of the same, a main furnace chamberbetween saidtube'bank and said tube group, means for firing said :main furnace, a series multipass-superheater disposed in said superheating cavity and screened by said spaced group of water tubes, an auxiliary furnace chamber laterally adjoining the outer side of said'superheater'tubes, means for independently firing said auxiliary furnace chamber and a single heating gas outlet flue at the outer side of said tube bank and arranged to receive all of the heating gases flowing from both of said furnace chambers, said flue being so located that the heating gases from said auxiliary furnace chamber tendto flow over said superheater, through the main furnace chamber and across said tube tank before enteringsaidflue, said steam flow in said superheater being in alternating counter andpar- 'allel flow heat transfer relationship with respect to the gases flowing from said auxiliary furnace.

9. A marine boiler consisting of setting; an upper .steam and water drum; a laterally offset lower water drum; a bank of inclined steam generating tubes connectingsaid upper and lower drums; a pair of spaced water headers arranged below said upper drum; a spacedvgroup of vertically arranged water tubes connecting the upper drum to each of said lower pair of water headers, said spaced group of tubes forming therebetween a superheater cavity and said pair of spaced waterheaders' cooperating to form a hopper-bottornfor. said .superheater its cavity to facilitate cleaning the same; -a mainfurnae chamber between said tube bank and said tube group; :means for firing said main furnace; at superheatcrri cluding a pair of vertical, juxtapositioned headers, one of :said header-s having a diaphragm means dividing the same into a plurality of chambers and plurality of vertically stacked, horizontally extending U-shaped tubes :counecting chambers of said latter header ,to said other :header for establishing a criss-crossing steam flow path between said headers said U-shape tubes being disposed in said superheater cavity and screened by said spaced ;,g 0111) of water tubes; an auxiliary furnace chamber laterally adjoining the outer side of said superheater-tubes;

auxiliaryfurnace chamber tend to, flow over said super- ,heater in alternating parallel and counter flowheat transfer relationship to'the steam flow through said superheater, thence through the .mainfurnace chamber and .across-said tube bank before entering said flue.

10. A marine boiler comprising of a'setting having -a main furnace cavity; an auxiliary furnace cavity; a gas .convection pass associated with said auxiliary furnace :cavity and disposed between said furnace cavities, said convection pass including a hot gas zone and a relatively coolergas zone; means for independentlyfiring each of said furnace cavities; an upper stream and water drum;

,a-laterally offset lower water drum; a bank of inclined steam generating tubes connectingsaid upper and lower .drums; a pair of spaced water headers arrangedbelow said upper drum; a spaced group of vertically 7 arranged water tubes connecting the upper drum to each of said lower pair of water headers, said spac.ed group f tubes forming therebetween a superheater cavity, said pair of spaced water headers enabling said superheater cavity to ,be extended a maximum extent and said spaced water .headers cooperating to form a hopper-bottom for said .superheater cavity to facilitate cleaning of the same, said -mainfurna ce being disposed between saidtube bankand said tube group; a superheater including a-first section and asecond section, said'first section having a first pair ofvertically disposed headers consisting of an inlet header and, an associated header, said inlet header having a dia phragm means dividing the same into a plurality of chambers, a plurality'of 'U-shaped horizontally extending tubesconnecting said chambers of said inlet header withsaid associated header for-establishing a steam flow path between said first pair of headers having a portiou which is-generally in counter flow heat transfer relationshipto saidgas flow and a secondserially connected portion which is generally in a parallel heat transfer ,relationship to the gas flow, said U-shaped tubes being disposed in the hot zone of said superheater cavity whereby said ,steam flowing therethrough is superheated to an intermediate temperature; said second section including asecond pair of vertically disposed headers including an outlet header and an associated header, said outlet header having a diaphragm means dividing thetsame into a plurality of chambers, a plurality of U-shaped, horizontally extending tubes connecting said chambers of said outlet header to said associated header for establishinga steam ,-flow path between said second pair of headers having a portion which is generally in counter flow heat transfer relationship to said gas flow and a second serially consnectedportionwhich is generallyin a parallelheat trans- :fer relationship to the .gas flow, said latter U-shaped tubes being disposed in said cooler zone of said superheater cavity and a tube meansconnecting said'sections so that the steam flows from said first superheater section to said second section whereby the intermediate superheated steamse r tcdtinsai fi t-S c i i hly heated i '15 adjoining the hot zone of said superheater cavity so that the heating gases from said auxiliary furnace tend to flow relative to the steam flow in the superheater whereby said steam is superheated to a relatively high temperature while the superheater tube temperatures are maintained below their high temperature corrosion limit.

11. A marine boiler comprising of a setting having a main furnace cavity; an auxiliary furnace cavity; a gas convection pass associated with said auxiliary furnace cavity and disposed between said furnace cavities, said convection pass including a hot gas zone and a relatively cooler gas zone; means for independently firing each of said furnace cavities; an upper stream and water drum; a laterally oflset lower water drum; a bank of inclined steam generating tubes connecting said upper and lower drums; a pair of smaller spaced water headers arranged below said upper drum; a spaced group of vertically arranged water tubes connecting the upper drum to each of said lower pair of water headers, said spaced group of tubes forming therebetween a superheater cavity, said pair of spaced water headers enabling said superheater cavity to be extended to a maximum extent and said spaced water headers cooperating to form a hopperbottom for said superheater cavity to facilitate cleaning of the same, said main furnace being disposed between said tube bank and said tube group; a superheater includ- -inlet header having a diaphragm means dividing the same into an upper and lower chamber, a plurality of U-shaped horizontally extending tubes connecting said upper and lower chambers of said inlet header with said associated header for establishing a steam path flowing from the upper chamber of said inlet header to said associated header and thence from said' associated header to said lower chamber of said inlet header, said U-shaped tubes being disposed in the hot zone of said superheater cavity whereby said steam flowing therethrough is superheated to an intermediate temperature; said second section including a second'pair of vertically disposed headers including an outlet header and an associated header, said outlet header having a diaphragm means dividing the same into an upper and lower chamber, a plurality of U-shaped, horizontally extending tubes connecting said outlet header chambers to said associated header for establishing a steam path flowing from said lower chamber of said outlet header to said second associated header and thence from said latter associated header to said upper chamber ofsaid outlet header, said latter U-shaped tubes being disposed in said cooler zone of said superheater cavity, and a relatively large diameter connecting tube connecting said lower inlet header chamber to said lower outlet header chamber so that said intermediate superheated steam generated in said first section flows to said second section to be highly heated therein; said auxiliary furnace being disposed adjoining the hot zone of said superheater cavity so that the heating gases flowing therefrom is utilized to control the superheat of said steam.

12. A marine boiler comprising of a setting having a main furnace cavity; an auxiliary furnace cavity; a gas convection pass associated with said auxiliary furnace cavity and disposed between said furnace cavities, said convection pass including a hot gas zone and a cooler gas zone; means for independently firing each of said furnace cavities; an upper steam and water drum; a laterally offset lower water drum; a bank of inclined steam generating tubes connecting said upper and lower drums; a pair of smaller spaced water headers arranged below said'upper drum; a spaced group of vertically arranged water tubes connecting the upper drum to each of said lower pair of water headers, said spaced group of tubes forming therebetween a superheater cavity, said pair of spaced water headers enabling said superheater cavity to be extended 16 to.a maximum extent and said spaced water headers cooperating to form a hopper-bottom for said superheater cavity to facilitate cleaning of the same, said main furnace being disposed between said tube bank and said tube group; a superheater including a first section and a second section, said first section having a first pair of vertically disposed headers consisting of an inlet header and an associated header, said inlet header having a diaphragm means dividing the same into an upper and lower chamber, a plurality of U-shaped horizontally extending tubes connecting said upper and lower chambers of said inlet header with said associated header for establishing a steam path flowing from the upper chamber of said inlet header to said associated header in a counter flow heat transfer relationship to the gas flow and thence from said associated header to said lower chamber of said inlet header parallel flow heat transfer relationship 'to the gas flow, said U-shaped tubes being disposed in the hot zone of said superheater cavity whereby said steam flowing therethrough is superheated to an intermediate temperature, said second section including a second pair of vertically disposed headers'including an outlet header and an associated header, said outlet header having a diaphragm means dividing the same into an upper and lower chamber, a plurality of U-shaped, horizontally extending tubes connecting said outlet header chambers to said associated header for establishing a steam path flowing from said lower chamber of said outlet header to said second associated header that is generally in a counterflow heat transfer relationship to the gas flow and thence from said latter associated header to said upper chamber of said outlet header in a generally parallel flow heat transfer relationship to the gas flow, said latter U-shaped relative heating gas flow to steam flow is such that the steam is highly superheated while the superheater tube temperatures are maintained below their high temperature corrosion limit.-

13. A marine boiler consisting of a setting having a main furnace cavity; an auxiliary furnace cavity; a gas convection pass associated with said auxiliary cavity disposed between said furnace cavities, said convection pass including a hot gas zone and a relatively cooler gas zone; means for independently firing each of said furnace cavities; an upper steam and water drum; a laterally offset lower water drum; a bank of inclined steam generating tubes connecting said upper and lower drums; a pair of smaller spaced water headers arranged below said upper drum; a spaced group of vertically arranged water tubes connecting the upper drum to each of said lower said'tube group; a superheater including a first section and a second section, said first 'sectionlhaving a first pair of vertically disposed headers consisting of an inlet header and an associated header, said headers each having a diaphragm means dividing the same into a plurality; of chambers, a plurality of U-shaped horizontally extending tubes connecting the chambers of said headers for establishing portions having alternating parallel and counterflow'heat transfer steam flow paths between said first pair of headers, said U-shaped tubes being disposed in the hot zone of said superheater cavity whereby said steam is superheated therein to an intermediate, temperature, and a second pair of vertically disposed headers including an outlet header and anassociated header, said latter headers each having a diaphragm means dividing the same into a plurality of chambers, a plurality of U- shaped, horizontally extending tubes connecting the chambers of said last mentioned headers for establishing serially connected alternating parallel and counter flow heat transfer steam flow paths between said second pair of headers, said latter U-shaped tubes being disposed in said cooler zone of said superheater cavity, and a plurality of small diameter cross-over tube means connecting said first section to said second section for directingtsaid intermediate superheated steam flow from said first superheater section to said second section whereby said intermediate superheated steam is highly heated' in the latter section; said auxiliary furnace being disposed adjoining the hot zone of said superheater cavity so that the heating gases flowing therefrom are utilized to control the superheat temperatures of said steam.

14. The invention as defined in claim 13 wherein said small diameter cross-over tubes consist of a plurality of U-shape tubes horizontally disposed in the convection gas pass whereby said cross-over tubes function as additional superheating tubes.

15. A marine boiler comprising of a setting having a main furnace cavity; an auxiliary furnace cavity; a gas convection pass associated with said auxiliary furnace cavity and disposed between said furnace cavities, said convection pass including a hot gas zone and a relatively cooler gas zone; means for independently firing each of said furnace cavities; an upper steam and water drum; a laterally offset lower water drum; a bank of inclined steam generating tubes connecting said upper and lower drums; a pair of smaller spaced water headers arranged below said upper drum; a spaced group of vertically arranged water tubes connecting the upper drum to each of said lower pair of water headers, said spaced group of tubes forming therebetween a superheater cavity, said pair of spaced water headers enabling said superheater cavity to be extended to a maximum extent and said spaced water headers cooperating to form a hopperbottom for said superheater cavity to facilitate cleaning of the same, said main furnace being disposed between said tube bank and said tube group; a superheater including a first section and a second section, said first section having a first pair of juxtaposed vertically disposed headers consisting of an inlet header and an associated header, said headers each having a diaphragm means dividing the same into an upper and lower chamber, a plurality of U-shaped horizontally extending tubes connecting said upper and lower chambers of said headers for establishing a serially connected alternating parallel and counter flow heat transfer steam path relative to said gas flow, said steam flowing from the lower chamber of said inlet header to the lower chamber of said associated header, thence from said lower chamber of the associated header to said upper chamber of said inlet header and then from said upper chamber of inlet header to the upper chamber of said associated header, said U-shaped tubes being disposed in the hot zone of said superheater cavity whereby said steam 'fiowing therethrough is superheated to an intermediate temperature, said second section including a second pair of juxtaposed vertically disposed headers including an outlet header and an associated header, each of said second pair of headers having a diaphragm means dividing the same into upper and lower chambers, a plurality of U-shaped, horizontally extending tubes connecting the upper and lower chambers of said second pair of headers for establishing serially connected alternating parallel counter flow heat transfer steam path relative to said gas flow, said steam flowing from the upper chamber of said second mentioned associate header to the upper chamber of said outlet header,

thence fromsaid upper outlet header chamber to the lower chamber of said latter associated header and then from said latter lower chamber-to the lower chamber of said outlet header, said latter U-shaped tubes being disposed in said cooler zone of said superheater cavity, and a plurality of small diameter cross-over tubes connecting the upper chambers of the associated headers of each section, so that said intermediate heated steam generated in said first section flows to said second section -to be highly heated therein; said auxiliary furnace being disposed adjoining the hot zone of said superheater cavity so that the heating gases flowing therefrom is utilized to highly superheat said steam.

16. For usein a marine boiler having a limited predeterminate effective superheater heat absorption space in a gas, convection passhaving a hot zone and a relatively cooler. zone, the improvement of a superheater having maximum heat absorption surfaces adapted to be positioned in said limited effective heat absorption space comprising a first superheater section including a first pair of headers having a plurality of nested U-shaped tubes connecting said headers for directing a steam flow between said headers, said tubes extending across the hot zone of said space; means for controlling the direction and velocity of the steams flowing in said tubes between said headers whereby said steam is directed in alternating parallel and counter-flow heat transfer passes relative to the gas flow whereby said steam is superheated to an intermediate temperature; a second superheater section including a second pair of headers having a plurality of nested U-shaped tubes connecting the same for directing a steam flow therebetween, said latter mentioned U-shaped tubes being disposed in the cooler zone of said space; means controlling the direction and velocity of the steam flow through said tubes connecting said second pair of headers whereby said steam is directed in an alternating parallel and counter flow heat transfer steam flow relative to said gas flow and means connecting said first and second sections in series whereby the intermediate superheater steams generated in said first section is highly superheated in said second section while metal temperatures of the superheater parts are maintained below their high temperature corrosive limit, the velocity of the steam in the second section being greater than that in said first section to facilitate maintenance of tube temperatures in said second section.

:17. For use in a marine boiler having a limited predeterminate eflfective superheater heat absorption chamber in a gas convection pass, the improvement of a heat absorption chamber having adjacent progressively decreasing gas temperature zones, a superheater having maximum heat absorption surfaces adapted to be positioned in said limited effective heat absorption chamber comprising a first superheater section including a first pair of headers having a plurality of nested U-shaped tubes connecting said headers for directing steam flow between said headers, said tubes extending across the hottest portion of said chamber, means for controlling the direction and velocity of the steams flowing in said tubes between said pair of headers whereby said steam flows therebetween in alternating parallel and counterflow heat transfer passes relative to the gas flow for superheating the steam therein to an intermediate superheat temperature and a second superheater section including a second pair of headers having a plurality of nested U- shaped tubes connecting the same for directing a steam flow therebetween, said latter mentioned U-shaped tubes being disposed in a cooler portion of said chamber, means controlling the direction and velocity of the steam flow through said tubes connecting said second pair of headers whereby said steam is directed in an alternating parallel and counter-flow heat transfer relative to said gas flow and means connecting said first and second sections in series whereby the intermediate superheater steams generated in said first section are highly superheated in said section in a manner whereby metal temperatures of the superheaterparts are maintained below their high temperature corrosive limit, said velocity of the steam in the second section being greater than that in said first Section to facilitate maintenance of tube temperatures in said second section. I

l8. A marine boiler consisting of a setting, an upper steam and water drum disposed centrally of. said setting, a lower water drum disposed laterally of said'upper drum, a bank of inclined steam generating tubes connecting said upper drum and laterally disposed lower drum, a pair of transversely spaced water headers positioned below and parallel to said upper drum, means for bottom supporting said spaced water headers, transversely spaced groups of vertically arranged screen tubes connecting said spaced water headers to said upper drum and forming therebetween a vertically elongated superheater cavity, refractory means cooperating with said pair of spaced water headers to define a hopper bottom for said superheater cavity having its lowerend positioned between said spaced water headers, means forming an access opening for said hopper bottom between said spaced water headers, a main furnace chamber between said inclined tube bank and one of said groups of vertically arranged screen tubes, means for firing said main furnace, a steam superheater having a multiplicity of horizontally arranged tubes disposed in and extending substantially throughout the height of said superheater cavity between said groups of vertically arranged screen tubes, an auxiliary furnace chamber laterally adjoining the outer side of said superheater tubes, said spaced water headers being arranged at approximately the samelevel as the bottoms of said main and auxiliary furnace chambers, means for independently firing said auxiliary furnace chamber, and a single heating gas outlet flue at the outer side of said inclined tube bank and arranged so that all of the heating gases produced in the main furnace are discharged directly to the flue after flowing over said inclined tube bank and the heating gases from said auxiliary furnace chamber are discharged to said outlet flue only after flowing'over said superheater, through the main furnace chamber and across said inclined tube bank.

References Cited in the file of this patent UNITED STATES PATENTS 2,791,900 Banker July 2,

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