US2207497A - Fluid heat exchange apparatus - Google Patents

Description

y 9, 1940- D. H. N. MAYO 2,207,497

FLUID HEAT EXCHANGE APPARATUS Filed Jan. 17, 1936 5 Sheets-Sheet 1 INVENTOR. Dana Mayo ATTORNEY.

Jul)? 9, 1940- D. H; N. MAYO 2,207,497

FLUID HEAT EXCHANGE APPARATUS Filed Jan. 17, 1936 5 Sheets-Sheet 2 F55: 2 Fig: 3

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Dav/ 7a 9 N Md/a y 9, 1940- D. H. N. MAYO 2,207,497

FLUID HEAT EXCHANGE APPARATUS Filed Jan. 1'7, 1936 5 Sheets-Sheet 3 INVENTOR. Dana [MA Maya ATTORNEY.

y 9, 1940- D. H. N. MAYO 2,207,497

FLUID HEAT EXCHANGE APPARATUS Filed Jan. 17, 1936 s Sheets-Sheet 4 g 6 Fi 7 I 88 INVENTOR. Dana f/ M Mayo y 9, I940- D. H. N. MAYO ,4

FLUID HEAT EXCHANGE APPARATUS Filed Jan. 17, 1956 5 sh t s 5 U A F J v Super-heater J: 52 a 208 511 r11 6215- 206 5 4: Economizer f I: Q h 5 D X w ATTORNEY.

Patented July 9, 1940 UNITED STATE FLUID HEAT EXCHANGE APPARATUS Dana H. N. Mayo, Ridgewood, N. J., assignor to The Babcock & Wilcox Compa y, Newark, N. J., a corporation of New Jersey Application January 17, 19 6, Serial No. 59,483

use of the gases which may result when gases by-pass a superheater.

It is also an object of the invention to provide a steam boiler with improved means for preventing accumulations of slag upon the heating surfaces when a slag forming fuel is burned in the boiler furnape. 1

A further object of the'invention is toprovide a sectional header boiler having boiler slag screen tubes associated therewith in a novel manner, and fluid cooledfurnace walls so associated with the screen tubes that there may be relative movement between the furnace walls and the screen tubes without permitting the leakage of furnace gases outwardly or of air inwardly.

A further object of the invention is to provide a water tube steam boiler in which the economizer and superheater are located in separate gas passes through which furnace gases pass on the way to the stack, changes in boiler load, superheat variations, and draft losses being so correlated as to maintain an efiective control of superheat without loss of thermal efficiency.

Another object of the invention is to provide a steam boiler and superheater organization having a furnace so fired and so arranged with reference to the superheater and steam generating differing widely from side to side of the furnace while the gases are approaching two parallel g'as exit passages, as a means for controlling superheat. 40 A still further object of the invention is to provide a high capacity steam boiler with a multiple stage furnace, one stage'of which is adapted for molten slag removal and provided with a furnace slag screen between the furnace stages and a multiple first stage, all for the purpose of permitting a wide range of variation of boiler load while maintaining slag flow in the first stage and the freezing of slag particles in the second stage.

Other objects of the invention will appear as the accompanying description proceeds.

The invention will be described with reference to the accompanying drawings, in which:

Fig. 1 is a diagrammatic view in the nature of a vertical section taken on the line ll of Fig. 3,

section that it can deliver gases at temperatures showing a steam boiler constructed in accordance with the teachings of the invention.

Fig'. 2 is a view in the nature of a vertical section taken on the line 22 of Fig. 1.

Fig. 3 is a view in the nature of a vertical sec 6 tion taken on the line '33 of Fig. 1.

Fig. 4 is a view in the nature of a vertical section showing the gas seal construction between the top of the furnace water wall and the uptake headers of the boi1er..

Fig. 5 is a view similar to'Fig. 4, but showing a construction by which the downtake headers may be associated with the top of a water wall of the furnace. I

Fig. 6 is a view in the nature of a vertical section showing a modification of the structure shown in Fig. 4.

Fig. 7 is a view similar to Fig. 5, but illustrating the manner in which the slag screen tubes of Fig. 4 are'joined to the downtake headers and the mud drum. I

. Fig. 8 is a detailed view showing a modification v of the Fig. '7 structure.

Fig. 9 is a partial view in the nature of a vertical section illustrating the control over the absorption of heat radiantly transmitted to the fluid cooled walls above the furnace slag stream.

Fig. 10 is a view in the nature of a diagrammatlc plan illustrating the dual primary furnace with a partition separating its parts and the two part gas, exit'passage with a dividing partition extending at right angles to the furnace partition.

In a modern steam power plant such as would require the boiler illustrated in Fig. 1 of the drawings, very high steam pressures are used because of the increased thermal efficiency of the associated prime movers when operated with steam at such pressures, but very high steam temperatures are necessary for eflicient use of such high pres- 40 sures.

These temperatures are carried as near to the danger point for the metal, as is practically feasible, and it becomes important that the variations of these temperatures be kept 'withinvery close limits, and, especially, that the upper limit be not exceeded. To this end, the Fig. 1 boiler has two parallel gas passes l0 and I2 with the superheater M located in one of those passes and all of the furnace gases flowing through either or both of these gas passes. Furnace gases emerging from these passes discharge into agas outlet duct l6, and the proportion of the total weight of the furnace gases passing over the superheater may be controlled by the operation of one or both the regulators I8 and 20. These regulators are indicated as positioned at the outlets of the gas passes I and I2 and arranged in such a manner that adequate mixing of the gases in the duct I6 is promoted. As shown, the regulators I8 are mounted upon horizontal pivots, while the regulators 20 are mounted to swing on vertical pivots.

The furnace gases passing beyond the regulators proceed through the duct I6 and over the tubes of a first economizer section 22 to an air heater 24. The feed-water inlet for the economizer section 22 is shown at 26, and feed water proceeds from the economizer 22 through an outlet pipe 28 to a second economizer section 30 having its tubes positioned in the gas pass I2 and connected to the water space of the drum 32 by the feed water tubes 34.

Situated below the superheater I4 and the economizer 30 is a bank of inclined steam generating tubes 36. They are connected at their lower ends to downtake headers 38, and the latter are directly connected to the water space of the drum 32 by the downtake tubes 40. These downtake tubes extend along one side of the gas pass I0 and along the other side of this gas pass there is a wall including extensions of the steam generating tubes 42. They are directly connected to the header 44 which, in turn, is connected to the drum 32 by the tubes 46. Suspension rods 48 are connected as shown to the beam 50 to support the extensions of the tubes 42 and the wall 52 dividing the gas passes I0 and I2.

The upper ends of the steam generating tubes communicate with the sectional headers 54 from the upper ends of which the circulators 56 extend along the outer wall of the gas pass I2 and thence upwardly to the drum 32.

The lower tubes directly connecting the headers 54 to the headers 38 are boiler slag screen tubes and they are preferably arranged as clearly indicated in Figs. 4 and 5. As here indicated,- the tubes 60. extend from the inner faces of the headers 54 across the path of the furnace gases and parallel of the tubes of the bank 36. At their lower ends they are connected to the inclined lateral faces of the headers 38. The lowermost tubes 62 of the boiler slag screen are preferably expanded at their upper ends into the lower ends of the headers 54. They extend downwardly therefrom a certain distance and are then bent to extend in parallelism with the tubes of the bank 36 to a position near the lower ends of the headers 38. There they are bent so as to be normal to the lateral face of the cross header or mud drum 64. The latter is connected to the headers 38 by means of a number of short nipples 66. Other slag screen tubes 68 are connected to the headers 54 in the same manner as the tubes 62 and they extend downwardly from the headers 54 in single row alignment with the tubes 62. A short distance below the headers 54 the tubes 68 are bent as indicated in Fig. 4 so that they will be positioned above the tubes 62, as shown. At their lower ends they again come into single row alignment with the lower ends 62 and enter the cross header 64 at its side.

Modifications of the arrangement of elements shown in Figs. 4 and are indicated in Figs. 6, 7 and 8 of the drawings. In the latter figures, the uptake headers I0 are directly connected to the downtake headers I2 by the horizontally inclined steam generating tubes I4 and the boiler slag screen tubes I6 and I8 extend into the lower ends of the lower headers I0 in single row formation. At their lower ends, the tubes I6 communicate with the headers I2 along their lateral faces, but the tubes I8 communicate directly with the cross header 80 which is connected to the headers I2 by the nipples 82. In the modification shown in Fig. 8. the cross header 84 is of circular cross section, the arrangement of elements in this figure being otherwise the same as the arrangement of those indicated in Fig. '7.

The headers I0 are associated with a furnace wall by a gas seal construction which permits relative movement between the headers and the wall without allowing furnace gases to escape or air to enter the furnace. This construction includes a floating angle 86 having its vertical flange confined within a guideway 88 formed by the side walls of the headers I0 and the plate 90 welded to the headers. The horizontal flange of the angle 86 can move within a guideway 92 formed between the upper surfaces of the furnace wall blocks 94 and 96 and a plate 98 which may be fixed to the block 96. The blocks 94 and 96 together with the blocks I00 are secured to the furnace wall tubes I02 which may be connected by the headers I04 and suitable circulators into the boiler circulation.

Fig. 4 shows the uptake headers 54 and the upper ends of the boiler slag screen tubes 62 and 68 to be associated with a furnace wall in a manner similar to that indicated in Fig. 6. In Fig. 4, the furnace wall tubes I06 communicate at their upper ends with the header I08 suitably connected into a fluid circulation. The tubes I06 are arranged in wall formation and the spaces between them are closed by furnace blocks some of which are shown at H0 and H2. The upper surfaces of the blocks II2 are preferably horizontal. Above them is located a wear plate II4 which has a part of a bracket II6 spaced therefrom to form a guideway II 8 for the horizontal flange of the floating angle I20. This flange may have slots to receive the bolts I22 which are fixed to the blocks II2 to maintain the parts in their operative positions. Similarly, the vertical flange of the angle I moves within a guideway I24 formed by a wear plate I26 and another part of the bracket H6, and the vertical flange may be slotted to receive bolts I28 which are fixed to blocks I secured to the upper ends of the slag screen tubes 62 and 68, as shown.

The lower ends of the boiler slag screen tubes 62 and 68 may be protected by refractory faced blocks I32 and I34. These blocks are preferably clamped to the tubes at a position adjacent the side wall mud drum 64. The horizontal flange of the angle I36 is fixed to the mud drum 64 with its vertical flange vertically guided in a passageway formed by the wall blocks I38 and the tube brackets I40. The latter along with the blocks I38 and I42 are clamped to the wall tubes I44, and the latter may be connected by the header I 46 and suitable circulating tubes into a fluid circulation.

Figs. 7 and 8 show arrangements of elements somewhat similar to that shown in Fig. 5, but in the former, the headers 80 and 84 have depending bars I50 and I52 directly welded thereto. These bars in one case, contact with the wall blocks I54 and are movable along their outside surfaces to permit relative vertical movements between the mud drum and the wall tubes I56. In the other case, the bar or strip I 52 rests against the wall blocks I58. The latter are secured to tubes I60, connected through the drum I62 and suitable circulators, into a fluid circulation.

As indicated in Fig. 1 of the drawings, wall tubes I44 extend downwardly from the headers I46 along the furnace wall I62. They extend past the slag tap floor I64 to a position where they are connected to the lower header I66. This header is supported ona pedestal I68. Along the opposite furnace wall I'I0 the tubes I06 are similarly connected to a header I12 mounted upon a pedestal I14.

As shown in Figs. 2 and 3 of the drawings, there are two primary, or first stage combustion chambers I and I82 of a two stage furnace. They are separated by upright wall tubes I84 and I86 communicatingrespectively at their lower ends with headers I88 and I90 which may be connected by the fioor tubes I92 and I84 to headers I96 and I98. The tubes I84 have inclined extensions 200 which communicate with an upper header 202 and are arranged to form half of a furnace slag screen between the first stage furnace chamber I82 and the second stage furnace space which extends from the furnace slag screen upward to the boiler slag screen including tubes 62 and 68. The tubes I86 have similar slag screen extensions 20I. They communicate at their upper ends with the header 204, which like the header 202 may be appropriately connected into the fluid circulation. of the boiler.

As shown, each of the two first-stage chambers of the furnace at the bottom of the installation shown in Figs. 2 and 3 is fired by downshot burners 206 and 208. The fuel supplied by these burners may be pulverized coal, the combustion causing slag, particles to be carried in suspension by the furnace gases.

The burners 206 are capable of independent firing, and a number of them are located in row formation at the position indicated in Fig. 3. The burners 208 of Fig. 2 are similarly positioned in row formation, and similarly capable of independent firing. They receive their secondary air through a duct 2) which is similar to the duct 2 I2 at the opposite side of the boiler.

When the upper headers 2I4 and the lower I headers 2I6 are connected by the walltubes 2I8 as shown in Figs. 2 and 3, the burners 206 and 208 are arranged so as to be positioned along horizontally inclined portions of these tubes, and arranged to project the fuel into the furnace between the tubes.

The tubes 200 and 20I may be covered with refractory material so as-to constitute a high temperature furnace slag screen, and adjacent tubes in upper and lower rows may be so covered by refractory that the furnace gases leaving the combustion chambers I80 and I82 will be obliquely deflected as they enter the com-,

bustion space below the bank of steam generating tubes 36. This arrangement of the tubes 200 and 20I also serves to apportion the absorption of radiant heat by the fluid cooled sides of the walls of the second-stage furnace above the first stage furnaces, and to limit the extent to which radiant heat from the latter may reach the former. The first stage chamber is maintained as hot as possible and the second stage as cool as possible.

Referring particularly to Fig. 9 of the drawings, it will be seen that the furnace slag screen tubes 200 are positioned across the furnace in vertically spaced rows. These tubes are also partially, or wholly, covered with refractory bodies which are so arranged that they tend to form oblique passages, imposing limitations upon radiation from the primary furnace stage. These refractory bodies may be arranged as shown in Fig. 9, where the refractory bodies on'the upper tubes extend obliquely downward to positions adjacent other refractory bodies which extend obliquely upward from offset lower tubes. When the screen tubes indicated in Fig. 1 are arranged in this manner, there may be opposite inclinations of the radiant heatspassages between the tubes on opposite sides of the position indicated at B. As shown, these passages incline toward the left along the part of the screen BC and incline toward the right along that part of the screen BD. Thus, when the furnace wall DE is of much greater extent than the opposite wall portion CF, the major portion of the heat received radiantly from the combustion chamber G by the heat exchange surfaces beyond the screen will be received by the wall DE and the side wall portions adjacent thereto. This arrangement of elements in the screen also tends to maintain the gases approaching the boiler slag screen H at such a low temperature that there will be adequate chilling of the slag particles carried in suspension by the furnace gases. This will prevent excessive accumulations on the tubes of the boiler slag screen H and at times entirely prevent all slag adherence, in view of the cooperating features of the multiple stage fumace' and boiler slag screen.

Referring again to Figure 9 of the drawings, the oblique lines LE, RM, and TS indicate generally the direction of the passage of radiant heat through the furnace slag screen (consisting of the tubes 200) to the right-hand side of the sec and stage of the boiler and the tubes I I0. Obviously, not all of the radiant heat'will proceed aiong such lines, but these lines are indicatory of the control imposed upon the passage of.

radiant heat beyond the furnace slag .screen.

- The furnace slag screen passages through which the primary furnace stages radiate to the furnace Wall DE are distributed throughout the major portion BD of the furnace slag screen, as clearly indicated, and the passages throughout the smaller remaining portion BC of the slag screen are inclined oppositely so that radiant heat will pass along lines similar to the line KB.

Besides the radiant heat limitations above indicated it would be evident that the furnace slag screendistinctly limits the passage of radiant heat therethrough to the boiler slag screen H.

The boiler slag screen formed by the tubes 82 and 68 may be considered as a low temperature slag screen to supplement the cooling by gas radiation in the second stage furnace, and it will be noted that both the furnace slag screen and the boiler slag screen are arranged so that a high percentage of the furnace gases must contact with their tubes. They are arranged transversely of each other so as to produce what may be called a crossed grid, or sieve effect, In other words, the longitudinal axes of the tubes of the upper slag screen are in vertical planes which are transverse to the vertical planes in which the longitudinal axes of the tubes of the lower screen are positioned. This arrangement of the multiple stage furnace with the two sets of screen tubes not only effectively prevents accumulations of slag upon the steam generating tubes and upon the tubes of the heating surface above the bank of steam generating tubes, but it also promotes effective and thorough combustion, and a thorough mixing of the combustion products throughout the entire cross section of the furnace.

With the arrangement shown. there are two sets of burners on opposite sides of a multiple high temperature first stage furnace zone. These separate sets of burners deliver separate streams of furnace gases and other combustion products upward to a plurality of parallel gas passes above the boiler slag screen. In one of these gas passes, there is a superheater, and the wall separating these gas passes is so arranged that the furnace burners alone, or by both sets of burners operating simultaneously, but whatever the adjustment of all of the burners of either set may be. there may be the same'divislon of combustion products between the two gas passes in which the auxiliary heating surfaces are located.

By operating the burnersat one end of the row of one set, and at the end below the superheater gas pass differently from those burners at the other end of the row, the weight and temperature of the furnace gases entering the two passes may be varied. The superheat may be thus adjusted, and when the burners are thus operated in correlation with the action of the regulators "and 20, the control of superheat and the control of the weight of the gases passing through the different gas passes is exceedingly close.

It is important that the temperature in the first stage of the furnace be as high as possible, in the interest of good combustion, and for the purpose of insuring that slag will be maintained in a molten condition so that it will run freely. It is equally important that no molten slag be permitted to reach the upper heat exchange surfaces so as to freeze thereon as insulating deposits and gas flow obstructions. The furnace slag screen separating a high temperature first stage of .the furnace from the low temperature second stage contributes to this as does also a relatively larger volume of the second stage with its water cooled boundary walls. The division of the first stage of the furnace into a plurality of parts also contributes materially to advantageous functioning of the boiler at light loads. When the boiler load is reduced the furnace gets cooler and at some loads slag will cease to run. When during the operation of both parts of the first stage of the furnace, the furnace becomes excessively low in temperature, the burners for one part of the furnace may be turned off and the burners at the other side of the furnace may be turned up correspondingly. This action will preserve proper slag conditions for a much lower boiler load than would be possible without the multiple first stage.

It will be noted that the steam generating tubes in front of the parallel gas passes have a steep slope and that their ends enter sectional headers. This arrangement of elements adds more heating surface for a given tube spacing, and a given width of tube bank. It also increases the gas flow areas between the tubes and decreases gas velocity. Another result of the employment of such a steep tube bank is an increase of radiant heat absorption from the second stage space with a consequent cooling of the gases approaching the tube bank. with such an increase in'radisnt heat absorption. there is a decrease in convection heat absorption from the gases flowing over the steam generating tubes. 5 By reason of the increased absorption of radiant heat in the heating space above the bank of steam generating tubes and below the superheater, there is adequate cooling of the gases and consequent freezing of slag.

Such a steam generating installation as that indicated in Fig. 1 ofthe drawings may have a capacity of about 750,000 pounds steam per hour when a normal amount of fuel is being burned. The feed-water temperature to the economizer is is 325 and the heat release rate is 40,000 B. t. u. per cu. ft. per hour. The superheat is 910 and the steam pressure is 1275 lbs. per square inch.

Referring again to the superheater indicated in Fig. 1 of the drawings, it includes an inlet U header Ill communicating with the steam space of the drum through the tubes "2. The upper section of the superheater may be connected to an intermediate drum 2" which is connected by the coils 2" with the outlet header ill.

Referring to Figure 10 of the drawings the quadrilateral UVWX represents a cross-section of that part of the installation having the multiple first stage furnaces and the line CD represents the wall formed by the tubes I and I86 so of Figures 2 and 3. .This is the division wall between the first stage furnaces. The walls! is the partition separating the up passages in one of which the superheater is positioned and in the other of which the economizer is located. as The burners I" and 2|. are shown in their opposite row arrangements, and the rectangle AJNQ represents a cross-section of the installation at a position above the header I.

.ingacrossthepathoffurnacegasesandconnected into a steam boiler circulation, means for burning a slag forming fuel in the furnace so that the furnace gases carry slag particles in suspension, tubes extending across the path of furnace gases so as to form a high temperature furnace slag screen. means for connecting said tubes into the boiler circulation, and other parso allel tuba extending in a direction transversely related to the tubes of the furnace screen and positioned beyond the furnace screen so as to form a secondary combustion chamber beyond the furnace.

2. In a water tube steam boiler, means delineating a high temperature furnace zone in which slag forming fuel is burned, unequal opposite walls delineating a furnace zone of lower temperature, a furnace slag screen consisting of spaced tubes extending across the path of furnace gases between said cones, and a steeply inclined boiler slag screen at one side of said low temperature sone, spaced tubes of the furnace slag screen being so arranged in oblique rows and so provided with refractory coverings that the major part of the heat transmitted by radiation from the high temperature zone through the furnace screen is absorbed by the larger areas of furnace wall adjacent the higher end of the boiler slag screen. a

3. Ina water tube steam boiler; a furnace having a combustion chamber in which a slag forming fuel is burned; fiuid heat exchange tubes exposed to the furnace gases, and water cooled 7s forming a primary combustion chamber, means 'for burning a slag forming fuel in said chember, means forming a secondary. combustion chamber above the primary chamber, a high temperature fluid cooled slag screen between said chambers, high inclination steam generating tubes forming a low temperature slag screen above the secondary combustion chamber, and means for maintaining a pool of molten slag in the furnace below said screens, said high temperature screen being constructed and arranged to promote the maintenance of the upper screen at a relatively low temperature by minimizing the heat radiantly transmitted from the primary combustion chamber to the upper screen.

5. In fluid heat exchange apparatus, means forming a combustion chamber, means for buming a slag forming fuel in said chamber, a first set of tubes forming a relatively low inclination slag screen above the combustion chamber, a second set of tubes of relatively high inclination spaced substantially above the first set to forma low temperature slag screen, and means cooperating with said sets of tubes to enclose a secondary combustion-space above said chamber.

6. In a water tube steam boiler, a .furnace, tubes delineating a wall separating the furnace into a plurality of combustion chambers and having upwardly diverging extensions forming slag screens across-the outlets of the chambers, means for so burning a slag forming fuel in the furnace that the flames are directed toward said wall from opposite directions, walls forming a secondary combustion space above the slag screens, and low temperature slag screen tubes extending substantially parallel to the first mentioned wall above said space.

7. In fluid heat exchange apparatus means forming two gas passes arranged for. gas flow therethrough in parallel, a common flue communicating with the outlet of each pass, means forming fluid heat exchange surfaces in said flue,

' and a damper for each of said passes said dampr and ers being mounted to turn on angularly related axes at the outlets of the separate passes for mixing the gases in said flue.

8. In a steam boiler, means forming a lower water chamber, means forming an upper water chamber, inclined steam generating tubes directly connecting said chambers, spaced furnace wall tubes arranged as a part of a furnace wall with its upper end adjacent the upper water chamber, sealing means permitting relative horizontal and vertical movements 'of said wall and the upper chamber while preventing the escape of furnace gases therebetween, said means including a floating angle, a similar furnace wall adjacent the lower chamber, similar sealing means between the lower chamber e last named furnace wall, and means for b g fuel in the furnace.

In a water tube steam boiler, an uptake header construction at one side of a gas pass, a downtake header construction at the opposite id of the gas pass, steam generating tubes extending across the gas pass and directly connecting said constructions at their facingsides, a. mud drum extending across the bottom of the downstake header, and slag screen tubes par,-

allel to the generating tubes and connecting the bottom of the uptake header construction directly'to the mud drum, the portions of the slag screen tubes immediately adjacent the bottom surfaces of the uptake header being upright andconnected to the header bottom which is substantially normal to the axes of those portions of the tubes.

10. In a steam'boiler, a furnace, means for burning a slag forming fuel in the furnace, steam generating tubes, and a plurality of rows of tubes constituting separate fluid cooled slag screens extending across the path of the furnace gases forwardly of the generating tubes, said slag screens being spaced vertically with the tubes of one screen having their longitudinal axes transversely related to vertical planes in which the longitudinal axes of the tubes of the other screen are positioned.

11. In a steam boiler, a furnace, means for burning fuel in the furnace, a plurality of parallel gas passes receiving the furnace gases, a first economizer section in one of said passes, a superheater in another of said passes, a bank of steeply inclined steam generating tubes extending across the path of the furnace gases passing to said gas passes, means changing the proportioning of the flow of furnace gases between said passes under varying load conditions, the gas passes having such relative flow areas and theeconomizer and superheater surfaces being such that the furnace gases at the exits of the respective passes are of the same order of temperature at full load operation, an air heater receiving the gases from both of said passes, and a second economizer section interposed relative to the air heater and the exits of said passes and receiving all of the'furnace gases from said passes before the gases contact with the surfaces of the air heater.

12. In a steam boiler, a. furnace, meansfor burning fuel in the furnace, a, plurality of parallel gas passes receiving the furnace gases, a. first economizer section in one of said passes, a superheater in another of said passes, a bank of steeply inclined steam generating tubes extending across the path of the furnace gases passing to the entrances to said gas passes, means proportioning the 'flow of furnace gases between said passes to different degrees under different boiler load conditions, the gas passes having such relative flow areas and the economizer and superheater surfaces being such that the temperatures of the furnace gases at the exits of the respective passes are of the same order at full load operation, an air heater receiving the gases from both of 'said passes, and a second economizer section interposed relative to the air heater and the exits of said passes and receiving all of the furnace gases from said passes before the gases contact with'the surfaces of the air heater.

13. In a vapor generator, a furnace, uptake headers, downtake headers, a cross header beneath the downtake headers, a bank of inclined steam generating tubes directly connecting the uptake headers to the cross header and the downtake headers and extending across the path of gases passing from the furnace, a water wall including upright tubes defining a furnace wall adjacent the upper ends of the lower tubes of said bank, said lower tubes having their upper ends bent so as to extend upwardly alongside the wall tubes in a wall junction zone and into the lower end walls of the uptake headers, wall closure means supported and cooled by the wall tubes in said zone, similar means supported and cooled by the upwardly extending ends of the generating tubes in said zone, and a device between said means maintaining a gas-tight seal between the wall and the generating tubes while permltting relative movements between them.

14. In a vapor generator, a furnace, a bank of inclined steam generating tubes extending across the path of gases passing from the furnace, a water wall including up i ht tubes defining a furnace wall adjacent the upper ends of the lower tubes of said bank, said lower tubes having their upper ends bent so as to extend upwardly alongside the wall tubes in; a wall junction zone, wall closure means supported and cooled by the wall tubes in said zone, similar means supported and cooled by the upwardly extending ends of the generating tubes in said zone, and a device between said means maintaining a substantially gas-tight seal between the wall and the generating tubes while permitting relative movements between them.

15. In fluid heat exchange apparatus, a boiler setting, a furnace, tubes presenting heating surfaces exposed to the furnace gases, means for burning a slagging fuel in the furnace, and sets of spaced tubes extending transversely of each other and between different pairs of setting walls and forming a double slag screen in the nature of a crossed grid presented transversely of gas flow and extending over the entire gas flow area.

16. In a high pressure steam boiler installa: tion, wall tubes defining a primary furnace zone of high temperature, means for burning fuel in said zone, a large volume secondary furnace zone defined by fluid cooled surfaces absorbing a high degree of radiant heat, fluid cooled tubes forming a furnace screen extending across the path of the furnace gases as they flow upwardly from the primary zone to the scondary zone, means forming parallel gas passes extending upwardly from the secondary zone, inclined steam generating tubes extending across the path of the furnace gases beyond the secondary zone and at the inlets of said parallel gas passes, an economizer including spaced tubes extending across the path of furnace gases in one of said passes, a superheater including spaced tubes extending across the path of the furnace gases in the other of said passes, means regulating the relative quantities of furnace gases passing through the parallel passes to protect the superheater during starting up conditions and thereafter maintain a desired superheat over a wide range of boiler loads.

17. In fluid heat exchange apparatus, a high temperature furnace stage in which fuel is burned, fluid cooled walls of unequal extent defining a low temperature furnace zone in which the furnace gases are cooled by the transmission of radiant heat therefrom to said walls, a furnace which are directed toward the one of said walls having the greater area.

18. In fluid heat exchange apparatus, a furnace, said furnace including opposite fluid cooled walls of unequal extent, spaced vapor generating tubs extending across the path of furnace gases at 'a position beyond said walls. fuel burning means, and a furnace screen extending across the furnace at a position forwardly of unequal areas of said walls and forwardly of the-vapor generating tubes, said screen consisting of a plurality of spaced rows of tubes with the center planes of the tubes of said rows transversely arranged with reference to the center planes of the foremost of said steam generating tubes, the screen tubes of one of said rows being so arranged with reference to corresponding tubes of another of said rows that the radiant heat received by said opposite walls from that part of the furnace forwardly of the screen is so limited that the wall of greater extent and greater heat absorptive capacity receives the greater proportion of the total radiant heat.

19. In fluid heat exchange apparatus, wall tubes defining a plurality of slag tap furnaces with an interposed dividing wall, means for independently firing the furnaces with a slag forming fuel,

means forming a plurality of gas passes arranged in parallel and receiving furnace gases generated in either or both of the furnaces, a dividing wall separating said passes and arranged transversely of the dividing wall between said furnaces, spaced tubes constituting convection heating surfaces in said passes, and means controlling the heat exchange in one of said passes by regulating the amount of bypassing of that pass by the furnace gases proceeding through the other pass, the arrangement being such that, only one of the furnaces may be operated at low loads and yet furnace temperatures will be maintained at slag tap values and said control of heat exchange in one of said passes will be effected in the same manner as at high loads when all of the furnaces are oprated at slag tap temperatures.

20. In a vapor generator, a furnace, a bank of steam generating tubes extending across the path of gases passing from the furnace, a water wall including tubes defining a furnace wall adjacent the lower tubes of said bank, said lower tubes having portions bent so as to extend generating tubes in said zone, and a device between said means maintaining a substantially gas-tight seal between the wall and the generating tubes while permitting relative movements between them.

21. In fluid heat exchange apparatus, a furnace including an independently movable row of water tubes associated with adjoining furnace wall tubes, expansion joint and gas sealing means at the juncture of said row of tubes and said wall tubes, said row of tubes and wall tubes being arranged in parallelism at the zone of the seal, and the juncture of said wall tubes and said row of tubes being such that the direction of relative movement caused by expansion or contraction corresponds to the axis of the tubes in the sealing zone.

DANA H. N. MAYO.

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