US2271643A - Fluid heat exchange apparatus - Google Patents

Description

Feb. 3, 1942. D. s. JACOBUS FLU ID HEAT EXCHANGE APPARATUS 4 Sheets-Sheet 2 Filed Jan. 21, 1958 INVENTOR. David SJacobufs Ba-K.

AT'II'ORNEY.

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FLUID HEAT EXCHANGE APPARATUS Filed Jan. 21, 1938 4 Sheets-Sheet 4 Figfc? INVENTOR.

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a vertical section.

Patented Feb. 3, 1942 FLUID HEAT EXCHANGE APPARATUS David S. Jacobus, Montclair, N. J., assignor to The Babcock & Wilcox Company,

Newark,

N. .L, a corporation of New Jersey 7 Application January 21, 1938, Serial No. 186,017 11 Claims. (01. 122-430) This invention relates to fluid heat exchange apparatus, and, in lone example, it is particularly concerned with improvements in water tube steam boilers.

One effective and widely used type of water tube steam boilers involves upright steam generating tubes arranged in one or more banks between upper and lower drums. Furnace gases pass over the tubes, and, to meet various conditions of service, the tube banks may be bafiied transversely or longitudinally. It is an object of my invention to provide such improvements in apparatus of this type that the requirements of modern high pressure and high temperature steam power plants may be effectively met. Such installations, in the interests of high efficiencies, operate at high superheats and, as the associated steam turbines are apt to be damaged by excessively wide variations in the steam temperatures, it is important that such variations be limited. Another object of my invention is to provide particular means for regulating and limiting such variations in superheated steam temperaturein this type of boiler.

For high superheated steam temperatures and especially with a high ratio of heat of superheat, to heat of steam generation (which is typical of high pressures for a given steam temperature), a relatively large superheater tube surface is necessary, but I avoid excessive superimprovements in arranged to provide for flow of the furnace gases transversely of the banks of tubes. The baflles also provide for the flow of gases through a superheater by-pass across parts of the tubes ad jacent the submerged water chamber.

, Fig. 2 is a'horizontal section, parts of which are taken at the different levels indicated bythe section line 2-2 of Fig; 1.

Fig. 3 is a transverse section on the plane indicated by the line 3-3 of Fig. 1. This view shows the arrangement of tubes at the entrance of the transverse superheater by-pass.

heater cost and obtain the desired high superheated steam temperature by locating the superheater in gas zones in which the temperatures are as high as possible consistent with the desired conditions of non-adherence of the particles of slag or ash suspended'in the furnace gases. I also provide means whereby a superheater is adequately screened from the radiant heat of the furnace, in the interests of avoiding tube damage due to overheating by such radiant heat.

I also provide an arrangement including a superheater which is unusually large with reference to the banks of water tubes which permit of any type of bafliing of the latter, and any detail of design of the former without interference or limitation of one on the other, and which permit of control of superheated steam temperature.

- Other objects of my invention will appear from thefollowing description which refers to accompanying drawings showing preferred embodiments of my invention.

In the drawings: Fig.1 is a diagrammatic view in the nature of This view illustrates a threedrum boiler with upright tubes and with baflies Fig. 4 is a transverse section taken on the plane indicated by the line 4-4 of Fig.1 and showing the arrangement of the tubes in the slag screen. Fig. 5 is a diagrammatic view in the'nature of a vertical section showing another embodiment of my invention.

Fig. 6 is a detail view of the arrangement of "superheater tube loops which may be used in the Fig. 5 embodiment to prevent excessive accumulations of ash or slag upon the superheater tubes first contacted by the furnace gases.

' Fig. '7 is a transverse section taken on the plane indicated by the line 1-1 of Fig. 6 and illustrating the spacing of superheater tubeswhereby the superheater slag screen is provided by the superheater tubes themselves.

Fig. 8 is a diagrammatic view in the nature of a vertical section showing an additional embodiment of my invention in which a superheater of the pendant type is used in conjunction with means providing for the control of superheat by increasing or decreasing the gas flow over apart of the superheater surface.

, In the drawings:

Fig. 1 illustrates a three-drum bent tube boiler in which the submerged drum lU'is connected to the upper drums l4 and l6by the spaced banks of tubes l8 and 20. A superheater 22'receives steam from the drum- I4 through the intermediacy of the saturated steam supply tubes 24 and the superheater inlet header 2B.

The superheater is contacted by hot gases from the furnace 30 which is shown as fired with pulverized coal by means of the burners 32 and.

Ash particles suspended in the furnacetgases as they leave the furnace are prevented from sticking to and excessively accumulating err-the tubes of the superheater and choking the same by reason of the effect of the slag screens 40 and 42 and the cooling effect of gases by gaseous radiationin the radiant heat absorption chamber 44.

Particles of ash in suspension in the furnace gases which may. have been so hot as to be sticky or molten at the furnace exit will have their temperature so lowered that they are no longer in such a sticky condition that they will adhere to and accumulate upon the superheater tubes.

The slag screen 40 at the furnace exit, which provides similar gas and ash particle cooling and also screening from the radiant heat of the furnace, is formed by widely spaced bent tubes which extend from the drum I to the header 46. This header discharges steam and water through the wall cooling tubes 48 into the drum I6. The tubes 48 and the header 46 are preferably suspended from steel work by means of the hangers 50.

An inner circulation circuit is formed by the drums, the banks of steam generating tubes I8 and 26, and the tubes of the slag screen 42. The latter includes the baffle defining tubes 52 and 54, and the risers 56. The tubes 52 and 54 are fanned out at their upper ends to have appropria'te gas flow area between them and appropriate slag screen spacing, and they are similarly fanned out at their lower ends at the entrance of the superheater by-p'ass 60. Between these two positions these tubes are in balile defining alignment, and the spaces between the tubes are closed by refractory material to form the gas directing baflle 62. This bafiie extends from the superheater Icy-pass to the gas outlet of the radiant heat absorption chamber 44, and the tubes defining the baffle may have superheater supports 64 welded thereto.

Furnace gases, after leaving the slag screen '40, normally pass from the gas radiation 'chamber 44 (which has water cooled walls) over the slag screen 42 and then downward over the tubes 'III of the superheater 22. Thereafter, they are caused to pass transversely of both banks of steam generating tubes I8 and through the first gas pass I2. The drawings show this gas pass to be defined at its upper side by a hori- 'zontal baffle I4 which contacts at its forward edge with an upright baffle I6 supported by the steam generating tubes 78 and 80 connecting the drum III to the drum I6. wall of the gas pass I2 is formed by the baffle 82 which extends rearwardly from the lower end of the baflle 62. This bafile also obviously forms the upper limit of the superheated by-pass 60.

In normal operation the furnace gases which have proceeded through the first gas pass I2, have their direction of flow reversed so that they return across the banks of tubes I8 and 26 through the second gas pass 84. The direction of the gas flow is again reversed around the forward end of the baffle 85 and between that baflle and the vertical baflle I6 previously referred to. Thereafter, the gases pass directly to the flue 96 in the third gas pass 88.

When the boiler load increases and the tendency of the superheat is to become too high, the regulator 92 at the outlet of the superheater by-pass is operated 'soas to permit a sufiicient share of the gases to pass directly through the superheater by-pass 60 to prevent rise of superheat, and then to the inlet of the second gas pass 84. The regulator 92 may be automatically controlled in response to superheated steam temperature Variations beyond desired values, and to this end, the operating arm 94 (see Fig. 2) may be appropriately connected with a temperature actuated control system suitable for the purpose.

Fig. 2 of the drawings shows the setting arrangement of the various parts of the Fig. 1 embodiment, including the front wall IOIL'the side The lower horizontal walls I62 and I64, and the rear wall I06 along the line of the tubes 48. This view also shows the relationship of the upper furnace wall header I08 to the other pressure parts. This header forms a part of a wall cooling system for the furnace 30, some of this system being illustrated in Fig. 1 as including the wall tubes III), the headers II2 and H4, and the tubes H6 and H8. The wall tubes H6 and H8 may be connected at their lower ends to similar headers which are appropriately connected into the boiler circulation. From the upper furnace wall headers I06 and I I2 suitable risers such as those shown at I20 may communicate with one of the upper boiler drums.

Fig. 3 of the drawings shows the slag screen arrangement of the tubes 54 and 52 with reference to the tubes of the bank 20, and Fig. 4 shows, in a similar manner, the relationships of the screen tubes 56 to the tubes of the furnace slag screen 40.

The looped tubes I0 of the superheater discharge superheated steam into a superheater outlet header I22 which is protected on two sides from the hot gases by the baffles I4 and I6. This header may be protected from the gases in the gas pass 84 by means of ceramic refractory ma terial I24. The header is preferably supported at its ends at the sides of the boiler setting.

Other details of the installation indicated in Fig. 1 of the drawings include the steam circulators I26 and I28 directly connecting the steam spaces of the drums I4 and It, the roof circulators I30 connecting the header I32 with the drum IS, the hangers I34 for supporting the header I32, and the similar hangers I 36 suspending the superheater inlet header 26 from suitable steelwork.

When the headers 26, 46, and I3 2 are supported as above indicated and the drums I4 and I6 are suspended from steelwork so as to leave the submerged drum 10 free to move vertically in response to changes in metal temperatures, the entire boiler system (excluding the furnace) is so constructed that wide temperature ranges will not set up excessive stresses. 7

It is to be noted that the embodiment of my invention above described includes banks of upright tubes associated witha furnace and a superheater in such a way that the furnace gases are free to flow from the furnace toward the superheater and the steam generating tubes at a position near the upper part of the setting. This association of elements is combined with a superheater by-pass in which the furnace gases fiow across the parts of the tubes of the upright banks which are adjacent the submerged water chamber.

In water tube boilers of this type having vertically disposed tube banks baffled to provide an elongated gas flow path to promote heat absorption by cooling the gases in the interest of efficiency, it is necessary to so locate the by-pass for gases around the superheater as to sufficiently cool these gases which are hotter than the gases that have passed over the superheater by so much as the superheater has reduced gas temperature. For this reason the bypassed gases must be led into the main gas stream at a point in their flow path suifi'cientl'y remote from the flue connection of the setting which is normally at the upper rear near an upper 'drum. To meet "this condition theby 'pass in Fig. 1 is adjacent the lower drum and its outlet adjacent contact with the superheater tubes in the uppass I80 immediately above the furnace slag the controller 92, atthe exit of the front water tube gas pass I2 of the main stream. I

Both the main gas stream 1n gas pass I and the bypassed gas stream in gas pass 60 have substantially the same length of path over water tubes, so the smaller quantity of bypassed gases may be cooled more than the larger quantity of main stream gases and so compensate for the cooling of the latter by the superheater, before the two streams mix beyond the controller 92.

- i There is also an advantage in contacting lower parts of the water tubes rather than the upper ends, because at the upper ends there is a maximum of steam in the tubes and locally intense heating'by hot gases at the top might cause them to become .dry and to overheat. In addition, the

gases in the space 44 above the slag screen 40 may nothave the same temperature throughout and if convection currents are set up thereby, the

cooler gases will be at the lower level from which drawings. The spacing of the superheater tubes,

and, especially those tubes which first contact with the furnace gases, is also a wide spacing.

One advantage of installing the superheater tubes on wide spacings is that opportunity is thereby provided to add superheater loops to provide additional surface for the superheater if desired at any time after the original installation is made. In general, it is also advantageous to use a comparatively wide spacing for the tubes of the superheater where, as in the present invention, the superheaterv is placed so as to be subjected to high temperature gases from the furnace. The tendency of the tubes to overheat or burn out is minimized, and there is much less chance of trouble on account of deposits of soot or slag externally of the superheater tubes. Such a superheater may give a more uniform superheat at different loads than a superheater with a closer tube spacing placed at a position farther from the furnace and thus subjected to the action of cooler gases.

The superheater I50 included in the Fig. 5 embodiment of my invention has horizontal tubes like that of Fig. 1 and is a self-draining superheater, but unlike that of Fig. 1, it has upflow I of gases instead of downflow, and in it I provide certain tube loops of greater width than the remaining loops. I, furthermore, position the wider loops in staggered arrangement so as to provide a superheater slag screen. This is particularly indicated in Figs. 6 and 7 of the drawings wherein the adjacent wide loops I52 and. I54 provide, respectively, the tube lengths I56 and IE8, on the one hand, and the tube lengths I60 and I62, on the other hand. Thus, there are two provisions which result in a wider spacing or slag screen arrangement of the superheater tube lengths which are first contacted by the furnace gases. One resides in the provision of the wider tube loops, and the other in the staggered arrangement of the wider loops. The narrower loops I10 may be considered as loops of standard width, providing the relatively narrow tube spacing indicated by the two rows of tubes I12 and I14 in Fig. 7 of the drawings,

r In the Fig. 5 embodiment, the furnace gases screen I82 which corresponds to the slag screen 40 of the Fig. 1 embodiment.

After passing across the superheater tubes, the gases turn and pass transversely of the upper ends of tubes connecting the upper middle drum I84 with the submerged drum I86. When the regulator I88 is in the dotted-line position, some of the gases do not contact with the superheater. They proceed through the superheater by-pass I90 defined by the tube supported baffles I92, I94,

and I96. A secondby-pass is shown between the endof baffle I96 and. the superheater, which may be closed partly or wholly by extending the end of baffle I96 as indicated in dotted lines, as a convenient means of adjusting superheat to meet different operating conditions such as a changein fuel, independently of control with variation of load.

Upon passing through the regulator port 200, the by-passed gases from pass I90 are directed transversely of the tubes in the second and third gas passes 202 and 204', respectively, joining the remainder of the furnace gases which have passed over the superheater and transversely of the upper ends of the tubes connecting the drum I84 with the drum I86. Thereafter, all of the furnace gases pass along the tubes 2I0 to the flue 2|2. The baflie 2I4, supported by and extending along the tubes 2I6 joining the drums I84 and I86 co-operates with the other baffles and the setting walls and boundaries to cause the described furnace gas flow.

In theFig. 5 embodiment, as in that of Fig. 1, the rear drum 2I6 is the steam off-take drum. It is connected by the steam circulators 2") to the superheater inlet header 220. The latter is preferably located out of contact with the furnace gases and at a position exteriorly of the furnace wall defined by the risers 222 which directly connect the header 224 with the front drum 226.

Steam circulators 228 connect the drums I84 and 226 and similar steam'circulators 230 afford direct communication between the drums I84 and 2I6. These circulators also form a convenient means for supporting the insulating material 232 whcih is a part of the roof of the setting. There are also water circulators supporting refractory which form top boundaries of the gas flow spaces.

Insofar as the furnace 240 of the Fig. 5 installation is concerned, it is within the purview of the invention that this furnace may be similar to that of the Fig. 1 embodiment, fired by pulverized fuel burners and provided with watercooled walls. Tubes of some of the latter are indicated at 242 and 244. They are connected to headers into such a system as that described with reference to Fig. 1. The upper water wall headers are shown at 246 and 248.

All of the pressure parts of the boiler indicated in Fig. 5 are suspended from the upper drums so as to avoid damage by stresses which might otherwise result from wide temperature construction indicated generally at 250.

are permitted by the expansion joint and seal construction includes the refractory elements 252 movable with the upright parts of the tubes of the slag screen I82 and the refractory elements 254 secured to and movable with the furnace wall defined by the tubes 244. These elements are preferably so related that they maintain a gastight juncture between the furnace and the boiler .while permitting the relative movements caused tubes 280 which are shown extending vertically downwardly from the drum I84. In this case, the local superheater supports are adequately cooled by reason of their good heat transfer relationship with the water cooled main support tubes, and danger of damage to the supports by overheating is eliminated.

The bafile supporting tubes 262 and the other tubes 264 extending through the superheater bypass [98 are curved away from the upper end of the superheater to provide the by-pass inlet 266. The extent of this inlet below the wide superheater loops 52 and I 54 determines the extent to which the gases may be by-passed through the fixed and the regulatable by-passes without coming into any substantial contact with the superheater loops.- At the lower ends of the tubes 262 and 264, there are forward bends so as to provide the space 210 for operation of the regulator I88.

In the embodiment of my invention indicated in Fig. 8 of the drawings, I provide longitudinally bafiied water tube banks like Fig. 5, but unlike Fig. l, I employ a superheater 300 with vertically arranged tube loops. These loops may be suspended from the inlet header 302 and the outlet header 384 which are supported upon the beam 306 extending from the front drum 308 to the middle drum 3l0. The superheater receives its steam through the saturated steam supply conduit 312 directly connecting the steam off-take drum 3 l 4 with the superheater inlet header 302.

The steam off-take drum is directly connected with the lower water chamber 3I6 by a bank of tubes 3 i8 extending through the third gas pass 320. This gas pass is separated from the second gas pass 322 by a bafiie 324 which extends from the steam off-take drum downwardly to a position spaced from and above the submerged drum 3l6.

In the second gas pass 322, tubes 326 directly connect the middle upper drum 3m with the drum 3l6. One side of this gas pass is formed by the bafiie 324 and the other side is defined by the battle 330 extending along the tubes 332. This bafile extends to the gas flow regulator 334 which controls the flow of furnace gases through the superheater by-pass 336. This by-pass is defined on one side by the baffle 330 and on the other side by the bafile 338 which extends along and is-supported by the tubes 340.

The baffle 338 terminatesat a position about mid-way the heightof the superheater and is This spaced from a transverse bafiie 342 which may have a portion 344 shown dotted extending substantially to the superheater and which, if not so extended, provides an 'adjustably fixed gas bypass. At the lower end of the controlled superheater by-pass 336, there is a transverse baflle section 346 which extends up to one side of the port or opening which is controlled by the regulator .334. This baffle section forms, in effect, an extension of the baffle 338, and a further extension is formed by the baflle section 350 which closes :the space between the section 346 and the drum 3!.6.

Slag screen tubes 350, 352, and 354 extend from the drum 316 across the furnace gas exit 356 to a position adjacent the upper end of the furnace water wall 360. Atthis position the slag screen tubes are 'bent intosingle row alignment so as to define a boiler setting wall 362. These tubes extend upwardly along this wall and are connected 'at their upper ends .to the/water space of the drum The boiler circulatory connections are completed by the water circulators 37.0 directly connecting the drums 308 and M0, similar circulators 312 connecting the drums 310 and 3, the steam circulators 314 between the drums 308 and 3|0, and the similar steam circulators 316 establishing direct communication between the drums 3|0 and'3l'4.

The furnace construction of the Fig. 8 embodiment may be similar to the furnace construction of'the embodiments previously described, including water walls which are exemplified in part by the wall 360 along which the wall tubes 380 extend to the upper water wall header 382. On the other side of the furnace, water wall tubes 384 extend downwardly from the drum 386 along the wall 388.

While my invention has been described with reference to certain particular embodiments which have been selected for the purposes of illustration, it is to be appreciated that the invention is not limited thereto. It is rather of the scope commensurate with the scope of the subjoined claims.

What is claimed is:

1. In a water tube' steam boiler, a plurality of upper drums, means forming a submerged lower chamber, banks of tubes connecting the drums with said chamber, a furnace, a superheater in front'o'f the bank of tubes connecting the for- --ward upper drum with said chamber and positioned-at a level intermediate the levels of the chamber and said forward drum, the furnace delivering hot gases to the space beneath the superheater, screen tubes extending across the path of furnace gases at a position between the furnaceand the superheater, means for connecting the screen tubes into boiler circulation, baffles forming two separate gas paths for the travel of the gases in parallel from a position forwardly 'of the-superheater to a position beyond the first bank of tubes, one of said gas pathsconstituting 'a superheater by-pass and leading from the gas space beneath the superheater over some of the watertube surface provided by 'said tubes, and a regulatorlocated rearwardlyof said tube surface and at the outlet of said by-pass.

2. The -method of maintaining substantially constantoutlettemperatures from a fluid heater having parallel paths for a heating fluid. which method comprises passing a fluid in enclosed streams and in heat exchange relationship with theheating fluid in oneof said paths-by causing.

the

heating fluid to pass transversely of said streams a plurality of times to generate a vapor in said one path, causing the generated vapor to pass to a superheating zone, passing the heating fluid in the other of said paths first in heat exchange relationship to the generated vapor in the superheating zone, and causing the heating fluid in said other path to pass once over or around said enclosed streams in the last mentioned path and then join that in the first path and pass therewith transversely of said enclosed streams a plurality of times.

3. In a multiple drum bent tube steam generator, a plurality of banks of upright steam generating tubes, a furnace the gases from which pass across said tubes, a superheater, baffle means between the superheater and the furnace to shield the superheater from the direct radiant heat of the furnace and cause the gases to pass transversely of the superheater tubes, gas pass wall members extending transversely of said tubes, one of said members co-operating with said baffle means to form a superheater by-p-ass in which part of the furnace gases are directed transversely of the tubes of said banks without contacting the superheater, and regulator means whereby desired proportions of furnace gases are caused to by-pass the superheater, said regulator means located rearwardly of said banks of tubes so that the furnace gases must pass across and be cooled by said tubes before contacting with the regulator, the furnace gases from the superheater and from the icy-pass joining rearwardly of said tubes and then passing transversely of the tubes again.

4. In a water tube steam boiler, upper steam and water chambers, means forming a submerged lower chamber, banks of tubes connecting the upper chambers with the lower chamber, a furnace, a superheater in front of the tubes connecting the lower chamber with an upper chamber and positioned at a level intermediate the levels of the upper and lower chambers, the furnace delivering hot gases to the space beneath the superheater, screen tubes extending across the path of furnace gases at a position between the furnace and the superheater, means for connecting the screen tubes into boiler circulation, bafiies forming two separate gas paths for the travel of the gases in parallel from a position adjacent the superheater to a position beyond the first bank of tubes, one of said gas paths provided by a superheater by-pass' and leading from the gas space adjacent the superheater over some of the water tube surface provided by said. tubes and to a position beyond the superheater,

, and a regulator located rearwardly of said tube surface and at the outlet of said by-pass.

5. In a water tube steam boiler, a plurality of of upper drums, means forming a submerged lower chamber, banks of upright tubes connecting the drums with said chamber, a furnace, a superheater in front of the bank of tubes connecting the forward upper drum with said chamber and positioned at a level intermediate the levels of the chamber and said forward drum, the furnace delivering hot gases to the space beneath the superheater, screen tubes extending across the path of furnace gases at a position between the furnace and the superheater, means for connecting the screen tubes into boiler circulation, baffies forming two separate gas paths for the travel of the gases in parallel from a position adjacent the superheater to a position beyond the first bank of tubes, one of said gas paths constituting a superheater by-pass leading-from the gas space adjacent the superheater over the lower portions only of some of the water tube surface provided by said tubes, and a regulator located rearwardly of said tube surface and at the outlet of said by-pass.

6. In a water tube steam boiler, a plurality of upper drums, means forming a submerged lower chamber, banks of tubes connecting the" drums with said chamber, a, furnace, a superheaterin front-of the bank of tubes connecting the forward upper drum with said chamber and p'osi-fi tioned at a level intermediate the levels of the chamber and said forward drum, the furnace delivering hot gases to the space beneath the superheater, screen tubes extending across the path of furnace gases at a position between the furnace and the superheater, means for connecting thescreen tubes into boiler circulation, baffles forming two separate gas paths for the travel of the gases in parallel from'a' position adjacent the superheater to a position beyond the first bankof tubes, one of said gas paths constituting a superheater lay-pass and leading from the gas space adjacent the superheater over some of the water tube surface provided by said tubes, and a regulator located rearwardly of all of said banks of tubes and at the outlet of said by-pass.

7. In a water tube steam boiler, a plurality of upper drums, means forming a submerged lower chamber, banks of tubes connecting the drums with said chamber, a furnace, a superheater in front of the bank of tubes connecting the forward upper drum with said chamber and positioned at a level intermediate the levels of the chamber and said forward drum, the furnace delivering hot gases to the space beneath the superheater, screen tubes extending across the path of furnace gases at a position between the furnace and the superheater, means for connecting the screen tubes into boiler circulation, bafiies forming two separate gas paths for the travel of the gases in parallel from a position adjacent the superheater to a position beyond the first bank of tubes, One of said gas paths constituting a superheater by-pass and leading from the gas space adjacent the superheater over some of the water tube surface provided by said tubes, and a regulator located rearwardly of all of said banks of tubes and at the outlet of said by-pass.

8. In fluid heat exchange apparatus, a furnace, a vapor generating section including spaced upright tubes subjected externally to the transverse fiow of the furnace gases, a superheater receiving the vapor generated by said section, means including a plurality of baffles transversely related to said tubes and causing the furnace gases to pass transversely over the tubes in a plurality of serially connected passes, said superheater being so disposed relatively to the furnace and said tubes that the furnace gases must pass in effective heat transfer relation to the superheater before they can proceed through all of said passes and over the tubes, said means also forming a superheater by-pass across said tubes at a position below said passes, and a regulator so controlling the gas flow through the by-pass that the superheat is maintained at a substantially constant value while boiler load changes.

9. In a superheater and steam generator installation, a furnace, upwardly extending steam generating tubes subject externally to the heat of the furnace gases, means connecting the lower or inlet ends of said tubes and including a water chamber, means in communication with the up- .per ends of said tubes and including a steam and waterseparator, downcomers connecting said means to complete a circulation circuit, tubes connected into the steam generator circulation and forming a radiant heat screen across the path of the gases at a position operati-Vely between the furnace and the superheater, a superheater including spaced tubes disposed across the path of the furnace gases at a position ahead of some of said tubes, bafiles separating gas passes arranged in parallel for the passage of gases from a position ahead of the superheater (with respect to gas flow) to a position beyond at least some of said steam generating tubes, one of said gas passes constituting a superheater by-pass and arranged to include only the lower parts of some of the steam generating tubes adjacent the lower chamber, said by-pass causing some of the furnace gases to by-pass the entire superheater, and a gas flow regulator disposed across one of said passes and arranged to be contacted by the gases only after the latter have been cooled by some of said tubes, parts of some of said tubes being disposed at a position beyond the outlets of both of said gas passes and being arranged to cool and mix the gases received from said passes.

10. In a water tube steam boiler, upper drums, a lower drum, spaced banks of tubes connecting the lower drum to the upper drums, a furnace, a superheater, bafiies forming two separate gas paths for the travel of the furnace gases in parallel from a position forwardly of the superheater to a position beyond the first bank of tubes, one of said gas paths constituting a superheater bypass leading from the gas space beneath the superheater and across said banks of tubes at a position adjacent the lower drum, and a gas flow regulator located rearwardly of the superheater and in the outlet of said by-pass and operating to control the amount of bypassing gases, the superheater bypass confining the bypassing gases to contact the lower parts of the tubes of said banks adjacent the lower drum.

11. In a water tube steam boiler, upper and lower drums, a furnace, spaced banks of upright steam generating tubes extending across the path of the furnace gases with each bank connecting an upper drum to a lower drum, a, superheater, bafiiemeans so associated with said banks of tubes as to form two gas passes leading from the furnace to a common outlet position rearwardly of two of said banks of tubes, the superheater being disposed in one of said passes and the other of said passes constituting a superheater bypass, a gas flow regulator damper positioned rearwardly of two of said banks of tubes and so disposed with reference to the outlets of said gas passes that its movements may simultaneously and conversely afiect and control the gas flow through the separate passes, means for moving said regulator toward or away from the closing position for one of said gas passes and thereby conversely regulating the flow of gases through the other gas pass.

DAVID S. JACOBUS.

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