US2201619A - Steam generator - Google Patents

Description

y 1940- w. D. LA Mom 2,201,619

STEAM GENERATOR Filed Nov. 23, 1933 2 Sheets-Sheet 1 INVENTOR Wall?! Dou Mala/7017 ATTORNE y 21, 1940- w. D. LA MONT 2,201,619

' smm GENERATOR Filed Nov. 23, 1933 2 Sheets-Sheet 2 INVENTOR War/fer fiou [as la onf ATTORNEY Patented May 21, 1940 UNITED STATE STEAM GENERATOR Walter Douglas La Mont, North Colebrook, Conn., assignor toW. D. La Mont Inc., Wilmington, Del., a corporation of Delaware Application November 23, 1933, Serial No. 699334 19 Claims.

This invention relates to high speed steam and power producing apparatus and high speed methods of operating the same.

It deals with supercharged steam boilers and high speed, light weight, power plants using such a boiler, especially a boiler burning fluid fuels, in which all fluids; namely, the fuel, the air (for supporting combustion), and the main working fluid in the tubes of the boiler, each flow at extremely high velocities in the performance of their several duties.

It further concerns the co-ordination at all speeds, of the velocities of all flowing fluids, to insure the maximum and constant evaporation of the main working fluid in a minimum period of time.

It is the object of my invention to provide a steam generator of comparatively small size for its output capacity embodying a combustion chamber with auxiliary passages associated therewith containing tubes conveying water and/or steam adapted to be traversed by the combustion gases with least hinderance to the passage of said gases and with least draft loss.

It is a further object of my invention to provide tubes in passages surrounding the combustion chamber spaced in such a manner that the proper resistance to gas flow is developed, along all points of its travel. The tubes in thepassages are also disposed to protect the walls of the boiler against excess heat efiects and to control the heat transfer relationships between the several types of tubes in the boiler.

Other objects and purposes will appear from the more detailed description of the invention following hereinafter taken in conjunction with the accompanying drawings wherein:

Figure 1- is a sectional view of my high speed steam boiler, and l V Figure 2 is a sectional view of a different embodiment of my high speed steam boiler showing an arrangement of the convection steam generator and fluid heater tubes which enables a more rapid flow of the combustion gases through the boiler.

I have found, with my supercharged light weight steam generator, that it is necessary to get as high a rate of heat transfer as possible from the convection heating surface, in order to use a minimum amount of surface in this part of the apparatus for reducing the gas temperature and thereby keep the weight of this surface to a minimum. V

The recent advance in design of supercharging air fans of high speed and emciency, small size and light weight delivering air at high pressure with low power loss makes possible very close spacing of the convection heating surface with use of very high gas velocities and complete disruption or upsetting of the gas in its travel over the convection heating surface. The critical condition of gas flow, can be reached and utilized to a degree heretofore impossible with the limited draft loss formerly available for use with steam generators. v

By using tapered gas passages in the steam generating apparatus, including the passages for air as well as for fuel gas, the high velocities initially used in said passages, may be maintained and even gradually increased or decreased, as desired, to obtain desired velocities with the changing volume and density of the gas as it is cooled or heated.

I streamline many of my fluid passage ways throughout the boiler structure, especially at the turns and at changes in direction-of the flow of gases, high velocity of gas flow can be maintained throughout the system with small draft loss at these points leaving the main draft loss available forhigh speed travel over the heating surfaces where such loss is more than repaid by the increased heat transfer rates obtained.

In streamlining the steam generator I use a smooth turn, where the combustion chamber inlet end casing 22!, meets the waterwall casing 220 to guide any gas flowing radially from the burner to the sides to turn said gases smoothly toward'the outlet end of the combustion chamber.

At the outlet end of the combustion chamber, 35 I use a circular bulbous nose 223, projecting toward the interior ofthe combustion chamber at the central portion of the bottom casing to spread and guide the high velocity gases toward the outer circumference of the combustion chamber 40 at this point; and where the gases are to be guided into the entrance of the convection heating surface. Y

The bulbous central portion 223, in the casing 222, is followed by a portion depressed 224, relative to the interior of the combustion chamber, and this portion in turn is followed by a smooth curved turning 224, of the casing 222, leading to the convection gas passage wall 231, so that radially from the central portion of the top casing to the circumference, the said casing 222, is first bulbous, then depressed, then curved, relative to theinterior of the combustion chamber, to guide the gases in a smooth streamlined flow from the center'of the combustion ch'amberl,

ber wall portion 224.

The convection heating passage I21, is tapered from the bottom of the steam generator toward the top, to obtain the proper high velocity for the heated gas as it changes in volume and density during the cooling of the gas by the convection generator tubing 52, as the heated gas flows from the bottom of the combustion chamber spirally upward toward the top of the tapered convection gas passage I21.

The top of the tapered convection gas passage I21, is curved making a circular burnt gas pas' sage I26, connecting the convection steam generator tapered passage I21, with the inlet end of the fluid heater tapered passage H5, the curve of circular gas passage I26, being streamlined to guide the gases smoothly into the fluid heater passage H5.

At the bottom of the convection gas passage H5, a row of small diameter air preheater tubes 65, are used, secured into the vertical outside casing 225, of the convection gas passage, with a close spacing of their openings. The outside casing 231, of the convection gas passage 'is streamlined, curving to guide the high velocity gases into the openings of the air preheater tubes 65.

The air preheater tubes 66, are also curved at the bottom ends, to guide the gases entering them, upward to their outlet.

Each air preheater tube 65, is tapered so that the proper gas velocity inside of it is obtained to meet the changing volume and density of the gas therein as it is cooled by the air travelling in the opposite direction at high velocity on the outside surface of said tube 65.

The tapered air preheater tubes 65, leave the bottom of the outer convection gas, fluid heater tapered passage, outer casing 225, at an angle to the vertical and spiral upwards close to said casing in a 'smooth spiral to guide the gases upward and the air downward.

At the bottom of the fluid heater circular passage H6, and outlet to the air preheater tubes,

the air preheater tubes 65, conveying the burnt gases are streamlined outward in a smooth curve to guide the gases into the stack gas passage. The stack gas passage outer casing 228, is streamlined with a smooth curve at the point where the gases from the air preheater tubes 65, enter said passage and said casing curves upward toward the stack. The inner and outer stack gas passage casings 221 and 228, forming two dome shaped pieces with the stack gases guided smoothly in its flow between them up to the stack opening I I8,.the two dome shaped pieces forming an expanding gas passage so as to decrease rather than to increase the velocity of the gases, nolonger needed, as they travel toward the central portion of the domes to turn up-into the stack- I The stack opening III, is in turn curved 229 where it meets the central part of the dome forming the stack gas casing 228, guiding the gases smoothly from this point to the atmosphere.

The stack 230, is venturi shaped as it leads to the atmosphere.

The airfrom the discharge lead of the supercharger fan' 5, enters the outside casing 236, of

' the circular air passage I20, tangentially of said passage at a central part.

This gives the air a centrifugal r whirling motion in the circular air'passage I26, leading to the air preheater tapered spiral air passages I H.

The whirling air now enters between the spiral air preheater tubes 65, and the outer casing of the tapered convection gas fluid heater passage H5, and the air preheater tapered air passage outer casing 232.

The outer casing 232, of the air preheater, and the outer casing 233, form the air passage I2I, for the air preheater in-which are placed the closely spaced spiral row of tapered air preheater tubes 65.

The curved portion of the bottom casing 222, of the combustion chamber, and convection gas passage H6, with the dome shaped outer casing 236, of the circular air passage and outer casing 232 of air passages I2I form a tapered smooth curved passage I20, for the air guiding it and increasing its velocity as-it whirls and begins entering the air preheater passage I2I, between the spiral air preheater tubes 66. I

The tapered ends of the, air preheater tubes 65, also assist to permit the air to enter between them with a minimum of draft loss.

The air travelling in the air preheater passage I2I. between the spiral air preheater tubes 66, is given a further whirling motion as it passes in a combination of spiral and cross flow motion past and between the tubes 66, downward into the circular air chamber I26, and then upward to circular air inlet to burner entrance I22, to the burner 2. l

The tangential lead 23I, from the supercharger fan to the dome like outer casing 236, of the circuiar air passage I26, is placed on that side of the dome casing 236, which will give the air a whirling motion in the same direction as the whirling motion imparted to the air by the spiral air preheater tubes 66.

The casings of the air preheater air passages I2l, form a tapered passage, so arranged, that the proper velocity of the air is obtained as it passes between the tapered air preheater tubes 65, in counterflow to the gases therein, proper allowance being made for the change in volume and density of the air as it is heated and the tapering of the air preheater tubes 66, and the decreased amount of surface present in each tapered tube 65, toward the outlet end compared to the inlet end per unit of length of each tube 66. V

Heated air leaves the air preheater passage III, with a whirling motion and is guided by the streamlined. burner housing 233, in a smooth curve into the curved burner throat wall 236 guiding the air entering the'burner 2.

The spiralled air preheater tubes 66, have the direction of their spiral arranged so that the whirling air travelling therefrom, to the curved guide vanes of the burner 2, will continue to whirl in the same direction as it enters and is directed by said vanes into the burner 2.

The spiralled superheater tubes 6|, and waterwalltubes 34, have the direction of their spirals arranged so that air whirling from the burner 2, will continue to whirl in the same direction with the gas formed as the gases traverup the combustion chamber Ill, among the spiralled waterwall tubes 36-, and superheater tubes 6|, to the combustion chamber outlet end wall 222.

The superheater tubes terminating at their outlets at disk 62A are provided with pressure drop devices 363. The inlet jimotion of the water walls 34 is at disk 62 adjacent to the distributor I the steam generating apparatus is removed by the eration of the steam by the convection gases and The spiralled convection steam generator tubes 52, in the convection gas passage I21, have the direction of their spirals opposite to that of the waterwall tubing 34, and the superheater tubing arranged so that when the combustion gases reach the combustion chamber outlet end wall 222, and turn upward travelling in a combination of cross flow and spiral flow among the spiralled convection steam generator tubes 52, the gases will continue to whirl in the same direction as they whirled in the combustion chamber I06, spiralled fluid heater tubes 53, in the tapered fluid heater passage 5, have the direction of their spirals arranged opposite to that of the convection steam generator tubes 52, so that the gases will continue to whirl in the same direction as they whirled in the convection steam gen erator tapered passage I21, the combustion chamber I06, the burner guide vanes of burner 2, the air preheater air passages I2l, and from the tangential air inlet passage H9, from the discharge of a supercharger fan.

I have found, that with supercharged combustion, initial temperature in the combustion zone can be attained of such degree, that a large part of all of the steam generation required for the steam generating apparatus can be obtained from the waterwall surface and by using my new type of properly protected superheating surface in said combustion chamber, as previously described, practically all of the superheat required can be obtained from said surface.

As a result, by using my new type of fluid heater, described herein, practically all of the heat of the convection gases can be utilized by said fluid heater down to the point where the remaining heat to be absorbed of said gases by airpreheater.

This results in a new type of steam generating apparatus, using waterwall steam generating surface and superheating surface mainly in the'combustion chamber, fluid heating surface in the con vection gas passage, the final heat of the gases being removed by air preheater heating surface.

This arrangement gives full advantage of the maximum heat heads available relative to the gases and fluids always in counterflow.

It eliminates the use of a large amount of superheating surface and convection steam generation surface in the convection gas passage (placed parallel with or in combination with the fluid heating surface), thereby allowing the fluid heater full benefit of its available heat head, resulting in a lower gas temperature, leaving said surface then would otherwise occur as the gases go to the air preheater.

I have found, that supercharged combustion makes possible the attainment of high initial temperatures entering the convection gas passages.

Streamlining of the steam generating apparatus, especially where the gases turn, or change direction, makes possible the use of high velocity of gases with a minimum of draft loss from turns or changes in direction of gases.

I have found that, with my high speed steam generators with supercharged combustion, a large amount of power can be produced from a small combustion chamber. High initial temperatures are produced in said combustion chamber sending gases of high initial temperature to the convection surfaces. To reduce the temperature of the convection gases, it is general practice to complete the superheating of the steam, the genthe preheating of the air by the convection gases. j

In order to keep my units in a compact form all convection surfaces must be grouped around my comparatively small combustion chamber. If cross flow is used or parallel flow on straight tubes, the length of gas travel available is very short without using many abrupt180 turns of the gas, with the gas travelling repeatedly back and forth on said surfaces. It is very desirable to obtain longer gas travel or a type of gas travel over the surface which-produces a more disruptive effect or upsetting of the gas than is obtained by present methods with cross flow or parallel flow.

I have also found that supercharged combustion makes possible the obtaining of high initial temperatures entering the convection gas passages. I

Streamlining of the steam generating apparatus, especially where the gases turn or change direction makes possible the use of high velocity of gases with a minimum of draft loss from turns or changes in the direction of gases.

New types of efficient supercharger air fans of small size and light weight make possible the use of draft loss to an unusual degree for obtaining high rates of heat transfer in the convention surfaces by allowing upsetting of the gas, disruption and attainment of the critical condition of flow of gas to an unusual degree.

As a result, the use of gas flow parallel to the tube surfaces in small tapered heat lanes and of flow and brought into more intimate and complete contact with the heat transferring surface than is possible with either cross flow or parallel flow for a given gas velocity and draft loss; thereby giving a higher rate of heat transfer to or from the convection gases than has been previously obtained.

I call the use of acombination of cross flow with parallel spiral flow; spiral cross flow.

The term spiral cross flow is meant to designate a flow of gases over a heating or cooling surface or surfaces, wherein the gas travels over said surface or surfaces in a mixed combination of motions, giving cross flow of the gases across the surfaces and parallel spiral flow along said surfaces.

I have found, if one or more spiral or coiled tubes are placed in a convection gas passage and both walls of said passage are brought close to said tubing throughout the length of the tubing, so that said tubing throughout its length .lies between said walls, and if the space between said tubing and said walls, for travel of the gas flow in cross travel over the tube surface, is so arranged relative to the space available, for travel of the gas parallel to the tubing in parallel spiral fiow of the gas along the spiral, that the gas in travelling in cross flow will meet with more resistanceor draft loss than will occur, if the gas travels in parallel spiral flow along the spiral in its travel in said convection gas passage resulting in a combination of motions on said tubing of cross flow past the tubing and parallel flow along the spiral of the tubing.

It is desirable, in order to obtain and maintain spiral cross flow, to have the velocities of the gases, such at all times, that they will always meet with more resistance to cross flow than to parallel flow, in their travel through the convection gas passage. The degree of resistance to cross flow can of course be can'ied to the point, where a spiral tube is tangent to both walls or a combination of spiral tubes, or tangent to each other and to the walls and only spiral flow can be obtained, but unless the confinement of the gases relative to cross flow compared to spiral flow is of real degree, giving greater resistance to cross flow than to parallel spiral flow, then the amount of spiral flow obtained will not be sufllcient in combination with the cross flow action to give real combinations of the two motions with its disruption and upsetting of the gases and real increase in heat transfer rate over corresponding, but separate use of cross flow or spiral flow.

I have found, that in order to obtain the maximum benefit from use of spiral cross flow the convection gas passage with the spiral tube or tubes in it should be tapered from the point where the gases enter the passage to the point of exit, said taper to be arranged to give the proper 'gas velocity and resistance to cross flow relative the gas as it travels through the spiral cross flow convection gas passage.

My preferred method is to make the resistance to cross flow of the gas greater than the resistance to spiral flow but I may use any degree of resistance of cross flow relative to spiral flow depending on the velocities of the gases and other features of any specific design.

It is intended that any design arranged to give a combination of cross flow and spiral flow of the gases in travelling through a heat transfer passage will come within the scope of this inven-.

tion.

Where the heat effects are very high the passage may be lined with tubing adjacent to each other eliminating the need of a close contact of the tubing with the metal walls and a carefully designed spacing apart of the tubing on these walls to meet the given heat load.

Where the heat effects are low and the spacing of the tubing merely a question of obtaining the maximum transfer results to the entire tube surface, metal-tapered passages may be used and the tubes. spaced only in reference to the heat transfer to the tube surface,

It is a general characteristic of my circumferential heat exchanging passages for such passages, to taper from a ring shapedinlet opening of wider width, to a ring shaped outlet opening to a narrower width, and where tubes or other heat exchange elements occupy such passages in spiral arrangement, the distance between such tubes (as they spiral in the wider circumferential portion of the passage to the narrower circumferential portion of the passage), is, in accordance with my invention, closer, the tubes are progressively more closely packed, or lay nearer to each other.

The reason for this more closely packed arran'gement of the tubes is, so that as the heat is withdrawn from the burnt gases, releasing their heat to the cooler walls of the tubes containing rapidly flowing boiler working fluids (or rapidly flowing air, if it is the intake air, receiving the heat, i. e., in the air preheater), the velocity of the flow of the heating gases is not slowed down, due to the diminishing volume and density of the hot gas on account of the removal of its heat, but that by diminishing the volume of the circumferential space and circumferential spiral space through which the gases flow, as those gases flow from a hotter zone to a cooler zone, the high velocity of the gases will be kept up, or maintained, this high velocity assisting materially in, and increasing the effectiveness and efliciency of, the heat transfer taking place between the hot burned gases and the working fluid or the air, on the other side of the walls receiving heat from said hot burned gases.

. I have also found, that in order to obtain the maximum benefit from spiral cross flow where multiple spiral or coiled tubes are used, the tubes should be distributed uniformly or nearly uniformly across the cross section of the gas passage dividing the heat lanes, so that unequal spaces are not left between tubes as the gas tends to travel in cross flow over said tubes, further since the space between a side wall and an adjacent tube makes a passage of less resistance to the gas in cross flow than a corresponding space between two tubes said space at the side walls should preferably be smaller 'than the space between tubes.

In my present invention, when I add the use of a convection steam generating gas passage I 21, with its convection steam generatingtubing 52, to the use of waterwall steam generating tubing 34, and superheating tubing Si, in combustion chamber I86, and fluid heater tubing 53, in tapered gas passage H5; I arrange for spiral cross flow of the gases in the convection steam generator tapered gas passage I21.

The convection steam generator gas passage I21, containing the convection steam generator tubing 52, is tapered with the passage decreasing in cross section as the gases pass through it from inlet to outlet said taper being arranged to give the proper velocity of the gas throughout its travel through the passage as the gas is cooled decreasing in volume and changing its density.

In my convection steam generator tapered passage l21, in some designs I use three tubes although any number of tubes may be,used to meet .the proper requirements for a given design.

. At the bottom of the steam generating apparatus these three tubes are arranged in a compact group parallel to each other and secured to a disc 63C. This disc with a hollow cone distributor 63B, is secured to the discharge lead from the boiler circulating pump, so that the circulating pump discharges directly into each convection generator tube 52,- as described for the fluid heater tubes 53. The three convection generator tubes 52, enter the bottom casing of the convection generator tapered gas passage I21, at a point between the circumference of the inner and outer casing where the three tubes coil in a spiral until they reach the top casing of the convection gas pas sage.

Since each tube 53, of the convection generatortubing is coiled on a different initial diameter it is not necessary to have the convection generator tubes enter the convection gas passage I21, at

i widely separated points, as described for the relative to the diameter of the waterwall casing,

220, that if the waterwall'casing 220, begins to l overheat it will expand and will contact with the convection steam generator tube 52, before the alloy metal of the waterwall casing 220, can reach a temperature to cause oxidization of the metal.

The inner coil of the convection steam generating tubing 52, is not adjacent to the waterwall casing 220, except when the waterwall casing goes to high heat and expands, because otherwise a considerable amount of the radiant heat received by the superheater tube would pass by conduction fromthe superheater tubing to the waterwall casing and from the waterwall casing to the convection generator tubes 52, thereby decreasing the amount of superheat received by the superheater.

Further it is desirable to have a passage between the convection gas passage walls and the convection generator tubes 52, to cause the gas in cross flow past the convection generator tubes 52, to completely encircle these tubes.

When the spirals of the convection generator tubes 52, reach the top of the tapered convection steam generator gas passage I21, they pass through this top casing in a manner similar to the way they enter the bottom casing.

In my present invention I have arranged for spiral cross flow in the convection gas passage containing my fluid heater and in the air preheater passage containing the air preheater tubes.

The convection gas passage I I5, containing the fluid heater tubing 53, is tapered with the passage decreasing in cross section as the gases pass through it from the top toward the bottom said taper being arranged to give the proper velocity of the gas throughout its travel through the passage as the gas is cooled decreasing in volume and changing its density.

In my fluid heater I use two small diameter moderate length tubes 53. At the bottom of the steam generating apparatus these two tubes are arranged in a compact group parallel to each other and secured to a disc 623. This disc with a hollow cone distributor 53A, is secured to the discharge lead from the feed pump, so that the feed pump discharges directly into each fluid heater tube, as previously described.

Since each tube 53, of the fluid heater is coiled on a different initial diameter it is not necessary to have the fluid heater tubes enter the con.- vection gas passage at four diametrically opposite points.

The tube of the lowest of the two spirals enters the convection gas passage first, followed closely by the tube forming the next higher spiral.

i The spiral of each fluid heater tube, except the inner spiral, is wound on a diameter which tapers, so that the coil forms the frustrum of a cone.

Each coil forms the frustrum of a cone, of different size so that when the two coils are together in the convection gas passage the tubing is distributed dividing the heat lanes in cross travel, as previously described.

The inner spiral is wound on a diameter so arranged relative to the diameter of the outer convection generator casing 231, that if the outer casing 231, begins to overheat it will expand and will contact with the fluid heater tube 53, before the alloy metal of the outer casing 231, can reach a temperature to cause oxidation of the metal.

The inner coil of the fluid heater is not adjacent to the outer casing 231, except when the outer casing 231, goes to high heat and expands.

Further it is desirable to have a passage between the convection gas passage walls and the inner and outer fluid heater tubes to cause the gas in cross flow to completely encircle these tubes.

When the spirals of the two fluid heater tubes reach the top of the convection gas passage H5,

they pass through this top casing in a manner similar to the way they enter the bottom casing, the top spiral inthis case turning upward first, followed closely by the lower spiral. The two tubes 53, are then led from the top casing to the water level cylinder, passing through stufiing boxes wherever they pass through a casing.

I claim:

l. Ina steam generator, a Wall forming an open ended combustion chamber, a burner at one end thereof and an end wall at the other end thereof spacedfrom the open end of said combustion chamber, a lateral wall outside of the wall of said combustion chamber arranged to define a passage on the outside of said combustion chamher, a lateral wall outside of said first lateral wall and arranged to define a second passage on the outside of said first passage, a rounded endwall bridgingthe two passages and spaced from said first lateral wall for guiding smoothly the combustion gases passing from said first passage to said second passage, and spirally coiled tubes conducting fluid media disposed in said combustion chamber and passages for extracting the heat from the combustion gases in the course of the passage thereof therethrough.

2. In a steam generator, a Wall forming an open ended combustion chamber, a burner at one end thereof and an end wall at the other end thereof spaced from the open end of said combus tion chamber, a lateral wall outside of the wall of said combustion chamber arranged to define a passage on the outside of said combustion chamber, a bulbous protuberance on said end wall centrally of said'combustion chamber for guiding the combustion gases from said chamber into said passage, a lateral wall outside of said first lateral wall and arranged to define a second passage on the outside of said first passage, a rounded end wall bridging the two passages and spaced from said first lateral wall for guiding smoothly the combustion gases passing from said first passage to said second passage, and spirally coiled tubes conducting fluid media disposed in said combustion chamber and passages for extracting the heat from the combustion gases in the course of the passage thereof therethrough. I

3. In a steam generator, a wall forming an open ended combustion chamber, a burner at one end thereof and an end wall at the other end thereof spaced from the open end of said combustion chamber, a lateral 'wall outside of the wall of said combustion chamber arranged to define a tapered annular passage on the outside of said combustion chamber decreasing in crosssection in the direction of gas flow, a bulbous protuberance on said end wall centrally of said combustion chamber for guiding the combustion gases from said chamber into said passage, a lateral wall outside of said first. lateral wall and arranged to define a second passage on the outside of said first'passage, arounded end wall bridging the two passages and spaced from said first lateral wall for guiding smoothly the combustion gases passing from said first passage to said second passage, and spirally coiled tubes conducting fluid media disposed in said combustion chamber and passages for extracting the heat from the combustion gases in the course of the passage thereof therethrough'.

4.-In a steam generator, a wall forming an open ended combustion chamber, a burner at one end thereof and an end wall at the other end thereof spaced from the open end of said combustion chamber, a lateral wall outside of the wall of said combustion chamber arranged to define a passage on the outside of said combustion chamber, a bulbous protuberance on said end wall centrally of said combustion chamber for guiding the combustion gases from said chamber'into said passage, a lateral wall outside of said first lateral wall and arranged to define a second tapered annular'passage on the outside of said first passage decreasing in cross-section in the direction of gas-flow, a rounded end wall bridging the two passages and spaced from said first lateral wall-for guiding smoothly the combustion gases passing from said first passage to said second passage, and spirally coiled tubes conducting fluid media disposed in said combustion chamber and passages for extracting the heat from the combustion gases in the course of the passage thereof therethrougli.

5. In a steam. generator, a wall forming an open ended combustion chamber, a burner at one end thereof and an end wall at the other. end thereof spaced from the open end of said combustion chamber, a lateral wall outside of the wall of said combustion chamber arranged to define a taperedannular passage on the outside of said combustion cha ber decreasing in cross-section in the direc ion of gas flow, a bulbous protuberance on said end wall centrally of said combustion chamber for guiding the combustion gases from said chamber into said passage, a lateral wall outside of said first lateral wall and. arranged to define a second tapered annular passage on the outside of said first passage decreasing in cross-section in the direction of gas flow,

a rounded end wall bridging the two passages and spaced from saidfirst lateral wall for guiding smoothly the combustion gases passing from said first passage to said second passage, and spirally coiled tubes conducting fluid media disposed in said combustion chamber and passages for ex-- tracting the heat from the combustion gases in thecourseof the passage thereof therethrough.

6. The combination set forth in claim 1 wherein said last mentioned spirally coiled tubes come prise a steamgenerating tube in said combustion chamber.

, 'z. The combination set forth in claim 1 wherein said'last mentioned spirally coiled tubes comprise steam generating and steam super heating tubes in said combustion chamber.

8. The combination. set forth in claim 1 wherein said last mentioned spirally coiled tubes oomprise a steam generating tube in said combustion chamber and a steam superheating tube between said steam generating tube and said combustion chamber wall shielded by said steam generating tube.

9. The combination set forth in claim 1 wherein said last mentioned spirally coiled tubes comprise a steam generating tube in said first passage.

10. The combination set forth in claim 1 whferein said last mentioned spirally coiled tubes comprise a feed-water preheater tube in said second passage.

11. The combination set forth in claim 1 wherein said last mentioned spirally coiled tubes comprise steam generating tubes in said first passage and feed-water preheater tubes in said second passage.

12. The combination set forth in claim 1 wherein said last mentioned spirally coiled tubes comprise a steam generating tube in said combustion chamber, a steam generating tube in said first passage and a feed-water preheater tube in said second passage.

13. The combination set forth in claim 1 wherein said last mentioned spirally coiled tubes comprise steam generating and steam superheating tubes in said combustion chamber, a steam generating tube in said first passage and a feedwater preheater tube in said second passage.

14. The combination set forth in claim 3 wherein said last mentioned spirally coiled tubes comprise a steam generating tube in said first passage having the walls thereof more closely packed as the tube advances toward the narrow end of the tapered passage.

15. The combination set forth in claim 4 wherein said last mentioned spirally coiled tubes comprise a feed-water preheater tube in said second passage having the coils thereof more closely packed as the tube advances toward the narrow end of the tapered passage.

16. The combination set forth in claim 1 wherein said last mentioned spirally coiled tubes wherein said last mentioned spirally coiled tubes.

comprise steam superheating tubesin said combustion chamber adjacent the wall thereof and tubes in said first passage normally spaced from said combustion chamber wall which are adapted to make contact therewith in response to the expansion of said combustion chamber wall on account of excessive heat eil'ects. 18. The combination set forth in claim 1 wherein a water wall tube lines the end wall of the combustion chamber.

19. The combination set, forth in claim 2 wherein a spirally coiled steam generating tube is disposed adjacent to the end wall and conforms to the bulbous protuberancetherein.

WJAL'I'lElH'. DOUGLAS LA MONT.

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