US3107656A

US3107656A - Boilers having a combustion chamber encircled with water tubes

Info

Publication number: US3107656A
Application number: US77987A
Authority: US
Inventors: Raymond F Mcneal
Original assignee: CHICAGO DOWNDRAFT FURNACE CO
Current assignee: CHICAGO DOWNDRAFT FURNACE CO
Priority date: 1960-12-23
Filing date: 1960-12-23
Publication date: 1963-10-22
Anticipated expiration: 1980-10-22

Description

Oct. 22, 1963 s R, F, MCNEAL 3,107,656

BOILERS HAVING COMBUSTION CHAMBER ENCIRCLED WITH WATER TUBES Filed Dec. 23, 1960 4 sheets-sheet 1 INVENTOR. J) R) N Ra /ma ia f: life/V04! Oct. 22, 1963 R. F. M NEAL 3,107,656

BOILERS HAVING A COMBUSTION CHAMBER ENCIRCLED WITH WATER TUBES Filed Dec. 23, 1960 4 Sheets-Sheet 2 /2z&

I l a l I I I I I I 3 1/ I I l I I I, I I l I i l 33 33 K 204 \L w L I l I IN V EN TOR. I Pay/wand I: Me li/ezzl 1 BY $5 W W Oct. 22, 1963 R. F. M NEAL 7 3,107,656

BOILERS HAVING A COMBUSTION CHAMBER ENCIRCLED WITH WATER TUBES Filed Dec. 23, 1960 4' Sheets-Sheet 3 1 MA] I INVENTOR. Egan/2d fT/ll-Vl eal A TTOR YS Oct. 22, 1963 R. F. M NEAL 3,107,656

BOILERS HAVING A COMBUSTION CHAMBER ENCIRCLED WITH WATER TUBES Filed Dec. 23, 1960 4 Sheets-Shet 4 1 a i I g I i I INVENTOR. Paywaxm 5 4/ 4 9 ATT RNE-YS 3,107,656 BOILERS HAVING A CGMBUSTION CHAMBER ENCIRCLED WITH WATER TUBES Raymond F. McNeal, Chicago, 111., assignor to Chicago Downdraft Furnace 60., Chicago, 111., a corporation of Illinois Filed Dec. 23, 19%, Ser. No. 77,987 16 Claims. (Cl. 122-436) This invention relates to the construction of boilers and, more particularly, concerns the construction of a greatly improved high efiiciency type boiler employing a water tube construction.

As those familiar with the art of boiler construction are aware, a most important problem facing the boiler industry in the construction of relatively small sized boilers of large heating capacity. In my prior United States Letters Patent No. 2,891,520 dated June 23, 1959, 1 have disclosed a substantially improved furnace construction particularly adapted to substantially increase the efficiency of presently existing boilers. The principles of oil burner fuel ignition and control described and claimed in my earier patent also have great importance in originally designed furnaces. While the specific furnace construction illustrated in my above-noted prior patent may, of course, be incorporated in an original furnace design, I have found that a very material improvement may be achieved in constructing original equipment furnaces in accordance with the principles of the invention hereinafter set forth.

In accordance with the present invention, I provide a furnace having a generally longitudinally extending combustion chamber having a surface facing the combustion gases comprised of spaced water tubes separated by refractory or other material preventing the flow of combustion gases laterally between the water tubes. More specifically, the combustion chamber preferably comprises a relatively elongated tubular chamber having encircling water tubes each lying in a plane generally transverse to the fiow of combustion gases and each opening downwardly into a lower longitudinally extending header and upwardly into individual vertical risers extending into a water chamber. The material positioned between adjacent encircling tubes is arranged to cover only the area between the tubes and leaves the encircling tubes substantially completely uncovered in the combustion chamber area and also uncovered throughout a substantial area on the outside of the combustion chamber. This uncovered outside area is placed in direct contact with the flue gases leaving the combustion chamber prior to the entry of the flue gases into several boiler passes, for example, of fire tubes passing through the above-mentioned water chamber. By providing dual contact of the combustion gases with the encircling water tubes, a substantial increase in heat transfer efliciency is provided in the boiler of the present invention. As a result, a smaller boiler is capable of providing capacity achieved only through substantially larger boilers in the prior art installations or, similarly, boilers of prior art over-all dimensions are capable 'of substantially greater output.

It is, accordingly, an object of the present invention to provide a new and improved boiler construction.

Another object of the invention is to provide a combined Water tube-fire tube boiler construction.

Still a further object of the invention is to provide an improved boiler having an increased number of efiicient flue gas passes and, accordingly, improved heat transfer efliciency.

A feature of the invention resides in the provision of a generally elongated combustion chamber having a plurality of spaced encircling water tubes having a substantial portion thereof subject also to contact with flue gases after said gases leave the internal combustion chamber.

Still a further object of the invention is to provide a simple and extremely inexpensive refuse incinerator.

Yet a further feature of the invention is the provision of a refuse chamber positioned generally at the end of the combustion chamber removed from the fuel inlet and baifled therefrom by means of a flue gas deflecting bafi'le.

Still other and further objects and features of the present invention will at once be apparent to those skilled in the art from a consideration of the attached drawings wherein several preferred embodiments of the present invention are shown by way of illustration only, and wherein:

FIGURE 1 is a side elevational view in cross-section of a boiler constructed in accordance with the principles of the present invention;

FIGURE 2 is a cross-sectional view taken along the line II--II of FIGURE 3 and more fully illustrating the internal construction of the boiler;

FIGURE 3 is a fragmental view illustrating a modified form of the invention illustrated and described herein;

FIGURE 4 is a side-elevational view of a modified form of theinvention; and

FIGURE 5 is a orossisectional view taken along the line VV of FIGURE 4.

As shown on the drawings:

As may be seen from a consideration of FIGURE 1, the boiler of the present invention comprises an elongated boiler generally indicated m 10 having a water chamber 11 through which pass a plurality of longitudinally extending fire tubes 12. The tubes 12 conduct flue gases in heat contact relation with the water in the chamber 11 and, as more fully developed below, control the flow .of the fiue gases in a multiplicity of passes from the combustion area of the furnace to the flue or exhaust stack 13. In the embodiment illustrated, the combustion gases are derived from the combustion of oil or the like introduced into a diverging-converging fuel ignition chamber 14 in a diverging (fuel spray pattern. As the fuel progresses downstream in the direction of the flow arrows 15 continued combustion generates heat conducted directly to encircling water tubes 16. The Water tubes 16 are separated approximately at the lower half of the furnace by firebrick or other refractory lining 16 and, approximately above the center line of the chain her, by a refractory lining material 18. The material 18 does not, as may be seen from a consideration of the drawings, however, cover the upper side of the encircling water tubes 16. Instead, as shown, the upper surface of the individual water tubes is exposed to the combustion gases as they are directed backwardly over thetop of the combustion chamber 14, thereby providing additional direct heat transfer between the combustion gases and the water tubes 16. Additionally, each of the encircling water tubes 16 is provided with a vertical riser 20 which projects upwardly from the individual tube 16 to the second pass or chamber 21 through the boiler crown sheet 22 into the water chamber 11 where the risers 20 open slightly below the surface of the water indicated at 11a.

It will be observed from the above, and from a consideration of the drawings, that the combustion gases make a first pass through combustion chamber 14. In this first pass the heat is conducted from the combustion gases di rectly to the water tubes :16 throughout the entire circle thereof. At the end of the first pass the gases are turned, in chamber 23, and proceed toward the right as viewed in FIGUREl via second pass chamber 21. In chamber 2.1 heat is transferred directly to the water tubes -16 and the risers 20 thereof. Additionally, in the second pass,

heat is transferred directly to the crown sheet 22 and from thence into the water in the main water chamber of the boiler.

As the flue gases pass out of chamber 2. 1 toward the right as viewed in FIGURE 1, they are turned laterally, in a generally horizontal pattern, required by a horizontally extending baffie 25, and pass back toward the left by way of fire tubes 12a as indicated in arrows 26. After passage toward the left by way of fire tubes 12a, the gases emerge in chamber 27 and are directed into fire tubes 12b as shown by arrows '28. This flow is controlled by horizontal baffle 29 and causes the combustion gases to proceed to the right into turnaround chamber 30 from whence the gases pass through fire tubes 120 into flue gas stack chamber 31 and thence out the stack 13.

As a result of the arrangement above specified, the combustion gases make five horizontal passes through the complete length of the boiler in an exceedingly small space and, in each case, in high efficiency transfer contact with the boiler water.

As a result of employing two passes of water tube heat transfer, substantially improved boiler efiiciency is achieved. As will be clear, water passing to the water tubes :16 by way of lower headers 19 positioned at the bottom of the boiler, will be heated very rapidly and will, accordingly, rise very rapidly toward the surface of the water lla in the chamber -11. 'By additionally heating the risers 20 in the second pass, this heating is intensified and the velocity of the circulating water is again increased. The result of the extremely rapid water circulation in the water tubes causes rapid circulation of the water throughout the boiler and with such increased circulation, an increase in boiler efiiciency. It will be noted that water from the chamber 11 is fed to the lower header 19* by way of generally vertically extending connector .types 33.

In accordance with the present invention, it is preferred that a diverging fuel spray is provided by conventional diverging cone-type burner 35. The specific burner element does not, however, comprise a part of the present invention and conventional burners, as employed with the diverging-converging furnace illustrated in my prior Patent No. 2,891,520 may readily be employed.

In view of the provision of two passes in direct communication with the water tubes 16, turnabout passage or chamber 23 is provided at the left-hand end of the boiler. This permits the turning flue gases to be efiiciently employed for purposes of burning refuse. Thus, refuse chamber 36 is provided with a convenient door opening 37. This chamber 36 is baiiled against direct flame impingement by baflie abutment38 but the swirling gases in the chamber 23 provide ready ignition of refuse material and permit the burning of such refuse without any ad Vance effects on the normal flow of combustion gases from the burner 35 through the furnace to the stack 13.

In the embodiment illustrated in FIGURE 1, the individual Water tubes :16 are shown as separated by refractory material 1 8. However, it is contemplated that the first and second passes of the boiler may be separated by a modestly heat-conductive material having good resistance to combustion gas corroding. For example, stainless steel or similar moderately heat-conductive material may be placed between the tube '16 as shown in FIGURE 3 and 18a. The generally arcuate strips 18a are preferably continuously secured to the tubes 16 by welding as at 18b thereby providing additional heat-conductivity from the fiue gases to the water tubes 16 only in the first and second passes.

In the embodiments illustrated in FIGURES 1 through 3, I have illustrated the invention as applied to a combination water tube-fire tube boiler. A modified form of the boiler is, however, shown in FIGURES 4 and 5. As there shown, a boiler, often termed the package-type boiler by those skilled in the art, is provided. This boiler construction employs the dual pass combustion 4 chamber arrangement described in connection with FIG- URES 1 through 3 but substitutes water tube passes for the tire tube passes described above.

As shown in FIGURES 4 and 5, the boiler of this embodiment is generally indicated at and comprises a pair of water drums and 111. The water level is illustrated at I111a in the upper water drum 111. Combustion gases are introduced into the combustion chamber 114 along the lines of arrows 115 generally following the contours of the diverging-converging combustion space formed by the tubes 116. As in the case of the embodiment illustrated in FIGURES 1 through 3, the space between the adjacent circular tubes 116, indicated at 118,

comprises refractory material or, if desired, stainless steel or similar material above mentioned. In either event, it will be clear that combustion gases entering the combnstion chamber by way of burner 135 is forced to pass completely through the combustion chamber 114 into turnaround chamber 123. In chamber 123 the gases are turned backwardly upon themselves toward the right as viewed in FIGURE 4 and pass the full length of the furnace via chamber 121. At the right-hand end of the furnace the gases are turned as indicated by arrows 126 and pass backwardly again upon themselves by way of chamber 122.

As illustrated in FIGURE 5, chamber 121 is formed by the outside surfaces of the tubes 116 and by the exposed surfaces of water tubes 120 and 1200. As viewed in FIGURE 5, the right-hand side of chamber 121 is formed by a layer of refractory material positioned between adjacent water tubes 123 connecting drum 1510 and 111. Similarly, on the pass backwardly through pass 122 the tubes 123 have their right sides exposed to the combustion gases. However, the right-hand side of chamber 122 comprises a sheet of refractory material 124 which completely covers generally vertically extending tubes 125 leaving only their right-hand sides exposed. The exposed right-hand sides of the tubes 125 are heated by gases passing through chamber 126, which chamber leads to the furnace fine. It will be seen that chamber 126, which provides contact with flue gases of the lowest temperature, with water-carrying

tubes

125 and 127 provides a chamber in which the water tubes are at the lowest furnace temperature. As a result, although the water in

tubes

125 and 127 is heated, the relatively cool temperature of the water permits it to move downwardly in the circulation pattern to provide upward circulation through tubes 120 and 1123 which are, of course, at relatively high temperatures.

In the arrangement shown in FIGURES 4 and 5, the lower water drum .110 is shown connected to tubes 120a by way of a lower header pipe 131). The header pipe 130 may, if desired, be eliminated and tubes 1213a directly connected to lower drum 110. However, in the construction illustrated, the lower header pipe 130, which is connected to the water drum 110 by way of vertical risers 131 is preferably employed in order to eliminate the collection of mud, and possible burnouts, in the water drum 119. By providing insulating material 132 in the bottommost portion of the furnace, tube or pipe 130 is maintained in a relatively cold condition. The pipe may be flushed longitudinally of the furnace very readily and in view of the fact that the pipe 130 is always relatively cold, the small accumulation of mud therein before such cleaning will not endanger the furnace.

It will be apparent to those skilled in the art that variations and dimensions may be undertaken without departing from the scope of the present invention. The sizes of the various conduits may, accordingly, be varied to suit individual installations. It has been found satisfactory in this regard, however, to employ 2 /2" tubes for the

water tubes

16 and 116 with 3"

risers

20, 20a, and 1213, 126a and correspondingly proportioned conduits as illustrated.

It will be appreciated, further, that as a result of the multi-pass contact boiler installation herein proposed, a substantially improved heat transfer boiler construction is provided. Since, as above noted, variations may be em ployed without departing from the scope of the novel concepts of this invention, it is my intention that the scope of the invention be limited solely by that of the hereinafter appended claims.

I claim as my invention:

1. in combination in a boiler having a water space, a combustion chamber positioned below said water space, said chamber comprising a generally tubular space having a plurality of longitudinally spaced water tubes therein, each tube encircling the chamber in a plane generally transverse to the longitudinal axis thereof and in direct contact with combustion gases passing through said chamber, means introducing fuel at one end of said chamber, means positioned between said encircling tubes for preventing the lateral passage of combustion gases between adjacent tubes but leaving a substantial part of the outer periphery of said tubes uncovered, means connecting said encircling tubes to said water space, and means turning said gases backwardly upon themselves after passing through said chamber for direct contact with said outer periphery of said encircling tubes.

2. In combination in a boiler having a water space, a combustion chamber positioned below said water space, said chamber comprising a generally tubular space having a plurality of longitudinally spaced Water tubes therein, each tube encircling the chamber in a plane generally transverse to the longitudinal axis thereof and in direct contact with combustion gases passing through said chamer, means introducing fuel at one end of said chamber, means positioned between said encircling tubes for preventing the lateral passage of combustion gases between adjacent tubes but leaving a substantial part of the outer periphery of said tubes uncovered, means connecting said encircling tubes to said water space, means turning said gases backwardly upon themselves after passing through said chamber for direct contact with said outer periphery of said encircling tubes, a plurality of fire tubes extending through said water space and having openings at opposite ends thereof, and means directin said combustion gases through said fire tubes following their passage over the outer periphery of said encircling tubes.

3. in combination in a boiler having a water space, a combustion chamber positioned below said water space, said chamber comprising a generally tubular space having a plurality of longitudinally spaced water tubes therein, each tube encircling the chamber in a plane generally transverse to the longitudinal axis thereof and in direct contact with combustion gases passing through said chamber, means introducing fuel at one end of said chamber, means positioned between said encircling tubes for preventing the lateral passage of combustion gases between adjacent tubes but leaving a substantial part of the outer periphery of said tubes uncovered, generally vertically extending riser conduit means connecting each of said encircling tubes to said Water space above said combus tion chamber, and means turning said gases backwardly upon themselves after passing through said chamber and into direct contact with the outer periphery of said encircling tubes and with said riser conduit.

4. In combination in a boiler having a water space, a combustion chamber positioned below said water space, said chamber comprising a generally tubular space having a plurality of longitudinally spaced water tubes therein, each tube encircling the chamber in a plane generally transverse to the longitudinal axis thereof and in direct contact with combustion gases passing through said chamber, means introducing fuel at one end of said chamber, means positioned between said encircling tubes for preventing the lateral passage of combustion gases between adjacent tubes but leaving a substantial part of the outer periphery of said tubes uncovered, generally vertically extending riser conduit means connecting each of said encircling tubes to said water space above said combustion chamber, and means turning said gases backwardly upon themselves after passing through said chamber and into direct contact with the outer periphery of said encircling tubes and with said riser conduit and the bottom surface of said water space. p

5. In combination in a boiler having a water space, a combustion chamber positioned below said water space, said chamber comprising a generally tubular space having a plurality of longitudinally spaced water tubes therein, each tube encircling the chamber in a plane generally transverse to the longitudinal axis thereof and in direct contact with combustion gases passing through said cham ber, means introducing fuel at one end of said chamber, means positioned between said encircling tubes for preventing the lateral passage of combustion gases between adjacent tubes but leaving a substantial part of the outer periphery of said tubes uncovered, generally vertically extending riser conduit means connecting each of said encircling tubes to said water space above said combustion chamber, means turning said gases backwardly upon themselves after passing through said chamber for direct contact with said outer periphery of said encircling tubes, a plurality of fire tubes extending through said water space and having openings at opposite ends thereof, and means directing said combustion gases through said fire tubes following their passage over the outer periphery of said encircling tubes. I

6. In combination in a boiler having a water space, a combustion chamber positioned below said water space, said chamber comprising a generally tubular space hav-' ing a plurality of longitudinally spaced water tubes therein, each tube encircling the chamber in a plane generally transverse to the longitudinal axis thereof and in direct contact with combustion gases passing through said chamber, means introducing fuel at one end of said chamber, means positioned between said encircling tubes for preventing the lateral passage of combustion gases between adjacent tubes but leaving a substantial part of the outer periphery of said tubes uncovered, generally vertically extending riser conduit means connecting each of said encircling tubes to said water space, means turning said gases baclewardly upon themselves after passing through said chamber for direct contact with said outer periphery of said encircling tubes, a plurality of fire tubes extending through said water space and having openings at opposite ends thereof, and means directing said combustion gases through said fire tubes following their passage over and contact with the outer periphery of said encircling tubes and with said riser conduit means and the bottom surface of said water space.

7. In combination in a boiler having a water space, a combustion chamber positioned below said water space, said chamber comprising a generally tubular space having a plurality of longitudinally spaced water tubes therein, each tube encircling the chamber in a plane generally transverse to the longitudinal axis thereof and in direct contact with combustion gases passing through said cham ber, means introducing fuel at one end of said chamber, means positioned between said encircling tubes for preventing the lateral passage of combustion gases between adjacent tubes but leaving a substantial part of the outer periphery of said tubes uncovered, generally vertically extending riser conduit means connecting each of said encircling tubes to said water space above said combustion chamber, means turning said gases backwardly upon themselves after passing through said chamber for direct contact with said outer periphery of said encircling tubes, a plurality of fire tubes extending through said water space and having openings at opposite ends thereof, and means directing said combustion gases through said fire tubes following their passage over the outer periphery of said encircling tubes, and longitudinally extending lower header conduit means interconnecting the bottom of the respective encircling tubes at a point below said combustion chamber and away from the heat thereof and further connected with the bottom of said water space whereby water circulating upwardly through said encircyling tubes as a result of heat applied thereto by said combustion gases is replenished by water from said water space by way of said lower header.

8. In combination in a boiler having a water space, a combustion chamber positioned below said water space, said chamber comprising a generally tubular space having a plurality of longitudinally spaced water tubes therein, each tube encircling the chamber in a plane generally transverse to the longitudinal axis thereof and in direct contact with combustion gases passing through said chamber, means introducing fuel at one end of said chamber, refractory means positioned between said encircling tubes for preventing the lateral passage of combustion gases between adjacent tubes but leaving a substantial part of the outer periphery of said tubes uncovered, means connecting said encircling tubes to said Water space, and means turning said gases backwardly upon themselves after passing through said chamber for direct contact with said outer periphery of said encircling tubes.

9. In combination in a boiler having a water space, a combustion chamber positioned below said water space, said chamber comprising a generally tubular space having a plurality of longitudinally spaced water tubes therein, each tube encircling the chamber in a plane generally transverse'to the longitudinal axis thereof and in direct contact with combustion gases passing through said chamber, means introducing fuel at one end of said chamber, heat conducting corrosion resistant means positioned between and in heat transfer contact with said encircling tubes for preventing the lateral passage of combustion gases between adjacent tubes but leaving a substantial part of the outer periphery of said tubes uncovered, means connecting said encircling tubes to said water space, and means turning said gases backwardly upon themselves after passing through said chamber for direct contact with said outer periphery of said encircling tubes.

10. In combination in a boiler having a water space, a combustion chamber positioned below said water space, said chamber comprising a generally tubular space initially diverging and subsequently converging and having a plurality of spaced water tubes therein, each tube encircling the chamber in in a plane generally transverse to the longitudinal axis thereof and in direct contact with combustion gases passing through said chamber, means introducing fuel at one end of said chamber, heat conducting corrosion resistant means positioned between and in heat transfer contact with said encircling tubes for preventing the lateral passage of combustion gases between adjacent tubes but leaving a substantial part of the outer periphery of said tubes uncovered, means connecting said encircling tubes to said water space, and means turning said gases backwardly upon themselves after passing through said chamber for direct contact with said outer periphery of said encircling tubes.

11. In combination in a boiler having a water space, a combustion chamber positioned below said Water space, said chamber comprising a generally tubular space having a plurality of spaced water tubes therein, each tube forming a part of the surface thereof for direct contact with combustion gases passing through said chamber, means introducing fuel at one end of said chamber, means positioned between said tubes for preventing the lateral passage of combustion gases between adjacent tubes but leaving a substantial part ofthe outwardly facing periphcry of said tubes uncovered, means connecting said tubes to said water space, means turning said gases backwardly upon themselves after passing through said chamber for direct contact with the said outer periphery of said tubes, a plurality of fire tubes extending through said water space and having openings at opposite ends thereof, and,

means directing said combustion gases through said fire said encircling tubes.

12. In combination in a boiler having a water space, a combustion chamber positioned below said water space, said chamber comprising a generally tubular space having a plurality of spaced Water tubes therein, each tube forming a part of the surface thereof for direct contact with combustion gases passing through said chamber, means introducing fuel at one end of said chamber, means positioned between said tubes for preventing the lateral passage of combustion gases between adjacent tubes but leaving a substantial part of the outwardly facing periphery of said tubes uncovered, means connecting said water tubes to said Water space at a point below but adjacent the upper surface of the water therein, means turning said gases backwardly upon themseleves after passing through said chamber for direct contact with the said outer periphery of said tubes, a plurality of fire, tubes extending through said water space and having openings at opposite ends thereof, and means directing said combustion gases through said fire tubes following their passage over the outer periphery of said encircling tubes.

extending water space, a longitudinally extending combustion chamber positioned generally parallel to said water space, said chamber comprising a generally tubular space having a plurality of longitudinally spaced water tubes therein, each tube encircling the chamber in a plane generally transverse to the longitudinal axis thereof and in direct contact with the combustion gases passing through said chamber, means introducing fuel at one end of said chamber, means positioned between said encircling tubes for preventing the lateral passage of combustion gases between adjacent tubes but leaving a substantial part on the outer periphery of said tubes un-' covered, means connecting said encircling tubes to said water space, and means turning said gases backwardly upon themselves after passing through said chamber for direct contact with said outer periphery of said encircling tubes.

14. In combination, a boiler having a longitudinally extending water space, a longitudinally extending combustion chamber positioned generally parallel to said water space, said chamber comprising a generally tubular space having a plurality of longitudinally spaced Water tubes therein, each tube encircling the chamber in a plane generally transverse to the longitudinal axis thereof and in direct contact with the combustion gases passing through said chamber, means introducing fuel at one end of said chamber, means positioned between said encircling tubes for preventing the lateral passage of combustion gases between adjacent tubes, generally vertically extending riser conduit means connecting the top of each of said encircling tubes to said water space at a point above said combustion chamber and generally vertically extending riser conduit means connecting each of said encircling means to said water space below said combustion chamber, and means turning said gases backwardly upon themselves after passing through said chamber and into direct contact with the outer periphery of said encircling tubes and with said riser conduits.

15. In combination, a boiler having a longitudinally extending water space, a longitudinally extending combustion chamber positioned generally parallel to said Water space, said chamber comprising a generally tubular space having a plurality of longitudinally spaced water tubes therein, each tube encircling the chamber in a plane generally transverse to the longitudinal axis thereof and in direct contact with the combustion gases passing through said chamber, means introducing fuel at one end of said chamber, means positioned between said encircling tubes for preventing the lateral passage of combustion gases between adjacent tubes but leaving a substantial part on the outer periphery of said tubes un- 13. In combination, a boiler having a longitudinally covered, means connecting said encircling tubes to said water space, and means turning said gases backwardly upon themselves after passing through said chamber for direct'contact with said outer periphery of said encircling tubes, said water space comprising a pair of vertically spaced water drums, one positioned above said combustion chamber and the other positioned below said combustion chamber.

16. In combination, a boiler having a longitudinally extending water space, a longitudinally extending combustion chamber positioned generally parallel to said water space, said chamber comprising a generally tubular space having a plurality of longitudinally spaced water tubes therein, each tube encircling the chamber in a plane generally transverse to the longitudinal axis thereof and in direct contact with the combustion gases passing through said chamber, means introducing fuel at one end of said chamber, means positioned between said encircling tubes for preventing the lateral passage of combustion gases between adjacent tubes, generally vertically extending riser conduit means connecting each of said encircling means to said water space below said combustion chamber, and means turning said gases backwardly upon themselves after passing through said chamber and into direct contact with the outer periphery of said encircling tubes and with said riser conduits, said water space comprising a pair of vertically spaced water drums, one positioned above said combustion chamber'and the other positioned below said combustion chamber.

References Cited in the file of this patent UNITED STATES PATENTS 668,755 Orvis Feb. 26, 1901 2,480,440 Berwanger Aug. 30, 1949 FOREIGN PATENTS 265,780 Switzerland Mar. 16, 1950