US2080404A - Boiler - Google Patents

Description

May 18, 1937" r N. HUNTER ET AL BOILER Filed May 2, 1955 4 Sheets-Sheet l INVENTORS May 18, 1937.

L. N. HUNTER ET AL BOILER Filed May 2, 1935 4 Sheets-Sheet 2 Wm NN as mm ||l IIAU III I INVENTORS May 18, 1937. I N. HUNTER ET AL 2,030,404

BQILER Filed May 2, 1955 4 Sheets-Sheet s INVENTORS May 18, 1937.

L. N. HUNTER ETAL BOILER 4 Sheets-Sheet 4 Filed May 2, 1955 IVENTOR$ mw wk MNQE V Patented May 18, .1937

UNITED STATE BOILER Louis N. Hunter and John W. Hall, Johnstown, ,Pa.,"assignors to National Radiator Corporation, Johnstown, Pa., a corporation of Maryland Application May 2, 1935, Serial No. 19,401

8 Claims.

This invention relates to boilers, and more particularly to compact boilers particularly designed foruse with oil burners. I

According to the present invention there is provided a boiler of small size adaptable for use either in steam or hot water heating systems, or for use with hot water supply systems, and which is developed especially for efficient use with oil burning equipment. The burning of fuel oil is most effectively accomplished in a refractory lined combustion chamber. It cannot be efiiciently carried out in a metal combustion chamber having water-cooled walls. The reason for this is that the water-cooled walls of a combustion chamber cool the fuel oil particles to a point where combustion is not carried out efficiently or completely. i In a refractory combustion chamber, the heat is conducted through the walls less rapidly, with the result that the inner walls of the combustion chamber become highly heated and any fuel particles, which come into contact with them, instead of being cooled are raised to the combustion temperature. The burning of fuel oil also requires a definite appreciabletime, so that an elongated combustion chamber affords the best conditions for combustion. It has been proposed to use metal boilers for use with fuel oil burners by lining the combustion chamber with a refractory material, but such arrangements do not, develop ahigh degree of efliciency. The reason for this is, first, that the shape of the combustion chamber is not such as to give the best flame travel for burning fuel oil and, secondly, for the reason that so much of the heatabsorbing surface'of the boiler is covered with refractory that theheat is not supplied to the water in the boiler with suflicient rapidity.

In designing a boiler of small compact type, considerable difliculty is encountered from the standpointof construction. In the first place, in any boiler as much of the combustion chamber as possible should be water-backed. Also any boiler which is assembled from plates and using tubes, has to be constructed in such way that in assemblingthe boiler access can be had to the various parts for the purpose of making welds. Also the construction of the boiler must be such that access can be had to all places where welding has been done, to enable the boiler to be readilyrepaired and to enable the tubes to be cleaned. Where an opening is provided inthe,

boiler wall to give access to the interior, this opening must be provided with a removable cover. It is not ordinarilyfeasible, particularly in a low priced boiler, to have any portion of this cover water-backed. The cover plate must be insulated. Where such an insulated cover is used, it has to be provided at the expense of losing so much water-backed surface in the combustion chamber. In a small boiler, an opening to give a workman access to the interior ofthe boiler must bejust as large as in a large boiler. In other words, in condensing the size of a boiler all of the parts cannot be made smaller in the same ratio. Any attempt, therefore, to make standard large type boilers in, a small size involves a considerable problem because as the size of the boiler diminishes, the ratio of water-backed surface to insulated surface decreases. I

Also it will be seen thatwhere spaceto accommodate a man can beiconveniently provided in a large boiler, such a space if incorporated into a very small boiler is all out of proportion to the remainder of the design of the boiler, with the result that the small boiler will not have the same efficiency per unit of fuel burned as willa large boiler of the same design. I a

The present invention provides a boiler especially designed to be constructed in small sizes wherein all of the boiler area is available for ready access both in assembling and in repairing the boiler, wherein a refractory combustionchamher is provided in such manner as to give a relatively long combustion space but without covering toomuch of the metal walls of the combustion, chamber. The present invention further provides a boiler with a single removable cover plate through which access to the interior ofthe boiler may be had without the workman actually getting into the structure, thearrangement being such that the area of the interior of the boiler which is not water-backed is relatively small, giving. a relatively high area of water-backed surface. The invention further provides a compact boiler having a reverse flow of gases therethrough, but wherein thisreverse flow of gases is obtained with a single bank of fire tubes, whereas steel boilers of the compact type have heretofore generally been provided with two banks of tubes, one for the'iorward travel of gases and one for the rearward travel of gases.

Small boilers of the type to which the present invention pertains are frequently required in buildings where there are no basements or where the cellars will not accommodate a boiler, these boilers frequently being set up on the wooden floors of buildings. The present invention provides ina small structure a wet bottom boiler, i. e., a boiler in which the water space extends under the bottom of the combustion chamber, as

well as at the sides and over the top of the chamber. This is highly desirable not only from the standpoint of efficiency, particularly in a small boiler, but from the safety feature provided in having the intervening body of water between The entire assembly is one which can be cheap-' ly and conveniently manufactured and sold and which has proven to have a high degree of emciency.

The invention may be readily understood by reference to the accompanying drawings, in which Figure 1 represents a longitudinal vertical section through one form of boiler embodying our invention; 1

Figure 2 is a transverse vertical section in the plane of line II--II of Figure 1;

Figure 3 is a view similar to Figure 1 of a slightly modified construction;

Figure 4 is a transverse section in the plane of line IVIV of Figure 3;

Figure 5 is an end elevation of the boiler shell with the refractory combustion chamber removed andwith the cover plate removed;

Figure 6 is a longitudinal section in the plane of line VI-VI of Figure 5; Figure 7 is a view similar to Figure 5 showing the upper portion of the boiler of Figure 5 especially modified for use in hot water heating systems or hot water supply systems, the previous structures being primarily intended but not necessarily limited to low pressure steam generating boilers;

Figure 8 is a longitudinal section in the plane of line VIII-VIII of Figure 7;

Figure 9 is a front elevation of one of the in-,

termediate combustion chamber sections, the contour of the metal combustion chamber into which the refractory combustion chamber is set being indicated by dot and dash lines;

Figure 10 is a perspective view of the intermediate combustion chamber section shown in Figure 9;

Figure 11 is a perspective view of a refractory baille which is preferably used in conjunction with the combustion chamber sections of the type shown in Figures 9 and 10;

Figure 12 is a front elevation of the front section of the refractory combustion chamber used in the modification .shown in Figures 3 and 4';

Figure 13 is'a transverse vertical section in the plane of line XIII-XIII of Figure'l2; and

Figure 14 is a view showing an end elevation of one of the intermediate refractory combustion chamber sections used in the modification shown in Figures 3 and 4.

Referring to the drawings, the construction of the boiler can best be followed by reference to Figures 5 and 6. The shell of the boiler comprises .a front plate 2 and a rear plate 3 and a wrapper sheet 4. The Wrapper sheet encircles the peripheries of the plates 2 and 3 and is welded thereto.

extension being designated 6. Inside the shell so formed is a combustion chamber comprising a metal cylinder 1. The cylinder 'lhas a rear end wall 8 which is spaced inwardly from the rear plate 3 providing a water-backed surface at the rear end of the combustion chamber. The front end of the metal shell I is cut away at the top thereof. At the rear of this cut-away portion in the combustion chamber 1 is a vertical plate 9. This plate, in conjunction with the top plate l0 and side plates ll, forms an uptake. This uptake is, except at the front thereof, surrounded by water, the walls I I being spaced inwardly from the sides of the wrapper sheet 4. The forward end of the metal combustion chamber 1 is provided with a closure plate l2 which is cut away to conform to the cut-away portion 6 in the front plate. A water space I3 is thus provided between the front plate 2 and the plate l2. This water space is closed by the narrow U-shaped plate I which is welded to the plate l2 and to the marginal edges of the cut-away portion 6 of the plate 2.

Passing through the plate 9 at the back of the uptake is a number of fire tubes l5 which extend through the water space in the boiler above the top of the combustion chamber 1 through the rear plate 3 of the boiler. Two rows of tubes which constitute a single bank for carrying gases of combustion from the uptake to the rear of the boiler, are shown. These tubes are further shown as being provided with twisted baffles IS.

The boiler structure is supported on pedestal plates IT. A water intake connection is provided near the base of the boiler in the back plate 3, this connection being designated I8; An outlet connection is provided in the top of the wrapper sheet, this outlet being designated l9. Along each side of the interior of the cylindrical combustion chamber 1 we preferably provide an angle bar 20 for the purpose hereinafter described.

In the structure just described, it will be seen that practically the entire combustion chamber 1 is water-backed, and that the uptake formed at the front of the combustion chamber is also water-backed. The single opening 5 in the front plate constitutes the only opening giving access to the interior of the boiler. Since the boiler is of small size, access can be had to any of the welds inside the structure for the making of welds or for the repairing of them. For instance, a workman reaching in through the opening 5 in the front plate can repair the weld designated at 8a between the back plate 8 and the cylindrical combustion chamber 1. Through the same opening a workman is given access to the inner ends of the fire tubes I 5 either for tightening them, repairing them or cleaning them. The other ends of the fire tubes are accessible from the outside of the boiler.

We have shown a small by-pass opening leadingfrom the back plate 8 through the rear wall 3,.this by-pass being designated 2i. It is for the purpose of providing a relief opening for use with a gate such as shown in our copending application, Serial No. 24,059, filed May 29, 1935. which will be hereinafter more fully described.

Referring now to Figures 1 and 2, there is provided inside the cylindrical metal combustion chamber 1 a refractorycombustion chamber designated generally as 22, this refractory combustion chamber being of less diameter than the combustion chamber 1 and preferably being eccentrically positioned in the metal combustion chamber 1. The combustion chamber 22 in the form shown in Figure 1 is generallyof circular cross section. It comprises a front refractory form 23 having a small opening 24 therein which registers with the opening 6 in the front plate of the boiler. plurality of intermediate sections 25 and at the innermost end of the combustion chamber is a back refractory section 26, which section has a back wall portion 26a resting against the back wall 8 of the metalcombustion"chamber.j Provision for the escape of gases is made through two outwardly and upwardly opening ports 21 in this rearmost section 26. The back section 26 is formed as an integrally cast refractory. The in termediate sections 25 are each preferably formed in two parts as showninFigures 9 and 10, 25a designating the lower part and 251) the upper part. The two complementary parts 25a and 252) have interlocking edge portions forming a substantially gas-tight seal. The bottom section 25a is provided with a thickened portion 250 terminating in shoulders 2511. These shoulders are arranged to engage under the angle bars to as-. sist in holding the sections in place.

The front refractory section23 is also preferably made with a lower part 23a and an upper part 232). The refractory sections 23 and 25 are preferably made in two parts for two reasons. The first is that by making them in this manner the refractory combustion chamber can be read- I fly assembled insidethe completed boiler shell by insertion of the parts through the front opening 5 in the front plate 2. The second reason for making these refractory sections in two parts is that they have considerably more resistance to breaking under varying thermal conditions. Frequently where they are made integrally, they are fragile and break when the furnace is heated up. Moreover, by the refractory combustion chamber being installed and assembled in this manner, itcan be readily opened up at any time for inspection or for giving access to the end of the burner. Also, replacement parts can be installed very readily,and in all but the back section, with little disturbance to the rest of the refractory combustion chamber structure. Inassembling the refractory combustion chamber in the boiler structure, the rear refractory section 26 ,is first lowered into the combustion chamber through the door 5 at the front of the boiler. Then it is pushed back, being kept in such position that it will properly engage the angle bars 20. Once it is engaged by the angle bars 20, it can he slid back readily and will be kept in the desired position. After the back section is in place, the parts of the intermediate section can be put in through the door 5 and assembled, the two parts of the front section being put in last. This manner of assembling the refractory combustion chamber inside the boiler eliminates the requirement for any door in line withthe combustion chamber itself. It will be seen, for instance, that if an opening were provided in the back wall through which this refractory combustion chamber had to be inserted and l for which a closure would have to would be considerably reduced or the closure wouldhave to be of an expensive and complicated construction having water circulating space therein and connections which would communicate with other parts of the boiler. By reason of the fact that the refractory combustion chamber is eccentrically positioned in Back of the front section 23 is a be provided, the amount of water-backed surface. in the boiler the cylindrical metal combustion chamber, a passage for the gases of combustion is provided around the outsideof the refractory combustion chamber. This passage or space is designated 28. The burned gases which leave the rear of the combustion chamberthrough the ports 21 enter this space 28 and travel toward the front of the boiler to the uptake at the front ofthe boiler. The walls of the metal combustion chamber over which these forwardly traveling gases pass are water-backed so that the gases will yield a considerable amount of their heat to the water in the boiler as they travel forwardly to the uptake. At the' same time, combustion of the fuel particles is completed before the gases leave the refractory combustion chamber. Bringing the gases into contact with the Water-backed walls after they leave the refractory combustionchamber,therefore, does not interfere with combustion.

Where the refractory combustion chamber is circular, the space 28 between the outside of the refractory combustion chamber and the interior of the cylindrical shell I is greatest at the top of the refractory combustion chamber. gases tend to naturally riseto this space, tending to produce relatively colder pockets further down on the sides of the outside of the refractory combustion chamber in the zones marked 28'.

In order to'prevent this andgive a better distribution of heat, we contemplate that refractory baffles 29 be set on top of the refractory combustion chamber in the space 28. These tend to partially obstruct the free flow of gases above the center of the top of the refractory combustion chamber and cause more of the gases to flow into the zones 28'.

The front wall of the boiler is provided with a removable cover 30 for the opening 5. This cover is lined with a heat insulating material 30a. It is provided with a window 3|. The position of the window is directly in line with the space 28 and affords vision into this space directly along thetop of the refractory combustion chamber. It affords a view of the gases that leave the combustion chamber, so that the flame conditions.

the volume of smoke, etc., can be more readily observed than where the window looks directly into the refractory combustion chamber.

Secured to the front plate of the boiler below the door 33 is an oil burner conventionally indicated at 32. This oil burner is provided with a flange 33 that rests against the front of the boiler and which may be bolted'to the front of the boiler. Thus it will be seen that the oil burner is supported on a water-cooled surface. This prevents over-heating of the oil burner. The discharge end of the oil burner, of course, projects through the opening 6 in the front plate. Where desired, the opening 6, instead of being a U-shaped extension of the opening 5, may be a fully circular opening, as shown in Figure l, with a water circulating space at 34 above the top of the oil burner.

At the rear of the boiler there is a smoke ho od Fire tubes I5 discharge into the smoke hood,

The hot The boiler shown in Figures 3 and 4 is generally similar to the arrangement shown in Figures 1 and 2,. and corresponding reference numerals havebeen used to designate the corresponding parts. The only difference in the two structures is that in the arrangement shown in Figures 3 and 4 the refractory combustion chamber instead of being fully circular as it is in Figures 1 and 2, is ovular in transverse cross section with the major axis of the oval vertical. The refractory combustion chamber in this case comprises a rearmost refractory section 38 and a number of intermediate sections 39, and a forward section 43. The intermediate sections 39 have a lower part 39a and an upper part 39b, the two parts interfitting as shown in Figures 4 and 14. The front section 40 also comprises a lower part 40a and an upper part 40b, the two parts being shaped to fit together as shown in Figures 12 and 13, the two parts forming a circular opening to receive the end of the burner. It will be noted from Figures 4 and 14 that the structure has greater vertical dimension than horizontal dimension. The result of this is that the space 28 at the outside of the refractory combustion chamber is relatively restricted along the center of the top of the refractory combustion chamber and more open along the sides. This serves to give a distribution of the gases around the outside of the refractory combustion chamber, which is more uniform than where acircular combustion chamber is used, and bafiles similar to the baffles 29 are not, therefore, necessary.

With this type of combustion chamber, the center line of the oil burner is slightly higher than where the refractory combustion chamber is circular, with the result that Where, as shown in Figure 1, it is desirable to have a water 'space 34 over the top of the oil burner and below the door 30, it is quite practical in the arrangement shown in Figures 3 and 4 to use the U-shaped opening 6, which has been more specifically described and which is cheaper than the arrangement shown in Figure 1.

The various boilers shown in Figures 1 to 6, inclusive, arevshown as being primarily designed as steam boilers. In a ste'am boiler, it is desirable to have considerable space at the top of the boiler above the normal water line in which steam can collect. This steam space is designated 4| in the various figures. Fora hot water heating system or for a hot water supply system, this steam space 4| is not necessary. Figures 7 and 8 show arrangements particularly intended for hot water heating or hot water supply systems. The lower part of the boiler construction in Figures 7 and 8 would be the same as that shown in Figures 1 and 2 or 3 and 4. The'two end plates designated 45 and 46, corresponding to the plates 2 and 3, are of less vertical height, so that the wrapper sheet 41 is relatively closer to the bank of fire tubes designated 48, providing a relatively small chamber 49.

Boilers made in accordance with the present invention are wet-bottom boilers, i. e., the water space extends entirely under the combustion chamber. According to the present invention a single opening at with a single uptake in the forward portion of the boiler provides access to all of thetubes and to all of the welds. The boiler can be made of different sizes, using the same size'end plates and making the overall length vary. A practical overall length for a boiler emb'odying the present invention is 36 inches from the from; plate to the rear plate. All of the weldson the inside of the boiler are, therefore, within easy reach through the doorway 5 in the front plate.

The present invention provides a refractory lined combustion chamber in which the oil is burned. It provides, however, an exposed metal wall in the combustion chamber through which the hot gases can transfer heat to the boiler fluid. Only a very small area of the fire box is directly covered with refractory. The present arrangement provides for the forward flow of burned gases through the space 28 and then a rear flow through the single bank of fire tubes. By reason of the fact that the gases travel forwardly around the outside of the refractory combustion chamber, it is unnecessary to provide any bank of tubes for the forward travel or to have any uptake at the rear of the boiler. The boiler has a relatively large area, in proportion to its size around the combustion chamber waterbacked. The only surface which is not waterbacked is that provided by the single door 30. Boilers embodying the principles of the present invention have demonstrated a remarkably high efiiciency for a compact small boiler.

While we have specifically shown and described certain preferred embodiments-of our invention, it will be understood that various changes and modifications are contemplated therein within the scope of the following claims.

We claim:

1. A boiler comprising a shell structure having front and rear plates which are substantially fiat and having a wrapper sheet, said boiler having a hollow metal combustion chamber therein near the bottom thereof, the side walls of which are spaced from the wrapper sheet and the bottom of which is spaced from the wrapper sheet, and the end walls of which are spaced from the front and back plates of the boiler and which form with the front and back plates part of the water space in the boiler, the combustion chamber being provided with an uptake at the top of the forward end thereof, fire tubes leading from the uptake back through the structure and through the rear plate thereof, a refractory combustion chamber the metal combustion chamber and being closed throughout the greater refractory combustion chamber opening into the metal combustion chamber adjacent the rear end thereof, there being a gas circulating space inside the metal combustion chamber above the refractory combustion chamber extending forwardly to side of the combustion chamber, the opening being of such size as to and providing the only openingfor giving access forming water walls of the boiler, the combustion chamber being provided with an uptake at portion of its length, the

the top of the forwafd end thereof, fire tubes leading from the uptake back through the structure and through the rear plate thereof, a refractory combustion chamber inside themetal combustion chamber extending throughout the greater portion of the length of the metal combustion chamber and being closedthroughout the greater portion of its length, the refractory combustion chamber openinginto the metal combustion chamber adjacent the rear endthereof, there being a gas circulating space inside: the metal combustion chamber above thel refractory combustion chamber extending forwardly to said uptake, said front plate having an opening therein in front of the uptake affording access to the inner ends of the fire tubes and to the inside of the combustion chamber, andaclosure for said opening, said closure having-a window therein substantially in line with the gas circulating space inside the metal combustion chamber over the top of the refractory combustion chamber.

3. A boiler comprising a shell structure having front and rear plates and an enclosing wrapper sheet, a metal combustion chamber inside the shell positioned adjacent to the bottom thereof but spaced away from thebottom, the forward end of the metal; combustion'chamberbeing provided with an uptake, and a refractory combustion chamber eccentrically positioned in the metal combustion chamber'and supported on the bottom of said metal combustion chamber in heat conducting relation thereto, said refractory combustion chamber being closedthroughout the greater portion of its length butopening at the rear end thereof into the metal combustion chamber, and a single bank of fire tubes leading from the uptake to the back wall of the boiler, the metal combustion chamber having end walls which constitute water walls of the boiler.

4. A boiler comprising a shell structure having front and rear plates and an enclosing wrapper sheet, a metal combustion chamber inside shell positioned adjacent the bottom thereof but spaced away from the bottom, the forward end of the metal combustion chamber being provided with an uptake, and a refractory combustion chamber eccentrically positioned in the metal bustion chamber, said refractory combustion c laznber being closed throughout the greater portion of its length but opening at the rear end thereof into the metal combustion chamber, a single bank of fire tubes leading from the uptake to the back wall of theboiler, the front plate of said boiler shell being provided with a single opening at the front of the uptake through which access may be had to the inner ends of the fire tubes and to the interior of the metal combustion chamber, and a closure plate for said opening, the front plate of theboiler also having an opening which registers with an openingin the front of the refractory combustion chamber and of smaller diameter than the metal combustion chamber and arranged for cooperation with a fuel oil burner, said metal combustion chamber being substantially cylindrical, the front end of the metal combustion chamber cooperating with the front end of the boiler to provide a water space at the front of the boiler around the burner opening, said refractory combustion chamber being higher than it is wide, the top and sides of the refractory combustion chamher being spaced from the top and sides of the metal combustion chamber, thereby providing for the circulation of gases around the top and sides of the refractory combustion chamber from the i bustion the rear end thereof forwardly to said uptake, the bottom of the refractory combustion chamber resting on the bottom of the metal combustion chamber in heat conducting relation there with so as to exclude gases from under the combustion chamber.

5. A boiler comprising a shell structure formed of a front plate, a back plate and an enclosing wrapper sheet, a metal combustion chamber having front and rear walls insidesaid shell structure adjacent the bottom thereof but spaced from the bottom and sidewalls of the wrapper sheet and having its ends spaced from the front and rear plates of the boiler whereby it islsubstantially surrounded by the water space of the boiler, the metal combustion chamber having means at the top of the forward end thereof providing an uptake, the front plate having an opening therethrough at the front ofsaid uptake through which access may be had to the interior of the metal combustion chamber, the boiler having fire tubes leading from the uptake through the back wall of the boiler shell structure, said the metal combustion chamber, and a refractory combustion chamber inside the metal combustion chamber extending longitudinally thereto and being of less, height and width than the metal combustion chamber, said refractory combustion chamber beingformed of sections which i can, be inserted through said opening at the walls of the wrapper sheetand having its ends spaced from the front and rear plates of the boiler whereby it is substantially surrounded by the water space of the boiler, the metal combustion chamber having means at the top of the forward end thereof providing an uptake, the front plate having an opening therethrough at the front of said uptake through which access may be had to the interior of the metal comchamber, the boiler having the tubes opening being disposed mainly above the top of l leading from the uptake through the back wall of i the boiler shell structure, said opening being disposed mainly above the top of the metal combustion chamber, and a refractory combustion chamber inside the metal combustion chamber extending longitudinally, thereto and being of less height and width than the metal combustion chamber, said refractory combustion chamber being formed of a number of transverse sections which sections areof such dimension that they can be inserted through said opening at the front of the uptake and the refractory combustion chamber assembly by access afforded through said opening after the boiler is assembled, the front of the boiler and the front section of the refractory combustion chamber being provided with an alined opening for cooperation with an oil burner, the refractory combustion chamber being closed through substantially its entire length but opening into the metal tion chamber comprising strips cooperating with the shoulders on the sections'of the refractory combustion chamber for maintaining the. refractory sections in place. a

'7. A boiler comprising a shell structure formed of av front plate, a back plate and an enclosing wrapper sheet, a metal combustion chamber inside said shell structure adjacent the bottom thereof but spaced from the bottom and side walls of the wrappersheet and having end walls which are spaced from the front and rear plates of the boiler to form aqwater space at the front and rearthereof whereby it is substantially surrounded by the water space of the boiler, the metal combustion chamber having means at the top of the forward end thereof providing an uptake, the front plate having an opening therethrough at the front of said uptake through which access may be had to the interior of the metal combustion chamber, the boiler having fire tubes leading from the uptake through the back wall of the boiler shell. structure, said opening being'disposed mainly above the top of the metal combustion chamber, and a refractory combustion chamber inside the metal combustion chamber-extending longitudinally thereto and being of less height andwidth than the metal combustion chamber, said refractory combustion chamber being formed of a number of transverse sections which sections-are of such dimension that they can be inserted through said openingat the front of the uptake andthe refractory combustion chamber assembly by access afforded through said boiler is assembled, the front opening after the of the boiler and the front section of the refractory combustion chamber being provided with an alined opening .front plateof the boiler and for cooperation with an oil burner, the refractory combustion chamber being closed through substantially its entire length but opening into the metal combustion chamber adjacent the rear end thereof, some of said refractory sections also being divided-lengthwise of the axis of the combustion chamber to relievethem of thermal strains.

8. A boiler comprising a shell structure having substantially fiat front and rear plates of generally 'ovular contour and a wrapper sheet around the edges of said plates forming an enclosing wall structure, a cylindrical metal combustion chamber in the lower part of said shell having its end walls spaced inwardly from the end walls of the boiler shell and having its side walls spaced inwardly from the wrapper sheet, a refractory'combustion chamber supported on the bottom of said metal combustion chamber and eccentrically positioned therein, said refractory combustion chamber opening into the metal combustion chamber near the rearmost end thereof, an uptake being provided at the front of the metal combustion chamber located mainly above the top of said refractory combustion chamber, fire tubes extending from the uptake through the back plate of said shell, the front plate of the boiler being provided with a removable closure oversaid uptake, and an oil burner supported on the front plate of the boiler, the the front of said refractory combustion chamber having registering openings for cooperation with the burner, the burner being mounted on a'portion of the front plate of the boiler which is water-backed.

I LOUIS N. HUNTER.

JOHN -W. HALL.

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