US2142956A - Heat exchange apparatus and method - Google Patents

Description

Jan. 3, 1939. o. c. SCHAUBLE HEAT EXCHANGE APPARATUS AND METHOD Filed June 2, 1936 u b l e B E311? Sm ATTORNEY.

INVENTOR.

Otto C. Scha Patented Jan. 3, 1939 UNITED STATES PATENT OFFICE Lummus Company, New

ration of Delaware York, N. Y., a. corpo- Application June 2, 1936, Serial No. 83,033

11 Claims.

The invention disclosed herein relates to a fluid heater and its furnace and is especially directed to the construction of a furnace suitable for the heating of oil in tubes.

My invention refers particularly to an oil heater having its furnace divided into combustion and convection zones by an internal partition or bridge wall, and with the tubular heating surface formed in coils for forced circulation of oil therethrough. The coils are preferably arranged so that some are heated by convection from the hot ,gases of combustion while other coils may be subjected to direct radiant heat from the burning fuel in the combustion chamber.

An object of the invention is to provide a means for effectively cooling the walls of such a heater which will maintain their temperatures within safe working limits and insure continuous operation of the furnace over long periods.

A further object is to cool the furnace walls by means of air circulated in passages associated with the walls, and in a manner which is particularly adaptable to furnaces operating under natural draft conditions.

The invention also includes a new and improved form of furnace having a central convection flue disposed between two combustion chambers, with an appropriate arrangement of fluid heating tubes disposed in each chamber and the flue.

In describing my invention I shall refer to the accompanying drawing identified as follows:

Fig. 1 showing a sectional elevation of a furnace utilizing my invention, Fig. 2 being a vertical half-section of Fig. 1 taken along the line 22 on a vertical plane through the hollow bridge wall.

The drawing shows the double furnace arrangement as defined by a hearth I, a roof 2, end walls 3, and side walls 4. The bottom wall or hearth is elevated above a fioor 5 to form aduct 6 for the flow of cooling air as will be described more in detail hereinafter. Burners 1 are mounted in the lower portions of end walls 3. Partition walls or bridge walls 8 separate the combustion chamber 9 at each end from the centrally disposed convection passage I0 through which the hot gases of combustion flow downwardly upon leaving the furnace chamber on their way to the waste gas flue II and thence to a stack (not shown) Oil heating tubes l2, l3, and M are shown arranged in coils about the combustion chamber for exposure to radiant heat from the burning fuel andother tubes 15 disposed within the convection passage or tube chamber for heating by convection from the hot gases contacting therewith. The several sets of tubes are shown serially connected, the cool oil entering at 16 and leaving the series at ll. The exact sequence of flow is of no great importance for my present purpose but is so described and illustrated mainly for convenience. The arrangement of the coils, however, is important in that it provides for effectively heating some of the tubes by radiation in the combustion chamber, without risk of damage to the tubes by direct impingement of the flames. Furthermore, the arrangement of separate combustion chambers as shown, makes it possible to provide the correct proportion of radiantly heated surface to surface heated by convection, and to obtain a higher overall efficiency than would result with all of the radiantly heated surface located in a single large combustion chamher.

The bridge walls 8 are made hollow to provide spaces for air circulation, these air spaces being closed at each end by means of the casing plate 18 which may be regarded as forming a continuation or a part of thefurnace side wall 4. Horizontally disposed baffles l9 and 20 provide within the hollow bridgewall serially connected passages 2l, 22 and 23 for the flow of cooling air. These passages are of successively increasing flow areas, the air entering the upper passage 21 through inlet 24 in the end plate [8, passing next through the larger and intermediate passage 22 and finally through the lower and largest passage 23. The construction is duplicated at the opposite end of the wall, Fig. 2 representing only a section through one half of the setting width.

The circulated air leaves the lowermost passage 23 in each bridge wall through openings 25 where it joins the stream of spent gases from the furnace, the gas and air both being drawn into the waste gas flue by the natural draft afforded by the stack. The air inlet openings 24 are fitted with adjustable dampers 26, and outlet openings 25 with adjustable dampers 2'! for proper regulation of the air flow through the horizontal coo-ling passages. In the case of the plurality of exit dampers 2'! these may be conveniently controlled for simultaneous operation, as shown, through a rod 28 and control handle 29.

The flow of air through the hearth cooling passages 5 may also be controlled by regulating dampers 30 across the inlet openings 3i, the air discharging into the lowermost bridge wall passage 23 and combining with the air from that passage for flow through, openings 25 and final 5 discharge from the setting with the spent gases.

With the foregoing arrangement of parts it will be seen that by means oi the induced draft afforded by the stack, cool atmospheric air will be drawn into the several wall cooling passages or ducts and will cause the cooling air to be positively circulated through those passages to provide eifective cooling of the respective walls. The cooling air is discharged into the stream of flue gases at a point subsequent to their contact with the fluid heating tubes and this circulation is maintained separate from the flow of heating gases through the furnace. Consequently there is no impairment of combustion conditions within the furnace and no cooling or dilution of the heating gases prior to their contact with the fluid heating surfaces. The air absorbs a certain amount of heat in its circulation through the cooling passages but Whatever loss may result is practically negligible in that it is compensated for by the fact that, for equal values of heat absorption, the total amount of convection surface required with the gases of higher temperature, is less than would be the case with gases that have been diluted and cooled.

A further benefit derived from the invention lies in the fact that with the subetmospheric pressures in the wall cooling passages, there is no leakage of cold air into the furnace chamber and consequently no cooling from this source of the furnace gases or of heating surfaces that may be in proximity to such wall as in the case of tubes [2 and M which lie adjacent the hearth.

While in the specific embodiment I have referred particularly to a double form of furnace it will be understood that certain features of. the invention may be applied equally well to other forms of furnaces such as one having only a single firing chamber, and it is, therefore, my purpose to include these and other variations of construction within the scope of the appended claims.

I claim:

1. An oil heater comprising a furnace chamber and a tube chamber, a hollow bridge wall separating said chambers except at their upper ends, a bank of convection heated tubes in said tube chamber, an outlet fiue connected to said tube chamber below said tube bank, an atmospheric air inlet to the upper end of the space in said bridge wall, and a passage connecting the lower end of said bridge wall space to said tube chamber below said tube bank, said outlet flue affording direct and undivided discharge of gas and air from said tube chamber to the atmosphere.

2. An oil heater comprising a furnace chamber and a tube chamber at one end thereof'connected their upper ends, a bank of convection heated tubes in said tube chamber, an outiet flue connected to said tube chamber below said tube bank, and a cooling passage extending below the floor of said furnace chamber having an atmospheric air inlet at one end and its opposite end connected to said tube chamber below said tube bank, said outlet flue affording direct and undivided discharge of gas and air from said tube chamber to the atmosphere.

3. In combination, a furnace having walls defining combustion and convection chambers, fluid-heating tubes exposed to heat of combustion within the respective chambers, the tubes of said combustion chamber lying adjacent a wall having an air passage associated therewith. means connecting said air passage with said convection chamber for inducing a positive circulation of cooling air through said passage at a pressure less than the pressure within the chamber, and causing said cooling air to be discharged into the stream of hot gases of combustion subsequent to their contact with tubes in the convection chamber.

4. In combination, a furnace having enclosing walls and an interior wall dividing said furnace into combustion and convection chambers, fluidheating tubes contiguous to a Wall of each cham ber, air passage associated with said walls and provided with inlet and outlet connections for inducing positive circulation of cooling air through said passages at pressures less than the pressures within the chambers, said air passages being connected to the atmosphere at their inlet ends and to a region of lower pressure within said convection chamber at their outlet ends.

5. In combination, a furnace having enclosing walls and an interior wall dividing said furnace into combustion and convection chambers, fluidheating tubes contiguous to a wall of each chamber, air passages associated with said Walls, means inducing positive circulation of cooling air through said passages at pressures less than the pressures within the chambers, and means connecting said air passages with said connection chamber for causing said cooling air to be discharged into the stream of hot gases of combustion subsequent to their contact with tubes in the convection chamber.

6. A fluid-heating furnace including an internal partition wall dividing the furnace chamber into combustion and convection zones having a communicating passage for heating gases therebetWeen, said partition wall having a hollow interior provided with bafiles to direct the flow of cooling air, said bafiles forming serially connected flow passages of successively increasing crosssection, means providing for inflow of cooling air to a passage of relatively small cross-sectional area, and for outflow from a passage of larger cross-sectional area, means maintaining a flow of. heating gases through said zones separate from the flow of air through said passages, and means subjecting said convection zone and said outflow passage to equal pressure conditions.

'7. A fluid-heating furnace including an internal partition wall dividing the furnace chamber into a combustion chamber and a convection flue having a communicating passage for heating gases therebetween, said partition wall having a hollow interior provided with bafiles to direct the flow of cooling air, said bafiies forming serially connected flow passages of successively increasing crosssection, means providing for inflow of cooling air to a passage of relatively small cros sectional area, and for outflow from a passage of larger cross-sectional area into said convection flue adjacent its outlet, said last named passage having communication with the outlet of another wall cooiing passage whereby air from said other passage is combined with said first quantity for discharge therewith through said outflow means.

8. An oil heater having a furnace comprising oppositely disposed combustion chambers with top, bottom and end walls, a convection flue between the chambers and separated from each by a bridge wall, burners in the end walls and directed toward the corresponding bridge walls, radiantly heated tubes lying adjacent the top and bottom walls, other tubes disposed within the convection flue, air passages associated with each bottom wall and bridge wall, and means connecting the outlet ends of said flue and air passages for inducing a flow of cooling air through said passages independent of the flow of heating gases substantially throughout their exposure to said tubes.

9. A fluid heater having a furnace comprising oppositely disposed combustion chambers, a con vection passage located between said chambers and separated therefrom by upright walls each having their upper ends spaced from the furnace roof to provide a passage for heating gases from a combustion chamber to said convection passage, a bank of fluid conducting tubes in said convection passage, air passages within said upright walls and openings in a side wall of each of said air passages communicating directly with said convection passage at a position below said tube bank, and means inducing a flow of gas downwardly through the convection passage and a flow of. air downwardly through said wall passages.

10. The method of operating a heat exchanger having fluid heating surface and a combustion chamber at each end with an intermediately disposed convection flue separated from each combustion chamber by a hollow bridge wall with means for admitting air to the interior thereof, which includes firing the combustion chambers with elements of combustion, passing fluid in contact with the heating surface, admitting air to the interiors of said hollow bridge walls, and maintaining a stack draft sufiicient to induce a flow of combustion gases through the furnace in contact with fluid heating surface and to sustain an independent flow of cooling air through the hollow interior of each bridge wall entirely out of contact with said heating surface and separate from said gases except at their discharge from said flue.

11. The method of operating a heat exchanger having fluid heating surface and a combustion chamber at each end with an intermediately disposed convection flue separated from each combustion chamber by a hollow bridge wall with means for admitting air to the interior thereof, which includes firing the combustion chambers with elements of combustion, passing fluid in contact with the heating surface, admitting air to the interiors of said hollow bridge walls, maintaining a stack draft sufficient to induce a flow of combustion gases through the furnace in contact with fluid heating surface while sustaining an independent flow of cooling air through the hollow interior of each bridge wall entirely out of contact with said heating surface and separate from said gases except at their discharge from said flue, and regulating the flow of air through the interiors of the hollow bridge Walls.

OTTO C. SCHAUBLE.

CERTIFICATE OF CORRECTION. Patent No. 2,11 .2,956. January 5, 1959.

OTTO C. SCHAUBLE.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows Page 2, second column, line 12, claim for "passage" read passages; page 5, second column, line 22, claim 11, for "while sustaining" read and to sustain; and

that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Officeo Signed and sealed this 7th day of March, A,D 1959.

Henry Van Arsdale.

(Seal) Acting Commissioner of Patents.

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