Furnace system

July 16, 1963

3,097,686

R. D. MORROW

FURNACE SYSTEM

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United States Patent Office

3,097,686

Patented July 16, 1963 forming the major heating chamber of the furnace system.

Combustion products from chamber 24 pass outwardly in the direction of the arrow through a second check valve 26 to a conventional uniflow vortex tube 28. Vortex tube 28 is the type sometimes referred to as a RanqueHilsch tube first described by G. Ranque in U.S. Patent 1,952,281. In the system illustrated the vortex tube is of the uniflow type with the relatively hot and cold gas outlets positioned at the same end of the tube.

It is well known that in operation a vortex tube divides a compressed gas into two moving streams each with a different temperature. The outer stream is substantially hotter than the inner one. The exact mode of operation is not fully understood and several theories have been advanced for explaining the operation of these tubes. One of the most widely accepted theories presumes that the gas is broken up into separate helical gyrating layers with the inner layer compressing the outer layer through centrifugal force and giving up some of its energy to the outer layer. The energy given up is represented by -an increase in temperature of the outer layer and a decrease in temperature of the inner layer each of which may be separately removed from the same end of a uniflow tube by means of suitably positioned and throttled concentric apertures. It has been found that a maximum temperature differential between the exiting relatively hot and cool gas streams is obtained by a division of 30% of cold gas and 70% hot gas. Temperature differentials of as much as 100° F. are not unusual.

As shown the vortex tube 28 comprises a generator chamber 30 and a vortex generator 32 having a tangential inlet 34 through which the high pressure gases gain access to the central tubular channel 36 of the vortex tube. The gases are caused to spiral through the tube so the cooler portions of -the gas collect in a central stream and the warmer portions collect in an outer annular stream surrounding the cooler gas. The central cooler stream is extracted through a central restriction 38 and passes to atmosphere through outlet conduit 40. Hotter portions of the flue gas pass outwardly through the outer restriction 42 to a hot gas feed back line 44.

Feed back line 44 supplies the hotter portion of the exhaust or flue gases to the inlet conduit 12 where these hotter portions are mixed with the incoming air supplied to a blower 14 and tend to preheat this air. In operation, the air-fuel mixture feed to the combustion chamber is controlled so that it contains approximately 200% excess air. This excess air serves to sustain complete combustion and further lowers the temperature in the combustion chamber to an acceptable value.

The combustion chamber and vortex tube are surrounded by an insulating jacket 46 containing a heat exchange fluid such as water as indicated at 48 which takes heat produced in the combustion chamber from the outer surface of the vortex tube 36 and from the hot gas feed back line 44. Cold water may be supplied to the water jacket through inlet 50 from a suitable supply and the hot water is drawn off through outlet conduit 52.

In operation, as the air fuel mixture burns in the combustion chamber the pressure in the chamber rises forcing the flue gases into the vortex generator of the vortex tube. Water is circulated over the chamber and tube extracting heat to be used for any -suitable hot water heating system application such as tap water or for use in a hot water type radiant heating system. The products of combustion are removed from the center -or colder section of the vortex tube through outlet conduit 40. The excess air tends to be retained in the outer air stream of the vortex tube and is returned to the high pressure side of the combustion chamber.

FIGURE 2 shows a schematic diagram of a modified

3,097,686 FURNACE SYSTEM

Robert D. Morrow, Baltimore, Md., assignor to Product Development Associates, Ltd., Baltimore, Md.

Filed May 12, 1960, Ser. No. 28,588 ⁵

Claims. (Cl. 158—1)

This invention relates to a furnace system for heating water or another suitable fluid, medium and more particularly to a heating system wherein the hotter portions of 10 the flue gases -are fed back into the input of a combustion chamber.

Various systems are known wherein portions of the exhaust products or flue gases are fed back to the input of a combustion chamber to improve the overall efficiency of a heating system. However, these systems suffer from the serious disadvantage in that there is little or no selectivity exercised with respect to which portions of the flue gas are recirculated through the system. In most instances the feed back gases are selected on a quantity basis with -a certain percentage passing through a ratio valve or other type of valving system so that a certain portion of the entire exhaust gas composition is recirculated to the combustion chamber.

The present invention provides a heating system having substantially increased efficiency which incorporates a selective feed back of flue gases from the exhaust system of a combustion chamber to the input wherein the fed back exhaust gases are mixed with fuel and air entering the combustion chamber. The selectivity is exercised through a vortex tube which separates the exhaust gases into relatively warm and cold components. The cold component is permitted to exhaust to the atmosphere and only the warm component is fed back to the input of the heating system. In this way it is possible to reduce the temperature of the exiting gases from the system and consequently substantially increase the thermal efficiency of the furnace. It is theoretically possible by actually cooling the exhaust gases below atmospheric temperature to obtain a thermal efficiency for the heating system of the present invention of over 100%.

It is therefore, a primary object of the present invention to provide a novel heating system having increased efficiency.

Another object of the present invention is to provide a heating system having selective feed back of portions of the flue gas exhaust to the system input.

Another object of the present invention is to provide a heating system with flue gas feed back and incorporating means for separating the exhaust gas into distinct components and feeding back only the hotter component to- the system input.

These and other objects and advantages of the invention will be more apparent upon reference to the following specification, claims and appended drawings wherein: ⁵⁹

FIGURE 1 is schematic diagram showing in simplified form the basic heating system of the invention and,

FIGURE 2 is a schematic diagram of a modified embodiment of the heating system of the present invention.

Referring to the drawings and particularly to FIGURE 1, the heating system of the present invention generally indicated at 10 comprises a gas inlet conduit 12 which supplies either ambient or super charged air to the input of an air blower 14. Fuel is supplied from any suitable ₆₅source to the system through a supply pipe 16 connected to a restricted portion 18 in the output line 20 of the blower which restricted portion defines a venturi connection so that the pressurized air flowing from outlet 20 through the restriction 18 draws fuel from pipe 16. The 70 pressurized air-fuel mixture passes through a check valve 22 in the direction of the arrow to a combustion chamber

3,097,686 embodiment of the heating system of the present invention with like elements bearing like reference numerals. In the system of FIGURE 2 the blower is eliminated and in its place the combustion chamber is fed by means of a novel injecter and check valve arrangement. As in the embodiment of FIGURE 1, water to be heated is circulated through the jacket 46 from inlet conduit 50 by suitable means such as the circulating pump 54 and is drawn off through conduit 52.

The hotter portion of the exhaust or flue gases is drawn off from the periphery of the Hilsch tube and fed back through line 44. A portion of the combustion products is fed through pipe 58 from the combustion chamber 24 into a converging-diverging nozzle 60 where the combustion products attain supersonic velocities. The stream of high velocity combustion products impinges on ambient air supplied by way of line 62 and check valve 64 imparting velocity to the air molecules. The air and combustion products enter a diffuser 66 where they are compressed to a pressure higher than the pressure existing in the combustion chamber. This high pressure air and combustion mixture then picks up the fuel at the throat of venturi 68 and enters the combustion chamber through line 70 to sustain the steady flow combustion process. In so doing the mixture passes through check valves 72 and 74.

The fuel is fed from a suitable source to line 75 and through a venturi 76 where it picks up a small amount of ambient air from line 78. The fuel and small quantity of ambient air enter the system at venturi 68 between the two check valves 72 and 74. The air-fuel mixture supplied by way of venturi 68 into the combustion chamber is adequate during the starting of the furnace. However, once the furnace is started the gases flowing through the injecter comprising nozzle 60 and diffuser 66 acts to pull more air from line 62. The increased pull of air from line 62 in turn acts to pull more fuel by way of venturi 68 as it passes through the venturi between the check valves and the system automatically builds up to an operating level. The check valve 64 in the air line serves only to prevent reverse flow in the event of a malfunction in the injecter.

It is apparent from the above that the present invention provides a novel heating system of substantially increased efficiency which theoretically may possess a thermal efficiency greater than 100% by actually cooling down the exhaust gases below ambient temperature. An important feature of the present invention is the selective feed back of a hot component of exhaust gas to the combustion chamber inlet with the separation of the exhaust gas into a hot component being accompanied by a separation of the remaining portion of the exhaust gas into a colder component.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.