US1851745A - Method of combustion - Google Patents

Description

March 1932- A. u. WETHERBEE METHOD OF COMBUSTION Original Filed July 21, 1927 2 Sheets-Sheet l March 29 1932. U, WETHERBEE 1,851,745

METHOD OF COMBUSTION Original Filed July 21, 1927 2 Sheets-Sheet 2 Patented Mar. 29, 1932 UNITED STATES PATENT OFFICE ASHUR U. WETHERBEE, 0F EVANSTON, ILLINOIS, ASSIGNOR :lO AUTOGAS CORPORA- 'IION, OF CHICAGO, ILLINOIS, A CORPORATION OF DELAWARE METHOD 0] COMBUSTION Original application filed July 21, 1827, Serial No. 207,399. Divided and this application filed December 27, 1927. Serial No. 242,563.

My invention relates to combustion of gaseous fuel, and the object of the invention is, broadl to provide a more economical method 0 developing the heat generated by combustion of a gaseous fuel. This application is divisional of my copending application, Serial No. 207,399, filed July 21, 1927.

While throughout the specification and claims herein I refer to the fuel as gas or as being gaseous, I do not intend to limit the invention to the burning of a fixed gas, as the principles of the invention and the structural features herein disclosed are applicable to the combustion of any fuel of sufficient fineness that it acts substantially as a gas, that is, either vaporized, atomized, or pulverized to a degree where its combustion is capable of occurring with substantially explosive rapidity.

The specific problem which I have set out to solve is the provision of a method for burning city gas with high economy of heat development and transfer, and having the ability to stop and start operation of the burner with ease and certainty.

Where known methods of utilizing gas combustion for house heating service have been employed, the cost has generally been excessive as compared with the cost of other fuels. This is particularly true in connection with known types of steam or hot water systems which have been worked out in connection with the combustion of solid fuel. It has been a generally accepted fact that with known types of steam or hot water boilers or furnaces, the substitution of gas fuel for the solid fuel, for which such boilers or furnaces were designed, has been out of the question because of inefficiency and consequent excessive cost.

I have studied the problem and come to the conclusion that the reason for this is largely chargeable to the method of heat transfer involved.

In the combustion of solid fuels there is always a mass of incandescent solid fuel which radiates heat. Where gas is burned in the Bunsen type of burner, the flame, although short, has very small heat radiating power. It appears to be a known fact that radiation from a given mass is a function of temperature of that mass and other characteristics thereof.

According to the law of Stefan and Boltzman, radiation of heat from a given mass is approximately proportional to :the difference between the fourth power of the absolute temperature of the heated mass and the temperature of the receiving surface.

I have therefore taken, as the primary consideration in my invention, the possibility of transferring the heat from the combus tion of the gas to the boiler walls by employing a mass of suitable character involving the maximum amount of heat radiation.

As a means for providing the incandescent mass, I employ a mass of refractory of large superficial surface and of a loose granular or foraminated structure. In the preferred embodiment later to be described, I utilize relatively thin fiat chips of fire-brick laid on a. solid base of refractory. The mass of loose refractory is heated by the combustion of gas within the body of the same.

I am aware of the employment of a somewhat similar scheme of combustion within a mass of loose refractory material originally patented by Lucke, but, as I shall point out later, there are very important and essential differences between my method and that of the prior art. I am also aware of the use of targets against which a blast burner is directed for the production of a radiating mass. As I shall point out later, there are serious objections to the use of such a method of combustion in the service in which my invention is particularly useful, namely, domestic heating.

For the development of maximum temperature of the mass, the heat of the flame must' be as great as possible. To this end no excess air should be admitted and, at the same time, no unburned fuel should be passed out of the stack in the interest of economy. It is one of the essentials of my invention that there must be as complete mixing of the gas and supporting air as possible.

For house-heating service, the combustion should be capable of automatic control, i. e., preferably off and on, or, alternatively,

up and down, and, above all, there must be no danger of explosion at any time, nor should there be any appreciable explosive puff When the burner comes on after being shut off, or when the burner is shut off after an operation. Likewise, the burner must be so constructed that the flame cannot strike back into any confined space, both because of danger of explosion and because of danger of injury to the burner by excessive heat.

The avoidance of explosions or explosive puffs requires that the gas be not confined and that there be at no time a volume of mixed gas and air in the burner or furnace capable of creating a disturbance.

One of the features of my invention provides for mixing the gas and air substantially at the point where the same enter the combustion space. The mixture is then this mass of loose refractory .and carry on combustion at a high rate, i. e., at substantially an explosive rate. The mass of loose refractory becomes incandescent and the radiation of heat occurs from the lateral face of the bed, i. e., from the'exposed upper surface. The propagation of heat rays is therefore at substantially right angles to the general direction of the burning gases. By this means only a small mass needs to be heated up to start and a large radiating surface is provided. This great ratio of radiating surface to mass permits of-a much greater rate of fuel combustion within a given space than has been possible heretofore. Overheatin%of any part of the mass is prevented.

y propagation of heat radiation from the side or flank of the path of gas travel, the length of the flame is not of importance.

I am aware that it is old to fire upward through a mass of refractory and project the heat in the same direction, but the prior art has this inherent defect, namely, that the central inner part of the mass attains a high degree of incandescence which can radiate only through interstices of the upper layers. The

top layers are an effective barrier to radia-v tion from the central mass. The major part of combustion is at the center and, hence, the top layers, from which effective radiation must occur, if at all, are unheated by direct contact with the fire. If the input of combustible material is too great, then burning over the mass occurs. If the input is too small, the fire occurs wholly inside the mass and the top layer effectively prevents radiation.

In my burner the length of flame and, hence, the amount of fuel burned may be greater or less, without interfering with proper development of incandescence and free radiation fronithe burner.

There are many features of novelty incidental to the above main features which will be apparent from the following detailed specification and claims, taken in connection with the accompanying drawings which illustrate an embodiment of my invention.

In the drawings Fig. 1 is a plan View of a burner embodying my invention;

Fig. 2 is a vertical section taken on the line 2-2 of Fig. 1 shown on an enlarged scale; and

Fig. 3 is a similar section through a portion of a modification.

Referring now to Figs. 1 and 2, I provide a bowl 1, which is preferably constructed of sections. This bowl is made of fire-brick of high heat resisting and insulating properties. The sections are provided with overlapping joints 2-2 so as to prevent an open crack where the sections come together.

This bowl constitutes, in reality, a plate or disc of refractory insulating material for radiating the heat developed by gas combustion upwardly and for preventing the travel of heat there developed downwardly through the mass of the same.

The section 3 contains a recess 4 in which there is disposed a spark plug 5, the metallic shell of which is suitably grounded and the central electrode of which is connected through suitablecontrol apparatus with a source of high tension current.

I have, for the sake of clearness, omitted from the present disclosure the control apparatus, reserving the same for a later applimixture readily.

The bowl or disc 1 is seated on a supporting frame comprising the ring 6. This ring 6 in turn is supported by three or more posts 7 resting upon a foundation 8. These posts are preferably sections of' pipe having pipe. flanges 9 at their lower ends and having their upper ends disposed in pockets 10 and engaging the lugs 11 through the medium of a threaded nut 12 by which the height of the posts may be adjusted.

The lugs 11 on the ring 6 extend inwardly and are apertured to receive the clamping bolts 13 for clamping the mixer 14. to the frame.

The mixer 14 comprises an outer gas chamber 15 and an inner air passage 16 within which is disposed a helical directing vane 17 for producing a whirling action of the air passing through the passage 16. The lower end of the mixer 14 comprises a cylindrical threaded extension 18 connected by a pipe clbow 19 to an air inlet pipe 20, this pipe 20 in turn leading to the delivery of a fan or blower (not shown). The gas chamber 15 communicates through a hollow lateral boss 21 and pipe fittings 2223, which latter, in the present case, are 45 degree Ls, with the gas inlet pipe 24. The air pipe 20 is provided with a throttle valve 25 and the gas pipe 24 is connected with a similar throttle valve 26, these two valves being connected by a stem 27 and having a suitable operating handle 28 for simultaneous adjustment. The gas pipe 24 leads to the city main through a pressure regulator, preferably of the mercury type, for holding the gas pressure substantially constant at all times. It is apparent that the butterfly valves 25 and 26' may be independently regulated, but after the pressure regulator for the gas has been suitably adjusted to the delivery of the blower connected to the air-pipe 20, a simultaneous adjustment of air and gas, such as is possible by the butterfly valves 2526, is desirable.

The gas chamber 15 empties into the air pas sage 16 above the vane 17 through a slot 29. The gas and air then proceed from the outlet of the mixer 14 through a short passageway 30, which passageway is, in the form shown in Figs. 1 and 2, provided as a central aperture in a disc or plate 32 of firebrick, let into a recess or counterbore in the bowl or plate 1. The mixer 14 extends up through the central opening 32 which is formed in the disc or bowl 1.

The opening 30 in the disc 32 is covered by a cap 33 of fire-brick or like material, sup ported on a central spider 34, which spider has a series of directing vanes preferably, but not necessarily, helically disposedin a direction opposite to the twist ofthe d recting vane 17 The spider 34 1s conically formed at its lower end to seat in the conical upper end of the opening 30 for centering these two parts with respect to each other. The cap 33 is preferably cemented to the spider 34 so that the lower edge of the cap 33 is held a fixed distance above the plate 32 to provide a peripheral slot or outlet 35 around the periphery of the cap 33.

Along its outer margin, where the plate 32 comes flush with the surface of the bowl or disc 1, I provide a series of projections disposed a short distance from the rim of the cap 33. Flat chips 38 of fire-brick rest at their inner edges against the cap 33 and are supported away from the surface of the disc 32 and bowl 1 by the projecting ends or projections 37 Chips graduated in size are then laid in overlapping rings in the fashion of shingles from the central chips 36 to the outer edge of the bowl 1 with the smaller chips disposed at the outer periphery of the bowl 1.

In effect, the bowl 1 comprises the central disc 32 as well as the outer sections. The central disc 32 is, in this case, made of a single piece, but this is not essential, since, due to the great heat to which it is subjected, it expands and contracts and tends to crack in case it is made of one piece.

As shown in Fig. 3, I prefer therefore to make the gas passages of metal throughout until they discharge into the zone of combustion.

It will be seen that by disposing the coarser chips at the center and raising them slightly above the floor of the bowl, a relatively free passageway for the mixture of gas and air is provided within the central part of the bowl and the passageway becomes more and more restricted to the outer rim by the use 'of graduated chips.

I have found the use of such chips of firebrick highly satisfactory, but I do not aim to convey the impression that other forms of granular material may not be used.

Now the construction which I have shown, namely, the flat thin chips of refractory material, that is broken fire-brick, serves to perform this function sufliciently well to direct the flow of burning gases out along the surface of the bowl 1 so that burning occurs within the mass of broken refractory, even though it is very thin, and the heat thus de veloped is projected off by radiation substantially normal to the surface of the granular mass. It will be seen that by the shingling effect the gases are diverted downwardly toward the surface of the bowl 1 and thereby are held more or less in contact with the same.

I have tried the burner without the layer of granular refractory. It will burn gas, but two things are noticeably absent; first, only a very small amount of radiant heat will be developed; and, next, only a small amount of gas can be burned within the bowl as compared with the amount that can be burned when the layer of loose refractory is disposed thereupon.

Preferably in the operation of the device, the blower is started and the spark plug is caused to act, and thereafter the gas is admitted through the pipe 24. When combustible mixture reaches the spark plug, it will be ignited and it will burn back to substantially the edge of the cap 33.

' If the amount of mixture delivered to the burner is increased, the edge of the flame reaches out furthentowards the periphery of the bowl 1, thereby increasing the area of the refractory material that isradiating energy, and if the amount of fuel supplied is decreased then the flame recedes in the refractory layer towards thecap 33; but the size of the flame within the limits of the burner is immaterial, or substantially so for the development of radiant heat. The amount of fuel which. can be burned per unit of time in a burner of this character is amazing.

The efiiciency of the device as a radiator of heat is very high, because of the large radiating area as compared to the volume of gas The spider 34 may be made integral with the metal cap 42-, or it may be made separately. The spider 84 has suitable vanes which serve both to support the cap and also to direct the mixture. The nozzle gap 44 is formed between two metallic surfaces, namely, the

llange 45 of the cap and a companion flange 46 of a neck member 47 which forms an extension of the air passageway 16 above the vane 17 and the peripheral inlet 29 from the gas chamber 15.

I wish to call attention to the very small volume of mixture which can at any time exist between the slot 29 and the slot 44, in the form shown in Fig. 3, or between the slot 29 and the slot 35, shown in Fig. 2. The volume of combustible mixture is so small at any time that, even if the same should be ignited, no serious injury can be done, particularly in View of the fact that the cap 33 or is held in place only by its own weight. The velocity of the gases through this part of the path is normally so great that combustion does not strike back. In addition, mixing is carried on in such a short space that a combustible mixture, as such, is not attained until substantially the very outlet into the combustion space.- Hence, in starting or stopping combustion under automatic control, the objectionable explosive start or stop of the prior art is not encountered.

Tests which I have made on this burner, in conjunction with a standard and well known cast iron boiler very widely sold for domestic heating, and designed for the combustion of solid fuels such as coal or coke, show amazingly high efficiencies.

These tests were made with a burner in which the bowl 1 had a diameter of 18", and being 2 thick at the center and 3% thick at the periphery. The weight of the bowl 1 was approximately 45 lbs, and the weight of the firebrick chips 5 lbs.

Due to the small mass of the chips 38, and their being spread out in a thin layer, the appearance of incandescence was almost immediate, especially in a ring ust outside the point 37. This ring of incandescence spreads very rapidly, and the temperature increases rapidly, until a balance is obtained between the heat absorbed from the combustion and that radiated to the boiler. Numerous observations with a reliable optical pyrometer show a temperature of approximately 3000 F., or slightly more, these observations being taken through'the interstices between the chips. Since the points observable are those which radiate heat through the interstice, the temperature of the point seen is less than the majority of these surfaces, which are radiating and/or reflecting heat back and forth between each other. It is believed that the temperature of the lower side of the chips approximates 3300 F., as there are very visible evidences of the softening of the surfaces of these chips now being used, which are of i the brand known as Empire, which softens atthat temperature.

' It is evident that with a single layer of chips, such as were used in these tests, having the under side of such chips at such a high temperature, gives a maximum of radiation to the heat absorbing surface.

Two of these tests were run in strict accordance with the code of the American Gas Association, under the direction and supervision of two technical experts of a prominent public utility company, and with the cooperation of their laboratory in obtaining accurate determinations of'the heating value, density, etc. of the gas used.

In one of these tests, the output of the boiler was 87.4% of the rating given it by the Master Steam Fitters Code of Chicago, and an efficiency of 81.2% was obtained, based on the higher heating value of the gas. In

;the other test, the output of the boiler was 176.8% of the Master Steamfittcrs Code. and an efliciency of 76.45% was obtained. Since very little convected heat absorption is posfrom a minimum of 2.05 to 3.75 of water,

due to excess air was very little, as shown by the following analysis of the flue gases:

CO 13. 2 12. 0 O 3.9 4.6 CO 0.0 0.0

Total 17. 1 17. 5

The percentage of excess air shown is much below that obtained in large central station power plants, with very large combustion volume surrounded by hot refractories as compared with this case where the unit volume is very small and surrounded by walls cold as compared with the heat of combustion.

It will be appreciated that in Fig. 1 I have shown only a small part of the sur ace of the bowl covered with the chips of fire-brick, but that in practice the entire upper surface is so covered.

The sections of the bowl 1 are preferably held by dowel pins, such as shown at 47 in Fig. 2 for loosely holding the parts together upon the frame ring 6. The vane member 17 is preferably formed on an increasing pitch in conical shape, and it will be observed that, in general, the cross section of the passage for the mixture of air and fuel continues to be restricted through the outlet at or 44. The lower end of the vane member 17 comprises a ring which is set in a recess in the lower part of the mixer 14 and held therein by a pin 48.

Instead of having the top surface of the bowl 1 smooth, I may provide the same with a series of projections which serve, in part, to support the chips 38.

In both forms of my invention illustrated, the fuel mixture is projected from the nozzle radially thereof and in a thin sheet between the thin upper layer of refractory and the layer of refractory forming the bowl. Due

' to the inclination of the chips constituting the thin upper layer of.refractory, the flaming fuel mixture is deflected downwardly toward the refractory bowl so that combustion occurs between the two layers of refractory,

- and the thinupper layer of refractory is quickly heated to incandescence by heat derived from combustion of the fuel mixture. Since the fuel mixture is projected in sheet form between the two layers of refractory and substantially parallel thereto, and is deflected downwardly toward the refractory bowl, little or no combustion occurs above the upper face of the thin upper layer of refractory. This is advantageous as avoiding the creation of inert gases above this thin layer of refractory which gases would tend to interfere with maximum radiation of heat I from the outer face ofthe thin upper refractory layer. The relation of the two layers of refractory and the direction and manner of projection of the burning fuel mixture between these refractory layers, are of importance as contributing to maximum efiiciency.

I do not intend to limit the invention to the details shown or described.

I claim 1. The method of developing heat from the combustion of fuel, which consists inproviding a thinsheet of refractory material, mixing the fuel with air to provide a rapidly burning mixture, projecting the mixture while burning along one face of the sheet and deflecting it away from the other face of the sheet therebymaintaining the burning mixture at the first mentioned face of the sheet irrespective of normal variations in velocity of the mixture, heating the refractory sheet to incandescence by heat derived from combustion of the fuel mixture, and radiating heat from the other face of the layer of refractory material.

2. The method of developing heat from the combustion of fuel, which consists in providing a thin sheet of refractory material,

projecting a rapidly burning fuel mixture while burning along one face of the sheet and maintaining the zone of combustion substantially constant with respect to said surface of the sheet, heating the refractory material to incandescence by heat derived from combustion of'the fuel mixture, and radiating heat from the other face of the sheet of refractory material.

3. The method of developing heat from the combustion of fuel, which consists in projectone of which layers is thin and is formed of refractory material, confining the combustion of the fuel to the space between the two layers, heating the layer of refractory mate- .rial to incandescence by heat derived from combustionof the fuel mixture, and radiating heat from the outer surface of said refractory layer. V

5. The method of developing heat from the combustion of fuel, which consists in projecting a thin sheet of rapidly burning fuel mixture from a central area substantially radially between two layers of material dis-' posed in proximity to each other and extending substantially radially from said central area, one of said layers being thin and of refractory material, heating the thin layer of derived from combustion of the fuel mixture,

d and radiating heat from the outer surface of said thin layer of refractory material.

6. The method of developing heat from the combustion of fuel, which consists in projecting a rapidly burning fuel mixture between two layers of refractory material disposed in proximity to each other, the fuel being projected substantially parallel to the la ers and one of said layers being thin, deflecting the burning fuel mixture toward the other layer and thereby maintaining the zone of combustion between the layers and within the outer face of the thin layer, heating the thin layer of refractory material to incandescence by heat derived from combustion of the fuel mixture, and radiating heat from the outer face of said thin refractory layer.

7. The method of developing heat from the combustion of fuel, which consists in projecting a rapidly burning fuel mixture between two layers of refractory material disposed in proximity to each other and in superposed relation, the upper layer being thin, deflecting the burning fuel mixture downwardly toward the upper face of the lower layer of refractory, heating the upper layer of refractory to incandescence by heat derived from combustion of the fuel mixture between the layers, and radiating heat from the upper face of said upper layer.

In witness whereof, I hereunto subscribe my name this 22nd day of December, 1927.

ASHUR U. WETHERBEE.

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