US2959140A - Smokeless and odorless incinerator - Google Patents

Description

Nov. 8, 1960 H. FRIEDBERG sMoxELEss AND oDoRLEss INCINERATOR I5 Sheets-Sheet 1 Filed Aug. 21, 1957 IN VEN TOI?. HARRY Felt-Daems v BY W, @0, Z

A TTOENE'YS Nov. 8, 1960 H. FRIEDBERG 2,959,140

sMoKELEss AND onoRLEss INCINERATQR Filed Aug. 2l, 1957 5 Sheets-Sheet 2 IN VEN TOR.

` /AEE Y FTQ/95526 BY l W, azu,

A 7 TORNEKS Nov. 8, 1960 H. FRIEDBERG sMoxELEss AND onoRLEss INCINERATQR Filed Aug. 21', 1951 s sheets-sheet s IN VEN TOR. Meer FAQ/05526 BY W, W7u,mff4

SMOKELESS AND ODORLESS IN CINERATOR Harry Friedberg, ICleveland, Ohio, assignor to Waste King Corporation, Los Angeles, Calif., a corporation of California Filed Aug. 21, 1957, Ser. No. 679,334

4 Claims. (Cl. 110-18) This invention -relates to improvements in a smokeless and odorless domestic incinerator.

One of the objects of the present invention is to combine in `a single domestic lincinerator a number of elements and structures which have been previously kno'wn, together with some which are now as herein disclosed, so that there is the smallest possi-ble offensive odor in the ilue gases discharged into the atmosphere; smoke is eliminated; solid particles are eliminated from the ilue gases; the temperatures developed in the incinerator are held so low that combustible surfaces, such as iloors and walls upon which or near which the incinerator is installed are not subjected to any form of lire hazard; and any garbage load charged into the incinerator is not subjected to the processes of putrefaction but is efficiently reduced to ashes.

Another object of the present invention is to combine in a single domestic incinerator a means for slowly dehydrating a moist charge in the furnace chamber, a means for then igniting and burning the charge at a slow combustion rate so as to avoid overloading the discharge ilue with an excessive amount of products of combustion, Ian ash trap to eliminate particulate matter larger than fifty microns, and some matter between twenty-live and ifty microns, an after burner or secondary combustion device for burning small particulate matter in the form of aerosols traveling out `of the furnace chamber with the products of combustion, and a stack' dilution device which aids in the slow combustion previously mentioned and which also aids in keeping the discharge flue pipe to such a temperature that it is not a fire hazard t-o combustible iloors and Walls located near the incinerator.

Other objects include the arrangement of the parts to carry out the functions mentioned above, and further objects yand advantages of my invention will be set forth in the accompanying description and clearly defined in the appended claims.

In the drawings,

Fig. 1 is a vertical sectional view taken centrally through an embodiment of my invention and generally along the line 1--1 of Fig. 2;

Fig. 2 is a fragmental perspective View of a portion of the device of Fig. l with certain parts broken away and the ash trap moved out of its operative position in order to more clearly show the construction of the parts; while lFigs. 3, 4 and 5 are respectively a front elevational view, a top plan view, and a side elevational View of the secondary combustion device seen at the upper right hand portion of Figs. 1 and 2.

It has become evident for some time that awakened interest in air pollution problems would inevitably dictate that refuse incinerators be so designed that they would not contribute to the air pollution problem. I believe I am the iirst to combine in -a single incinerator all of the features herein disclosed and so interrelated that a1- most any combination `of domestic refuse can be consumed in the incinerator with practically no air pollution rarice whatsoever. Each part of my device contributes to the eiliciency and functioning of the whole yand each element contributes to the unitary result.

Referring now to Figs. 1 and 2, a furnace chamber '10 is formed by means of a front wall 11, side walls 12, a rear Wall 13 and a bottom wall 14. The front Wall includes an offset portion 11a for the accommodation of an ash drawer 15, which may be removed for dumping through a suitable opening in the casing utilizing the handle 16. Practically, the furnace and the ash pit are all a single chamber merely being separated by a grate 17 which may be reciprocated by means of handle 18 which is welded to a bracket 19 which is in turn welded to the grate. A false rear Wall 20 is provided for the furnace chamber 10, this wall being the front lwall of an ash trap to be described later. There is a partial top wall 21 covering the space between the side walls 12 and extending substantially the distance between the walls 13 and 20 already described. Other than this, the furnace chamber is open at the top as indicated at 22 for the introduction of material to lbe burned.

The ash trap comprises a front wall 20 mentioned previously on the side toward the furnace chamber, two generally parallel side walls 23 rigid with the front wall and extending rigidly therefrom yand resting snugly inside of the side Walls 12 of the furnace chamber sheets. The trap also has a bottom wall 24 which slopes from the front downwardly toward the rear and stops short `of the rear wall 13 of the furnace chamber section so as to -allow material collected on the said bottom wall 24 to work toward the rear and fall downwardly into the ash trap 15 deected by a baille member 25 secured to the rear wall 13.

Within the ash trap, impingement bafile plates are provided to catch the larger particles which come over with the products of combustion, to `dissipate the kinetic energy of such particles, and thus permit them to fall substantially vertically downward in the ash trap. I-n the present instance, the ash trap is provided with a roof plate 26 rigidly connected to the front plate 20 and to the side plates 23 and sloping slightly downwardly toward the rear. A V-shape baille plate 27 extending substantially vertical has upper tongues 27a less than the full width of the legs of the V-shape baille extending upwardly through suitable openings in the roof plate 26, and tongues 27b at the lower end of a similar character extending through suitable openings in the bottom plate 24. When the plates 24 and 26 are rigidly assembled in the ash trap as shown in the drawings, the V-shape baille 27 is firmly held in the position shown. Other baille plates 28, two being shown on each side of the baille 27, are arranged generally parallel to the -arms of the baille 27 and each baille plate spaced slightly rearwardly from the plate immediately forward of it, and overlapping at that point, so as -to provide llow openings 29 extending the full height of the bailles between the two adjacent bailles 28 on each side and between the baille 28 and baille 27 on each side of the latter. The plates 28 are held in place like the baille 27 by means of upper tongues 28a extending through plate 26 and lower tongues 28b extending through plate 24.

Preferably, the ash trap is removably mounted in the furnace. In the drawings, this is accomplished by providing two U-shaped seats 30, one secured to each of the side walls 12 and adapted to receive the lower edge of plate 20 of the ash trap. This provides a simple pivotal mounting so that the ash trap may be swung from the operative position of Fig. 1 to an inspection position of Fig. 2, or thereafter the ash trap could be lifted out of place. It will be noted that most of the weight of the ash trap lies toward the right of the pivot seats30 as in Fig. 1

and therefore this device willnorrnally return from the tilted position of Fig. 2 to the operative position of Fig. 1. Two metal screws are shownat 31 which engage through sui-table openings 32 in an upstanding flange attached to the plate 20 and engage in other suitable openings 33 in a flange connected with thetop plate 21 to securethe ash trap in its operative position. These are necessary when shipping the device but otherwise would not'be called for.

The ash trap above described substantially seals oft' the right hand side of the furnace chamber as viewed in Fig. 1 save for an opening through which the products ofcombustion pass outwardly to the flue. This opening is' preferably covered with a coarse screen of hardware cloth or heavier rods as indicated at 34.

The flue pipe 35 is connected to the ue collar 36 in the customary manner and is at the same level as the opening covered by the screen 34. At this same level, a secondary combustion device 37 is provided. This device preferablyconstructed of a suitable ceramic refractory material so as to provide -a maze of material adapted to stand the high temperatures encountered there and to give intimate contact between highly heated surfaces and the unconsumed particles in the gases leaving the furnace chamber 10, together with a supply of secondary air or oxygen so that all of these small particles are consumed in the secondary combustion device and do not pass out through the ilue pipe 35. The particular device 37 is clearly shown in Figs. 3, 4 and 5. It consists of a vertical back plate 38, a horizontal top plate 39, a centrally located vertically extending partition plate 40, and a plurality of arcuate plates 41 which pass through suitable openings in the partition plate 40. The arrangement is such that the arcuate members 41 act as balfles'so that the products of combustion cannot pass straight through the secondary combustion device but instead are diverted and come into contact with highly heated surfaces. lThe secondary combustion device is held in place by two bolts 43 which attach the same to the plate 13.

Means is provided to slowly dry out any moisture in the material charged into the furnace chamber 10. Means is also provided for heating the secondary combustion device 37 to a temperature preferably 1200 degrees Fahrenheit or higher. My present invention combines these two functions by the use of a combined burner shield and duct 44, preferably of cast iron or the like, having a generally horizontal duct-like portion 44a connected by suitable bolts to the front wall 11 of the furnace chamber. There is a registering opening through the front wall 11 which registers with the hollow opening through the burner shield which is otherwise generally cylindrical in section and generally imperforate. The burner shield has a rearward generally vertically extending portion 44h which extends upwardly and terminates just below the secondary combustion device 37. The parts are so arranged, as clearly seen in Fig. 1, that much of the weight of the burner shield is held on the baffle member 25. .Preferably, but not necessarily, the horizontal portion 44a of the burner shield is generallyi ovoid in section as clearly seen in Fig. 2 with the arcuate end of smaller radius upwardly so that material does not readily lie on the top of the burner shield. Preferably also, but not necessarily so, the vertically extending portion 44!) is gradually changed to a rectangular section and ared outwardly as it extends upwardly so that the terminal upper end is generally rectangular in form with its longer dimension generally parallel to the plate 38 of the secondary combustion de- Vice.

Means is provided for'heating the burner shield portion 44a substantially continuously to a temperature below 400 degrees Fahrenheit, the preferredl value being between 250 and 290 degrees Fahrenheit. This is'the ideal tcmperature for this 4portion of the burner shield, in order to enableit to radiate that portion of the infra-red spectrum which hasthe ygreatest ability to .penetrate the' charge inV the. furnace; In: vso doing, dehydration withoutcombus# tion of the charge is readily accomplished. Such dehydration, as is well known, stops bacterial action by the removal of moisture and tends "to eliminate the production of alcohols which otherwise would subsequently be oxidized to aldehydes. The aldehydes are major corporates producing offensive odors vand have been blamed for the irritating nature of the smog which is a plague in some of our major cities. The temperature of the horizontal burner shield portion 44a is such, due -to the constantly applied heat as to never rise high enough to ignite the charge in the furnace chamber 10, or to cause the same to smolder. In the present embodiment, this means for heating the horizontal portion 44a to the dehydration temperature is the small burner 45 which I have called the main burner because it operates all of the time. This burner is designed for a uid fuel such as gas or oil. The form here shown burns gas continuously and consumes 800 to 1000 yB.t.u. per hour of natural gas. 'Ihis is somewhat less than one cubic foot of gas per hour.

Means is provided for heating the secondary combustion device 37 preferably to a temperature of 1200 degrees Fahrenheit or higher so as to provide incandescent surfaces which will cause the combustion of finely divided particles otherwise passing out of the furnace chamber 10 to the flue pipe 35. This could be a separate means, but I prefer to combine it with the aforesaid burner shield and duct and have, therefore, bent the same upwardly to provide the vertical duct-like portion 44h to carry combustion gases to a point directly beneath the secondary combustion device. Atthe same time, it is desirable periodically to ignite the dehydrated charge in the furnace chamber 10. i thus accomplish both of these purposes by providing a burner 46 of greater heating capacity than the burner 45 so that periodically the burner 46 may be ignited so as to raise the burner shield portion 44a to a temperature high enough to ignite the charge in the furnace chamber while the products of combustion of the burner 46 travel up the burner shield portion 44b to heat up the secondary combustion device to the desired temperature. To accomplish this double purpose, the burner 4'6 which I call the after burner, is provided with ya capacity of 20,000 to 30,000 B.tu. per hour using natural gas. It will thus be noted that the fuel capacity of the burner 46 is between 20 and 40 times greater than that of the burner 45. This after burner 46 has many functions. When energized, it heats the horizontal burner shield portion 44a to a temperature in excess of 800 degrees Fahrenheit which is more than ample to ignite a charge in the furnace chamber 10 which is in contact with the burner shield. Approximately 25 percent of the energy released by the after burner is used up in igniting the charge. When burning, the after burner aids in establishing and maintaining a proper and satisfactory draft in the venting system connected with the Hue pipe 35. At an input of 20,000 B.t.u. per hou-r, the after burner sends up the chimney approximately 200 cubic feet of flue gases `and excess air per hour. This is a considerable amount and imparts a useful velocity to the iiue gases. The other function of'the after burner has been mentioned, namely, to superheat the products of combustion of a burning or smoldering charge and bring the ceramic maze of the device 37 to a temperature at which catalysis can function. It is believed unnecessary to describe the air and fuel supply to the burners 45 and 46 which are of a standard construction and supplied with the usual safety devices. The after burner 46 is actuated by a combination tirner` This could be provided in several ways but l-as here shown,

atmospheric air is introduced as follows. Referring to the lower left hand portion of Fig. 1, there is provided an opening 48 which allows air to enter, under stack draft pull, from the atmosphere to the space between the furnace chamber walls and the surrounding casing. At this particular point, a bottom plate 49 provides the casing member nearest the foor and a space is provided between this and plate 14. The entering then passes in the direction of the arrows of Fig. 1 between these two plates and then upwardly on the outside of plate 13 and between this plate and the rear wall of the surrounding casing. There is an opening 50 through plate 13 at a suitable point along side the burner shield portion 44b. Here, the cold air enters the ash trap and travels upwardly along side the hot burner shield 4411 (when burner 46 is operating) and thus the heated air passes over the ceramic maze of the device 37 during that time when the device 37 is being heated to a very high temperature by burner 46. Thus, the gases from the furnace charge mix with the preheated combustion air entering through the opening 50 and, because of the elevated temperature in the device 37, the extra oxygen and the contact with the ceramic maze surfaces, the gases are caused to burn in a secondary combustion which burns the hydrocarbons to carbon dioxide and steam. It is interesting to note that the flue gases leaving the secondary combustion device 37 are much hotter than when they entered it.

.As mentioned previously, I use a barometric draft dilution device in order to hold the combustion in the furnace chamber at a rate where the products of combustion can be handled and give a smokeless and odorless incinerator. This device indicated generally at 51 in Fig. l is like that shown and claimed in my copending application Serial No. 525,955, filed August 2, 1955, for Barometric Stack Dilution Device. The present application covers the novel combination of this stack dilution device With the secondary combustion dev-ice 37.

The stack dilution device includes a closed passageway 52 of rectangular section which communicates at the upper end with the ue pipe 35 at a very short distance outsidethe vent collar 36 as clearly seen in Fig. l. At its lower end, the passageway 52 communicates with a box 53 of larger cross section than the passageway 52. This box is completely closed save for a slotted .opening 54 at the bottom side thereof. The arrangement is such that air entering from the atmosphere through opening 54 must make three right angle bends before it passesl out the ue 35. The passageways 52 and 53 are of such a size as `to require a stack draft in excess of .025 inch to .030 inch (water gauge) to overcome the resistance of the passageways 52 and 53. Experience has taught thatV at draft pressures of .030 or less, combustion in the incinerator chamber 10 is sufficiently slow so that it is completed within the combustion chamber and practically none takes place in the flue pipe. Since the average chimney, under primed conditions, rarely has a draft in excess of .010 inch of water gauge, there is no problem of excessive draft in the furnace chamber 10 except at such time as the after burner 46 is energized so that the large volume of products of combustion pass out the ue 35 from the burner shield 44 as Vpreviously described. The operation of the stack dilution device 51 is such that when the draft at the liue collar 36 passes .015 inch Water gauge, a very small amount of air enters at the opening 54. At such time as the draft pressure in the ue 35 increases, when the higher rates of combustion prevail after burner 46 is lit, more and more air enters atthe opening 54 so that the draft pressure at the flue collar 36 is held below .025 or .030. At these higher rates of combustion, the cold air owing through the passages 53 and 52 enters the flue pipes 35, cooling the flue pipe and its gases over the ue length entirely, reducing the iiue pipe and gas temperature to a safe level. An additional arrangement which holds the top of the ue pipe 35 to a safe temperature just outside the incinerator is the introduction of a false top 35a in the ue pipe exactly like that shown at 35 in my above mentioned copending application, which serves the double purpose of protecting the top of the flue pipe from direct contact with the hot gases passing through the main portion of the ilue pipe and at the same time provides a space between the partition member 35a and the top of the ue pipe so that air entering in the direction of the broken line arrows of Fig. 1 may travel directly through this passageway ahd cool the top of the flue pipe at that point.

In the operation of my incinerator a compromise is necessary in that I limit the amount of air introduced into the combustion chamber 10. This is necessary in order to control the rate of combustion at a desired level. If sufficient air for complete combustion were permitted to enter the burning zone, combustion would be too rapid and the major portion of the burning gases would be found in the venting system, `giving rise to red hot iiue pipes and conditions hazardous to combustible material in close proximity to the ue pipe. I, therefore, restrict the amount of air delivered to the combustion chamber to slow down combustion, to obvia-te burning in the venting system. and to keep ue temperatures within reasonable limits. This is accomplished by the stack dilution device 51. Too rapid combustion releases more flue gases than the average venting system can handle. In devices not constructed according to my teachings, this evidence of too large a volume of ue gases is evidenced by outward leakage around the charging door, seams, etc. A properly operating incinerator has a neutral pressure zone some inchesbelow the charging door. This is a fairly definitely marked plane, below which the liuc gases are expanding and leak out of every possible opening, and above this neutral pressure zone air is sucked into the combustion chamber. This zone dictates the position of the vent collar 56. The charging `door is above this zone and air is sucked into the combustion chamber through the door seat. This charging door is indicated at 55 closing and opening just above the open top 22 of the furnace chamber 10. The charging door is pivoted to the casing at 56 and is provided with a handle 57 for manual operation. Also, if desired, an ear 58 may be extended rearwardly rigid with the door 55 and there attached to a link 59 which extends forwardly and downwardly to a point 60 where it is pivotally attached to a foot lever 61 which in turn is pivotally mounted on the frame or casing at 62.

Because I limit the rate of combustion in the chamber 10, for the reasons mentioned above, there are occasions when the amount of air entering the combustion chamber results in unburned gases reaching the flue system. This condition is corrected by utilizing the secondary combustion device 37. The net result of this combination is that l burn the combustibles in the chamber 10 at a controlled rate but nevertheless insure that no unburned material, or substantially none, passes out the ue pipe 35.

The function of the mounting of the ash trap on 'the hinge brackets 3i) is to facilitate access to the interior of the ash trap and access to the secondary combustion device 37, by tilting the ash trap forwardly on its bottom pivots as illustrated in Fig. 2. It will be noted that there is a recess 24a cut in the bottom plate 24 of the ash trap to lit around the upstanding portion Mb of the burner shield. Also, there is a recess 20a cut into the bottom edge of the plate 20 of the ash trap so as to lit over the burner shield portion 44a and this recess is large enough to permit the tilting action shown in Fig. 2.

The operation of my incinerator should now be apparent. Material to be consumed is placed in the furnace chamber 10 by opening the charging door 55. The burner 45 preferably operates continuously and maintains a temperature below 400 degrees Fahrenheit in the lburner shield portion 44a which slowly dehydrates any moisture in the charge. At periodic times, the after burner 46 is turned on which increases the temperature of the burner shield portion 44a to the ignition lpoint of the charge and the hot gases `from burner 46 travel up the burner shield portion 44]; heating the secondary combustion device 37 to incandescence. At the same time, additional air entering through the opening 50 travels along the hot burner shield portion Mb so that it is preheated before reaching the secondary combustion device to aid in additional combustion of unburned products there. All this time, the stack dilution device S1 is limiting the amount of com.- bustion air drawn into the furnace chamberlll as previously described. The air for combustion enters through the opening 48 near the lower left hand corner of the drawing in Fig. l and passes between plates 14 and 49 as previously described. There are other openings as indicated in plate ld and 63, and also alongside the side plates 12, where air may pass upwardly through a passageway between front wall 11 and the front wall of the casing, this passageway being indicated at 64. Other air passes upwardly through the passageway between rear plate 13 and the rear wall 65 of the surrounding casing. This passageway is marked 66. The air passing up passageways 64 and 66 and like passageways between the side walls i2 and the generally parallel walls of the casing at those points, `all passes through the open 'top 22 of the furnace chamber as shown by the curved arrows in Fig. l. Thus, substantially all of the combustion air for the charge in the furnace enters from the top. The amount of this air is restricted by the stack dilution device 51 previously described. As the products of combustion pass out the opening inthe upper portion of wall 20 of the ash trap and through the screen 34, the heavier particles impinge upon the bafes 27 and 28 and drop downwardly into `the ash trap. Since the bulk of the air flow is across the top of the ash trap, the lower portion thereof is very quiescent and the particles settle to the bottom of the ash trap and later fall into `the ash pit. The rest of the products of combustion pass through the secondary combustion device 37 where the smaller particles are cornpletely consumed utilizing the excess oxygen supplied by the air entering through the opening 50 as previously described. All of the products then pass out Ithe flue pipe 3S which is further coo-led by additional air drawn through the passageways 52 and 53. At the same time, the top of the Hue pipe at the exit from the incinerator is cooled by the air passing between the plates 35a and the top of the flue pipe. Thus, all of the factors which I have described combine together to give a substantially completely smokeless and odorless incinerator.

What is claimed is:

1. In a domestic incinerator, walls forming a furnace chamber open at the top and having front and rear walls and two opposed side walls and a bottom wall, a casing surrounding said chamber on all sides and spaced outwardly therefrom, there being an opening in the upper end of said casing for the introduction of the charge to be consumed, there being registering openings through said furnace chamber rear wall and casing rear wall near the top of said rear wall and a hollow ue connection extending through and engaging all sides of said registering openings, a hollow combined burner shield and duct extending from said front chamber wall horizontally through a lower portion of said chamber to a point near said rear chamber wall and then extending upwardly to a point slightly below the level of said flue connection, an ash trap comprising a front partition Wall extending approximately the entire distance across said chamber between said opposed side walls from the top thereof down to a level below said burner shield and duct, said trap having walls extending rearwardly from said front partition wall, said partition wall being imperforate save for a through opening horizontally opposite said llue connection, baille means supported in said trap permitting only non-linear gaseous llow through said baffle means, a secondary combustion device positioned at said flue connection near the topof said upwardly extending burner shield and duct, and providing a maze of ceramic material able to withstand a temperature of at least 1200 degrees Fahrenheit through which products of combustion must pass from said' furnace chamber to said ilueconnection, there being a small opening through said rear furnace wall adjacent said upwardly extending portion of said burner shield and duct and communicating with the'atmosphere for supplying combustion air to said secondary combustion device.

2. An incinerator comprising an outer casing, an inner casing within the outer casing, partitioning means in the inner casing forming on one side thereof a combustion chamber and on the other side thereof a secondary combustion zone and a ily-ash trapping zone, an exhaust ue communicating with the upper portion of said chamber and adapted to be connected to a draft source, ra secondary combustion catalyzer disposed in said zone adjacent the junction between said due and said chamber and on the chamber side thereof, partition means near the exhaust side of said combustion chamber compelling products of combustion to leave said chamber through an opening substantially horizontally opposite said ue and catalyzer, baille means betwen said opening and said catalyzer preventing straight line ow of products of combustion therethrough, a combined burner shield and duct mounted inthe lower portion of said outer casing extending horizontally partially therethrough and then bending upwardly and terminating at a zone adjacent said catalyzer on the chamber side of said partitioning means, means providing a supplemental source of oxygen to said catalyzer, a main and after burner fluid fuel burner means in said outer casing and communicating with said burner shield and duct at a point spaced from the upward bend of the same, said main burner means having a capacity for heating said burner shield and duct to a temperature under 400 degrees Fahrenheit, said after burner means having a capacity for heating said burner shield and duct to a temperature over 800 degrees Fahrenheit, and a stack dilution device providing communication between the atmosphere and said ue approximately at the junction between said llue and said chamber holding the draft from said source under approximately 0.030 inch water gauge whereby an induced flow of air from atmosphere through said device is thus operative to cool said flue during high rates of combustion in said chamber.

3. An ineinerator comprising an outer casing, an inner casing within the outer casing, partitioning means in the inner casing forming on one side thereof a combustion chamber and on the other side thereof a secondary combustion zone and a fly-ash trapping zone, an exhaust ue communicating with the upper portion of said chamber and adapted to be connected to a draft source, a secondary combustion catalyzer disposed in said zone adjacent the junction between said liuc and said chamber and on the chamber side thereof, partition means near the exhaust side of said combustion chamber compelling products of combustion to leave said chamber through an opening substantially 4horizontally opposite said iiue and catalyzer, ba-le means between said opening and said catalyzer preventing straight line ow of products of combustion therethrough, a combined burner shield and duct mounted in the lower portion'of said outer casing extending horizontally partially therethrough, 'ineans providing a supplemental source of oxygen to said catalyzer, burner means for heating said combined shield and vduct only to a temperature under 400 degrees Fahrenheit, burner means for heating said catalyzer to approximately 1200 degrees Fahrenheit, means for igniting a charge in said chamber, and a stack dilution device providing communication between the atmosphere and said flue approximately at the junction between said ue and said charnber holding the draft from said sourceV under approximately 0.030 inch water gauge whereby an induced-'flow of air from atmosphere kthrough said device is thus oper ative to cool said ue during high rates of combustion in said-chamber.

4. The combination of claim 2 wherein said means providing a supplemental source of oxygen to said catalyzer comprises a passageway communicating at one end with atmosphere and extending adjacently along said upwardly bent portion of said burner shield and duct and 5 communicating on its opposite end with said chamber.

References Cited in the le of this patent UNITED STATES PATENTS 964,568 shannon July 19, 1910 10 10 Shannon Jan. 10, 1911 Cummings Mar. 10, 1925 McKinley Aug. 6, 1935 Martin June 21, 1955 Hebert Aug. 23, 1955 Short et al July 3, 1956 Bratton Aug. 5, 1958 Triggs Aug. 19, 1958

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