US2122929A - Combustion apparatus - Google Patents

Description

July 5, 1938. w. D. CARTER COMBUSTION APPARATUS Filed April 27, 1934 Fig.1.

WITNESSES:

INVENTOR: 52 mm A W Patented July 5, 1938 PATENT. OFFICE COIWBUSTION APPARATUS William Douglas Carter, Caldwell, N. J.

Application April 27, 1934, Serial No. 722,646

,2 Claims. (01. 158-1) This invention relates primarily to jet or injector means for recirculating the hot gases in a fire-box or combustion chamber, so as more thoroughly tomix the gases and bring about complete combustion with a minimum of excess air.

The process of combustion, like many other chemical reactions, is best accomplished by thoroughly agitating or stirring the proper quantities of the constituent elements, and not through the addition "of an excessive amount of one of the elements; nevertheless it is a common practice with many types of oil-burners to create turbulence and mixing of the gases by means of a blast of excess air forced or drawn. into the fire-box.

,, As a matter of fact, in most furnaces, Whether oil,

gas, or even solid fuels are used, a large excess of air is usually supplied to insure safety and complete combustion of the fuel. This results in noisy combustion and impaired efficiency generally recognized in the art.

With my invention, a minimum quantity of excess air is admitted to the fire-box (except during the short ignition period hereinafter described). Some of the necessary amount of air is conducted under pressure to the nozzle of an injector. The injector is so positioned as to induce a re-circulation of the hot combustion gases which would otherwise escape to the stack after substantially one passage through the fire-box. These recirculated gases mingle with the preheated jet of air issuing from the injector nozzle inside of a refractory or fire-resisting draft-tube, wherein the gases are further pre-heated and then discharged into the freshly supplied combustible gases and air. This operation serves to re-heat, agitate, and dilute the unburned gases so as to spread the flame throughout the fire-box and promote slower, quieter, and more complete combustion before the final products pass out through the stack. Of course the extent of dilution, and the rapidity of combustion are subject to wide adjustment depending upon service conditi'o-ns.

While other fuels such as alcohol may be burned, the apparatus will be described primarily in its oil-burning application.

The general object of this invention therefore, is to recirculate the air and fuel gases in the combustion chamber so as to promote thorough mixture and combustion before allowing the resultant gases to pass up the stack.

Another object is to provide a gentle blast of hot recirculated gases directed so as to mix with the incoming fuel gases and air.

Another object is to provide an injector tube of heat resisting material in the path of the flame, through which the hot gases are recirculated and. blown into the newly supplied combustible mixture.

Another object is to provide two nozzles connected with the same air-pressure means-one for mixing air directly with the oil spray, and the other as a source of agitation for promoting the mixture of all the hot gases in the fire-box or combustion chamber.

Another object is to preheat the compressed air before it reaches the jet in the recirculating tube, so as to increase the volume of said air and thereby to minimize the amount of air required.

Another object is to increase gradually the air pressure on the fuel atomizing nozzle, as the temperature of the fire-box rises, and thereby to improve the ignition and starting characteristics of the oil burner.

Another object is to provide a refractory target against which both the new fuel supply and the recirculated gases are directed so as to promote the mixing thereof.

Another object is to recirculate the chilled and partly burned gases which lie adjacent to the heat-absorbing walls of the combustion space.

Another object is to prevent the sound from the air compressor from emanating through the nozzle.

Another object is to insure safety by supplying excess air during the short ignition period only.

The preferred constructions through which the above objects are attained, are hereinafter fully described and claimed, having reference to the accompanying drawing in which:

Figure 1 is a vertical side elevation of my oil burning mechanism, partly in section, wherein a vertically disposed recirculation tube of conical shape is directed toward a target formed on the floor of the fire-box.

Figure 2 is a diagrammatic elevation showing a modified arrangement employing a curved or horn-shaped recirculation tube bent to discharge against one side of a target, while the incoming fuel is directed against the opposite side of the target.

Figure 3 is a diagram of a third arrangement wherein the recirculated hot gases and the fuel spray are both directed horizontally toward each other.

Figure 4 is another side elevation, mostly in section, illustrating another adaptation of my invention to a conventional type of pressure-atomizing oil burner wherein the oil is atomized by oil pressure means, and all of the air is supplied by means of a blower.

Like numerals refer to similar parts in the inwardly projecting nipples I6. formed in the wall I for the entrance of the air and nozzle 20.

4 for identification purposes.

tional excess air inlet opening 1 is shown in wall I and is provided with a door 8 hinged at 9 to wall I. An arm II is fixedly attached to the shaft of the control motor it. The link 12 is pivotally attached at one end to the outer end of arm ll and at the other end to door 8 so as to open and close the excess air opening I automatically during the ignition period.

The floor 3 is covered with refractory lining l3 forming a target, and the lower face of wall I is lined with fire bricks l4certain onesof which bricks are leaned across ports 6 as indicated in Fig. l to form bafiles l5 around which the secondary air from ports 6 may enter the firebox. One or more exit or flue openings are formed in the top wall 2 and surrounded by the Other ports are pressure conduit l1 and the fuel conduit I8. The air conduit I1 communicates through a heater section I!) with the air-nozzle 2B which is .attached to and supports the gas recirculation tube 2|. This tube contains one or more inlet openings 22 formed at or near one end, and a main discharge opening 23 at the other end thereof. Other discharge openings such as 24 may also be provided.

'The air compressor 25 (see Fig. 1) discharges through the discharge pipe 26 into the upper part of the mufiler receiver 21 which in turn communicates at itslower end with conduit 28. The latter communicates with air conduit l1 and with the elbow shaped fuel conduit I8 at the end of which is connected the fuel spray nozzle 29. with the lower end of muifler receiver 21.

The drain hole '30 in pipe 26 communicates Oil supply pump 3!, which is supported by bracket The modification shown in Figure 4 contains the additional flue pipe manifold 34, and the rectangular refractory target 35. This arrangement utilizes what is conventionally termed a pressureatomizing type of oil burner having a centrifugal blo'wer'tfi and the communicating wind-pipe 31. The by-pass opening 38 provides a discharge from'the wind-pipe31 to the heater section 19 Air also passes through nozzle 43 to the fire-box. The highpressureoil spray nozzle 39'is connected to the end of oil pressure conduit Mlthe last leading from an oil pressure means analogous to 3| but not shown in Figure l. In fact the centrifugal blower 36 may be considered analogous to the air compressor 25 in Fig. 1 since both constitute air pressure means; wind pipe 37 is analogous to pipe 26, bypass opening 33 to 23, nozzle 39 to fuel spray nozzle'29, and conduit Ml to fuel conduit I8, although different numerals are given in Figure With the arrangement shown in Fig. 4 a conventional type of circular shutter M, to which is attached the actuating arm 42; is pivotally linked by means of link l2 to the arm H of the control motor l0.

The operation of my oil burning apparatus is as follows: Referring first to Figure 1, the compressor 25 is assumed to be delivering air through the discharge pipe 26 into the mufiier receiver '21, where the sudden volumetric enlargement and reversal of direction of flow serve to cushion any pulsations and thereby minimize the sound "which otherwise Would be carried on with the air stream and emanate as an objectionable noise from the nozzles. The air leavingthe muffier receiver 2! is divided into two streams, one passing upward through pipe l1, heater section I9, and the communicating nozzle to form the air-jet which is blown downward through the recirculation tube 2|; and the other stream continuing through conduit I8 and the nozzle 29 Where it is discharged into the fire-box as indicated. Simultaneously it will be assumed that the fuel oil pump 3i which is connected to a suitable source of oil supply not shown, is operating to deliver oil under pressure through the control valve 32 and pipe 33 into the air conduit 28, at a point where the air-stream will conveythe oil through I8 to the fuel nozzle 29 from which it is sprayed into the fire-box. Suitable gas or electric ignition means, not shown but of conventional type, is provided to ignite the spray of fuel as it enters the fire-box. It is important that no oil be allowed to accumulate in the'muffler receiver 21 to'be blown suddenly through nozzle 29 when the burner is started; and the drain hole 30 is provided to drain the receiver when the burner stops operatin Itwill beevident that the proportions of air flowing through each of the nozzles, will depend upon the relative frictional resistance encountered in the two parallel streams. Assuming that the amount of oil delivered through conduit 18 is constant, and therefore that the friction of the air encountered from the oil passing with the air through I8 and nozzle 20, does not vary, then a definite proportion of air will flow through each nozzle depending upon the relative physical proportions of the two lines, including the nozzles. Such will be the condition the instant before ignition takes place.

After the fire is established, the air passing through the pre-heating coil or section [9 expands with the heat imparted to it, so that its volumeis greatly increased while the frictional resistance of its conduit and nozzle is not changed materially. Hence the amount or weight of the air flowing through nozzle 20 will materially decrease, while the proportion discharged through the fuel nozzle 29"will increase.

Several advantages are gained by this arrangement: In the first place, quieter and more reliable ignition is obtained with the low initial pressure prevailing at the fuel nozzle 29 before section l9 becomes heated, while the gradual increase in pressure at nozzle 29, as the fire-box becomes hot, greatly improves the atomization and turbulence required for the best combustion. The pre-heated air in the jet issuing from nozzle 20 prevents-cooling the gases which are sucked in through ports 22 anddischarged downward through the recirculation tube 2 l. Furthermore, the preheating of the air effects a material economy in the total amount of airrequired to operate the burner.

It will be apparent that a very small quantity 'of high pressure air discharged from nozzle 20 will 'cause' the recirculation of a relatively large amount of hot gases in the fire-box. These hot gases are taken preferably from a point near the flue or exit end of the fire box and carried through the recirculation tube in which they are reheated and discharged at the part of the firebox at which the incoming oil is sprayed, so as to mix'with the freshly supplied oil gases, and

with the secondary air also admitted at this point.

The hot recirculated gases serve to heat the incoming secondary air and to vaporize any stray particles of oil, and by increasing the turbulence of all of the gases produces-a uniform combustible mixture and an efficient fire. Simultaneously with the above action, additional secondary air is continually being drawn into the fire-box from the cavity behind the leaning bricks or baflies l which cavity is in communication with the air port 5 through the square ports 6. Owing to the recirculation of the hot gases within the fire-box a minimum quantity of secondary air is required but in order to assure an ample supply of air when starting, and before the chimney draft has reached its full running intensity, the excess air inlet 1 is opened automatically by means of the control motor I0, arm H and connecting link l2. In about one minute, or when ignition is established, the control motor lowers the door 8 and closes inlet 1 in an obvious manner. This arrangement insures an adequate amount of air for starting and still permits a minimum but efiicient setting of the air supply through 5 dur-- ing the ensuing operating conditions when the fire-box is hot and the draft normal. The air port 5 may be throttled by any obvious means to obtain the proper setting above referred to, after which no further adjustment is usually required.

The walls I and the top 2 of the fire-box transfer heat from the hot gases to the fluid medium in contact with their outside surfaces. This transfer of heat tends to cool the gases within the firebox adjacent to the walls, and sometimes prevents complete combustion of the gases close to the walls. For this reason the inlet openings 22 are advantageously located close to the wall and top of the fire-box as indicated in Figure 2 so as to recirculate these slightly chilled gases and thereby promote complete combustion before the gases finally pass through nipples IE to the stack. Nipples IE project into the interior of the fire box so as not to withdraw these partly burned gases from the wall or top surfaces before they can be recirculated.

The recirculation tube 2| may be made of any heat resisting material, preferably a refractory substance which becomes red or white hot, thereby aiding combustion and adding to the visual attraction of the fire.

Figure 2 also shows a curved type of recirculation tube 2! and a refractory target 35 positioned so as to receive the impact of the hot recirculated gases against one side and the fresh stream of fuel against the other side thereof. The atomized oil issuing from the nozzle 29 is usually vaporized by the heat of the flame before reaching the target, and the two streams of gas are thoroughly mixed around the edges of the target; or through openings or passages, such as M, which may be provided through the target.

Figure 3 shows diagrammatically, a third arrangement wherein the hot gases are drawn from the top wall of the fire-box through opening 22 into the recirculating tube 2 I, and directed through discharge opening 23 in a horizontal direction counter to the incoming atomized stream nozzle 39 from which it is sprayed into the firebox as indicated. Simultaneously air is blown by means of the centrifugal blower indicated by 36, through wind pipe 31 and by-pass opening 38. Part of the air flows directly into the firebox with the oil spray, and the remainder is bypassed through the preheating conduit section !9 to the nozzle 26 located inside of the recirculation tube 2|. In this arrangement all of the air for combustion is supplied through the blower 36. The proportion of air entering the fire-box through the nozzle-like restriction 43 is here again increased as the temperature and therefore the volume of the air passing through the preheater "conduit section l9 increases.

Various types of control devices and ignition means, all well known in the art, may be employed in connection with my apparatus; separate high-pressure air-pumping means, such as 25 in Fig. 3, may be employed for supplying air to the nozzle in the recirculation tube; and still other means for preparing fuel for combustion may be used in combination with my recirculation equipment; all without departing from the spirit of my invention.

Where the expression spray-nozzle is used in the claims, it will be understood to mean the terminal part of a conduit having an orifice through which, or by means of which, finely divided particles of fuel are projected into the fire-box. The spray-nozzle mayor may not discharge another fluid such as air simultaneously with the fuel. The term air-nozzle differentiates from the spray-nozzle primarily through the fact that the former discharges no fuel but does discharge a jet of air for creating turbulence in the fire-box or combustion chamber.

What I claim, and desire to secure by Letters Patent, is:

1. In an oilburning apparatus, the combination of a fire-box, a target against which impinging gases are mixed in the fire-box, a liquid-fuel spray-nozzle, means supplying liquid fuel to the spray-nozzle, the spray-nozzle being directed toward the target, a gas recirculation tube, said tube having openings formed therein communicating with the firebox, one of said openings being directed toward the target, an air nozzle, and means supplying air under pressure to the airnozzle, the air-nozzle being so positioned as to discharge a jet of air through the tube toward the target whereby gases from the fire-box are also impelled through the tube against the target.

2. In an oil-burning apparatus, the combination of a fire-box, a target in the fire-box, a liquidfuel spray-nozzle, means supplying liquid fuel to the spray-nozzle, the spray-nozzle being directed toward the target, a gas recirculation tube, said tube having openings formed therein communicating with the fire-box, one of said openings being directed toward the target, an airnozzle, so positioned as to discharge a jet of air through the tube toward the target, an air-heating conduit in the fire-box communicating with the air-nozzle, and means supplying air under pressure to both the air-heating conduit and the fuel spray-nozzle whereby hot air is delivered through the air-nozzle and cooler air is delivered simultaneously with the liquid fuel through the liquid fuel spray-nozzle.

WILLIAM DOUGLAS CARTER.

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