US2745476A - Flashback-proof gas burner and mixer - Google Patents

Description

May 15, 1956 J. TETE 2,745,476

FLAsHBACK-PROOF @As BURNER AND MIXER Filed Deo. 4, 1952 FIGJ FIG. 2

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FLASHBACK-PRG'QF GAS BURNER AND MEYER John Teti, Wilmington, Del., assignor to AirReduction Company, Incorporated, New York, N. Y., a corpora- `tion of New York Application December 4, 1952, Serial No. 324,017 -3 Claims. (Cl. 15S-27.4)

This invention relates principally to gas burners, especially those of the oxyacetylene type such as those used for cutting, welding, flame treating and similar operations. More particularly it relates to a gas burner which constitutes a modification of those disclosed in Patent No. 2,618,322, and assigned to the same assignee as is this application.

One of the problems that has always confronted the gas burner art generally and the oxyacetylene cutting, welding and llame treating art in particular is the prevention of backfires and iiashbacks. vThough sometimes these terms as used synonymously, there is a well recognized distinction between them. Hence the term backfire means a recession of the liame, usually explosive, into the torch or burner from the face thereof. The term iiashback, on the other hand, means a continued burning of the llame somewhere within the torch or burner upstream from its normal position at the tip or burner face. As used herein, the two terms are intended to have the distinctive meanings set forth. Abackire, if controlled, is not particularly harmful or dangerous, but a flashback is likely to be both destructive and dangerous. A fiashback, for even a few seconds, may overheat a torch so badly that it becomes useless. Moreover, in the .case of acetylene, the flashback may cause dissociation which may even occur upstream from the place where the gases meet to form a combustible mixture.

rl`he gas burners disclosed in the aforesaid Patent No. 2,618,322 are so constructed that the volume of mixed gases is kept down to an amount that is harmless, thereby controlling backfire, and means are provided for quenching the products of combustion resulting from a backfire and eliminating all points at which the flame could re-ignite and be sustained in the burner, thereby eliminating the possibility of flashback.

A gas burner according to that application comprises a burner block having preferably a plurality of smooth -walled burner oriiices. The upstream ends yof the burner orifices communicate with a narrow slot into which are fed separately a fuel gas and a combustion supporting gas. The gases are delivered to the slot at locations such that each gas must flow through a vportion of the slot in a direction parallel to the opposing walls which define the narrow dimensions of the slot before reaching the entrances of the burner orifices, and the dimension of the slot in one direction transverse the direction-of the flow of the gases through it is such that a mixtureof the gases will not burn therein. In some constructions the 'two gases mix to a certain extent within the slot prior to entering the burner orifices, while in other constructions `the mixing of the gases takes place -substantially at the entrance end of the' burner orifices. Also in certain constructions there is an individual slot for supplying each burner orifice, whereas in others several burner orifices may be Supplied from a single slot. Preferably in all constructions the walls of the slots and those surrounding the burner orifices are of sufcient thickness and mass and heat absorbing capacity to deactivate'burned mixed gases passing therethrough as a result of a backfire sufiiciently to prevent flashback.

While the above-described burners are most satisfactory for certain applications, it has been found that-they are not Well adapted for certain other aplications. In no case, however, does the lack of adaptability relate tto States Patent O 2,745,476 Patented May 15, 1956 ice 2 their ability to control backfires and to `eliminate ythe possibility of flashbacks. Thus the burner orificepatterns of the aforesaid burners are dependent upon the slot .patterns thereof. It is therefore ditlicult, for instance, fto

employ those burners vas round area burners simply be- Icause the slots require comparatively large areas. Hence the above-described burners are most adaptable for a line flame arrangement rather than a Wider area flame arrangement.

Also, in the former burners, where thorough and complete mixing is essential, it is'necessary thateach burner orifice have a length of the order of 40 times its diameter. For most burner applications such thorough mixing is Inot required, but in those cases Where it is required 'this limitation may be cumbersome and in some applications even impossible of attainment.

Furthermore, for certain applications it is necessary in order to satisfactorily employ the former burners to limit the burner orifice diameter to a diameter that will result in gas velocities at the entrance of the flame orifice above the blow-away velocity. Of course in certain instances it may be desirable to have a burner that has burner orifices larger than this maximum.

It is the primary object of this invention to provide a gas burner or torch which possesses the backreeontrolling and fiashback eliminating characteristics of the ,previous burners, yet does not possess the limiting characteristics thereof as set forth above, vbut rather `permits great fiexibility in the size, shape and distribution of the 'burner orifices and removes the gas mixing `problem associated with the former burner which resulted in .certain instances in the requirement for relatively longl burner orifices. Accordingly, the gas burner or .torch of this invention comprises what may be termed a mixing section which is substantially identical to a burner of the .aforementioned application. However, to this basic structure an orifice plate or block is affixed so as to cover the discharge ends of what were in the former burnervthe burner orifices. The orifice plate or block is provided with a recess which forms with vthe discharge 4face of the mixing section a relatively shallow slot communicating with all of the formerly termed burner orifices vwhich will in the burner of this invention be termed mixing passageways, the shallow slot sometimes hereinafter being referred .to as a distributing slot or chamber. The orifice plate is provided `with one or more burner orifices extending from the distributing slot .to the burner face. These burner orifices may be distributed in the orifice plate in such-a manner as to give the desired flame pattern. tHowever, none should fall directly across the distributing slot from. a mixing passageway.

The apparatus above described may without substantial ymodification be employed also as a universal -type ygas mixer. For such use the orifice plate is provided with a single discharge orifice adapted to be connected toa Wide variety of gas-burning apparatus each of whichwill `be thereby made flashbackproof.

The gas burner or mixer of this invention will enow be more specifically described in connection with the accompanying drawings in which:

Fig. 1 is a transverse vertical section taken throughione form of flashback-proof multi-llame burner embodying the invention;

Fig. 2 is a longitudinal vertical section taken along line k2 2 of Fig. l;

Fig. 3 is a longitudinal horizontal section taken along .line 3 3 of Fig. 1;

Fig. 4 is a fragmentary sectional view similar to Fig. 3 illustrating a modification that maybe made in the gas passage arrangement employed in the burner of Figs. "l through 3;

Y Fig. 5 is a horizontal section of the burner of Figs. 1

through 3 taken along line 5 5 of Fig. 2; and

Fig. 6 is a vertical section of a gas mixer embodying the invention.

The burner illustrated in Figs. l, 2, 3 and S comprises a block 20 through which manifolding or distributing chambers 21 and 22 are drilled. One of the two gases to be mixed, such as oxygen, is admitted to one end of the distributing chamber 21 through a supply conduit 23 (Fig. 3). l The other end of the distributing chamber 21 is closed by a plug 24. The other gas, a fuel gas such as acetylene, is admitted to one end of the distributing chamber 22 through a supply conduit 25, the other end of this distributing chamber being closed by a plug 26. The oxygen from the distributing chamber 21 passes down through a series of supply passages 27 to a dat Vshallow recess 28 formed in the lower face of block 20. Similarly, the acetylene from the distributing chamber 22 passes down through a series of supply passages 29 to the same recess 2S. Another block 30 is secured to the lower face of block 20 by any suitable means covering the recess 2S at its lower side and making a narrow slot of the recess which may be termed a mixing slot. A row of mixing passageways 31 are formed in the block 30 so that they communicate with the mixing slot 28. These mixing passageways 31 lead downwardly to the lower face of block 30, as may be seen in Figs. 1 and 2. This much of the present burner is identical to a burner according to the invention of the aforesaid Patent No. 2,618,322.

According to this invention, a third block 32 is secured to the lower face of block v30 by any suitable means. This block is provided with a tiat, shallow recess 33 which, when block 32 is secured to block 30, overlies the discharge ends of mixing passageways 3i and forms a shallow slot which may be termed the distributing slot. A number of rows of burner orifices 34 are formed in block 32 so that they communicate with the distributing slot 33 and lead to the discharge face 32a of the burner. These discharge passageways 34 may be arranged in any suitable or required pattern, provided only that they preferably do not fall directly opposite the exit ends of mixing passageways 31. Furthermore, their size may vary considerably.

It will be seen that the oxygen and acetylene delivered to the distributing chambers 21 and 22 enter the mixing slot 28 through the supply passages 27 and 29, the oxygen entering the mixing slot at its left side, as viewed in Fig. l, and the acetylene entering this slot at its right side. The two gases flow inwardly toward each other until they meet, and then flow downwardly through the mixing passages 31 in which they are further mixed. From the mixing passages 3l, the mixed gases ow into distributing slot 33 and thence through the burner orifices 34, the gases being mixed even further in distributing slot 33 and burner orifices 34. When the gas mixture issuing from the latter is ignited, it produces the burner flame. In this form of burner it will be noted that no substantial mixing of the gases takes place, until each reaches the vicinity of the mixing passageways 31. However, in other forms by a different arrangement of the supply passageways 27 and 29, mixing may take place within the mixing slot 28.

The burner depends primarily for its ashback-proof property on that portion of its structure contained in blocks 20 and 30 which may, as previously stated, be identical to the structure of a gas burner according to the invention set forth in the aforesaid Patent No. 2,618,322, though, for comparable overall mixing of the gases in the burner the length of mixing passageways 31 may in the present be considerably less than in the previous burner. As explained in Patent No.` 2,618,322, the slot 23 has one dimension ci which does not exceed a critical value at Aor below which any gas mixture in the slot will not burn. This does not mean that the slot passage will halt ame propagation or detonation, but it is suiciently narrow to prevent the gases from continuing to burn in it or at the upper ends of the mixing passageways 31. The absolute value of the dimension d may vary for different gases and for different size mixing passageways. It has been found, however, that the maximum value the dimension d should have for an oxyacetylene burner is in the range from .012" to .016. The exit area through which the gases leave the slot passage 28 is a product of the circumference of the discharge passageways 31 and the dimension d. For the gas iiow involved, this area should be sufiiciently small to keep the gas velocity at this point above the dame blow-away point.

As further pointed out in Patent No. 2,618,322, ashback is impossible with this construction for the following reasons. When the backiire occurs, the burning gas mixture in the mixing passageways will be forced with explosive rapidity backwards through the slot 28, and possibly even up into the supply passageways 27 and 29 leading to it. All of the gas mixture burns, after which the llame goes out. As soon as the pressure Wave subsides, the burned gases are forced downstream again by the incoming oxygen and acetylene. The only place the fresh incoming gases could possibly burn would be in the mixing passageway 3l., or possibly in the slot 28 immediately adjacent the entrance to the mixing passageways, since these are the only places where mixture of the two gases is present.

As above described, the dimension d of the slot 28 is such that the gases cannot4 continue to burn in this slot probably because of the quenching effect of the walls of the slot on the gases. Where the gases mix and pass into the mixing passageways 31, their velocity is too high to maintain the llame at this place, and the passageways themselves are sufficiently smooth walled to prevent a iiame from hanging in them. Therefore any flame fed by the gases after this mixing will tend to recede to the entrance ends of the passageways 31 or to blow out to the exit ends thereof.' Since it is impossible for the ame to be sustained at the entrance end of the passageway due to the high gas velocity at this place, it will automatically be blown out to the exit ends thereof. As a matter of fact, in most cases the products of combustion from the backre will be deactivated suiciently by the quenching action of the walls of the slot 28 and of the walls in mixing passageways 31 to prevent them from re-igniting the fresh incoming gases when the latter mix. Also the quenched products of combustion will form a slug which precedes the fresh incoming gas mixture, expelling any hot, unquenched products of combustion from in front of the new incoming gas mixture as it progresses downstream in the burner.

The same ashback-proof property above described in connection with that portion of the present burner which is similar to the burner disclosed in Patent No. 2,618,322 is just as fully possessed bythe burner of the present invention. Y rihus the portion of the present burner made up of blocks 20 and 30 Will, as in the previous burner, extinguish the receding flame of a backiire and prevent reignition of the fresh incoming gas mixture at least until it leaves mixing passageways 31. It has been found that if distributing slot 33 has one dimension s which does not exceed .060 to .090", the presentvburner, when fully assembled, will be stable if what has. been termed the mixing section thereof (blocks 20 and 30) is stable when operated without the added block 32. The insulating slug of quenched products of combustion of a backfire which precedes the fresh incoming mixture of gases downwardly through mixing passageways 31, through slot 33 and discharge passageways 34, prevents the ignition of the new mixture of gases before it has passed into and through discharge passageways 34. These passageways too are preferably smooth walled. The walls of slot 33 also have a quenching'eiiect on the products of combustion and serve to increase the amount thereof deactivated to below the point at which ignition of the incoming fresh gas mixture would be caused.

Whereas in the burner illustrated in Figs. 1-3, all of the mixing passageways 31 are fed through a single narrow mixing slot 28, this is not essential. As previously indicated, the mixing section of the present burner made up of blocks 20 and 30 may be of varied forms, for instance any of the forms disclosed in Patent No. 2,618,322. Thus in Fig. 4 there is illustrated a burner in which each mixing passageway 31 is fed by a separate slot 28. Each such slot 28' of this burner will have a critical dimension d as did the slot 28 of the burner of Figs. 1 through 3.

Perhaps the most important characteristic of the gas burner of this invention is the flexibility permitted in the l size and distribution of the burner discharge passageways. Thus with the present burner, larger flames may be provided and a wide variety of flame patterns permissible, whereas the burner of the aforesaid Patent No. 2,618,322 is most adaptable for a line llame arrangement rather than a wide area flame arrangement because of the required shape in the latter of mixing slot or slots 28. In both the former burner and the present burner it has been found that the distance between the junctures of the oxygen supply passageways and the mixing passageways with slot 28 must be of the order of g or more.

In designing the burner of this invention, it may be categorically stated, as previously indicated, that if the mixing section thereof made up of blocks 20 and 30 is stable when operated alone, then the burner of this invention will be stable, provided the slot 33 in block 32 has a dimension that does not exceed .060" to .090".

In certain applications, space limitations may prevent the use of the new burner. In such cases, however, the desirable flashback-proof characteristics thereof may be retained by using the previously described apparatus as a mixer having an auxiliary burner tip that can be accommodated by the space limitations. The use of one such apparatus as a flashback-proof gas mixer is illustrated in Fig. 6 and comprises cylindrical blocks 20 and 30' secured together in any suitable manner. A mixing slot 28 is formed by blocks 20 and 30' and is adapted to have fed thereto acetylene through supply passageways 29 and oxygen through supply passageway 27 formed in block 20'. Mixing passageways 31 formed in block 30' communicate with mixing slot 28" and place it in communication with a distributing slot 33 formed by securing an end plate 32 by any suitable means to block 30'. The end plate is provided with a single discharge passageway 34', the outer end of which is internally threaded and adapted to receive a means for conveying a mixture of the gases discharged through passageway 34 to any suitable burner tip.

The principles of operation of this mixer apparatus in quenching backiires and preventing ashbacks are the same as that previously set forth in connection with the gas burners of Figs. 1-5 and the critical dimensions set forth in connection with the description of such gas burners apply equally to the mixer of Fig. 6. Thus, the dimension d of slot 28" should not exceed .016" and one dimension s of slot 33' should not exceed .090.

The terms of orientation and direction used in the foregoing description apply to the forms of burner illustrated when they are used in the vertical position, i. e., with the ame jets directed downwardly, but it should be understood that the burners may be used in any position.

I claim:

1. Apparatus of the type described comprising separate inlet passageways for fuel gas and a combustion supporting gas, a discharge face, a discharge passageway leading to the discharge face, a shallow slot upstream from said discharge face and communicating with said discharge passageway, a mixing passageway upstream of said narrow slot and leading to said slot, said discharge passageway and said mixing passageway being out of alignment with each other whereby a mixture of gases must pass through a portion of said shallow slot in passing from said mixing passageway to said discharge passageway, a mixing slot upstream of the mixing passageway and in communication therewith, and means to deliver said fuel gas and said combustion supporting gas separately from their respective inlet passageways to said mixing slot at locations such that each may flow through portions of said mixing slot in a direction parallel to the opposite walls thereof which define the narrow dimension thereof before reaching the entrance to the mixing passageway, the; narrow dimension of the mixing slot not exceeding about .016 inch at any place so that a mixture of gases introduced thereto will not burn therein, the shallow slot communicating with both the discharge passageway and mixing passageway having one dimension transverse the direction of liow of the gas mixture from the mixing passageway to the discharge passageway which is not at any place greater than about .090 inch.

2. An anti-ashback gas burner comprising separate inlet passageways for a fuel gas and a combustion supporting gas, a discharge face, a plurality of discharge passageways leading to the discharge face, a shallow distributing slot upstream from said discharge face and in communication with said discharge passageways, mixing passageways upstream of said narrow discharge slot and leading to said slot, a mixing slot upstream of said mixing passageways and in communication therewith, and means to deliver said fuel gas and said combustion supporting gas separately from their respective inlet passageways to said mixing slot at locations such that each gas must ow through portions of said mixing slot in a direction parallel to the opposite Walls thereof which define the'narrow dimension thereof before reaching the entrance to the mixing passageways, the narrow dimension of the mixing slot being at any place such that a mixture of the gases introduced thereto will not burn therein, the plurality of discharge passageways being distributed in any desired palttern as long as none is in alignment with one of said mixing passageways whereby the mixture of gases must pass through a portion of said shallow distributing slot in passing from said mixing passageways to said discharge passageways, and the shallow slot having one dimension transverse the direction of tlow of the mixture of gas therethrough which does not at any place exceed .090 inch.

3. Apparatus of the type described comprising a block having a plurality of discharge orifices, a shallow distributing slot upstream of said orifices and in communication therewith, a mixing passageway upstream of said shallow slot and communicating therewith, all of said plurality of discharge orifices being out of alignment with said mixing passageway whereby a gas mixture must` ilow through a portion of said shallow distributing slot in passing from said mixing passageway to said discharge orifices, means for supplying a fuel gas to said mixing passageway, and means for supplying a combustion supporting gas to said mixing passageway, said fuel gas supply means and said combustion supporting gas supply means each consisting of a restricted passageway with one dimension transverse to the direction of gas ilow therethrough which is, at any place throughout the extent of gas flow through said passageway, not greater than about .016 inch and such that a mixture of gases will not burn therein, and one dimension of said shallow distributing slot transverse the direction of ilow of the gas mixture therethrough not at anyplace exceeding .090 inch.

References Cited in the le of this patent UNITED STATES PATENTS 2,378,001 Drummond June 12, 1945 2,396,765 Walker Mar. 19, 1946 2,618,322 Conta et al. Nov. 18, 1952 2,618,539 Conta et al Nov. 18, 1952 2,618,540 Teti Nov. 18, 1952

Claims (1)

1. 2. AN ANTI-FLASHBACK GAS BURNER COMPRISING SEPARATE INLET PASSAGEWAYS FOR A FUEL GAS AND A COMBUSTION SUPPORTING GAS, A DISCHARGE FACE, A PLURALITY OF DISCHARGE PASSAGEWAYS LEADING TO THE DISCHARGE FACE, A SHALLOW DISTRIBUTING SLOT UPSTREAM FROM SAID DISCHARGE FACE AND IN COMMUNICATION WITH SAID DISCHARGE PASSAGEWAYS, MIXING PASSAGEWAYS UPSTREAM OF SAID NARROW DISCHARGE SLOT AND LEADING TO SAID SLOT, A MIXING SLOT UPSTREAM OF SAID MIXING PASSAGE-

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