US2685921A - Method of preventing flashbacks in gas burner systems - Google Patents

Description

g- 1954 H. H. ROBINSON, JR

METHOD OF PREVENTING FLASHBACKS IN GAS BURNER SYSTEMS Filed March 3, 1949 FIG. I

FIG. 3

INVENTOR HARRY H. ROBINSON JR.

BY Z f 4 42 .M

ATTO R N EYI Patented Aug. 10, 1954 UNITED STATES PATENT QFFICE METHOD OF PREVENTING FLASHBACKS IN GAS BURNER SYSTEMS Harry 'H. Robinson, Jr., Staten Island, N. Y., as-

signor to xiii-Reduction Company, Incorporated, a corporation of New York Application March'3, 1949, Scriai'No. 79,442

5 Claims. 7 (Cl..158-118) This invention relates to gas burners, especially those of the oxyacetylene type, and particularlyto a method and apparatus for preventing or minimizing the occurrence of flashbacks in gas burners.

One of the problems that has always confronted the gas burner art generally, and the oxyacetylene cutting, Welding and flame-treating art in particulanis'the prevention of back fires and flashbacks. The terms backfire and flashback are frequently used synonymously, but it is intended that herein there be maintained a definite distinction between them. A backfire is the rapid recession of the flame from the discharge face cf the burner upstream into the burner, usually back to the mixer while a flashback is a continued burning of the gases within the burner following a backfire Backfires are generally caused by some temporary reduction in gas flow, and while they'are'a'nuisance and undesirable, they are not usually serious. However, flashbacks may be very damaging, and unless immediately extinguished, may result in the necessity of making costly and time-consuming repairs.

The principal object of this invention is to provide a new method of preventing or minimizing the occurrence of flashbacks in oxyacetylene and other gas burners.

A further objeect is to provide apparatus by which the new method may be carried out.

The invention is based on the discovery that the injection of a small amount of water, or other suitable vaporizable liquid'into at least one of the gases supplied toa burner prior .to the formation of a combustible mixture of the gases will effectively prevent or at least minimize the occurrence of flashbacks.

According to the invention, in a gas burner system in which twogases such as oxygen and acetylene are fed separately to a mixer which supplies the combustible mixture of the gases to the tip of the torch or other burner, a small amount of a vaporizable liquid, such as water, is injected continuously during the operation of the burner into one or both of the gasstreams either upstream of the'mixer or after the gases enter the mixer but before they'have had an opportunity to mix. In an oxyacetylene burner system it is suiflcient to inject the vaporizable liquid into only one of the gas streams, and the particular stream into which it is injected is preferably the it will be in this phase when it is present in the gas mixture at the time of a backfire as hereinafter described. It should be suspended in the gas in finely divided form and therefore it is preferably in atomized condition when it is introduced into the gas or placed in atomized conition by the flowing gas stream into which it is introduced.

While I do not Wish to be confined to any particular theory as to why the presence of the vaporizable liquid in the gas mixture prevents a flashback after a backfire, it is thought to be as follows: When a backfire occurs, all of the mixed gases in the system burn with explosive rapidity and in so doing expand and are forced upstream of the mixer. After the pressure wave caused by the explosive burning of the mixed gases subsides, the fresh gases start flowing again toward the mixer, and after they mix they are ordinarily re-ignited by the lingering hot active products'of combustion and continue to burn at the mixing region, thereby producing a flashback. Presumably the water, or other vaporizable liquid, that is injected into at least one of the gas streams and is present in the form of small droplets, vaporizesand absorbs suflicient energy from the lingering active products of combustion of the backfire to deactivate these gases and thereby prevent them from re-igniting the mixture of the fresh gases. in the gas mixture in droplet or atomized form it presents a large surface area to promote rapid vaporization. Inasmuch as the principal function of the vaporizable liquid is to absorb heat, one advantage of utilizing water as the vaporizable liquid is that it has a high latent heat of vaporization, and therefore a small amount of Water'present in the combustible gas mixture will absorb a large quantity of heat from any active products of combustion that may be present in changing from its liquid phase to its vapor phase. Moreover, water is readily available in large quantities at low cost. For these reasons the preferred vaporizable liquid for introduction into one or both of the gas streams is water, but any other vaporizable liquid, preferably a noncombustible one, may be employed which will serve the purpose of cooling the products of combustion sufficiently to prevent them from reigniting the fresh mixture of gases.

Various types of apparatus may be employed for injecting the vaporizable liquid at the proper place into the gas supply of a burner system, two of which are shown in the accompanying drawing, in which:

Figure'l is adiagrammatic representation of Since the liquid is suspended an oxyacetylene gas burner system having means for injecting into one of the gas supply lines a liquid of the kind contemplated by the invention;

Fig. 2 is an enlarged detail View in vertical section of the liquid injector forming part of the burner system illustrated in Fig. l; and

Fig. 3 is a detail view in vertical section of another type of liquid injector that may be employed.

Referring first to Fig. 1, a multi-flame gas burner represented in simple form at [9 is supplied with a combustible gas mixture from a mixer H. Two gases, such as oxygen and acetylene, are fed to the mixer separately from storage cylinders l2 and [3 through supply lines it and 15. The water or other vaporizable liquid is delivered by a supply line it to an injector I! by which it is introduced in a controlled manner and in liquid phase into the oxygen stream in supply line it.

The water injector itself is shown in. greater detail in Fig. 2. It comprises a block 19 adapted to be connected in the oxygen supply line 1 1 and having a gas passage is extending length wise through it which constitutes, in effect, a portion of the oxygen supply line. A pipe 29 places the gas passage !9 in communication with a pressure chamber above the diaphragm 2! of a diaphragm-controlled valve The valve 22 controls the flow of water from the supply line 16 to a nozzle 23 adapted to inject the water in finely divided or atomized form into the oxygen as it passes through the passage it. As long as oxygen is being supplied to the burner there is suihcient pressure exerted on top of the diaphragm 21 to open the valve 22. and admit water to the injector nozzle 29. When no oxygen is passing through the passage 59 the pressure above the diaphragm 21 is insunicient to hold the valve 22 open, so it closes and shuts off the supply of water to the injector nozzle 23. Thus, water is prevented from accumulating in the system when the gas burner is not in operation.

Another form of water injector that can be substituted for that shown in Fig. 2 is illustrated in Fig. 3. The oxygen on its way to the gas burner flows through an aspirator 29 having an inlet nozzle 25 and an outlet passage 29 leading to the gas burner. The oxygen passing through the nozzle 25 draws water from a water supply tank El up through a pipe 29 and aspirates it so that the water in finely divided form is carried along in the oxygen stream. A constant supply of water may be maintained in the tank 2! in any well-known Way. Here again, when the burner is not in use and no oxygen is flowing to it, no water is introduced into the oxygen supply line.

Still other types or" liquid injectors may be employed, but it is preferable in every case that the injector be capable of stopping the water flow automatically when the gas flow is interrupted to prevent an accumulation of the liquid in the system.

While in the above-described gas burner system the liquid injector is associated with the oxygen supply line, it should be understood that it can be associated with the acetylene supply line 25 if it is desired to inject the vaporizable liquid into the acetylene stream, or a liquid injector may be associated with both gas supply lines if it is desired to introduce the vaporizable liquid into both of the gas streams. In any case, the vaporizable liquid is so injected into the gas supply that when a backfire occurs there will be suspended in the gas a small quantity of the vaporizable liquid in finely divided form so that it will prevent ignition of the newly formed com bustible gas mixture by the lingering hot products of combustion in the manner previously described. The vaporizable liquid may be injected into either or both of the gas streams at any point upstream of the mixing region. This may be upstream of the mixer itself or at the mixer, provided that in the latter case the mixer is of such a type that the vaporizable liquid can be injected into one or both of the gases before the gases have had an opportunity to mix.

As previously stated, the quantity of vaporizable liquid that must be injected into one of the gases supplied to the gas burner to prevent flashbacks is relatively small, especially when water which has a high latent heat of vaporization constitutes the vaporizable liquid. For example, it has been found that in an oxyacetylene gas burner system one cubic centimeter of Water per cubic foot of acetylene burned gave optimum flashback resistance. The quantity of water required will of course differ with different installations, but as a general rule it may be stated that the amount of water required in an oxyacetylene gas burner system ranges from .25 to 5.0 cubic centimeters per cubic foot of acetylene burned, although the invention, of course, is not limited even tothis water consumption range. This small quantity of water has no apparent effect on the functioning of the gas burner or the various operations performed by it such as welding and heat treatment of metal.

I claim:

1. in a gas burner system in which a fuel gas and a combustion-supporting gas are supplied separately to a mixing region and the gas mixture is fed to a place at which it is burned, the method of reducing the tendency of the mixed gases to continue burning after a backfire has occurred, which comprises continuously supplying a non-combustible vaporizable liquid in liquid phase to the mixing region in at least one of said gases by continually injecting the liquid in liquid phase into said one of the gases while on its way to said place of burning of the mixed gases in such quantity that the liquid is present at the mixing region in liquid phase.

2, A method according to claim 1 in which the ncn-combustible vaporizable liquid is Water.

3. A me cod according to claim 1 in which the fuel gas is acetylene and the combustion-supporting gas is oxygen.

4. A method according to claim 3 in which the non-combustible vaporizable liquid is water.

5. A method according to claim 4 in which the amount of water introduced is at least 9.25 cu. cm. per cu. ft. of acetylene supplied.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,213,159 Dalen Jan. 23, 1917 1,423,155 Ruff July 18, 1922 1,519,830 Goeriz Dec. 16, 1924 1,588,983 Noval: June 15, 1926 ,033,910 Russell Mar. 3, 1936 FOREIGN PATENTS Number Country Date 554,664 Germany July 14, 1932 941,332 Germany Jan. 28, 1937 694,129 Germany July 25, 1940

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