Method and apparatus for producing flame jet and controlling temperature and flame stability of same

Jime 14, 19&6 j. a. browning 3.255,802

METHOD AND APPARATUS FOR PRODUCING FLAME JET AND CONTROLLING

TEMPERATURE AND FLAME STABILITY OF SAME

Filed Sept. 5, 1953 3 Sheets-Sheet 1

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June 14, 1966 j. a. browning 3,255,802

METHOD AND APPARATUS FOR PRODUCING FLAME JET AND CONTROLLING

TEMPERATURE AND FLAME STABILITY OF SAME

Filed Sept. 5, 1963 3 Sheets-Sheet 2

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% FUEL IN MIXTURE

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June 14, 1966 j. a. browning 3,255,802

METHOD AND APPARATUS FOR PRODUCING FLAME JET AND CONTROLLING

TEMPERATURE AND FLAME STABILITY OF SAMB

Filed Sept. 5, 1963 3 Sheets-Sheet 3

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3,255,802

Patented June 14, 1966

United States Patent Office ¹

255 802

METHOD AND APPARATUS FOR PRODUCING FLAME JET AND CONTROLLING TEMPERATURE AND FLAME STABILITY OF SAME

James A. Browning, Hanover, N.H., assignor ίο Η. E. Fletcher Co., West Chelmsford, Mass., a corporation of Massachusetts

Filed Sept. 5,1963, Ser. No. 306,887

Claims. (CI. 158—4)

The present invention is a continuation-in-part of my copending application Ser. No. 666,680, filed June 19, 1957, now Patent No. 3,103,251, granted Sept. 10, 1953.

This invention relates to a method and apparatus for burning a fuel to form a flame jet and, more particularly, the invention is concerned with a method of producing a cooled flame jet wherein oxygen and an inert gas such as nitrogen are mixed with a liquid fuel and the fuel is burned at superatmospheric pressure in a confined combustion chamber to provide a relatively high velocity stream of products of combustion whose temperatures and flame stability may be varied in accordance with a controlled use of the inert gas component in the combustion chamber.

As disclosed in the above application, I have determined that a nitrogen cooled flame jet, as distinct from an oxyfuel flame jet in which pure oxygen is used as the oxidant, is capable of providing much lower flame temperatures than those possible with a conventional oxy-fuel jet. In this connection it has been found that use of a water coolant for the burner combustion chamber may be eliminated since appreciable amounts of thermal energy is absorbed by the inert nitrogen. In addition, the nitrogen cooled flame is found to provide for improved removal of spallable mineral bodies in carrying out channelling and other mineral working operations.

However, in producing a nitrogen cooled type flame jet in which the inert gas component occurs in an appreciable amount, various problems are encountered. For example, it is necessary to maintain the percent fuel introduced within definite limits which are neither too rich or too lean to support combustion. Flame stabilization of a nitrogen cooled type flame jet must be accomplished within much narrower stability limits than is the case with a pure oxygen-fuel jet. The region defined by these limits in any given instance may be conveniently referred to as the “region of stable burning” of a flame jet. Other factors which determine such a limiting region of stable burning are stream velocity and size of combustion chamber employed.

It is a chief object of the present invention, therefore, to provide an improved method and means for producing a .cooled flame jet such as the nitrogen cooled flame jet above-noted.

Another object of the invention is to provide an improved method and means for supplying and burning fuel in a combustion chamber in which a controlled quantity of inert gas may be constantly introduced. . It is a further object of the invention to devise a burner construction in which stable burning may be realized with relatively small burner sizes to provide a cooled flame jet.

These general objectives may, I find, be realized by controlling the introduction of fuel and inert gas into a combustion chamber in a predetermined maimer and also by controlling the movement of products of combustion which are produced within the combustion chamber.

I have determined that I may control the introduction of fuel advantageously by employing an elongated mixing space in which fuel, oxidant and inert gas are premixed at a temperature below that at which the fuel vaporizes and the mixture is then led into a combustion chamber. In this way I may utilize a liquid fuel such as kerosene and form a dispersion of relatively coarse fuel droplets. I further provide for the premixing space communicating with the combustion chamber through a special flame stabilizing section of the burner. By means of this arrangement I am enabled to provide for the liquid fuel droplets, oxidant and inert gas being brought together to produce a combustible mixture in which the coarse droplets are homogeneously distributed and yet the liquid fuel droplets occur in varying sizes and may burn for varying intervals of time.

I have further discovered that this combustible mixture containing a relatively large amount of inert gas may be burned in the combustion chamber to provide products of combustion whose movement and burning characteristics can be controlled in a highly unusual and novel manner. This discovery is based on a recognition of the fact that the reactants have a velocity of flame propagation in the combustion chamber which is limited by the nitrogen component in a significant degree.

Specifically, I find that by burning relatively coarse fuel droplets interspersed with finer droplets, in an environment in which the velocity of flame propagation is limited by a nitrogen component, and by providing a combustion chamber having predetermined physical characteristics, including a flame stabilizing surface through which the droplets are injected, it becomes possible to induce a recirculation of products of combustion at the flame stabilizing surface. By thus inducing a recirculation of the products of combustion at the point where incoming droplets pass into the combustion chamber, I provide for a continuous igniting action on incoming reactants from the premixing chamber. The recirculated portion of the products of combustion have been visually observed and are seen to become distributed in the shape of a torus located all the way around the fuel inlet in the flame stabilizing surface of the burner through which the mixture is injected. This igniting action makes possible operation of the flame jet using quantities of fuel on both the lean side and. the rich side to an extent not heretofore realized. It will be apparent therefore that for any given set of operating conditions an improved temperature control may be realized and the region of stable burning may be extended and more latitude is possible in the size of the combustion chamber which may be employed.

The nature of the invention and its other objects and novel features will be more fully disclosed from the following description of the preferred embodiments of the invention shown in the accompanying drawings, in which:

FIGURE 1 is a cross sectional view of a burner construction of the invention and having indicated diagrammatically therein premixing and toroidal flow of products of combustion;

FIGURE 2 is a cross sectional view taken on the line 2^-2 of FIGURE 1;

FIGURE 2&lt;z is a cross sectional view of a burner construction illustrating a modified form of premixing chamber;

FIGURE 3 is a cross sectional view of a burner construction illustrating still another form of premixing chamber;

FIGURE 4 is a cross sectional view of a burner construction having coolant circulating means associated therewith;

FIGURE 5 is a graph illustrating stabilized burning curves; and

FIGURE 6 is still another cross sectional view of a burner construction in which improved circulating means for reactants are provided.

The burner structures shown in FIGURES 1 to 3 inclusive, are intended to illustrate a means of carrying out the method of the invention in one simple form. In general, the invention method is initiated by introduc70

3,255,802 ing into an elongated premixing space under pressure a flow of liquid fuel such as kerosene, oxygen and an inert gas such as nitrogen and causing the liquid fuel to become dispersed at temperatures below that at which kerosene becomes a vapor. The liquid droplets occur in varying sizes and are substantially homogeneously, distributed throughout the oxygen and nitrogen. It should be observed that kerosene at temperatures of 100° F. and higher may occur in a mist or droplet form and will become a kerosene vapor at approximately 440° F.

The resulting mixture is conducted from the premixing space through an aperture into a combustion chamber which has a flame stabilizing surface surrounding the aperture. The flow of fuel droplets and oxidant through the aperture takes place at a relatively high velocity Vi and the mixture decelerates to a velocity V₂ in the relatively greater volume of the combustion chamber.

In the combustion chamber the mixture burns at superatmospheric pressure at a velocity of flame propagation which may be expressed as a velocity V_p. The limit velocity of this flame propagation is a function of the quantity of nitrogen in the combustion chamber, and by regulating input of fuel droplets in accordance with the ratio of oxygen to nitrogen supplied, and by controlling the flow of the total mixture, the velocity Vi is always maintained greater than the velocities V₂ and V_p. Velocity V₂ is always maintained less than V_p. With these requirements observed and a suitable combustion chamber size utilized the flame burns continuously without being extinguished and a lowering of temperature dependent upon the quantity of nitrogen employed is constantly realized in the stream of products of combustion leaving the combustion chamber. It has been found that with combustion chamber diameters less than one inch, it is exceedingly difficult if not impossible to sustain high specific mass flows. In the method of the invention good results have been obtained with burner diameters of from 2 to 4 inches in producing the nitrogen cooled flame jet.

Considering these steps in relation to FIGURE 1 of the drawings, numeral 2 denotes a tubular premixing chamber having a premixing space 4. Supported through one end of the member 2 is a fuel supply pipe 6 which is connected to some suitable fuel supply such as a kerosene tank and pumping apparatus not shown in the drawings. The extremity of pipe 6 is located in spaced relation to an inner surface 7 of the member 2 to provide for flow of liquid fuel under pressure into the premixing space.

Also extending into the premixing chamber 2 is an oxygen supply conduit 10 with control valve 10α and a nitrogen supply conduit 12 with control valve 12α. These members are also connected to respective oxygen and nitrogen tanks having suitable valve means for supplying these gases under pressures which can be regulated in a conventional manner.

Attached to the premixing chamber 2 by threads 11 is a second tubular body 14 which has a combustion chamber 16 therein. The combustion chamber preferably consists of a cylindrical member and when threaded over the premixing body 2 is closed at one end by the portion 7 of the premixing chamber. Formed through the end wall 7 is an aperture A through which gases and fuel can pass at relatively high velocity Vi into the combustion chamber 16 and decelerated to a relatively lower velocity V₂. At its opposite end the tubular body 14 is formed with a tapered portion 18 which terminates in a flame jet outlet 20.

An important feature of the structure described is the combination with a premixing chamber of an orificed body having a relatively large annular area 24 which extends around the fuel injection aperture A at a relatively abrupt angle thereto. This provides a flame stabilizing surface against which products of combustion may be recirculated when the burner is operated in accordance with the method of the invention.

In producing a flame jet with the structure described the burner may be started by furnishing liquid fuel through the member 6. Oxygen is supplied through the member 10 and fuel and oxygen are forced through the aperture A being ignited in the combustion chamber by some suitable igniting means of conventional nature commonly employed in flame jet operation. Thereafter, a supply of nitrogen may be introduced through the conduit 12 and the quantity of oxygen employed is substantially reduced.

In reducing the ratio of oxygen contained in the total mixture (which results from introducing oxygen with an inert gas such as nitrogen, for example as these gases occur in atmospheric air) the region of stable burning earlier referred to in the specification changes sharply as is illustrated in FIGURE 5 and the precent fuel and stream velocity must be regulated to avoid flame extinction.

Subject to these limiting conditions oxygen under a pressure of, for example, 6 atmospheres and nitrogen in the form of atmospheric air under a pressure of 90 p.s.i. gauge is expanded at high velocity into the premixing chamber with' the result that fuel discharged through the member 6 is subjected to a high degree of turbulence in the premixing chamber and becomes broken up into a dispersion of liquid droplets substantially homogeneously dispersed in the oxygen and nitrogen. This mixture after passing through the aperture A is decelerated to a velocity V₂ which is less than Vi above-noted and the mixture burns in the combustion chamber to produce products of combustion. A portion of the reactants sointroduced burns almost instantly and the resulting products of combustion are emitted from outlet 20 to form a flame jet whose temperature is lowered by the nitrogen present.

In accordance with the invention another portion of the products of combustion including partially combusted coarse droplets are caused to recirculate in the manner illustrated by the curved arrows shown in FIGURE 1 in a toroidal path of travel. The recirculated portion of the flame is contained against the flame stabilizing surface 24 and guided radially inwardly to contact with incoming portions of the combustible mixture at aperture A so as to ignite continuously these portions.

It is found that this recirculation develops to a significant degree when an appreciable quantity of nitrogen is present in the combustion chamber and it is understood to be due to the fact that the nitrogen limits the velocity of flame propagation. It is pointed out that the recirculated portion contains reactants as well as products of combustion. The fuel contained in this recirculated portion is comprised of both large and small droplets as well as vapor. Thus there is, in some instances, a short interval of time in which burning droplets may move into contact with incoming combustible mixture. The toroidal shape of the path of recirculating droplets has been visually observed and appears substantially in the form shown in FIGURE 2 as a torus T.

An essential feature of the burner construction, therefore, is the provision of a substantial annular surface area 24 surrounding the aperture A and toward which surface burning droplets may be recirculated and guided inwardly towards the stream of incoming fuel mixture. In order for the recirculation of burning droplets to take place without the flame front actually flashing back into the premixing chamber, it is further essential that the velocity Vi of the incoming fuel mixture be greater than the velocity V_p of flame propagation, while at the same time providing for the velocity V_p of flame propagation being greater than the velocity V₂ of the reactants.

These relationships I have found may be maintained by regulating the ratio of oxygen to nitrogen and by controlling the flow of total mixture into the combustion

3,255,802 chamber. The controlling steps, it will be seen, are made possible because of the action of the nitrogen in limiting the velocity of flame propagation so that Vi can be maintained greater than V₂ and flashing back prevented.

As an instance of a typical burner operation to provide a cooled flame jet in accordance with the invention, the following values for a fuel-air mixture are cited whereby the necessary regulation is accomplished.

Compressed air at 90 p.s.i. gauge from an air compressor is metered by a valve to supply a flow of 354 standard cubic feet per minute to the burner. Fuel oil is delivered at 100 p.s.i. gauge to an atomizing nozzle at a flow of 1.92 pounds per minute. A nozzle exit diameter of 1,250 inches produces a chamber pressure of 32 p.s.i. gauge with a resulting flame jet of 3,650 ft./sec. at 2,530° F. under identical reactant flow conditions but with a 1.750 inch diameter nozzle, the chamber pressure is reduced to 8 p.s.i. gauge with a jet velocity of 2,300 ft./sec. at 3,300° F. In each case the burner chamber measured 2,450 inches inside diameter by 15.5 inches long. Orifice “A” was 0.750 inch diameter.

In FIGURE 2a, I have illustrated a modified form of burner construction in which ! provide a premixing member 2' and combustion chamber member 14', together with oxygen and nitrogen supply conduits 10' and 12' and control valves 106 and 126, and a liquid fluid injector 6'. The construction and operation of this form of burner is similar to those of the burner of FIGURES 1 and 2 with the exception of the mixing chamber 4' which is constructed with a relatively small elongated passageway 5 formed in a tubular body 9. The passageway 5 communicates with an aperture A' as shown. For some types of fuel a superior premixing of fuel and oxidant may be realized and a better control of droplet size achieved with this structure.

In FIGURE 3,1 have illustrated another form of burner in which even better control of droplet formation and distribution in an oxidant may be realized. In this arrangement a combustion chamber 14 of the type corresponding to chamber 14 and 14' of FIGURES 1 and 2, has threaded to one end thereof a cylindrical housing 28. At the outer end of housing 28 is a second cylindrical body 30 of a smaller diameter than member 28. Supported in the cylindrical body 30 are air conduits 32 and 34 with control valves 32α and 34α which supply a flow of air under pressure to the chamber space 36 and then into the chamber space 38 which is of relatively larger diameter. Turbulent air contained in the space is forced through orifices as 40 in a foraminated fuel distributing sleeve 42 which is threaded into the orificed flame stabilizing shoulder 33. A fuel pipe 44 is connected to the opposite end of the sleeve 42 and provides for a flow of fuel through the sleeve in a relatively restricted passageway which is constantly subjected to turbulent jets of air entering the opening 40. A very high degree of droplet dispersion in the oxidant gasses may be obtained with this arrangement and is particularly effective with combustion chamber of relatively small diameter in the 2 to to 4 diameter range.

I may desire to operate the method of the invention with the use of a coolant for cooling the combustion chamber walls where a precise control of combustion chamber temperature may be important. FIGURE 4 illustrates a premixing chamber with a burner capable of utilizing oxygen enrichment and having water cooling. Air entering through a pipe 51 is controlled by valves 52α and 51α in members 49 and 49α passes from the annular volume 52 through holes 54 contained in the fuel injector 53. Fuel is introduced through the spray nozzle 50 and is mixed thoroughly with the air flow by the turbulent action set up in the premixing chamber 55. Oxygen, as required to increase the total oxygen content in the air, is conducted through a tube 56 and a passageway 57 to enter the combustion chamber 59. The re6 striding nozzle section 60 may or may not be utilized, depending on whether high exit velocity is required. With this arrangement I combine special water cooling means as shown. Water enters a conduit 62 and passes along 5 an annular space 61 defined between the two concentrically arranged tubes 67 and 68. From the annular space water is circulated out through an exit pipe 63. By controlling the flow of coolant through the passageway described, desirable control of the temperature of the Ιθ combustion chamber may be realized.

Another form of burner in which air cooling is utilized in flame drilling a hole in a work body has been illustrated in FIGURE 6. In this form of burner a premixing chamber 310 is furnished with compressed air from a 15 conduit 312 and valve 312α and this air is turbulently mixed with fuel injected from a nozzle 314 and passed through a tubular member 316 into the combustion chamber 318 of a burner 320.

The burner 320 is provided with a flame stabilizing 20 surface 322 and is also constructed with an outer cylindrical part 324 to define an annular passageway 326. A flame jet is produced by nitrogen cooled products of combustion in the manner already described and is emitted through a restricted outlet 328. In addition, there 25 is provided a second air supply system consisting of a separate air conduit 330 and valve 330α which supplies compressed air through passageways 332 into annular space 326. This secondary air passes along the annular space 326, cooling burner wall surface and then a part 30 of the air is discharged through ports 340 and caused to circulate between the outer burner wall 324 and a surface of rock 344 which defines a hole drilling by the flame. Another portion of the air is discharged through outlets 348 and combined with the jet flame to provide 35 both cooling of the flame and increased scouring and return of spalled material out of the hole.

While I have shown preferred embodiments of burners of the invention, it should be understood that other forms of burners and modified devices of the invention ⁴⁰ may be resorted to within the scope of the appended claims.