US3547568A - Burner apparatus for producing glass fibers - Google Patents

Description

Dec. 15, 1970 o. E. su-nsuzn BURNER APPARATUS FOR PRODUCING GLASSFIBERS 2 Sheets-Sheet 2 Filed April 12, 1968 INVEN m Donmfl E.SHI$L$ United States Patent O 3,547,568 BURNER APPARATUS FOR PRODUCING GLASS FIBERS Donald E. Shisler, Napoleon, Ohio, assignor to Johns- Manville Corporation, New York, N.Y., a corporation of New York Filed Apr. 12, 1968, Ser. No. 720,915 Int. Cl. F23r N US. Cl. 431-158 13 Claims ABSTRACT OF THE DISCLOSURE I An improved burner apparatus and method for use in the flame attenuation of glass filaments; The burner includes a refractory combustion tunnel having laterally elongated inlet and outlet openings for generating a relatively wide and flat hot gaseous blast of high temperature and high velocity for attenuating glass filaments. A thermally conductive orifice plate having a laterally elongated and vertically restricted orifice is positioned adjacent the inlet end of the tunnel and functions to pass a combustible gas mixture into the tunnel. The orifice has a width similar to that of the tunnel, but the height of the orifice is substantially smaller than the height of the tunnel. A plenum unit is located between the conduit through which the combustible gas mixture is supplied and the orifice and acts on the combustible gas mixture as it moves toward the orifice so that the combustible gas mixture as it moves through the orifice is distributed uniformly throughout the lateral and vertical extent of the orifice and issubstantially free of all eddies and turbulence. This construction provides relatively high gas velocity over a wide range of flow rates with relatively low back pressure upstream of the tunnel inlet and without any flashback problem.

DESCRIPTION OF THE INVENTION This invention relates generally to the processing of glass filaments and, more particularly, to an improved burner apparatus and method for generating a wide and flat hot gaseous blast for attenuating glass filaments.

It is common practice in the fiber glass industry to produce a multiplicity of continuous primary glass filaments simultaneously from a single melting pot, and then subject the filaments to a continuous hot gaseous blast to re duce the primary filaments to fine fibers for use as insulation or the like. As technological advances have permitted the number of filaments produced from a single melting pot to be increased, it has become increasingly difficult to provide a wider burner which produces a gaseous blast sufiicient to attenuate all the filaments uniformly, especially over long operating periods, while also achieving a long burner life. More particularly, one of the specific problems encountered has been how to increase the gas quantity flow rate through the burner at the required velocity without excessive increases in the back pressure and/or flashback problems. (As is well known to those familiar with this art, a flashback occurs when the flame from the burner tunnel flashes back through the tunnel inlet into the upstream equipment.)

It is, therefore, a primary object of the present invention to provide an improved tunnel-type burner apparatus and method for flame attenuating glass filaments which provides relatively high gas velocities and flow rates through the tunnel with relatively low back pressure upstream of the tunnel inlet, and yet has little or no tendency to produce flashbacks at low quantity throughput. In this connection, a related object of the invention is to provide such an improved burner apparatus and method which produces a wider attenuation blast than most burners proposed heretofore while maintaining the flow of incoming gases at the orifice with a velocity greater than the flame propagation speed.

Another object of this invention is to provide an improved burner apparatus and method of the foregoing type which provides a relatively large heat transfer surface in the area adjacent the inlet end of the tunnel so as to maintain a relatively low temperature upstream of the tunnel inlet. A related object of the invention is to provide such an improved burner apparatus and method which provides a relatively large heat transfer surface directly at the orifice leading into the inlet end of the tunnel.

It is a further object of the present invention to provide an improved burner apparatus and method of the type described above which achieves relatively high gas velocities and flow rates into and through the tunnel while maintaining a relatively small orifice area at the inlet and which provides a practically unlimited turn down range. More particularly, it is an object to provide such an improved burner apparatus and method which permits the combustion gas flow rate to be relatively low without flashback, and which extinguishes any flame that penetrates through the inlet orifice when the flow rate approaches the OE level.

A still further object of the invention is to provide such an improved burner apparatus and method which achieves all the above objectives in combination with good flame characteristics in the burner output.

Still another object of the invention is to provide such an improved burner apparatus which can be efliciently manufactured at a low cost from readily available materials.

Yet another object of the invention is to provide such an improved burner apparatus which is stable and reliable over relatively long operating periods.

Other objects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross sectional elevation view of a burner apparatus embodying the present invention;

FIG. 2 is a horizontal section taken along line 22 in FIG. 1;

FIG. 3 is an end elevational view of that portion of the burner attached to the inlet end of the combusion tunnel, with a fragment thereof broken away to show the inlet orifice to the combustion tunnel; and

FIG. 4 is a vertical section taken along line 4-4 in FIG. 3.

While the present invention is susceptible of various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the draw ings and will herein be described in detail. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but, on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as expressed in the appended claims.

Turning now to the drawings and referring first to FIG. 1, there is shown a burner 10 forming a refractory tunnel 11 for producing a hot gaseous blast suitable for use in flame attenuating a multiplicity of primary glass filaments, so as to reduce the filaments into fine fibers. The tunnel 11, which is formed by a plurality of refractory components encased by a metal housing 12, is laterally elongated along its entire length as can be seen in FIG. 2, for example. A major portion of the tunnel extending rearwardly from the outlet opening 11a is of uniform cross section, but the inlet opening 11b has a vertical dimension greater than that of the outlet opening 11a, with the bottom wall 110 of the tunnel tapering upwardly from the lower edge of the inlet opening toward the outlet opening. This feature, combined with the offset position of the inlet orifice to be described below, has been found to provide increased flame stability and reduced erosion of the refractory walls.

A number of different refractory materials may be used to form the tunnel 11 within the metal housing 12. In general, it is preferred to use a high density material to form the walls of the tunnel, so as to withstand the eroding effects of the high temperature and high velocity gases within the tunnel, while the materials spaced away from the tunnel toward the metal housing 12 are selected to have lower density and greater thermal insulating properties. Since the most severe erosion occurs in the forward portion of the tunnel, because of the higher temperature and the expanding volume of the gases in the forward region, the tunnel walls near the inlet end thereof may be made of a material that is somewhat less dense, and better insulating, than the material in the forward portion of the tunnel. A number of different refractory materials which satisfy the above criteria are known to those to those skilled in this art, but in one exemplary embodiment of the invention the forward tunnel wall components 13 are made of a castable refractory having a density on the order of about 100 lbs./ft. such as the aluminum oxidecalcium aluminate composition marketed by the Norton Company and designated 33-1; the rear tunnel wall components 14 are made of a lower density material such as the highly pure kaolin clay marketed by the Babcock and Wilcox Company and designated K-30 with a density of 52.3 lbs./ft. the outer components 15 are made of a more highly insulating material such as the castable refactory marketed by Johns-Manville Corporation and designated CA-Insulating Firecrete; and the component 16 beneath the rear tunnel wall component is made of a sillca felt marketed by Johns-Manville Corporation and designated Micro-Quartz felt.

In accordance with the present invention, a thermally conductive orifice plate is mounted on the inlet end of the refractory tunnel, and a plenum unit is connected between the orifice plate and a supply conduit connected to a source of a combustible gas mixture, with the orifice plate and plenum cooperating to form a passageway terminating in a single laterally elongated orifice substantially as wide as the inlet opening of the combustion tunnel and more restricted than the inlet opening in the vertical dimension. Also, the walls of the plenum unit taper gradually from the supply conduit to the orifice to provide laminar flow, that is substantially free of all eddies and turbulence, of the combustible gas mixture therethrough. Thus, in the illustrative embodiment, a metallic orifice plate 20 is fitted over a plurality of mounting bolts 21 projecting longitudinally from the rear end of the burner 10, and secured thereto by nuts 22 threaded onto the bolts 21. The head ends of the bolts 21 may be embedded within the refractory materials contained within the metal housing 12 during the formation and assembly thereof. To provide a gas tight seal between the orifice plate 20 and the burner housing 12, a gasket 23 is preferably placed therebetween.

It is important to note that the open area of the orifice leading into the inlet end of the combustion tunnel must be relatively small in order to prevent the flame within the combustion tunnel from flashing back into the equipment upstream of the tunnel. Thus, in order to increase the width of the orifice, as is required to produce an attenuating blast sufficiently wide for the greater number of primary filaments that can be produced from the modern melting pots, corresponding reductions must be made in the vertical dimension of the orifice. For example, in one embodiment of the invention, an increase in the width of the orifice to 8% inches required the height of the orifice to be reduced to 0.094 inch. While such a restricted orifice is of significant value in preventing flashbacks, it makes it extremely difficult to provide the required gas velocity and flow rate through the orifice into the combustion tunnel.

Accordingly, one of the important features of the present invention is the provision of a plenum unit 30 for supplying the combustible gas mixture to the burner through the orifice so that high throughput rates and velocities can be achieved even through extremely restricted orifices. The plenum unit connects the orifice to a conduit through which a combustible gas mixture is supplied and is designed to deliver the combustible gas mixture uniformly across the orifice while generating minimum turbulence and having minimum pressure loss. The plenum unit is designed to cause the flow of the combustible gas mix to be laminar in nature, that is, to be substantially free of all eddies and turbulence. This construction provides a high volume flow of gas with minimum loss of pressure in the transition. Additionally, the discharge from the orifice is uniform. Furthermore, because a larger proportion of the pressure from the supply system can be applied to the orifice, the orifice can be made of smaller cross sectional area. This causes the combustible gas mixture to issue from the orifice at a higher velocity for any given volume flow, leading to better combustion characteristics within the refractory tunnel, In addition, the higher velocity aids in preventing flashback of the flame into the supply system, the condition which occurs when the velocity of the advance of the combustive mixture falls below the velocity of propagation of the flame as determined by the particular mixture of gaseous fuel and air being used. The construction of the plenum unit from a thermally conductive material also aids in preventing flashback. A flame front propagating upstream into the orifice and against a velocity flow of combustible mixture which is less than the velocity of flame propagating comes into contact with a cool surface, which, by its conductive nature, reduces such flame front below its ignition temperature, thus quenching the flame. These features of the invention thereby provide a burner operable efficiently and safely over a wide range of operating conditions.

In the preferred embodiments of the invention, the plenum unit 30 includes an entranceway 31 (FIGS. 3 and 4) which is substantially coextensive with the discharge opening of a supply conduit 32 connected to a source (not shown) of a combustible gas mixture such as fuel and air. The entranceway 31 may be connected to the supply conduit 32 in any suitable manner, such as that illustrated in FIG. 4, but it is preferred to maintain the inner surface of the interconnection as smooth as possible to avoid the creation of turbulence in the gases flowing therethrough.

It will be appreciated that the discharge opening of the supply conduit 32 is considerably larger than the vertical dimension of the orifice associated with the tunnel inlet opening 11a, and considerably narrower than the width of the orifice. To effect the transition between these two disparate opening configurations, the walls of the plenum unit 30 taper gradually outwardly in the direction corresponding to the width of the inlet orifice and the tunnel 11, as indicated at 33 in FIGS. 3 and 4. After the walls of the plenum unit 30 have diverged to the full width of the inlet Orifice, they are tapered gradually inwardly toward each other in the direction corresponding to height of the inlet orifice, as indicated at 34 in FIG. 4, so that the exit end of the plenum unit is substantially coextensive with the inlet orifice. It will be appreciated that this gradual transition from the cross sectional configuration of the supply conduit 32 to the cross sectional configuration of the inlet orifice tends to avoid the creation of turbulent conditions within the plenum unit and, in fact, the plenum unit is specifically designed to provide laminar flow of the gas mixture therethrough under the operating conditions in which it is to be used. In other words, the dimensions and physical configuration of the plenum unit 30- are designed to provide laminar flow when a given gas mixture is passed therethrough at a given fluid velocity. As a result, the gas mixture is distributed uniformly over substantially the entire area of the orifice at the exit end of the plenum unit 30, and can be discharged through the orifice into the combustion tunnel at relatively high velocities and flow rates, and with a relatively small back pressure in the region between the supply conduit 32 and the orifice plate 20. Thus, a high gas velocity and flow rate and low back pressure can be achieved even with extremely restricted orifices such as the 8% inches by 0.094 inch orifice mentioned previously. For example, in one embodiment of the illustrative design having the aforementioned orifice size and a tunnel 8% inches wide, inch high at the inlet opening, and /2 inch high at the outlet opening, the back pressure within the plenum unit was found to vary from 14 to 52 ounces per square inch when the gas flow rate was varied from 500 to 1000 cubic feet per hour, which is significantly lower than the back pressure in burners known heretofore. The back pressure in this example Was measured by inserting a pressure gage through a small aperture 40 ,4 inch) associated with a lateral coupling member 41, the aperture 40 and coupling member 41 being located adjacent a region of relatively low velocity within the plenum unit so as to measure primarily static pressure.

It is understood that the foregoing description of the preferred embodiment of the invention is given for illustration purposes only. It is recognized that the construction of the plenum unit may vary so long as the operational characteristics are maintained. Accordingly, the two step change from the circular supply conduit 32 to the orifice 35, as illustrated in FIGS. 3 and 4, could be accomplished in one step provided the laminar flow, h1gh throughput rates and velocities, and pressures could be maintained. Also, it is recognized that changes in shape and size of the supply conduit 32 would result in corresponding changes in the shape of the plenum unit so as to obtain the above described operational characteristics. Furthermore, although the plenum unit illustrated in FIGS. 3 and 4 is curved, it is recognized that the unit if desired could be made straight. However, it is noted that significant results, as described herein, have been achieved by the construction of the preferred embodiment as illustrated in FIGS. 3 and 4.

In addition to the increased gas velocities and flow rates and reduced back pressure, the laminar flow plenum unit provided by this invention maintains a relatively low temperature on the input side of the orifice plate 20, thereby providing a further safeguard against flashback. For example, with a temperature of 2600 F. at the entrance portion of the refractory tunnel, the temperature 1n the plenum unit 30 an inch or so upstream of the orifice plate 20 is typically in the range of about 100 to 140 F. Furthermore, because of the restriction of the plenum unit as it approaches the orifice plate, to conform with the orifice configuration, a major portion of the outside surface of the orifice plate 20 is exposed to the ambient atmosphere to provide a further means for dissipating heat to maintain a low temperature in the area immediately adjacent the tunnel inlet opening.

Still another advantage of the present invention is that the turn down range for the burner is virtually unlimited. That is, it has been found that the gas velocity at the inlet end of the combustion tunnel may be maintained above the flame propagation speed until the off rate is approached, i.e. with a natural gas and air mixture down to a rate of about 5 cubic feet of gas per hour. Even at the extremely low rates of 5 cubic feet per hour or less, the flame is extinguished as soon as it propagates into the orifice, by virtue of the fact that the heat is quickly absorbed and dissipated by the metal orifice plate and plenum unit due to the excellent heat transfer characteristics of these components. Consequently, the burner has an extremely wide range of operation with practically no danger of a flashback to the gas mixing equipment upstream of the burner.

In one working example of the present invention, the entranceway 31 of the plenum unit 30 was dimensioned to be coupled to a conventional two-inch pipe. The lateral expansion in the direction of the tunnel orifice, i.e., section 33 of the unit 30, began 2%. inches from the end of the entranceway and flared from a width of 2 inches to a width of 8% inches (as viewed in FIG. 3) with the constant dimension (see FIG. 4) being 1% inches. In section 34 of the plenum unit 30, the Width was maintained constant at 8% inches, while the dimension corresponding to the orifice height was gradually reduced from 1% inches to 0.094 inch. The tunnel and orifice dimenions were the same as mentioned previously.

In accordance with one particular aspect of this invention, the exit end of the plenum unit extends through the orifice plate so that the exit opening of the plenum unit forms the orifice for admitting the combustible gas mixture into the combustion tunnel. Thus, in the illustrative embodiment, the exit end 35 of the plenum unit 30 extends through a complementally formed opening in the orifice plate 20 and terminates flush with the inside surface thereof. This construction has the advantage of providing a smooth uninterrupted surface all the way from the supply conduit 32 to the inlet end of the combustion tunnel 11, thereby further insuring against any turbulence or interruption of the laminar flow in this critical region.

It will be understood that the term plenum unit is used herein because the unit 30 serves as a means of distributing the combustile gas mixture from the main conduit to the input orifice.The plenum unit provided by this invention diifers from most conventional plenum chambers, however, in that it is specifically designed to provide laminar flow, rather than turbulent flow, in the transition region between the supply conduit and the input orifice.

As can be seen from the foregoing detailed description, this invention provides an improved burner apparatus and method which is capable of providing the relatively high flow rates required for wide combustion tunnels, and without the danger of flashbacks. The gas velocity can be maintained above the flame propagation speed over a Wide range of flow rates, including relatively low flow rates such as are encountered during burner turn down. Furthermore, a low back pressure is maintained upstream of the tunnel inlet, and the temperatures in this same region are also maintained at a low level so as to provide a further safeguard against flashback. In addition, the burner can be manufactured at a low cost from readily available materials, and has a long operational service life. In fact, even when it becomes necessary to replace the refractory materials within the tunnel portion of the burner, it is not necessary to replace the orifice plate and the plenum unit; these latter components most conventionally are made of metal, and can be simply connected to a new tunnel structure. This operation can be repeated many times before it is necessary to replace the orifice plate and/ or the plenum unit.

It is to be understood that all the details in the foregoing description of the invention need not be strictly adhered to and that various changes and modifications may suggest themselves to one skilled in the art, all falling within the scope of the invention as defined by the suboined claims.

What I claim is: i 1. A burner apparatus for use in the flame attenuation of glass filaments, said apparatus comprising the combination of a refractory combustion tunnel having laterally elongated inlet and outlet openings, said inlet opening have a vertical dimension greater than that of the outlet opening and said tunnel having a Wall taperin-g inwardly from the inlet opening towards the outlet opening, an orifice plate at the inlet end of said tunnel and defining a laterally elongated and vertically restricted orifice for admitting a combustible gas mixture into said tunnel, a supply conduit for providing said combustible gas mixture, a plenum unit between said supply conduit and said orifice plate, with an exit end of said plenum unit being substantially coextensive With said orifice, a portion of said plenum unit adjacent said exit end being of gradually increasing transverse cross sectional configuration in the direction from said exit end toward said supply conduit and means associated with said plenum unit for acting on said combustible gas mixture after it leaves said conduit so that said combustible gas mixture as it moves through said orifice is distributed uniformly throughout its lateral and vertical extent and so that it is substantially free of all eddies and turbulence.

2. A burner apparatus for use in the flame attenuation of glass filaments, said apparatus comprising the combination of a refractory combustion tunnel having laterally elongated inlet and outlet openings, an orifice plate at the inlet end of said tunnel and defining a laterally elongated and vertically restricted orifice for admitting a combustible gas mixture into said tunnel, a supply conduit for providing said combustible gas mixture, a plenum unit between said supply conduit and said orifice plate with an exit end of said plenum unit being substantially coextensive with said orifice, a portion of said plenum unit adjacent said exit end being of gradually increasing transverse cross sectional configuration in the direction from said exit end toward said supply conduit so that said combustible gas mixture as it moves through said orifice is distributed uniformly throughout its lateral and vertical extent and so that it is substantially free of all eddies and turbulence.

3. A burner apparatus as set forth in claim '2 wherein said orifice plate is made of metal.

4. A burner apparatus as set forth in claim 2 wherein said plenum unit is made of metal.

5. A burner apparatus as set forth in claim 2 wherein the width of said orifice is considerably greater than the corresponding dimension of the discharge opening of said supply conduit and the height of said orifice is considerably smaller than the corresponding dimension of the discharge opening of said supplyconduit.

6. A burner apparatus as set forth in claim 2 wherein the exit end of said plenum unit extends through said orifice plate so that the exit opening of the plenum unit forms the orifice for admitting said gas mixture into said tunnel.

7. A burner apparatus as set forth in claim 2 wherein said orifice is vertically positioned closer to the upper edge of said inlet opening of said tunnel than to the lower edge of said inlet opening.

8. A burner apparatus as set forth in claim 2 wherein the vertical dimension of said inlet opening of said tunnel is greater than the vertical dimension of said outlet opening, and the bottom wall of said tunnel is tapered upwardly from the lower edge of said inlet opening toward said outlet opening.

9. A burner apparatus for use in the flame attenuation of glass filaments, said apparatus comprising the combination of a refractory combustion tunnel having laterally elongated inlet and outlet openings, a thermally coductive orifice plate at the inlet end of said tunnel and defining a laterally elongated and vertically restricted orifice for admitting a combustible gas mixture into said tunnel, a supply conduit for said combustible gas mixture with a discharge opening having a transverse cross sectional configuration substantially greater than the transverse cross sectional configuration of said orifice, and a plenum unit having an entranceway adjacent said discharge opening of said conduit and connected thereto for receiving said combustible gas mixture from said conduit, said plenum unit havin an exit substantially coextensive with said orifice and connected thereto for passing said gas mixture through said orifice into said tunnel, and the walls of said plenum unit between said entranceway and said exit being gradually tapered in the direction from said entranceway to said exit to act on said combustible gas mixture as it passes through said plenum unit so that said combustible gas mixture as it passes through said orifice is distributed uniformly throughout the lateral and vertical extent thereof, has substantially no eddies or turbulence therein, and has suffered substantially no loss of pressure.

10. A burner apparatus as set forth in claim 9 in which said orifice has a uniform vertical dimension of about 0.1 inch or less across the entire width thereof.

11. A burner apparatus as set forth in claim '10 in which said orifice has a width of at least 8 inches.

12. A burner apparatus as set forth in claim 9 wherein said orifice is vertically positioned closer to the upper edge of said inlet opening of said tunnel than to the lower edge of said inlet opening.

13. A burner apparatus as set forth in claim 9 wherein the exit end of said plenum unit extends through a complementally formed opening in said orifice plate so that the exit opening of the plenum unit forms said orifice for admitting the gas mixture into the combustion tunnel.

References Cited UNITED STATES PATENTS 2,623,579 12/1952 Furkert 43 l-353 3,048,217 8/1962 Denniston 65-16 3,327,503 6/1967 Labino 6516 S. LEON BASHORE, Primary Examiner R. L. LINDSAY, 1a., Assistant Examiner US. Cl. X.R. 6516; 431-353

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