US3887134A - Gas burner - Google Patents

Abstract

A burner for use with a gaseous fuel having a low caloric value, the burner having a mixing chamber terminating at one end in a burner nozzle with the gas and air being introduced to the chamber at an angle to a given radial of the chamber to cause the air and gas to swirl in the chamber for thorough mixture prior to combustion, the gases passing through the burner nozzle to increase the velocity resulting in improved burner performance.

Description

United States Patent Hacker June 3, 1975 [54] GAS BURNER l,9l6,370 7/1933 Hayes, Jr. et al. 263/19 [75] Inventor: David Solomon Hacker, Evanston, FOREIGN PATENTS OR APPLICATIONS 54s 24| 2/1927 Germany 239/403 Assignee: John Mohr & sons, Chicago France r r [22] Fil d Apr- 1969 Primary Examiner-Lloyd L. King Assistant Examiner-John J. Love 21 A l. N 811988 1 pp 0 Attorney, Agent, or Firm-Baker & McKenzie [52] US. Cl. 239/404; 239/433; 431/170 57 ABSTRACT [51] Int. Cl B05b 7/00 A burner for use with a gaseous fuel having a low [58] Field of Search 239/405, 404, 403, 399, l l h b h h b 239/430 433 468 543 263/19 431/170 one va ue,t e urner avrngamlxrnge am er terminatmg at one end in a burner nozzle with the gas and [56] References Cited air being introduced to the chamber at an angle to a given radial of the chamber to cause the air and gas to UNITED STATES PATENTS swirl in the chamber for thorough mixture prior to 970941 9/ I910 Moore 263/19 combustion, the gases passing through the burner nozl.257,524 2/1913 PfOSBY el zle to increase the velocity resulting in improved 1.4Sl,063 4/1923 Anthony 239/405 X burner performance. 1,826,776 l0/l93l Gunther 239/403 X 1,874,970 8/1932 Hall 239/403 3 Claims, 6 Drawing Figures M n n SHEET Inventor DAVID 5. HACKER 5 W1 Dmld 8.5M

fl-Hrornegus GAS BURNER The present invention relates to an improved burner and more particularly to a burner for use with gases of a low caloric content.

Burners for use with gases having a low caloric value generally contemplate some degree of fuel enrichment to achieve efficient operation. Existing systems generally operate on the principle of a turbulent diffusion burner where air and gas are mixed in the area where combustion is contemplated. Such systems, however, have disadvantages in that there is only a limited range of operation for the burner during combustion and combustion efficiency generally is relatively poor, even at optimum operating conditions, due to incomplete mixing of fuel with air before combustion.

It is desirable in considering combustion apparatus for regenerative stoves to provide devices which will perform efficiently even with fuel having a low caloric value and which will have a wide turn down range with stable operation. More specifically, because of its availability it is desirable to use gas from the blast furnace itself. A typical blast furnace gas, without enrichment, has a heating value of about 80 to 90 BTUs per cubic foot; contains about 27 percent CO and has a theoretical adiabatic flame temperature of about 2,400F.

Recent developments in flame technology and in the understanding of combustion parameters have not generally been effectively utilized in the design of combustion equipment for use in steelmaking, such as in regenerative stoves. It is recognized, however, that improved combustion characteristics can alter thermal efficiency of existing installations and the economics of overall plant performance.

This can be demonstrated by the fact that burners currently applied to regenerative stoves require large combustion chambers to achieve complete combustion due to poor mixing at the burner. With efficient mixing the combustion chamber volume can be reduced thereby providing more space for checkerwork which improves the performance of the regenerative stove.

Some present designs for combustion equipment intended to burn blast furnace gases utilize a diffusion flame principle which characteristically permits fuel and air to interact at the interface of the mixing zone in the burner. This generally results in inadequate mixing and reduces temperature uniformity; establishes an operating condition which gives rise to severe gradients in close contact with the brickwork of the regenerative stove; results in local burnout of the brickwork because of local hot spots and results in operating conditions where measurement of dome temperature of the regenerative stove is ineffective to sense the local hot spots since this is a measurement of the average gas temperature in the dome.

One burner design which has been developed to overcome some of the functional problems noted above involves a version of a multiport burner. However, this type of burner is sensitive to air-fuel ratios and usually exhibits a significant pressure drop across the burner port.

Another burner design which has been developed to overcome some of the problems noted above is one involving parallel jet mixing to realize the desired fuel/air exchange essential to establish and maintain combustion conditions.

The present invention is directed to the provision of an improved burner for use with gases of low caloric value that is operable over a relatively wide velocity range and which exhibits minimum pressure drop during use with improved mixing and temperature operating characteristics in the burned gases.

The design of a high capacity burner requires an ap' propriate operative match of the characteristics of a plug-flow type burner with a peripheral inlet section to provide a swirl-type mixture of fuel and air prior to combustion of the mixture. It should be observed that blow-off can be minimized with a burner design of this type. The burner structure defined herein involves premixing of fuel and air by a swirl action and an increase in burning intensity by acceleration of the gases through a converging nozzle-type exit port or any orifice.

It is, accordingly, a general object of the present invention to provide an improved burner particularly suited for use with fuel having a low caloric value and capable of burning large quantities of this fuel in a combustion chamber with less volume than normally required.

Another object of the present invention resides in the provision of an improved burner for use with regenerative stoves.

A further object of the present invention resides in the provision of an improved burner wherein fuel and air are tangentially introduced into a mixing chamber to provide a swirl mixture of the fuel and air.

An additional object of the present invention resides in the provision of an improved high capacity burner wherein the swirl components of the fuel and air extend the operating limits of the burner.

A further object of the present invention is in the pro vision of an improved burner where the gases are mixed by a swirling action in the mixing chamber with a minimal pressure drop.

Another object of the present invention resides in the provision of an improved burner that is economical to construct; that takes advantage of improved operating techniques; that is easy to use and is reliable in use.

Additional objects of the present invention reside in the provision of an improved burner structure and operation with the burner being integrally formed in the combustion chamber and adapted for construction using ceramic materials; wherein the arrangement of inlet ports provides a counterflow with thorough fuelair mixture and where flow of the fuel-air mixture through an orifice increases the mixture velocity to provide rapid expansion, turbulence and reduce flashback and blowoff tendencies.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, together with further objects and advantages thereof will best be understood by reference to the following description taken in connection with the accompanying drawings, in which:

FIG. I is a schematic view of a regenerative stove system for use with a blast furnace and in which the improved burner of the present invention is employed;

FIG. 2 is an illustrative side elevation, in section, of a burner design utilizing the concepts set forth herein;

FIG. 3 is a fragmentary top view of the burner of FIG. 2 taken along line 3-3 of FIG. 2;

FIG. 4 is a side elevation of another form of burner of the present invention illustrating the convergent nozzle in the chamber and the ports through which fuel and air are introduced to the chamber;

FIG. 5 is a top view of the burner illustrated in FIG. 4; and

FIG. 6 is a schematic illustration of a form of the burner disclosed herein with introduction of fuel and air tangentially to the chamber in a manner which will establish a counterflow action thereof for proper mixing of fuel and air just prior to combustion but within the saftey of the chamber.

Combustion may be defined as rapid, high temperature oxidation where the oxidation reactions occur predominantly in a narrow region of high chemical reactivity in the gas phase. Generally, the essential elements of all common organic fuels are carbon and hydrogen. Accordingly, the process of combustion is highly dependent upon, for example, element concentration, initial gas temperatures and the manner of mixing the fuel and air.

The burner structure and mode of operation disclosed herein combine the desirable operating characteristics necessary to define and sustain combustion, especially with fuels having a low calorie value such as blast furnace gas.

The burner disclosed herein will specifically be described for use with blast furnace gas and in a regenerative stove associated with a blast furnace. It should be noted, however, that the concept of the burner and mode of operation has general applicability in similar circumstances for applications other than the one specifically described.

Referring more particularly to the drawings a blast furnace stove is illustrated in part, at 10 in FIG. I. The stove installation includes the shell 11, checker chamber 12, combustion chamber 13, gas burner 14, gas connection 15, combustion air connection 16, hot blast connection 17, cold blast connection 18, breeching 19 and stack 20. With a normal two-pass stove, during the gas cycle gas and combustion air are burned and the products of combustion pass upward through the combustion chamber 13, downward through the checker chamber 12 brickwork and out of the stove through the breeching 19 to a waste gas stack 20. In the blast cycle, cold blast from a blower is introduced to the bottom of the checker chamber 12 and as it passes upward through the chamber is heated by the hot brickwork. After being heated it passes downward through the combustion chamber 13, and out through the hot blast connection 17 to the blast furnace. Several valves, not pertinent to this disclosure, are used to control the flow of gas, combustion air, cold blast and hot blast.

One configuration of the burner 14 which may be employed in the stove I0 and which embodies the principles set forth herein is illustrated in FIGS. 2 and 3.

The outer shell 11 of the stove 10 is provided with openings to receive a continuation of the gas pipe 15 and air pipe 16 to introduce the combustion mixture to the mixing chamber 23 of the burner 14. As shown in FIGS. 2 and 3, the air (24) and gas (25) conduits extend tangentially into the mixing chamber 23 of the burner such that a counterflow develops within the chamber to define a condition for optimum mixture of the gas and air prior to combustion of the mixture. In the particular configuration of FIGS. 2 and 3 the gas is introduced at a lower portion of the chamber 23, be-

gins to swirl in the chamber (counterclockwise in FIG. 3) and moves toward the convergent throat 26 of the burner. It should be noted that the convergent throat or venturi 26 may be in the form of a simple orifice of a given size without departing from the spirit of the present invention. Air is introduced to the chamber 23 above the gas flow to the chamber and swirls in the chamber in a clockwise direction which, of course, is opposed to the direction of flow of the gas. The swirling counterflow of air and gas defines means for thorough combination of these materials within the chamber as the mixture moves toward the throat 26. Air and gas are continually introduced to the chamber 23 to force the previously introduced mixture to the throat 26 and through it. As the mixture moves through the throat it must speed up due to the restricted throat area. The mixture is ignited on the downstream side of the throat and combustion spontaneously continues at the flame front which is oriented in the burner in response to flow rates of the mixture. The convergent nozzle 26 at the burner exit serves to accelerate the gases to increase the burning intensity. The nozzle 26 also is important in development of stable combustion characteristics and avoidance of oscillatory combustion.

The effect of introducing the fuel and air into the chamber to define swirl mixing conditions in the chamber is to extend the operating limits of the burner with a minimal pressure drop in the burner compared to an open flow system. The flame holding capabilities of the burner improve with the swirl mixing action in the burner to minimize flashback and blowoff.

Mixing of the fuel and air in the burner itself defines conditions which yield a more stable combustion zone. It also should be noted that premixture of fuel and air (mixed before introduction to the burner) may give rise to a hazardous condition if proper flame holding devices are not utilized.

Another burner structure utilizing the swirl concept disclosed herein is illustrated in FIGS. 4 and S. The burner is illustrated generally at 74 and is defined by an outer wall 76 enclosing the mixing chamber 80. The chamber 80 is provided with a converging nozzle 82 at one end thereof to define means for speeding the exit flow of gases from chamber 80.

Gases for combustion are introduced to the chamber 80 in a manner which results in one or more of the introduced gases swirling within the chamber to facilitate mixing of the gases. In the specific burner configuration of F IGS. 4 and 5 fuel may be introduced to the chamber 80 in an axial flow pattern upstream of the air inlet. The primary fuel flow then extends from upstream of the air inlet toward the nozzle 82 in the general direction designated by arrow 84. An undisturbed conventional flow of this kind will not result in the desirable combustion characteristics of the burner disclosed herein.

Air for the combustion mixture is introduced through the port 86 to an open channel 88 in the burner wall. A series of angularly disposed ports 90 extend from the channel 88 to the chamber 80 at a position in the chamber along the axial flow path of the fuel and upstream of the nozzle 82. The burner structure of FIGS. 4 and 5 is schematically illustrated in FIG. 6 and the operation thereof may readily be understood by reference to this illustration.

The swirl or counterflow characteristic necessary to define the fuel air mixing conditions set forth herein is provided by the counterflow of air to the chamber 80. The gas enters chamber 80 upstream of the air openings 90 and flows toward the nozzle 82 in the general direction designated by arrow 84. The openings 90 along either side of the central axis A-A of port 86 are oriented to introduce the air in a swirl motion along opposed walls of the chamber. The air sweeps into the chamber in opposite directions to provide a counterflow and to provide for mixture of the fuel and air within the chamber 80 so that mixing occurs upstream of the nozzle 82.

With the burner concept set forth herein 1 have found that mixing of the fuel and air can be realized in the burner and can be improved by introduction of the swirl components in the chamber thereof by introducing either the fuel or air (or both) into the chamber at an angle to a given radial of the chamber. The swirl components of the gases in the chamber serve to augment rapid mixing of the fuel and air while minimizing any pressure drop which would affect combustion characteristics of the burner.

It will also be noted, as shown best in FIG. 2 and in the dotted lines in FIG. 3, which define the burner chamber, that the cross-section of the chamber is formed generally in the shape of a pair of adjacent, op-

posed circle segments; FIG. 3 indicates that said circle segments have a major axis and a minor axis.

One of the important aspects of the invention resides in the counterflow of the gases in the chamber whereby the gases swirling in the chamber will cause rapid diffusion. For example, the burner of FIGS. 4, S and 6 is of the type where only one of the gas streams is introduced into the chamber other than along the central axis of the chamber. In this burner the air is directed in opposed paths into the chamber to cause a controlled turbulence and to promote the rapid diffusion characteristic of the burner design with the air rapidly mixing into the main axial flow stream of the fuel.

The important aspects of the improved burner construction and operation of the present invention reside in a combination of features and the mode of operation not employed in the present burner structures for use with regenerative stoves. One of these features resides in the provision of the burner structure in combination with the combustion chamber of the stove. This feature is desirable since it will minimize the flashback or blowoff tendencies otherwise occasionally inherent in such burners. Moreover, if a flashback were to occur the danger would be minimized with the burner structure embodied wholly within the combustion chamber of the reheat stove. It can readily be seen that with a burner defined externally of the stove a flashback could result in a dangerous condition.

Another advantage of providing the burner within the combustion chamber resides in the fact that the burner may be made of ceramic material which is relatively low cost in comparison to the steel shell otherwise used in external burner structures.

The nozzle structure embodied within the burner provides for an increase in the gas velocity above the flame velocity to thereby minimize flashback tenden cies. Accordingly, a safer burner structure is provided with the configuration set forth herein. Also, the arrangement of ports associated with the burner structure provides an even distribution of gas and air within the burner to define a swirling counterflow of materials and provide a better mixture of combustion.

While I have shown and described a specific embodiment of the present invention it will, of course, be understood that other modifications and alternative constructions may be used without departing from the true spirit and scope of this invention. I therefore intend by the appended claims to cover all such modifications and alternative constructions as fall within their true spirit and scope.

What I claim and intend to secure by Letters Patent of the United States, is:

l. A regenerative stove burner assembly for low caloric fuel gas, said burner assembly including, in combination,

structure forming a burner chamber,

said burner chamber being elongated in an axial direction, and having an axial cross-section formed generally in the shape of a pair of adjacent, op posed circle segments,

a fuel gas inlet conduit,

a combustion air inlet conduit,

at least one of said inlet conduits opening into the burner chamber generally tangentially with respect to the circular arc of one of said circle segments, said fuel gas and combustion air inlet conduits being disposed in opposed relation to one another to thereby provide intimate intermixing of said fuel gas and combustion air, and

said burner chamber terminating in a venturi shaped burner nozzle constructed and arranged to support a flame a short distance downstream from the most constricted portion of the nozzle,

said burner assembly being composed of ceramic material, whereby it may be located within a regenerative stove.

2. The regenerative stove burner assembly of claim 1 further characterized in that the axial cross-section of said burner chamber is longer in one direction than in a direction at right angles thereto, whereby a major axis and a minor axis are defined.

3. The rejenerative stove burner assembly of claim 1 further characterized in that both said fuel gas inlet and said combustion air inlet open tangentially into the burner chamber in opposed relation to one another.

Claims (3)

1. A regenerative stove burner assembly for low caloric fuel gas, said burner assembly including, in combination, structure forming a burner chamber, said burner chamber being elongated in an axial direction, and having an axial cross-section formed generally in the shape of a pair of adjacent, opposed circle segments, a fuel gas inlet conduit, a combustion air inlet conduit, at least one of said inlet conduits opening into the burner chamber generally tangentially with respect to the circular arc of one of said circle segments, said fuel gas and combustion air inlet conduits being disposed in opposed relation to one another to thereby provide intimate intermixing of said fuel gas and combustion air, and said burner chamber terminating in a venturi shaped burner nozzle constructed and arranged to support a flame a short distance downstream from the most constricted portion of the nozzle, said burner assembly being composed of ceramic material, whereby it may be located within a regenerative stove.

1. A regenerative stove burner assembly for low caloric fuel gas, said burner assembly including, in combination, structure forming a burner chamber, said burner chamber being elongated in an axial direction, and having an axial cross-section formed generally in the shape of a pair of adjacent, opposed circle segments, a fuel gas inlet conduit, a combustion air inlet conduit, at least one of said inlet conduits opening into the burner chamber generally tangentially with respect to the circular arc of one of said circle segments, said fuel gas and combustion air inlet conduits being disposed in opposed relation to one another to thereby provide intimate intermixing of said fuel gas and combustion air, and said burner chamber terminating in a venturi shaped burner nozzle constructed and arranged to support a flame a short distance downstream from the most constricted portion of the nozzle, said burner assembly being composed of ceramic material, whereby it may be located within a regenerative stove.

2. The regenerative stove burner assembly of claim 1 further characterized in that the axial cross-section of said burner chamber is longer in one direction than in a direction at right angles thereto, whereby a major axis and a minor axis are defined.

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