US3437322A - Air-heating gas burner - Google Patents

Description

April 8, 1969 J. H. FLYNN AIR-HEATING GAS BURNER Filed June 21.- 1966 INVENTOR omfi'iym United States Patent US. Cl. 263-19 8 Claims ABSTRACT OF THE DISCLOSURE A burner installation located in an air stream to be heated has a burner casing with a flame surface to which lead main and pilot flame ports for flames directed downstream of the air stream. The installation further provides a chamber surrounding the burner casing and having an outlet in line with the flame surface and spaced therefrom downstream of the air stream, as well as an inlet which faces upstream of the air stream, with the cross-sectional area of the inlet being so much smaller than that of the chamber that the latter serves as an expansion chamber substantially without any vacuumatic effect of the air passing therethrough on the flames.

This invention relates to gas burners in general, and to air-heating gas burners in particular.

The type of gas burner with which the present invention is concerned is a gas-fed flame burner installed within a directed utility stream of air or the like for heating the same, with the burner flame being directed downstream of the passing air. Such burners are used as air heaters for all kinds of space heating especially, though not exclusively, in industrial establishments, and they are also used for other purposes such as heating large volumes of air or noncombustible gases in industrial processes, for example. It is among the more important requirements of these heaters that for a burner in any installation the heat of the burner flame must flash the temperature of the passing air or gas to a usually high peak at maximum operational stream velocity. This requires, in turn, that the burner flame must maintain in the air or gas stream a zone of very high heat intensity. Another important requirement of these heaters is flexibility in operation over a wide range, to the end of heating passing air or gas usually at full stream velocity to the same or different temperature peaks.

Among known flame burners that would best meet the aforementioned requirements of these heaters are those of high-capacity flame performance which are supplied with a quantitatively regulatable combustible mixture of prefably fixed air-gas ratio for sustaining the flames without any outside or secondary air and, hence, produce flames of high heat-output at widely regulatable flame velocity or drive independent of the velocity of the passing air or gas stream. However, in these high-capacity burners the main or operating flames are sustained by pilot flames without which the main flames would extinguish since the rate at which the combustible mixture is fed to the latter is usually greater than the rate of flame propagation, and it is for this reason that these burners are of no avail as air heaters since the air passing the burners at most operational stream velocities creates at the flame side of the burners a notable vacuum in which no pilot flames can persist. Recourse has, therefore, been had to burners of modified construction and operation in which at the more prevalent higher operational flame settings, the usual pilot flames are lacking, with the flame ports being then supplied with more or less pure gas and the combustion air therefor being largely secondary air diverted from the air stream to-be-heated into combusting admixture with the gas beyond the flame ports for maintenance of operating flames. However, while these modified burners are generally satisfactory, they are lacking in a few, but important, respects. Thus, the drive of the flames is dependent upon, and hence limited by, the velocity of the diverted combustion air from the passing stream, so that the flames lack any appreciable drive and are massed in rather close proximity to the burners which thereby are unduly subjected to heat. Also, correct regulation of the gas admitted to these burners for complete combustion on admixture with the diverted combustion air from the passing stream at varying operating velocity of the latter involves rather intricate gas flow control. Further, these burners do not lend themselves to many applications involving efficient heating of gas streams that lack air or oxygen and, hence, are incapable of furnishing the combustion air for the burners without which the latter cannot perform anywhere near their maximum capacity.

It is the primary aim and object of the present invention to provide an air or gas heating flame burner which in its performance is superior to, and has none of the shortcomings of, the aforementioned modified burners,

by converting a flame burner to one having the aforementioned high-capacity flame performance in an air or any other gaseous stream.

It is another object of the present invention to provide the aforementioned converted flame burner at even less cost than the aforementioned modified burners.

It is a further object of the present invention to make provision in the aforementioned converted flame burner for effectively shielding from the vacuum effects of the passing air or gas stream on the burner those critical flame areas of the burner adjacent the flame ports where such vacuum effects would otherwise extinguish the pilot flames, and even the main flames if the pilot flames were not extinguished, so that on any velocity of the passing stream the pilot flames will remain undisturbed and sustain the main flames at any heat-output and drive as fully as though the surrounding air or gas were not moving. In thus achieving high-capacity flame performance of a burner in an air or gas stream, the flame will, on regulation for maximum heat-output and drive, strike particularly deep into the passing stream beyond the burner and there maintain an extensive and highly heated zone which does not unduly heat the burner but in which the streaming air or gas will at even maximum velocity have some definite dwell and be in most intimate heat-exchange relation not only with the flame itself but also with its proclucts of combustion.

Another object of the present invention is to achieve in a flame burner the aforementioned shielding of the critical flame areas from the vacuum effects of the passing air or gas stream, by providing the burner at its flame side with a channel which is open downstream of the passing air or gas and of a depth to contain the pilot flames and the critical base area of the main flames, and continuously delivering to this channel secondary air or noncombustible gas at a volumetric flow rate at which it will prevent any flame-extinguishing vacuum formation at the critical flame areas by the passing air or gas stream to-be heated without, however, having any adverse effect on the stability of the flames at any setting of the latter.

A further object of the present invention is to provide a flame burner with the aforementioned channel in which the secondary air or gas is supplied by the passing stream to-be-heated by being simply diverted from the latter into the channel.

It is another object of the present invention to provide a flame burner in which the aforementioned channel is formed as part of a hood around and spaced from the burner to define an expansion chamber into which air or gas from the passing stream is admitted through restricted openings in the hood, and in which the pressure and velocity of the thus admitted air or gas is much reduced for its flow at proper volumetric rate to the channel part thereof. With this hood arrangement, burner conversion to high-capacity flame performance is of exceeding structural simplicity and entails the least cost, especially since the formation of the hood in identical complemental sheetmetal sections of simple shapes and for their ready clamp on to the burner is indicated. Also, by forming the hood in complemental sections, the same need not even be provided with air or gas admission openings and the latter may, instead, be provided by a gap between the mounted hood sections which advantageously faces upstream of the passing air or gas to-be-heated so that the admitted air or gas will have a maximum cooling effect on the burner. Further, the hood may advantageously be of general teardrop shape in cross-section with the narrow end forming the channel part, whereby the passing gaseous stream tobe-heated undergoes least turbulence and has reformed into a smooth-flowing stream when passing through the heat zone maintained by the burner flames. Moreover, by diverting the secondary air or gas from the stream to-be-heated into the exhaust chamber prior to its pass through the channel, the volumetric flow rate of secondary air or gas through the channel will prevent flameextinguishing vacuum formation at the critical flame areas without having any adverse effect on the stability of the flames at any setting of the latter.

It is a further object of the present invention to provide the converted burner with the aforementioned hood, of which the latter is for its general teardrop shape in section formed conveniently of a part-cylindrical wall part and therewith tangentially continuous, opposite planar wall parts which converge to the channel opening, and each planar wall part is provided with a simple inward baffle which diverts the passing secondary air or gas into more direct flow against the flame end of the burner for its sweep of the entire flame area within the channel 50 as to leave not the least space therein for any vacuum formation by the passing gaseous stream to be heated.

Further objects and advantages will appear to those skilled in the art from the following, considered in conjunction with the accompanying drawings.

In the accompanying drawings, in which certain modes of carrying out the present invention are shown for illustrative purposes:

FIG. 1 is a side view of a flame burner embodying the present invention;

FIG. 2 is a section through the burner as taken on the line 2-2 of FIG. 1; and

FIG. 3 is a cross-section through a burner embodying the invention in a modified manner.

Referring to the drawings, and more particularly to FIGS. 1 and 2 thereof, the reference numeral designates a flame burner for heating a stream of air or other non-combustible gaseous matter, hereinafter referred to as air for brevity of expression. The burner 10 is to this end suitably mounted, in this instance, within a duct 12 in which a stream of air flows in the direction of the arrows 14 past the burner in order to be heated by the burner flames F.

The burner 10 has a longitudinal burner casing 16 with an internal chamber 18 and main and pilot burner slots 20 and 22 which extend substantailly over the length of the casing 16. The burner slots 20 and 22, which are provided in a flame surface 24 of the casing 16, are in communication with the chamber 18, with spaced restricted ducts 26 in the casing providing in this instance for communication between the chamber 18 and the pilot burner slots 22 (FIG. 2). Arranged in the burner slots 20 and 22 are burner ribbon assemblies 28 and 30 which define main and pilot flame ports 32 and 34, respectively. The casing chamber 18 is through a conduit 36 supplied with a combustible air-gas mixture which on ignition at the flame ports 32 and 34 sustains main or operating flames F and pilot flames p, respectively. The chamber 18, which is part-cylindrical about the burner axis x, is in this instance formed by a through-passage in the casing 16 which is closed at both ends by covers 38 that are mounted at 40 on end flanges 42 of the casing. The burner casing 16 is in this instance symmetrical about a plane P in which the burner axis x lies and which intersects the flame surface 24 midway of its width (FIG. 2).

The burner described so far may be entirely conventional, and the same may be operated for high-capacity flame performance at which the air-gas mixture supplied to the chamber 18 will sustain the main and pilot flames F and p without any outside or secondary combustion air. Customarily, air and gas are premixed at a given ratio in a usual premixer (not shown) and the mixture conducted to the chamber 18 at widely variable volumetric flow rates for sustaining burner flames of correspondingly variable velocities or drive. The air-gas ratio of the mixture is usually chosen for optimum heat-intensity of the flames, and the main flames F are at their maximum setting of particular high velocity or drive and also forward projection, but they would extinguish without pilot flames 12 since the rate at which the combustible mixture is fed to the main flames is usually greater than the rate of flame propagation. However, if the burner described so far were subjected in the duct 12 to an air stream at even one of the lower operational velocities of the latter in most any space-heating or other installation, the vacuum created in the vicinity of the flame surface 24 of the burner by the passing air would extinguish the pilot flames p and, hence, also the main flames F, and if such vacuum would perchance not extinguish the pilot flames p it may well extinguish the main flames F by interrupting them at their base 1). Accordingly, the burner described so far is of no avail for high-capacity flame performance in an air stream of most any operational velocity.

In accordance with the invention, the present burner is by structurally simple and quite inexpensive conversion adapted for high-capacity flame performance in an air stream of most any, and even the highest, operational velocities. To this end, provision is made to shield the critical flame areas of the burner, i.e., the pilot flames p and base b of the main flames F, from the inevitable vacuum produced by the passing air stream. This is accomplished in a broader sense by providing the burner with a channel formation outwardly from the flame surface of the burner casing of which the sides of the channel flank the critical flame areas of the burner, and continuously delivering to this channel at the level of the flame surface secondary air or non-combustible gas at a volumetric flow rate at which it will prevent any flame-extinguishing vacuum formation at the critical flame areas by the passing air stream to-beheated without, however, having any adverse effect on the stability of the main and pilot flames at any setting thereof. More particularly, this channel formation is part of a secondary chamber 50 which is preferably defined by a separate hood 52 over the burner casing 16. The hood 52 has opposite end walls 54 and a peripheral wall 56, In the preferred form of the hood 52, its peripheral wall 56 has a part-cylindrical portion 58 and tangentially continuing planar portions 60, of which the part-cylindrical wall portion 58 rests against, and is at 62 secured to, the end flanges 42 of the burner casing 16, While the planar wall portions 60 converge toward, and define with the end walls 54, an opening 64 in the secondary chamber 50 which is in line with the flame ports 32, 34 and outwardly spaced from the flame surface 24 of the burner casing. The end walls 54 of the hood 52 partly close the secondary chamber 50 at its opposite ends between the end flanges 42 of the burner casing 16 and the opening 64, while the end flanges 42 themselves close the remainder of the secondary chamber 50 at its ends (FIG. 2). The end walls 54 of the hood 52 are in this instance parts of plates 66 which are separate from the peripheral hood wall 56 and conveniently clamped between the end flanges 42 of the burner casing and the covers 38 thereon, and the separate end walls 54 are in this instance further secured at 68 to outward flanges 70 at the opposite ends of the peripheral hood wall 56.

The part of the secondary chamber 50 between the flame surface 24 and opening 64 is in the form of a channel 72 which is open to the remaining part 74 of the chamber 50 at both sides 76 and 78 of the flame surface 24 (FIG. 2). The depth of this channel part 72 of the secondary chamber 50 is in any event adequate to shield the critical flame areas of the burner directl from the passing air stream to-be-heated, and this channel depth is preferably only several times the maximum height of the pilot flames p as roughly shown (FIG. 2), so that virtually the entire main flames beyond their base b project at most operational settings beyond the opening 64 of the secondary chamber 50 and directly into the passing air stream to-be-heated.

The secondary air or non-combustible gas, which is to flown through the channel part 72 of the secondary chamber 50 for preventing therein a flame-extinguishing vacuum formation by the passing air stream to-be-heated, is preferably and advantageously derived from the passing air stream itself. To this end, the hood 52 is provided, preferably at the burner side opposite the flame surface 24, with a restricted slot 80 which extends over the longitudinal extent of the secondary chamber 50 and through which air from the passing stream is admitted into the latter. The secondary chamber 50 serves as an expansion chamber in which the admitted air undergoes considerable reduction in pressure and velocity, and whatever turbulence the air may develop immediately on its admission into this expansion chamber will largely be quelled as it approaches the channel part 72 of this chamber, This makes for fairly smooth and moderate-velocity flow of the admitted air into and through the channel part 72 of this chamber and out through the opening 64 into the passing air stream, at which it will prevent at the critical flame areas of the burner any flame-extinguishing vacuum formation by the passing air stream to-be-heated without, however, adversely affecting the stability of the flames. In fact, in the preferred formation of the channel part 72 of this chamber by the converging planar wall portions 60 of the hood (FIG. 2), the flow of the admitted air through this channel part is so smooth that it has been found advantageous to pass this flowing air into even closer proximity to the pilot flames p and the base b of the main flames F. This is achieved in this instance by providing the converging wall portions 60 of the hood with baflles 82 which extend over the length of the channel part 72 and divert the passing secondary air generally over the flame surface 24. The secondary air is thus flown toward the critical flame areas of the burner, and this is preferred in this specific or any other formation of the channel part 72, since the pilot flames then operate with particular assurance in a virtual non-vacuum zone under all conditions and, hence, support and keep ignited the main flames from minimum to maximum heat output. The baffles 82 in this preferred channel construction are suitably secured by exemplary screws 84 to the converging hood walls 60. Also secured by some of the same screws 84 to the peripheral hood wall 56 are spacer brackets 86 of exemplary V- shape which rest against the burner casing 16 and afford the hood additional support on the latter. Admission of the secondary air into the secondary chamber 50 through the slot 80 also makes for maximum cooling of the burner casing 16 and exit end 64 of the chamber by this secondary air.

The hood 52, and in this instance its peripheral wall 56, is preferably and advantageously formed in two identical complemental sections 88 and 90 which are provided with longitudinal flanges 92 that are kept spaced to define the described slot 80 for admission of the secondary air, with these flanges 92 having to this end interposed spacers 94 that are held in place by bolts 96 which additionally lock the mounted sections 88 and to each other. Preferably, the peripheral hood wall 56 is with its converging planar wall parts 60 so disposed that the secondary chamber 50 is in cross-section also symmetrical about the plane of symmetry P of the burner casing 16 (FIG. 2), whereby the flow of secondary air to the channel part 72 is evenly divided on the opposite sides 76 and 78 of the flame surface 24. Further, the hood 52 is in cross-section of teardrop-like shape (FIG. 2) which offers comparatively little resistance to the passing air stream to-be-heated, with the passing air having at the hood opening 64 largely reformed into a smooth-flowing stream which does not adversely affect the stability of the main flames F at any, including their maximum, drive and, hence, projection from the hood opening 64, and is in intimate heat-exchange relation with the main flames as well as with their products of combustion over the high-intensity heat zone of formidable extent maintained by these flames.

Reference is now had to FIG. 3 which shows a modified air-heating flame burner 10a that differs from the described burner 10 of FIGS. 1 and 2 primarily by having a secondary chamber 50a which is of smaller size and volume and also surrounds only part of the burner casing 16a. In this modified burner, the hood 52a may in most respects be constructed like the described hood 52, except that the part-cylindrical portion 58a of the peripheral hood wall 56a extends between the end flanges 42a of the burner casing 16a and bears against the side of the casing opposite the flame surface 24a thereof to divide the part 74a of the secondary chamber 50a into non-communicating sections 100 and 102 which are, however, in communication with the channel part 72a of the secondary chamber at opposite sides of the flame surface 24a of the burner casing. The part-cylindrical portion 58a of the peripheral hood wall 56a has at its opposite ends leg formations 104 by which it is mounted on the end flanges 42a of the burner casing. Air from the passing stream to-be-heated is admitted into the chamber sections 100 and 102 through longitudinal openings 106 which are formed in the peripheral hood wall 56a preferably by striking therefrom baffles 108 which direct air from the passing stream into the openings 106 and, hence, into the secondary chamber 50a.

The invention may be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention, and the present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming wi'hin the meaning and equivalency range of the appended claims are intended to be embraced there- What is claimed is: 1. A burner adapted for installation in a conduit for a gaseous stream to-be-heated, comprising a longitudinal burner casing having a flame surface facing upstream of the stream and main and pilot flame ports leading to said flame surface; and a longitudinal chamber with opposite end walls and an inner peripheral surface surrounding said casing over its longitudinal extent and spaced therefrom over at least the greater part of the circumference of the casing including said flame surface, said chamber having a longitudinal outlet in line with said flame surface and spaced therefrom downstream of the stream, and longitudinal inlet means facing upstream of the stream and being in comparison to the space between said casing and peripheral wall surface of said chamber of such restricted cross-sectional area that said space acts as an expansion chamber in which admitted gas from the stream has substantially no vacuum effect and said inner peripheral surface of said chamber has on opposite sides of said flame surface baffle portions for directing passing gas toward said flame ports.

2. A burner adapted for installation in a conduit for a gaseous stream to-be-heated, comprising a longitudinal burner casing having a flame surface facing downstream of the stream, and an internal chamber and therewith communicating main and pilot flame ports of which said ports lead to said flame surface; and a hood surrounding said casing and having end walls and a peripheral wall defining another chamber with an opening in line with said ports and spaced from said flame surface downstream of the stream, of which the part of said other chamber between said flame surface and opening is in the form of a channel open to the remaining chamber part on both sides of said flame surface; and port means in said remaining chamber part facing upstream of the stream and being in comparison to the space between said casing and peripheral wall of said other chamber of such restricted cross-sectional area that said space acts as an expansion chamber in which admitted gas from the stream has substantially no vacuum effect, and said peripheral hood wall rests against said casing on the side thereof opposite said flame surface to divide said remaining chamber part into non-communicating chamber sections of which each is provided with said port means.

3. A burner as in claim 2, in which said port means are longitudinal slots in parts of said peripheral hood wall defining said non-communicating chamber sections, respectively.

4. A burner adapted for installation in a conduit for a gaseous stream to-be-heated, comprising a longitudinal burner casing having a flame surface facing downstream of the stream, and an internal chamber and therewith communicating main and pilot flame ports of which said ports lead to said flame surface; and a hood surrounding said casing and having end walls and a peripheral wall defining another chamber with an opening in line with said ports and spaced from said flame surface downstream of the stream, of which the part of said other chamber between said flame surface and opening is in the form of a channel open to the remaining chamber part on both sides of said flame surface, and said peripheral hood wall has a part-cylindrical section and tangentially continuing plane sections to and converging on said opening, so that said hood is a teardrop-like shape in cross-section; and port means in said remaining chamber part facing upstream of the stream and being in comparison to the space between said casing and peripheral wall of said other chamber of such restricted cr0ss-sectional area that said space acts as an expansion chamber in which admitted gas from the stream has substantially no vacuum effect.

5. A burner as in claim 4, in which said casing has annular end flanges forming parts of said end hood walls, and said part-cylindrical section of said peripheral hood wall rests on and is secured to said end flanges.

6. A burner as in claim 4, in which said plane wall sections are provided within said channel part with longitudinal baflies for diverting a gaseous medium flowing from said remaining chamber part into said channel part toward said flame surface.

7. A burner as in claim 4, in which said hood is formed in two complemental parts symmetrical about a plane in which the axis of said part-cylindrical wall section lies and which extends midway of said opening.

8. A burner as in claim 7, in which said chamber in said casing is part-cylindrical about said axis, and said casing is also symmetrical about said plane which intersects said flame surface midway of its width.

References Cited UNITED STATES PATENTS 3,055,145 9/1962 Lindsay. 1,729,149 9/ 1929 Brown et a1. 2,196,829 4/ 1940 Hess.

CHARLES J. MYI-IRE, Primary Examiner.

EDWARD G. FAVORS, Assistant Examiner.

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