US3391981A - Forced air draft burner construction for combustible gases - Google Patents

Description

July 9, 1968 T. s. VOORHEIS ETAL 3,391,931

FORCED AIR DRAFT BURNER CONSTRUCTION FOR COMBUSTIBLE GASES Filed June 13, 1966 3 Sheets-Sheet 1 V 8 I a g 0E m .|\N 4|Y 0 8 mw my 4 W 4 Ow n val LH MT i A k R fi i l 1H,. l li m NE MN I vm m E .m \w wm 11/ I mm mm mm mv 6 mm B ,7?

y 1968 T. s. VOORHEIS ETAL 3,

FORCED AIR DRAFT BURNER CONSTRUCTION FOR COMBUSTIBLE GASES 3 Sheets-Sheet 2 Filed June 13, 1966 INVENTORS TEMPLE S. VOORHE/S BY RALPH R. VOSPER c! N! aumswcl ATTORNEYS y 1968 T. s. VOORHEIS ETAL 3,

FORCED AIR DRAFT BURNER CONSTRUCTION FOR COMBUSTIBLE GASES Filed June 15, 1966 3 Sheets-Sheet 5 7 FIGS I40 INVENTORS TEMPLE S. VOORHEIS BY RALPH R. VOSPER WWW ATTORNEYS Uflited States Patent FORCED AIR DRAFT BURNER CONSTRUCTION FOR COMBUSTIBLE GASES Temple S. Voorheis, Atherton, and Ralph R. Vosper, Santa Clara, Calif., assignor to Coen Company, Burlingame, Calif., a corporation of California Filed June 13, 1966, Ser. No. 557,198 9 Claims. (Cl. 431-185) ABSTRACT OF THE DISCLOSURE A burner adapted to form to concentric annular air delivery paths between which paths is provided an annular opening for introducing fuel. Means for spinning air traveling in two paths in opposite directions is included. The annular fuel opening is defined by structure that converges toward such opening from a region of larger cross-sectional area so that fuel material is accelerated as it approaches the annular opening. Because of such acceleration, fuel particles such as contained in sander dust and blast furnace gas can be efficiently airborne.

This invention relates to a forced air draft burner construction and more particularly to a burner for the combustion of gases containing solid or liquid particulate matter, or fluidized combustible material such as sander dust or other dry organic material capable of being airborne.

Utilization as fuel of certain industrial waste products such as coke oven gas, blast furnace gas, fluidized materials, or the like, herein sometimes referred to simply as combustible gases, has long been sought. Numerous problems accompany the use of such combustible gases; for example, it is relatively difiicult to obtain good mixing of the gaseous fuels with combustion air to achieve relatively complete combustion; and, even if such mixing were achieved, the various solid and/or liquid particles found in coke oven and blast furnace gases tend to clog the gas jets of conventional burners. This is also true of sander dust and other forms of fluidized organic combustible material. Moreover, such industrial waste products are normally available at relatively low pressures, and prior art burners with which I am familiar generally exhibit some difliculty in sustaining fire at such low pressures. Even if means could be provided to increase these pressures, fluctuations in the flow of such industrial waste materials would require innovations to :prevent explosive buildup of material within the furnace immediately after a period of decreased flow which is insufficient to support combustion at the burner throat. Moreover, even with normal flow rates, such combustible gases, particularly the fluidized organic materials, tend to be entrained unevenly through the fluid carrier which causes unevenness in fuel quality and may lead to undesirable particulate accumulations in the fuel system.

Thus it is an object of this invention to provide a forced draft burner having a novel fuel chamber for receiving various combustible gases of the type described above from sources including those having a relatively low pressure. The chamber is designed to mix thoroughly the fuel components and accelerate the mixture into a gas passage for ejection through an annular opening at one of the chambers into the throat of the burner between layers or zones of turbulent and relatively rapidlymoving combustion-supporting gas, such as air. The outer layer of air is provided from an annulus air zone and the inner layer from a core air zone to achieve maximum mixing of the combustible gases with the air. The combustible airgas mixture may then be ignited and thereafter continuously burned with the flame front originating near the throat of the burner and extending outwardly into a furnace chamber or the like.

More specifically, it is an object of this invention to provide a forced draft burner having a throat structure which may be mounted in an opening extending through a furnace wall. A fuel-conveying chamber is provided in axial alignment with the opening of the throat structure and includes an inner cylindrical shell surrounded by a housing spaced radially outward from the shell to form a gas passage between the shell and housing. The end of the housing and the end of the inner cylindrical shell nearest to the throat opening are arranged in near alignment with each other and form an annular opening which is adjacent to the throat of the burner. Toward the other end of the fuel chamber, a scroll-shaped gas inlet chamber is provided to accelerate and direct a flow of combustible gas into and through the gas passage of the fuel chamber for discharge through the annular opening toward the burner throat. Means are also provided to direct an annular stream or air outwardly and axially from around the housing or annulus air zone into the burner throat, and a cylindrical tsream of air outwardly and axially from within the cylindrical shell or core air zone into the throat, thereby producing a highly combustible mixture of combustible gas and air in the region bounded by the throat of the burner.

A feature and advantage of this invention is that the scrollshaped inlet chamber provides cyclone acceleration of the incoming combustible gases. Such acceleration forces the relatively low pressure incoming gases through the gas passageway for ejection through the annular opening into the throat of the burner, and increases turbulence to cause a more uniform mixture of combustible particles within the gas and the gas stream itself.

Another feature and an advantage of this invention is the relatively large annular cross section of the gas passage and annular opening of the fuel-conveying chamber. Such relatively large cross section permits the flow of combustible gases through the gas passage and annular opening of the chamber without undue clogging by the various particles entrained in such fuels.

Another object of this invention is to provide an annulus air zone register and a core air zone register each comprising a plurality of air stream deflector blades having means to vary the position of the blades in respect to the direction of the air streams from the zones.

A feature and an advantage of the above object is that the air streams from the annulus and core air zones may be set into counter-rotating swirls which further enhance the mixing of the com-bustible gas and air.

It is another object of this invention to provide a burner for ordinary gas or oil to maintain a level of sustaining fire at the burner throat. Such sustaining fire assures combustion even when the supply of gaseous fuel ejected from the fuel chamber drops below the minimum level for maintaining firing.

A feature and an advantage of the last stated object is that explosive accumulations of gaseous fuel are generally prevented from forming within the chamber being fired by my novel burner.

Another object of this invention is to provide a forced draft burner having a fuel chamber comprising an inner shell and an outer shell forming a fuel-conveying chamber therebetween at one end thereof and a fuel inlet chamber or passageway at the other end. The inner shell is shaped to have a conical portion and a cylindrical sec tion formed continuous with the large diameter end of the conical portion. The outer shell or housing surrounding the inner shell is located with one end spaced radially outwardly from the smaller end of the conical portion of the inner shell to form an annular opening facing the throat of the burner. A duct is provided to introduce combustible gas into the inlet chamber formed between the housing and the cylindrical portion of the inner shell, the stream of gas being introduced in a path generally tangent to the outside of the cylindrical shell and normal to the longitudinal axis thereof. The inlet chamber is further shaped to direct the gas stream in a generally helical path and with increasing velocity into the fuel-conveying annulus of the fuel chamber for ejection through the annular opening. The helical course of decreasing cross-sectional area (in the direction of movement of the gas stream), and the convergent conically shaped annular passageway of the fuel-conveying section, tend to accelerate the gaseous combustible fuel and maintain suspension therein of relatively heavy particulate matter, such as sawdust or the like. Means are also provided to direct first and second air streams axially outwardly from the outer surface of the housing and from the inside of the shell toward the region bounded by the throat of the burner to cause mixing with the gaseous combustible fuel ejected through the annular opening.

Numerous other objects, features and advantages will become apparent to one skilled in the art upon a reading of the following specification and by referring to the accompanying drawing.

Turning now to the drawing, FIG. 1 is a sectional side elevation of my novel burner construction in which certain details of conventional fabrication techniques are shown in simplified form and deflectors are omitted from the annular opening at section 33;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1;

FIG. 2A is a sectional view taken along line 2A2A of FIG. 1;

FIG. 3 is a fragmentary isometric view taken along line 33 in FIG. 1 and showing deflectors of one type added; 4

FIG. 4 is a partial view taken along line 3-3 of FIG. 1 and showing deflectors of another type; and

FIG. 5 is a simplified sectional elevation showing an alternate embodiment of portions of the structure shown in FIG. 1 embodying my invention.

Referring to FIG. 1, my novel burner is indicated gen erally at A and is shown mounted for operation in a furnace whose refractory brick wall 12 is formed with opening 13 shaped to fit around refractory throat ring 14 of the burner. Combustible gas from an external source of relatively low pressure is conveyed in the direction of arrow 16 (FIG. 2) through duct 17 into cyclone portion 31 of the fuel chamber indicated generally at B. The

combustible gas conveyed within portion 31 is directed into a generally helical swirling motion accompanied by a relatively high degree of local turbulence which thoroughly mixes the components of the fuel. At the same time, the fuel travels axially through gas passage 46 as indicated by flow lines 18. The swirling combustible gas is then expelled in the direction of arrows 20 through annulus 19 into the region bounded by the burner throat assembly generally indicated at C. The annulus opening is radially large enough so combustible gases containing solid and liquid particles pass freely through the opening. As the gaseous fuel approaches the burner throat, it is combined with air from the annulus air zone at E, and the core air zone at F, and ignited by means of a conventional gas burner ring as indicated at 27 or the oil burner indicated at 28.

The windbox indicated generally at D is secured to my novel burner structure to provide a source of pressurized air which is forced through the annulus air zone register at G and the core air zone register indicated at H. Air passing through the annulus air zone register is directed in a generally swirling path indicated by arrows 21 into the zone bounded by the burner throat assembly between throat profile member 22 and the outer peripheral surface of housing 23. Air passing through the core air zone register at H is also directed in a generally swirling path as indicated by arrows 24 in a direction of swirl opposite to that of the swirl of the air from the annulus air zone. The core air is also conveyed axially through inner cylindrical shell 26 and discharged from the end of the cylinder at F into the region bounded by the burner throat assembly at C.

The air discharged through the annulus air zone register, and through the core air zone register, are in a highly turbulent, generally counter-rotating state which causes intimate and relatively complete mixing with the combustible gas discharged from annulus 19. Such combustble mixture is initially ignited by a flame produced through conventional gas ring 27, or, alternatively from the oil burner at 29. Thereafter combustion is maintained by the source of combustible gas as it continues to supply a sulficient discharge through annulus 19. If the source supply of gaseous fuel should fluctuate to decrease the discharge through annulus 1? below the level of maintaining burner firing, the combustion of conventional fuel at the firin ring indicated at 27, or the oil burner at 28, is maintained at a suitable level to insure continuing combustion of whatever gaseous fuel passes through the burner throat. This sustains at least a minimal firing level and prevents accumulation of unburned gaseous fuel within the furnace which could cause an undesirable explosion. Conventional apparatus (not shown) is provided to increase the gas ring or oil burner fuel flow to maintain proper furnace temperatures, if necessary. Standard safety devices may also be employed to limit furnace temperatures in the event of excessive gaseous fuel flow.

The fuel chamber indicated at B comprises inner cylindrical shell 26 and the outer housing indicated at 29 which in turn consists of two portions, the cyclone or scroll portion indicated at 31 and the circular cross section portion indicated at 32. The outer housing is shown in the drawing generally concentric and coaxial with inner shell 26, but exact relative locations may be varied provided the housing and shell are located to form annular opening 19 having a relatively wide radial interval between peripheral edge 33 of shell 26 and peripheral edge 34 of outer housing portion 23. The outer portion of the cyclone section at 31 is formed by scroll wall 36 whose cross-sectional profile, best seen in FIG. 2, describes about one complete turn of a spiral having maximum radius 37 and minimum radius 38, which normally is at least as great as the housing outside radius 39. Flange walls 42 and 43 extend radially inwardly from each edge of scroll sheet 36, wall 42 being secured to circular section 23 and wall 43 extending from the rearward portion of cyclone 31 to inner shell 26.

Duct 17 is formed to a depth dimension 41 substantially equal to the difference in radii 37 and 38 of the cyclone portion and to a width dimension (not shown) equal to width 40 of scroll wall 36. During operation of the burner, relatively low pressure combustible gas is conveyed in the direction of arrow 16 through duct 17 passing through tangent zone 44 into the cyclone or scroll portion 31. After passing zone 44, the gaseous fuel is immediately deflected by outer scroll sheet 36 in a spiral path defined generally by the spiral profile of the cyclone section. The decreasing inside radial boundary of the cyclone portion formed by sheet 36 causes turbulent mixing and accelerates the gaseous fuel conveyed therethrough until it reaches the region therein of minimum radius 38 in the immediate vicinity of gas passage 46. The relatively higher pressure of the slower moving gas entering at tangent zone 44 forces the accelerated gas through gas passage 46 for ejection through annular opening 15!, and annular opening 19 is formed radially wide enough so gaseous fuels containing solid and liquid particulate matter passes therethrough freely without clogging or sticking to the opening. The combustible gas travels through gas passage 46 with both an axial component of movement toward the annular opening and a circumferential component of movement around cylindrical shell 26 imposed by the initial cyclone portion. This results in a combustible gas path describing a generally helical or swirling movement accompanied by local turbulence as indicated by path arrows 18. (Although path arrows 18 are shown on the drawing in limited number, these are understood to represent a total mass of combustible gas moving throughout the gas passage.) As the combustible gas flows out through annular opening 19 into the zone bounded by the burner throat assembly at C, it is intimately mixed with the turbulent and swirling air streams emanating from the annulus air zone and core air zone as described above. Such mixing produces the combustible air-gas fuel mixture which is ignited in the throat of the burner ring.

The annulus air zone register indicated generally at G in FIG. 1 comprises a plurality of register blades 47 arranged circumferentially around housing wall 23. The blades are pivotally supported by rods 48 including one rod having an extension bar 49 which extends outwardly through openings in supporting plate members 51, 52, 53 and 57. Register blade drive 54 supported on plate 56 is suitably connected to bar 49. Each of rods 43 is suitably pivotally supported between plates 57 and 58, and the rods are provided with gear sector 59 secured thereto adjacent to plate 57. Each of the gear sectors is operably engaged to ring gear 61 mounted in a conventional manner (not shown nor described herein). Thus, as register blade drive 54 is rotated, the gear sector 59 secured at one end of bar 49 is rotated which in turn shifts all of the other gear sectors 59 secured to rods 48 and blades 47. Shifting the position of register blades 48 varies the direction of air that flows from the windbox indicated at D through the annulus air zone indicated at E. The action of the register blades also causes the air to swirl and flow in the direction of arrows 21 into the zone bounded by the burner throat assembly. A more detailed description of an annulus air zone register similar to that described here is set forth in my US. Patent No. 2,838,103 entitled Forced Air Draft Burner Construction, granted June 10, 1958.

The core air zone register indicated at H in FIGS. 1 and 2A comprises blades 63 mounted on rods 64 to which are secured gear sectors 66 operably engaged with ring gear 67 mounted in a conventional manner adjacent to wall 53. The mechanical arrangement of the core air zone register is similar in all respects to that of the annulus air zone register indicated at G, except that the blades may be shaped to a somewhat different profile; and certain minor modifications may be preferred in respect to gearing details depending upon the particular operating characteristics desired.

It is sometimes preferable to link together the drives of the annulus air zone register and the core air zone register to provide air streams having -ii'ferent swirl and flow characteristics from the annulus and core air zones. Such linkage arrangement generally depends upon the type of fuel being used to ignite and sustain firing of the combustible gas being utilized by my novel burner,

Depending upon the type of combustible gas used, I have found it desirable to provide annular opening 19 of the fuel chamber with one of at least two types of deflector assemblies such as those shown in FIGS. 3 and 4. In FIG. 3 I show one type including outer deflector blocks 71 suitably secured to outer housing wall 23 and inner deflector blocks 72 secured to inner cylindrical shell wall 26, immediately outwardly of annular opening 1%. Outer deflectors 71 are positioned alternately with inner deflectors 72 therebetween. Deflector blocks '71 are boited or otherwise suitably secured to outer ring 73 which in turn is attached by conventional means to lip angle 74, and angle 74 is circumferentially secured to outer edge surface 23a about the entire circumference of housing surface 23. Inner blocks 72 are suitably secured to inner ring 76 which in turn is attached to angle 77, and angle 77 is suitably secured about the inner edge surface 26a. In

addition, inner ring 76 has secured thereto at generally equally spaced intervals radial-straightening vanes 78.

Blocks 71 and 72 are shaped to form sloping faces 79. As combustible gas is ejected through annular opening 19, the sloping faces deflect such fuel in the direction and in the paths indicated by arrows 82 and 83. Straightening vanes 78 also tend to reduce the swirl of the ejected combustible gas, and this tends to direct the fuel more effectively into the turbulent annulus and core air streams. I have found this type of deflector arrangement particularly effective in achieving good mixing of gaseous fuel and air when my novel burner is used to burn fuels containing dispersed liquid and/or solid materials, i.e. such as coke oven or furnace gases.

In FIG. 4 I show still another type of deflector arrangement which has been found particularly effective in my novel burner when burning fluidized particulate matter such as sander dust or the like. In this type of deflector arrangement small cylindrical cell elements 84 are arranged and suitably secured at generally equal circumferential intervals 36 between housing wall 23 and inner cylindrical shell wall 25. As fluidized particulate organic combustible material is expelled through annular opening 19, cylindrical elements 84 tend to disperse the gaseous fuel flow into zones of movement having increased turbulence. This improves the degree of mixing with the air in the throat of the burner from the annulus and core air zones and hence increases efliciency of operation.

Another embodiment of a portion of my invention is shown in PEG. 5. The numerals therein correspond to those seen in FIGS. 1, 2, and 2a, except that the hundreds series digits are used to distinguish the alternate components which correspond to those shown in the aforementioned figures. The alternate portion shown in FIG. 5 corresponds generally to the fuel chamber indicated at B in FIG. 1 and is intended as a replacement thereof when certain types of combustible gaseous fuels are utilized in my invention. The remainder of the structure of my invention shown in FIGS. 1, 2, and 2a may be provided substantially as shown with the aforementioned alternate fuel chamber making only minor mechanical modifications thereto.

In the alternate embodiment of the fuel chamber shown in FIG. 3 combustible gases are conveyed through relatively wide portion 1310 of the fuel inlet chamber or pa age which corresponds to zone 44 shown in FIG. 2

ained hereinabove. In the alternate embodiment, hower, outer wall 13-6 of the fuel inlet passage does not scroll-like profile as does its counterpart 36 shown 1 and 2; instead, curved wall 136 is of constant diameter curvature. However, rearward flange wall 143 is s aped in a generally helical configuraion advancing toward and eventually joining inner flange wall 142 (the joinder of wall 143 to wall M2 is not shown in the sectional view of FIG. 5). Inner cylindrical wall 126a, seen the region between walls 142 and 143, is of a constant diameter curvature; and, in combination with flange walls 1422, 1'43 and outer cylindrical portion 136, forms fuel inlet chamber or passage 131 having a varying cross section w ich decreases from the initial inlet portion 1310 to its terminus at the point of contact of wall 1 1 3 with wall 142.

The cross-sectional area of inlet passage 131 may be seen to be the product of interval dimension 14%, which remains constant, and depth dimension 145 which varies from a maximum, indicated by dimension 145a to zero. The decrease in depth dimension 145 provides a convergent annular inlet fuel passageway which causes acceleration of gaseous fuel introduced and conveyed therethrougb. Such acceleration tends to lessen the likelihood that particulate material in the gaseous fuel, such as sawdust for example, will drop out of circulation from its gaseous carrier and hence cease being airborne. Moreover, it will be noted that the cyclone acti n on the cornbustible fuel effectuated by convergent inlet passage 131 tends to force the heavier airborne particles radially outwardly toward outer wall 136 of the fuel inlet passage. The outer portion of fuel passage 131 bounded by wall 136 in turn is in fluid communication with fuel-conveying portion 132; and hence heavier airborne particles are caused to be conveyed into the fuel-conveying section. Thus, the alternate embodiment shown in FIG. may be preferred when my novel device is applied to combustible gases containing relatively large and heavy particulate matter, such as sawdust and the like.

It will also be noted from FIG. 5 that the alternate embodiment of the overall fuel chamber differs from that explained earlier in respect to FIGS. 1, 2, and 2a in that outer wall 123 of the fuel conveying portion defines a conical rather than a cylindrical envelope compared to shell 23 shown in FIG.1; and outer wall 123 is formed in alignment with outer wall 136 of the fuel inlet passage.

- Similarly, inner shell wall 126 may also be of a conical shape although of generally smaller diameter than shell 123; and conical shell 126, at its point of maximum diameter, is suitably joined to the outer edge of inner flange plate 142.

The effect of the conically convergent fuel-conveying passage 132 formed by walls 123 and 126 described above is to cause continued acceleration of the gaseous fuel introduced and conveyed therethrough, it being apparent that the convergence and descrease of cross-sectional area of the fuel-conveying passage occurs in the direction of flow of the gaseous fuel. By causing the same quantity of gaseous fuel to be conveyed through a passage of constantly decreasing cross section, the fuel velocity therethrough is caused to be accelerated. Such acceleration further enhances maintaining relatively heavy particles in suspension in the gaseous fuel being conveyed therethrough, thereby increasing the overall efliciency of the system and preventing clogging of the fuel carrying elements by inhibiting the dropping out of airborne particles.

Although I have described my invention in the foregoing specification in some detail, this has been done for the purpose of clarity of understanding in the illustration of one embodiment of my invention. It is understood that upon a reading of this specification, and by referring to the accompanying drawing, numerous variations within the spirit of the invention and scope of the appended claims may occur to one of ordinary mechanical skill in the art.

What is claimed is:

1. A forced draft burner for the combustion of combustible gas comprising: a cylindrical shell; a housing surrounding at least a portion of the length of said shell and spaced radially outwardly therefrom to form a gas passageway therebetween, said housing having one end positioned near one end of said cylindrical shell to form an annular opening therebetween; means to direct a first air stream in a first generally helical path through the region radially inward 'and axially outward from said one end of said housing; means to direct a second air stream in a second generally helical path through the region radially and axially outward from said one end of said shell, said second air stream helical path being of an opposite hand in respect to said first air stream helical path; deflector means secured to said one end of the shell and housing to deflect a stream of combustible gas being ejected through said annular opening, whereby such combustible gas is caused to have increased turbulence and is directed toward predetermined zones of mixing with said first and second air streams; and means in fluid communication with said gas passage between said shell and housing to direct a flow of combustible gas therethrough and eject the fuel outwardly through said annular opening, said deflector means comprising a plurality of outer deflector blocks; means securing said outer blocks in a spaced circular array axially outwardly from said one end of the housing with one side of each of said outer blocks extending radially inwardly of said housing and facing said annular opening, said one side of each of said outer blocks shaped to deflect a stream of gas ejected through said annular opening in a direction radially inward of said housing; a plurality of inner deflector blocks; means securing said inner blocks in a spaced circular array axially outwardly from said one end of the shell with each inner block positioned between a pair of said outer blocks, and last said means positioning each of said inner blocks with one side extending radially outwardly of said shell and facing said annular opening, said one side of each of said inner blocks shaped to deflect a stream of gas ejected through said annular opening in a direction radially outward of said shell.

2. The forced draft burner as dened in claim 1 and wherein said deflector means comprises: a plurality of rod-shaped members each having a first end secured to the inside surface of the housing near said one end and a second end secured to the outside surface of the shell near the one end.

3. The forced draft burner in claim 1 and a plurality of plates; means mounting said plates upstream of said deflector means with at least a portion of one edge of each plate facing said gas passageway and the faces of each plate being at least partially in axial alignment with said shell, whereby said plates act as vanes to influence the flow pattern of a stream of combustible gas being ejected through said annular opening.

4. A forced draft burner for the combustion of combustible gases of the type having a throat for placement within an opening through a furnace wall, and means located near said throat to ignite a mixture of combustible gas and air, comprising: a cylindrical shell; means mounting said cylindrical shell in axial alignment with said throat and with one end of the shell near the throat; a housing surrounding said cylindrical shell and forming therebetween an inlet chamber around one portion of the shell and a gas passageway around the other portion of the shell, the end of said housing forming said gas passageway being spaced radially outwardly from said one end of the shell and located adjacent thereto to form an annular opening facing said throat of the burner; duct means to introduce a stream of combustible gas into said inlet chamber in a path generally tangential to the outside of said cylindrical shell and normal to the longitudinal axis thereof, said inlet chamber being shaped to direct such a stream of gas in a generally helical path around said cylindrical shell with a decreasing outer radius of travel and an axial component of movement toward and into said gas passageway for ejection through said annular opening; means to direct a first stream of air axially outwardly from the outer surface of the housing at said one end and into the region bounded by the throat of said burner; and means to direct a second stream of air through said shell and axiallyoutwardly from said one end of the shell into the region bounded by the throat of said burner, whereby a stream of combustible gas ejected from the annular opening of said housing is mixed with said first and second streams of air to form a combustible mixture of gaseous fuel and air in the region bounded by the throat ring of said burner.

5. The forced draft burner defined in claim 4 and wherein the cross section of said housing forming the outside surface of said inlet chamber defines a spiral with a minimum radius equal to at least half the cross-sectional dimension of said housing forming the outside surface of said gas passageway; and said duct means is located to introduce said stream of combustible gas into said inlet chamber immediately adjacent to the portion of said housing having the maximum radius described by said spiral.

6. The method of preparing for igniting and continuously burning a stream of low pressure gas containing combustible particulate matter comprising the steps of: accelerating said stream of low pressure gas in a generally helical path and decreasing the radius of curvature of said helical path in the direction of forward motion of said gas and particulate matter, whereby the turbulence of said gas stream is increased and said particulate matter is disbursed through the gas stream; forcing said gas stream and particulate matter into an annular zone; forcing a first stream of air into said annular zone and circulating said air in a generally circular path having a first direction of motion through the annular zone; forcing a second stream of air into said annular zone and circulating said air in a generally circular path having a second direction of motion through the annular zone; and mixing by said steps of forcing said gas stream and particulate matter with said streams of air and forming a combustible mixture of gas, air and particulate matter.

7. A forced draft burner for the combustion of combustible gases of the type having a throat for placement within an opening through a furnace wall, and means located near said throat to ignite a mixture of combustible gas and air, comprsing: an inner shell having a conical portion and a cylindrical portion, said cylindrical portion being formed continuous to the large diameter end of said conical portion; means mounting said shell in axial alignment with said throat with the smaller end of said conical portion near the throat; a housing surrounding said inner shell and forming therebctween an inlet chamber around said cylindrical portion of the shell and a gas passageway around the conical portion of the shell, one end of said housing being spaced radially outwardly from the smaller end of said conical portion and located adjacent thereto to form an annular opening facing said throat of the burner; duct means to intorduce a stream of combustible gas into said inlet chamber in a path generally tangential to the outside of said cylindrical shell and normal to the longitudinal axis thereof, said inlet chamber being shaped to direct such a stream of gas in a generally helical path around said cylindrical portion of said inner shell with a decreasing longitudinal dimension in the direction of movement of the combustible gases into and through said gas passageway for ejection through said annular opening; means to direct a first stream of air axially outwardly from the outer surface of said housing at said one end and into the region bounded by the throat of said burner; and means to direct a second stream of air through said inner shell and axially outwardly from said one end of the shell into the region bounded by the throat of said burner, whereby a stream of combustible gas ejected from the annular opening of said housing is mixed with said first and second streams of air to form a combustible mixture of gaseous fuel and air in the region bounded by the throat ring of said burner.

8. The forced draft burner according to claim 7 and wherein the axial cross section of said inlet chamber decreases in the direction of travel of the combustible gases introduced therethrough; and said duct means is located to introduce said stream of combustible gas into said inlet chamber in the portion of the chamber having the maximum axial cross-section area.

9. The method of preparing for igniting and continuously burning a stream of low pressure gas containing combustible particulate matter comprising the steps of: accelerating said stream of low pressure gas in a generally helical path and decreasing the cross-sectional area of the zone of gas passage in the direction of forward motion of said gas and particulate matter, whereby the turbulence and velocity of said gas stream is increased and said particulate matter is disbursed and the tendency to remain suspended in the gas stream is increased; forcing said gas stream and particulate matter into an annular zone; forcing a first stream of air into said annular zone and circulating said air in a generally circular path having a first direction of motion through the annular zone; forcing a second stream of air into said annular zone and circulating said air in a generally circular path having a second direction of motion through the annular zone; and mixing by said steps of forcing said gas stream and particulate matter with said streams of air and forming a combustible mixture of gas, air and particulate matter.

References Cited UNITED STATES PATENTS 2,838,103 6/1958 Voorheis 15811 3,049,173 8/1962 Costello et al. 158-11 X 3,275,057 9/1966 Ward 15811 FOREIGN PATENTS 1,378,995 10/ 1964 France.

FREDERICK L. MATTESON, JR., Primary Examiner.

E. G. FAVORS, Assistant Examiner.

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