Forced air draft burner construction for combustible gases

July 9, 1968

T. S. VOORHEIS ETAL

3,391,981

FORCED AIR DRAFT BURNER CONSTRUCTION FOR COMBUSTIBLE GASES

Filed June 13, 1966

Sheets-Sheet 1

<img file="US3391981A_D0001.tif" />

FIG. I

ATTORNEYS

July 9, 1968

T. S. VOORHEIS ETAL

3,391,981

FORCED AIR DRAFT BURNER CONSTRUCTION FOR COMBUSTIBLE GASES

Filed June 13, 1966

Sheets-Sheet ?.

<img file="US3391981A_D0002.tif" />

<img file="US3391981A_D0003.tif" />

ATTORNEYS

July 9, 1968

T. S. VOORHEIS ETAL

3,391,981

FORCED AIR DRAFT BURNER CONSTRUCTION FOR COMBUSTIBLE GASES riled June 13, 1966

Sheets-Sheet 3

<img file="US3391981A_D0004.tif" />

INVENTORS

TEMPLE S. VOORHEIS

BY RALPH R. VOSPER

ATTORNEYS

United States Patent Office

3,391,981

Patented July 9, 1968

3,391,981

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

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 difficult 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 difficulty 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 rapidly-moving combustion-supporting gas, such as air. The cuter 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 5 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 ₁₀ 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 15 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 an20 nular 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 com25 bustible gas and air in the region bounded by the throat of the burner.

A feature and advantage of this invention is that the scroll-shaped inlet chamber provides cyclone acceleration of the incoming combustible gases. Such acceleration 30 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 an40 nular 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 hav45 ing 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 50 the mixing of the combustible 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 55 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 GO 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 cham65 ber or passageway at the other end. The inner shell is shaped to have a conical portion and a cylindrical section 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 70 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 com3,391,981 bustible 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 3—3;

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

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

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

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 generally 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 II 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 sufficient discharge through annulus 19. If the source supply of gaseous fuel should fluctuate to decrease the discharge through annulus 19 below the level of maintaining burner firing, the combustion of conventional fuel at the firing 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 co-axial 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 19, 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

3,391,981 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 rep- 5 resent 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 an- j₀nulus 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 15 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 20 is suitably connected to bar 49. Each of rods 48 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 man- 25 ner (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 SO 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 35 of an annulus air zone register similar to that described here is set forth in my U.S. 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 ⁴⁰and 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 45 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. 50

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 different swirl and flow characteristics from the annulus and core air zones. Such linkage arrangement generally depends upon the type of 55 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 deflec- 60 tor 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 19. Outer ⁰⁵deflectors 71 are positioned alternately with inner deflectors 72 therebetween. Deflector blocks 71 are bolted 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 ¹23a 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 75 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 86 between housing wall 23 and inner cylindrical shell wall 26. 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 efficiency of operation.

Another embodiment of a portion of my invention is shown in FIG. 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 wiih the aforementioned alternate fuel chamber making only minor mechanical modifications thereto.

In the alternate embodiment of the fuel chamber shown in FIG. 5, combustible gases are conveyed through relatively wide portion 131α of the fuel inlet chamber or passage which corresponds to zone 44 shown in FIG. 2 explained hereinabove. In the alternate embodiment, however, outer wall 135 of the fuel inlet passage does not form a scroll-like profile as does its counterpart 36 shown in FIGS. 1 and 2; instead, curved wall 136 is of constant diameter curvature. However, rearward flange wall 143 is shaped in a generally helical configura'ion advancing toward and eventually joining inner flange wall 142 (the joincier of wall 143 to wall 142 is not shown in the sectional view of FiG. 5). Inner cylindrical wall 126a, seen in the region between walls 142 and 143, is of a constant diameter curvature; and, in combination with flange walls 142, 143 and outer cylindrical portion 136, forms fuel inlet chamber or passage 131 having a varying cross section which decreases from the initial inlet portion 131a to its terminus at the point of contact of wall 143 with wall 142.

lhe cross-sectional area of inlet passage 131 may be seen to be the product of interval dimension 149, 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 therethrough. 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 action on the combustible fuel effectuated by convergent inlet passage 131 tends to force the heavier airborne particles radially out3,391,981 wardly 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. 5 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 2α 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.l; 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 efficiency 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.