Adjustable Flame Burner

My invention relates to a burner structure suitable for use in industrial furnaces such as soaking pit and reheat furnaces and more particularly, burner structures of the adjustable flame type.

Large industrial furnaces of the metallurgical or other heat treating type require precisely controlled temperature distribution to achieve product quality and/or satisfy subsequent processing operations. In the case of soaking pits for heating steel ingots, burners are normally operated at a maximum rated capacity to bring the ingots up to rolling temperature as fast as possible and thereafter the burners are cut back so as to maintain the proper temperature while the ingots are thermally soaked.

In reheat furnaces, for example side-fired walking beam furnaces, a fixed flame burner simply can not control the temperature distribution since the presence of such furnace conditions as the movement of gases through the furnace, different stock sizes and productivity rates create variable flame requirements.

These problems were recognized in U.S. Pat. No. 3,771,944 of which I am a co-inventor. In that patent, an adjustable flame burner is disclosed which permits adjustment of the flame characteristics under various operating conditions. Another patent which discloses burner structures for soaking pits is U.S. Pat. No. 3,418,062. In that patent a concentric burner structure is disclosed in which a low capacity burner is concentrically mounted within a high capacity burner giving varied, albeit limited options of operation.

While the above two burners have proven quite successful, the need still remains for an improved adjustable flame burner having a wide range of flame characteristics for any given application.

I have now developed such a burner which exceeds the capabilities of previous adjustable flame burners and which has the optional capability of acting as a maintained energy burner as well. My burner will yield a violently short, high release combustion pattern that will either burn in a short cyindrical fashion or break into a high release coanda-type flame having a large flame diameter with effectively zero forward velocity. Alternately, my burner can produce a high intense flame approximately three times as long as the previously described flame and have an essentially zero radical component. My burner is adjustable between these two extreme conditions to provide a wide variety of flame characteristics.

My adjustable flame burner includes a burner body having a baffle with a discharge face forming a forward wall thereof. The fuel duct extends co-axially with the longitudinal axis of the burner and passes through the burner baffle. A first set of spaced combustion sustaining gas apertures extend axially with the burner and radially outward of and parallel to the fuel duct. A second set of radially spaced combustion gas apertures extend through the baffle at an acute angle to the apertures of the first set and intersect with the apertures of the first set at or substantially adjacent the discharge face. The second set of apertures are also offset or skewed with respect to the central burner axis. Means are provided to adjust the relative amount of combustion sustaining gas through the first and second set of apertures. The angle of intersection between the two sets of burners is in the range of 45.degree. to 65.degree. and preferably on the order of 65.degree.. When combined with a port block, the port block should have a length to diameter ratio in the range of 0.7 to 1.5. A third set of air apertures exiting the baffle upstream of the intersection of the first and second set may be employed.

FIG. 1 is a section taken along section lines I--I of FIG. 2 and showing my burner in conjunction with a port block;

FIG. 2 is an end view of the burner;

FIG. 3 is a section taken along section lines III--III of FIG. 4 and showing a modified form of the burner;

FIG. 4 is an end view of the modified form of the burner;

FIG. 5 is an end view of the portion of the burner of FIGS. 3 and 4 showing the spin passageways in phantom; and

FIG. 6 is a schematic in graph form showing the flame configuration over a range of operating conditions.

My adjustable flame burner is applicable to a number of industrial heating furnaces but finds particular application to metallurgical furnaces such as soaking pits and reheat furnaces such as walking beam side-fired furnaces or longitudinally-fired furnaces.

The burner, generally designated 10, is mounted to a furnace wall 12 by means of a mounting plate 15 in the conventional manner, FIG. 1. The furnace wall 12 includes an opening aligned with the burner 10 and exiting into the furnace chamber (not shown), which opening is known as port block 34. Port block 34 is cylindrical in shape and has a diameter D and an axial extent L. While port block 34 is normally cylindrical throughout its axial length, it may include a diverging tapered exit way 35 as shown.

The burner 10 includes a burner body 14 having a refractory baffle 16 forming the forward wall thereof, FIGS. 1 and 2. Baffle 16 has a frustoconical shaped discharge face 18 which increases in diameter in the downstream direction. A central fuel duct 26 extends along the burner body central axis, passes through baffle 16 and exits at the upstream end of discharge face 18. Fuel supply fitting 32 connects to fuel duct 26 to provide the appropriate gaseous, liquid or solid fuel, or combinations thereof, the details of which do not form a part of this invention.

Surrounding central fuel duct 26 and within the burner body 14 is air chamber 28 having air inlet 29 for connection to an air source, FIG. 1. The forward wall of chamber 28 is formed of baffle 16. A series of air apertures 20 which are radially disposed about the central burner axis extend through the baffle 16 from the air chamber 28 to the discharge face 18. Air apertures 20 extend substantially parallel with the burner central axis.

A second air chamber 30 is annularly disposed about the first air chamber and is generally positioned partially downstream thereof, FIG. 1. Air chamber 30 has an inlet 31 for connection to an air source. Air chamber 30 also terminates at baffle 16 and a plurality of axial air apertures 22 extend through baffle 16. Air apertures 22 are angularly disposed with respect to air apertures 20 so that each aperture 20 intersects with a corresponding aperture 22 at an acute angle and at or substantially near the discharge face. This angle of intersection is referred to as the spin angle and is generally on the order of 45.degree. to 65.degree. with 65.degree. being preferred. Air apertures 22 are also skewed with respect to the longitudinal center line of the burner so as to produce a swirling air input. In other words, a plane passing through the longitudinal axis of each air aperture 22 also passes through the exit end of an air aperture 20 and such a plane is offset from a plane through the center line of the burner. At the point of intersection of the two apertures, the air through apertures 22 may actually be a diverging or converging spin.

Standard control means 33 can be used to adjust the relative amount of air or other combustion sustaining gas passing through the first set of air passages 20 and the second set of air passages 22, respectively. In addition, automatic control means can vary the heat release pattern over a series of operating conditions. The details of these various controls do not form a part of this invention.

When all of the combustion air is passed through air passages 22, the combination of the spin angle and the offset from the central burner axis produces a rotary or swirling action on the combustion air when the air jet impinges within the burner tunnel or port block. This yields a violently short, high release combustion pattern that will either burn in a short cylindrical fashion or break into the high release coanda-type flame, with the flame diameter increasing substantially with effectively zero forward velocity to flame and products of combustion.

Alternately, when all the combustion air passes through the axial air passages 20 the spin is eliminated and the air is accelerated axially producing a high intense flame approximately three times as long as the flame achieved using the spin angle. Since the two series of air jet coincide at a point substantially at the discharge face, a tunable flame release pattern can thereby be achieved by altering the percentage of air through the respective air passages 20 and 22.

A number of flame release patterns achieved by altering the air input between the limits of 100% spin and 100% axial is illustrated in FIG. 6. The operating data for the tests given in Table I.

At 100% spin (FIG. 6A) the flame was about 21/2' long and some 2' in diameter. It was blue-violet with blue tails at the exit of the port with no visible color in the port area. At 75% spin and 25% axial flow (FIG. 6B) the flame was 31/2' long and 11/2' in diameter. The flame color was blue-violet exiting the port with orange tails. At 67% spin and 33% axial flow (FIG. 6C) the flame length was 4' long and 2' in diameter. The flame color exiting the port was violet with hazy orange tails. As the spin was decreased to 60% and the axial flow increased to 40% (FIG. 6D) the overall dimensions of the flame remained about the same except that the flame developed a violet center portion about 1' in diameter and an outer orange ring at the port area. At 50% spin and 50% axial flow (FIG. 6E) the flame length increased to 41/2' and the diameter reduced to 11/2'. The flame was violet to orange in the center with orange tails about the port area. At 40% spin and 60% axial flow (FIG. 6F) the flame length was 5' long and 11/2' in diameter. The flame had a long, blue-violet center with orange tails surrounding the center portion. At 33% spin and 67% axial flow (FIG. 6G) the flame increased to 51/2' long and 11/2' in diameter. The color and shape were about the same as the preceding flames, except the flame edge became more jagged.

As the spin was further reduced to 25% and the axial flow increased to 75% (FIG. 6H) the flame size and color remained the same as the preceding flame. However, the orange tails became more sharply defined and less jagged.

At 100% axial flow (FIG. 6I) the flame length increased to 61/2' with a 10" diameter increasing to an 18" diameter near the end of the flame. The flame had a long white center portion with a blue ring at the port exit and orange tails at the flame end. Whereas the port was hot in the other tests, in this test the port was streaked with both hot and cold areas.

The ratio of the diameter (D) of the port block to the length (L) of the port block is also important to provide the desired adjustable flame characteristics. I have found that ratio of diameter to length should be in the range of 0.7 to 1.5. The various apertures should have an axial length of some 2 to 21/2 times greater than the diameter of the aperture to assure proper flow along the center line of the aperture.

A modified form of the invention is illustrated in FIGS. 3 through 5. This embodiment is similar to the earlier embodiment in that a burner body 14' terminates in a forward wall defined by baffle 16'. A pair of air chambers 28' and 30' communicate with passages 20' and 22' respectively, which pass through the baffle 16' and converge at the discharge face 18' at an acute angle with one another and offset from a plane through the burner center line. A central fuel duct 26' extends along the burner longitudinal axis as in the earlier embodiment. The only difference in this embodiment is that an additional air chamber 36 is formed annularly about central fuel duct 26' in communication with axial air passageways 38 which extend through the baffle 16' and exit in an inner firing port 40 formed by baffle 16'. Inner firing port 40 is upstream of the intersection between air passages 20' and 22'.

The burner functionally performs as the burner illustrated in FIGS. 1 and 2 throughout the normal operational envelope. However, it has the additional feature of being a maintained energy burner so that when the air flows below 33%, the air passages 38 will utilize the available system pressure for mixing, thereby increasing the combustion intensity.

In both embodiments, the desired flame characteristics can be obtained since the burner is adjustable between the steep rotational spin angle generated by the air through the inclined passages to the pure axial compartment achieved by passing all the air through the passageways extending parallel to the burner longitudinal axis.