Exhaust gas afterburner

Oct. 29, 1968

3,408,167

R. B. BURDEN, JR

EXHAUST GAS AFTERBURNER

Filed Aug. 17, 1965

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Buckhorn, Blore, Klarquist a Sparkman

ATTORNEYS

3,408,167

Patented Oct. 29, 1968

United States Patent Office

3,408,167 EXHAUST GAS AFTERBURNER Roy B. Burden, Jr., Sherwood, Oreg., assignor, by mesne assignments, to General Incinerators of California, Inc., San Diego, Calif., a corporation of California Filed Aug. 17, 1965, Ser. No. 480,405

Claims. (Cl. 23—277)

ABSTRACT OF THE DISCLOSURE

A tubular afterburner structure having an inlet end connected to a source of gas borne wastes and a burner ring surrounding the waste flow path within the burner tube. An annular air chamber surrounds the waste flow path immediately upstream from the burner ring. Combustion air is introduced tangentially into the air chamber to provide a unidirectional rotary flow of air within the chamber. This flow is introduced through openings in the chamber into the waste flow path to impart to wastes traveling downstream in such path a uniformly whirling motion which is maintained as the wastes pass by the burner ring, so that they are ignited and burned while thus whirling, thereby prolonging and intensifying the burning to result in more complete destruction of the wastes.

The present invention relates to the field of waste incineration, and more particularly relates to an afterburner for destroying the waste products of incomplete combustion from an incinerator or other primary combustion device.

Air pollution has become a major health problem in most of the larger metropolitan areas of the world. Most incinerating devices now used by industry, apartment buildings, hotels, restaurants and others are so old or poorly designed that they contribute significantly to the air pollution problem by discharging into the atmosphere large amounts of pollutants in the form of smoke, fly ash, noxious odors, gases and fumes.

Accordingly a primary object of the present invention is to provide an afterburner for use with incinerators and other primary combustion devices which effectively destroys most pollutants found in the flue gases of such devices.

Another primary object of the invention is to provide a new and improved afterburner which can be installed on existing primary incineration devices, without changing the existing manner of charging and firing the primary incinerator.

A more specific object is to provide a new and improved afterburner which destroys waste products while they are suspended in an exhaust gas stream.

Another object is to provide a new and improved burner apparatus which maintains the waste products in suspension in the flame zone of the burner for a prolonged period of time to insure their complete combustible destruction by imparting to the waste products a cyclonic motion.

Still another object is to provide burner apparatus having a new and improved means for imparting a cyclonic motion to the waste products borne in the exhaust gas stream whereby a more complete combustion of the waste products than heretofore possible is obtained.

Another object is to provide a new and improved afterburner which is simple in construction and easy, efficient and economical to manufacture, install, operate and maintain.

In United States Patent 2,879,862, issued March 31, 1959, to the present inventor, an afterburner device for destroying waste products in flue gases is disclosed. However, the afterburner of the present invention is an improvement over the device of such patent in that the lower expansion and settling chamber and appurtenants of the latter have been eliminated because the present improved afterburner is capable of destroying the greatest majority of the waste particles that had to be settled out and physically removed from the former apparatus. One of the ways in which the improved afterburner of the present invention effects more complete combustion of waste products than the former is through provision of an improved means for imparting a cyclonic motion to the waste products before they ever reach the combustion zone of the afterburner through the introduction of a rapidly whirling stream of secondary combustion air into the flow path of the afterburner upstream from a burner ring. This is to be contrasted with my earlier afterburner which sought to impart a whirling motion to the waste products and exhaust gas stream only after the same had passed by the burner ring into the combustion zone, and only through directional placement of fluid jets on the burner ring, which proved entirely inadequate for the purpose.

An important feature of the afterburner of the present invention is the provision of a wind chamber upstream from the annular burner ring in which secondary combustion air is rapidly whirled and from which such air is then introduced tangentially into the downstream flow of waste products to impart to cyclonic motion to the waste products. The resulting cyclonic motion imparts such a high angular velocity to the waste products that their downstream speed is slowed appreciably, whereby such products remain in the flame zone of the burner for a prolonged period of time while traveling at a high angular velocity, thus assuring substantially complete combustion thereof. One of the results is that little, if any, visible smoke or fly ash commonly seen emitting from ordinary incinerators can be seen escaping from the stack of an incinerator equipped with the afterburner of the present invention.

The above and other objects and advantages of the present invention will become more apparent from the following detailed description which proceeds with reference to the accompanying drawings wherein:

FIG. 1 is a side elevational view of a flue-fed incinerator equipped with an afterburner in accordance with the present invention;

FIG. 2 is a transverse sectional view, on an enlarged scale, taken along the line 2—2 of the afterburner of FIG. 1;

FIG. 3 is a longitudinal sectional view, on the same scale as FIG. 2, taken along the lines 3—3 of FIG. 2 showing the internal details of construction of the inlet end portion and flame zone of the afterburner;

FIG. 4 is a transverse sectional view, on the same scale as FIGS. 2 and 3, taken along the line 4—4 of FIG.· 3 showing the details of the wind chamber of the afterburner; and

FIG. 5 is a partial vertical sectional view on a smaller scale than FIGS. 2 through 4, through the upper portion of an incinerator equipped with a modified afterburner in accordance with the present invention.

With reference to the drawings, FIG. 1 discloses a conventional flue-fed incinerator, or primary burner 10, including a door 12 covering an opening through which the incinerator is charged with waste materials to be burned and a lower, clean-out door 14 having adjustable draft openings 16. The upper portion of the incinerator includes a short base section 18 of a flue stack which surrounds a top opening in the incinerator through which waste particle-bearing flue gases escape from the incinerator. Normally an ordinary flue stack (not shown) would be fitted on the base 18 to discharge the flue gases and particles directly into the atmosphere, largely in the form of smoke, fly ash and fumes.

However, in the incinerator of FIG. 1 the ordinary flue stack is replaced by a tubular, upright afterburner

3,408,167

..... ₄ structure 20 having an inlet end 22 secured to the base section 18 and an upper, outlet end opening 24 from which flue gases are discharged into the atmosphere after passing through the afterburner. The afterburner 20 is constructed in two sections, including a lower section 20A 5 containing most of the internal elements of the afterburner and an upper, stack section 20B, which are connected together by suitable fasteners at annular flanges 26.

Referring now to the sectional views of FIGS. 2 and ₁₀3, the afterburner includes a tubular outer wall, the interior of which defines a flow path 30 for flue gases and gas-borne waste products proceeding downstream through the afterburner. The outer wall is composed of an outer casing 32 of metal such as steel and an inner refractory 15 lining 34. The inlet or upstream end 22 of the afterburner includes an inlet end opening 36 through which flue gases and gas-borne waste products carried upward through the flue outlet of the incinerator are introduced into the flow path of the afterburner. 20

The refractory lining 34 terminates at a distance axially inwardly or downstream of the inlet end opening 36. At the terminus of the inner lining is a burner ring 38 of cast iron or other suitable material having a plurality of outlet openings 40 spaced circumferentially of the burner 25 in an upwardly inclined surface thereof. Combustible fluid such as natural gas from a remote source (not shown) is directed into the interior of the burner ring under pressure through a pipeline 42 and discharged through the openings 40 into the flow path 30, where it is ignited by 30 suitable ignition means (not shown) of well-known construction in the art provided as an integral part of the burner unit. A suitable closure valve 43 is provided in pipeline 42 for regulating the flow of fluid to the burner ring. 35

An annular inner wall 44 extends longitudinally between the base of the burner ring 38 and the inlet end 22 of the afterburner. Such wall is inwardly concentric with respect to the outer casing 32 to define an annular wind chamber 46 radially outwardly adjacent the flow 40 path, upstream from the burner ring. The wind chamber is enclosed at its upper end by a flange portion 48 of the inner wall, which supports the burner ring, and an outer rim 50 of the burner ring. The lower end of the wind chamber is closed by a lower flange 52 of the inner wall which is seated on the lower end wall 22 of the outer ³casing.

Referring to FIGS. 3 and 4, a lower portion of the outer casing 32 which defines the outer wall of the wind chamber is provided with an opening 54 through which ₅θ a stream of secondary combustion air is introduced into the wind chamber by a tangential passageway, or duct 56, of an air blower 58 (FIG. 1). The blower 58, which may be of conventional construction, is connected by an electrical conductor cable 60 to a switch in a control unit ₅₅59 and thence to an electrical input supply (not shown). When the blower is energized, a stream of secondary combustion air is blown tangentially into the wind chamber and, because of the annular nature of the chamber, the air is caused to flow within the chamber in a rotary θθ unidirectional path as indicated by the arrows in FIG. 4.

The inner wall 44 of the chamber is provided with four equally circumferentially spaced-apart openings 62 which open into the central flow path 30. Inner wall segments which are cut to provide such openings remain attached _ggto the inner wall along one edge thereof and are bent at an angle to project upstream into the wind chamber so as to define a series of deflectors 64. These deflectors direct the spinning air in the chamber through the openings 62 and tangentially into the main flow path 30 of 70 the afterburner. Once in the flow path, the rapidly spinning secondary combustion air imparts a whirling, or cyclonic, motion to waste particles and gases passing downstream in the flow path adjacent the wind box, thereby giving them a high angular velocity while slowing con- 75 siderably their downstream rate of speed. The portion of the flow path between the inlet opening 36 and the burner ring 38 also serves as a mixing chamber in which the secondary combustion air and waste products to be burned are intermixed in readily combustible proportions before the mixture passes through the center of the burner ring and into the flame zone thereof.

Spaced downstream from the burner ring is a circular baffle plate, or impingement disc 66, which is mounted centrally in the flow path by four supporting legs 68, anchored at their outer ends in the refractory lining 34. The legs and baffle plate are preferably made of stainless steel or other heat- and corrosion-resistant material. The baffle plate serves to slow the downstream flow of waste products so that they,will remain suspended within the flame zone between the baffle plate and burner ring long enough to become heated to their combustion points. However, the baffle plate is of lesser diameter than the flow path at such plate so that the whirling stream of gases can pass downstream around the peripheral edge of the baffle plate.

Operation

In operation the door 12 of the incinerator is opened and waste materials to be burned are discharged into the incinerator where a suitable fire is provided and fed by primary combustion air through the draft openings 16 in the lower access door 14. As soon as the incinerator is charged, a switch in the control housing 59 is actuated to turn on the blower and thus blow secondary combustion air into the afterburner. The switch can be wired, if desired, to simultaneously open valve 43 to admit combustible fluid into the burner ring 38 and ignite the same.

Although the blower switch may be manually operated, the operation of the afterburner could be made automatic by providing the same with a suitable smoke detection device which would automatically actuate a switch to turn on the blower and burner ring and maintain the same in operation so long as the incinerator 10 remained charged so that smoke continued to be emitted from the incinerator through flue stack 18.

In an experimental embodiment of the illustrated afterburner, it was found that an average of only 3.3 pounds of waste matter were discharged from the outlet end of the afterburner in every ton of flue gas as compared with an average of 30 pounds per ton discharged from flue-fed incinerators which are not equipped with an afterburner. The combustible fluid or gas demand for such unit amounted to approximately 700 cubic feet per hour. The overall height of the afterburner was 10 feet, and the exterior diameter of the same was 20 inches. The diameter of the flow path downstream from the burner ring was 16 inches, and the diameter of the flow path upstream from the burner ring measured 12 inches. The ring burner in such unit had a capacity of from 250,000 to 2 million B.t.u.’s. The distance from the top of the burner ring to the impingement disc was 16 inches with the impingement disc itself having a 12-inch diameter. The metal portions of the afterburner, such as the wind box and baffle plate, which are exposed to the corrosive action of the combustion products are preferably made of stainless steel or other corrosion-resistant material. It is to be understood that the above specifications are illustrative only, and are not to be construed as limitations of the invention.

FIG. 5 illustrates a modification of an afterburner in accordance with the invention adapted to be installed in conjtmction with an existing stack 72 of an incinerator 74, only the upper portion of which is shown. In this modification, the upper portion of the incinerator is provided with a bypass opening 76. The afterburner itself comprises a tubular structure 78 which defines a bypass flow path 80 which bypasses the lower portion of the existing flue stack 72. The bypass is accomplished by providing a closure 82 which blocks the opening in the base of the existing flue stack. An induced draft fan 84 at the inlet

3,408,167 end of the bypass flow path diverts the flue gases and particles into such flow path. The fan includes an impeller 86 positioned in the flow path just upstream from a wind box 88 constructed in accordance with the wind box previously described with respect to FIGS. 3 and 4.

The impeller is rotated by a drive shaft 90 supported in an upright position by a pedestal support 92 extending into the flow path through a lower horizontal wall portion of the afterburner. The drive shaft is rotated through a pulley and belt arrangement 94 by an electric motor 96 mounted on a suitable bracket atop the incinerator.

The bypass flow path extends from the outlet opening of the incinerator 76 a short horizontal distance and then makes a right-angle bend and proceeds vertically upwardly past a burner ring 98. Spaced downstream from the burner ring, the flow path 80 bends inwardly at approximately a 45-degree angle toward the existing stack structure 72, and it intersects the flow path 100 of the existing stack at 102.

It will be noted that the modified afterburner construction does not utilize an impingement disc downstream from the burner ring, it being found unnecessary in view of the fact that the changes in the direction of the bypass flow path provide a sufficiently slow updraft without such plate. The desirability of an impingement disc and induced draft fan will vary with each installation.

Although not illustrated in FIG. 5, the upright support 92 for the induced draft fan may be provided with a water jacket whereby the drive shaft 92 can be water-cooled by suitable conduits leading into the upright support where the temperature of the products from the incinerator are excessively hot, as for example, greater than about 600° F. Similarly, the burner ring 98 is provided with an interior water chamber 104 into which water is pumped through a conduit 106 to cool the burner when the flue gases and other products from the incinerator are excessively hot.

Having illustrated and described a preferred embodiment of the invention and a modification thereof, it should be apparent to those skilled in the art that the invention permits of other modifications in arrangement and detail.