US2491704A - Cover-type furnace with open-flame burner and depending baffle for directing and spreading flame - Google Patents

Description

Dec. 20, 1949 s. BLooM COVER-TYPE FURNACE WITH OPEN-FLAME BURNER AND DEPENDING BAFFLE FOR DIRECTING AND SPREADING FLAME Filed June 5, 1947 /f/ f, f/f/ ATTORNEYS Patented Dec. 20, 1949 COVER-TYPE FURNACE WITH OPEN-FLAME BURNER AND DEPENDING BAFFLE FOR DIRECTING AND SPREADING FLAME Frederick S. Bloom, Pittsburgh, Pa. Application June 3, 1947, serial No. 752,228

2 Claims.

This invention relates to a heat-treating furnace and, in particular, to a furnace of the cover type having provision for direct heating by open flames.

Cover-type furnaces as previously constructed have usually been heated by radiant tubes or electric resistors. Radiant tubes are costly and deteriorate in time. Electrical heating is much more expensive than heating by combustion. In both types of furnaces, furthermore, diiliculty is experienced in heating the bottom of the charge at the same rate and to the same final temperature as the top. This is because of the tendency of the atmosphere gases within the cover to rise when heated and the fact that heat loss from the furnace occurs largely through the base. Temperature differences of as much as 100 between the top and bottom of the charge may exist unless the heating cycle includes a soaking period of several hours. Uniform heat-treating may thus be obtained only at the expense of reduced output.

Cover-type furnaces heated by open flames from burners have been proposed heretofore but have not been used to any extent, so far as I am aware, because they are subject to the above described difcuity to an even greater degree than radiant-tube or electric-resistor furnaces. Flames and combustion gases from burners naturally tend to rise. In addition, the inner cover usually placed over the charge has a greater area available for absorbing heat adjacent the top of the charge than in the neighborhood of the bottom. Open flames from burners, furthermore, shorten the life of the inner cover if fired directly against it, as with the normal burner arrangement.

I have invented a novel furnace of the cover or hood type heated by open flames which overcomes the aforementioned objections. In a preferred embodiment, I provide ports in the furnace wall with luminous-flame burners on the outside and bailles or deector plates overlying the ports, mounted on the inner surface of the wall and spaced therefrom so as to direct the flame issuing from the ports downwardly and spread it laterally. I thus insure efficient delivery of heat to the bottom of the charge as well as to the top thereof. The baille plate preferably has a shoulder or flange adjacent its upper edge which olfsets the remainder of the plate from the furnace wall and prevents the flame from ascending until it has passed downwardly or laterally from the port. This causes the lower portion of the furnace wall to be blanketed by a. widespread ame,

without changihgthe luminous characterthereof.

I preferably provide blocks of refractory material suitable for laying in the furnace wall, each having a port therethrough and a dei'lector baille secured to the inner surface of the block overlying the port. A burner is mounted on the exterior of the furnace adapted to fire into each port.

For a complete understanding of the invention, reference is made to the accompanying drawing illustrating the present preferred embodiment and the following detailed description and explanation. In the drawings,

Figure 1 is a transverse section through a cover-type furnace having the invention incorporated therein;

Figure 2 shows a portion of Figure 1 to enlarged scale, i. e., the port block, the burner firing therethrough and the deector baille mounted on the interior surface thereof, the parts being shown in section along the vertical plane through the axis of the port;

Figure 3 is an elevation of the inner face of the port block and its baille; and

Figure 4 is an elevation of the burner.

Referring in detail to the drawings, a furnace according to my invention comprises a base lli and a cover Il removably disposed thereon for heating a charge I2 enclosed in an inner protective cover I3. The base l0 comprises a structural frame I4 having a hearth of refractory material i 5 laid thereon. A support I6 is'disposed centrally on the hearth I5. Inner and outer sealing channels il and IB formed on the base are adapted to receive the lower edges of the inner cover i3 and a flange I9 depending from the lower edge of the cover Il, respectively.

The cover li comprises a side wall 20 and a roof 2i of refractory material laid up within a binding composed of structural members 22 and sheathing plate 23. Outlet openings 2 la are provided in the furnace roof to permit the escape of waste combustion gases. Port blocks 24 are laid in appropriate positions in the side walls 20 and have ports 25 extending therethrough..

Burners 26 mounted on the exterior of the furnace are adapted to fire through the ports 25. Each burner includes an air chest 21- to which is connected a pipe 28 from any suitable source of air under pressure. A burner nozzle 29 extends inwardly from a fuel chamber 30 in the lower portion of the air chest and a fuel-supply pipe 3| is connected thereto. Air flows from the -chest 21 through holes 32 into the space surrounding the nozzle 29, and, on ignition of the resulting combustible mixture, the burner fires a luminous flame through the port 25.

The burner has a neck 33 extending into the port and is secured to the furnace wall byv bolts 34 engaging lugs 35 extending laterally from the air chest.

A deilector plate or barile 36 is secured to each port block 24 in position to overlie the inner end of the port 25. The baille has a shoulder or flange 31 adjacent its upper edge which engages the inner face of the block, the remainder of the plate being offset a short distance therefrom. The plate may be conveniently secured in place by providing holes for the passage of the bolts 34. Lugs 38 adjacent these holes are adapted to engage the heads of the bolts and prevent turning thereof when the nuts are turned on the outer ends of the bolts.

The baille 3B serves to deflect downwardly and spread laterally the ame discharged from the port 25 by the burner 26, in somewhat the manner indicated at 39 in Figure l. As shown in the drawings, the space between the baille and the inner surface of the furnace wall is open at the bottom and sides of the plate and closed at the top. As a result, llame issuing from the port is caused to descend and diverge laterally before it starts to ascend. This deflection of the llame does not change the luminous character thereof materially. By spreading the flame laterally, the baille plate causes the inner surface of the iur nace wall adjacent the lower edge thereof to be blanketed with luminous flame. The flame travels downwardly in a thin sheet parallel with the furnace wall. The burners are so located that the llame loses most of its velocity on striking the furnace base. The burning gases then curl upwardly and the luminosity of the flame continues in the upward travel only to the height of the burners, the air-gas ratio being preferably adjusted to prevent luminous amcs from rising higher than the centerline of the burners. In this way, a high heat-radiating eiect is obtained from the luminous llame, giving an eine-lent method of heat transfer, with little or no flame impingement or wiping action against the inner cover since the llame has largely spent itself in its travel downward and laterally before it can come in contact with the inner cover. What actually happens is that the flame is directed downwardly parallel with the wall, dams up at the bottom, and rises up to about the height oi the burner centerline but does not deect toward the cover to any great extent.

The baille 36 should be of heat-resistant alloy such as a chromium-nickel steel. A baille of this metal is not injured by the impingeinent thereon oi the flame issuing from the port if the space i' between the plate and furnace wall is made sufficiently small, i. e., 2 or less.

Several novel and desirable results are achieved by the furnace construction described above. In the ilrst place, the initial downward velocity component imparted to the flame and combustion gases causes a greater portion of the heat to be supplied to the charge adjacent the base than would be imparted thereto in the absence of the deectors. It is possible thereby to bring all por,- tions of the charge up to the desired iinal ternperature at substantially the same rate with a minimum differential in temperature between the top and bottom of the charge. This differential may be as low as C. The prolonged soaking period which has been necessary heretofore is thus eliminated with a consequent reduction in the length of the overall treating cycle and a consequent increase in output. Finally, the lateral spread of the flame effected by the baille may be as much as 2' on either side of the burner. This permits an increase in the space between the center lines of adjacent burners from the foot or so previously customary to approximately 4.

Although I have illustrated and described only a preferred embodiment of the invention, it will be recognized that changes in the details of construction illustrated may be made without departing from the spirit of the invention or the scope of the appended claims.

I claim:

l. In a cover-type furnace having an inner wall for enclosing a charge and an outer wall spaced from and enclosing the inner wall with means closing the space between the lower portions of the outer and inner walls, the improvement comprising a series of gas burner nozzles positioned in laterally-spaced openings in the outer wall and adapted to fire luminous llames toward the opposite inner wall, a at baille plate disposed in spaced, overlying relationship adjacent each opening, and means closing the space between the portion of the outer wall just above each opening and the upper portion of the adjacent baille plate, the lower portion of the baille plate being disposed parallel to the portion of the outer wall below the opening to cause the luminous llame from the burner in each opening to fan out downwardly along the outer wall until the said means closing the space between the lower portions of the walls causes the flame to be deected upwardly along the adjacent inner wall, whereby the inner wall opposite the spaced burners is heated substantially evenly laterally and from bottom to top.

2. In a cover-type furnace having an inner wall for enclosing a charge and an outer wall spaced from and enclosing the inner wall with means closing the space between the lower portions of the outer and inner walls. the improvement comprising a series of gas burner nozzles positioned in laterally-spaced openings in the outer Wall and adapted to fire luminous flames toward the opposite inner wall, a flat baille plate disposed in spaced, overlying relationship adjacent each opening, said plate being of heat-resistant metal alloy spaced not more than two inches from the adjacent outer wall, and means closing the space between the portion of the outer wall just above each opening and the upper portion of the adjacent baille plate, the lower portion of the baille plate being disposed parallel to the portion oi the outer wall below the opening to cause the luminous llame from the burner in each opening to fan out downwardly along the outer wall until the said means closing the space between the lower portions of the walls causes the flame to be deflected upwardly along the adjacent inner wall, whereby the inner wall opposite the spaced burners is heated substantially evenly laterally and from bottom to top.

FREDERICK S. BLOOM.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,913,170 McCutcheon et al. June 6, 1933 2,145,074 Dreiein Jan, 24, 1939 2,174,052 Woodson Sept. 26, 1939 2,436,024 Smith Feb. 17, 1948

Images