US2361557A - Multiple hearth furnace - Google Patents

Description

Oct. 31, 1944. w. s. MARTIN 2,361,557

MULTIPLE HEARTH FURNACE Filed March 4, 1942 3 Sheets-Sheet 1 INVENTOR WARREN S. MARTIN 2. 24 I1 23 25 1; ATTORNEY Oct. 31, 1944. w. s MARTIN 2,361,557

MULTIPLE HEARTH FURNACE Filed March 4. 1942 s Sheets-Sheet 2 INVENTOR WARREN s; MARTIN Oct. 31, 1944. I w s R-rm 2,361,557

MULTIPLE HEARTH FURNACE Filed March 4. 1942 3 Sheets-Sheet 3 3Ib 28b WARREN S. MARTIN BY D ATTORNEY and having means for Patented Oct. 31, 1944 UNlTED STATES PATENT OFFICE MULTIPLE nmn'rn FURNACE Warren s. Mai-an, Hassapequa, N. r. Application March 4, 1942, SerialNo. 433,274

9 Claims. (Cl. 214-21) This invention relates to improvements particularly adapted for use in multiple hearth furnaces of the type in which a furnace is divided into compartments between thetop and a plurality of superimposed hearths of which the lowermost may be the bottom of the furnace, and the material deposited on the top hearth is fed downwardly from hearth to hearth by rabbling means acting to feed the material either inwardly to central discharge means or to peripheral discharge means, the arrangement of discharge uppermost hearth'of such a furnace in such a manner as to utilize a greater part of the upper surface of such hearth more efliciently than heretofore. A further object is to providematerial supply means whereby the material to be treated will be fed substantially uniformly to a substantial annular area. on the hearth so that a. large part of the hearth surface will be used effectively as the rabbling means moves the material to the means being different for adjoining hearths.

More particularly the invention relates to improvements in feeding the material to the upper part of the furnace in such a manner that the material-receiving surfaces of the uppermost hearth or hearths will be utilized to the greatest advantage.

Heretofore it has been a common practice to supply material to the uppermost hearth through a chute passing through the top of the furnace preventing the escape therethrough of heated rial be deposited near the" center. of an uppermost hearth having peripheral discharge means or openings the rabbling means over such hearth will, when operating, act to work the material to the periphery for discharge to the next lower hearth- It will be evident that the rabbling means not distribute the material uniformly around the central part of the uppermost hearth but will leave a bare portion of the hearth'bounded approximately at its outer side by a curve extending from a position approximately beneath the inner side of the chute, in the general shape of an expanding spiral until it reaches the peripheral part of the hearth, containing the outlet means or openings. Obviously such bare portion of the uppermost hearth reduces proportionally the heating capacity of the furnace and may also result in reduced efliciency of the next-lower hearth due to improper distribution thereon. A corresponding loss of efliciency would also be encountered if the material were supplied to the Peripheral part of the uppermost hearth and fed toward a central discharge means or opening. A plurality of' supply chutes mightreduce the mute area on the uppermost hearth but might introduce other difliculties.

An important object of the invention is to provide means whereby a furnace hearth or the upper part of a multiple hearth furnace may be used to greater advantage thus increasing the efllciency of the furnace. Another object of the invention is to provide means for feeding material to the outlet or discharge means associated with such v hearth.

The present invention may be carried out by depositing the material to be treated on a rotary distributing platform having a substantially circular edge and then gradually feeding material over said edge to fall on an annular area on said uppermost hearth. Then the rabbling means will distribute the material substantially uniformly over the effective surface of the hearth on its way toward the outlet means. Such uniformity of distribution on the uppermost hearth will also air orgases. If the mate- I tend to produce greater uniformity of distribution of material on the next lower hearth, and therefore increase the capacity of the furnace by drying material more rapidly.

Other objects, features and advantages will appear upon consideration of the following detailed descriptionand the drawings in which:

Fig. iis a vertical section of the upper part of a multiple hearth furnace comprising an embodiment of the present invention;

Fig. 2 is a horizontal section taken along the line 22-of Fig. 1;

Fig. 3 is a detail partly in section of the arrangement at the central part of the furnace top;

Fig. 4 is a vertical-section of a modified form of multiple hearth furnace involving the present invention;

' Fig. 5 is a horizontal section taken along line 5-5 of Fig. 4; p

Fig. 6 is a vertical section similar to Fig. 4, of a miutiple hearth furnace embodying a second modified form of the invention? and Fig. I is a section taken along the line 1-1 of Fig. 6.

Referring to the drawings. there is illustrated in Fig. 1 a vertical section of the upper part of a vertical multiple a substantially round peripheral wall II, a top H, an uppermost hearth l3, having at its periphery outlet or discharge means preferably comprising a plurality of outlets or drop holes ll hearth furnace ,ll having may drop to the next lower hearth (not shown).

The first two hearths I3 and I5 are usually used for drying purposes and hearths below hearth 15 are ordinarily used forburning the material dried in the compartments above the two dryinghearthsl3andl5.

Material after deposit on the hearth maybe distributed over the hearths and moved toward the outlets by rabbling means which may comprise a rotary vertical shaft ll passing through the central opening ii of hearth l5 with a substantial space to spare, and passing through suitable gas seals at the center of the uppermost hearth l3 and at the center of the furnace top 12. Above the hearths l3 and 15 are radial arms approaches the circular outer edge of the platform where it is substantially a continuation of the outer wall of the chute. The material on such annular area of the hearth i3 is in position to be acted on by the rabbling means and worked over to the peripheral outlets or drop holes 14, the supply of material to the various drop holes being fairly uniform thus assuring it carried by the shaft 11 and provided with downwardly projecting members or blades IS with their forward surfaces so inclined that those above the hearth 13 move material to the periphery and those above hearth 15 move material to the centralopening l6.

- The description thus far might apply to many furnaces heretofore in use. In such prior furnaces it was a common practice to feed the material to the uppermost hearth by means of a .chute passing through the top of the furnace and having a device serving to prevent the escape of any substantial amount of furnace gases through the chute. As already described the material would immediately be worked outwardly and leave bare a part of the hearth bounded I at its outside by a more or less definite line in the general form of a spiral gradually increasing in distance from the center of the hearth until it reached the circle of drop holes at the periphery of the hearth.

According to the present invention it is proposed to distribute the material fed into the uppermost compartment of the furnace over an annular area of the uppermost hearth, concentric with the hearth itself, so that the material will be spread over the hearth with substantial uniformity and substantially all of the hearth surface will be utilized. In carryin out the invention in connection with a furnace (Figs. 1 and 2) of which uppermost hearthhas outlet openings at its periphery, the material is introduced through a chute 28 under control of a weighted flapor gate 2| which acts to prevent the escape of gases. From the chute the material drops on a horizontal support .or platform 22 just below the lower end of the chute and mounted to turn about the axis of the shaft I1 and having circular outer edge 23 of which the center lies in said axis. .Preferably the support 22 is connected to said shaft to rotate there with. The lower portions of the outer and inner walls of the chute 20 may be considered parts of the spiral blade and consequently the ends of the spiral blade 24 may be described as overl pping. In order to distribute properly on the hearth material supplied to said support, it is necessary to discharge material on the support gradually over said circular edge thus depositing'it in an annular area on the hearth I 3. Such an ,efiect may be produced by means of a generally spiral fixed unloading blade 24 (Fig. 2) in the general form of a spiral starting as substantially a continuation of the inner wall of the lower end of the chute and gradually increasing in distance from the axis of the shaft ll until it reasonable uniformity on the upper surface of the next lower hearth.

Obviously the shape of the blade as a -whole may be varied without changing its operation,

the essential feature of the blade being that its material-engaging face must be suitably shaped to produce the desired action. In order to feed the material smoothly from the chute 20 to the support 22 it is desirable to bring the lower end of the chute close to the support and to omit the discharge side of the lower end of the chute inside the furnace so that the material is free to be removed by the rotating support. Preferably also the inner end of the unloading blade constitutes an extension of the inner wall of the chute at its lower end and the outer end of the blade is attached to the outer wall of the chute. The construction just described is shown very clearly in Figs. 2 and 3. It will be evident that the unloading blade serves as a cam.

The present invention may be applied to mul- 'tiple hearth furnaces of types heretofore in use without any substantial change in the general furnace construction. In order to maintain the same working conditions in the compartment above the uppermost hearth of the furnace the tral portion having at its bottom an opening of somewhat greater diameter than the diameter of the support 22, as illustrated in Figs. 1 and 3.

The top l2 proper may be provided at its cenin diameter from the upper surface of the hearth [2 to the lower surface thereof. The opening in the hearth may receive a tapered flange 25 of a ring 26 of suitable matter such as metal, said ring 28 also being provided with a flange 21 to engage the upper surface of the top l2 around the central opening. The ring 26v may be turned in above the flange 21 so as to present at its top a horizontal seat to support a cap 28 which carries part of the gas seal around the shaft ll and.also carries a chute 20 which maybe made integral therewith.

In this embodiment of the invention the support 22 is in the form of an annulus resting on an upwardly projecting flange of the shaft I'I, thus requiring the lower end of the chute 20 to be brought close to the shaft l'l. According to this arrangement the chute 20 may be inclined inwardly to feed the material to the top of the support 22. Besides being attached to the lower end of the chute 20 the unloading blade 24 may be supported by suitable means from the cap 28 a at points remote from the chute.

As illustrated in Fig. l the uppermost compartment of the furnace communicates with a duct or flue 30 which may be used for supplying air if the furnace be of the down-draft type, or if the furnace be of the up-draft type. the gases may be withdrawn through duct 30 under the inter with a tapered circular opening decreasing fiuence of draft producing means such as a stack- (not shown). It will be evident that the arrangemen-t of drop openingsv M around the periphery of the hearth l3 serves to assist in con-' trolling the gas flow and to render such flow more uniform than with a. central drop opening in the uppermost hearth.

The support 22 of Fig. l must be of substantial width and as the material fed to said support must be passed over the circular outer edge of said support, it will ordinarily be deposited on the hearth. l3 at a, substantial distance from the shaft 11. However, shown in Fig. 4, use may be made of an annular support 2211 spaced from the shaft I! so that the material deposited on the support 22a will be fed over the circular inner edge thereof, thus enabling the material to be deposited on the hearth l3 near the shaft H. The support 22a may be supported by suitable arms 3| projecting from the shaft I1. With this arrangement of the support 22a the opening in the furnace top I2 must, as shown in Fig. 4, be larger than in Fig. 1, thus enabling the chute 20a to be positioned farther from the shaft I1 and to be ar-- ranged vertically. As illustrated in Fig. 4 the cap 280, may be substantially flat and supported at its periphery on a ring 26a.

with the arrangement Due to the fact that the material is discharged over the inner edge of the support 220., the unloading plate 24a must be changed accordingly from the form shown in Fig. 2 so as to force the material inwardly during rotation of the support or plate 2211, as indicated in Fig. 5. In this form of the apparatus the flat cap may be relatively close to the support 22a and the unloading blade engages the lower side of the cap and is attached thereto. A portion of the outer end of the blade 24a may be considered as the outer wall of the chute beneath the cap and an extension 32 of the. inner end of the blade proper may serve as the inner wall of the chute, there being no front or rear wall. 2

Where the material is dropped to the hearth l2 over an area so close to the shaft H, as shown in Figs. 1 and 4, there is very little danger of the material entering the discharge flue 30. However, any such tendency might be met by providing a dwell portion, for example in the form of a circular arc, in the part of the unloading blade nearest said flue 30.

In Figs; 6 and 7 there is illustrated an application of the invention to a furnace in which the.

uppermost hearth l3b has a central drop opening Nb and the rabbling device above the hearth l3b has its blades arranged so as to feed the material towards the central drop opening. In the form illustrated in Fig. 6, the usual top of the furnace may be omitted and replaced by a cap 28b extending completely across the furnace and having at one point along its periphery, a chute 20b through which material can drop to loading blade 24b may engage the lower surface of the cap 281) and be attached directly thereto, the outer end of the unloading blade being located beneath the outer side of the chute and the other end may be located beneath the inner side of the chute or the charging opening. In this form the chute does not extend below the cap, but the blades are connnected by a rear 1 support 22b immediately in front of the entrance of flue 30b and may pass into the same. However, such an effect-may be prevented by forming the blade 24b with a dwell portion 24c opposite the flue 29b. Such dwell portion 240 may be in the form of an arc of a circle aboutthe axis of the shaft as a center.

The design of furnace shown in Figs. 6 and 7 is more adaptable to relatively small units of which the diameter is in the neighborhood of eight to ten feet. I

It will-be evident that by depositing the mater'ial to be treated, in an arc of a circle on the uppermost hearth in accordance with the present invention, the material will be distributed substantiallyuniformly over the surface of said hearth. In this way substantially the whole upper surface of the uppermost hearth may be utilized, thus producing more uniform treatment and having the effect of increasing the capacity a support 22b, preferably annular in form, positioned near the inner surface of the peripheral wall of the furnace.

The support 22b may be sustained by means of arms'3lb which maybe integral therewith, projecting from the shaft I! to the support at any convenient intervals around the shaft. In view of the omission of the usual thick top of the furnace, the cap 28b may rest on the top of the peripheral wall of the furnace and the support 22b may be located rather close to the cap. It

should be understood that the support 22b and arm 3Ib when formed integrally may be split for convenience in assembly (Fig. 7). The unof the furnace for drying and burning.

It should be understood that various changes may be made and that certain features may be 'used without others, without departing from the true scope and spirit of the invention. i

What I claim is:

1. In a furnace having a central vertical rotary shaft, a horizontally arranged annular hearth providing a central opening in which said shaft is located, gravity outlet means arranged at one edge of said annular hearth and rabbling means carried by said shaft to work material on said hearth to said gravity outlet means; means for feeding material to said hearth to cause substantially uniform distribution of said material thereover by said rabbling means, comprising a support rotating with said shaft and having a generally circular discharge edge adjacent to the edge of the hearth remote from said outlet means, blade means in the general form of a spiral with overlapping ends above said support and held against rotation therewith, one of said overlapping ends being adjacent to said circular edge of the support and the other end being remot therefrom, and means for supplying material to the space between said overlapping ends.

2. The combination as set forth in claim 1, in which the location of the gravity outlet means is at the outer edge of the hearth and the circuwhich the location of the gravity outlet means is at the outer edge of the hearth and the circular edge of the support is the inner edge thereof and is adjacent to the inner edge of said hearth.

5. The combination as set forth in claim 1, in

8. The combination as set forth in claim 1, in

which the end edge of the end of said blade means remote from the circular edge of the support is connected by a generally radial wall to the other end portion of said blade means.

9. The combination as set forth in claim 1, in which the furnace has a lateral gas outlet above said hearth, the location of the gravity outlet means is at the inner edge of the hearth, the circular edge of the support is its outer edge, and the blade means is located with overlapping ends at a side of the furnace remote from said gas outlet and has a generally circular portion concentric with said shaft and located adjacent said gas outlet to avoid discharge of the material through said gas outlet.

WARREN S. MARTIN.

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