US2061708A - Furnace - Google Patents

Description

Nov. 24, 1936. G. R. LEWERS FURNAC E Filed Dec. 24, 1934 2 Sheets-Sheet 2 lNVENTOR eozye F. L 660-975 ATTQRNEYS Patented Nov. 24, 1936 UNITED STATES PATENT OFFICE FURNACE Application December 24, 1934, Serial No. 758,911

1 Claim. (01. 202-104) My invention relates to improvements in the burning or roasting of solids containing vaporizable, combustible material such as oil saturated mineral absorbents. My invention is of special value and application in connection with the burning of such mineral absorbents to recover them for reuse.

Burning operations to recover oil satulated mineral absorbents', such as fullers earth, clays and like materials, to recover them for reuse, are commonly carried out in tiered multiple hearth furnaces provided with rotary rabbles driven from a common shaft. extending vertically through the several hearths, the oil saturated absorbent being supplied to the uppermost hearth, the oil content of the absorbent being utilized as fuel for the operation, and the burned product being discharged from the lowermost hearth.

In Letters Patent No. 1,943,976, granted January 16, 19.34pm my, application, I have described an improved method of conducting such burning operations to recover oil saturated mineral absorbents, which, aspracticed in such tiered multiple hearth furnaces, involves in effect theseparation of the furnace into two parts, an upper part in which absorbed oil is vaporized from the absorbent without substantialcombustion of this oil and a lower part in which the burning of the absorbent may be completed in much the usual manner. My present invention provides an improved apparatus for carrying out operations of this general character involving further the complete elimination of combustion from that region in the furnace within which separation of absorbed oilby vaporization from the absorbent without combustion of such oil is effected.

The improved apparatus of my invention, embodied in a tiered-multiple hearthfurnace of otherwise conventional construction, comprising a series of superimposed hearths and a corresponding series of rabble arms, having rotary I rabbles, rabble teeth or a combination of both, driven from a common vertical shaft for moving solids over the several hearths and generally downwardly through the furnace, comprises means for isolating the atmosphere of the hearths in the upper part of the furnace from that of the hearths in the lower part, combustion chambers arranged beneath the hearths in the upper part of the furnace with means for isolating the atmosphere in these combustion chambers from that over the hearths in the upper part of the furnace, and means for indirectlytransferring heat from the combustion chambers to solids moving over these hearths in the upper-part of the furnace, and means for conveying solids downwardly from hearth to hearth in the upper part of the furnace through these combustion chambers but out of contact with the atmosphere in these combustion chambers. My invention 5 thus provides compact, efiicient and economically constructed and operated apparatus for maintaining optimum processing conditions.

In the apparatus of my invention, the means for conveying solids through these combustion chambers but out of contact with the atmosphere therein, from hearth to hearth in the upper part of the furnace, are provided in the form of tubes closed with respect to the combustion chambers and extending therethrough connecting apertures 15 in each hearth with aligned apertures in the roof of the-next lower hearth. To facilitate the transfer of heat from the combustion chambers to the solids moving over the hearths in the upper part of the furnace, these tubes are with advantage made of material of high thermal conductivity, carborundum, iron chrome alloys, cast iron, and the like. These tubes may be baffled to increase the heat transfer. Inserts of similar material may also be arranged in the roofs, and in the r floors as well, of the combustion chambers to the same end. Heat transfer to solids moving through such tubes is, however, particularly effective. Repairs are facilitated by making such tubes removable.

My invention will be further described in connection with the accompanying drawings, which illustrate the apparatus of my invention. It is intended, and will be understood, that this fur- In the accompanying drawings:

Fig. 1 is a fragmentary elevation in section, with parts broken away, of a furnace embodying my invention;

Fig. 2 is a section on line 2-2 of Fig. 1;

Fig. 3 is a section on line 3-3 of Fig. 1, showing the details of the construction of drop tubes embodied in this furnace; and

Fig. 4 is a section showing a modified construction of drop tubes.

In the furnace illustrated I represents a chute through which the oil saturated mineral absorbent is supplied to the uppermost hearth 2" by means of a conventional screw feed mechanism l5. Material deposited on the hearth 2 is carried by the rotation of rabbles l6 attached to rabble shaft I1 across the hearth 2 to be dropped to the hearth 4 by means of drop tubes I8 extending through 9, II], II, I2, I3, and I4, from the last of which it is discharged through outlet 2I to conventional collection means. Air for combustion in the hearths 8, 9, II), II, I2, I3, and I4 also enters through the outlet 2 I. Gas outlet connections 22 leading to a condenser or stack (not shown) are provided at the top of the furnace for vapors from the absorbent undergoing treatment.

Combustion chambers 3 and 5 provided with openings 23 and 24, respectively, for burners (not shown) are interposed between distillation hearths 2 and 4 and distillation hearths 4 and 6, respectively. Gases formed in combustion chambers 3 and 5 escape through flues 25 and 26, respectively, and are not permitted to come in contact with material undergoing treatment in the distillation zones. Inserts 21, for. example, of material of high thermal conductivity are preferably placed in the floor and roof of the combustion chambers in order to facilitate the transfer of heat from the combustion chambers to the absorbent moving across the surfaces of the distillation hearths. Theseinserts may consist of carborundum, chrome alloy, chrome or cast iron, for example. The main body of the floor and roof may be made from firebrick or other suitable material.

Drop tubes I8, which are shown in the drawings as connecting alternate distillation hearths, may be made of metallic or ceramic material. Steel chrome alloys, steel nickel alloys, cast iron chrome alloys, carborundum or chrome may be used. By the provision of these drop tubes connecting successive distillation zones, the absorbent is subjected to burning or roasting without coming into contact with the heating medium. This feature of the improved apparatus of my invention enables the burning operation to be carried out with indirect heating of the absorbent, thereby elimimating the difficulties due to uncontrolled combustion commonly present when the absorbent is heated by direct contact with the heating medium, in a particularly advantageous manner. tubes I8 are advantageously arranged to be easily removable. The construction of these tubes'is shown in 'detail in Figs. 3 and 4 of the drawings.

As shown in Fig. 3, drop tube I8 is mounted about a tube 28 fixed in the opening in the floor of the combustion chamber. Drop tube I8 is provided at its top-with a collar or edge 29 resting upon a ledge in the opening in the roof of the combustion chamber. The drop tube is secured in position by the use of fire clay, for example, which also serves as a seal, preventing the escape of combustion gases to thedistillationhearths. In the modification illustrated in Fig. 4, the drop tube is shown as consisting of an upper portion I 8a. and a lower portion I8b;provided with interlocking edges 30 and 31, respectively, set in a sand seal, for example. The lower portion of the drop tube is shown mounted about a collar 32 set ing 36.

Drop

fire clay, for example. In the construction shown in either Fig. 3 or 4, the drop tube may be readily removed by breaking the fire clay seal and lifting the tube until ity is clear of the openings through which it extends.

In carrying out a burning operation for the revivification of oil saturated fullers earth, for example, the mineral absorbent is supplied to the uppermost hearth 2 by means of a screw feed mechanism I5 and subjected to indirect heating by heat from the combustion chamber 3 in its passage over the hearth 2. From hearth 2 the absorbent passes by drop tubes I8, extending through combustion chamber 3 to hearth 4, from whence it is carried by the rabbles I6, in a generally downward direction, through the furnace passing successively across the hearths 6,1,8, 9, III, II, I2, I3, and I4, from the last of which it is discharged through outlet 2I to collection means. Vapors evolved from the absorbent undergoing treatment in distillation hearths 6 and I pass through drop tubes I8 to hearth 4 and from hearth 4 through drop tubes I8 to hearth 2 from which they escape through gas outlet connections 22 to a condenser or stack (not shown). An opening 35 is shown provided in hearth 9 for burners (not shown) to complete the burning of the absorbent. Burners may, however, be located on one or more of the hearths in the lower section of the furnace, depending on the amount of heating necessary to complete the burning operation. Combustion gases and vapors driven off from the absorbent in the lower or oxidizing part of the furnace escape through stack opening 36 and are not permitted to come in contact with material in the upper section of the furnace. sages for the escape of gases to the stack open- Pyrometer means, such as those shown at 38, may be provided for indicating the temperature to which the absorbent is heated.

As previously noted the appartaus of my invention is in effect divided into two parts, an upper part in which separation of absorbed oil by vaporization from the absorbent, without combustion of such oil is effected, and a lower part in which the burning of the absorbent is completed in much the usual manner. Passage of material through the chutes 20 to maintain a seal to prevent passage of gases from the lower part of the furnace to the upper part of the furnace may be controlled in any conventional manner.- In the apparatus illustrated in Fig. 1 counterpoised closure means 40 adapted to maintain a predetermined weight of material in the chutes 20 are shown.

The apparatus of my invention enables the burning operation to be carried out under highly advantageous conditions. By the provision of distillation hearths heated indirectly by combustion chambers having tubes sealed with respect to the combustion chambers extending therethrough, the absorbent is burned out of contact with the heating medium both in its passage over the distillation hearths and in, the passage through the tubes and the separation of absorbed oil is effected in the upper part of the furnace by Ports or openings 31 provide pas-- vaporization from the absorbent without combustion of the oil and difiiculties due to uncontrolled combustion are avoided. Further, the separation of oil in the upper part of the furnace avoids irregularities or uncontrolled combustion on the hearths in the lower part of the furnace to which the material from which oil has been separated by vaporization on the hearths 2, 4, 6, and I is (not shown), inserted through aperture 35. The

supply of fuel from these burners, being independent of the rate of supply of the absorbent to these hearths is readily susceptible to control.

The temperature to be employed in the burning operation will vary depending on the particular material being treated. In burning operations for the recovery of oil saturated clays, fullers earth, for example, the absorbent may be heated to temperatures from 700 F. to 1250? F.,

in the hearths in the upper part of the furnace. -Heat necessary to complete burning of the abshows improved absorption efiiciency. In somecases, the absorptive efiiciences of the absorbent are actually battered as compared to fresh, unused absorbent, when recovered in the apparatus of my invention. The useful life of the absorbent may also be prolonged when recovery is effected in the apparatus of my invention. Recovered in the apparatus of my invention, the absorbent may be reused as many as twenty times, or more, for example, before its efliciency as an absorbent falls to a point making repeated use uneconomical.

I claim:

In a multiple hearth furnace, comprising a series of superimposed hearths and a corresponding series of rabble arms driven from a common vertical shaft for moving solids over the several hearths and generally downwardly through the furnace, the improvement which comprises means for isolating the atmosphere over hearths in the upper part of the furnace from that over hearths in the lower part, combustion chambers arranged beneath the hearths in said upper part with means for isolating the atmosphere in said combustion chambers from that over the hearths in said upper part and with means for indirectly transferring heat from said combustion chambers to such solids moving over the hearths in said upper part, and removable tubes closed with respect to said combustion chambers and extending through each of said combustion chambers for conveying solids downwardly respectively

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