US2018242A - Rotary hearth furnace - Google Patents

Description

Oct; 22, 1935. F. F. VON SCHLIPPENBACH 2,018,242

ROTARY HEARTH FURNACE Filed April 21,

2 Sheets-Sheet 1 Fig.1

Oct. 22, 1935. F. F. VON SCHLIPPENBACH 2,018,242

ROTARY HEARTH FURNACE Filed April 21, 1934 2 Sheets-Sheet 2 Patented Oct. 22, 1935 UNITED STATES 2,018,242 ROTARY HEARTH FURNACE Felix Freiherr von Schlippenbach, Malaga, Spain, assignor to American Lurgi Corporation, New York, N. Y., acorporation of New York Application April 21, 1934, Serial No. 721,799 In Germany April 25,1933

16 Claims.

This invention relates to a rotary hearth furnace, which is used for the production of lead by the roasting reaction process.

The roasting reaction process for the treatment of sulphidic lead ores consists, as is well known in the art, in blowing air through tuyeres into the hot ore which rests on a bath of molten lead. By the introduction of air lead sulphide is partially roasted and forms lead oxide and lead sulphate which react with the other part of lead sulphide, producing sulphur dioxide gas and molten metallic lead which trickles down through the charge into the lead bath. The

\ molten lead and the residues of the process are removed from the furnace from time to time and in the same proportion as fresh sulphidic ore is added.

This new ore which is mixed usually with some fuel, as coal or coke, sinters or melts together very soon and this makes it necessary that the charge in front of the tiwres be rabbled quite often thus enabling the air introduced by the nozzles to pass through the charge in a finely distributed form. In the past the so-called Scotch hearth furnace was used to carry out this process, the ore being rabbled by hand. This .work was extremely difficult for the workmen, who were constantly in the danger of being lead-poisoned by the fumes escaping from the open hearth furnace. order to increase the production the Scotch hearth furnace was improved later by the provision of water-cooling, increasing the number of tuyres; extension of the hearth to arlength of 2400 mm., and above all through the introduction of stirring equipment, to such an extent that, at the present time, one third of the total lead output is produced by the roasting reaction process.

The type of mechanical rabbled furnace which has found the widest application at the present time is the Newnam open hearth furnace which is described in detail in Liddell, Handbook of Non-Ferrous Metallurgy, page 899-900.

Against the advantage of using stirring apparatus, however, certain disadvantages must be considered. The apparatus is complicated, since three different movements are involved in its operation. Automatic reversing at the ends of the hearth is, feasible, but unreliable and, in addition, the apparatus must be stopped for a period of 60 to 90 seconds after completing the stirring, so that reversing of the rabbling machine by hand is necessary.

The worst drawback however, is that, in breaking up the charge, the rabble loosens it to such an extent that, even with full draught and the employment of hoods, the air blast through the tuyere inevitably forces lead fumes into the room occupied by the workers, through the wide-open breast of the furnace, with the result that, in the long run, lead-poisoning of the workers is unavoidable. 'Moreover, they are greatly troubled by the radiant heat, especially in summer, since they stand, without protection, at a short distance from the hot, open breast.

The rotary hearth furnace of the present invention removes these three defects.

The invention consists in a hearth furnace, which is annular and rotates around its axis and which is almost completely enclosed by a hood. One or more rabbling apparatus are provided and the bars of the rabbling apparatus pass through the hood at one point through a small hole.

It is an other object of the invention to provide a central windbox by which the air is distributed to the various tuyeres.

A further object of the invention is to provide the furnace with an annular water-cooled wall which also rotates and issituated above the inner part of the hearth. It is also within the contemplation of the invention to rotate only the hearth and the windbox and the cooling chamber while the hood and the rabbling apparatus remain stationary.

A further object of the invention is to drive the stirrer by an eccentric spaced from the hood and to which one end of the stirrer is fastened,

a roller being provided on the hood, at that point where the bar projects through the hood to give a support for the bar of the stirrer.

Other objects and advantages will become apparent from the following description taken in con-junction with the drawings, in which:

Fig. 1 illustrates diagrammatically and by way 40 of example, a preferred embodiment of rotary hearth furnace.

Fig. 2 is another embodiment of the rotary hearth furnace according to the invention, and

Fig. 3 is a cross-section on the line ab in away from the furnace is reduced by half in comparison with that of the known furnace. This is of importance because the condensation of the fumes is materially facilitated, improved and cheapened.

Under the described circumstances the velocity of the air in the door openings is twice as great as before, thus preventing lead fumes and gases from being forced through the doors into the working room. As most of the fumes occur during the rabbling operation it is of advantage to have the rabbling devices located at a. certain distance from the working door.

Incrustations over, in front of and below the tuyres are prevented, inasmuch as the strokes of the rabble overlap, which cannot occur in the known hearth furnace constructions during the intermittent advance of the stirring apparatus, this latter condition necessitating frequent cleaning out of the furnace by hand--a hot and inconvenient operation causing great loss of time.

In order more clearly to disclose the invention, reference is made to the accompanying drawings, which illustrate diagrammatically and by way of example, a preferred embodiment of rotary hearth furnace.

In said drawings:

I is the circular, half-round section trough of the hearth, 2 a channel-iron spider running on the king-post 3 and rollers 4 and with which rotate the members I, 9, IO, M and I6, whereas the members l2, l3, l4, 6, 8, 28 and 2! are stationary. 5 is the drive, consisting of crown wheel, driving pinion and motor, with speed-reducing gear. 8 is a driven disc or eccentric imparting a substantially elliptical movement to the rabble I, which rests on the roller 8, so that the semicircular wall of the hearth, and the mouths of the tuyeres are cleared of incrustations.

Moreover the rotation of the hearth, the speed of the disc 6 and the width of the rabbleare so arranged that, for example, with a rabble 40 mm. wide, the hearth only travels through a distance of 35 mm. between two movements of the bar,

thus causing the strokes to overlap so that no' portion of the hearth can remain unscraped.

9 is the windbox, with the taper tuyeres 9a.

Ill is the annular cooling jacket which is connect ed with pipes (not shown in the drawings) to introduce and take away the cooling medium and has a cooling surface 44% smaller than in existing furnaces of the same hearth furnace. II is a water tank into which dips the air pipe l3 attached to the stationary hood l2. hopper mounted in the said hood. I5 is an adjustable scraper for dislodging the charge material, carried on the ledge i6, behind the door, in order to cover the hot charge and pi' event vaporization. I1 is the working door for removing the slag and. pushing back any of the hot charge that has rolled down on to the outer ledge l8. This ledge is on a lower level than the inner flange l8a, in order to prevent any lead, gaining access between it and the windbox. I9 is the outlet channel for the lead rising from below. 20-- is the gas outlet, provided with a valve 20a for regulating the draught. 2| is a conical hood carried by the air pipe l3 and preventing dust from falling into the water tank II and between the latter and the cooling jacket I 0.

' Bar 1 of the rabbling mechanism may or may not be water cooled and has an edge at its free end which may be interchanged. Its driving mechanism is mounted laterally in relation to the working doors in such a manner that the i4 is the feed.

fumes issuing from the tuyeres underneath the loosened charge impinge, laterally in relation to the door, against the wall of the hood, which is provided only with a hole for the passage of the rabble, so that no fumes can escape into the li workroom.

Since the charging of the furnace proceeds automatically, only one man is needed at the door opening to remove the slag and push back any of the charge that has rolled forward, whereas the Newnam hearth with stirring apparatus necessitates considerably more manual work.

In the case of a modern Newnam furnace 2400 mm.- long, with open breast and top hood, the free aperture, withan area of 1.44 sq. metres, is 4.4 times as great as the door (0.8 x 0.4 metre) of the rotary hearth of the present invention.

. In the rotary hearth furnace of the present invention the volume of the exit gas can be about half or less of that of a Newman open hearth 20 furnace.

This cuts down considerably the cost of condensing fumes and gives at the same time a higher degree of protection for the workmen as the velocity of air entering the hearth furnace 25 under such conditions is still about 2.2 times as great as that of the'open hearth, thereby eifec: tually preventing the escape of fumes into the working room and the man in front of thedoor is practically not inconvenienced by the heat.

Figs. 2 and 3 show another apparatusfor carrying out the invention.

The hearthl which rests on the iron wheel 2, rotating onrollers 4 and the drive 5 are the same as in Fig. l. The inner flange I8a, the outer ledge l8, the outlet for the molten lead I 9, the'rabbling device 6, ,1, 8, the feedhopper H, the scraper l5, ledge 66 and the gas exit and 20a can also be constructed in the same manner.

In Figs. 2 and 3 the air is introduced from below. The king post 23 is made hollowfor this reason and is connected with the wind pipe 24. The tuyeres 25 are interchangeable and may be made of cast iron. They are connected in a. gastight manner with the cooperating part of the wind-box 22.

The hearth I consists of four or more segments and is surrounded by heat-insulating material 26. The hood 21 has double-walls in order todecrease the radiation of heat.

The cooling .jackets 28 are made of different parts, which can be removed separately from the furnace in case of repair through, an opening in the hood, which can be closed by a cover plate Fig. 2 shows a hood, which does not cover' the center of the hearth furnace and which allows easy access to the back-wall 30 and to the man- 'hole 3| in the wind-box 22.

contains water or sand to produce a gast-ight seal 65.

between the stationary hood 2! and the rotating parts i, 22, 28, 32, etc.

A special seal between the lower edges of the hood 21- and the outer flange l8 of. the hearth is usually not necessary but care is taken that 7,,

the distance between these two parts is as little as possible.

The number of working doors may be in direct proportion to the number of chargingand rabbling devices or may be different, if special ,5

work has to be done. In Fig. 2 a furnace with doors and two scrapers and two rabbling devices is shown.

The cooling water runs from pipe 36 for instance to an annular trough 31 which is fixed on the cylindrical wall 32. The trough 31 rotates and is connected by pipes 38 with the diflferent jackets which have overflows 39 and run-off pipes 40 which lead to the stationary run-off trough 4|.

The molten lead runs from the spout l9 to a container 42 which is mounted on a car 43 running on a track around the furnace pulled by the hearth, to which it is fastened.

Otherwise, the furnace according to Figs. 2 and 3 may be constructed in the same way as described in Fig. l.'

With a hearth of increased area, the furnace is accordingly provided with a larger number of tuyeres, working doors, lead outlets, scrapers and rabbling devices for breaking up the charge.

I claim:

1. A rotary hearth furnace for the production of lead from sulphide ores comprising an annular rotary hearth, a stationary hood above same, said hood extending close to the outer rim of the hearth, a windbox in the center of the hearth with tuyeres which open on to the hearth, a rabbling device with a stirrer which extends through an opening in the hood to the hearth, means for delivering ore to the hearth, means for tapping lead from the hearth, and a working door for handling the charge on the hearth.

2. A rotary hearth furnace for the production of lead from sulphide ores comprising an annular rotary hearth, a stationary hood above same, a windbox in the center of the hearth with tuyeres which open on to the hearth, a rabbling device with a stirrer which extends through an opening in the hood to the hearth, means for delivering ore to the hearth, means for tapping lead from the hearth, and a working door for handling the charge on the hearth, the rabbling device being arranged laterally adjacent the working door.

3. A rotary hearth furnace for the production of lead from sulphide ores comprising an annular rotary hearth, a stationary hood above same, a windbox in the center of the hearth with tuyeres which open on to the hearth, a rabbling device with a stirrer which extends through an opening in the hood to the hearth, a working door for handling the charge on the hearth, means for delivering ore to the hearth, means for tapping lead from the hearth, the rabbling device and. the means for delivering ore to the hearth being arranged each laterally adjacent the working door so that the charge shortly after being rabbled and worked is covered with fresh ore.

4. A rotary hearth furnace for the production of lead from sulphide ores comprising an annular rotary hearth, a stationary hood above same, a windbox in the center of the hearth with tuyres which open on to the hearth and taper toward their openings, a rabbling device with a stirrer which extends through an opening in the hood to the hearth, means for delivering ore to the hearth, means for tapping lead from the hearth, and a working door for handling the charge on the hearth.

5. A rotary hearth furnace for the production of lead from sulphide ores comprising an annular rotary hearth, a stationary hood above same, a windbox in the center of the hearth with tuyeres which open on to the hearth, rabbling devices each of which comprises a stirrer which extends through an opening in the hood to the hearth, a water cooled wall above the inner rim of the hearth, means for delivering ore to the 5 hearth, means for tapping lead from the hearth and workingdoors for handling the charge on the hearth, each working door being situated between a rabbling device and a means for charging ore to the hearth, the rabbling .device lying 10 before and the charging means behind the door with reference to the direction of rotation of the hearth.

6. A rotary hearth furnace as defined in claim 1 in which the rabbling device comprises a water 15 cooled bar, a revolving disc to which one end of the bar is rotatably secured situated outside the hood and spaced therefrom, and a roller underneath the opening in the hood for supporting the bar.

7. A rotary hearth furnace as defined in claim 1 in which the rabbling device comprises a bar, a revolving disc to which one end of the bar is rotatably secured situated outside the hood and spaced therefrom, a roller underneath the open- 25 ing in the hood for supporting the bar and an exchangeable edge on the free end of the bar.

8. A rotary hearth furnace as defined in claim 1 in which the rabbling device comprises a water cooled bar, a revolving disc to'which one end of the bar is rotatably secured situated outside the hood and spaced therefrom, a roller underneath the opening in the hood for supporting the bar and an exchangeable edge on the free end of the bar. 35

9. A rotary hearth furnace as defined in claim 1 in which the rabbling device comprises a bar, a revolving disc to which one end of the bar is rotatably secured situated outside the hood and spaced therefrom, and a roller underneath the 40 opening in the hood for supporting the bar, the tuyres being so located with respect to the path of movement of the free end of the bar as to be kept open thereby. 10. A rotary hearth furnace as defined in claim 45 l in which the hearth is approximately semicircular in vertical cross-section and in which the outer edge of said hearth is lower than its inner edge, the outer edge having an outlet for the lead. 1

11. Arotary hearth furnace as defined in cla 5 in which the water cooled wall above the inner rim of the hearth is made up of replaceable sections.

12. A rotary hearth furnace for carrying out 55 a continuous roasting reaction process comprising an annular hearth of substantially semi-circular cross-section having an outer flange provided with a discharge spout at a lower level than the inner edge of the hearth, a spider, a 6 king post and rollers rotatably supporting said hearth, a stationary hood above the hearth, a rabbling device comprising a bar actuated by an eccentric and supported by a roller and extending through the hood to the hearth, a windbox in 65 the center of the hearth with tapered t uyeres opening on to the hearth, a water cooled wall extending upwardly around the inner edge of the hearth, a charging hopper, a ledge rotating with the hearth upon which charge material is deposited from said hopper, an adjustable'scraper for scraping charge material from said ledge on to the hearth, means for supplying. air to the windbox through said king post, a dust hood above the windbox, and a working door in the first named hood.

13. A rotary hearth furnace for smelting lead ores which comprises a horizontal rotatable hearth having a ring like trough,- a windbox located in the central region of said hearth, a plurality of tuyeres associated with the inner rim of said hearth, a stationary hood operatively associated with said hearth and defining therewith an enclosed chamber, rabble arms projecting through said hood for stirring material in said hearth, a working door in said hood for working material in said hearth, means for rotating said hearth, means for radially reciprocating said rabble arms, means for feeding a charge to said hearth through said hood means for'conveying air to said tuyeres, means for withdrawing gases from said enclosed chamber, and means for withdrawing smelting products from said hearth.

14. A rotary hearth furnace for smelting lead sulphide ores which comprises a horizontal rotary hearth having an annular trough, means for rotating said hearth around its vertical axis, an internally cooled substantially annular back extending upwardly from the inner rim of said hearth and rotating therewith, a windbox located in the central region of said hearth, a plurality 'of tuyres associated with the inner rim of said rotary hearth at spaced intervals of the circumference thereof, a stationary hood operatively associated with said hearth and defining therewith an enclosed chamber, rabbles extending through said hood for stirring material in said hearth, an eccentric drive for radially reciprocating said rabble arms, working doors in said hood for working material in said hearth, said working doors being at a spaced interval from said rabbles, means through said hood for feeding a charge to said hearth, means for conveying air to said tuyeres, means for withdrawing gases through said hood, and means for withdrawing smelting products from said hearth.

15. A rotary'hearth furnace for smelting lead sulphide ores' which comprises a horizontal rotatable hearth having an annular trough, means for rotating said hearth around its vertical axis, a substantially annular water jacket extending upwardly from the inner rim of said hearth and rotating therewith, a windbox located in the central region of said hearth, a plurality of tuyres associated with the inner rim of said hearth at spaced intervals of the, circumference thereof, a stationary hood operatively associated with-said, hearth and defining with said hearth and with. said jacket a substantially enclosed chamber, rabble-arms extending through said hood for stirring material in said hearth, means for radially reciprocating the working end of said rabblem arms in a substantially elliptical path, working doors in said hood for working material in'said hearth, said working doors being located at spaced intervals from said rabble-arms, means through said hood for feeding a charge to said hearth, 1 5

means for conveying air to said tuyres, means for withdrawing gases through said hood, and means for withdrawing smelting products from said hearth.

16. A rotary hearth furnace for smelting lead 29;-

sulphide ores which comprises a horizontal ro-. tatable hearth having an annular trough, means for rotating said hearth around its vertical axis, a substantially annular water cooled jacket extending upwardly from the inner rim of said hearth 25.

and rotating therewith, a windbox located in the central region of said hearth, a'plurality of tuyeres associated with the inner rim of said hearth at spaced intervals of the circumference thereof, a

stationary hood eperatively associated with said 30-.

rotary hearth and defining with said hearth and with said water cooled jacket an enclosed chamber, rabble-arms extending through said hood for stirring material in said hearth,

an eccentric drive outside of said hood and at a spaced interval therefrom for axially reciprocating said rabbles, means through said hood for feeding a charge to said hearth during the rotation thereof at regions spaced fromsaid rabbles, working doors in said hood for working the charge in said hearth, each working door being situated after a rabble and before a feeding device with respect to the direction of rotation of the hearth, means for conveying air to saidtuyeres, means for withdrawing gases from said hood, and means for withdrawing smelting products from said hearth.

FELIX FREIHEER VON SCI-ILIPPENBACH.

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