US2646900A

US2646900A - Ore treating furnace

Info

Publication number: US2646900A
Application number: US6743A
Authority: US
Inventors: Carl W Sisco
Original assignee: Erie Mining Co
Current assignee: Erie Mining Co
Priority date: 1948-02-06
Filing date: 1948-02-06
Publication date: 1953-07-28
Anticipated expiration: 1970-07-28

Description

July 28, 1953 c. w. slsco 2,646,900

ORE TREATING FURNAC'E Filed Feb. e., 194s v e 'sheets-sheet 2 If-n.. u u l July 28, 1953 Filed Feb. e. 1948 fsa-Xb C. W. SISCO' ORE TREATING FURNACE 6 Sheets-Sheet 3 .my 2s, 1953 Filed Feb. 6, 1948 C. W. SISCO ORE TREATING FURNACE 6 Sheds-Sheet 4 July 28, 1953 c. w. slsco 2,646,900

ORE TREATING FURNACE Filed Feb. e, 1948 5 sheets-sheet 5 July 28, 19

Filed Feb. 6,

C. W. SISCO ORE TREATING FURNACE 6 Sheets-Sheet 6 Patented July 28, 1953 ORE TREATING FURNACE Carl W. Sisco, Toledo, Ohio, assignor toy Erie Mining Company, Hibbing, Minn., a corporation of Minnesota Application February 6, 1948,' Serial No. 6,743

12. Claims.

This invention relates in general to furnaces and in particular to an improved method of and apparatus for maintaining the stockline of a fur-V nace for thermally treating solids such as ore fragments, pellets of finely divided mineral solids such as ore concentrates and the like, at a pre-A selected. level.

The invention is particularly adapted to stockline control in an ore furnace of the pelletindurating type disclosed andrclaimed in an application for United States letters patent Serial No. 605,861, filed July 19, 1945, now Patent No. 2,533,142, by Percy H. Royster, entitled Heat Treating Solids, and will be so described and illustrated in the present application. However, l wish it to be understood that the invention is not limited to this particular type of furnace but rather can be applied to any other type ,of shaft furnace wherein the fluent solid material to be treated is continuously fed into the furnace at the top and discharged at the bottom thereof.

Generally speaking, the new method of stockline control involves the steps of continuously measuring the stockline in the furnace and controlling the rate of the discharge from the latter in accordance with the measurements taken to the end that a rise in the stockline above the preselected level results in an increase in the discharge rate of the furnace while a fall in the stocliline below the preselected level results in a decrease in the rate at which the material is highly desirable when the invention is applied to an indurating furnace of the type described in the above mentioned Royster patent application but can be omitted under some circumstancesV in other furnace applications. Various arrangements for practicing the method can be employed but in the present application, the

. preferred apparatus is comprised in general of a feeler type of level measuring device which rides continuously in substantially surface con-y tact with the stockline in the furnace, except when the stockline sinks to a very low level, and an associated electrical control circuit Awhich transforms any change in the measured level of the stockline into a change in speed 'ofl the discharge device.

(Cl. 21d-18.2)

Another aspect of the invention is to provide a discharge control for a furnace of the class described whereby the motion of a part of the device by which the material is fed into the furnace and the varying level of the material in the furnace combine to effect a change in the rate of operation of the discharge feeder for the material.

A .still further aspect of the invention is to provide a discharge control system for furnaces in which fluent material is treated, the conditions requisite to its functioning being the uniformly moving part of a device that feeds the material into the furnace and the variable level of the material by means of which a discharge feeder is automatically regulated to maintain the level of the material, i. e. the stockline, substantially at a preselected height in the furnace.

The foregoing and other objects and advantages of the invention will become more apparent from the following description and the accompanying drawings which illustrate a preferred embodiment of the invention as applied to the type of indurating furnace disclosed in the aforesaid Royster patent application.

ln the drawings, Fig. l is a diametral vertical section of the furnace, the feeders for loading the material intothe top thereof and the feeder for discharging the material from the bottom being shown somewhat schematically in order to simplify the drawings; Figs. 2 and 3 are larger scaled plank and side elevations, respectively, of the feeler mechanismby which the stockline of the material is measured; Fig. 4 is a schematic diagram showing vthe circuit arrangement for the principal operating components ofthe new control; and Figs. 5, 6 and 7 are sub-circuit diagrams illustrating the positions of the various elements in the control for widely different levels of the stockline.

Referring now to the drawings, and to Figs. 1-3 in particular, the ore pellet indurating furnace designated generally by numeral 9 is seen to be comprised of a pair of thermally insulated chambers Il), il disposed one above the other and which are interconnected by a central cominunicating passageway l2 of restricted crosssectional area through which the ore pellets I3 descend by gravity during the heat treating process from the upper chamber IB to the lower chamber Il. The furnace wall structure is so designed that the ore pellets during their downward course through the furnace leave a substantially annular void ifi between the lower part of the upper chamber ill and the tapered free surface i5 of the pellet'charge, and a similar annular void l5 between the upper part of the lower chamber H and the tapered free surface l? of the pellet charge. ri'he upper and lower annular voids ifi, it are connected through conduits i3, i3 to the exit and intake ends of a combustion chamber 2l having a burner unit 22 y which fuel is injected and burned.

Functionally associated with the combustion chamber 22 is a blower 23 for carrier gas such as air, the discharge from which takes place through a distribution head 2d located within the lower part of the lower chamber Il. Blower 23 forces a current of the carrier gas in an initially unheated state upwardly through the ore charge in the lower chamber Il to the annular void l5, thence through conduit I9 into combustion chamber 2! where it takes on heat from the burning fuel. The now hot gas passing outwardly through conduit I8 is distributed around the void lli and iiows upward through the ore pellet charge in the upper chamber l0 to heat treat and harden the pellets. The carrier gas is ultimately discharged to atmosphere through the open top of chamber i9 at a temperature which in the ideal case is not materially above that at which the cool pellets enter the furnace.

Under ideal operating conditions, the volume of carrier gas per unit of time introduced into the lower end of chamber H from the blower 23 is so adjusted with regards to its heat capacity and the heat capacity of the ore pellets in the lower chamber that substantially all, cr at least a very large part of, the heat carried into the lower furnace chamber by the heat treated pellets descending from the upper furnace chamber lil is abstracted from the pellets during their downward progress through the lower furnace chamber to the end that the pellets are ultimately discharged from the bottom of the lower chamber at a temperature which is not materially higher than that of the carrier gas as introduced into the lower chamber.

The ore pellets to be heat treated can be loaded into the top of chamber lll by various known types of loaders but the particular type preferre is described in detail in a pending application for United States Letters Patent, Ser. No. 784,220, led November 5, 1947, by Ernest G. de Coriolis and Rollie P. Campbell for a Furnace Loading Mechanism. particular type of loader, shown somewhat diagrammatically in Fig. l, is seen to be comprised of a power driven vertical spindle 25 rotating on an axis coincident with the vertical furnace axis and three motor driven

loaders

26, 21, 25 located in a vertical spaced relation and having down.- wardly inclined reciprocating trays which overlap. The motor elements of the loaders are shown schematically by coils 29, 3@ and 3l. The topinost loader 25 is stationary and receives the ore pellets in a raw i. e. initially moist state from an ore processing station (not shown) ahead of the furnace. The two lower loaders 2l, 2S are mounted upon a rotatable carriage 32 that is secured to and driven by the spindle 25 at a relatively slow speed which, for example, can be of the order of one revolution per minute. As the loaders 2l, 28 reciprocate and simultaneously slowly rotate, the ore pellets will be ultimately discharged from chutes 33 associated with the lowermost loader 28 and deposited in layers onto the stockline 34 of the -pellet charge within the furnace chambers.

Electrical power for driving the spindle 25 and the loaders 26-28 is obtained from a suitable In the vpresent application, this source over a circuit which is described later in more detail and the motor connections for the two rotating loaders 2, Z8 are made by way of slip rings 35.

During a normal operation of the complete system for forming and treating the pellets, the latter are fed continuously into the top of the furnace and progress downwardly therethrough to a discharge feeder capable of being operated at a variable rate, the latter beine adjusted automatically in accordance with the principles of the present invention to maintain the stoclzline Sli at a substantially constant level. The discharge feeder may be of any conventional type such a star gate, rotary disc, belt unloader or reciproeating unloader. The latter type is illustrated in the present application and is seen to be conN stituted by an inclined chute 35i leading from a bottoni opening in the lower furnace chamber I i to a motor driven, reciprocating tray 3l. The motor element of the unloader is shown schematically as a coil 3S that is energized with direct current of variable amplitude over a control cirn cuit that will presently be described, so to automatically adjust the discharge rate of the pellets from the furnace as may be rcdu ed to maintain the pellet stoclzline 3d at the preselected level near the top of the upper furnace chainber Hl.

The device for measuring the stockline level 5ft is comprised of a cup il or feeler secured to the lower end of an arm 42. rhe upper end of the latter is fixed to a shaft d3 which .-s journalled in openings in spaced plates :33:5 for rotation on a horizontal axis with the rise and fall of cup il! which iloats on the surface of 'the pellet charge, i. e. at stockline 32,. Rotation of shaft i3 is imparted through linkage ifi to another shaft l? also arranged for rotation on a horizontal axis and supported by journal brachw ets 4B. Projecting radially from shaft il and. non-rotatable with respect thereto are a of arms 4Q, 5G arranged at different angles with re spect to the axis of shaft ll. Arm carries a mercury type switch 5 I and arm 5l? similarly carries a mercury switch 52 but at a different angun lar position (see Fig. 3) as regards the switch contact axis so that the two switches open or close a circuit through their contacts at different angles of repose. Linkage :le is so arranged that a rise in the cup 4I resulting in clockwise rotation of shaft d3, as viewed from Fig. 3, effects a counterclocliwise rotation of shaft l? and the switches 5l, 52 supported thereon, vice versa.

When the feeler cup il occupies the position shown in Fig. 3 where the stockline 3d is at the normal level, switches 5|, 52 will both be open. A drop in the stockline below the normal level will have no effect upon either of the switches 5i, 52 so far as the circuits through their contacts are concerned but, nevertheless, results in a decrease in the operating rate of the pellet discharge device 3'? at the bottom of chamber il. However, a limited rise in the stockline above normal causes switch 52 to close; and a still further rise in the stoclrline to a so called cutoff level causes switch 5l to close. Closure of switch 52 eifects an increase in the operating rate of discharge device 3l while closure of switch 5I is effective to stop the three pellet loading devices 25-28. More about these controls will be said later.

I prefer that the stockline measuring device be arranged to rotate with the two

rotatable loading devices

21, 28. Accordingly as seen in Figs. 1 and 2, the plates 44, 45 and the bearing brackets 48 for the cup 4|, shaft 43, linkage 46, shaft 41 and switches 5|, 52 are secured upon the loader carriage 32 that is comprised of a pair of spaced

channel beams

54, 55 and plates 56, 51 which extend horizontally at the top of the furnace. The cup 4|, as seen in Fig. 1 is located on cordance with a changel in levelof the s tockline 34 is shown schematically in Fig. 4. Asfpreviously explained, the discharge feeder includes a tray 31 that is reciprocated electrically by a motor of the vibrator type, represented schematically by coil 38. Pulsating direct current for energizing coil 38 in rapid succession is derived from a diode 58 that functions as ahalf wave rectifier, the latter operating off an alternating current source indicated by

lines

58, 66. Transformer 63 is used to supply the power for heating the lament of diode 56.

The operating rate of the discharge feeder is varied by varying the Ymagnitude of the current that passes through coil 38. An increase in current will effect an increase in the-rate at which the pellets are removed from the furnace chamber while a decrease in current is effective to slow down thhe pellet discharge. Regulation of the current ow through motor coil 38 is obtained from a rheostat 64 including a resistance winding 65 connected in series therewith. lIhe effective or in-circuit resistance of the rheostat is adjusted by a wiper arm 68 that is attached to and rotated by a shaft V|51 that is coupled to the armature 68 of a drive motor 89 operated from the A. C. lines 59-60. Motor 69 is provided with a pair of field ycoils 10, 1| which are alternatively energized for driving it in one direction or the other. The motor is of conventional type and includes a set of reduction gears (not shown) for reducing the speed of shaft 61 to approximately 1/5 R. P. M. for driving the rheostat arm 66. Y

Motor 66k is energized only periodically and runs for a brief period during each revolution of the

pellet loaders

21, 28 and the stockline level measuring cup 4|; the direction of motor rotation will depend upon the stockline level and the duration is controlled by a metering cam 12 having a raised cam surface 12a., extending through an arc of approximately 20, in conjunction with a pair of limit switches 13, 14 that are actuated by this cam. The metering cam 12, is mounted to rotate with shaft 25 which as will be remembered rotates quite slowly at l R. P. M.

If the stockline is above the normal level as measured by the cup 4|, the armature 68 of motor 69 will rotate clockwise thereby also turning rheostat arm 66 from the mid position on the resistance winding 65 clockwise and reduce the amount of resistance in circuit with the motor coil 38 driving the discharge feeder tray 31. If the stockline be at or below the normal clockwise to increase the vin-circuit resistance of rheostat 64 and thereby reduce the current through motor coil 38.

Associated in circuit with the limit switches 13, 14 and the control in general are four relays 15, 16,711 and 18. Relay 15 has a pair of contacts 15a, 15b and functions to place the entire control into operation or stop it. Energization of relay 15 is obtained from the

line conductors

59, 60 and is controlled by a pair of push button Start and Stop switches 8|, 82, respectively. Relay 16 is of the latch type having a latching coil 16a and a trip coil 1612. Momentary energization of coil 16a, effects a closure of the relay contact 16e and the blade 16d for the latter is then held in this position by a latching device consisting of pawl 16e and spring 16f. When the trip coil 1612 is momentarily energized, pawl 16e is pulled away from the blade 16d allowing spring 16g to open the contact 16o. As will be seen from the circuit diagram, closure of limit switch 13 by cam 12 energizes the latch coil 16a of relay 16 and the subsequent closure of limit switch 14 by this same cam energizes the trip coil 1612.

Relay 11 has an energizing coil 11a and three sets of contacts 11b, 11e and 11d. In the deenergized state, relay contacts 11b, 11e are open and contact 11d closed. When relay coil 11a is energized, contacts 11d open and contacts 11b, 11e close.

Relay 18 has an energizing coil 18a, and a pair of contacts 18h, 18e. Contact 18h closes and 18C opens when coil 18a is energized; when deenergized, contact 1811 opens and 18e closes.

The control circuit is completed by a cam 83 mounted on the shaft'61 to rotate therewith and which includes a raised cam surface 83a the center of which is radially aligned with the rheostat arm 66. Actuated by the cam surface 83a are a pair of

limit switches

84, 85. Switch 84 is actuated by the cam surface 83a when the rheostat arm 66 has turned to an extreme position in a counterclockwise direction and switch 65 is actuated when arm 66 has shifted to a corresponding position in a clockwise direction. As will be explained later in more detail, limit switch 84 functions to stop the operation of the discharge feeder 31 completely, while switch 85 functions to stop the loaders 26-28.

Operation In general the control system is arranged so that once during each revolution of the

pellet loaders

21, 28, the pellet discharge feeder 31 receives an impulse t0 increase or decrease its speed depending upon the level of the stockline 34. The relative adjustment in angular displacement around the metering cam 12 of limit switches 13 and 14 will determine the period that the rheostat drive motor 69 is energized and therefore governs the change in setting of the rheostat arm 66 for each revolution of the

pellet loaders

21, 28. In the illustrated circuit, limit switches 13--14 are approximately 96 apart. Hence for each revolution of cam 12, motor 69 will be energized for 15 seconds, During this period, shaft 61 driving the rheostat arm Y66 will have turned through 18 since shaft 61 was stated to operate at 1/5 R. P. M.

It should be made clear that the control system hunts continuously. That is to say, the setting of the rheostat arm 66 changes by an increment of 18 for each revolution of the loaders '21,` 28 and cup 4|, either clockwise or counterclockwise dependent upon the position of the cup M. When the latter is at or below the nor'- mal stockline level indicated on the drawing in Fig. 4, mercury switch 52 remains `open and the discharge feeder 31 decreases its operating rate by one increment for each revolution of the

loaders

21, 28 that this condition prevails. When the cup -lll rises above the normal level, mercury switch 52 will close and the discharge feeder 31 increases its operating rate by one increment for each revolution of the

feeders

21, 28 that this condition obtains.

A change in level of the stockline may be due to one or a combination of several conditions. The rate at which the raw" initially moist pellets of ore fines (e. g. concentrates) are supplied to the loaders 25-25 may vary slightly thus causing a temporary drop or rise in the stockline. Then too, the vore pellets are somewhat irregular in shape and this leads to the formation of temporary voids in the column of pellets within the furnace that cause the stockline level to vary temporarily. Whatever may be the cause of the stoclrline variation, it is most essential that the stockline of the pellet column be maintained as closely as possible at the level designated on the drawing as normal For a more detailed explanation of the manner in which the control system operates, reference is now made to the circuit diagrams shown in Figs. 4 to 7. To place the system in operation, the Start push button 8| is pressed momentarily. This completes a circuit starting from line 59 through Stop button 82 and Start button 8l to the coil of relay 15 and to the other side of the line 65. This energia-es relay 15 closing its contacts 15a and '55 Closure of contacts 15a establishes a holding circuit for the coil of relay 15 to keep it energized after the Start button 8! is released. Closure of contacts 15b energizes line 86 which supplies power for the remainder of the control components in the system.

The control system for regulating the rate at which the discharge feeder 31 removes the pellets from the bottom of the pellet column is so adjusted that when cup 4| is positioned at the normal level, arm lt5 of control rheostat @il will be in a more or less central position and likewise the cam 83 will be in a central position with both limit switches 8s and 85 released and their contacts in their normal positions as shown in Fig. 4. This being the case, a circuit will have been established starting at line 5S through the filament and plate of diode 58, closed limit switch contact Ma, approximately one half of the resistance winding 55 of rheostat 64 to the discharge feeder coil 38 and to the other side of the line 59. Since this circuit passes through the diode 58 the current reaching the discharge feeder coil (-28 is unidirectional in character and is pulsing at the rate of the Si! cycle alternating current impressed on the system. Under these conditions, the discharge feeder 31 will remove the ore pellets from the pellet column in lower chamber il at a rate that is substantially the mean between its minimum and maximum rates.

Let it now be assumed that the cup il is positioned at the normal level as the carriage 32 rotates and metering cam surface 12a, actuates limit switch 13 to close switch contact 13a. Relay 11 controlled through mercury switch 52 will remain deenergized and its contacts will remain in the positions shown in Figure 4. That is, contacts 11b Aand 11C will be open and contact 11d closed. Closure of contact 13a will now complete a circuit from line 5a through closed relay contact 15b, limit switch contact 13a to the latch coil 16a of relay 16 and then to the other side of the line 60. This energizes relay i6 closing its contact 1&0 which completes a circuit from line 59 through relay contact 15b, relay contact 15C, relay contact 11d, limit switch contact th to the decrease winding 'ii of the rheostat drive motor 5S and then to the other side of the line 65.

The rheostat drive motor starts in a counterclockwise direction to drive rheostat arm 66 in the decrease speed direction. This increases the in-circuit resistance of rheostat 64 thereby reducing the current supplied to feeder coil 38, decreasing the magnitude of its vibrations and thus reducing the rate at which the ore is being discharged. The pulsing rate of the unidirectional current being impressed on the feeder coil 38 remains unchanged. As the ore loaders 21-28 continue to revolve, cam surface 12a releases limit switch 13 opening its contact 13a and deenergizing latch coil 16a of relay 15 but its contact 16C still remains closed because of the latch mechanism. As the loaders 21-28 continue to revolve, cam surface 12a. contacts limit switch 14 closing its contact 14a.. A circuit is completed from line 59 through relay contact 15b, limit switch contact 14a to the trip coil 16h of relay 16 and then to the other side of the line 66. Relay contact 16o opens, breaking the circuit to the decrease winding 1l of the rheostat drive motor 69. The motor armature 68 stops and. the rheostat arm 66 is positioned one increment lower on winding 65 than the previous revolution. As the loaders 21, 26 continue to revolve, cam surface 12a releases limit switch 14 opening its contact 14a. This deenergizes trip coil 15b of relay 16 and the system is now reset and ready for the next cycle.

Since the discharge feeder 31 is now operating at a slower rate, the ore level will tend to rise above the normal level. The corresponding rise in the feeler cup 4l will result in a closure of mercury switch 52. This completes a circuit from line 59 through relay contact 15b, limit switch Contact 1413, mercury switch 52 and slip rings 81 on spindle 25 to the coil 110. of relay 11 and thence to the other side of the line 6l). This energizes relay 11, closing its contacts 11b, 11e and opening contact 11d. Closing of contact 11b establishes a holding circuit for relay 11 to keep it energized in case the stockline might drop slightly and open mercury switch 52 before the revolution of the loaders 21-28 is complete. As the loader mechanism revolves, metering cam surface 12a contacts limit switch 13, closing its contact 13a, completing a circuit from line 59 through closed relay contact 15b, limit switch contact 13a, to the latch coil 16a of relay 15 and then to the other side of the line 60. This energizes relay 16, closing its contact 16C which completes a circuit from line 59 through relay con tact 15b, relay contact 16o, relay contact 11o, limit switch contact 85h to the increase winding 10 of the rheostat drive motor 69 and then to the other side of the line 60.

The armature '68 of the rheostat drive motor starts in a clockwise direction to drive rheostat arm 66 in the increase speed direction. This decreases the in-circuit resistance of rheostat 64 thereby increasing the current through feeder coil 38, increasing the magnitude of its vibrations and thus increasing the rate at which the ore is being discharged. As the ore loaders 21,

28 continue to revolve, cam surface 12a releases limit switch 13 opening its contact 13a, and deenergizing latch coil 16a of relay 16, but its contact 16e still remains closed because of the latch mechanism. As the loader continues to revolve, cam surface 12a. contacts limit switch 14 closing its contact 14a and opening contact 14h which breaks the circuit to the energizing coil 11a of relay 11. Relay contacts 11b and 11c now reopen and contact 11d recloses. At the same time, a circuit is completed from line 59 through relay contact 15b, limit switch contact 14a to the trip coil 1Gb of relay 16 and then to the other side of the line 6G. Its contact 16e opens breaking the circuit to the increase winding 10 of the rheostat drive motor 69. The motor armature 68 stops and the rheostat arm 66 is positioned one increment faster than the previous revolution. Since the discharge feeder 31 is now operating at a faster rate, the ore level will tend to lower. As the loader continues to revolve, cam surface 12a, releases limit switch 14, opening its contact 14a. This deenergizes trip coil 16h of relay 16 and the system is now re-set and ready forvthe next cycle.

Assuming that the stockline falls to the normal level before the metering cam 12 again actuates limit switch 13, the cup 4l will have likewise dropped to the normal level. Thus the next time contacts 13a of limit switch 13 are closed, motor 69 will drive the rheostat arm 66 in a counter-clockwise direction and thereby once again decrease the operating rate of the discharge feeder 31. The stockline 34 now rises above the normal level which then results in an increase in the operating rate of the discharge feeder 31.

This periodic and alternate decrease and increase in the operating rate at which the pellets I3 are removed from the bottom of the pellet column in chamber Il will continue under normal operating conditions thus maintaining the stockline 34 at substantially a constant level.

Next, let it be assumed that for operational causes the stockline 34 has sunk to an abnormally low level as shown in Figure 5. This might happen if the loader mechanism should stop suddenly or if a large void might have occurred in the furnace during the operation, and the ore suddenly dropped to ll this void. In this case, it is desirable to stop the discharge feeder 31 t0 prevent the stockline of the furnace from dropping too low. In this eventthe stockline would remain below the normal level for several revolutions of the

loaders

21, 28 and cup 4|. As previously described, for each revolution of the loaders that the stockline is at the normal level or below, the rheostat arm 66 Will be displaced one increment (i. e. 18) counter-clock- Wise so that after a few revolutions, the motor driven rheostat arm SG will have taken the position shown in Figure 5. Cam 83 likewise will have taken a position similar to rheostat arm 36, since it is driven from the same shaft 61. Cam surface 83a now actuates limit switch 84, opening its contacts 34a and 8th. This will break the impulse circuit which has previously existed from line 59 through relay contact 15b, relay contact 16e and relay contact 11d, limit switch contact 84h to decrease Winding 1l and then to the other side of the line 6B. Opening of limit switch contact 84a opens the circuit to motor coil 38 of the discharge feeder tray 31 thus stopping the'latter. The discharge feeder will now remain cut off until the stockline rises above the normal level.

10 Next let it be assumed that for operational causes, the stockline 34 has risen to an abnormally high level, as indicated in Figure 6. In this case, it is desired that the discharge feeder 3l operate at its maximum rate. As explained previously, in the operation of the system, when the stockline 34 rises above the normal level, the corresponding rise in cup 4! results in a closure of mercury switch 52. If this condition persists during successive revolutions of the loader, the rheostat arm 66 would be advanced clockwise by increments of 18 increasing the ore discharge rate of the discharge feeder 31 with each revolution of the loader, until the maximum rate is reached. This will require several revolutions of the loader. When this happens, cam surface 83a will actuate limit switch 35, opening its contact 85h. This breaks a circuit from line 59 through relay Contact 15b, relay contact T60, relay contact 11e, limit switch contact 85h to the increase Winding 10 and then to the other side of the line 60. .'Ihe rheostat arm 655 will now remain at this maximum rate position until such time as the stockline 34 drops back to the normal level or below.

Let it now be assumed that for operational causes, the rate at which the pellets are fed onto the stockline 34 is greater than the maximum rate at which the ore can be removed from the bottom of the column by the discharge feeder 31. If this occurs, the stockline 3ft would ultimately rise above the rim of the upper furnace chamber lil and spill over the side.v To prevent such an occurrence, a circuit has been arranged to stop the loader feeders 2li-28 when the stockline 34 and hence cup 4l reach the level labeled cut-off. Referring now to Figure 7 which indicates this condition, when cup lll reaches the cut-off level, mercury switch 5I closes. This completes a circuit from line 59 through relay contact 15b, mercury switch 5i and slip rings 31 to the coil 18a of relay and to the other side of the line iii). 'I'his energizes relay 18, closing its contact 18h and opening contact 18e. Closing of contact 18h, establishes a holding circuit through limit switch contact 85a to keep relay 18 energized. Opening of contact 13e breaks the circuit by which the coils 29-3I of the ore loaders 26-28 are energized from the

line conductors

59, 60 thus stopping the loaders until the stockline 34 has dropped to the normal level. When this occurs, the rheostat arm 66 will begin to move by increments in a counterclockwise direction thus permitting contacts 85a of limit switch 85 to open and break the holding circuit for relay coil 18a. Relay contact 18a now recloses and restarts the loaders Z-E.

In conclusion, it will be appreciated that the novel method of an apparatus for controlling the discharge rate of a furnace of the class described makes it possible, under normal operating conditions, to maintain the stockline of the column of material being treated at a substantially constant level. Any tendency on the part of the stockline to drop below the predetermined normal level for an appreciable period is met by a decrease in the rate at which the material is removed from the bottom of the column, and the extent of the decrease varies directly with the length of time that the stockline remains below the normal level. Conversely, a rise in the stockline above the normal level for an appreciable period is met by an increase in the rate at which the material i-s removed from'the bottom of the column, and in this case also, the

1l extent of the rate increase varies directly with the time that the stockline remains above the normal level.

By so adjusting the change in rate at which the material is removed from the bottom of the column of material, it is self evident that restoration of the stockline to its normal range in level from a higher or lower level caused by an abnormal condition in the descending material column is assured Within the least possible time. Then too, automatic cut-off of the feeders for loading the material onto the stoclrline in the levent of an extremely high rise in the stockline coupled With automatic restarting of these feeders when the stockline has returned to the normal level, as Well as an automatic cut-oif of the discharge feeder for removing the material from the bottom of the column when the stoclzlne sinks to an extremely low level coupled with subsequent automatic restarting thereof when the stockline has returned to its operating range in level also are of material assistance in improving the recovery factor of the system.

Finally, I Wish it to be understood that while in accordance with the patent statutes, have described and shown a preferred arrangement by which the pesent invention may be practiced, various modications of the construction may be made by those skilled in the art without departing from the spirit and scope of the inven tion as dened in the appended claims.

I claim:

1. In a furnace of the type for heat treating a column of fluent material continuously descending therethrough, a feeder mechanism movable over the mouth of said furnace for loading the material onto the stockline of the column, means for ascertaining the actual level of the stockline, a device having a variable discharge rate for normally removing material continuously from the bottom of rthe column, means for periodically effecting predetermined incremental changes in said discharge rate, and means ccntrolled by said level-ascertaining means for determining the sense of said rate change in accordance with the actual level of said stockline as related to a predetermined normal level.

2. A furnace as defined in claim l and which further includes means actuated in response to a predetermined abnormal rise in said `s'tockline above said normal level for stopping said feeder mechanism, and means actuated in response to an abnormal stay of said stockline below said normal level for stopping said material removing device.

3. A furnace as de'iined in claim l and which further includes means stopping said device for removing material When the latter reaches a predetermined minimum discharge rate, and means stopping said feeder mechanism upon Va predetermined rise in the stockline above said normal level after said device for removing material reaches a predetermined maximum discharge rate.

4. In a furnace of the type for heat treating a column of fluent material continuously descending therethrough, a feeder mechanism movable over the moutn of said furnace for loading the material onto the -stock'line of the column, a device having a variable discharge rate for normally removing material continuously from the bottom of the column, 'means for periodically effecting predetermined incremental changes in said discharge rate, and a sto'clline measuring device `cooperative with 'said discharge 'rate changing means for determining the sense vof the rate change in accordance with the actual level of lsaid stockline as related to a predetermined normal level.

5. In ra furnace `of the type for heat treating a column of fluent material continuously descending therethrough, a feeder mechanism movable over the mouth of said furnace for load ing the material onto the stocliline of the column, a device having a variable discharge rate for normally removing lmaterial continuously from the bottom `of the column, means operated in timed relation with the operation of said vfeeder mechanism for periodically effecting predetermined incremental changes in said discharge rate, la stockline measuring ydevice for ascertain'- ing the actual level of said stocliline, yand means cooperating with said stockline measuring device for determining the sense 'of said ra-te change in accordance with the actual level of said stockline as rela-ted to a predetermined normal level. y

v6. In a furnace of the type for heat treating a `column of iiuent material continuously de scending therethrough, a feeder mechanism rotatable about the major laxis of the column for loading 'the material onto the stockiine of the column, a float on said 'stockline rotatable with said feeder mechanism, a devi-ce having a variable discharge rate for removing material from the kbottom of the column, means operated in timed relation with the rotation of said feeder mechanism Afor periodically effecting predetermined incremental -ch'anges in said discharge rate, and means including said float for determining the sense of said rate change 'in accordance with the float position.

7. lin `a furnace of the type for heat treating a column of -fluent material descending therethrough, a feeder mechanism for loading the mater-iai onto the 'st'ockli-ne lof the column, `a device for removing material from 'the bot-t m 'of the column and which includes 'an adjustable control member for vary-ing the `rate at which `the material is removed, -a reversible -Inot'or coupled to said control member, circuit means for effecting periodic energization of said motor to run 'for predetermined periods in one direction -or the other to thereby effect corresponding changes 'in the Aadjustment of said control member, and means deter-mining `the running direction of said motor in accordance with the actual level of 'said stockline as related to a predetermined normal level.

8. In a furnace of the type for heat treating a column of vfluent material descending therethrough, a feeder mechanism rotatable about the major axis of the column for loading the material onto the stockline of the column, an electric motor driven device for removing material from the bottom of the column and which includes in the motor 'circuit thereof va r'h'eostat for varying the operating rate of 'the inotor to thereby vary the rate at Vvlfiiicn the 'material is removed, a reversible motor coupled said rheostat, means operated in 'timed 'relation with the rotation of said feeder mechanism for effecting periodic energization-s of said rheostat motor to run for predetermined periods in one direction or the other to ythereby 'effect corresponding changes in the adjustment of said rheos'ta't, a float member on said stockl'ine, and means controlled by said float 'member for determining the running -direction of s'a'id iheos'tat motor.

9. In a furnace of the type for heat treating a column of fluent material descendin-g therethrough, a feeder mechanism for loading the material onto the stockline of the column, an electrically operated device for removing material from the bottom of the stockline and which includes in circuit therewith an adjustable control member' for varying the rate at which material is removed, a reversible motor coupled to said control member, circuit means for periodically energizing said motor to run for predetermined periods in one direction or the other to thereby effect corresponding changes in the adjustment of said control member, and means determining the running direction of said motor in accordance with the actual level of said stockline as related to a predetermined normal level.

10. A furnace as dened in claim 9 wherein said means for determining the running direction of said motor is comprised of a float member on said stockline, and relay means in said motor circuit means controlled by said float member.

l1. In a furnace for heat treating a column of fluent material descending therethrough, an electrically operated feeder mechanism for loading the material onto the stockline of the column, an electrically operated device for removing material from the bottom of the column and which includes in circuit therewith an adjustable control member for varying the rate at which material is removed, a reversible motor coupled to said control member, circuit means controlled in timed relation with the operation of said feeder mechanism for periodically energizing said motor to run for predetermined periods in one direction or the other to thereby effect corresponding changes in the adjustment of said control member, a oat member on said stockline, relay means in said motor circuit controlled by said float member for determining the running direction of said motor, a pair of limit switches actuated alternatively upon predetermined totalized runs of said motor in opposite directions, means controlled by one of said switches to open the respective energizing circuits for said material removing device and said motor, a relay controlling the circuit through which said feeder mechanism is energized, switch means actuated by said float member upon a predetermined rise in said stockline for energizing said relay to interrupt the energizing circuit for said feeder mechanism, and means controlled by the other of said limit switches for likewise opening the energizing circuit to said motor and completing a holding circuit for said relay.

l2. In a shaft furnace of the type for heat treating a column of fluent material continuously descending therethrough, a feeder mechanism movable over the mouth of said furnace for loading the material onto the stockline of the column, a iioat on said stockline movable with said feeder mechanism, a device having a variable discharge rate for normally removing material continuously from the bottom of the f column, means periodically effecting predetermined incremental changes in said discharge rate, and means including said iioat for determining the sense of said rate changes in accordance with the oat position.

CARL W. SISCO.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,350,627 Ten Broeck et al. Aug. 24, 1920 1,852,385 Weigert Apr. 5, 1932 2,277,879 Ness et al. Mar. 31, 1942 2,408,221 Michel Sept. 24, 1946