US3050299A

US3050299A - Method and apparatus for controlling feed to shaft furnace

Info

Publication number: US3050299A
Application number: US822298A
Authority: US
Inventors: Thomas F Reed
Original assignee: United States Steel Corp
Current assignee: United States Steel Corp
Priority date: 1959-06-23
Filing date: 1959-06-23
Publication date: 1962-08-21
Anticipated expiration: 1979-08-21
Also published as: GB939602A

Description

T. F. REED Aug. 21, 1962 METHOD AND APPRATUS FOR CONTROLLING FEED T0 SHAFT FURNACE Filed June 23, 1959 N @uw INVENTOR. 77/0/1/45 F. @50

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3,050,299 METTI-101) AND APPARATUS FOR CNTROLLING FEED Tt) SHAFT FURNACE Thomas F. Reed, Pittsburgh, Pa., assigner to United States Steel Corporation, a corporation of New .ersey Filed .lune 23, 1959, Ser. No. 822,298 2 Claims. (Cl. 263-29) or disk and then heat the balls to the point of incipient fusion in a shaft furnace. The balls feed to the top of the furnace, attain a maximum temperature in a combustion zone a few inches below the stocklne, and discharge from the bottom. The usual feeding means includes a conveyor whose discharge end continually traverses the furnace above the stockline and deposits balls over the whole area. Typical conveyor arrangements for this purpose are shown in Davis Patent No. 2,757,782 and De Vaney et al. Patent No. 2,834,484.

Desirably the combustion zone remains at a uniform constant level, but in practice its level tends to deviate non-uniformly. To correct such deviations the traversing drive for the conveyor commonly is equipped with a speed control device which causes the discharge end of the conveyor to dwell over some spots on the burden and pass quickly over others. Previously known means through which the speed control device receives its intelligence include a mechanical feeler, as shown in De Vaney et al. Patents Nos. 2,792,132 and 2,834,484, or a temperature measuring device, as shown in Sisco Patent No. 2,739,800. A feeler senses the level of the stockline profile and causes the conveyor to dwell over low spots and pass quickly over high spots. A temperature measuring device senses the temperature of combustion gases from different spots on the burden and causes the conveyor to dwell over hot spots and pass quickly over cool spots. Thus the feeler tends to maintain a level stockline, and the temperature measuring device a uniform combustion gas temperature, but I have observed neither afforns exactly the form of control that is needed.

An object of the present invention is to provide an improved method and apparatus for controlling feed of material to a shaft furnace in which control is effected in accordance with the relative permeability of the furnace burden to fiow of gases.

A further object is to provide an improved method and apparatus for controlling the traversing drive of a conveyor which feeds a shaft furnace whereby the discharge end of the conveyor dwells over spots in the furnace burden of high permeability and passes quickly over spots of low permeability.

A more specific object is to provide an improved control method and apparatus of the foregoing type in which the velocity of combustion gas at different spots over the burden is measured with an anemometer or the equivalent, the temperature at these spots is measured with a thermocouple or the equivalent, these measurements are combined to furnish an indication of gas velocity at a standard temperature, and this indication is used to effect control of the traversing drive.

In the drawing:

FIGURE l is a diagrammatic vertical sectional View of the upper portion of a shaft furnace whose feed means is equipped with a control apparatus in accordance with my invention; and

FIGURE 2 is a schematic diagram of an electric circuit suitable for use in my apparatus.

FIGURE l shows the upper portion of a conventionall shaft furnace 10 for indurating balled iron ore fines. The

furnace can be either rectangular or circular in cross sec-v tion, and its feed means can lbe of any suitable type for traversing the top, for example as shown in the afore-v mentioned patents. For purposes of illustration, the feed means is shown diagrammatically as including a conveyor belt 12, a movable carriage 13 on which the belt is mounted, a fixed support 14 for the carriage, and a. variable speed traversing drive motor 15. Preferably the furnace has a hood 16 above its feed means and a stack 17 above the hood. The furnace wall has a suitably curtained opening for admitting the feed means, as known in the art. The feed means feeds balls to the furnace where they form a burden B. Air is introduced to the' and escape through the stack. The burden has the usuall combustion zone C.

ln accordance with the present invention, carriage 13` carries an anemometer 18 and a thermocouple 19 positioned over the burden B adjacent the spot to which con-V veyor 12 discharges balls. As the conveyor traverses the furnace, the anemometer measures the velocity at which combustion gases pass through the burden at each spot and generates a voltage proportionate thereto. thermocouple measures the temperature of these gases and generates another voltage proportionate to this temperature. The latter voltage is used to compute the velocity of combustion gases at a standard temperature (32 F.). The permeability of the bed below the spot where velocity is measured is of course directly proportional to the velocity at standard temperature. Both the anemometer and the thermocouple per se are conventional instruments; hence they are not shown in detail.

' The gas velocity at standard temperature can be computed by multiplying the anemometer reading lby the ratio where Tis the temperature indicated by the thermocouple. FIGURE 2 shows schematically one form of circuit for accomplishing this computation. The anemometer 18 and thermocouple 19 transmit voltages proportionate to the velocity and temperature to

conventional voltage amplifiers

20 and 21 respectively. These amplifiers are equipped with volume controls 22 and 23, which are adjusted manually to place the voltage outputs of the two ampliers on scale. The negative output terminals of both amplifiers are electrically connected to one end of a potentiometer slide wire 24. A bias voltage source 28 is connected between the negative output terminal of amplifier 21 and the slide wire to furnish a voltage proportionate to the term 460 of the foregoing ratio. The positive output terminal of amplifier 21 is electrically connected to the other end of this slide wire. The positive output terminal of amplifier 20 is electrically connected to the arm 25 of the potentiometer through a conventional self-balancing device 26. Thus a voltage proportionate t-o the absolute temperature (460-I-T) is applied across the full length of the slide wire 24 and a voltage proportionate to the anemometer reading across a variable portion of the slide wire determined by the position of arm 25. When the circuit balances, no current flows from amplifier 20. The self-balancing device 26 and arm 25 are mechanically connected as indicated by a dotted line 29, whereby the self-balancing device automatically positions arm 25 to balance the circuit in this way. With proper calibration, the position of the arm when the circuit is in balance indicates the relative permeability of the burden.

FIGURE 2 also shows schematically one form of speed Patented Aug. 21, 1962` The control device for the traversing drive motor 15. This device includes a second potentiometer 27 in the iield circuit of this motor. The arm of potentiometer 27 is mechanically linked to arm 25, as indicated by a dotted line 30, whereby potentiometer 27 is automatically adjusted with adjustment of

potentiometer

24, 25 and regulates the speed of the traversing drive motor accordingly. For example if the anemometer 18 and the discharge end of conveyor 12 reach a spot where the burden has unduly high permeability, the potentiometer arm 25 moves clockwise to restore balance in the control circuit. Potentiometer 27 is adjusted to increase the field strength of motor 15 and thus reduce the speed, whereby the discharge end of the conveyor dwells over this spot. The reverse action occurs when the discharge end of the conveyor reaches a spot of low permeability. In feed devices which employ more than one traversing drive motor (for example De Vaney Patent No. 2,834,484), the potentiometer 27 can automatically be connected in the eld circuit of the appropriate motor through suitable relays, or else each motor can be equipped with its own potentiometer.

I have observed that the combustion zone of the furnace remains more accurately at the desired location when feeding is controlled in accordance with permeability than with either the stockline profile or the gas temperature. The difficulty with a control based on prole is that the usual balls are not uniform and some tend to compact. Consequently there is no direct relation between the depth of burden and its permeability. I have found it is questionable whether temperature varies predictably with permeability.

While I have shown and described only a single embodiment of my invention, it is apparent that modifications may arise. Therefore, I do not wish to be limited to the disclosure set forth but only by the scope of the appended claims.

I claim:

1. In a shaft furnace which includes a feeder adapted to deliver material to the top of the furnace, a traversing drive for said feeder, and a speed control device for said drive, the combination therewith of an apparatus for adjusting said speed control device comprising means for measuring the velocity of combustion gases passing through the furnace burden adjacent the spot where the feeder is delivering material, separate means for measuring the gas temperature at approximately the same spot, computing means operatively connected with said velocity measuring means and said temperature measuring means for determining the gas velocity at a standard temperature and thereby providing an indication of the relative permeability of the burden to ow of gases below this spot, and means operatively connecting said computing means with said speed control device to increase the feed rate over spots of relatively high permeability and decrease the feed rate over spots of relatively low permeability.

2. A method of controlling feed to a shaft furnace to which material feeds from a traversing feeder, said method comprising measuring the velocity of combustion gases passing through the burden adjacent the spot where the feeder is delivering material, developing a first voltage proportionate to the velocity measurement, separately measuring the temperature of the combustion gases at approximately the same spot, developing a second voltage proportionate to the absolute temperature measurement, balancing said first voltage against said second voltage to obtain an indication of the gas velocity at a standard temperature and thus of the relative permeability of the burden to flow `of gases below this spot, and varying the rate of traverse in accordance with said indication to increase the feed rate over spots of relatively high permeability and decrease the rate over spots of relatively low permeability.

References Cited in the file of this patent UNITED STATES PATENTS 2,175,541 Probert Oct. l0, 1939 2,306,811 Kennedy Dec. 29, 1942 2,310,924 Becker Feb. 16, 1943 2,711,837 Henry et al Iune 28, 1955 2,739,800 Sisco Mar. 27, 1956 2,752,231 Bearer June 26, 1956