Patent GB-659899-A (GB)
Title: Ore treating furnace
IPC: F27B1/26
Filed: 1949-01-24
Abstract: 659,899. Automatic level control systems. ERIE MINING CO. Jan. 24, 1949, No. 1878. Convention date, Feb. 6, 1948. [Class 38 (iv)] [Also in Group XII] The rate of discharge from a shaft furnace is controlled by the level of the stockline and provision is made for stopping the otherwise continuous charging and discharging mechanism if said level rises or falls to a dangerous extent. The invention is shown applied to an ore pellet indurating furnace which includes superposed chambers 10 and 11 connected by a restricted throat 12 and also connected to the exit and intake ends respectively of a combustion chamber 21 which is supplied with heated air passing through the treated pellets in the chamber 11 from a blower 23, charging apparatus comprising motor-reciprocated shoots 27. 28 attached to a rotary shaft 25 and supplied with pellets by a fixed motor-reciprocated shoot 26, and a motor-reciprocated discharge shoot 37. The pellets are distributed evenly over the stockline 34 by auxiliary shoots 33 attached to the reciprocated shoot 28. A cup 41 resting on top of the charge is secured to an arm 42 fixed to a rotary shaft 43 and rotation of said shaft due to the variation in level of the stockline 34 is transmitted through linkage 46 to a further shaft 47 fixed to which at different angles are arms 49 and 50 carrying mercury switches 51 and 52 respectively. When the stockline is at a normal level both switches 51 and 52 are open and they remain open if the stockline drops though the rate of pellet discharge through the reciprocating shoot 37 then decreases, whereas if the stockline rises, it first closes the switch 52 increasing the operating rate of the discharge shoot 37 in a manner described later and further rise to a cut-off level (see Fig. 4) closes the switch 51 stopping the reciprocating charging shoots 26-28. The cup 41 and its associated apparatus is mounted diametrically opposite the two rotatable shoots 27, 28 on a carriage 32 which also rotates with the shaft 25 and which includes a pair of spaced channel beams 54, 55 connected by crossmembers in which the shaft 43 is journalled. Control system, Fig. 4. The discharge shoot 37 is reciprocated by an electric vibrator motor represented by a coil 38, pulsating D.C. for which is derived from a diode 58 that functions as a half-wave rectifier operating off A.C. lines 59, 60 through a transformer 63. The operating rate of the discharge shoot varies with the current passing through said coil 38 which is regulated from a rheostat 64 including a resistance winding 65 connected in series therewith and has a wiper arm 66 rotated at ¢ r.p.m. by a shaft 67 driven from a motor 69 which runs for a definite period during each revolution of the shaft 25, and is provided with a pair of field coils 70 and 71 which are alternately energized to charge the direction of drive. The duration of this period is controlled by a metering cam 72 attached to said shaft 25 which rotates at 1 r.p.m., said cam actuating limit switches 73 and 74 disposed approximately 90 degrees apart. Incorporated in the control system are four relays 75-78 and a cam 83 on the rheostat shaft 67. The relay 75 controls the whole system when the start button 81 is pressed momentarily, a latch-type relay 76 co-operates with limit switches 73 and 74 to energize or de-energize the "increase" or " decrease " field coils 70 and 71, a third relay 77 remains de-energized until the mercury switch 52 is closed and a fourth relay remains de-energized until the mercury switch 51 is closed. The cam 83 may actuate a limit switch 84 stopping the discharge shoot 37, or a limit switch 85 which causes the discharge shoot 37 to operate at top speed. With the above control system the discharge shoot 37 receives an impulse to increase or decrease its speed once per revolution of the shaft 25 and with a normal stockline level, actuation of the limit switch 73 will energize the " decrease " winding 71 moving the wiper arm 66 one increment of 18 degrees in an anticlockwise direction, the stockline will rise closing the mercury switch 52 and the next actuation of the limit switch 73 will energize the relay 77 and the " increase " winding 70 to restore the arm 66 to its original position. Should the stockline fall to an abnormally low level each revolution of the shaft 25 will displace the arm 66 through one increment in an anticlockwise direction until the cam 83 actuates the limit switch 84 which opens the circuit to the motor coil 38 stopping the discharge shoot 37. With an abnormally high stockline, the mercury switch 52 will remain closed and each revolution of the shaft 25 will displace the arm 66 through one increment in a clockwise direction until the cam 83 actuates the limit switch 85 where it is held with the motor 38 operating at full speed until the stockline drops. If the charging rate is still excessive the stockline will rise further until the mercury switch 51 closes, energizes the relay 78, and breaks the circuits to the charging shoot motors 29-31. When the stockline 34 drops to the normal level the limit switch 85 is released, and the relay 78 is de-energized allowing the motors 29-31 to restart and the arm 66 will move in increments in an anticlockwise direction gradually slowing the rate of discharge of the pellets.