US2964308A - Apparatus for charging low-shaft arc furnaces - Google Patents

Description

Dec. 13, 1960 H. WALDE 2,964,308

APPARATUS FOR CHARGING LOW-SHAFT ARC FURNACES Filed June 9i 1958 INVENTOR.

Hermann Walde vtcorney United States Patent hce l 2,954,308 Patented Dec. `13, 1960 APPARATUS FR CHARGING LOW-SHAFT ARC FURNACES Hermann Walde, Mulheim, Germany, assignor to DEMAG-Elektrometallurgie G.m.b.H., Duisburg, Germany, a corporation of Germany Filed June 9, 1958, Ser. No. 740,783

1 Claim. (Cl. 266-9).

This invention relates to a method and apparatus for preparing charge for a low-shaft ore reducing electric furnace.

The charge used in electric reduction furnaces generally includes ore, coke and lime which is fed to the furnace at the top of the shaft and allowed to sink slowly into the melt. In order to achieve satisfactory ore reduction, it is necessary that the ore be pre-reduced prior to final reduction in the melt. Gases liberated inthe final reduction rise through the charge disposed in the shaft above the melt and react chemically with the charge to effect a partial or pre-reduction thereof. In high-shaft furnaces, the height of the shaft allows a sufficiently large volume of charge to be disposed above the melt so that each unit of charge is exposed to the gases for a period of time which is adequate to effect satisfactory pre-reduction. In low-shaft furnaces, however, the amount of charge above the molten ore is too small to allow adequate pre-reduction merely by the action of the gases within the furnace.

An object of the invention is to provide a new and improved method and apparatus for pre-reducing ore prior to charging of a low shaft ore reducing electric furnace.

A further object of the invention is to provide charging apparatus for a low-shaft electric furnace vwherein gases liberated during the final reduction of the furnace charge are utilized to pre-reduce the ore. A still further object of the invention is to provide such charging apparatus with a means for heating coal in a reduced atmosphere to produce coke and coal gas wherein the coke is utilized in the furnace charge and the coal gas is mixed with the furnace gas for ore pre-reduction. Another object is to provide such pre-reduction apparatus with a lime kiln wherein said furnace and coral gases arealso utilized in said lime kiln.

Still another object of the invention is to provide furnace charging means wherein the ore to be reduced is agitated in an atmosphere of gases liberated in the furnace during nal reduction and wherein said ore is conveyed to said furnace in an atmosphere of said gas.

Other objects of the invention will be apparent from the detailed description of the drawing which schematically illustrates a furnace having charging apparatusv according to the invention.

The charging apparatus for a lowshaft ore reducing electric furnace according to the invention includes ore agitating and conveying means for agitating the ore to be used in charging the furnace and conveying said agitated ore to said furnace, means 12 for conducting a portion of the gases liberated in the furnace 14 during final reduction of said ore to said ore agitating means whereby said ore is pre-reduced. The combination according to the invention may also include an autogenous coking apparatus 16 having means for heating coal in a reduced atmosphere 18 wherein coke and coal gas are formed, means 20 for conducting a portion of the coal gas to said ore during the agitation thereof and means to convey said coke to the furnace. In addition, conduit means 24 and 26 may be provided for conducting a second portion of the furnace and coal gases respectively to a lime kiln 27. Conduit means 28 is also provided for conducting the lime to the electric furnace.

Referring now to the drawing in greater detail, the ore reducing electric furnace includes a shell 30 of suitable refractory material mounted on a suitable base 32 and three electrodes 34 (two of which are shown) supplied by means of bus bars 36 from a conventional power transformer, not shown. The electrodes may be positioned with respect to the charge by any suitable positioning means 39 in a manner well known in the art.

The ore pre-reduction means includes a substantially cylindrical inclined kiln 40 having a sealed upper end 42 and a lower open end 44. Suitable means 45 are provided for rotating the kiln during operation, and an ore hopper 46 having a tubular spout 47 at its lower end admits ore into the interior of the kiln through its sealed upper end 42. The hopper 46 is adapted to receive pelletized or pulverized ore 48 which may be fed to the hopper 40 through tubular member 47 in a quantity controlled by a suitable valve 49.

A plurality of agitating vanes 5t) is disposed on the inside wall of the kiln in a spaced apart helical pattern whereby the ore 48 fed into the kiln at the upper end 42 of the kiln 40 will be picked up by the agitating vanes 50, as they approach the lowest point of their circular path, and dumped by said vanes as they approach the highest point in their path. The agitating vanes 50 are inclined at a slight angle with respect to the axis of the kiln so that the end of each vane closest to the lower end 44 of the kiln 40 is substantially lower than the other end whereby the ore picked up by each vane 50 tends to slide off the lower end of the vane toward the lower end 4 4 of the kiln 40. In this manner the ore is conveyed from the upper end 42 of kiln 40 to the lower end 44 where it is then discharged into a charge mixing receptacle means 51. The charge is discharged from mixer 51 into a hopper 68 and is then conveyed to the furnace 14 by suitable conduits 70. A nozzle 52 extends through the upper end 42 of the kiln 40 and includes an inner tubular conduit S4 and an outer tubular shell 56 surrounding the conduit S4 and having an orifice 58 in the end thereof disposed within the kiln 40.

The gases liberated in the furnace 14 during the final reduction of the charge 38 are conducted to nozzle 52 by means of a pump 59 having its input 60 connected to the furnace 14 and its output connected to conduit 61, a second conduit 62 tapped into conduit 61 and a third conduit 63 serially connecting conduit 54 of nozzle 52 and conduit 63. A suitable valvel 64 is disposed between conduits 62 and 63 so that the flow rate of the furnace gases to the nozzle 52 can be controlled. The nozzle 52 is disposed in upper end 42 of kiln 40 at a point below the end of spout 47, which feeds the ore 48 into the kiln 40, so that as the ore 48 enters the kiln 40 it will traverse the path of the gas stream from nozzle 52 whereby heating of oreY to pre-reduction temperature will be facilitated.

The kiln 4t), the charge mixer 51 and the charge hopper 68 are hermetically sealed except for vent 66 in charge hopper 68 which draws the gases through the kiln 40 in the same direction as the ore travels and also draws the gas into the charge mixer 51 and the charge hopper 68. In this manner the gas passes continuously around the ore particles as they are agitated. Also, by placing the nozzle in the same end of the kiln 40 as the ore input means 47 and venting the gas through the other end of the kiln, the ore remains in the gas stream for a longer period than would be the case if the gas and ore traveled in opposite directions. Pump 59 maintains the pressure in the system sufliciently above the ambient pressure so that the ore 48 is maintained in a reducing atmosphere while it traverses the kiln 40, the charge mixer 51 and the ore hopper 68 so that it cannot be reoxidized by the ambient air. Vent 66 may exhaust to the atmosphere or be connected to any suitable heat exchange means for pre-heating the materials used in the system.

The pre-reducing apparatus according to the invention may also be provided with an autogenous coking apparatus 16 which includes a coke oven 18 for heating coal in a reduced atmosphere whereby coke and coal gas are produced, means 20 for conducting the coal gas to nozzle 52 and means 22 for conveying said coke to the charge mixer 51. The coke oven 18 includes a shell 71 of suitable refractory material having a substantially planar rectangularly shaped roof 72 which is inclined with respect to the horizontal and four sidewalls depending from said roof, three of which 73, 73' and 73" are shown. The lower edges of the side walls define the periphery of a rectangular opening in the bottom of the shell 71. A continuous traveling grate 74 is driven beneath the opening in shell 71 at a predetermined speed by suitable driving means 76. A coal hopper 90 delivers coal, at a rate controlled by closure means 92, to the continuous grate 74 at the side wall 73 of shell 71 adjacent the lower end of the roof 72, the direction of grate travel being from the hopper toward wall 73" whereby the coal is carried into the furnace. Means (not shown) are provided to heat the coal to combustion temperature as it traverses the oven 18. A plurality of tuyeres 78 are disposed beneath the grate 74 and each is connected to an air compressor 80 by means of conduits 82 whereby a plurality of air blasts may be delivered to the oven 18. Valves 84 in each of the conduits 82 control the quantity of the air delivered to each of the tuyeres so that only sufficient oxygen is available in the oven 18 to support incomplete combustion of the coal whereby coke and coal gas are produced. An opening 94- is provided in sidewall 73" adjacent the raised side of roof 72 for drawing olf the coal gas.

The means 22 for conveying the coke from oven 18 to the furnace 14 includes a hopper 96 which surrounds the side of grate 74 at wall 73 and an inclined conduit 93 havin r its upper end connected to the bottom of hopper 96 and its lower end opening into charge mixer 51. A conveying screw 100 is disposed within conduit 98 and may be driven by any suitable means (not shown) at a predetermined speed whereby the coke which spills oit the end of grate 74 into hopper 96 is picked up by screw 100 and carried into the charge mixer 51.

The means for conducting the coal gas to the pre-reduction kiln 40 includes a first conduit 102 connected to the opening in side 73' of shell 71, and a second conduit 104 which connects conduit 102 with shell 56 of nozzle 52. The inclination of roof 72 on oven shell 71 facilitates the collecting of the furnace gas at opening 94. Pump 59 maintains the pressure of the furnace gas at a substantially higher value than the pressure of the coal gas so that as the furnace gas passes from inner conduit 54 of nozzle 52 through orice 58 under this higher pressure, it aspirates the coal gas out of shell 56 thereby creating a partial vacuum in the coal gas conducting means 20 which facilitates the flow of coal gas from the coke oven 18 to the kiln 40. The mixture of coal gas and furnace gas has a high hydrogen and carbon monoxide content which reacts with the ore, such as iron oxide, to partially deoxidize the ore. The waste gases such as CO2 formed in the pre-reduction are vented out of hopper 68 through vent 66.

The reducing apparatus according to the invention may also be provided with a lime kiln 27 in which limestone is reduced to lime by means of coal gas and furnace gas. Conduits 24 and 26 leading to lime kiln 27 are respectively connected to conduit 61, which is connected to the furnace 14, and conduit 102, which is connected to coke oven 18, whereby a portion of the furnace gas and coal gas is conducted to the lime kiln. Valves and 112 in conduits 24 and 26 respectively control the rate of flow of the gases to the lime kiln 27. The lime is conveyed to the charge mixer 51 by means of conduit 28 which has a valve 114 for controlling the flow rate of the lime.

Because the integrated system, according to the invention, utilizes the hot gases produced in the furnace and in the coke oven in ore pre-reduction and in the lime kiln, the energy input per ton of metal reduced is substantially lower than was heretofore attainable in the prior art.

I claim:

In combination with a low-shaft electric reduction furnace wherein gases are liberated during nal r'eduction of a charge, ore pre-reduction means including a cylindrical chamber mounted for rotation about its longitudinal axis and being inclined at an acute angle with respect to the horizontal, a plurality of agitating vanes on the interior of said chamber and being disposed in a spaced apart relation with respect to each other, means for introducing ore to the upper end of said chamber whereupon said ore will be conveyed by said agitating vanes to the lower end of said chamber upon rotation thereof, nozzle means extending through the upper end of said chamber at a point below said ore introducing means, whereby said ore passes said nozzle as it enters said chamber, oven means for heating coal in a reduced atmosphere to produce coke and coal gas, kiln means adapted to receive limestone, conduit means for conducting a rst portion of said furnace and coal gases to said nozzle means whereby said nozzle means directs said furnace and coal gases against said ore to effect pre-reduction thereof, said conduit means also conducting a second portion of said furnace and coal gases to said kiln means for preheating said limestone, means for venting the lower end of said chamber whereby the gases therein travel in the same direction as said ore, and a hermetically sealed furnace charging means connected to the lower end of said chamber and to said kiln means and said oven means for conveying said pre-reduced ore, said coke and said preheated limestone to said furnace.

References Cited in the lile of this patent UNITED STATES PATENTS 1,819,239 Greene Aug. 18, 1931 2,747,988 von Haken May 29, 1956 2,675,307 Klugh et al. Apr. 13, 1957 2,805,142 Arata Sept. 3, 1957 2,805,929 Udy Sept. 10, 1957

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