US3257016A - Method for charging ore concentrate balls to a shaft-type furnace for indurating ore pellets - Google Patents

Description

June 21, 1966 P. A. lLMONl 3,

METHOD FOR cmmeme ORE CONCENTRATE BALLS TO A SHAFT-TYPE FURNACE FOR INDURATING ORE PELLETS Original Filed June 4, 1963 m 0% W SSS/l0 Arm QM p 3.9 v #flg PRIOk ART rear ATTORNEYS United States Patent 3,257,016 METHOD FOR CHARGING ORE CONCENTRATE BALLS TO A SHAFT-THE FURNACE FOR IN- DURATING ORE PELLETS Pehr Adrian Ilmoni, Strassa, Sweden, assignor to Erie Mining Company, a corporation of Minnesota Continuation of application Ser. No. 285,484, June 4, 1963. This application Mar. 8, 1965, Ser. No. 438,004 3 Claims. (Cl. 214-152) The present invention is related to a method for charging pellets or small balls or mineral solids, eg. ore con centrate balls, to a shaft-type indurating furnace having a generally vertical shaft with an elongated rectangular cross-section. This application is a continuation of my US. patent application Serial No. 285,484, filed June 4, 1963 (now abandoned).

For the charging of blast furnaces for iron production one extensively uses today ore pellets, i.e., indurated or sintered pellets of iron ore concentrates. These pellets are manufactured by shaping moist pulverized ore material pulp or concentrate into balls in a suitable way, which balls are subsequently dried and indurated. It is known to carry out this drying and indurating process of the green (i.e., non-indurated) balls in a vertical shaft-type furnace normally having a shaft with an elongated rectangular cross-section, in which process hot combustion gases and possibly also fresh air are blowninto the charge column,- occupying the shaft, through.

openings in the Walls of the shaft and, for the fresh air, possibly also through the lower end ofthe shaft. Such a shaft-type furnace operates continuously, i.e. the green concentrate balls are more or less continuously fed onto the column of charge material present in the shaft, which material gradually descends through the shaft during the drying and subsequent indurating process to leave the furnace through the lower end of the shaft. In methods hitherto known the green concentrate balls were charged to the furnace in such a way that they were fed onto the material present in the shaft of the furnace in two or possibly several parallel strands extending across the mouth of the shaft parallel to the longer sides of the shaft. The reason for this method of charging the green concentrate balls was partially that the strain on the charging device was small, which charging device normally consisted of a charging carriage movable above the upper opening of the shaft.

In such a furnace for indurating pellets it is, however, extremely important that the temperature within the indurating zone of the shaft be kept within predetermined, comparatively narrow, limits in order that the indurating process shall be satisfactory. Thus the concentrate balls which are dried in the uppermost part of the charge column are to be kept at such a temperature during the indurating process that the ore particles within the balls are adequately sintered together so that hard, mechanically rugged, pellets are obtained without adjacent concentrate balls being simultaneously sintered together into larger masses or chunks which give a product of inferior quality. Thus, it is important to provide a temperature as uniform as possible over the entire cross-sectional area of the shaft within the indurating zone of the furnace, which, in its turn, requires that the distribution within this indurating zone of the combustion gases and the fresh air blown into the shaft is as uniform as possible. 7

With the previous method for charging the green concentrate balls to the furnace, however, it has turned out to be extremely diflicult to obtain such 'a desired uniform gas and temperature distribution in the indurating zone of the furnace. This was found to be due to the fact that the material present in the shaft of the furnace does 3,257,016 Patented June 21, 1966 'iCe . 2 not consist exclusively of whole concentrate balls but also comprises a certain (more or less small) percentage of finer materials. Certainly one tries to feed only undamaged whole concentrate balls to the furnace but it is not possible to prevent breakage of some of the balls into chips and still smaller particles in the charging device and during the charging process proper, i.e. when the balls fall down onto the stockline of the charge column already present in the furnace. This is augmented by the very violent drying to which the green (damp) concentrate balls are subjected when they arrive in the furnace, during which drying period a portion of the balls burst to pieces. As the green concentrate balls are fed onto the stockline of charge column of material present in the shaft in the form of ridge-like strands extending parallel to the longer sides of the shaft, as stated above, 'theundamaged whole concentrate balls will to a large extent roll and slide along the sides of these strands down into the furrows between the strands, whereas on the contrary broken balls, chips and finer particles on the whole remain within the ridge-likes'trand. Consequently, the material in the shaft of the furnace is divided into vertical zones with substantially undamaged whole balls extending beneath the fur rows in the upper surface of the material and vertical zones comprising a substantial precentage of chips and finer material beneath the ridge-like strands in the upper surface of the material. As these different zones do not have the same penetrability for the combustion gases and the fresh air and as they, with the previously known method for charging the green concentrate balls to the furnace, will extend substantially perpendicularly to the direction of the ducts for blowing the combustion gases into the shaft, which ducts are preferably arranged in the longer side of the shaft, a very uneven gas and tempera- 'ture distribution is obtained in the indurating zone of the shaft resulting in the disadvantages mentioned above. This uneven gas and temperature distribution is further accentuated by the fact that the path for the combustion gases from the inlet ducts is longer when the gases flo toward the center of the shaft and upwards than is the flow through the shaft closer to the longer sides of theshaft, due to which circumstance a reduced gas flo is obtained in the center of the shaft.

It previously had been attempted to eliminate these disadvantages by providing in the upper end of the shaft vertical air-cooled, or in any other suitable way cooled, flanges, so-called divider plates, of high quality material as for' instance chromium-nickel alloy, protrudinginto the shaft from the long sides of the shaft. Although it is possible in this way to achieve a more uniform temperature distribution within the indurating zone of the shaft, this measure makes the furnace'complicated and expensive. Further, these divider plates are subject to a very heavywear due to which they are rapidly destroyed and must be replaced after 1%2 months. This causes frequent interruptions in the operation of the furnace and high costs for the maintenance of the furnace.

The object of the present invention is to provide a new and improvement method for charging the fresh (green) concentrate balls to the stockline of a charge column of a shaft-type furnace for indurating pellets of ore or other mineral solids of the type mentioned above, which method gives a more uniform gas and temperature distribution and, hence, a more nearly uniform induration treatment within the indurating zone of the shaft, and which does so without the use of divider plates.

The method according to the invention is substantially characterized in that the green concentrate balls are fed onto the stockline of the charge column present in the shaft of the furnace in substantially parallel strands ex- 9 m3 tending across the upper opening of the shaft and substantially perpendicularly to the long sides of the shaft.

As also with the method according to the invention the green concentrate balls are fed to the shaft of the furnace in the form of parallel strands, the material present in the shaft of the furnace will also in this case be divided into vertical zones substantially comprising whole undamaged balls and a substantial portion of chips and finer particles respectively. As however these zones with the method of charging the green balls according to the invention will extend substantially parallel to the direction of the heating gas ducts arranged in the longer sides of the shaft for blowing the combustion gases into the shaft, it has been found that a substantially more uniform gas and temperature distribution are obtained in the indurating zone of the shaft, due to which the troublesome and expensive divider plates become unnecessary. Further, a substantial reduction of the total heat consumption is achieved. Thus, practical tests have proved that by the sole expedient of changing the method for charging the green concentrate balls to the furnace from the previously known method to the method according to the invention it is possible to obtain a reduction of the total heat consumption of up to 15%, and simultaneously the furnace can be operated without any divider plates.- A particularly favorable result is the uniform of induration treatment, throughout the column of pellets, obtaining when the provisions of the present process are observed.

It has further been found that in certain cases it may be desirable, when using the method for charging the green concentrate balls according to the invention, to feed the green concentrate balls in two additional strands running parallel to the longer sides of the shaft adjacent to said sides in addition to the strands extending across the opening of the shaft perpendicularly to the longer sides of the shaft.

In the following the invention will be further described with reference to the accompanying drawing, in which FIG. 1 shows schematically the upper end of a shaft type furnace for indurating ore pellets in a vertical section perpendicular to the longer sides of the shaft, to which furnace the concentrate balls have been charged in the previously known method and which furnace is provided with divider plates;

FIG. 2 is a similar section of a shaft type furnace for indurating ore pellets without divider plates, to which the green concentrate balls have been charged according to the method according to the present invention;

FIG. 3 is a schematic plan view of the upper shaft opening of a furnace for indurating ore pellets, to which the green concentrate balls has been charged according to the invention; and

FIG. 4 illustrates a feeding course substantially yielding the pattern shown in FIG. 3.

The shaft-type furnace shown in FIG. 1 is provided with mains, or manifold ducts, 2 extending along the longer sides 1 of the shaft, which ducts are connected to e.g. separate combustion chambers (not shown in the drawing) and which by means of smaller transverse ducts 3 discharge heating gas into the shaft of the furnace along the longer sides thereof. Thus, combustion gases are blown into the shaft through these ducts 2 and 3. The ducts 2 may also be extended along the short sides of the shaft and may also be provided with transverse ducts corresponding to the ducts 3 for the combustion gases discharging into the shaft from the short sides of the shaft. The furnace originally was further provided with vertical, air-cooled, divider plates 4 of chromiumnickel alloy protruding into the shaft from the long sides 1 of the shaft and adjacent the stockline of the column within the same. The green concentrate balls were charged to the furnace through the upper opening 5 of the shaft down onto the material already present in the shaft and the charging was, at the furnace shown in FIG. I, performed according to the previously known method in that the concentrate balls were charged in three strands 6 extending across the opening of the shaft parallel to the long sides of the shaft. Due to this the upper surface of the material present in the shaft displayed substantially the form shown in vertical section in FIG. 1. The whole (i.e., undamaged) balls would in this case to a large extent roll or slide down into the furrows situated between the ridge-like strands 6, whereas chips and finer material substantially remained within the strands. Due to this, the material present in the shaft was divided into vertical zones A and B extending down through the shaft, as schematically shown in FIG. 1. The zones A which extended beneath the feed strands 6 comprises a substantial portion of chips and finer particles, whereas the zones B extending beneath the furrows in the upper surface between the strands 6 substantially comprised only undamaged whole balls. Due to this division of the material in the shaft perpendicularly to the direction of flow for the combustion gases blown into the shaft through the ducts 3 a very uneven gas and temperature distribution obtained within the indurating zone of the shaft. Attempts were made to compensate for this uneven gas and temperature distribution by means of the air-cooled divider plates 4 which, however, were expensive and had to be replaced very frequently.

In the method according to the invention, on the contrary, the concentrate balls are, as schematically shown in FIG. 3, charged onto the stockline of the material already present in the shaft in parallel strands which extend across the upper opening of the shaft and substantially perpendicular to the long sides 1 of the shaft. In FIGURE 3 the feeding strands are schematically indicated by means of hatched areas 7.

In this way a substantially homogenous distribution of the material in the shaft is achieved across the shaft in the direction perpendicular to the longer sides 1 of the shaft, as shown in FIG. 2. In a vertical section perpendicular to the one shown in FIG. 2, i.e. parallel to the longer sides 1 of the shaft, the material in the shaft will of course with the charging method according to the invention display an undulated upper surface and zones, corresponding to the zones A and B in FIG. I, extending vertically downwards through the shaft. With the method of charging the concrete balls according to the invention, however, these zones will evidently be substantially parallel to the flow direction of the combustion gases blown into the shaft through the ducts 3 and will consequently be much less disturbing to the gas and temperature distribution in the indurating zone of the shaft, which distribution may be maintained sufficiently uniform without the use of expensive and troublesome divider plates.

In certain cases it may according to the invention be advantageous to feed the green concentrate balls to the shaft in two additional strands 8 running along and adjacent the longer sides 1 of the shaft, as schematically indicated in FIG. 3.

The charging of the concentrate balls according to the method of the present invention may be performed by means of conventional charging devices comprising e.g., a conveyor belt, the discharge end of which can be moved in the desired pattern above the shaft opening of the furnace. Illustrative of apparatus generally operable when suitably revised as to its programming for carrying out this procedure is that disclosed in US. Patent 2,834,484, DeVaney and Beggs. As shown in FIG. 4, the ideal stockline pattern can be substantially attained by a repetition of the following program of conveyor movements:

Beginning the cycle at point a, in the northwest corner of the mouth of the shaft, the conveyor moves at a predetermined depositing rate to point b (in the southwest corner of the rectangle), thereby laying down a long strand 7 of pellets parallel and adjacent to the west (short) wall of the shaft. From point b the conveyor is moved diagonally to point 0 so rapidly as not to deposit any pellets: then the conveyor is indexed from c to d at a depositing rate to lay down a short strip 8' parallel to and adjacent the north (long) wall. Then, the conveyor moves, at a depositing rate, from point d in a direction parallel to the short wall of the shaft, to lay down the second long strand 7 of pellets. In this manner an odd number (from three to nine, both inclusive) of parallel strands are laid down. As illustrated, in a succession of these diagonal and parallel movements second, third, fourth, fifth and sixth and and short strips 8' are laid down and third, fourth, fifth, sixth and seventh long strands 7 landing at point b in the southeast corner. From point b the conveyor is indexed, at depositing rate, along the south wall laying down strand 8 of pellets and landing at point e in the southwest corner. Finally, the conveyor is rapidly moved to starting point a, at a rate of movement so rapid that no pellets are deposited, to begin a repetition of this feed cycle.

I claim:

1. The process of charging fresh ore concentrate balls to the stockline of a charge column in a shaft-type pellets indurating furnace having an elongatedly rectangular cross-section involving moving over the stockline a ball feeding means which deposits a strand of the fresh balls onto the stockline when moved in a feeding pass at a feed-depositing rate and which does not deposit balls when moved at a different deposition-avoiding rate characterized in that said feed pattern is provided by repeatedly carrying out a cycle of operations each cycling consisting essentially of the following steps in sequence: in a first feeding pass of the ball feeding means across the stockline from a point adjacent a first corner of said stockline depositing a first strand of the green balls substantially parallel to and adjacenta first shorter side of the stockline; in each of a series of subsequent feeding passes of said ball feeding means across the stockline depositing a relatively short strand of the green balls parallel to a first longer side of said stockline and an additional strand of the green balls parallel to said first strand and spaced from said first strand, the serially last of said additional strands being adjacent to a second shorter side of said stockline, and depositing an elongated strand of the green balls parallel to and adjacent a second longer side of said stockline.

2. The process of charging fresh ore concentrate balls to the stockline of a charge column in a shaft-type pellets indurating furnace having an elongatedly rectangular cross-section which comprises moving over the stockline a ball feeding means which deposits a strand of the fresh balls onto the stockline when moved in a feeding pass at a feed-depositing rate and which does not deposit balls when moved at a different, deposition-avoiding rate, depositing the fresh balls onto the stockline in a repeated feed pattern comprising a series of parallel, relatively narrow, substantially uniform strands and alternating valleys across the area of the stockline, said strands and valleys extending substantially perpendicularly to a first longer side of the stockline, and depositing an elongated strand of the fresh balls along and adjacent a longer side of the stockline.

3. The process of charging fresh ore concentrate balls to the stockline of a charge column in a shaft-type pellets indurating furnace having an elongatedly rectangular cross-section which comprises moving over the stockline a ball feeding means which deposits a strand of the fresh balls onto the stockline when moved in a feeding pass at a feed-depositing rate and which does not deposit balls when moved at a different, deposition-avoiding rate, depositing the fresh balls onto the stockline in a repeated feed pattern comprising a series of parallel, relatively narrow, substantially uniform strands and alternating valleys across the area of the stockline, said strands and valleys extending substantially perpendicularly to a first longer side of the stockline, depositing an elongated strand of the fresh balls along and adjacent a longer side of the stockline and depositing a series of short strips adjacent the other longer side of the stockline the short strips being contiguous with ends of the short strands.

References Cited by the Examiner UNITED STATES PATENTS 3,137,398 6/1964 Steffenson 214-18 GERALD M. FORLENZA, Primary Examiner. HUGO o. SCHULZ, Examiner.

R. G. SHERIDAN, Assistant Examiner.

Claims (1)

1. THE PROCESS OF CHARGING FRESH ORE CONCENTRATE BALLS TO THE STOCKLINE OF A CHARGE COLUMN IN A SHAFT-TYPE PELLETS INDURATING FURNACE HAVING AN ELONGATEDLY RECTANGULAR CROSS-SECTION INVOLVING MOVING OVER THE STOCKLINE A BALL FEEDING MEANS WHICH DEPOSITS A STRAND OF THE FRESH BALLS ONTO THE STOCKLINE WHEN MOVED IN A FEEDING PASS AT A FEED-DEPOSITING RATE AND WHICH DOES NOT DEPOSIT BALLS WHEN MOVED AT A DIFFERENT DEPOSITION-AVOIDING RATE CHARACTERIZED IN THAT SAID FEED PATTERN IS PROVIDED BY REPEATEDLY CARRYING OUT A CYCLE OF OPERATIONS EACH CYCLING CONSISTING ESSENTIALLY OF THE FOLLOWING STEPS IN SEQUENCE: IN A FIRST FEEDING PASS OF THE BALL FEEDING MEANS ACROSS THE STOCKLINE FROM A POINT ADJACENT A FIRST CORNER OF SAID STOCKLINE DEPOSITING A FIRST STRAND OF THE GREEN BALLS SUBSTANTIALLY PARALLEL TO AND ADJACENT A FIRST SHORTER SIDE OR THE STOCKLINE; IN EACH OF A SERIES OF SUBSEQUENT FEEDING PASSES OF SAID BALL FEEDING MEANS ACROSS THE STOCKLINE DEPOSITING A RELATIVELY SHORT STRAND OF THE GREEN BALLS PARALLEL TO A FIRST LONGER SIDE OF SAID STOCKLINE AND AN ADDITIONAL STRAND OF THE GREEN BALLS PARALLEL TO SAID FIRST STRAND AND SPACED FROM SAID FIRST STRAND, THE SERIALLY LAST OF SAID ADDITIONAL STRANDS BEIONG ADJACENT TO A SECOND SHORTER SIDE OF SAID STOCKLINE, AND DEPOSITING AN ELONGATED STRAND OF THE GREEN BALLS PARALLEL TO AND ADJACENT A SECOND LONGER SIDE OF SAID STOCKLINE.

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