CA1190417A - Suction sintering method and apparatus therefor - Google Patents
Suction sintering method and apparatus thereforInfo
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- CA1190417A CA1190417A CA000392677A CA392677A CA1190417A CA 1190417 A CA1190417 A CA 1190417A CA 000392677 A CA000392677 A CA 000392677A CA 392677 A CA392677 A CA 392677A CA 1190417 A CA1190417 A CA 1190417A
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- suction
- sintering
- grate
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Abstract
ABSTRACT OF THE DISCLOSURE
A suction-sintering charge of high permeability and stable structure is produced on a mobile suction-sintering grate or in a stationary or mobile suction-sintering pan by compacting a moist material mixture (18) to be sintered to form a coherent cake (19), held together mainly by capillary forces, which cake is then broken into pieces having a size suitable to form a suction-sinter charge (14). The water content of the material mixture (18) is adjusted so that substantially the minimum of fuel is consumed at the intended sintering temperature, and the compaction pressure is so adapted relative to the selected water content, corresponding substantially to the minimum fuel consumption, that the pore volume of the resultant cake (19) is not totally filled by the amount of water present in said mixture.
A suction-sintering charge of high permeability and stable structure is produced on a mobile suction-sintering grate or in a stationary or mobile suction-sintering pan by compacting a moist material mixture (18) to be sintered to form a coherent cake (19), held together mainly by capillary forces, which cake is then broken into pieces having a size suitable to form a suction-sinter charge (14). The water content of the material mixture (18) is adjusted so that substantially the minimum of fuel is consumed at the intended sintering temperature, and the compaction pressure is so adapted relative to the selected water content, corresponding substantially to the minimum fuel consumption, that the pore volume of the resultant cake (19) is not totally filled by the amount of water present in said mixture.
Description
V~L~7 A SUCTION SINTERING METHOD AND APPARATUS THEREFCR
_*_*_ The presen-t invention relates to a method for producing a charge of high permeability and stable structure on a mobile suction-sintering grate or in a stationary or mobile suction-sintering pan, comprising the steps of compacting a moist material mixture to be sintered, preferably between at least one pair of pressure-loaded rolls, to form a coherent cake, the particles forming said cake being held together mainly by capillary forces, and breaking the cake into pieces of a size suitable for formning a suction-sinter charge. The in-vention also relates to apparatus for carrying out the method.
Suction sintering is primarily applied for the purposeof agglomerating finely divided iron-oxide material into a form suitable for charging to a blast furnace, and represents a substantial cost in the manufacture of crude iron. Conse-quently, it is important that as much sinter as possible isproduced per each unit of qrate area, in order to reduce in-vestment, maintenance, fuel and electrical-energy costsO
With regard to sinteriny capacity, -the most important factor is the permeability of the charge. The more yas drawn through the charye per un:it of tirne, the less time required to e~ect a satisfact~ry sintering operation. The pexmeability of the charge can be increased in a number of ways. The most usual method in this respect is to increase the amount of coarse particulate return-sinter admixed with the charge.
Large quantities of coarse return-sinter, however, increase the ar,1ount of fuel required per unit of weight of final sinter, and incur additional handling costs. Furthermore, in certain instances it is necessary to crush the final sinter, in order to obtain the requisite amount of return-sinter. An-other method often used is one in which the charge mixture issubiected to a subsequent rolling process in a drum. Al-though the perrneabLlity of the charge is increased to a certain
_*_*_ The presen-t invention relates to a method for producing a charge of high permeability and stable structure on a mobile suction-sintering grate or in a stationary or mobile suction-sintering pan, comprising the steps of compacting a moist material mixture to be sintered, preferably between at least one pair of pressure-loaded rolls, to form a coherent cake, the particles forming said cake being held together mainly by capillary forces, and breaking the cake into pieces of a size suitable for formning a suction-sinter charge. The in-vention also relates to apparatus for carrying out the method.
Suction sintering is primarily applied for the purposeof agglomerating finely divided iron-oxide material into a form suitable for charging to a blast furnace, and represents a substantial cost in the manufacture of crude iron. Conse-quently, it is important that as much sinter as possible isproduced per each unit of qrate area, in order to reduce in-vestment, maintenance, fuel and electrical-energy costsO
With regard to sinteriny capacity, -the most important factor is the permeability of the charge. The more yas drawn through the charye per un:it of tirne, the less time required to e~ect a satisfact~ry sintering operation. The pexmeability of the charge can be increased in a number of ways. The most usual method in this respect is to increase the amount of coarse particulate return-sinter admixed with the charge.
Large quantities of coarse return-sinter, however, increase the ar,1ount of fuel required per unit of weight of final sinter, and incur additional handling costs. Furthermore, in certain instances it is necessary to crush the final sinter, in order to obtain the requisite amount of return-sinter. An-other method often used is one in which the charge mixture issubiected to a subsequent rolling process in a drum. Al-though the perrneabLlity of the charge is increased to a certain
2 ~g~7 extent by this method, it is necessary to control accurate-ly the amount oE moisture present, and normally the amount of water needed is more than is justified by the thermal pro-gress of the sintering operation at the desired low level of fuel consumption. Nei-ther does rollin~ a mixed charge in a drum produce a stable charge. Instead, the charge produced tends to become compacted when subjected to the high underpressure desirable in suction sintering operations in respect of high plant capacity, when sin-tering fine, particu-late material.
In a number of cases attempts have been made to increase the permeability of the charge by micro-pelletizing one or more of the iron-oxide products making up the charge. How ever, this technique requires the provision of additional and expensive pelletizing apparatus, such as drum or pan pelletizers. Only extremely fine-grain material can be micro-pelletized, and normally it is necessary to use a binder, together with an accurately controlled addition of water, which may result in bogging in the lower regions of the charge during the sintering process, i.e. the mutual ad-hesion of respective particles in the bottom region. Another drawback is that the charge consit~ents are not mixed together with a thoroughness suffic:ient to favour desired formation of slag during the sintering and blast-furnace operations.
In many parts of the world, iron-oxide is highly en-riched i.n order ~irs-tly to increase -the iron content and secondly to remove con-taminents, such as phosphorous. In such working-up processes, prior to being enriched the ore must be ground down to such a small particle size as to render the resultant fine concentrate unsuitable or suction sintering.
Examples of such concentrates include the ~id-Swedish and Northern-Swedish concentrates which have been purified of phosphorous and which are thus very fine. In order to find a market for such materials, ~t has been elected to sinter them to pellet form. Sintered pellets, however, are not ideal agglomerates for treatment in blast furnaces, neither with respect to shape nor chemical composition, and in many in-~9~ 7 s-tances the sinter obtained from suction-sintering processes is preferred, no-t ieast because it can be made self-fluxing, i.e. the sinter can be made to include constituents neces-sary for the blast furnace.
In addition to fine particulate ore concentrates, there are many fine particulate iron-containing materials which cannot, at present, be agglomerated by suction sin-tering techniques. Examples of such concentrates include pyrite cinders, dust from oxygen-blowing processes, and other very fine metallurgical intermediate productsO
~ne attempt to find a solution with regard to a fine-particulate sinter charge is illustrated in Swedish Patent Specification No. 212 742, according to which a moist charge-mixture is subjected to high-frequency vibrations, to form a coherent cake which is placed in -the form of small pieces on a sinter grate and sintered. The aforementioned pieces are passed through a screen and classified in a manner so that the coarser fraction of the charge lies nearest the grate and the finer fraction lies on top of said coarser fraction.
Difficulties were encountered, however, when trying to put this method into practice. A relatively high moisture content was required in order -to obtain a plasticity suitable to form a cake. When the particulate material was vibrd-ted, the surfaces Oe the ca]ce became moist, which resulted in adhe-~5 sion to the surface supporting said cake. In addition, it was diEficult to achieve high-frequency vibration of sufficient penetration depth.
An object of the present invention is to provide a novel and advantageous method for producing a highly permeable suc-tion-sinter charge of stable structure, by which the dis-advantages discussed above can be at least substantially over-come.
To this end there i5 provided a method of the kind stated in the introduction, which is further characterized by adjusting the wa-ter content of -the material mixture to a level at which substantially the minimum of fuel is con-~I
sumed at the sintering temperature intended; and by so ad-justing the com~action pressure in relation to the set water content, corresponding substantially to the minimum fuel consumption, that the pore volume of the resultant cake is not totally filled by the water present in said mixture~ In this way, the aforementioned disadvantages are overcome in a simple manner. In suction-sintering a mate-rial bed formed in accordance with the invention, there is formed, when the bed is ignited at the upper surface thereof a combustion layer which is thin relative to the thickness of the bed and which moves downwardly through the entire bed while air is drawn by suction through said bed. Air which has been heated by cooling the already heated overlying part of the bed is charge~ to said layer, while gas from the com-bustion layer dries and heats the nearest underlying bedlayer. In this respect, the water content is of great signi-ficance to the course taken by the sintering operation, since with the amount of air charged per unit oE time constant, the water content determines the speed at which the front of the combustion layer moves down through the bed. On the other hand, the speed of the cooling layer following the combustion layer, and in which cooling layer the sintered charge material is cooled by the incoming air, is deterrnined by the highest temperature reached in the hed and the amount of air drawn therethrough, the speed of said combustion layer being constant when a constant amount of air is supplied and with a cons-tant highest temperature. The combus-tion layer and the cooling layer, however, will only move at mutually the same speed when the water content is that utilized in the method ac-cording to the invention, whereat, as before mentioned,there is obtained a desired thin combust:ion layer, which af-fords substantially minimum fuel consumption at desired sintering temperature. If the water content is reduced, the speed at which the combustion layer moves will increase but not the speed of the cooling layer, whereat the fronts of the two layers will move apart and there will be obtained a thick combustion la~er, requiring more fuel to be added in order to reach the desired combustion temperature. The reason why, in this case, a reduced water content results in an increased fuel consumption is that the sinter contains more residual heat when the combustion layer reaches the grate. If the water content is, instead, increased above the value at which the combustion and cooling layers move at the same speed, the speed at which the front of the combustion layer moves will decrease. The speed at which the colling layer movesr howeverf is unchanged. Besause of this, the sintering temperature will gradually fall, and may even fall to a level at which the charge will be extinguished, and hence the higher water content must be compensated fGr by increasing the amount of fuel supplied. Thus, at every given sintering temperature there is a determinable water content, which is adjusted in the method according to the invention so as to ob-tain the lowest possible fuel consumption. The cake formed by compacting the material in accordance with the invention may not, however, contain free moisture on the surfaces thereof, since otherwise the cake pieces become sticky and bake together in the charge placed on he grate, and when producing the cake by rolling, cause the rolls to slip against the cake, and a mechanicall~ weak cake is obtained. If the pores of the formed cake are unable to accomrnodate the amount of water necessary -to provide for the lowest possible fuel consumption, so that surface water occurs when pressing the rnaterial to cake form, it would seem an obvious thing to decrease the amount of water.
This would mean that more fuel must be charged, nowever. Thus, it has been found in accordance with the invention necessary to adjust the pore volume of the cake by regulating the com-paction pressure such that the cake is able to accornmodate therequisite amount of water. The extent to which the pores are filled, however, must not be extensively low, since, to a large extent, it is capillary forces which hold the cake to-gether. In this respect, it has been found that the pores ofthe pressed cake should be filled to at least 60 %, pre~erably ~0 - 90 ~,.
D ~ ~0~7 In the conventional preparation of a sinter charge it has been found necessary, in many cases, to add more water than required from the thermal aspect, in order to obtain a permeable charge, which means that more fuel is consumed.
S This is not necessary when preparing a sinter charge in accordance with the method of the invention proposed here, which constitutes a highly important advantage.
If the pressed cake is too thick, there is a risk of the fuel, normally fine coke particles, being entrapped so as to delay the ignition of the fuel. Because of this, the cake thickness should not exceed 12 rnm, and should not be smaller than 4 mm, since otherwise the cake will be too weak to enable it to be broken up in a predeterminable manner into pieces having a size suitable to form a suction-sinter charqe.
Furthermore, in order to obtain yood gas distribution and heat transfer between gas and goods in the sinter charge, the compacted cake should be broken up into pieces having a largest dimension of at most 20 rnm, preferably of at most 15 mm.
The resistance to suction of a mixture of two particle sizes is greater than the total suction resistance of the two particle classifications per se. ~ecause of this it has been found to be of advantage when the compacted cake, sub~
sequent to being broken up, is classified in a screening apparatus to form a relatively coarse particulate material fraction, which is placed nearest the grate, and a fine particulate material fraction, which is placed upon the coarse fraction. In this respect, it is to particular advantage when the classifying process is adapted so that the major part of the material, preferably about 2/3rds thereof, is present in the coarse material fraction lying neares-t the grateO The fact that the upper layer of the charge comprises the finer particles, rnakes it easier to ignite the charge. This also improves the transfer oE heat between goods and gas at that stage of the sintering process where stabilization of the front of the combustion layer is desirable. In addition, fuel can be saved by mixing fine, particulate additional fuei with the finer particulate fraction, since less fuel can then be used for the remainder of the charge.
As before mentioned, the invention also relates to an apparatus for producing on a mobile suction-sintering grate or in a stationary or mobile suction-sintering pan a highly permeable charge of stable structure, said apparatus com-prising means for compac-ting a stream of moist material-mixture to be sintered, to form a coherent cake, which is then broken up into pieces of a size suitable to form a suc-tion-sinter charge, said apparatus further including in ac-cordance with the invenkion means for so adjusting the com-paction pressure in relation to the water content of the material mixture that the pore volume of the cake formed is not completely filled by the water present in the material mixture. This arrangement enables the object of the invention to be realized with the use of means of simple construction.
Further charac-terizing features of the apparatus and advantages afforded thereby are disclosed in the following claims and illustrated hereinafter.
The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 illustrates schematically a first embodiment of the invention, Figure 2 illustrates schema-tically a second embodi}nent of the invention, and Figure 3 illus-trates schematically a third embodiment of the invention, in which bed layers are formed, one upon the other, by means of roll pairs arranged back-to-back in one and the same frame structure.
In Figure 1 the reference 10 identifies a mobile suc-tion-sintering grate, which is only partially shown, the bot-tom of the underlying suction box 11 being shown at 12.
Located on the grate 10 is a hearth layer 13 which comprises a coarse particulate material and which is intended to pre vent overheating of the grate 10 during a suction-sintering operatlon~ It '~7ill be seen from the drawings that as the grate moves slowly forwards in the direction of arrow 15, there is gradually formed on the grate 10 a bed 14 of mate-rial to be suction-sintered.
Arranged above the grate are means for compacting a moist material mixture 18 arriving on a conveyor 17 to form a coherent cake 19, said means in the illustrated embodiment having the form of a rolling mill identified generally at 16.
The moist material mixture may, for example, comprise a fine particulate iron-ore concentrate, fine particulate, iron-.10 -containing metallurgical intermediate products, coke dust and slag formers, whereat the fuel and water content are ad-justed with respect to one another so that substantially the minimum of fuel is consumed at the requisite sintering tempera-ture. The conveyor 17 is provided with a weighing device 20 and is driven at a speed such as to supply a constant amount of material to the rolling mill 16 per unit of tir.e. The string of material passing to the rolling mill is smoothed out or level-led by means of a scraper device 21, so that said string or stream of material has a uniform thickness along that part of the rolls 22 and 23 of the rolling mill active in compacting the material.
Connecting to the outfeed si.de of the roll palr 22, 23 is a slide plate haviny a flat bottom 24, which forms a down-wardly inclined support plate for receiving and yuiding the cake 19 forrned by the rolls 22, 23, to a location directly above the grate 10. As the cake 19 passes over the lower edge 25 of the plate 24, the cake is broken, by the action of gravity, into pieces having a size suitable to form a suction-sinter charge. The size of the pieces obtained can be varied by suit-able adjustment between, inter alia, the amount of materialmixture 18 supplied per unit of time and the roll pressure, which parameters determine the cak~e thickness and the mechani-cal strength of the ca~se, at least to a certain extent. The plate 24 may be arranged so as to enable it to be adjusted to different anyles relative to the horizontal. The angle at which the plate is inclin~d to the horizontal, howeverr shall be small enough to ensure that the friction generated between the plate and the cake 19 will prevent the cake from being broken upon the plate by gra~itational forces acting on said cake, before the cake reaches the edge 25, o~er which the cake is broken.
The rolls 22, 23 are driven synchronously by means of a respective motor (not shown) or a common motor, and are journalled in a rolling stand, which in the illustrated embodiment is supported by the ceiling of the building housing the suction-sintering plant, a part of said ceiling being shown at 26. Only one rolling stand, identified by reference 27, is illustrated in Figure 1. The other rolling stand has substantially the same design. The lower roll 23 is journal-led in a part 28 of each rolling stand, while each end o~ the other roll 22 is journalled in one arm 29 of a double-arm lever pivotally mounted at 30 in the associated rolling stand 27, che other arm of said lever being identified by reference 31. Acting against the other arm 31 is a hydraulic piston-cylinder device 32, which endea~ours to swing the lever in a direction in which the ro l 22 is urged towards the roll 23.
A double-arm lever with associated piston-cylinder device is provided for each end o~ the roll 22. The levers ma~, to ad-vantage, be rigidLy connected -toyether, so tha-t they are swung synchronously. Further, the arrangement is such that the plane cont~inin~J the axes of the rolls 22, 23 is substantially per~
pendicuJar to the plate 24, so that the cake 19 is supported by the plate 24 immediately it leaves the roll pair 22, 23l thereby eliminating the risk of unintentional, pr~mature dis-integration of the cake.
~ guide plate 33 which slopes downwardly rom the plate 24 connects with 'che lower edge 25 of the plate 24~ over which edge 25 the cake 19 is caused to disintegrate, said plate 33 beinq arranged to guide 'che cake pieces tc a screening appa-ratus 34, where they are divided into a relatively coars~
particulate fraction, which is placed nearest che grate 10 on top of the hearth layer 13 to form a lower layer 35 of the 1 ~
charge bed 14, and a relatively fine particulate fraction, which is placed on top of the layer 35, to form an upper layer 36 of the bed 14. In this way, screening oE the cake pieces is adapted so that the layer 35 will contain approxi-mately 2/3rds or more of the total amount of material in thebed.
In the illustrated embodiment, the screening apparatus 34 has the form of a drum comprising an outer casing of po1y-gonal cross-sectional shape provided with screen openings.
Extending along the whole of the length of the drum are out-wardly projecting, substantially radial ~lades 37. The screen-ing openings ma~ comprise slots which pass through the drum casing and extend peripherally thereof between mutually ad~
jacent blades 37. The width of the slots may, to advantage, be in the order of 10 mm. The drum is rotated clockwise by means of a motor (not shown), whereat coarse cake-pieces fall-ing onto the drum from the guide plate 33 will not pass through the screening openings, but will be moved to -the right, as seen in Figure 1, by the blades 37 and fall down onto the grate 10, as indicated at 38, to form the bed layer 35. The smaller cake-pieces will enter the drum through the screening openings and pass straight through said drum, to form a stream 39 of rela-tively fine particulate material, said finer pieces ~eing chargecl.
to the layer 35 already Eormed on the grate, to form the upper charye layer 36. As illustrated in Figure 1, desirable, fine additlves, such as fine, particulate additional fuel, can be homogenously mixed into the upper layer 36. To this end there is provided a conveyor 40 on which the fine particulate addi-tive material 41 is conveyed to the screening apparatus 34, through which said additive material is caused to pass whilst being admixed with the finer fraction of the material arriving from the guide plate 33. As shown at 42, the conveyor 40 is arranyed to co-ac-t with a weighing device, to enable correct metering of the additive material to the drum, and with a scraper device 43 for levelling out the stream of additive material passing to the screening apparatus ~4, so that said stream of additive material is of uniform thickness over the whole of its width.
For the purpose of obtaining, by rolling, a cake 19 having the correct properties there is provided a control means, generally referenced 44, by means of which the roll 5 pressure can be automa-tically adjusted and monitored so l:hat the cake 19 obtains the correct porosity relative to the amount of moisture present in the mixture 18, preferably so that the pores of the cake 19 are filled with water to a given percent-age within the range of 60 - 90 ~ by volume, within which 10 range the cake obtains the desired mechanical strength. The control means includes a pump 45, the suction side of which is connected to a hydraulic liquid sump 46 and the pressure side of which is connected to each hydraulic piston cylinder device 32, via a line 47. A return line 48 extends from the line 47 15 back to the sump 46, there being arranged in the return line 48 a regulatable throttle valve 49, the degree to which the valve 49 is throttled determinin~ the pressure exerted by each piston-cylinder device 32 on the arm 31, and therewith the roll pressure. The val~7e 49 is controlled from a known comparison 20 circuit 51, via a control line 50, said circui-t being arranged to receive on an input line 52 a signal which corresponds to a selected set-point value of the thickness of the cake 19. The comparison circuit 51 receives, via a line 53, an input signal.
sent by a -transducer 54 arranged to sense the thickness of the 25 cake 19, sa:id input slynal corresponding to the instantaneous cake thickness, whereat the comparison circuit 51 compares the signals from the lines 52 and 53 and when the signal obtained on line 53 deviates from the value corresponding to the set-point value of the thickness of said cake 19, adjusts the out-30 put signal on the line 50 so as to increase or decreasethe throttling effect exerted by the valve, thereby to change the roll pressure to a magnitude at which the desired cake thickness will be obtained.
As will be understood, the screening apparatus 34 and 35 the conveyor 40 can be omitted from the apparatus illustrated in Figure 1 when classification of the pieces obtained when disintegrating the cake 19, and the supply of additive material 41 is unnecessary. Further, it is, of course, possible to control the manufacturing process of the sinter charge in a different way to that illustrated and described. It will also be understood that the sintering grate 10 may be sta~
tionary and the apparatus producing the sinter charge arranged form movement along the grate.
In order to improve -the accuracy at which the material fraction 39 of finer particle size is placed on the grate when fractioning the material by means of the screening ap-paratus 34, there is arranged inside the screening drum a guide plate 55 which is journalled on the shaft 57 of the screening drum via end pieces 56, and the angle of inclination of which guide plate can be adjusted by rotation about said shaft 57.
Coinciding or substantially coinciding elementq in Figures 1, 2 and 3 are identified with the same reference nume-rals and will not be described in detail in the following de-scription of Figures 2 and 3, which illustrate a first and a second modifi.cation of the apparatus shown in Figure 1.
In the Figure 2 embodiment there is arranged above the support plate 24 adjacent the lower end thereof a d.riveable spiked roller 58, which :i.s pre~erably a variable-speed roller and which is intended to Eorrn f:ractural impressions in the cake l9 or to completely disintegrate the cake, the slze of the cake pieces being determined by the distance between -the spikes and the peripheral speed of the roller. For the sake of clarity, the motor driving the spiked roller 58 and the means supporting said roller have not been shown in Figure 2. The cake pieces obtained fall from the lower edge of the plate 24 in a stream 59, which forms an upper layer 60 of the bed 14 on top of a bed layer 61 previously placed on the grate 10 and the hearth layer 13. The bed layer 61 may be formed with the aid of a further roll pair (not shown) located to the righ-t, as seen in Fiyure 2, of the illustrated roll pair, and the mate-ri~l of the layer 61 may have a different composition or a dif-ferent r~lean particle size to the material of the layer 60.
As will be understood from the aforegoing, when prac-ticing the invention according to the embodiment illustrated in and described with reference to Figure 2, two separate roll pairs 22, 23 and ancillary equipment, arranged at some distance apart, are required to build the bed layers 60, 61 on the grate 10. While such an arrangement may be perfectly adequate, it requires a relatively large amount of space and equipment. Figure 3 illustrates an embodiment of the invention where the space required has been cut down by combining the two pairs of rolls in a common, compact unit.
Thus, Figure 3 illuskrates a mobile suction-sintering grate 10, on which the bed layers 60, 61 are formed by means of the two roll pairs 22, 23, and 22',23' arranged in one and the same open-frame structure 62, thereby obviating the need to provide two mutually spaced, separate layer-forming sta-tions and reducing the amount of space required. As shown in the Fig~lre, the open-frame structure comprises mutually spaced vertical members 63l top horizontal members 64 attached to ceiling 26 and bottom horizontal members 65, only one such top and bottom horizontal member being shown.
In the Figure 3 em~odiment, the roll pairs 22, 23 and 22', 23' are arranged back-to-back, so that the infeed sides of re-sp~c~ve roll pairs face one another. ~s will be seen from Figure 3, the infeed sides of respective roll pairs lie in a common storage vessel 66, into which material to be sintered is poured from a single conveyor 17. As with the previously described embodiments, -the conveyor 17 is arranged to co-act with a doctor on scraper means 21, for smoothing the material 18 conveyed by the conveyor 17. Connecting with the outfeed side of respective roll pairs 22, 23 and 22'/ 23' is a sup-port plate 24, which is inclined at an angle at which, while allowing a cake string to be moved down the plate 24 by the forces exerted thereon by the part of the cake issuing from the roll nip is not sufficiently large to cause the cake to slide down the plate under the influence of gravity at a speed liable to cause premature disintegra~ion of the cake.
As shown in Figure 3, each of the slide plates 24 has arranyed in the vicinity of the end thereof remote from re-spective roll pairs a spiked roll 58 mounted fox rotation on a bracket 67 carried by a respective vertical member 63.
5 Similar to the Figure 2 embodiment, the spiked rolls 58 are intended to break the coherent cakes on plates 24 into pieces of given size, said size being dependent on the spacing of the spikes on said rolls and on the peripheral speed thereof.
The roll pairs 22, 23 and 22', 23' of the Figure 3 embodiment are arranged in a manner resembling the mounting of the roll pairs 22, 23 of the Figure 1 and Figure 2 embodi-ments. Thus, the upper roll 22 or 22' of the roll stand shown to the left of the Figure is journalled for rotation in a fi~ed stand part 28, while the lower roll 23 or 23' of said roll pair is journalled on one arm 29 of a rotatable double-arrn lever journalled at 30 to the fixed stand part 28. The other arm 31 of respective double-arm levers is pivotally at-tached to the piston of a piston-cylinder device 32, which endeavours to swing the lever in a direction in which the rolls 20 23, 23' are urged towards the rolls 22, 22'. As with the roll pair of the emboaiments previously described, the arrangement is such that the planes containing the axes of th~ rolls 22~
23 and 22', 23' are substantially perpendicular to respective sli.de plates 24.
~lthouyh not ShOWIl in Figure 3 ea~h of the roll pairs is yoverned hy a control rneans 44 similar to that described with reference to Figure 1.
In order to ensure that the particulate material 18 in the vessel 66 is sufficiently friable to enable it to be picked up by the rolls of each roll pair, there is provided means for agitating the heap of material contained by the vessel 66, either constantly or at given periods. In the il-lustrated embodiment, the agitating means comprises at least one piston cylinder device having on the distal end of the piston roa 68 of said device a bar 69 which is parallel with the roll axes and i5 arranged to be moved into and out of the 15 ~ 7 heap of ma-terial 18 con-tained by the vessel 66. The bar 69 is provided with surfaces of such shape and size as to ensure that the material is stirred as the bar enters and leaves said heap, thereby to prevent bogging and to ensure a fri-able mass. As shown in the Figure, the cylinder 70 of the piston-cylinder device is secured to the frame structure 62 via a bracket 71. In operation, material 18 is fed to the vessel 66 by means of the conveyor 17, and is kept in a fri-10 able state in said vessel by means of the reciprocatingly movable bar 69. The material 18 is then picked up by the roll pairs 22, 23, and 22', 23' and compacted therebetween to form a coherent cake having the porosity desired, said porosity being controlled by said control means, as with the 15 Figure 1 embodiment. Each cake is moved down its respective support plate 24 to a spiked roll 58, which disintegrates the cake into pieces of given si~e. The pieces then fall onto the grate 10, forming either the layer 60 or the layer 61, depend-ing on the pOSitiGn of the plate 24 from which said pieces 20 fall, relative to the movement path of the grate 10, as clear-ly shown in the Figure. In order to provide a bed layer 61 of comparatively coarse material, the spikes of the spiked roll 58 associated with rolls 22', 23' may have a wider spacing than the spikes of the other roll 5~.
As will be understood, further modiEications of the apparatus accordiny to the inven-tion are possible within the scope of the invention. Thus, the pair or pairs of rolls may be arranged obliquely to the lonyitudinal direction of the grate or -the rolling equipment may be separate from the suc-30 tion-sinter:ing grate, whereat the finished sinter-charge material is delivered to the grate by means of suitable con-veying means, optionally via a charging or storage bunker.
The favourable effects which can be obtained by means of the invention will be evident from the fo:llowing examples, 35 in which a]l contents are given in percent by weight.
34~7 A material mixture comprising about 60 ~ Grangesberg concentrate GAC (fine particulate concentrate having a high iron content and a specific surface area of 550 cm2/g), about 32 % of anokher concentrate having a ]ower iron content, and about 8 % slag former, of which 4 ~ was burnt lime, was ad-mixed with 5 ~ coke dust, 8 % limestone and about 25 % returnsinter having a particle size beneath 6 mm, to form a suction-sinter charge mixture. This mixture, which was composed to provide a highly basic sinter, was moistened to a water con-tent o~ 7 %. The moist mixture was rolled to form a cake whose pores were filled with water to about 85 ~ by volume and which was then disinte~rated and screened in the manner described with reference to Figure 1 and illustrated in said Figure, there being used rolls having a diame-ter of 350 mm and a roll pressure of about 400 kp per cm of effective roll length. The screening slots in the screening drum had a width of 10 mm, whereat about 30 % of the material passed through the screening drum to form the ~in~r upper layer of the charye bed, the height of which reached to about 320 mm above the hearth layer, which was 20 mm high. Sintering was effected with an underpressure of 1500 mm water column. The sintering time was about 10 minutes (including a standard addition of 2 minutes), -there being obtained a production of about 42.5 ton~ per rn2 grate area and 24 hours. When subjected to a tumbler ~est, the resultant sinter, which was hard-burnt, had a value of about 60 ~. The aforegoing represents the result of a number of sintering tests subsequent to obtaining the stated approximate 25 % balance between input and output re-turn sinter. (For the tumbler test there was used a tumbler drum having a length of 900 mm and a diameter of 990 mm. The charge comprised 20 kg sintered material having a particle si~e of 20 - 40 mm, and the drum was rotated 200 revolutions during 8 minutes. Percentage by weight of tumbled material having a particle size exceeding 6 mm was measured.) A charge of the same composition but prepared in a con--17 ~ ~ ~ V ~ ~ ~
ventional manner, without rolling, gave with all other sinter-ing conditions equal a production of about 33 tons per m2 grate area and 24 hours, i.e. a production which was almost 30 % lower than the production obtained when practicing the method according to the invention.
A material mixture comprising about 60 ~ Grangesberg concentrate GPC (pellet-sinter concentrate having a high iron content and a specific surface area of 1600 cm /g), about 32 ~ of another concentrate having a lower iron content and about 8 ~ slag former, o~ which 4 ~ was burnt lime, was ad-mixed, for the purpose o~ forming a suction-sinter.charge mixture, with 4 % coke dust, 8 % limestone and about 22 %
return sinter ~6 mm). This mixture was moistened to a water content of 7 % and was ro~ed in accordance with Example 1 above to form a cake, t.he pores of which were filled with water to about 80 % by volume, whereafter the cake was dis-integrated by means of a spiked roller in accordance with Figure 2 and layed on a sinter grate, without being screened, to form a bed havin~ a height of about 350 mm over the hearth layer which was 20 mm high.
Subsequent to being dried, a sample of the mater.ial disintegrated by rneans of the spiked roller had the following particle ~ize distribution:
Particle size (mm)Percentage (~I
> 8 12.2 8 - 6 26.2 6 - 4 16.5 4 - 2 16.3 2 - 1 11.9 1 - 0,2 10.8 ~ 0.2 ~.1 The sintering operation was carried out in complete accordance with Example 1 above, and requi.red a time of 13 minutes (inclusive of the aforementioned two standard addi-tional rninutes) to carry out, there being obtained, subse-quent to reaching the return balance of about 22 %, a produc-tion of about 42 tons per m2 grate area and 24 hours. A
tumbler test as specified in Example 1 gave a result of about 65 ~.
It will be understood that such a fine concentrate as Grangesberg GPC could only be incorporated in extremely small quantities, when preparing suction-sinter charges in a conven-tional manner~
EX~MPLE 3 A material mixture comprising about 60 % Malmberget concentrate MPC 3 (pellet sinter concentrate having a high iron content and a fineness appro~imately the same as Granges-berg concentrate GPC), about 32 % of another concentrate having a lower iron content, and ahout 8 ~ slag former, of which 4 %
was burnt lime, was admixed, for the purpose of forming a suction-sinter charge mixture, with 4 % coke dust, 8 % lime-stone and about 23 % return sinter (<6mm). The mixture was moistened to a water content oE 7 % and rolled in accordance with Example 1 to form a cake, the pores of which ~ere filled with water to about ~0 ~ by volume, whereafter the cake was disintegrated by means of a spiked roller a~cording to Figure 2, and then placed on a sinter grate, without being screened, to Eorm a bed having a heiyht o~ about 350 mm above the hear-th layer, which was 20 mm high.
Sintering was effected in complete accordance with Example 1 above, and required a time o~ 13.5 minutes (inclusive of the 2 minute standard additional time), there being obtained, after reaching the return balance of about 23 %, a production o~ about 39.5 tons per m grate area and 24 hours. The tumbler test as specified in Example 1 gave a result of about 63 %.
It will be seen that such a fine concentrate as Malm-berget concentrate ~PC 3 could only be incorporated in an extremely small quantity, when preparing suction-sinter charges in a conventional rnanner.
It will readily be seen from the above description and ~xamples that the present invention provides a novel method and a novel arrangement of apparatus, capable of af~ording the following advantages:
1. Increased charge permeability, and therewith an in-crease in production per unit of grate area can be achieved, irrespective of the particle size of the input material.
2. The moisture content of the charge mixture can be held at the low level required for an optimal thermal sequence, ~0 thereby saving fuel.
In a number of cases attempts have been made to increase the permeability of the charge by micro-pelletizing one or more of the iron-oxide products making up the charge. How ever, this technique requires the provision of additional and expensive pelletizing apparatus, such as drum or pan pelletizers. Only extremely fine-grain material can be micro-pelletized, and normally it is necessary to use a binder, together with an accurately controlled addition of water, which may result in bogging in the lower regions of the charge during the sintering process, i.e. the mutual ad-hesion of respective particles in the bottom region. Another drawback is that the charge consit~ents are not mixed together with a thoroughness suffic:ient to favour desired formation of slag during the sintering and blast-furnace operations.
In many parts of the world, iron-oxide is highly en-riched i.n order ~irs-tly to increase -the iron content and secondly to remove con-taminents, such as phosphorous. In such working-up processes, prior to being enriched the ore must be ground down to such a small particle size as to render the resultant fine concentrate unsuitable or suction sintering.
Examples of such concentrates include the ~id-Swedish and Northern-Swedish concentrates which have been purified of phosphorous and which are thus very fine. In order to find a market for such materials, ~t has been elected to sinter them to pellet form. Sintered pellets, however, are not ideal agglomerates for treatment in blast furnaces, neither with respect to shape nor chemical composition, and in many in-~9~ 7 s-tances the sinter obtained from suction-sintering processes is preferred, no-t ieast because it can be made self-fluxing, i.e. the sinter can be made to include constituents neces-sary for the blast furnace.
In addition to fine particulate ore concentrates, there are many fine particulate iron-containing materials which cannot, at present, be agglomerated by suction sin-tering techniques. Examples of such concentrates include pyrite cinders, dust from oxygen-blowing processes, and other very fine metallurgical intermediate productsO
~ne attempt to find a solution with regard to a fine-particulate sinter charge is illustrated in Swedish Patent Specification No. 212 742, according to which a moist charge-mixture is subjected to high-frequency vibrations, to form a coherent cake which is placed in -the form of small pieces on a sinter grate and sintered. The aforementioned pieces are passed through a screen and classified in a manner so that the coarser fraction of the charge lies nearest the grate and the finer fraction lies on top of said coarser fraction.
Difficulties were encountered, however, when trying to put this method into practice. A relatively high moisture content was required in order -to obtain a plasticity suitable to form a cake. When the particulate material was vibrd-ted, the surfaces Oe the ca]ce became moist, which resulted in adhe-~5 sion to the surface supporting said cake. In addition, it was diEficult to achieve high-frequency vibration of sufficient penetration depth.
An object of the present invention is to provide a novel and advantageous method for producing a highly permeable suc-tion-sinter charge of stable structure, by which the dis-advantages discussed above can be at least substantially over-come.
To this end there i5 provided a method of the kind stated in the introduction, which is further characterized by adjusting the wa-ter content of -the material mixture to a level at which substantially the minimum of fuel is con-~I
sumed at the sintering temperature intended; and by so ad-justing the com~action pressure in relation to the set water content, corresponding substantially to the minimum fuel consumption, that the pore volume of the resultant cake is not totally filled by the water present in said mixture~ In this way, the aforementioned disadvantages are overcome in a simple manner. In suction-sintering a mate-rial bed formed in accordance with the invention, there is formed, when the bed is ignited at the upper surface thereof a combustion layer which is thin relative to the thickness of the bed and which moves downwardly through the entire bed while air is drawn by suction through said bed. Air which has been heated by cooling the already heated overlying part of the bed is charge~ to said layer, while gas from the com-bustion layer dries and heats the nearest underlying bedlayer. In this respect, the water content is of great signi-ficance to the course taken by the sintering operation, since with the amount of air charged per unit oE time constant, the water content determines the speed at which the front of the combustion layer moves down through the bed. On the other hand, the speed of the cooling layer following the combustion layer, and in which cooling layer the sintered charge material is cooled by the incoming air, is deterrnined by the highest temperature reached in the hed and the amount of air drawn therethrough, the speed of said combustion layer being constant when a constant amount of air is supplied and with a cons-tant highest temperature. The combus-tion layer and the cooling layer, however, will only move at mutually the same speed when the water content is that utilized in the method ac-cording to the invention, whereat, as before mentioned,there is obtained a desired thin combust:ion layer, which af-fords substantially minimum fuel consumption at desired sintering temperature. If the water content is reduced, the speed at which the combustion layer moves will increase but not the speed of the cooling layer, whereat the fronts of the two layers will move apart and there will be obtained a thick combustion la~er, requiring more fuel to be added in order to reach the desired combustion temperature. The reason why, in this case, a reduced water content results in an increased fuel consumption is that the sinter contains more residual heat when the combustion layer reaches the grate. If the water content is, instead, increased above the value at which the combustion and cooling layers move at the same speed, the speed at which the front of the combustion layer moves will decrease. The speed at which the colling layer movesr howeverf is unchanged. Besause of this, the sintering temperature will gradually fall, and may even fall to a level at which the charge will be extinguished, and hence the higher water content must be compensated fGr by increasing the amount of fuel supplied. Thus, at every given sintering temperature there is a determinable water content, which is adjusted in the method according to the invention so as to ob-tain the lowest possible fuel consumption. The cake formed by compacting the material in accordance with the invention may not, however, contain free moisture on the surfaces thereof, since otherwise the cake pieces become sticky and bake together in the charge placed on he grate, and when producing the cake by rolling, cause the rolls to slip against the cake, and a mechanicall~ weak cake is obtained. If the pores of the formed cake are unable to accomrnodate the amount of water necessary -to provide for the lowest possible fuel consumption, so that surface water occurs when pressing the rnaterial to cake form, it would seem an obvious thing to decrease the amount of water.
This would mean that more fuel must be charged, nowever. Thus, it has been found in accordance with the invention necessary to adjust the pore volume of the cake by regulating the com-paction pressure such that the cake is able to accornmodate therequisite amount of water. The extent to which the pores are filled, however, must not be extensively low, since, to a large extent, it is capillary forces which hold the cake to-gether. In this respect, it has been found that the pores ofthe pressed cake should be filled to at least 60 %, pre~erably ~0 - 90 ~,.
D ~ ~0~7 In the conventional preparation of a sinter charge it has been found necessary, in many cases, to add more water than required from the thermal aspect, in order to obtain a permeable charge, which means that more fuel is consumed.
S This is not necessary when preparing a sinter charge in accordance with the method of the invention proposed here, which constitutes a highly important advantage.
If the pressed cake is too thick, there is a risk of the fuel, normally fine coke particles, being entrapped so as to delay the ignition of the fuel. Because of this, the cake thickness should not exceed 12 rnm, and should not be smaller than 4 mm, since otherwise the cake will be too weak to enable it to be broken up in a predeterminable manner into pieces having a size suitable to form a suction-sinter charqe.
Furthermore, in order to obtain yood gas distribution and heat transfer between gas and goods in the sinter charge, the compacted cake should be broken up into pieces having a largest dimension of at most 20 rnm, preferably of at most 15 mm.
The resistance to suction of a mixture of two particle sizes is greater than the total suction resistance of the two particle classifications per se. ~ecause of this it has been found to be of advantage when the compacted cake, sub~
sequent to being broken up, is classified in a screening apparatus to form a relatively coarse particulate material fraction, which is placed nearest the grate, and a fine particulate material fraction, which is placed upon the coarse fraction. In this respect, it is to particular advantage when the classifying process is adapted so that the major part of the material, preferably about 2/3rds thereof, is present in the coarse material fraction lying neares-t the grateO The fact that the upper layer of the charge comprises the finer particles, rnakes it easier to ignite the charge. This also improves the transfer oE heat between goods and gas at that stage of the sintering process where stabilization of the front of the combustion layer is desirable. In addition, fuel can be saved by mixing fine, particulate additional fuei with the finer particulate fraction, since less fuel can then be used for the remainder of the charge.
As before mentioned, the invention also relates to an apparatus for producing on a mobile suction-sintering grate or in a stationary or mobile suction-sintering pan a highly permeable charge of stable structure, said apparatus com-prising means for compac-ting a stream of moist material-mixture to be sintered, to form a coherent cake, which is then broken up into pieces of a size suitable to form a suc-tion-sinter charge, said apparatus further including in ac-cordance with the invenkion means for so adjusting the com-paction pressure in relation to the water content of the material mixture that the pore volume of the cake formed is not completely filled by the water present in the material mixture. This arrangement enables the object of the invention to be realized with the use of means of simple construction.
Further charac-terizing features of the apparatus and advantages afforded thereby are disclosed in the following claims and illustrated hereinafter.
The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 illustrates schematically a first embodiment of the invention, Figure 2 illustrates schema-tically a second embodi}nent of the invention, and Figure 3 illus-trates schematically a third embodiment of the invention, in which bed layers are formed, one upon the other, by means of roll pairs arranged back-to-back in one and the same frame structure.
In Figure 1 the reference 10 identifies a mobile suc-tion-sintering grate, which is only partially shown, the bot-tom of the underlying suction box 11 being shown at 12.
Located on the grate 10 is a hearth layer 13 which comprises a coarse particulate material and which is intended to pre vent overheating of the grate 10 during a suction-sintering operatlon~ It '~7ill be seen from the drawings that as the grate moves slowly forwards in the direction of arrow 15, there is gradually formed on the grate 10 a bed 14 of mate-rial to be suction-sintered.
Arranged above the grate are means for compacting a moist material mixture 18 arriving on a conveyor 17 to form a coherent cake 19, said means in the illustrated embodiment having the form of a rolling mill identified generally at 16.
The moist material mixture may, for example, comprise a fine particulate iron-ore concentrate, fine particulate, iron-.10 -containing metallurgical intermediate products, coke dust and slag formers, whereat the fuel and water content are ad-justed with respect to one another so that substantially the minimum of fuel is consumed at the requisite sintering tempera-ture. The conveyor 17 is provided with a weighing device 20 and is driven at a speed such as to supply a constant amount of material to the rolling mill 16 per unit of tir.e. The string of material passing to the rolling mill is smoothed out or level-led by means of a scraper device 21, so that said string or stream of material has a uniform thickness along that part of the rolls 22 and 23 of the rolling mill active in compacting the material.
Connecting to the outfeed si.de of the roll palr 22, 23 is a slide plate haviny a flat bottom 24, which forms a down-wardly inclined support plate for receiving and yuiding the cake 19 forrned by the rolls 22, 23, to a location directly above the grate 10. As the cake 19 passes over the lower edge 25 of the plate 24, the cake is broken, by the action of gravity, into pieces having a size suitable to form a suction-sinter charge. The size of the pieces obtained can be varied by suit-able adjustment between, inter alia, the amount of materialmixture 18 supplied per unit of time and the roll pressure, which parameters determine the cak~e thickness and the mechani-cal strength of the ca~se, at least to a certain extent. The plate 24 may be arranged so as to enable it to be adjusted to different anyles relative to the horizontal. The angle at which the plate is inclin~d to the horizontal, howeverr shall be small enough to ensure that the friction generated between the plate and the cake 19 will prevent the cake from being broken upon the plate by gra~itational forces acting on said cake, before the cake reaches the edge 25, o~er which the cake is broken.
The rolls 22, 23 are driven synchronously by means of a respective motor (not shown) or a common motor, and are journalled in a rolling stand, which in the illustrated embodiment is supported by the ceiling of the building housing the suction-sintering plant, a part of said ceiling being shown at 26. Only one rolling stand, identified by reference 27, is illustrated in Figure 1. The other rolling stand has substantially the same design. The lower roll 23 is journal-led in a part 28 of each rolling stand, while each end o~ the other roll 22 is journalled in one arm 29 of a double-arm lever pivotally mounted at 30 in the associated rolling stand 27, che other arm of said lever being identified by reference 31. Acting against the other arm 31 is a hydraulic piston-cylinder device 32, which endea~ours to swing the lever in a direction in which the ro l 22 is urged towards the roll 23.
A double-arm lever with associated piston-cylinder device is provided for each end o~ the roll 22. The levers ma~, to ad-vantage, be rigidLy connected -toyether, so tha-t they are swung synchronously. Further, the arrangement is such that the plane cont~inin~J the axes of the rolls 22, 23 is substantially per~
pendicuJar to the plate 24, so that the cake 19 is supported by the plate 24 immediately it leaves the roll pair 22, 23l thereby eliminating the risk of unintentional, pr~mature dis-integration of the cake.
~ guide plate 33 which slopes downwardly rom the plate 24 connects with 'che lower edge 25 of the plate 24~ over which edge 25 the cake 19 is caused to disintegrate, said plate 33 beinq arranged to guide 'che cake pieces tc a screening appa-ratus 34, where they are divided into a relatively coars~
particulate fraction, which is placed nearest che grate 10 on top of the hearth layer 13 to form a lower layer 35 of the 1 ~
charge bed 14, and a relatively fine particulate fraction, which is placed on top of the layer 35, to form an upper layer 36 of the bed 14. In this way, screening oE the cake pieces is adapted so that the layer 35 will contain approxi-mately 2/3rds or more of the total amount of material in thebed.
In the illustrated embodiment, the screening apparatus 34 has the form of a drum comprising an outer casing of po1y-gonal cross-sectional shape provided with screen openings.
Extending along the whole of the length of the drum are out-wardly projecting, substantially radial ~lades 37. The screen-ing openings ma~ comprise slots which pass through the drum casing and extend peripherally thereof between mutually ad~
jacent blades 37. The width of the slots may, to advantage, be in the order of 10 mm. The drum is rotated clockwise by means of a motor (not shown), whereat coarse cake-pieces fall-ing onto the drum from the guide plate 33 will not pass through the screening openings, but will be moved to -the right, as seen in Figure 1, by the blades 37 and fall down onto the grate 10, as indicated at 38, to form the bed layer 35. The smaller cake-pieces will enter the drum through the screening openings and pass straight through said drum, to form a stream 39 of rela-tively fine particulate material, said finer pieces ~eing chargecl.
to the layer 35 already Eormed on the grate, to form the upper charye layer 36. As illustrated in Figure 1, desirable, fine additlves, such as fine, particulate additional fuel, can be homogenously mixed into the upper layer 36. To this end there is provided a conveyor 40 on which the fine particulate addi-tive material 41 is conveyed to the screening apparatus 34, through which said additive material is caused to pass whilst being admixed with the finer fraction of the material arriving from the guide plate 33. As shown at 42, the conveyor 40 is arranyed to co-ac-t with a weighing device, to enable correct metering of the additive material to the drum, and with a scraper device 43 for levelling out the stream of additive material passing to the screening apparatus ~4, so that said stream of additive material is of uniform thickness over the whole of its width.
For the purpose of obtaining, by rolling, a cake 19 having the correct properties there is provided a control means, generally referenced 44, by means of which the roll 5 pressure can be automa-tically adjusted and monitored so l:hat the cake 19 obtains the correct porosity relative to the amount of moisture present in the mixture 18, preferably so that the pores of the cake 19 are filled with water to a given percent-age within the range of 60 - 90 ~ by volume, within which 10 range the cake obtains the desired mechanical strength. The control means includes a pump 45, the suction side of which is connected to a hydraulic liquid sump 46 and the pressure side of which is connected to each hydraulic piston cylinder device 32, via a line 47. A return line 48 extends from the line 47 15 back to the sump 46, there being arranged in the return line 48 a regulatable throttle valve 49, the degree to which the valve 49 is throttled determinin~ the pressure exerted by each piston-cylinder device 32 on the arm 31, and therewith the roll pressure. The val~7e 49 is controlled from a known comparison 20 circuit 51, via a control line 50, said circui-t being arranged to receive on an input line 52 a signal which corresponds to a selected set-point value of the thickness of the cake 19. The comparison circuit 51 receives, via a line 53, an input signal.
sent by a -transducer 54 arranged to sense the thickness of the 25 cake 19, sa:id input slynal corresponding to the instantaneous cake thickness, whereat the comparison circuit 51 compares the signals from the lines 52 and 53 and when the signal obtained on line 53 deviates from the value corresponding to the set-point value of the thickness of said cake 19, adjusts the out-30 put signal on the line 50 so as to increase or decreasethe throttling effect exerted by the valve, thereby to change the roll pressure to a magnitude at which the desired cake thickness will be obtained.
As will be understood, the screening apparatus 34 and 35 the conveyor 40 can be omitted from the apparatus illustrated in Figure 1 when classification of the pieces obtained when disintegrating the cake 19, and the supply of additive material 41 is unnecessary. Further, it is, of course, possible to control the manufacturing process of the sinter charge in a different way to that illustrated and described. It will also be understood that the sintering grate 10 may be sta~
tionary and the apparatus producing the sinter charge arranged form movement along the grate.
In order to improve -the accuracy at which the material fraction 39 of finer particle size is placed on the grate when fractioning the material by means of the screening ap-paratus 34, there is arranged inside the screening drum a guide plate 55 which is journalled on the shaft 57 of the screening drum via end pieces 56, and the angle of inclination of which guide plate can be adjusted by rotation about said shaft 57.
Coinciding or substantially coinciding elementq in Figures 1, 2 and 3 are identified with the same reference nume-rals and will not be described in detail in the following de-scription of Figures 2 and 3, which illustrate a first and a second modifi.cation of the apparatus shown in Figure 1.
In the Figure 2 embodiment there is arranged above the support plate 24 adjacent the lower end thereof a d.riveable spiked roller 58, which :i.s pre~erably a variable-speed roller and which is intended to Eorrn f:ractural impressions in the cake l9 or to completely disintegrate the cake, the slze of the cake pieces being determined by the distance between -the spikes and the peripheral speed of the roller. For the sake of clarity, the motor driving the spiked roller 58 and the means supporting said roller have not been shown in Figure 2. The cake pieces obtained fall from the lower edge of the plate 24 in a stream 59, which forms an upper layer 60 of the bed 14 on top of a bed layer 61 previously placed on the grate 10 and the hearth layer 13. The bed layer 61 may be formed with the aid of a further roll pair (not shown) located to the righ-t, as seen in Fiyure 2, of the illustrated roll pair, and the mate-ri~l of the layer 61 may have a different composition or a dif-ferent r~lean particle size to the material of the layer 60.
As will be understood from the aforegoing, when prac-ticing the invention according to the embodiment illustrated in and described with reference to Figure 2, two separate roll pairs 22, 23 and ancillary equipment, arranged at some distance apart, are required to build the bed layers 60, 61 on the grate 10. While such an arrangement may be perfectly adequate, it requires a relatively large amount of space and equipment. Figure 3 illustrates an embodiment of the invention where the space required has been cut down by combining the two pairs of rolls in a common, compact unit.
Thus, Figure 3 illuskrates a mobile suction-sintering grate 10, on which the bed layers 60, 61 are formed by means of the two roll pairs 22, 23, and 22',23' arranged in one and the same open-frame structure 62, thereby obviating the need to provide two mutually spaced, separate layer-forming sta-tions and reducing the amount of space required. As shown in the Fig~lre, the open-frame structure comprises mutually spaced vertical members 63l top horizontal members 64 attached to ceiling 26 and bottom horizontal members 65, only one such top and bottom horizontal member being shown.
In the Figure 3 em~odiment, the roll pairs 22, 23 and 22', 23' are arranged back-to-back, so that the infeed sides of re-sp~c~ve roll pairs face one another. ~s will be seen from Figure 3, the infeed sides of respective roll pairs lie in a common storage vessel 66, into which material to be sintered is poured from a single conveyor 17. As with the previously described embodiments, -the conveyor 17 is arranged to co-act with a doctor on scraper means 21, for smoothing the material 18 conveyed by the conveyor 17. Connecting with the outfeed side of respective roll pairs 22, 23 and 22'/ 23' is a sup-port plate 24, which is inclined at an angle at which, while allowing a cake string to be moved down the plate 24 by the forces exerted thereon by the part of the cake issuing from the roll nip is not sufficiently large to cause the cake to slide down the plate under the influence of gravity at a speed liable to cause premature disintegra~ion of the cake.
As shown in Figure 3, each of the slide plates 24 has arranyed in the vicinity of the end thereof remote from re-spective roll pairs a spiked roll 58 mounted fox rotation on a bracket 67 carried by a respective vertical member 63.
5 Similar to the Figure 2 embodiment, the spiked rolls 58 are intended to break the coherent cakes on plates 24 into pieces of given size, said size being dependent on the spacing of the spikes on said rolls and on the peripheral speed thereof.
The roll pairs 22, 23 and 22', 23' of the Figure 3 embodiment are arranged in a manner resembling the mounting of the roll pairs 22, 23 of the Figure 1 and Figure 2 embodi-ments. Thus, the upper roll 22 or 22' of the roll stand shown to the left of the Figure is journalled for rotation in a fi~ed stand part 28, while the lower roll 23 or 23' of said roll pair is journalled on one arm 29 of a rotatable double-arrn lever journalled at 30 to the fixed stand part 28. The other arm 31 of respective double-arm levers is pivotally at-tached to the piston of a piston-cylinder device 32, which endeavours to swing the lever in a direction in which the rolls 20 23, 23' are urged towards the rolls 22, 22'. As with the roll pair of the emboaiments previously described, the arrangement is such that the planes containing the axes of th~ rolls 22~
23 and 22', 23' are substantially perpendicular to respective sli.de plates 24.
~lthouyh not ShOWIl in Figure 3 ea~h of the roll pairs is yoverned hy a control rneans 44 similar to that described with reference to Figure 1.
In order to ensure that the particulate material 18 in the vessel 66 is sufficiently friable to enable it to be picked up by the rolls of each roll pair, there is provided means for agitating the heap of material contained by the vessel 66, either constantly or at given periods. In the il-lustrated embodiment, the agitating means comprises at least one piston cylinder device having on the distal end of the piston roa 68 of said device a bar 69 which is parallel with the roll axes and i5 arranged to be moved into and out of the 15 ~ 7 heap of ma-terial 18 con-tained by the vessel 66. The bar 69 is provided with surfaces of such shape and size as to ensure that the material is stirred as the bar enters and leaves said heap, thereby to prevent bogging and to ensure a fri-able mass. As shown in the Figure, the cylinder 70 of the piston-cylinder device is secured to the frame structure 62 via a bracket 71. In operation, material 18 is fed to the vessel 66 by means of the conveyor 17, and is kept in a fri-10 able state in said vessel by means of the reciprocatingly movable bar 69. The material 18 is then picked up by the roll pairs 22, 23, and 22', 23' and compacted therebetween to form a coherent cake having the porosity desired, said porosity being controlled by said control means, as with the 15 Figure 1 embodiment. Each cake is moved down its respective support plate 24 to a spiked roll 58, which disintegrates the cake into pieces of given si~e. The pieces then fall onto the grate 10, forming either the layer 60 or the layer 61, depend-ing on the pOSitiGn of the plate 24 from which said pieces 20 fall, relative to the movement path of the grate 10, as clear-ly shown in the Figure. In order to provide a bed layer 61 of comparatively coarse material, the spikes of the spiked roll 58 associated with rolls 22', 23' may have a wider spacing than the spikes of the other roll 5~.
As will be understood, further modiEications of the apparatus accordiny to the inven-tion are possible within the scope of the invention. Thus, the pair or pairs of rolls may be arranged obliquely to the lonyitudinal direction of the grate or -the rolling equipment may be separate from the suc-30 tion-sinter:ing grate, whereat the finished sinter-charge material is delivered to the grate by means of suitable con-veying means, optionally via a charging or storage bunker.
The favourable effects which can be obtained by means of the invention will be evident from the fo:llowing examples, 35 in which a]l contents are given in percent by weight.
34~7 A material mixture comprising about 60 ~ Grangesberg concentrate GAC (fine particulate concentrate having a high iron content and a specific surface area of 550 cm2/g), about 32 % of anokher concentrate having a ]ower iron content, and about 8 % slag former, of which 4 ~ was burnt lime, was ad-mixed with 5 ~ coke dust, 8 % limestone and about 25 % returnsinter having a particle size beneath 6 mm, to form a suction-sinter charge mixture. This mixture, which was composed to provide a highly basic sinter, was moistened to a water con-tent o~ 7 %. The moist mixture was rolled to form a cake whose pores were filled with water to about 85 ~ by volume and which was then disinte~rated and screened in the manner described with reference to Figure 1 and illustrated in said Figure, there being used rolls having a diame-ter of 350 mm and a roll pressure of about 400 kp per cm of effective roll length. The screening slots in the screening drum had a width of 10 mm, whereat about 30 % of the material passed through the screening drum to form the ~in~r upper layer of the charye bed, the height of which reached to about 320 mm above the hearth layer, which was 20 mm high. Sintering was effected with an underpressure of 1500 mm water column. The sintering time was about 10 minutes (including a standard addition of 2 minutes), -there being obtained a production of about 42.5 ton~ per rn2 grate area and 24 hours. When subjected to a tumbler ~est, the resultant sinter, which was hard-burnt, had a value of about 60 ~. The aforegoing represents the result of a number of sintering tests subsequent to obtaining the stated approximate 25 % balance between input and output re-turn sinter. (For the tumbler test there was used a tumbler drum having a length of 900 mm and a diameter of 990 mm. The charge comprised 20 kg sintered material having a particle si~e of 20 - 40 mm, and the drum was rotated 200 revolutions during 8 minutes. Percentage by weight of tumbled material having a particle size exceeding 6 mm was measured.) A charge of the same composition but prepared in a con--17 ~ ~ ~ V ~ ~ ~
ventional manner, without rolling, gave with all other sinter-ing conditions equal a production of about 33 tons per m2 grate area and 24 hours, i.e. a production which was almost 30 % lower than the production obtained when practicing the method according to the invention.
A material mixture comprising about 60 ~ Grangesberg concentrate GPC (pellet-sinter concentrate having a high iron content and a specific surface area of 1600 cm /g), about 32 ~ of another concentrate having a lower iron content and about 8 ~ slag former, o~ which 4 ~ was burnt lime, was ad-mixed, for the purpose o~ forming a suction-sinter.charge mixture, with 4 % coke dust, 8 % limestone and about 22 %
return sinter ~6 mm). This mixture was moistened to a water content of 7 % and was ro~ed in accordance with Example 1 above to form a cake, t.he pores of which were filled with water to about 80 % by volume, whereafter the cake was dis-integrated by means of a spiked roller in accordance with Figure 2 and layed on a sinter grate, without being screened, to form a bed havin~ a height of about 350 mm over the hearth layer which was 20 mm high.
Subsequent to being dried, a sample of the mater.ial disintegrated by rneans of the spiked roller had the following particle ~ize distribution:
Particle size (mm)Percentage (~I
> 8 12.2 8 - 6 26.2 6 - 4 16.5 4 - 2 16.3 2 - 1 11.9 1 - 0,2 10.8 ~ 0.2 ~.1 The sintering operation was carried out in complete accordance with Example 1 above, and requi.red a time of 13 minutes (inclusive of the aforementioned two standard addi-tional rninutes) to carry out, there being obtained, subse-quent to reaching the return balance of about 22 %, a produc-tion of about 42 tons per m2 grate area and 24 hours. A
tumbler test as specified in Example 1 gave a result of about 65 ~.
It will be understood that such a fine concentrate as Grangesberg GPC could only be incorporated in extremely small quantities, when preparing suction-sinter charges in a conven-tional manner~
EX~MPLE 3 A material mixture comprising about 60 % Malmberget concentrate MPC 3 (pellet sinter concentrate having a high iron content and a fineness appro~imately the same as Granges-berg concentrate GPC), about 32 % of another concentrate having a lower iron content, and ahout 8 ~ slag former, of which 4 %
was burnt lime, was admixed, for the purpose of forming a suction-sinter charge mixture, with 4 % coke dust, 8 % lime-stone and about 23 % return sinter (<6mm). The mixture was moistened to a water content oE 7 % and rolled in accordance with Example 1 to form a cake, the pores of which ~ere filled with water to about ~0 ~ by volume, whereafter the cake was disintegrated by means of a spiked roller a~cording to Figure 2, and then placed on a sinter grate, without being screened, to Eorm a bed having a heiyht o~ about 350 mm above the hear-th layer, which was 20 mm high.
Sintering was effected in complete accordance with Example 1 above, and required a time o~ 13.5 minutes (inclusive of the 2 minute standard additional time), there being obtained, after reaching the return balance of about 23 %, a production o~ about 39.5 tons per m grate area and 24 hours. The tumbler test as specified in Example 1 gave a result of about 63 %.
It will be seen that such a fine concentrate as Malm-berget concentrate ~PC 3 could only be incorporated in an extremely small quantity, when preparing suction-sinter charges in a conventional rnanner.
It will readily be seen from the above description and ~xamples that the present invention provides a novel method and a novel arrangement of apparatus, capable of af~ording the following advantages:
1. Increased charge permeability, and therewith an in-crease in production per unit of grate area can be achieved, irrespective of the particle size of the input material.
2. The moisture content of the charge mixture can be held at the low level required for an optimal thermal sequence, ~0 thereby saving fuel.
3. When sintering, a small underpressure can be main-tained while achieving, at the same time, a high production, thereby reducing the amount of energy required to drive the fans.
4. The charge remains stable and will not compact during a sintering operation.
5. Sintering can be effected without admixing the charge with any other return material than return sinter.
6. ~ low level of ignition fuel and fuel admixed with the sinter charge can be maintained by employing a large charge-bed height.
7. Extremely fine particulate material, such as dus-t from steel manufacturing processes, ash from coal combusting process0s etc., can be sintered.
2~ ~. When cornpressing the charge mixture between rolls, only a low roll pressure is re~uired, for example a linear pressure of 150 - 1000 kp, preferably 200 ~ 800 kp, per cm of roll length, thereby greatly reducing the wear on the rolls.
2~ ~. When cornpressing the charge mixture between rolls, only a low roll pressure is re~uired, for example a linear pressure of 150 - 1000 kp, preferably 200 ~ 800 kp, per cm of roll length, thereby greatly reducing the wear on the rolls.
Claims (20)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for producing a moist suction-sinter charge of high permeability and stable structure on a mobile suction-sintering grate or in a stationary or mobile suction-sintering pan, comprising compacting a moist particulate material mixture to be sintered to form a coherent moist porous cake, in which the particles form-ing said cake are held together mainly by capillary forces, and breaking said cake into pieces of a size suitable for forming said suction-sinter charge, said method further comprising adjusting the water content of said material mixture, prior to compacting the same, to a level at which substantially the minimum of fuel is consumed at the sin-tering temperatures intended, and so adjusting the compac-tion pressure in relation to the set water content, corresponding substantially to the minimum fuel consump-tion, that the pore volume of the resultant cake is only partially filled by the water present in said mixture.
2. A method according to Claim 1, comprising forming a cake having a thickness in the range of 4-12 mm.
3. A method according to Claim 1, comprising compacting the material mixture to form a porous cake, the pore volume of which is filled with water to between 60-90%.
4. A method according to Claim 1, comprising breaking said cake into pieces having a largest size of at most 20 mm.
5. A method according to Claim 1, comprising classifying said pieces obtained by breaking said cake in a screening apparatus to form a relatively coarse parti-culate material fraction, which is layed nearest the grate, and a finer particulate material fraction, which is placed on top of the coarse particulate fraction.
6. A method according to Claim 5, comprising ad-mixing fine particulate additional material with said finer particulate material fraction.
7. An apparatus for producing a moist suction-sinter charge of high permeability and stable structure on a mobile suction-sintering grate or in a stationary or mobile suction-sintering pan, said apparatus including compaction means for compacting a stream of moist parti-culate material mixture to be sintered to form a coherent moist cake, and means for breaking said cake into pieces of a size suitable to form said sunction-sinter charge, said apparatus further comprising pressure adjusting means for so adjusting the compaction pressure in relation to the water content of the material mixture that the pore volume of the resultant cake is only partially filled by the water present in said mixture.
8. An apparatus according to Claim 7, comprising supply means for supplying moist particulate material mix-ture in a given amount per unit of time and with a given moisture content to said compacting means, and wherein said pressure adjusting means includes means for sensing the thickness of the cake and means for increasing or decreasing the compaction pressure exerted by said compac-tion means in response to a deviation of the sensed cake thickness from a selected set-point value.
9. An apparatus according to Claim 7, wherein the compaction means comprises at least one pair of pressure-loaded rolls having smooth or only shallowly grooved rolls, wherein a downwardly sloping support plate for supporting and guiding the cake exiting from said roll pair extends from the outfeed end of said roll pair to a location at which the cake is broken into pieces, the plate being in-clined at such a small angle that the friction generated between the plate and the cake prevents the cake from being broken by gravitational forces acting on the cake while said cake is located on said plate, and wherein the roll pair is arranged so that a plane which includes both axes of the rolls is substantially perpendicular to the support plate.
10. An apparatus according to Claim 9, wherein the compacting means comprises two pairs of pressure-loaded rolls, wherein said roll pairs are arranged back-to-back in an open frame structure common to both roll pairs, so that the infeed sides of respective roll pairs face each other, and wherein each said infeed side lies within a vessel arranged to receive material to be com-pacted.
11. An apparatus according to Claim 10, comprising means for agitating the material contained in said vessel.
12. An apparatus according to Claim 9, comprising a drivable spiked roller arranged above the support plate adjacent its lower end for breaking the cake into pieces having a sized determined by the mutual spacing of the spikes and the peripheral speed of said spiked roller.
13. An apparatus according to Claim 7, comprising a device located above the grate or pan for classifying the product formed by breaking said cake into a relatively coarse particulate fraction and a relatively fine particu-late fraction, and for placing the coarse particulate frac-tion nearest the grate and said fine particulate fraction on top of said coarse particulate fraction.
14. A method according to Claim 1, comprising compacting said moist particulate material mixture between at least one pair of pressure-loaded rolls.
15. A method according to Claim 1, comprising breaking said cake into pieces having a largest size of at most 15 mm.
16. A method according to Claim 5, comprising conducting the classifying operation in a manner such that the major part of the material is included in said coarse particulate material fraction.
17. A method according to Claim 5, comprising admixing fine particulate additional material with said finer particulate material fraction.
18. An apparatus according to Claim 9, wherein the lower end of the support plate is located directly above the suction-sintering grate or pan.
19. An apparatus according to Claim 12, wherein said spiked roller is a variable-speed roller.
20. An apparatus according to Claim 13, comprising means for separately supplying additional fine particulate material to said device.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000392677A CA1190417A (en) | 1981-12-18 | 1981-12-18 | Suction sintering method and apparatus therefor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000392677A CA1190417A (en) | 1981-12-18 | 1981-12-18 | Suction sintering method and apparatus therefor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1190417A true CA1190417A (en) | 1985-07-16 |
Family
ID=4121655
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000392677A Expired CA1190417A (en) | 1981-12-18 | 1981-12-18 | Suction sintering method and apparatus therefor |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1190417A (en) |
-
1981
- 1981-12-18 CA CA000392677A patent/CA1190417A/en not_active Expired
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