BE557615A - - Google Patents

Description

       

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   The present invention relates to the manufacture of cast iron from ore and a solid reducing agent, forming with the mixture of these elements agglomerates, which are then burned under the action of a stream of. forced air thus reducing them in part and making them

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 strongly adhere by a first heating operation, then by heating them again in a melting furnace to finally reduce them, melt them, carburize them and obtain the cast iron as a product.



   According to one characteristic of the invention, the process for manufacturing cast iron from iron ore and a solid carbon reduction agent consists in forming sufficiently coherent agglomerates, then in burning them under the action of a a forced air stream thereby causing the carbonaceous substance to undergo destructive distillation, and then converting the agglomerate into a product hereinafter referred to as coherent carbonized iron granules, in which part of the iron oxide was reduced to the metallic state, followed by heating the coherent granules to complete the reduction and melting, always in the presence of an initial amount of carbon sufficient to perform the bonding and thermal reduction operations. - ques and carburization of molten metal.

   The terms "carbonization-bound granules" and "carbonization-bound material" refer to the strongly bound residue obtained by the destructive distillation of the carbon-rich agglomerates of iron ore and fuels, such as coal, to obtain a graphitic matrix, such as can be obtained under the conditions specified in a madhine similar to that used to prepare ordinary agglomerates of iron ore,
The invention also comprises: a method of making pig iron from iron ore and a carbon reducing agent without using an ordinary blast furnace and under conditions which allow low tonnages to be processed economically. by a continuous operation with a constant flow and to interrupt

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 and slow down operations;

   a process for the production of graphitic matrix granules starting from premixes of non-coking iron ore and coal fines or of mixtures of coking and non-coking coal; a process for the manufacture of sufficiently coherent granules comprising a graphitic matrix and containing iron ore, the proportions of which are balanced so that the mixture is self-redacting at the reactive temperature and contains a sufficient quantity of carbon to effect - kill the carburizing of the cast iron you want;

   a process for the manufacture of sufficiently self-redacting agglomerated masses of a ferrous material comprising coherent and bonded graphitic matrices themselves containing a sufficient quantity of carbon to carry out the final reduction and carburization in the form of melting of the product, the strength is sufficient to withstand the pressures and conditions resulting from rapid charging, heating and reduction and melting in a melting furnace;

   a process for making coherent agglomerated masses of an intimate mixture of iron ore, a carbonaceous reducing agent and containing reduced iron and capable of being reduced and melted while maintaining their coherent and gas permeable state until they are melted, so that the reduction and the smelting proceed quickly and over a short path in the smelting furnace a process for making cast iron from the ore of iron and a carbonaceous reducing agent according to which the reduction is carried out by two separate heating operations,

   and wherein the fines of the ore and the reducing agent are formed into wet agglomerated masses which are treated in a heated zone to dehydrate.

 <Desc / Clms Page number 4>

 tation and destructive distillation with the .carbon agent ,. and a partial, but incomplete reduction of iron ore;

   then the bonded granules are treated by carbonization with bonding graphite matrices obtained during the first heating operation in a second heating zone to finally reduce them and melt them, usefully using the heat and the resulting gases of the smelting to complete the reduction and preheat the granules to the melting temperature, at the same time that the carbon of the initial mixture is maintained throughout the duration of the operation in intimate contact with the ore and the reduced iron, so to carry out the carburization and to regulate the effects of the re-oxidation and to shorten the total residence time in the final reduction and heating zone,

   
The term "self-reduction" in the description denotes a chemical ratio in the carbonization-bound granules whereby an amount of carbon intimately mixed with the iron ore is sufficient to reduce to the metallic state. The iron oxide contained in the granules bound by carbonization under the conditions of reduction existing in the melting furnace. The expressions "agglomerated" or "agglomerated mass" denote a coherent mass containing an intimate mixture of ore and reducing agent in relative proportions chosen so as to obtain sufficiently reducing granules and serve to denote the mass in its heat-treated form known as "granules or carbonized-bound material".



   The invention can be applied in practice by means of an installation shown schematically in the accompanying drawing in which: FIG. 1 is a schematic diagram of the successive processing operations,

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 EMI5.1
 fig \ 2 shows a variant of the heating installation which allows operation in different conditions.
 EMI5.2
 Example 1 - According to Fig. 11, a charge of iron ore (Bonson magnetite concentrates) is prepared in a mill 10 as a substantially dry powder. The composition and grain size of the crushed ore are as follows s
 EMI5.3
 .9..9.ill.P.Q.S i t t.

   9) 1- ore
 EMI5.4
 R.ol1rcent¯EL dry oids ¯
 EMI5.5
 
<tb> Iron <SEP> total <SEP> 61.6
<tb>
<tb> Mn <SEP> (evaluate) <SEP> 1.0
<tb>
 
 EMI5.6
 8i02 7.3 A120 3 3.7 Ca0 0.6 MgO 0.18 i0 0.80
 EMI5.7
 R <3pārt.it¯in the grain size of the broxed ore
 EMI5.8
 
<tb> Opening <SEP> of <SEP> meshes <SEP> of <SEP> Percentage <SEP> of <SEP> grains
<tb>
<tb> is, <SEP> mm <SEP> retained
<tb>
 
 EMI5.9
 +0.2? 2.64 -Oe25 +0.20 2.% -0.20 +0149 9124 o, ..4g +0.10? ll, l6. '-0.105 +0.074 13.44, -Ô'04 +05044 1 el6 9 46 8 Similarly; we grind a coal from Book Cliff, say no
 EMI5.10
 coking agent in commercial standards, in a crusher 11.



  The composition and grain size of crushed coal are as follows:
Composition, coal
 EMI5.11
 )? ource nt a [; f # .. lJ29i.ds c)
 EMI5.12
 
<tb> Volatile <SEP> materials <SEP> 37.8
<tb> Carbon <SEP> fixed <SEP> 56.2
<tb> Ash <SEP> 6.2
<tb> Sulfur <SEP> 0.62
<tb>
 
 EMI5.13
 Cpmpositnde JL cēndre de la coal.
 EMI5.14
 



  Percentaize Doids see) Cao o48 MgO <09a1 Si0 le7 AI 2 to3 2e7

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 EMI6.1
 1st artition of Larosseu these grains of coal b:;:,;) yée
 EMI6.2
 Mesh opening of Percentage of 2treat w ... ¯ tam ï s, mm ,, .... r ..... r retained +0.297 0.0 -0.297 + 0.210 0.08 - 0.210 i- 0 p 1 .C9 0.9 - 0.149 + 0.105 18.25 - p 1 +0.07 53 p 75 -o, 07 '+ 27.02 The crushed particles of ore are passed and
 EMI6.3
 of coal from mills 10 and 11 into a mixer 12 in which they mix intimately.

   The throughput of the mills 10 and Li is adjusted so as to obtain the desired relative proportions of ore and coal, for example 60 parts of ore fines and 40 parts of coal fines by weight. A proportion of 10 to 20% water by weight and preferably about 15% by a garden hose 50 is fed into the mixer so as to moisten the mixture and make it coherent, but not to wet it. It has been observed that with mixtures containing less than 10% water, granules of insufficient resistance are obtained in the operation.
 EMI6.4
 tion, next treatment. If the proportion of water in the mixtures is greater than about 20%, the granules obtained are too wet and too soft for the next operation.



   The contents of the mixer 12 are brought in with a
 EMI6.5
 bi t set at the upper end of a .13 granulating drum, for example with a diameter of 1.22 m and a length of 2) 44 m, rotating around an axis slightly inclined downwards towards its outlet end, for example at an angle of 7 with respect to the horizontal and rotating at a peripheral speed of about 67 m per minute. A garden hose 51 sends water sprayed into the granulating drum near its upper or loading end, in a proportion of about 2% by weight of the mixture.
 EMI6.6
 of ore fines and coal which arrives there eaçon to form granules.

   While the taI111 ") is running,

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 small agglomerated granules form initially and roll on top of each other over the rest of the mixture ve-
 EMI7.1
 ani; mixer 2 and progressively grow in size forming compact balls or spheres of increasing size which roll towards the lower outlet end of drum 13.



   The granules rolling out of the drum 13 pass over
 EMI7.2
 a double sieve 14, the upper perforated surface 14a of which retains the granules with a diameter greater than 15.9 mm and passes them through. a retaining channel 12. The lower perforated surface 14-b of the sieve retains granules with a diameter greater than .9 "mm but less than 7 $ 9 mm and allows smaller particles and fines from the mixture to remove.
 EMI7.3
 pass to fall on a conveyor 6 As an example, the double sieve 1- may have a length of about 1.2 m, a width of about 0.30 m, an inclination of 210 with respect to the horizontal and have a square mesh of 191 x 19.1 mm opening in the upper screen.



  The fines that fall on the conveyor 16 arrive
 EMI7.4
 in a retaining channel JL2.} from where a conveyor 18 brings them back to the loading end of the granular drum.
 EMI7.5
 their 13, in which they can grow into granules of the desired size. Too large granules retained by the upper sieve of the double sieve 14 and arriving in the gutter
 EMI7.6
 retainer 12 are carried by a conveyor 12 to the loading end of mixer 12, where they are crushed and distributed while the load from the drum.
 EMI7.7
 pelletizing 1.3. is being prepared. The granules of the desired size from the II + double sieve fall on a conveyor 20 which brings them to a hopper 21.



   When the granulating drum 13 and the double sieve
 EMI7.8
 w: l. work, granules of the desired size 9) 5 to 15 '; 9 mm slowly form over 20, 30 minutes after

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 beginning of the granulation operation. During this time, a large proportion of the mixture of fines arriving in the granulating drum 13 is recirculated through the double sieve 14 under the action of the conveyors 16 and 18 and of the retaining channel 17. After 30 to 45 minutes of operation, granules of the desired size are easily formed in a continuous fashion with a flow rate of 1.5 tonnes per hour.



   The granules arriving in hopper 21 are sufficiently coherent and self-reducing and their strength enables them to withstand the pressure and heating conditions which exist during the first heating operation. The granules exit in a continuous manner from the hopper 21 on. a moving grid 22 in a layer with a thickness of 76 to 127 mm.



   While the moving grid 22 advances the granules, an ignition device ignites them and they advance in a continuous movement in a heating zone represented schematically by the envelope of a wind box 24. They heat up. at a temperature of 1090 to 1260 C (that is to say a temperature below the slagging temperature of the mixture, to which it will be noted that no flux has been added according to this example) under the effect of a stream of oxygen-containing gas drawn into the casing 24 by an exhaust fan 25 at a flow rate of about 1200 cm3 / cm2 of the grid surface.

   As a result, the granules become dehydrated, then the coal undergoes destructive distillation and at the same time the carbon contained in the various granules causes a preliminary reduction, for example of 10 to 50%, of the iron oxide, so that the mass forms a carbonized bonded granule which comprises a graphitic bonding matrix of unexpected strength and particularly high in carbon content. The duration of

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 heating and blowing on the moving grate between the time when the green granules ignite and when the carbonized granules come out is about 8 to 12 minutes.



   The carbonized bonded granules leaving the moving screen 22 fall continuously onto a sieve 26 with a 6.35 mm mesh opening. The fines of the carbonized-bonded granules which pass through the screen 26 fall on a conveyor 27, then arrive on a conveyor 28 which brings them to the loading end of the mixer 12, where they become incorporated into the drum load. to granulate! #. The carbonized and oversized granules leaving the., Sieve 26 cool in the presence of air in a few seconds to the temperature of dark red, and can be stored or pass through a hopper 29. which makes them arrive regularly in a. melting furnace 30.



   The resistance and the quality of the granules bound by carbonization which arrive in the hopper allow them to withstand the pressure and load conditions existing in a melting furnace, in which the height of the load is for example 2, 44 m. The granules arriving at high temperature, during a continuous operation continue to be reduced. The quality of the bound granules can be defined by 1) the yield index 2) the degree of reduction and 3) their state of reducibility.



   The term "yield index" is a number which corresponds to the percentage of carbonized bonded granules which are retained on a sieve with a 4.76 mm mesh size. that is to say that the yield index represents the number of granules bound by carbonization coming from the moving grid which can be loaded and treated in the melting furnace without excessive loss of fines in the form of flying dust.

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 EMI10.1
 



  The term "degree of drafting" is a number which corresponds to the total percentage of reduced iron to the metallic level during the first heating operation and represents the ratio of the metallic iron of the carbonized-bound granules to the total iron of these. granules, expressed as a percentage by weight.
 EMI10.2
 



  The degree of metallic iron reaction of the granules xioo degree of reduction% - total iron of the granules xln0 The expression "3 state of reduction 3.bi13.tâ" is a number which corresponds to the percentage of the initial iron in the granules, which by final reduction gives metallic iron under the action of the carbon remaining in the granules. The state of reducibility is calculated by the following formula:

   
 EMI10.3
 Reliability status% =
 EMI10.4
 3s5 (% carbon in carbonized-bound granules) + ¯ (% ¯¯dē metallic iron in these granules) ----- x 100% total iron in carbonized-bound granules
Note that the value of the state of reducibility can be greater than 100, indicating that the mixture
 EMI10.5
 The original contained an excess of hard coal, which was rebuilt during the first heating operation and which is suitable for fuel for fuel and heating.

   An example of the composition of the carbon bonded granules thus prepared is as follows:
 EMI10.6
 
<tb> Iron <SEP> total <SEP> in <SEP> the <SEP> granules <SEP> linked <SEP> by <SEP> carbonization <SEP> 56%
<tb> Metallic <SEP> iron <SEP> in <SEP> these <SEP> granules <SEP> 17%
<tb> Carbon <SEP> in <SEP> these <SEP> granules <SEP> 15%
<tb> Degree <SEP> of <SEP> reduction <SEP> 30%
<tb> <SEP> index of <SEP> yield <SEP> 75%
<tb>
 
 EMI10.7
 124% reducibility state.



   The fact that it is possible to heat in a blown air stream containing oxygen crude granules containing up to 40% non-coking coal to form strong and coherent granules with a high residual carbon content is an unexpected phenomenon, because it is contrary to all known principles.

   It has been established without dispute and generally accepted that when the content of com-

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 fuel of an initial mixture of iron ore and fuel exceeds approx. 12 to 15% and this mixture is subjected to an ordinary agglomeration treatment, the fuel penny to be burned until it is more or less completely consumed so that whatever the content may be. The initial fuel content of the mixture, the residual fuel content after heating is approximately less than 1.%. By specially adjusting the heating operation, as will be seen in.

   In detail below, strong and coherent bonded granules are obtained with a high residual carbon content.



   On examining with the naked eye a granule bound by carbonization, it is found that it has the appearance of a dense, strong, coherent mass of amorphous carbon, very similar to that of charcoal, without visible indication of the presence of a molten material on the surface or on a broken fragment * It is observed in. microscope and in particular with high magnification that the structure of the granule is not homogeneous but is formed by four main elements:
1. A graphitic carbon matrix similar to a sponge. The porosity of this carbon matrix is microscopic and the diameter of its largest pores is of the order of 020635 mm.



   2. Very fine particles of metallic iron ranging in size from 0.00025 to 0.00125 mm often forming a border around larger grains of iron oxide, about 0.075 mm in diameter. .



   3. Grains of iron oxide dispersed in the carbon matrix which, with. magnification less than 500 diameters and light illuminates appear homogeneous, while in polarized light and higher magnification the oxide grains have a sharply defined "duplex" structure, which has extremely fine veins of metallic iron crisscrossing in the oxide.

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   4. Chains or groups of very small irregularly shaped patches of ore gangne on which no sign of fasion appears.



   A very remarkable feature of the structure of carbonized-bonded granules which appears microscopically under polarized light is that the carbon matrix is formed by graphitic carbon in very fine crystals instead of amorphous carbon. .

   The product generally obtained from the low temperature carbonization of hard coal consists of 100% amorphous carbon, while coke, which is the product of high temperature coal carbonization, contains at most about 10 to 20% of graphitic carbon, the remainder consisting of amorphous carbon, It is accepted from experience gained in the manufacture of graphite electrodes that the transformation of amorphous carbon into graphitic carbon requires a very long heating cycle (4 to 6 days) at a very high temperature, around 1980 C.

   It is therefore completely unexpected to find that, in order to prepare granules bound by carbonization, a heating cycle of a few minutes at a temperature of about 1150 to 1205 C in a current of air is sufficient. to completely transform the amorphous carbon into very fine crystal graphitic carbon and noting that the graphite obtained by heating for a very long time at high temperature has a coarse crystal grain structure. The reasons for this phenomenon are not known.

   We could admit that this is explained by considering that the coal particles are extremely fine, that they are in intimate contact with the very fine particles of iron oxide (which can exert an oatalytic action) and that the heating rate is extremely fast. '

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This product is distinguished from charcoal and coke by its bulk density, that of metallurgical coke being about 0.432%. fact that it has about 81% void in total, 45% of which is formed by the space between the particles and 36% by the voids inside the particles ,,

     The carbonized-bound granules have 74% total void of which about 29% is inside the particles and their bulk density is around 1200 kg / m3. Large cavities visible in the coke pieces do not exist in granules bound by carbonization.



   The carbonized bonded granules exiting hopper 29 arrive at the top of a melting furnace 30. A conveyor 31 feeds into the melting furnace. particulate coke of suitable size to heat and support the granules. Likewise, a conveyor 32 causes an appropriate flow to enter the melting furnace.

   An example of a charge introduced into a 25 cm diameter melting furnace is as follows;
 EMI13.1
 
<tb> Materials <SEP> Weight, <SEP> kg <SEP> Size, <SEP> mm
<tb>
<tb> Granules <SEP> linked <SEP> by <SEP> carbonization <SEP> 7 <SEP> 9.5 <SEP> to <SEP> 15.9
<tb> Coke <SEP> 1.8 <SEP> 19 <SEP> to <SEP> 31.5
<tb> Limestone <SEP> 1.35 <SEP> 6.35
<tb> Spath <SEP> fluor <SEP> 0.15 <SEP> 9.15
<tb>
 
A stream of air is brought into the melting furnace 3¯0 through nozzles 33 coming from a blower 34 and this flow of air rises through the charge of the furnace, causing the coke to burn which heats the masss and melts the iron of the reduced carbonized granules located in the lower part of the furnace,

   so that the molten iron forms in the lower part 35 of the furnace a mass covered with a layer 36 of slag formed by gangue and flux agents. Metallic iron undergoes carburization by reacting in the melting zone with residual carbon which

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 surrounds it and carburization ends as the molten iron drops pass through the lower layer. The reaction of iron ore during its reduction forms carbon oxides, largely carbon monoxide.



  The air flow acts on the carbon remaining in the lower, reduced, carbon bonded granules and on the heating coke of the shown example of heating the interior of the melting zone, by forming carbon dioxide which, on reacting again with the heated solid carbon, forms carbon monoxide gas.

   The carbon oxide passes from the bottom up through the top charge at a temperature at which the iron oxide in the granules of successive bottom to top portions of the charge is reduced by the action combination of this carbon monoxide and the carbon contained in the granules bound by carbonization, but in principle without melting or appreciably weakening the granules as they descend into the melting furnace as they approach the fu zone - if we.

   metal can be collected through a taphole 37 and slag through a taphole 38
For example, the internal diameter of the melting furnace 30 can be 25 cm, its height 2.44 mm above the nozzles and it can operate with a flow rate of 537 kg of iron per m2 of surface. of sole and per hour. Up to 99% of the metallic iron is collected. total iron contained in the granules which pass through the oven.



   By way of example, the conditions under which the 25 cm melting furnace is operated are as follows;

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 EMI15.1
 Stage 4 to 6 kg of air per minute 'in!;:'! 11 "@n oxygen from the wind 21 to 3 ''; at Tmpersto.ps from the wind 482 0 Te} .1elJ.r in humidity from the wind 5 g per kg of air Type <ï & coating: oven siliactui9 do3.aï: iaue gtt Q, $ !, weighted.



  SBO-sj.tion of cast iron obteauc-
 EMI15.2
 
<tb> Carbon <SEP> total <SEP> 2.5 <SEP> to <SEP> 4 <SEP>, 2
<tb>
<tb> Silicon <SEP> 0.3 <SEP> to <SEP> 1.2 <SEP>%
<tb>
 
 EMI15.3
 Manganese 09c79 a 0.24% Phosphorus 1903 0.09% Sulfur 00 '? at O30 Composition of the slag obtained:

   
 EMI15.4
 CaO 15 - 1- 47% Sj.02 10 to 43% MgO 5 "a 19% A1203 14 Fe
 EMI15.5
 
<tb> FcO <SEP> 1 <SEP> to <SEP> 5 <SEP>%
<tb>
 The total melting time of the carbon-bound granules
 EMI15.6
 1) onisation, allto-redllcteurs, coherents, clest-a-dJ.re the duration of the day in the furnace between the loading surface and the nozzles is about 30 minutes, while in: blast furnaces ordinary, this duration is measured in hours. Coherent, carbon bonded granules therefore exert a great influence on the speed of the smelting process compared to that of ordinary sinter feedstock of ore and coke.



   The rate of production of cast iron is significantly increased by increasing the diameter of the melting furnace. For example, the production rate in a melting furnace of a diameter
 EMI15.7
 inner meter of t.5 'cm iron 635 kg of font? p-ar z of sole surface per hour.



   The various operations of the process of the invention can be carried out continuously or in intermittent charges and independently with several granulation plants and several heating plants which feed the bound granules into a single melting furnace. The bound granules can be cooled and shipped to a different plant for reduction in a melting furnace. They constitute

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 thus kill a solid and resistant manufactured object which, separated from fines, can be shipped by truck and, because of its cohesion, can be loaded into furnaces with the addition of flux and fuel, in sufficient quantity to melt the gangue.

   It will be noted that the granules thus bonded by carbonization are self-reducing and sufficiently coherent because they contain a sufficient quantity of carbon to reduce the iron to the metallic state and to carburize the metal thus formed; or, according to fig.l, the carbonized bonded granules can retain the heat which they contain when leaving the moving grate if they are loaded directly at the exit of the moving grate into the melting furnace.

   Another solution is to discharge the hot, bound granules from the moving grate into a separate living furnace in which the burnt gases from the melting furnace continue to heat them for a time sufficient to increase the degree of heat. reduction,
An important advantage of the process of the invention consists in the possibility of carrying out the heating operations under the operating conditions indicated above, at the individual speeds most advantageous for the installation and the materials. choose and start and stop them separately at will.

   For example, with a blowing time of 15 minutes or less (generally less than 10 minutes, as shown in the following examples) on the moving grate to perform the carbonization bonding operation, and with a duration of stay for 30 minutes in the melting furnace, the installation can be completely stopped in less than an hour from the moment when the granulation operation in the rotating drum is interrupted, and it can be completely restarted after the same time. We can perform.

 <Desc / Clms Page number 17>

 stops similar to the corresponding instants necessary when the operations of bonding by carbonization and of fusion are carried out at different points.

   At this stage; the process is markedly different "from the operation of an ordinary blast furnace which must operate continuously for long periods of time, noting in particular that the residence time is measured in hours, this possible intermittence is of high value in small reduction facilities.



     Example 2 - To prepare the bonded, sufficiently coherent granules of Example 1, they are driven from the hopper 21 onto the moving grid 22 with a flow rate chosen so as to form a uniform layer of 75 to 125 mm d 'thick- only', then the granules are ignited;

   or, as shown in fig. 2, a drying device 54 can be inserted between the hopper 21 and the ignition device 23 and hot gas supplied to it from a chamber 56 by means of a suction fan 55. The hot gases can be used. from chamber 24 .. It is not possible to dehydrate the granules beforehand before they arrive in the hopper 21 because in the dry and uncarbonized state their resistance is insufficient, Pre-dehydration should be carried out in such a way as to avoid mechanically handling the dehydrated uncarbonized granules, prior to the first heating or the destructive distillation and thermal bonding operation.

   The preliminary dehydration can be carried out by passing through the layer of raw granules of the moving grate hot air or the products of combustion. The prior dehydration has the effect of reducing the time required for heating the granules, once they have ignited. The table below shows by way of example the effect exerted by a preliminary dehydration on the heating time after inflammation. These results were

 <Desc / Clms Page number 18>

 obtained on type grids with intermittent loads.



     @ Composition of the granules
 EMI18.1
 - -. - - lees
 EMI18.2
 Type No. of Grossel1l'Dl1re6 de Fer to- Fer me- Carbon Index State of the granules of the gra-heating% talli-% of yields, mm gemin que% delent bilit3% green law 13 to 16 21.5 56.5 25.4 Il, 5 66 116 106 sec 13 to 16 1025 58.0 31.4 11.5 58 123 107 green 16 to 19 26 57.0 25g9 1527 69 148 109 green 19 at 22 30 53, 17e5 175 66 143 110 sec 19 to 22 12, 9 157 1551 7 125 111 green 22 to 25 24 56e, I5, 7 11.9 65 102
 EMI18.3
 
<tb> 112 <SEP> sec <SEP> 22 <SEP> to <SEP> 25 <SEP> 13 <SEP> 52.2 <SEP> 25e2 <SEP> 18.2 <SEP> 77 <SEP> 170
<tb>
 
 EMI18.4
 Example - The quality of the bound granules is determined
 EMI18.5
 by carbonization by the three "1ndiëe.s' of Example 1 and this quality is obtained by adjusting the variable factors of:

   1) the composition of the initial mixture 2) the size of the granules, 3) the flow rate of the wind during the first heating operation, 4) the blowing time during the first heating operation, 5) the final temperature of the grate , 6) the temperature of the wind during the first heating operation, 7) the oxygen content of the wind during the first heating operation and 8) the thickness of the layer of granules on the moving grid during the first heating operation.



   The composition of the Initial mixture depends in part on the proportions of ore and coal, which can be for example 60 parts of ore to 40 parts of coal, 70 parts of ore to 30 parts of coal, etc. are given below.



   Composition of the composition of the granules initial mixture ¯ bound¯¯¯¯¯¯¯¯¯
 EMI18.6
 
<tb> n <SEP> from <SEP> to <SEP> weight, <SEP> Iron <SEP> to- <SEP> Iron <SEP> m- <SEP> Carbon <SEP> Index <SEP> State <SEP> of
<tb> 1-'test <SEP> ore / coal <SEP> tal <SEP>% <SEP> talli- <SEP>% <SEP> of <SEP> ren- <SEP> reducti-
<tb>
 
 EMI18.7
 - -. q! 1e% - .dement bilié% 163 85-15 48.5 10.1 18 8 66 16 8 80-20 4o, 3 1.0 2615 - 233 70-30 51eo ge2 le8 140 10 6o-4o 5110 30 4 26 3 240 16 50-50 +6; 8 23.6 32 5 292

 <Desc / Clms Page number 19>

 
The composition of the mixture. Initial also depends in part on the braid of the chosen iron ore.

   For example, some ores from direct shipment of concentrated minerals
 EMI19.1
 and successes are raw materials which are satisfactory in the process of the invention. For example, bound granules have been produced which are satisfactory.
 EMI19.2
 with a hematite ore from Mesabi. The composition of this ore and the grain size distribution of the crushed ore are as follows
 EMI19.3
 poml.o! itJ: .2.! l ore.



    Percentage
 EMI19.4
 
<tb> Fe <SEP> 50.2
<tb>
<tb> Mn <SEP> 0.6
<tb>
<tb> SiO2 <SEP> 14.1
<tb>
<tb>
<tb> A12 <SEP> O3 <SEP> 2. <SEP> 0
<tb>
<tb>
<tb> CaO <SEP> 0.57
<tb>
 
 EMI19.5
 .MgO 0 '0
 EMI19.6
 
<tb> Humidity <SEP> 8 <SEP> to <SEP> 12
<tb>
 
 EMI19.7
 E.:iP.e.r....titi011 from: l @ gx: o, l1rdes, J¯rai.! Lmine!:, <1i² brol
 EMI19.8
 
<tb> Opening <SEP> of <SEP> meshes <SEP> of <SEP> Percentage <SEP> of <SEP> grains
<tb>
 
 EMI19.9
 sieve., mm ..¯¯¯ .. retained ¯¯¯¯¯ + Oe2lO 1.1 -0.210 +0149 2e3. -.0;) 190.10p 80 -0105 + 0.074 Il, 3 -0.074 773 The carbonaceous material of example 1 is called coal
 EMI19.10
 non-coking; it is also possible to choose coking and weakly coking coal.

   For example, Columbia & Horse Canyon coal was used in fresh, low-coking condition and in non-coking storage condition. The composition of the coal and the distribution of the size of its grains after crushing are as follows.
 EMI19.11
 



  Composition, Columbia Coal 8c Horseg, anyon
 EMI19.12
 
<tb> <SEP> content in <SEP> humidity <SEP> to <SEP> the <SEP> state of <SEP> reception <SEP> 1.4%
<tb> Index <SEP> of <SEP> swelling <SEP> free <SEP> Nos <SEP> 1.5 <SEP> to <SEP> 2
<tb> Approximate <SEP> composition <SEP> (weight <SEP> sec)
<tb> Volatile <SEP> material <SEP> 37.5 <SEP>%
<tb> Carbon <SEP> fixed <SEP> 51.6 <SEP>%
<tb> Ash <SEP> 10.9 <SEP>%
<tb> Sulfur <SEP> 1.51%
<tb>
 

 <Desc / Clms Page number 20>

 Composition of the center (% of the DRY houilze)
 EMI20.1
 
<tb> CaO <SEP> 0.53 <SEP>%
<tb>
<tb> MgO <SEP> 0.125
<tb>
 
 EMI20.2
 6in sion
 EMI20.3
 
<tb> A12O3 <SEP> 3255 <SEP> il <SEP>
<tb>
 
 EMI20.4
 Repa.rti.t¯ion, d,

  e.lārosseu.r. des fears of crushed coal
 EMI20.5
 
<tb> Opening <SEP> of <SEP> meshes <SEP> of <SEP> Percentage <SEP> of <SEP> grains
<tb>
 
 EMI20.6
 sieve -2 mm retained + 0.210 1.1 -0.210+ a 12 - 6, -oel25 +0.110 627 -0, l10 + OeO74 2896
 EMI20.7
 
<tb> -0.074 <SEP> 28.6
<tb>
 
 EMI20.8
 Examples of the granules related: re-prepared with Columbia & Horse Canyon oil as carbonaceous material are as follows:

   
Composition of the bound granules
 EMI20.9
 Ratio No. m'nera * - / Total iron Iron metal- Carbon Index Melan-% tique de rensai ¯ ¯¯ initial ..-. ¯¯ -... ¯ ..¯¯¯ ,. ¯. ¯ ¯ ¯¯.¯ ... dement 92 80-20 6D, ç = 13, 7 4.0 75 9- 80-20 62, B 16e5 3e7 78 95 80-20 63, Q 13.1 530 71 97 ' 80-20, 64-,. 12.9 3? O 76
The carbonaceous material of the initial mixture may also according to the invention consist of lignite or other fuel of inferior quality.



   Granules of 9 to 15 mm were chosen in the course of Example 1, but the larger granules have been found to be very advantageous in certain types of melting furnaces. For example = with larger granules, a higher gas permeability of the melting furnace charge is obtained. Examples of larger granules which have given satisfactory results in this operation are given below, but larger granules can still be selected in certain melting furnaces according to the invention.

 <Desc / Clms Page number 21>

 



  Composition of granules
 EMI21.1
 --- ¯u- - - J, J8.¯L: .. ¯¯.¯ ----
 EMI21.2
 
<tb> N <SEP> of <SEP> Diameter <SEP> of <SEP> Iron <SEP> to- <SEP> Iron <SEP> m- <SEP> Carbon <SEP> Index <SEP> State <SEP> of
<tb>
 
 EMI21.3
 es- granules tal% gallic% yield- redueti- sai mm% demented 'iîi j 107 15.9x19 5720 259 157 69 142 110 19 x22.2 54pg 157 15l 78 125 112 222x2? - 52.2 22 18, 2 77 170 1'-l'5 222x2a4 5329 4.9 14a5 75 rice 146 22.2x2.4 5î 4s8 il6 75 82 192 1.9x22.2 6023 16.1 7.7 68 71 193 l?; 9x22.2 62.3 19.7 7.0 '7 71 286 22g2x2,! + 4/7 î7s4 11? 6 88 106 287 22.2x254 56a2 26, o 15e5 86 142
The blowing rate during the first heating operation refers to the amount of air (also designating the air modified by the addition of oxygen or by the products of combustion) pushes back through the pellets when ignited.

   By appropriately adjusting the value of the other heating variables referred to in detail below, the blowing rate can be varied in the following manner to obtain carbon bonded granules of acceptable quality.
 EMI21.4
 



  Composition of "bound granules ¯.¯¯ ¯ ¯ ¯ ---- -.---- -----
 EMI21.5
 
<tb> N <SEP> of <SEP> Flow <SEP> of <SEP> wind <SEP> Iron <SEP> to- <SEP> Iron <SEP> m- <SEP> Carbon <SEP> Index <SEP> State <SEP> of
<tb>
 
 EMI21.6
 the es em.3 / m2Ln ,, par tal,% metal reduction OM2 of surface% dement bi7.iteao of grid 249 .2Ô 9, - 6, 5 23.2 8 178 226 1200 55 9 5 181.3 197 82.7;

  Q5 1650 5'6? 6 17? O 1858 83 16 128 1950 54e4 18 ,? 17 72 146 203 2280 5,, 2 2127 1? / 1 79 135 131 24oo? 4.9 19? J.11-, 5 80 128 148 3030 54.9 190 11.8 78 110
The blowing time during the first heating operation is a function of the speed of the forward movement of the continuous grid, and by adjusting the other heating variables in an appropriate manner, this can be varied. duration to meet production conditions, as shown in the table below.

 <Desc / Clms Page number 22>

 



  Composition of linked grandies
 EMI22.1
 NI 'of Duration Wind flow Yer ---- to- Fer-- -ca-ri6fë Index State of the scui - cm3 / mina per tal,% l.Ii <7N.e% of return 'p¯ * dticti- flage cm2 of surge-% bilit9 min. grid ce 5-c-a 4), 0p 1650 5p-, .3 9) 6 19.6 76 152 't' - \ i-t 4.8 990 5 7 5 thread 18.9 11 ,? 78 100 4-C-3 521 990 57.0 21.2 13.9 76 il) + 4-C-2 t7 1290 55, 13) 0 1.1 78 119? -C-2 gt4 1290, 3 8, 8 14.7 71 IL1
The final grid temperature is an extremely useful measure of the quality of the Iles granules.



  It is preferably between 870 and 1093 C and it exerts an influence on the quality of the granules bound by carbonization, as indicated in the table below.



   Composition of the granules
 EMI22.2
 ¯¯-. ¯¯ ¯ ¯ ïi s - - --------- ---
 EMI22.3
 
<tb> N <SEP> of <SEP> Temperature <SEP> Iron <SEP> to- <SEP> Iron <SEP> m- <SEP> Carbon <SEP> Index <SEP> State <SEP> of
<tb>
<tb> the final <SEP> test <SEP> of <SEP> tal,% <SEP> tallique <SEP>% <SEP> of <SEP> ren- <SEP> rducti-
<tb>
<tb> ta <SEP> grid, <SEP>% <SEP> dement <SEP> bilit,
<tb>
<tb> C
<tb>
 
 EMI22.4
 130 zée0 55eo 2.7 13.7 70 92 225 870 5?! 0 12, 7.

   16.1 78 132 226 980 5595 18.3 19, 7 82 157 227 1093 5229 15 1? 8 81 134 127 1099 56.3 16, 8 12 9 69 110
The temperature of the wind during the first heating operation is that at which the air stream or the modified air stream enters the layer of granules once ignited, and by raising the temperature of the wind one can generally decrease the temperature. blowing time which is necessary to obtain carbon bonded granules - of acceptable quality, as indicated in the table below.



   Composition of bound granules
 EMI22.5
 Na cte TemD. Du Duration de Fer to- Per m4- Carbor.e Indtce State of the test wind, oC wind,% talli-% yield- - --.-. -..-; ' - u ¯¯.m1.lt.e.s. - - ¯. ¯.¯JQ6 -¯.¯¯¯deme.nt, ¯ b!, 1 i, t '¯¯¯ 206 21 10 3.3 20.1 131l 72 113 226 260 7 55.5 18.3 197 82 157 244 538 49 4 bzz 1923 80 164 147 799 6.5 54.9 1517 1525 72 127

 <Desc / Clms Page number 23>

   The oxygen content of the wind during the first heating operation can be increased by adding oxygen to the air stream or decreased by adding combustion products. The results obtained are given in the table below.
 EMI23.1
 



  Composition of the bound granules
 EMI23.2
 NO of Oxygen Iron to-P Iron ine Carbon Index State of the wind test, tDl5% gallic% of yield0Qcti-
 EMI23.3
 
<tb>% <SEP> en <SEP> vo- <SEP>% <SEP> dement <SEP> bility,%
<tb>
<tb> lume
<tb>
 
 EMI23.4
 153 4.2 55eo 1271 gel 76 80 151 622 55, D 17.1 10O, 7S 95., 'A0 118 a4 162 10.0 80 93 é75 16eo e> 6.6 17? O 18.8 3 z6 226 21 , 0 k 55.5 18.3 19.7 82 i.? 234 26.0 k 5328 1518 .8.7 6 179 32.0 61.6 1025 3.4 76 36 a Under these conditions, carbon bonded granules of acceptable quality are obtained.
 EMI23.5
 The thickness of the layer of granules on the moving grate exerts an influence on the quality of the product and is preferably not more than 50 mm for granules of to 15 mm and may be greater for larger granules.

   
 EMI23.6
 Examples of the layer thicknesses which produce bound granules of acceptable quality are the following Composition of the bound granules. ¯¯¯¯
 EMI23.7
 àv ce Size Thickness Iron to- Iron m- Carbo # Index State of the test of -ra- of coti- tal% talli-% yield4du.cti- nules, mm che, mm que% dement bi3.ïtsg 6-C-2 9 to 16 100 5'6, 1.2 1330 78 105 4.-C ... 2 9 to 16? 5 5'S 9 5 i3, o 15el 78 119
During the first heating operation, after having ignited the granules from above, it is preferable to pass a current of air (or modified air) through
 EMI23.8
 towards the layer from top to bottom, i.e. in the direction in which combustion is progressing.

   
 EMI23.9
 xe 4 - In the process for the preparation of the grains described by way of example in Example 1 they are formed

 <Desc / Clms Page number 24>

 in the green state from the initial mixture, by the movement of a granulating drum which slowly rotates around a substantially horizontal axis and into which an initial mixture of ore fines and carbonaceous material is charged.

   It is also possible to form with the initial wet or wet mixture granules, briquettes, extruded parts under pressure by means of presses, briquetting cylinders; pressure spinning machines, etc. According to the invention. Ordinary and current carbonaceous binders, such as starch, pitch, tar, molasses, lignin products, etc. can also be incorporated into the initial mixture. to increase the strength of the green granules or to facilitate their formation, but these additives are not necessary according to the invention.



   Example 5 - Likewise, the process described in Example 1 consists of a continuous operation, but satisfactory results have also been obtained by working with intermittent charges and this process is also part of the invention.



  For example, aggregates of green granules have been successfully heated on both moving grids and stationary grids at intermittent loads to obtain carbon bonded granules of acceptable quality. The table below gives the comparative results obtained with granules prepared continuously and by intermittent loads.



   Composition of bound granules
 EMI24.1
 
<tb> Type <SEP> Thick.de <SEP> Duration <SEP> deIron <SEP> to- <SEP> Iron <SEP> Mé-cARBON, <SEP> Index <SEP> State <SEP> of
<tb> i <SEP> grille <SEP> the <SEP> cut- <SEP> blow-off <SEP> tal,% <SEP> tallique <SEP>% <SEP> of <SEP> ren- <SEP> reductichemm <SEP > min <SEP>% <SEP> denies <SEP> bility
<tb>%
<tb>
<tb> mobile <SEP> 100 <SEP> 4 <SEP> 56.9 <SEP> 14.2 <SEP> 13.0 <SEP> 78 <SEP> 105
<tb> fixed <SEP> 100 <SEP> 4 <SEP> 55.2 <SEP> 21.7 <SEP> 15.1 <SEP> 79 <SEP> 135
<tb>
 
Example 6 - The aggregates of Example 1 are formed by individual, linked granules. Green granules can also be formed with the initial mixture so as to obtain groups of granules similar to bunches of grapes.

   We

 <Desc / Clms Page number 25>

 these groups of granules are obtained by incorporating coking coal into the initial mixture. For example, instead of forming the initial mixture with 40 parts of non-coking coal and 60 parts of ore, it is possible to obtain bunches of granules with 16 parts of coking coal, 24 parts of non-coking coal and 60 parts of ore, that is, 40% of the coal in the mixture consists of coking coal.



     It is also possible to form clusters of bound granules by spraying the layer of green granules or dehydratas on the moving grid of powdered iron ore.



   They were also obtained by preparing them in the green state by the process of Example 1, but of a somewhat smaller size, by passing these green granules through a second granulating drum into which they are fed. powdered iron ore and additional water, and allowing iron ore to accumulate on the green granules as a film comprising approximately 20% of the total weight of the finished green granule.



   Cluster masses of carbonized-bonded granules are of interest in the process of the invention because when they are loaded into the melting furnace, the permeability of the mass to the passage of gases from the stack becomes greater than that of separate granules or other aggregates.



  The table below indicates some of the methods and treatments which have given satisfactory results in the preparation of cluster-bound granules of acceptable quality.

 <Desc / Clms Page number 26>

 
 EMI26.1
 



  CQWQsJJi0.t:} dls.!. R.1! n! ll? JLJd.? s.



  N of Iron to- Iron metal- Carbon Index State of the test tal,% .iqlJ.er.fv% of ren- redticti- ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯.¯¯¯ .¯¯¯¯¯¯¯¯¯¯dement bilit8.% 60 parts of minr: .i ave0., Il:, slc of 24 parts of uncoated coal \ .. êi: l3-dJ; t- e t7 16 parts of coking hemilla
 EMI26.2
 301 5.3.4 14.6 132 72 1) +7 302, 3 1. 3 1. .. g r'r7 77 118
 EMI26.3
 "Dul) lex" granules covered with a film of iron ore representing 20% of the weight of the finished granule.
 EMI26.4
 Example 7 Various modifications of the mode of operation of the melting furnace described in Example 1 gave satisfactory results in practice.

   Granules
 EMI26.5
 linked by carbonization of the moving grate can be discharged directly into the upper part of the melting furnace without sieving and again at a temperature of around 815 C. But, under these conditions, the losses by flying dust are considerable, mainly due to fines obtained during the preparation of the bound granules. According to another variant, hot bound granules, coming from the moving screen, can be passed through a sieve with an aperture of approximately 4.76 mm , as in Example 1, and feed the excessively large granules into the melting furnace still at a temperature of about 815 C.

   A third variation is to cool the hot bound granules from the moving grate, sieve them when cooled and charge them at about room temperature into the melting furnace. These three variants make it possible to successfully obtain metallic iron in the melting furnace. According to the last two variants, the fines which pass through the strainer with an opening of approximately 4.76 mm mesh are returned to the mixer and recirculated in the drum to be granulated.

 <Desc / Clms Page number 27>

 
If part of the load of a 45 cm diameter melting furnace consists of hot sieved bonded granules the furnace output exceeds 1708 kg of pig iron per m2 of hearth surface per hour.



     The charge height of the carbonized-bound granules can be varied in a 25 cm diameter furnace between 0.9 and 2.44 m above the nozzles. In all cases, the iron in the granules is reduced to the metallic state in the melting furnace, but a height of about 1.8 m appears to be the most suitable for the operation of the furnace loaded with cold sieved granules.



   The melting furnace may include an acid coating based on inorganic silica, a basic coating based on dolomite or magnesia, or a neutral coating based on graphite. The composition of the limestone, silica and fluorspar streams was tested so as to obtain acidic or basic metallurgical slags in the melting furnace. It is easy to see for the specialists that it is possible to vary and regulate the metallurgical composition of the molten iron obtained in the melting furnace by the nature of the slag formed. Examples of the metallurgical slags obtained in the melting furnace are as follows
 EMI27.1
 N of CaO MgO Si02 A1203 F'e0 Basicity cast 408 18.3 23.8 1221 la $ 1.6 36.3 3 43.8 9.2 47 0.75
By operating the melting furnace as in Example 1, the wind is preheated to a temperature of about 482 C.

   A wind temperature below this value is not considered satisfactory when the main source of oxygen is air, and an even higher wind temperature is then advantageous.



   Sometimes the air blowing in the oven is enriched

 <Desc / Clms Page number 28>

 with oxygen and thus satisfactory results are obtained with a wind containing an oxygen proportion of between 21 and about 30%; and under certain conditions an even higher proportion of oxygen may be advantageous,
When the smelting furnace is operated under the conditions of Example 1, a large part of the fuel for heating the furnace consists of metallurgical coke. It has been found that the amount of metallurgical coke required can be significantly less in furnaces. of large volume.

   The metallurgical coke fulfills two functions in the furnace operating under the conditions of Example 1: 1) it serves as a heating fuel, and 2) it serves as a temporary mechanical support and improves the permeability of the furnace charge. passage of wind and free gases. Under certain conditions, the metallurgical coke can be completely removed. For example, the amount of heat of heating required can be achieved with relatively inexpensive hard coal, char and other like solid fuels to replace relatively expensive metallurgical coke. Fuel oils can be used by injecting them through nozzles with air and (or) oxygen.

   The role played by metallurgical coke in ensuring the permeability of the feed is unnecessary when the granules are larger as in Example 3 or in the form of clusters as in Example 6.



   The electric arc can be used in the melting furnace as a source of heat necessary for the reduction to the metallic state of the iron contained in the granules bound by carbonization and sufficiently reducing. Under these conditions, we do not have need for metallurgical coke as a fuel or to improve the permeability of the charge.

 <Desc / Clms Page number 29>

 



   When the melting furnace operates with air blowing or oxygen-free air, it has two air groups of OXYGEN epriCHI air, has two groups of nozzles. According to one of the trusses of realization of the pretica, the nozzles are closed by a ring of nozzles in the same horizontal plane. According to another form, a second ring of nozzles is arranged in a horizontal plane approximately 35 cm above the lower ring. These two types of nozzles make it possible to reduce a large quantity of iron in the metallic state.



   The size of the granules arriving in the smelting furnace can be between 6.0 and 31.7 mm. The size limits of the granules are determined during the continuous forming, first heating and melting operations so that at the lower limit they are large enough and therefore heavy enough with respect to their peripheral surface and to their section so that the wind at the chosen flow rate does not lift them and carry them into the chimney of the furnace, and that at the upper limit they are small enough so that heating during dehydration and carbonization operations does not does not cause an explosion under the effect of a sudden release of vapor or gas under pressure in the various granules,

   and that the heat is transferred in an appropriate manner during the melting operation so as to lower the load evenly.



  The size limits of 9 to 15 mm, 16 to 22 mm and 22 to 25 mm preferably chosen in the preceding examples are determined based on the possibility of adjusting the wind flow and the conditions between aforementioned limits during the carbonization and melting operations, without resulting in any appreciable loss in the stack or irregularity in the descent of the load.



  The volume proportions of the granules between the limits

 <Desc / Clms Page number 30>

 indicated are about 1: for small granules and 1: 1.5 for large ones, when the bound granules are supported by little or no coke at all, and it will be noted that the particles are less likely to settle or descend irregularly when they are roughly the same size * In general, the layer of larger granules may be thicker during the first heating operation, the wind flow may be greater and the higher final grid temperature, and the amount of carrier coke in the melting operation may be less.

   If the granules are smaller, the required drying time is shorter before they undergo the first heating operation.



   The bound granules which come from the first heating treatment are characterized by a surprising resistance and a reduction in weight by abrasion when the granules are rubbed on each other: It is found by examining under the microscope sections and portions of the granules that contain the iron ore and the reduced iron in the form of separate particles, which are only slightly or not fully bound by the elements melted from the ash; they are mainly and clearly linked to each other by a graphitic carbon matrix.



  The bonded granules are therefore clearly different from the masses bonded by sintering or by vitrification, which include connecting bridges formed by molten slag elements; but it should be noted that the granules can be obtained without the source of this carbon being coking coal. It should also be noted that these bound granules contain a sufficient amount of carbon to reduce and carburize the existing iron oxide (eg a "state of reducibility" of between 100 and 170 and

 <Desc / Clms Page number 31>

   a carbon percentage between 10 and with a reduced iron proportion between 9.2 and 31.4% (representing a reduction of 15 to 40% of the total iron).

   In some cases the resistance, indicated by the "index of return"; increases with the proportion of metallic iron contained in the particles, although the particles are independent of each other. Bound granules are distinguished from the coke which must be obtained with coking coal, they do not contain substantially any particles of iron oxides or metallic iron and their characteristic structure is porous but not compact.



   Of course, the invention should not be regarded as limited to the embodiments shown and described which have been chosen only by way of example.


    

Claims (1)

SUMMARY A - Cast iron manufacturing process characterized by the following points separately or in combinations: 1) Green granules are formed with a wetted mixture consisting in principle of iron oxide ore fines and carbonaceous reducing agent fines containing volatile matter, the carbon content of which is greater than that which is necessary to reduce the iron oxide of the ore, a layer of granules is ignited and a blown air current is passed through it containing 16 to 26% oxygen, the flow of the wind is adjusted so as to heat and maintain the granules at a temperature between 870 and 1260 C and we continue to pass this wind at a regulated flow until the iron in the oxide is partially reduced. ment and that the metallic iron content of the granules is between about 15 and 40% by weight of the total iron and the wind is stopped while the granules still contain about 6.5% by weight of carbon, this content being higher to that which is necessary to transform the iron of the oxides in the elementary state, thus causing the reducing agent to undergo destructive distillation and transforming it into a graphitic matrix in the form of a carbonization bond of the other elements of the oxides. granules. 2) The carbonaceous reducing agent consists of coal of the non-coking type. 3) The green granules undergo a first heating, dehydrating them and are then ignited and subjected to the action of the wind for a period not exceeding 15 minutes after the ignition of the layer of granules. 4) The fines of ore and of non-coking coal are mixed in proportions by weight of between 85; 15 <Desc / Clms Page number 33> and 50; 50 in the presence of 10 to 20% water, the mixture is shaken on a rotating surface in the presence of a proportion of sprinkling water of about 2% so as to form the green granules and to make them grow, the shaken mass is removed from this surface and the particles of a size less than 6 mm are separated from it which are made to return on the rotating surface, one separates from the mass the particles of a size greater than 31 mm, fragmented and returned to the rotating surface, forming a moving layer of the other immobile green granules in the layer; , the thickness of which is between 75 and 125 mm, the layer at the top is ignited while it advances, supporting the granules, the current of air containing 16 to 26% oxygen is passed through it. with a flow rate between 750 and 3030 cm3 per minute and 'per cm2 of surface of the layer, so as to pass the wind from top to bottom through the layer to make it burn and heat it at a rate sufficient to drive off the water in the vapor state in a maximum of 15 minutes and to cause the coal of the granules to undergo a destructive distillation and to carbonize it without causing the granules to burst, while reducing the iron in the oxide of the granules to a metallic state to a content of about! 5 to 40% by weight of the total iron and causing the layer to take a final temperature of 870 to 1260 ° C. so as to form a graphitic carbon bonding matrix in each granule, then the passing of the wind is stopped and the bound granules are discharged from layer 5 ') After having interrupted the blowing at a controlled rate, the granules are loaded directly hot, before cooling them appreciably, in a reduction chamber containing an additional flux, and they are heated again. <Desc / Clms Page number 34> calf to completely complete the reduction of the iron oxide they contain and form a fluid slag. B - Coherent and reducing granule, prepared by the aforementioned process and characterized in that it contains 40 55% by weight of total iron, of which about 15 to 40% are in the state of elemental iron, the remainder consisting of oxide iron, the iron being in the state of separate particles and the quantity of carbon being sufficient to reduce the iron oxide and having an excess of about 625% by weight of the granule in the form of a graphitic matrix forming a carbonized bond of the other elements of the granule, which is compact, non-porous to the naked eye and porous to the microscope.