SE463104B - PROCEDURE FOR THE PREPARATION OF METALLURGICAL COMPOSITION MATERIALS, MATERIALS PREPARED ACCORDING TO THE PROCEDURE, AND APPLICATION OF MATERIALS PREPARED IN THE PROCEDURE OF AN ANNUAL MELTING PROCEDURE - Google Patents

Description

is ... A ~ CJ? I: N The procedure for quality improvement and densification of lignite. described in the above-mentioned patents, is a process. which transfers soft brittle crude lignite, with a water content of about 60 2 in the broken state, to a hard, abrasion resistant, black solid with a water content of about 10%. During the process, the lignite, with the water content of the state of refraction, is subjected to shearing / rubbing in a selected kneading device for periods which may vary from 5 minutes or less to 1 hour or more depending on the hardness required in the finished densified product.

The shear has several functions, which are important in the present context. The carbon is transferred to fine particulate form, at least part of the water content, which was initially finely divided in the porous structure of the carbon, is converted into a liquid main phase, which causes the carbon to become wet and plastic and finally forms a very large number and areas of freshly split carbonates. These newly split surfaces take part in a bridge bonding process between particles, which ultimately causes the coal mass to harden and become much denser, while at the same time excluding and losing most of the original amount of water. Density increases from about 0.8 to 1.4 are not uncommon. Water loss occurs rapidly (eg 80 2 in 24 hours in stagnant air at 20 ° C) and maximum hardness is reached within 3-4 days. After rubbing, the plastic carbon is now subjected to compression under considerable pressure by suitable extrusion or high-pressure briquetting devices, e.g. a ring roller press. In a particular example, the compression device is in the form of a screw-driven piston-in-cylinder machine, which produces cylindrical products with a diameter of either 3 or 10 mm, which can be cut to any desired length. Applying pressure during extrusion is believed to be important in pressing the newly split surfaces of the carbon particles close together, thereby facilitating bridge bonding and greatly improving the rate at which bonding occurs. The use of high pressures during extrusion enables a significant reduction in the friction treatment time of the carbon. Times as short as 5 minutes or less become practically possible, especially if an efficient rubbing machine is used.

U) _pw (f U ~ l * ha CD HN.

The minimum time required for shear-rubbing of the crude lignite in the densification process is that which is sufficient for the formation of appreciable moisture and plastic characteristics in the coal mass. In practice, the required condition is confirmed by visual observation based on experience. The time period is a function of the working speed of the friction machine, the intensity of the shear effect achieved by the machine, and of the efficiency of the machine to constantly force the carbon into the shear zone.

At very short shear times, the carbon content of the carbon can be critical; if it is too low, the efficiency of the machine is greatly reduced. Experience shows that lignite with water contents of about 60% by weight shows optimal shear-rubbing properties, while water contents close to 54 2 (or less) are unsatisfactory.

Using a sigma kneading machine. working at a kneading shaft speeds of 40 and 20 revolutions per minute and a free space at the rotor wall of 0.3 mm, various lignite from Victoria and Germany have been successfully converted into extrudable plastic states within periods of 30 seconds shear rubbing. However, 30 seconds should not be considered as the minimum time, which is covered by the present requirements, as the time will be significantly controlled by the efficiency of the available machine. Any period which is sufficient to convert the crude lignite to an extrudable plastic state is suitable.

It should be noted that in practice short shear rubbing times, which give a limited reduction in the size of the lignite particles, can be compensated to some extent by the subsequent use of high extrusion pressures. In fact, a relatively dry plastic mass leads to the development of high pressures in the nozzle area of the extruder.

According to a preferred embodiment, the present invention relates to a continuous shear extrusion process. The very short rubbing times enable continuous work, whereby lignite in small pieces (5 mm or less) is continuously fed to a sigma-type shear rubbing machine at low speed (20-40 revolutions per minute). The design of this machine is intended to provide a residence time for the carbon in the shear zone of the required order of magnitude (as defined above) before it is taken out by a suitably placed discharge screw. The discharge screw supplies the moist rubbing-treated carbon to a spray head designed to provide the required compression pressure and provide sufficiently solid pellets to withstand moderate loads immediately after formation.

A machine that performs the described functions and has a discharge screw and press device integrally attached is the Sigma Knetmachine HKS 50, which is manufactured by Janke & Kunkel GmbH & Co., KH IKA-Werk Beingen. Although the invention is not to be limited by any presumed or hypothetical mechanism for the observed beneficial effects. it is probable that the densification will begin at a noticeable speed as soon as a sufficient amount of split / sheared carbon surfaces is available. This leads to a further improvement, whereby a continuous process is obtained, in which the carbon has a residence time in the rubbing (shear) zone, which is just sufficient for the production of materials which can be extruded efficiently in an extruder or high pressure extruder. .

Examination of the properties of the dried condensed lignite pellets, produced in this way, has shown that they retain their shape and often become harder when heated to higher temperatures. At between 300 and 400 ° C, volatile materials develop in the form of water vapor and low molecular weight organic substances (mainly phenols). above about 500 ° C only permanent gases are formed (mainly hydrogen, carbon monoxide, carbon dioxide and methane). Examination of the densified lignite has shown its potential usefulness in certain metallurgical applications, e.g. composite pellets. Although the invention is not to be limited by any proposed or theoretical mechanism for the observed beneficial effects of the present invention, it is likely that the following conditions are relevant: (a) friction of the crude coal to produce the be written moist or wet plastic mass provides a suitable carrier for the effective incorporation of finely divided particulate materials, such as finely divided metal ore or concentrate, (b) the fine state of distribution of the rubbed carbon leads to a very close physical connection between the particles in metal ore and the particles in plasticized carbon, the latter acting as a powerful reducing agent, (c) spontaneous loss of evaporation water occurs from the pellets during the densification reaction, thereby producing hard, dry pellets. which is particularly suitable for relatively rapid heating for metallurgical processes; residual carbon, which is in a highly reactive form, which is very closely linked to the phases intended for reduction. In this context, it should be noted that charred lignite is known to be an effective and rapid metallurgical reducing agent. In addition to the reactive carbon in the well-known lignite, the hydrogen present, and in particular hydrogen in nascent form, greatly improves the reduction reactions.

Extensive experimental studies have shown that finely divided ores and concentrates, especially oxidic iron ores, mix easily with the wet plastic carbon and when they are added while rubbing or shearing the latter, a uniform homogeneous mixture is obtained. Such a mixture can be easily extruded or briquetted and the pellets, beads or briquettes produced in this way dry and harden to a surprising extent. In some cases, the cured product shows rather reduced strength in the air-dried state, but this is often overcome by pyrolysis. In other cases there is an apparent reaction between the inorganic phase and the carbon constituents. resulting in a significant increase in the strength of the dried product.

The metallurgical behavior of various composite materials will be described in the following examples.

During the work on the present invention, it has been found that very fast reduction rates can be achieved in the composite pellets of lignite. As mentioned, it is likely that a significant contribution to the reducing effect of the system is obtained by newly developed atomic or nascent hydrogen, which is generated during pretreatment heating of the composite materials.

Polyhydric phenols probably contribute significantly to the pyrolytic hydrogen. but other reactive products may also be involved. The development of atomic hydrogen close to the phase intended for reduction means the possibility of extremely fast and efficient reduction of the solid ore particles.

In summary, composite materials of the present invention provide significant advantages in that they can provide: (a) effective bonding - in the cold state - of fine particulate ore or concentrate. (b) sufficient strength of the unsintered composite pellets or briquettes to enable successful handling for drying and subsequent feeding to preheating or pyroilysis furnaces. (c) rapid and efficient reduction of oxide ores, in particular iron oxide ores, but also comprising others, such as chromite ores, (d) an ideal means for the simultaneous transfer of both partially and substantially metallised pellets or briquettes together with coal to smelting furnaces, especially those which use recent new bath smelting processes, (e) reduced / metallized pellets or briquettes, which can be easily handled, transported and stored without risk of re-oxidation or to exhibit pyrophoric behavior, such as those with various types of pre-reduced composite iron ore products currently available. league.

Useful composite materials containing certain base metal ore AND KOIICGIICIIBt, t.êX. zinc concentration, can also be produced.

Example 1 In this preparatory experiment, composite pellets of densified lignite and iron ore were prepared as described below and then heated to determine the type and amount of gases. which developed. Composite pellets of dried densified lignite and iron ore, containing 75 2 iron oxide, were prepared using the procedure described in Example 2. Loy Yang coal from deposits in the Latrobe valley. Victoria, Australia was used. After preparatory pyrolysis in a nitrogen atmosphere at 400 ° C to remove water and low volatile organic volatiles, the pellets were placed in a quartz tube attached to a vacuum system.

When preparatory pumping had removed all air, the temperature of the pellets was gradually increased to 900 ° C. Samples of evolved gases at different temperatures were removed for analysis on a mass spectrometer. The main gases turned out to be hydrogen. 463 104 a carbon monoxide. carbon dioxide, methane and a small amount of water vapor. The approximate relative partial pressures of the first four products at the three temperatures are shown in Fig. 1.

At 600 ° C, hydrogen was the major constituent, followed by carbon monoxide and carbon dioxide (approximately equal amounts), with methane as the smallest constituent. As the temperature increased to 900 ° C, the hydrogen evolution became more prominent and the evolution of carbon monoxide also increased. Carbon dioxide evolution decreased markedly and methane evolution to a lesser extent.

From this experiment it is obvious that the densified pellets give a strong reducing atmosphere when heated to high temperatures. This atmosphere exerts a strong reducing effect, which is added to any direct reduction by the solid reactive carbon or the nascent hydrogen inside the composite pellets or briquettes.

Example 2 Compound beads or pellets were prepared with different proportions of fine iron oxide and carbon from Morwell, Victoria. Australia (N3372 borehole).

In each case, 200 g of crude carbon (60% water) was kneaded for 4 hours in a sigma-type kneader. as described in Australian Patent Specification 561586. 15 minutes before the end of kneading, selected amounts of weight of finely ground iron oxide (laboratory reagent material) were added to the plastic mass and the kneading was then continued long enough to obtain a thoroughly mixed even plastic mass. This was then extruded with a hand-driven screw extruder to produce cylindrical pellets. which initially had a diameter of 10 mm (about B mm after drying) and with a length ranging from 10 to 20 mm. The pellets were allowed to dry and harden in stagnant laboratory air at 20 ° C for seven days. The dried pellets were then subjected to pyrolysis in a stream of nitrogen, initially held for 1 hour in the temperature range of 300-400 ° C to remove residual water and low molecular weight organic volatiles, followed by further heating for 1 hour with an increase in temperature to 700 ° C. This later heating period was intended to determine whether a demonstrable reduction had begun within the intended temperature range. In one case (see below), pellets were heated to 1070 ° C. in this case in the reducing atmosphere generated by the pyrolysis of carbon.

Pellets were prepared with 10, 30, 50 and 75% by weight (calculated on the weight of dry carbon) iron oxide. The composite material with 10 2 iron oxide gave an average crush strength of 20 MPa, indicating the development of additional bonds during pyrolysis.

Compressive / crush strengths of the densified carbon pellets were determined after measuring the height (H) and diameter (D) of the pellets intended for testing by one micrometer.

The pellets were then placed on the anvil in a universal testing machine (Tirius Olsen Testing Machine Co. Willor Grove.

Pa.) And an axial load was applied over the flat ends until the pellets broke.

The compressive strength oc was calculated from the force F (determined from the maximum load that the pellet could withstand) according to the following formula: se = (4F / wnz) (H / D) ° 'All the composite materials were highly magnetic (especially 75: Ore: densified carbon mixture) after pyrolysis to 700 ° C, indicating production of reduced iron.

In one experiment, pellets containing 75 2 Fe 2 O 3 were placed in a quartz tube connected to a vacuum system. The tube was pumped free of all gases while heating to 500 ° C. The tube was then isolated from the pumps and the pressure change was observed as the temperature was further increased at approximately constant 46 ”104 10 speed to 1070 ° C. The results of these measurements are shown in Fig.2. at about 900 ° C a very rapid pressure increase began and it became necessary to pump off gas to keep the total pressure below atmospheric pressure. significant gas evolution continued until the experiment ended. The phenomena described in this experiment are typical of pellets containing iron oxide and indicate f) chemical reactions between the oxide and substances derived from carbon.

At 800 ° C the main reaction seems to be reduction of the iron oxide by evolved hydrogen with the production of water.

This reaction seems to be supplemented at about 900 ° C with reduction reactions, which include carbon monoxide and carbon with a significant net increase in the total gas pressure. at the end of this experiment, the pellets showed. while they were strongly ferromagnetic, no visible metallic iron. As the temperature was further increased using pellets such as electrodes in a direct current arc in an inert atmosphere, small balls of malleable iron formed very quickly.

Composite pellets containing 75 2 Fe 2 O 3 after preparative pyrolysis at 700 ° C, as described above, were further tested by dipping in a liquid iron bath. which was maintained at 1500 ° C. Gas evolution began immediately upon immersion and continued throughout the immersion period of 30 seconds. The pellets did not break, but continued to develop gas during rapid dissolution in the liquid iron. The dissolution rate was greatest on the side of the pellets which had been exposed to the highest temperature during the preparatory pyrolysis by contact with the oven wall; more reduced iron was probably present in that zone in the pellet, thereby increasing the rate of attack by the liquid iron. This experiment shows that the composite iron pellets in a pre-reduced state can be used as feed material to supply both iron and carbon to steel production furnaces through a new bath melting process.

It is to be understood that the invention is generally not limited to the particular details mentioned above.

Claims (10)

ll Patent claim A process for the production of metallurgical composite materials, characterized by the following steps: (8) forming a plastic mass; (b) finely divided ore and / or concentrate is mixed with the coal, either during or after step (a); (c) the mixture prepared in step (b) is compressed to produce a compressed mass; (d) the compressed mass is dried to produce the metallurgical composite. Process according to claim 1, characterized in that the compression step (c) is carried out by extruding the mixture. Process according to claim 1, characterized in that the drying step (d) is carried out at or near ambient temperature. Process according to claim 1, characterized in that the ore is iron ore or chromite ore. Process according to claim 1, characterized in that the ore or concentrate is zinc ore or concentrate. Process according to Claims 1, 2 and 3, characterized in that the lignite is subjected to shear forces to produce that from the use of finely divided iron ore in step (b) and that in step (c) the mixture is extruded from step (b). ) for the production of pellets. ms Ö \ CN .n, 12 10 7. Metallurgically composed material of improved lignite and finely divided ore and / or concentrate, characterized in that it is produced by u; (a) lignite is subjected to shear forces to produce a plastic mass; (b) finely divided ore and / or concentrate is mixed with the coal, either during or after step (a); (c) the mixture prepared in step (b) is compressed to produce a compressed mass: (d) the compressed mass is dried to produce the metallurgically composite material. 8. Use of a metallurgically composed material comprising quality-improved lignite and finely divided iron ore. Which is produced by (a) subjecting lignite to shear forces to produce a plastic mass: (b) finely divided iron ore and / or concentrate is mixed with the coal. either during or after step (a); (c) the mixture prepared in step (b) is compressed to produce a compressed mass; (d) the compressed mass is dried to produce the metallurgical composite in an iron smelting process in which the iron ore is reduced to metallic iron. The use of claim 8, characterized in that the composite material is heated in a liquid iron bath. 13 463 184 Use according to claim 9, characterized in that the composite material is subjected to a preparatory pyrolysis up to a temperature of about 700 ° C. after which it is immersed in a bath of liquid iron at a temperature of about 1500 ° C.