FI84840C - METALLURGICAL COMPOSITE, PROCESSER FOR FRAMSTAELLNING AV DESAMMA OCH ANVAENDNING AV DESAMMA. - Google Patents

Description

1 84840

Metallurgical composites, their manufacturing processes and their use

The invention relates to metallurgical composites, i.e. to composites and to processes utilizing these composites, as well as to the use of the composites in an iron smelting process.

In one embodiment of the invention, composites of metal oxide ores and good quality carbon are provided, as well as methods for their production.

The invention also relates to processes for treating composites to reduce metal oxides therein, e.g. melting processes a.

The good quality lignite used in this invention is preferably a product of the invention described in AU patent applications 24294/84 and / or 52590/86.

The lignite improvement / compaction process described in the aforementioned patent applications is a process that converts soft brittle raw lignite with a water content of about 60% freshly mined to a hard abrasion resistant black solid at a water content of about 10%. In the process, lignite with a freshly mined water content is massaged / rubbed in a selected kneader for periods ranging from 5 minutes or less to one hour or longer, depending on the hardness required in the final compacted product.

Massage performs several tasks that are important in this context. The carbon transforms into a finely divided granular form of at least a portion of the water content initially finely dispersed in the porous structure of the carbon, becoming a uniform aqueous phase which causes the carbon to become moist and plastic, and finally provides very large amounts and areas of freshly split carbon surfaces. These freshly split 2,84840 surfaces participate in interparticle bridging processes that ultimately cause the carbon mass to harden and condense, with most of the original water being removed simultaneously. Increases in density from about 0.8 to 1.4 are common. Water loss occurs rapidly (e.g., 80% in 24 hours of standing air at 20 ° C) and maximum hardness is reached in 3-4 days. After the rubbing, the plastic carbon is now pressed under considerable pressure by means of a suitable extrusion or high-pressure briquetting equipment, e.g. a ring press. In a specific example, the pressing device is a screw-operated piston-cylinder machine which produces pieces with a diameter of either 3 or 10 mm which can be cut to any desired length. The use of pressure during extrusion is thought to be significant as it presses the newly split surfaces of the carbon particles close together, thus facilitating bridge bonding and greatly improving the rate at which bonding occurs. The use of higher pressures during extrusion allows for a significant reduction in carbon rubbing times. Times as short as 5 minutes become possible, especially if an efficient scrubber is used.

The shortest time required for the rubbing and abrasion of crude lignite in the compaction process is that which is sufficient to develop a detectable moisture and plastic quality in the carbon mass. In practice, the required condition is determined visually by experience. Time is a function of the operating speed of the abrasive machine, the intensity of the friction effect produced by the machine, and the power of the machine to continuously press the carbon into the friction zone.

For very short rub times, the water content of the carbon can be critical. If it is too small, the power of the machine will be greatly reduced. Experience shows that lignite with water contents of about 60% by weight has optimal friction-abrasion properties, while water contents close to 54% (or less) are unsatisfactory.

li 3 84840 Using a sigma kneader with kneading arm speeds of 40 and 20 rpm and a rotor wall clearance of 0.3 mm, various lignite from Victoria (Australia) and Germany have been successfully converted to extrudable plastic states with 30-second rub-rub times. However, 30 seconds is not to be considered a minimum time according to the present invention, as the time will be determined to a considerable extent by the efficiency of the machine available. Any time sufficient to transform the raw brown coal into an extrudable plastic state will be appropriate.

It should be noted that the short friction-abrasion times which result in a limited reduction in the size of the carbon particles can be offset to some extent by the subsequent use of high extrusion pressures. In fact, a relatively dry plastic mass results in the development of high pressures in the nozzle region of the press.

In addition, a preferred embodiment of the invention provides a continuous friction-rubbing process. Very short abrasion times allow continuous operation in which lignite is fed in small lumps (5 mm or less) continuously to a low speed (20-40 rpm) sigma-type friction-abrasion machine. This machine is designed to provide a residence time of the required order of magnitude for the carbon in the friction zone (as defined above) before it is removed by a suitably positioned discharge screw11a. The discharge screw feeds moist rubbed carbon to the extrusion head, which is designed to provide the required extrusion pressure and to provide pieces strong enough to withstand reasonable loads immediately after formation.

The machine that performs the functions described above and has a discharge screw and extruder integrated is the Sigma Knetmachine HKS 50, manufactured by Janke & Kunkel GmbH & Co. KG. KH ΙΚΑ-Werk Beingen.

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Although it is not desired to be limited to any required or hypothetical mechanism for the observed beneficial effects, it is believed that compaction will begin to proceed at a substantial rate as soon as sufficiently split / ground carbon surfaces are available. This results in a further improvement by providing a continuous process in which the carbon has just enough residence time in the rubbing (rubbing) zone to produce a material capable of efficiently extruding in a high pressure die or press apparatus.

Research on dried concentrated lignite pieces prepared in this way has shown that they retain their shape and often become much harder gradually when heated to higher temperatures. Between 300-400¾ volatile substances are evolved in the form of water vapor and low molecular weight organic substances (mainly phenols).

At temperatures above about 500 ° C, only persistent gases are produced (mainly hydrogen, carbon monoxide, carbon dioxide and methane).

Studies of condensed lignite have shown its potential utility in certain metallurgical applications, e.g., composite fires.

While not wishing to be bound by any required or theoretical mechanism for the observed beneficial effects of the invention, the following is believed to be important: (a) Crushing of raw carbon to produce the above wet plastic mass provides a suitable excipient for efficient combination of finely divided granules such as ground metal ore or concentrates.

(b) The fine state of the rubbed carbon fraction contributes to the very close physical association of the metal ore particles with the plasticized carbon particles, with the latter acting as an effective reducing agent.

Il 5 84840 (c) Spontaneous evaporation of water from the pieces occurs during the compaction reaction, thus producing hardened dry pieces which are very suitable for relatively rapid heating for metallurgical purposes.

(d) When heated to a temperature above about 500¾, condensed lignite generates significant amounts of a gas mixture with a strong reducing nature.

(e) After pyrolysis, i.e. carbonization at low temperature, the pieces form residual carbon in a highly reactive form which is very closely related to the steps to be reduced. It should be noted in this connection that brown carbon particles are known to be effective and fast metallurgical reducing agents. In addition to the reactive carbon in condensed lignite, hydrogen, especially the hydrogen produced, greatly promotes reduction reactions.

It has now been found by extensive experimental research that fine ores and concentrates, especially iron oxide ores, mix easily with moist plastic carbon, and when added during carbon abrasion, a uniform homogeneous mixture results. Such a mixture is easily extruded or briquetted, and the pieces or briquettes thus produced dry and cure in a surprising amount. In some cases, the cured product exhibits a fairly reduced strength when air-dried, but this is often restored by pyrolysis. In other cases, there is an obvious reaction between the inorganic phase and the carbonaceous materials, which causes a considerable increase in strength in the dried product.

The metallurgical activity of the various composites is described in the examples later.

In the course of the work, it has become apparent that very rapid reductions can be achieved in lignite composite pieces.

As mentioned, it seems likely that a substantial 6,84840 increase in the reduction power of the system will be caused by the newly developed atomic or generated hydrogen that develops during the initial heating of the composites. Polyhydroxyphenols are likely to be major contributors to pyrolytic hydrogen, but other reactive substances may also be involved. The evolution of atomic hydrogen near the phase to be reduced allows a very rapid and efficient reduction of solid ore particles.

In summary, the composites of the invention offer significant advantages in that they have the ability to provide: (a) effective cold bonding of finely divided ores or concentrates, (b) sufficient strength to allow fresh composite pieces or briquettes to be satisfactorily treated by drying and subsequent preheating or preheating. for feeding, (c) rapid and efficient reduction of oxide ores, especially iron oxide ores, but also others such as e.g. chromite ores, (d) an ideal means for conveying both partially and substantially metallized pieces or briquettes r. (e) reduced / metallised pieces or briquettes that can be easily handled, transported and stored without risk of re-oxidation or spontaneous combustion, as has been shown to be the case with various types of currently available pre-melting furnaces; iron ore composites.

Useful composites containing certain base metal ores and concentrates, such as zinc concentrates, can be. also produces.

The essential features of the invention are set out in the appended claims.

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Example 1 In this preliminary experiment, compacted lignite-carbon-iron ore composites were prepared as described below and then heated to determine the type and amounts of gases evolved.

Dried compacted lignite-iron ore composite pieces containing 75% iron oxide were prepared using the method described in Example 2. The mine

Latrobe Valley, Victoria, Australia, stratification obtained

Loy Yang coal was used. After preliminary pyrolysis to remove water and low molecular weight volatile organic substances at 0 ° C under a nitrogen atmosphere, the pieces were placed in a silica tube attached to a vacuum system.

After the initial pumping had removed all the air, the temperature of the pieces was gradually raised to 900 ° C. Samples of gases evolved at three different temperatures were removed for analysis in a mass spectrometer. The gases were found to be predominantly hydrogen, carbon monoxide, carbon dioxide, methane, and small amounts of water vapor. The approximate relative partial pressures of the first four products at the three temperatures are shown in Figure 1.

At 600 ° C, hydrogen was the most abundant component, followed by carbon monoxide and carbon dioxide (approximately equal) with the least methane. As the temperature was raised to 900 ° C, the evolution of hydrogen became more and more predominant, while the evolution of carbon monoxide also increased. Carbon dioxide was reduced significantly and methane to a lesser extent.

This experiment shows that the compacted pieces provide a strongly reducing atmosphere when heated to high temperatures. This atmosphere provides a strong reducing effect in addition to all the direct reduction caused by solid reactive carbon in the composite pieces or briquettes or the resulting hydrogen.

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Example 2

Composite pieces were prepared using various proportions of fine iron oxide and coal obtained from a mine in Morwell, Victoria, Australia (borehole N3372).

In each case, 200 g of crude carbon (60% water) were kneaded for 4 hours in a sigma kneader as described in AU patent application 24294/84, 15 minutes before the kneading was stopped, selected amounts of finely divided iron oxide (laboratory reagent material) were added to the plastic mass, and long to obtain a thoroughly mixed uniform plastic mass. This was then extruded with a hand-operated screw press to produce cylindrical pieces, the pieces having a diameter of 10 mm (about 8 mm after drying), the length varying between 10 and 20 mm. The pieces were allowed to dry and cure in standing laboratory air at 20 ° C for 7 days. The dried pieces were then subjected to pyrolysis in a stream of nitrogen gas, initially maintained at 300-400 ° C for one hour to remove residual water and volatile low molecular weight organic matter, followed by further heating to 700 ° C. This latter heating cycle was intended to determine whether a noticeable reduction had begun in that temperature range. In one case (see below) the pieces were heated to 1070 ° C, in this case in a reducing atmosphere created by the pyrolysis of carbon.

Pieces were prepared containing 10, 30, 50 and 75% by weight (dry weight of carbon) of iron oxide. The 10% composites had a crushing strength of 17 MPa compared to 30 MPa for the corresponding pieces without iron oxide. After pyrolysis, 10% ferric oxide pieces showed an increase in average crushing strength to 20 MPa, indicating the development of additional bonding during pyrolysis.

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The compressive / crushing strength of the dried compressed carbon pieces was determined by the following measurement of the height (H) and diameter (D) of the pieces tested with a micrometer.

The pieces were then placed on the anvil of a general testing machine (Tirius Olsen Testing Machine Co., Willor Grove, Pa.), And an axial load was placed between the planar surfaces until damage occurred.

The compressive strength was calculated from the force F (determined from the maximum load of the piece) according to the following formula: ac = (4ρ / π ° 2) (H / D) 0'5

All composites were strongly magnetic (especially 75:25 ore compacted carbon mixture) after pyrolysis at 700 ° C, indicating the formation of reduced iron.

In one experiment, pieces containing 75% Fe 2 O 3 were placed in a silica tube attached to a vacuum system. The tubes were pumped empty of all gases while being heated to 500 ° C. The tube was then separated from the pumps and a pressure change was observed as the temperature was further raised to an approximately constant rate of 1070 ° C.

The results of these measurements are shown in Figure 2. At a temperature of about 900 ° C, a very rapid pressure rise began, and it became necessary to pump the gas out to maintain the total pressure below 1 atmosphere. Substantial gas evolution continued until the experiment was terminated. The phenomena described in this experiment are typical of iron oxide-containing fires and show chemical reactions between oxide and carbon-derived species.

At 800 ° C, the main reaction appears to be the reduction of iron oxide by evolved hydrogen to produce water 10,84840. This reaction appears to be complemented at a temperature of about 900 ° C by the reduction reactions caused by carbon monoxide and carbon, with a substantial increase in total gas pressure. At the end of this experiment, the pieces, although strongly ferromagnetic, did not show visible metallic iron.

As the temperature was further raised using the pieces as electrodes in a direct current arc in an inert atmosphere, spheres and wrought iron formed very rapidly.

Composite pieces containing 75% of ^ 2 ^ 3 after preliminary pyrolysis at 700 ° C, as described above, were further tested by immersing them in a liquid iron bath maintained at 1500 ° C. Gas evolution began immediately after immersion and continued throughout the 10 second immersion period. The pieces did not disintegrate, but continued to evolve gas while rapidly dissolving in liquid iron. The dissolution rate was highest on the side of the pieces that had reached the highest temperature when touching the furnace wall during the initial pyrolysis. Probably more reduced iron was present in this zone of the piece, thus promoting the etching rate of liquid iron. This experiment shows that pieces of composite iron in a pre-reduced state can be used as a feed material for both iron and; to feed coal to steelmaking furnaces using new bath smelting technology.

It is to be understood that the invention is not limited in general terms to the specific details discussed above.

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Claims (10)

1. Process for the production of metallurgical composite materials, characterized by the following steps: (a) lignite is subjected to shear forces to produce a plastic mass; (c) the mixture prepared in step (b) is compressed to produce a compressed pulp, (d) the compressed pulp is dried to produce the metallurgical composite material. Process according to claim 1, characterized in that the compression step (c) is carried out by extrusion of the mixture. Method according to claim 1, characterized in that the drying step (d) is carried out at or near ambient temperature. Method 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 in step (b), finely divided iron ore is used and in step (c) the mixture is extruded from step (b) to make pellets. 7. Metallurgically composed material of quality improved lignite and atomized ore and / or concentrate, characterized. from being produced by (a) subjecting coal to shear forces to produce a plastic pulp; (b) mixing finely divided ore and / or concentrate with the carbon, either during or after step (a); (c) the mixture prepared in step (b) is compressed to produce a compressed mass; (d) the compressed pulp is dried to produce the metallurgical composite. Use of a metallurgically-composed material comprising quality-enhanced lignite and atomized iron ore, which is prepared by (a) subjecting lignite to shear forces to produce a plastic mass; (b) mixing comminuted iron ore and / or concentrate 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 pulp is dried to produce the metallurgical composite in an iron smelting process, at which the iron ore is reduced to metallic iron. Use according to claim 8, characterized in that the composite material is heated in a liquid iron bath. Use according to claim 9, characterized in that the composite material is subjected to a preparative pyrolysis up to a temperature of about 700 ° C, after which it is dipped in a bath of liquid iron at a temperature of about 1500 ° C.