NZ215368A - Use of brown coal in metal production - Google Patents

Description

215368 ?9.ftP..W >ao5 s > NEW ZEALAND PATENTS ACT. 1953 No. Dale: COMPLETE SPECIFICATION "METALLURGICAL COMPOSITES AND PROCESSES" K/Wc, CRA SERVICES LIMITED, a company incorporated under the laws of the State of Victoria, of 55 Collins Street, Melbourne, Victoria, Australia hereby declare the invention for which >fc/ we pray that a patent may be granted to Riec/us, and the method by which it is to be performed, to be particularly described in and by the following statement:- 115368 METALLURGICAL COMPOSITES AND PROCESSES 5 This invention relates to metallurgical composites and processes utilizing those composites.

In one aspect the invention provides composites of metallic oxide ores and upgraded brown ^oal, and methods for producing same.

Processes for treatment of the composites to reduce the metallic oxides therein, including smelting processes, are also contemplated by the invention. r 368 The upgraded brown coal utilized in the present invention is preferably a product oE the invention described in our copending Australian Patent Application 24294/84, which was published on August 23, 1984, and/or 52590/86 (PG 9283) 5 The brown coal upgrading/densification process described in the abovementtoned copending patent applications is a procedure which converts soft friable raw brown coal with an as-mined water content of about 60% to a hard, attrition-resistant, black solid of a water content of about 10 10%. In the procedure the brown coal, with as-mined water content, is subjected to shearing/attr11ioni ng in a selected kneading device for periods which may vary from five minutes or less to an hour or more depending on the hardness required in the final densified product.

Shearing performs several functions which are of importance in the present context. The coal is converted to fine particulate form, part at least of the water content, originally finely dispersed in the porous structure of the coal, is converted to a bulk liquid phase which causes the 20 coal to become wet and plastic and finally very large numbers and areas of freshly cleaved coal surfaces are produced.

These freshly cleaved surfaces participate in inter-particle bridge bonding processes which ultimately cause the coal mass to harden and become much denser with simultaneous exclusion 25 and loss of most of the original water. Density increases from about 0.8 to 1.4 are not uncommon. Water loss occurs rapidly (for example 80% in 24 hours in still air at 20°C) and maximum hardness is attained within three to four days. After attritioning the now plastic coal is subjected to compaction 30 under appreciable pressure through suitable extrusion or high pressure briquetting devices, e.g., a ringroll press. In a particular example the compacting device is in the form of a screw operated piston-in-barrel machine which produces either 3 or 10 mm diameter cylindrical specimens which may be cut to 35 any desired length. Application of pressure during extrusion is believed to be significant in forcing the freshly cleaved OR 215368 surfaces of -oai parti:l'.'.s int > :1 0s1:1 proximity thus f a _* 1 1 1 t a t l rig bridge bonding and 30 greatly enhancing the rate at which bonding occurs. Th" us" of higher pressures during extrusion permits *oal jttritioninq times to be greatly 5 reduced. Times as short as five minutes or less become practicable particularly if an efficient attntioning machine is used.

The least time required for shearing-attritioning of raw brown coal in the dens 1f1 cat 1 on process is that which is 10 sufficient to qenerate perceptible moistness and plastic character in the mass of the coal. Tn practice the required condition is verified by visual observation based upon experience. The period of time is a function of the rate of operation -t>f the attntioning machine, the intensity of the 15 shearing action achieved by the machine and of the efficiency of the machine in forcing the coal constantly in.to the shearing zone.

In respect of very short shearing times the water content of the coal can be critical; if too low, machine 20 efficiency decreases severely. Experience indicates that brown coals with water contents of about 60% by weight display optimum shearing-attrition 1ng characteristics whereas water contents in the vicinity of 54% (or less) are unsatisfactory.

Using a sigma kneading machine operating with 25 kneading shaft speeds of 40 and 20 r.p.m. and a rotor-wall clearance of 0.3 mm, various brown coals of Victorian and German origin have been successfully converted to extrudable plastic states in periods of 30 seconds shearing attritioning. However 30 seconds should not be regarded as the minimum time 30 covered by the present claim .since the time will be governed to a significant degree by the effectiveness of the available machine. Any period sufficient to convert the raw brown coal to an extrudable plastic state will be appropriate.

It should be noted that, in practice short 35 shearing-attritloning times giving limited size reduction of the coal particles may be compensated to some extent by the OE _r 21Sioa - subsequent use of high "xtrusnn pr'-ssurcs. In fajt a relatively dry plastic mass leads t. \> the development of high pressures in the nozzle region ~>f the extruder.

A further preferred emboli im'-nt of the present 5 invention provides a continuous shearing-extrusion process.

The very short attntioning times permit continuous operation in which brown coal in small lumps (5mm or less) is fed continuously to a low-speed (20-40 revolutions per minute) sigma-type shear i ng-attritioning machine. The configuration 10 of this machine is designed to give a residence time for the coal in the shearing zone of the required order (as defined above) before being extracted by a suitably located discharge screw. The discharge screw feeds the moist attritioned coal to an extrasion head designed to give the required extrusion 15 pressure and provide pellets sufficiently firm to withstand reasonable Loads immediately after formation.

A machine which performs the functions described above and has a discharge scr-^w and extruder fitted integrally is Sigma Knetmachine HKS 50 manufactured by Janke 4 Kunkel 20 GmbH A Co. KH IKA-Werk Beingen.

Although we do not wish to be limited by any postulated or hypothetical mechanism for the observed beneficial effects, we believe that denslficatlon will begin to proceed at an appreciable rate as soon as sufficient 25 cleaved/sheared coal surfaces are available. This leads to a further improvement providing a continuous process in which the coal has a residence time in the attntioning (shearing) zone just sufficiently to produce material capable of being effectively extruded m a high pressure extrusion or pressing 30 device.

Investigation of the properties of dried densified brown coal pellets produced in this manner has shown that they retain their form and often become much harder on progressive heating to higher temperatures. At between 300 and 400°C 35 volatiles in the form of water vapour and low molecular weight organic substances (principally phenols) are evolved. Above OE i t ! i % II - f, 215 J 6d Q about 500 C permanent qas'_*s only (principally hydrogen, carbon monoxide, carbon dioxide ami met hano I arc produced. Our investigation of the dens i f i e<i or own coal has indicated its potential usefulness in certain metallurgical 5 applications, e.g. composite pellets.

Although we do not wish to be limited by any postulated or theoretical mechanism for the observed beneficial effects of the present invention, we believe that the following considerations are significant:- (a) Attntioning the raw coal to produce the aforesaid damp or wet plastic mass provides a suitable vehicle for effective incorporation of finely divided particulate materials, such as commirjuted metal ore or concent rates, 15 (b) The fine state of subdivision of the attritioned coal is conducive to a very close physical association of particles of metal ore with particles of plasticised coal, the latter acting as a powerful reductant, 20 (c) Spontaneous evaporative water loss occurs from the pellets during the densificat ion teaction so producing hardened, dry pellets which are particularly suitabLe for relatively rapid heating for metallurgical purposes, 25 (d) On heating above about 500°C the densified brown coal evolves substantial quantities of a gas mixture which is of a strongly reducing character, (e) After pyrolysis or Low temperature 30 carbonisation the pellets provide a residual carbon which is in a highly reactive form which is very closely associated with the phases to be reduced. In this context it should be noted that brown coal chars are known to be effective 35 and rapid metallurgical reductants. In OE 2% b'j « addition to the r'MJtive carbon in the densified brown coal, hydrogen, and particularly the nascent form of hydrogen present, enormously enhance reduction react ions.

We have established by extensive experimental investigation that finely divided ores and concentrates, particularly oxidic iron ores, mix readily with the wet plastic coal and, when added during attrition of the Latter, a smooth homogeneous mix results. Such mix is readily extruded or briquetted and the pellets or briquettes so produced dry and harden to a surprising extent. In some instances the hardened product shows rather reduced air-dried strength but this is frequently recovered on pyrolysis. In other cases there is an apparent reaction between the inorganic phase and coal constituents resulting in significant increases in the strength of the dried product.

The metallurgical behaviour of various composites will be described in the examples given later.

In the course of our work it has become apparent that very rapid rates of reduction can be effected in the brown coal composite pellets. As stated it seems likely that a substantial contribution to the reducing power of the system is provided by freshly evolving atomic or nascent hydrogen generated during preliminary heating of the composites. Polyhydroxy phenols are likely to be major contributors of pyrolytLC hydrogen but other reactive species may also be involved. Evolution of atomic hydrogen in close proximity to the phase to bo reduced has the potential for extremely fast and efficient reduction of the solid ore particles.

In summary, composites according to this invention offer significant advantages in that they have the capacity to provide:- OE (a) Effective bonding - in the cold - of fine particulate ores or concentrates, (b) Sufficient strength in the green composite pellets or briquettes to enable satisfactory handling for drying and subsequent feeding to pre-heating or 'pyrolysis' furnaces, (c) Fast and efficient reduction of oxide ores, particularly 1 ron oxide ores, but including others, such as, e.g. chromite ores, (d) An ideal means for conveying simultaneously both partially or substantially metallized pellets or briquettes together with carbon to smelting furnaces, particularly to those using recent new bath smelting technologies, 15 (e) Reduced/metallized pellets or briquettes which can be easily handled transported and stored without the risk of re-oxidation or of displaying pyrophonc behaviour as is experienced with various types of pre-reduced 20 iron ore composites now available.

Useful composites containing certain base metal ore and concentrates, e.g. zinc concentrates may also be produced.

Example 1 In this preliminary experiment densified brown coal 25 - iron ore composite pellets were prepared as described below and then heated to determine the type and amounts of gases evolved.

Dried densified brown coal - iron ore composite pellets containing 75% iron oxide were prepared using the 30 procedure described in Example 2. Loy Yang coal from the Latrobe Valley, in Victoria, Australia deposits was used.

After preliminary pyrolysis in a nitrogen atmosphere at 400°C OE ') A S?, . / to remove water and low molecular weight organic volatiles, the pellets were placed in a silica tube attached to a vacuum system.

When preliminary pumping had removed all of the air, 5 the pellets were raised progressively in temperature to 900°C. Samples of the gases evolved at three different temperatures were removed for analysis on a mass spectrometer. The principal gases were found to be hydrogen, carbon monoxide, carbon dioxide, methane and a small amount of water vapour. 10 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 constituent followed by carbon monoxide and carbon dioxide (approximately equal) wit>i methane the least abundant. As the temperature 15 was raised to 900°C hydrogen evolution became even more dominant while that of carbon monoxide also increased. Carbon dioxide diminished markedly and methane to a lesser extent.

It is evident from this experiment that the densified pellets produce a strongly reducing atmosphere on 20 heating to high temperatures. This atmosphere exerts a strong reducing effect additional to any direct reduction by the solid reactive carbon or the nascent hydrogen within the composite pellets or briquettes.

Example 2 Composite pellets were made with various proportions of fine iron oxide and coal from Morwell, Victoria, Australia (N3372 bore hole).

In each case 200 g of raw coal (60% water) was kneaded for 4 hours in a sigma-type kneader as described in 30 our pending application Aust. 24294/84. Fifteen minutes before terminating kneading, selected weights of fine iron oxide (laboratory reagent material) were added to the plastic mass and kneading then continued for long enough to give a thoroughly mixed smooth plastic mass. This was then extruded 35 with a hand operated screw extruder to provide cylindrical OE pellets initially of 10 mm diameter (about 8 mm after drying) and varying from 10 - 20 mm in length. The pellets were permitted to dry and harden in still laboratory air at 20°C for 7 days. The dried pellets were next subjected to 5 pyrolysis in a stream of nitrogen gas, initially being maintained for one hour in the temperature range 300 - 400°C to eliminate residual water and low molecular weight organic volatiles, followed by further heating for one hour with an increase of temperature to 700°C. This latter period of 10 heating was designed to determine whether detectable reduction had commenced in the temperature range concerned. In one instance (see below) pellets were heated to 1070°C, on this occasion in the reducing atmosphere generated by the coal pyrolysis/ Pellets were made with 10, 30, 50 and 75* by weight (based on dry coal weight) of iron oxide. The 10% composites gave an average ^rush strength of 17 MPa compared with 30 MPa for comparable pellets containing no iron oxide; on pyrolysis the 10% ferric oxide pellets displayed an increase to an 20 average crush strength of 20 MPa indicating the development of further bonding during pyrolysis.

The compresslve/crush strengths of the dried densified coal pellets were determined following measurement of the height (H) and diameter (D) of pellets to be tested 25 with a micrometer.

The pellets were then placed on the anvil of a universal testing machine (Tirius Olsen Testing Machine Co., Willor Grove, Pa.), and an axial load was applied across the plane ends until failure occurred.

The compressive strength was calculated from the Force F (determined from the maximum load the pellet withstands) according to the following formula:- OE 2 1 5368 - II - 1 a _ = (4FAD2) (H/D)0'5 All of the compositos were strongly magnetic (part lcularly the 75:25 ore: densified coal blend) after pyrolysis to 700°C, indicating the production of reduced iron.

In one experiment pellets containing 75% were placed in a silica tube attached to a vacuum system. The tube was pumped free of all gases whilst being heated to 500°C. The tube was then isolated from the pumps and the pressure change observed as the temperature was further increased at an 10 approximately steady rate to 1070°C. The results of these measurements are shown in Figure 2. At about 900°C a very rapid pressure rise commenced and it became necessary to pump gas away maintain the total pressure below one atmosphere. Substantial gas evolution continued until the experiment was 15 terminated. The phenomena described in this experiment are characteristic of pellets containing iron oxide, and are indicative of chemical reactions between the oxide and species derived from the coal.

At 800°C the pr incipal reaction appears to be 20 reduction of the iron oxide by evolved hydrogen with production of water. This reaction appears to be supplemented at about 900°C by reduction reactions involving carbon monoxide and carbon with a net substantial increase in total gas pressure. At the end of this experiment the pellets while 25 being strongly ferro-magnetic, did not display visible metallic iron. When the temperature was raised still further using pellets as electrodes in a DC arc in an inert atmosphere globules of malleable iron were produced very rapidly.

Composite pellets containing 75% Fe^O^ after 30 preliminary pyrolysis to 700°C as described above, were further tested by immersion in a bath of liquid iron maintained at 1500°C. Gas evolution commenced immediately on immersion and continued throughout the dipping period of 30 seconds. The pellets did not disintegrate but continued to 35 evolve gas whilst dissolving rapidly in the liquid iron. Rate OE > i ! * m- 2 ) 5 J v. of dissolution was greatest on that side of the pellets whirh has sustained the highest temperature by contact with the furnace wall during preliminary pyrolysis; presumably more reduced iron was present in that zone of the pellet thus 5 enhancing the rate of attack by the liquid iron. This experiment demonstrates that the composite iron pellets in a pre-reduced state may be used as feed material to supply both iron and carbon to steelmaking furnaces by a new bath smelting technology.

It will be clearly understood that the invention in its general aspects is not limited to the specific details referred to hereinabove.

OE

Claims (14)

2153^ -13- itta-efcffTws-pgriniMC the invENiiuir-*nE ac followo:

1. Process for production of metallurgical composites which comprises the following steps: la) subjecting brown coal to shearing forces to produce a plastic mass; (b) admixing finely divided ore and/or concentrate with the coal either during or after step (a); (c) compacting the mixture produced in step (b) to produce a compacted mass; (d) drying the compacted mass to produce the metallurgical composite.

2. Process according to claim 1 in which the compacting step (c) is effected by extruding the said mixture.

3. Process according to claim 1 in which the drying step (d) is effected at or near ambient temperature.

4. Process according claim 1 in which the ore is iron ore or chromite ore.

5.. Process according to claim 1 in which the ore or concentrate is a zinc ore or concentrate. 9776F21/2 -14-

6. Process for production of metallurgica1 composites containing iron ore and upgraded brown coal which comprises the following steps: (a) subjecting brown coal to shearing forces to produce a plastic mass; (b) admixing finely divided iron ore with the coal either during or after step (a); <c) extruding the mixture produced in step (b) to produce a compacted extrudate in the form of pellets; an<f <d) drying the pellets at ambient temperature.

7. Metallurgical composites produced by the process of any one of claims 1 to 6.

8. An iron smelting process characterised by heating composites produced by the process of claim 7 to a temperature at which the iron ore is reduced to metallic iron.

9. An iron smelting process characterised by heating composites produced by the process of claim 7 in a bath of liquid iron.

10. An iron smelting process characterised by subjecting composites produced by the process of claim 7 to a preliminary pyrolysis up to a temperature of about 700°C, followed by immersion in a bath of liquid iron at a temperature of about 1500°C. 9776F21/2 .. ... . ^ ..... — 21 53< fC

11. A process for production of metallurgical composites substantially as herein described with reference to any embodiment disclosed in the examples and/or the drawings.

12. A metallurgical composite produced by the process of claim 11.

13. A iron smeltinq process substantially as herein described with reference to any embodiment disclosed in the examples and/or the drawings.

14. Iron produced by the process of any one of claims 8-10 and claim 13. rr\c^