US 2441594 A
Description (OCR text may contain errors)
May 18, 1948. c. F. RAMSEYER 2,441,594 APPARATUS FOR BENEFICIATING NONMAGfiETIC ORES TO RENDER THEM MAGNETIC Fiied Jan. 12, 1944 All? PRE/YEA 7Z7? All? ORE PUMP FRO! CONVERTER Rim/0N6 IN VEN TOR.
PatentedMa yl8; 19 8 APPARATUS FOR BENEFICIATING I Q ON- MAGNETIC'ORES T BENDER momrrrc Charles F. Bamseycr, Old Greenwich, Conn, as-
signor to RA. Brassert & Company, New York, N. Y., a corporation 0! Illinois Application January 12, 1944, Serial No. 517,908
1 Claim. (c1. zoo-s) This invention relates to the continuous beneficiation of metallic oxides and has particulaireference to apparatus for rendering magnetic the normally non-magnetic iron ores, such as the hematites, limonites, carbonates and mixtures thereof, in order that they may be concentrated magnetically for further processing, such as reduction to iron.
As is well known, non-magnetic iron ores abound throughout the world. but-the expense of concentrating them by washing, jigging, tabling, flotation, or the like, renders the cost of the finished product prohibitive, but if these ores could be simply and inexpensively converted to material that is sufllciently magnetic to permit of relatively inexpensive magnetic concentration, such heretofore relatively useless ores would be-v come commercially useful.
The present invention provides simple apparatus for inexpensively beneficiatlng such low grade non-magnetic ores so that substantially all of the gangue therein may be readily removed by magnetic concentration according to .any one of several known processes, whereby the low grade ore is inexpensively converted into a high grade magnetic concentrate for reduction to iron by any of the several known processes.
In accordance with the invention, the nonmagnetic ore as mined, such as the siliceous hematite of the Lake Superior district, commonly known as taconite, for example, is first ground to an average fineness greater than fifty mesh, and is then pumped with an admixture of an the reducing gas under the conditions provided within the tube, i.- e., suspension of the particles in the gas so that the entire mass is rendered fluent or ffluidized" and actually fiows through the tube like a fluid. Inasmuch as the tube is externally heated the conversion takes place without contamination by combustion gases.
After the ore is thus converted into magnetic material to a degree such that at least about 25% excess of reducing gas under pressure, such as A water gas, cleaned producer gas, or other hydrogenor carbon monoxide-containing gas, through an elongated tube, preferably in coil form, that is externally heated to such temperature that at least partial conversion from FeaOz to Fea04 takes place without the formation of FeO, which means at temperatures below 1100 F. The preferred temperature range is lower, from "I50" to 850 F. and may be carried out successfully at temperatures as low as 500to 600 F., depending upon the physical nature of the ore, its fineness, the reducing gas employed, the pressure in the tube,
which, in addition to the velocity of the material through the tube, govern the length thereof. The actual time of conversion under these conditions is normally very short, a matter of a few minutes 1 and, under the most favorable conditions of fineness and high hydrogen gas content, a matter of seconds. The conversion is also aided by the exothermic nature of the conversion, the attrition between the particles and their envelopment in of each particle ismagnetic, which is sufilcient to cause the particle to respond to a magnetic field, the converted ore is separated from the gangue by aconventional magnetic process, preferably the wet magnetic process in view of the higher degree of concentration obtainable thereby. The heat for, externally heating the tube is preferably provided by the excess reducing gas not expended in the conversion, which is recovered and may be burned in the converter or furnace containing the tube. The fluidized raw ore and incoming cold gas mixture may be prev heated by heat exchange with the hot converted gas-ore mixtur'a'and the flue gases from the furnace may be employed to preheat the combustionsustaining air-supplied to the converter furnace burners, and the like. Y
It will be seen that the invention provides a very simple and eilicient way of continuously beneflciating large quantities of naturally non-. magnetic ores at the mine site, and makes available a valuable magnetic concentrate from .ores that were heretofore regarded as of low value because of expense of concentration or cost of transportation to concentration points, or both.
For a more complete understanding of the invention, reference may be had to the accompanying drawings, in which: Y f I Figure 1 illustrates, partially schematically, a preferred form of apparatus for conducting the beneficiation of non-magnetic ores according to the invention; and
Fig. 2 illustrates a modification in which the hot converted ore from the converter is passed in heat-exchanging relation with the raw ore being pumped to the converter.
Referring to Fig.1, the raw ore such as the aforementioned taconite as mined is supplied to hopper Ill and is preferably dried in drier ll,
" preferably by the waste heat of the converter centration, the material should be ground to a fineness such that not materially more than half is as coarse as 50 mesh and the balance finer. In the case of taconite and other siliceous hematites it is frequently necessary to grind them to 150 mesh in order to free the siliceous gangue, and in doing so at least half of the material is reduced to a fineness of 200 mesh.
The slightly heated finely-divided material is gravity fed to an ore preheater l3 in which the ore is preheated up to about 350 F., more or less, preferably by waste heat from the converted ore pumped through the coil l4 within the preheater l3 and over which the ore flows by gravity inheat exchanging relation.
The warmed raw ore is gravity fed from preheater l3 to ore pump l5 of the type that is provided with a motor-driven screw for advancing the material through and beyond the pump through tube I6, after the material is mixed with a gas supplied under pressure by pipe l1. Such pumps for pumping finely-divided solids are well-known in several arts, particularly those employed in the cement industry, and one form of such pump is marketed under the name Fuller-Kinyon. In adapting this form of pump to the present invention, the warmed raw ore is pumped through pipe l6 at the average velocity of about thirty feet per second, and the gas that is admixed therewith is a reducing gas supplied through pipe I! at a pressure of about one hundred pounds per square inch gauge or more. At this gas pressure and under the conditions of agitation and mechanical pressure produced by pum 15, the particles of raw ore are suspended in the gas and the entire ore mass is rendered fluent or fluidized? so that it flows like a fluid through pipe [6.
The reducing gas that is employed may be any suitable available gas containing substantial amounts of hydrogen or carbon monoxide, or both. An example of an-inexpensive gas that is suitable for the purpose is uncarburetted'water gas, usually comprising about 50% of hydrogen and of carbon monoxide by volume.
' Cleaned producer gas, although not as rich in reducing agentsmay also be used, or any other convenient reducing gashigh in hydrogen or carbon monoxide, or both, but preferably low in hydrocarbons since they are inert and some of them may decompose at the temperatures of operation of the process.
-The fluent mixture of ore and reducing gas flowing through pipe I6 is introduced into the upper end of the spiral tube N3 of the converter IQ for doWnWard spiral flow therethrough. The
capacity of ore pump IE is preferably such that a steady stream of the material flows at an average velocity of around thirty feet per second through a four inch diameter pipe 16, which is extended to the coil l8, also of four inch diameter tubing and preferably of a spiral diameter oi. ten to twenty feet and a length of eight hundred to two thousand feet, depending upon the several aforementioned variables.
The spiral l8 of converter 1| 9 is'enclosed in a suitable steel housing 20 lined with fire brick 21 or other. refractory material. The spiral I 8 is heated externally by one or more burners 22 positioned above the floor 23 of the converter and preferably supplied with gas as a fuel by pipe 24 from a source-to be described. The upper portion of the converter contains a reflecting cone 25 for radiating the heat in the hot gases laterally and downwardly toward the spiral I8 before the gases flow out the slots 28 through the stack 21 into the air preheater 28 which is used to preheat the combustion supporting air supplied to the burner 22 by pipe 29. The residual heat in the flue gases after they leave the air preheater 28 may be employed to dry the raw ore prior to grinding at l2, and to that end they are supplied by pipe 30 to drier II, as shown.
Converter spiral l8 preferably leads by tube 3| to the coil H of ore preheater II for heat exchange between the hot ore in the coil H and the finely-divided raw ore feeding thereover by gravity. The cooled ore is then delivered by pipe 32 to cyclone 33 where the converted ore is separated from the mixture of spent and excess reagent gas which is preferably supplied to pipe 24 for combustion at burner 22, so that the thermal content, both sensible and latent, of the combustible components of the oiT-gas is recovered and used. The converted ore, having been rendered magnetic by the conversion, is separated from the gangue in. the magnetic concentrator 34, which is preferably of the wet type in which the ore and gangue are conveyed through water and the magnetic ore separated from the gangue by electromagnets, as is shown. for example, in copending abandoned application Serial No. 485,195, filed April 30, 1943, by H. A. Brassert. The concentrate may be sintered or briquetted to a size permitting its use in a blast furnace or it may be directly reduced to iron in finely-divided form in accordance with known processes.
In the modification shown in Fig. 2, the heat of the converted ore after it leaves the converter 19 is transferred to the ore as it leaves the ore pump l5 instead of before it enters the ore pump as in Fig. 1. To this end, the ore preheater l3 contains two spiral coils 35 and 36, either concentric .or of the same diameter, each made of separate tubing and the turns of each spiral in contact with the corresponding turns of the other. Preferably the two coils 35 and 38 are integrally encased in cast iron for better heat exchange and the whole may take the form of a hollow cylinder or large diameter tube fittingwithin the insulating jacket 3'! of ore preheater [3' with its center being filled with the raw ore so that remaining heat may be transferred thereto. The lower end of one of thecoils, 35, is connected to discharge pipe l6 of ore pump l5 and its upper end to the converter spiral I8, while the upper end of the other coil, 36, is connected by pipe 3| to the lower end of the converter spiral l8 and its lower end is connected to pipe 32 leading to the cyclone separator. In this way the hot converted fluidized ore and spent gas mixture flows counter-currently to the raw ore and fresh reducing gas mixture and efliciently transfers heat thereto. Other methods of recovering the heat in the converted ore by heat exchange with the raw ore may be employed.
In operation of the apparatus described, the temperature at which the conversion or beneficiation of the ore and conditions under which that takes place are important. Unlike the reduction of iron oxides to iron, the conversion of F8203 to F6304 by hydrogen, for example, is slightly exothermic, and when the-ore is finely-divided. such as mesh hematite or limonite, the conversion at 750 to 800 F. is extremely rapid, taking place in a matter of seconds, partly 'due to the comparatively large surface area of the fine grains. Also as long as only a small amount of unreacted hydrogen is present under the conditions mentioned, the conversion will continue on,
to virtually complete reduction to F8304. With only carbon monoxide present as the reagent, a
which is catalyzed by finely-divided iron oxide.
However, since only conversion to the magnetic state is desired, and then not materially greater than is necessary, i. e. not more than 25% of the particle need be magnetic to permit magnetic concentration, the aforementioned factors, utilized according to the invention, make the very rapid and inexpensive conversion of the plentiful low-grade non-magnetic ores a, commercial possibility.
Only a low volume of gas, normally from twenty to thirty cubic feet at atmospheric pressure, is required to convey one cubic foot of pulverized material. Somewhat more than this is required to furnish the hydrogen component used in the conversion, but that additional volume only helps to fiuidize the mass for pumping. Only about onetenth of the as required for the reduction of F8304 to metallic iron is required to convert F8203 to F6304. With hydrogen in the gas, the temperature of conversion may be kept well below that at which undesirable non-magnetic FeO is formed as well as low enough so that but little of the carbon monoxide has time to break down to carbon dioxide and carbon due to the relatively brief time it is under pressure at the maximum temperature. Advantage is also taken of the exothermic nature of the reaction and the consequent rapidity thereof in the presence of hydrogen as one of the reagent components.
In order to avoid the use of too long a s iral l8 in the converter l9, or to increase the velocity therethrough and hence the output, the temperature to which the material in the spiral I8 is heated may be between 700 and 800 F. However, by increasing the pressure on the reducing gas to pipe II to upwards of one hundred pounds per square inch, the conversion may be effected at temperatures as low as 500 to 600 F. without increasing the size or the apparatus or reducin the velocity of throughput. The velocity may be regulated by adjusting the amount of gas fedto pump I5, whereby the degree of deoxidation may be regulated. The gas. pressure in the spiral l8 may be regulated by means of a throttling valve at the discharge end, such as is shown at 38.
The temperature of the converted material discharged from converter spiral l8 accordingly is in the neighborhood of the conversion temperature, i. e., between about 500 and 900 F., and by transferring this heat to the raw ore in preheaters l3 or l3 considerable thermal economy achieved. Likewise the surplus gas from the cyclone separator retains considerable sensible as well as its latent heat and this when added to the heat of the preheated air from 28, also provides an additional item of thermal economy, all conducive to inexpensive operation, rendering possible the commercial use of heretofore virtually useless low-grade non-magnetic iron ores.
Although certain preferred embodiments of the invention have been illustrated and described herein, it is to be understood that the invention is not limited thereby, but is susceptible of changes in form and detail within the scope of the appended claim.
I claim: I In apparatus for'beneficiating non-magneti ores to render them magnetic, the combination of an elongated tube, a pump connected to one end of said tube, means for supplying finely-divided ore to said pump for pumping through said tube, means for supplying a deoxidant gas to said tube for admixture with the ore therein to render the same fluent, means for heating said tube externally to cause the gas and the oxygen in the ore contained in said tube to react chemically to a. degree rendering the ore magnetic, an ore D heater exchanger interposed between the other end of said tube and said means for supplying ore to said pump for preheating the latter with the residual heat in the treated ore, and means at said other end of the tube beyond said are preheater for magnetically separating the magnetic particles from the gangue.
CHARLES F. RAMSEYER.
'. REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 519,902 Barton May 15, 1894 859,420 Wilfley July 9, 1907 1,969,264 Grant Aug. '7, 1934 2,198,560 Marshall Apr. 23, 1940 FOREIGN PATENTS Number Country Date 159,380 Great Britain Mar. 3, 1921 36,609 Norway Jan. 22, 1923