US3563726A - Production of metal from pulverent material by flash smelting in a vortex - Google Patents

Abstract

THE PRESENT INVENTION PROVIDES A REACTOR FOR PROCESSING FINELY-DIVIDED ORES INCLUDING A GENERALLY RECTANGULAR FURNACE CHAMBER HAVING BATH HEATING ELEMENTS EXTENDING THROUGH THE FURNACE ROOF AND DEPENDING TOWARD THE BATH. THE HEATING ELEMENTS ARE ARRANGED IN AT LEAST ONE ROW EXTENDING LENGTHWISE OF THE CHAMBER. AT LEAST TWO REACTANTS-INJECTING HIGH VELOCITY NOZZLES ARE PROVIDED BETWEEN EACH PAIR OF HEATING ELEMENTS AND ARE DIRECTED TO ESTABLISH A FREE-STANDING VORTEX UNSUPPORTED BY THE FURNACE WALLS, WHICH VORTEX IS LOCATED BETWEEN THE RESPECTIVE PAIRS OF HEATING ELEMENTS. A CHARGING PIPE FOR DELIVERING THE FINELY-DIVIDED ORE FEEDS THROUGH THE FURNACE ROOF AND DISCHARGES INTO A ZONE BETWEEN THE HEATING ELEMENTS AND EFFECTIVELY INTO THE FREE-STANDING VORTEX. THE HEATING ELEMENTS OF ONE EMBODIMENT COMPRISE ELECTRODES AND THE HEATING ELEMENTS OF ANOTHER EMBODIMENT COMPRISE FUELFIRED BURNERS.

Description

Feb. 16, 1971 H. l. ELVANDER ETAL 3,563,726

PRODUCTION OF METAL FROM PULVERENT MATERIAL BY FLASH SMELTING IN A VORTEX Filed Oct. '20. 1967 2 Sheets-Sheet I l/IIII/ IINVENTIORS Hans Ivar E/vander Erik O/o'fl R/bin Sands from m, Awmwmm FITToRNEYS.

Feb. 16; 1971 H. ELVANDER Em 3,563,726

PRODUCTION OF METAL FROM PULVERENT MATERIA BY FLASH SMELTING IN A VORTEX Filed Oct. 20. 1967 2 Sheets-Sheet 2 a. 4/. p115; L140 FUEL INVENTORS few 01 aF/w/A/Jm/as red/w ORNI'IYS United States Patent O 3,563,726 PRODUCTION OF METAL FROM PULVERENT MATERIAL BY FLASH SMElLTING IN A VORTEX Hans Ivar Eivander and Erik Olof Albin Sundstrom,

Skelleftehamn, Sweden, assignors to Boliden Aktiebolag, Stockholm, Sweden Continuation-impart of application Ser. No. 340,395, Jan. 27, 1964. This application Oct. 20, 1967, Ser. No. 676,894 Claims priority, application Sweden, Jan. 31, 1963, 1,102/63 The portion of the term of the patent subsequent to Jan. 23, 1985, has been disclaimer] Int. Cl. CZlc 7/00; C22b 9/00; C221! 7 8 U.S. Cl. 75-10 14 Claims ABSTRACT OF THE DISCLOSURE The present invention provides a reactor for processing finely-divided ores including a generally rectangular furnace chamber having bath heating elements extending through the furnace roof and depending toward the bath. The heating elements are arranged in at least one row extending lengthwise of the chamber. At least two reactants-injecting high velocity nozzles are provided between each pair of heating elements and are directed to establish a free-standing vortex unsupported by the furnace walls, which vortex is located between the respective pairs of heating elements. A charging pipe for delivering the finely-divided ore feeds through the furnace roof and discharges into a zone between the heating elements and effectively into the free-standing vortex. The heating elements of one embodiment comprise electrodes and the heating elements of another embodiment comprise fuelfired burners.

This is a continuation-in-Part of US. Ser. No. 340,395, filed Jan. 27, 1964 now Pat. No. 3,365,185.

BACKGROUND The present invention relates to the continuous production of metals from finely-divided oxidic or sulphidic ores and more particularly flotation concentrates, or other dressed products, by directly feeding the reactants to a furnace chamber heated to reaction temperature by electrical means, fuel-fired burners or the like.

It should be understood that the term finely divided as used herein is in reference to the normal particle size for materials found in flotation concentrates, that is, a particle size of l0400 micrometers.

The production of metals from a finely-divided charge without preparatory agglomeration, roasting or reduction steps is naturally desirable since in this way substantial simplification of the procedure and other advantages are obtained. Several methods based on this principle have been developed. A characteristic of the methods based on some form of flash smelting is that the process has been either completely autogenous, i.e., the heat developed in the reaction has been sufficient to impart to the reaction products the desired temperature and to maintain the reaction chamber at the correct temperature (possibly by preheating the reactants charged and/or by using reaction gas enriched with oxygen) or the energy demand has been satisfied by the addition of an extra supply of heat.

In other methods not using flash smelting the finelydivided material has been melted in fuel-fired or electrically heated melting furnaces. Thereupon, the molten mass may have been subjected to an oxidation or reduction treatment in the same reaction vessel or in another one. The latter methods are encumbered with obvious disadvantages.

In flash smelting, however, the heat generated in the reaction between, firstly sulphidic concentrates and oxidizing gas and, secondly, oxidic material and a reduction agent is, in many cases, insuflicient or in certain cases negative taking into account also the unavoidable heatlosses from the reactor chamber. Therefore, in these cases, when conducting a flash smelting process according to methods known hitherto, it has not been possible to bring the reaction products to the correct temperature or maintain the temperature of the reaction chamber, unless employing some form of external heat supply. This has been effected by additional heating or, in the case of sulphidic material, by effecting the combustion to such an extent that the metal to be produced is combusted during the production of heat.

BRIEF DESCRIPTION OF INVENTION The present invention provides a reactor for processing finely-divided ores including a generally rectangular furnace chamber having bath heating elements extending through the furnace roof and depending toward the bath. The heating elements are arranged in at least one row extending lengthwise of the chamber. At least two reactant-injecting high-velocity nozzles are provided between each pair of heating elements and are directed to establish a free-standing vortex unsupported by the furnace walls, which vortex is located between the respective pairs of heating elements. A charge pipe for feeding the finely-divided ore delivers through the furnace roof and discharges into a zone between the heating elements and effectively into the free-standing vortex.

In the case of oxidic materials intended for the production of iron, the invention involves a further advantage because the ability to produce reaction gas within the furnace from cheap fuels such as coal breeze, peat and brown coal. The slag formed may be further reduced directly by the introduction of solid or gaseous reducing agents into the furnace. The degree of oxidation of the slag formed from sulfidic ores is controlled in a corresponding manner. By injecting the gas in a manner to form isolated vortices and charging the ore concentrate therein, the reaction will proceed within the furnace cham her and not for the most part in a layer adjacent to the furnace wall which is the case for instance in cyclonesmelting known per se. For this reason the method according to the invention involves reduced attacks on the walls. To provide the desired reaction, the temperatures of the furnace chamber as well as the gas therein are designed to effect concentrate smelting. The amount of oxygen supply may be controlled. The injected gas, if necessary, may be preheated and the material to smelt dried to any suitable degree. The number of vortices may be varied in dependence of the desired output, and the injection and charging, respectively may be effected through the furnace roof or through inlets located at a high level of the furnace walls. The furnace may have a rectangular, square or circular horizontal cross-sectional area.

FIRST EMBODIMENT One embodiment of the present invention relates to the case in which it is more advantageous from an economical or technical point of view not to compensate the mini mum heat demand of the reaction by additional fuel combustion but rather to generate the additional heat required by electric heating. For reasons of construction, however, electrically heated furnaces have a low roof so that, within the restricted space, it is not possible without special precautions to perform the operations of drying, preheating, ignition and reaction within the normally re quired short period of time. t

With the present invention, it has surprisingly proved possible within the relatively restricted space of an electrically heated furnace to perform a production of metals from finely-divided oxidic or sulfidic ores. According to the invention, the free-standing vortex is developed between each electrode pair, said vortex being established by injecting reaction gas at high velocity through at least two nozzles disposed within the furnace chamber and directed tangentially with respect to an imaginary horizontal circle. The finely-divided ore is charged into the vortex or vortices. Suitable electrical heating means include Soderberg-electrodes which provide a heat generation within the slag bath according to the resistance principle.

In addition to the great simplification of the process achieved by the application of the invention in the production of lead from lead sulfide concentrate, a substantial saving of energy has been obtained. Hitherto the concentrate was sintered with partial roasting of the sulfur to form with heat generation oxy-sulfidic intermediate products. In electric furnace melting, a stoichiometric proportion between remaining sulfur and oxygen contained in the lead sinter was desirable for the purpose of obtaining lead and an SO -containing gas as end products. In flash smelting according to the inventive process, the heat which was previously lost in the sintering process is now transferred to the electric furnace and there substitutes part of the electric energy previously required, saving around 24 mW. h. per day. Furthermore, the electric energy previously required for effecting the sintering operation, i.e., for the operation of blowers and other apparatus, is no longer required. This energy saving approximates 8 mw. h. per day.

The increased amount of waste gas resulting from the inventive flash smelting conveys an increased amount of heat from the furnace. However, this heat is recovered by an increased steam production in a waste heat boiler connected to the smelting furnace.

SECOND EMBODIMENT In the event the use of electrical energy for heating purposes, according to the first embodiment of the invention, is found to be more expensive than the use of energy obtained by the combustion of solid, liquid or gaseous fuels, greater benefits may be derived from the second embodiment of the invention, which relates to a system for using such fuels to effect the necessary heating of the melt.

If sulphidic or oxidic ore concentrates are flash smelted r in a common fuel-fired furnace, wherein there is a hot smelt bed, the temperature of the flames (and thus the temperature of the entire furnace chamber) must be kept high, about 1500 C., in the exhaust gas outlet and considerably higher in the firing zone, because of the relatively poor transfer of heat between flames and bed. Usually this practice results in high wear and tear on the furnace lining, which action is further amplified by the fluxing effect which the reaction product with the concentrate exercises on the said lining material. Attempts to protect the furnace lining by cooling or possibly by replacing certain brick portions of the lining with cooling boxes result in extraction of heat from the bed which in turn results in poor heat economy.

If air is used as a reaction and combustion gas, the quantity of exhaust gas, and thereby the quantity of circulating dust, increases and adversely affects efficiency in comparison with flash smelting in electrically heated furnaces. This problem can be avoided by using oxygen or oxygen-enriched air; but this then causes the disadvantage of further elevated flame temperatures and high wear and tear on the lining of the furnace.

When producing lead by flash smelting a sulphidic concentrate, it is undesirable to reach an exhaust-gas temperature of higher than 1100 C., because of the high degree of volatilization of the lead and lead compounds and the resulting circulation of dust.

The solution of this problem is provided by the oxygengas/ oil burners developed during the past few years. Such burners afford an intensive local heating comparable with that provided by electrodes. With the second embodiment of the invention, substantially the same result is achieved as that when smelting with depending electrodes. Namely, an intensive local heating is achieved in the zones where the flames from the burners meet the slag bed and the area in the immediate vicinity thereof while the furnace lining is protected from the hot gases.

By employing the second embodiment of the present invention, it is possible to effect the production of metal from the finely-divided oxidic or sulphidic ores by developing one free-standing vortex between the fuel heating elements by injecting the reactants at a high velocity substantially tangential to an imaginary horizontal circle. The finely-divided ore is fed into said vortex within the zone between the fuel heating elements.

Since the hot gases of combustion from the oil burners are directed straight against the slag bed, an intensive local heating and smelting of the slag takes place. The slag is simultaneously subjected to a powerful agitating action. In this way, the slag can be heated to approximately 1400 C. and the temperature of the gas in the furnace chamber, at the same time, can be held at a constant level by the cooling effect that the reaction products exerts upon the gases rising from the bath, meeting them in counter-current and by mounting suitable cooling elements in the furnace chamber above the level of the bath. In case of lead smelting this cooling, in addition to causing vaporized lead products to condense and sublimate, further protects the brickwork. Thus, the furnace chamber temperature may be held at approximately 1100 C. in the gas outlet.

To compensate for the increased volume of gas when using burners instead of electrodes, the burners are operated suitably with oxygen-enriched air or pure oxygen. Similarly, depending upon the composition of the concentrate, it may prove necessary to replace the reaction gas in the vortices with oxygen or oxygen-enriched air.

When using a supply of additional heat in the manner described, it is thus possible according to the invention, despite the intensive local heating of the slag bath by the burners, to impart to the gas leaving the furnace substantially the same temperature as that obtained when smelting according to the first embodiment using suspended electrodes. This result can be accomplished by means of suitably controlling temperature transfer, i.e., primarily by controlling the cooling of the furnace chamber, and secondly, by increasing the oxygen used to maintain the amount of waste gas at the same level as when heating by means of electrodes.

When heating the furnace chamber with fuel-fired burners, the combustion in the flames which strikes the surface of the bath can be controlled so that reducing, neutral or oxidizing conditions can be maintained as required, whereby the losses of metal in the slag can be reduced.

The invention will now be illustrated in more detail with reference to the accompanying drawings wherein like reference characters refer to like structure and in which FIG. 1 is a horizontal view of an electric smelting furnace adapted for flash smelting of lead concentrate according to the invention. FIG. 2 is a cross-sectional view of the furnace along line II-II in FIG. 1. FIG. 3 is a detailed view showing a nozzle device for creating a tornado-like vortex and feeding lead concentrate into said vortex. FIG. 4 shows a vertical, longitudinal section of a furnace according to a second embodiment of the invention provided with fuel-fed burners for smelting lead concentrate. FIG. 5 shows diagrammatically a plan view of the furnace of FIG. 4.

The furnace shown in FIGS. 1 and 2 comprises a rectangular furnace chamber of small height in relation to the horizontal cross-sectional area of the furnace chamber and is provided with a number of heating electrodes 1-4, which may be Soderberg type electrodes. The electrodes extend downwardly into the furnace chamber through cooling boxes 6-9 disposed on the furnace roof, said cooling boxes having conduits (not shown) for the supply and withdrawal of cooling water. The basic construction of the furnace is known per se and is used in lead smelting. There is provided a number of nozzle sets arranged within the furnace chamber for the creation of upright tornado-like air vortices. Thus, in FIG. 1, between the electrodes 1 and 2, 2 and 3, and 3 and 4, respectively, three such sets of nozzles 10-13, 1417, and 18-21, respectively, are provided. Although it is possible to develop a vortex as described with two staggered substantially parallel directed nozzles, a greater number (such as four) arranged with mutually intersecting paths is preferred.

The nozzle device shown in FIG. 3 comprises a vertical blowpipe 22 extending through the furnace roof and terminating below the roof in a bend 23 of a direction such that the jet stream of air is blown generally tangentially in relation to an imagined horizontal circle between the respective electrodes. In front of the mouth of the blowpipe a charging tube 24 for lead concentrate debouches at the roof level. A branch pipe is connnected to the charging tube with one of its branches 25 extending coaxially with the charging tube 24 and the other branch 26 sloping at an acute angle with the vertical. The end of the branch 25 is covered by a lid 27 which may be removed for inspection purposes. The charging material is introduced through the branch 26.

In flash smelting of lead concentrate an airconcentrate mixture is injected directly into the furnace chamber through the three sets of four nozzle devices of the type illustrated in FIG. 3. The streams of concentrate supplied through the charging tubes 24 are caught by the compressed air injected through the respective nozzles 23 and entrained into the upright vortex which, due to the tangential injection, is formed without the aid of supporting walls. The furnace is heated by means of the electrodes 1-4 immersed in the slag layer, wherein due to the ohmic resistance of the slag the heat generated is sufficient to maintain the lead and slag contained in the furnace pot in a molten state.

The embodiment of the invention illustrated in FIGS. 1 to 3 has merely been advanced as a suitable example. Thus, it is possible to introduce the lead concentrate into the vortices through the same nozzles through which the air is injected. Another possibility is to provide pairs of opposite air nozzles at the long sides of the furnace to produce upright vortices between the electrodes, and to charge the concentrate through an opening above the center of each vortex.

With reference to FIGS. 4 and 5, the second embodiment will now be described in detail. The nozzle arrangement for the embodiment of FIGS. 4 and is the same as disclosed above and as illustrated in FIG. 3 herein. The streams of air are ejected generally tangentially in relation to an imaginary horizontal circle located between respective heating elements. Opening out in front of the mouth of the blower tube at roof level is a charging tube 24 intended for lead concentrate and fed by tube 100. Charging material is introduced through tube 100, the branch 26 and charging tube 24.

When flash smelting lead concentrate an air-concentrate mixture is injected straight into the chamber of a furnace shown in FIG. 4, through the three series of nozzle arrangements of the type shown in FIG. 3. Each nozzle series includes four nozzles. The furnace is heated by means of burners 109, 110 lowered down to the slag layer 107 above the metal bath 108. The burners are water cooled and suspended through the roof 102 of the furnace. The streams of concentrate passing through the charging tubes 24 are captured by the compressed air blown in through respective nozzles 23 and entrained into the free-standing tornado-like vortex, created without the support of walls as a result of the tangential injection of the mixture.

The burners 109, are of a known type and each comprises an outer, double-layer metal jacket 112 through which cooling water may be passed, the water being delivered through conduit 113 and removed through conduit 114. Extending centrally within the jacket 112 is a fuel feed tube 115. An oxygen-containing gas is passed, via a conduit 116, to the space of annular cross section formed between the outer metal jacket 112 and the central fuel tube 115. The fuel is mixed with the oxygencontaining gas at the mouth of the burner, which is directed downwards towards the slag bath, The flame thus formed is ejected against the slag bath. The burners can be fired with pulverous, liquid or gaseous fuel, e.g., carbon powder, fuel oil, generator gas or other fuel gases, and operated on air, oxygen-enriched air or oxygen. The burners are preferably fired with fuel oil and, according to the composition of the concentrate and the desired temperature, with air, oxygen-enriched air or pure oxygen and are of such construction that they give a limited flame but provide for an intensive local development of heat which causes a strong, local heating of the. slag bath, the temperature of which thus rises considerably above the temperature in the furnace of the chamber. By causing the burners to discharge a few decimeters above the surface of the slag bath, the hot gases of combustion of the burners are directed immediately against the slag which is thus subjected to a strong heating and agitating action. In this way the temperature of the slag will rise to approximately 1400 C. whereas the temperature of the gas in the furnace chamber can be maintained at a safe level by suitably cooling the furnace chamber. Therefore, when smelting lead according to the invention, the gas temperature can be kept at approximately 1100 C. This low gas temperature avoids undue wear on the furnace walls as stated above.

As can be seen from FIG. 5, the burners 109, 111 are supplemented with the burners 109', 110', in a front row and four charging tubes 24, 24' and nozzles 23 are arranged so that they inject reactants tangentially to an imaginary circle, whereby a vertical vortex is obtained, unsupported by the walls of the furnace.

As mentioned above, the use of burners causes an increase in hot gases in the furnace and therefore an effective cooling of the parts of said furnace subjected to the strongest mechanical and chemical actions is necessary, particularly when the burners are operated with oxygen or oxygen-enriched air. For this purpose, as disclosed in FIG. 4, the entire roof of the furnace may comprise a water-cooled sheet metal cover, or may be provided with cooling means, e.g., cooling pipes disposed in the brickwork of the roof of the furnace, whereby the heat can be utilized for generating steam. If necessary the walls may also be cooled in a like manner.

The embodiment of theinvention as disclosed in FIGS. 4 and 5 has only been described as a suitable example. For example, the lead concentrate may be introduced into the vortex through the same nozzles through which the air is injected. A second alternative is to arrange the air nozzles in the long sides of the furnace, pairwise in such a manner that standing vortices are created between the burners and to introduce the concentrate through an opening above the center of the vortex.

In addition to the disclosed advantages including a local heating of the charge and slight chemical and mechanical actions on the brickwork furnace and the possibility of operating said furnace at a higher level of efficiency than with conventional flash smelting furnaces, an effective agitation of the slag batch is obtained when using fuelfired burners. Furthermore, the flame may be adjusted as necessary by controlling the fuel-oxygen-ratio so that it is either oxidizing, reducing or neutral. The gases, which in the case of lead smelting leave the furnace at approximately the same temperature as when smelting with electrodes, are laden with, inter alia, sulphide oxide and floating dust of, for instance, lead oxide, zinc oxide, or vaporized lead which can be caught in separators in a manner known per se, while the heat content of the exhaust gases can be recovered in a waste heat boiler or some other form of heat exchanger.

Either the first or second embodiment of the invention, suitably modified, may also be used for reduction of oxidic ores, for instance in reduction of iron ore concentrates, wherein the iron ore concentrate is fed into a gas vortex established by injecting hydrogen and/or carbon monoxide containing gases, and, if necessary, admixed with solid reduction agents such as coke breeze. The reducing gas mixture may then be provided by injection of solid or liquid reducing agents with an oxidizing gas, preferably air. The air may be enriched with oxygen and, if desired, preheated. In the reduction operation, the iron ore concentrate, which may be admixed with powdered coal, is fed into a gas vortex provided by the injection of the preheated hydrogen and/or carbon monoxide containing gases.

It will be appreciated that various modifications can be made to the herein-disclosed examples of the invention without departing from the spirit and scope thereof.

What is claimed is:

1. A reactor for the production of metals from finelydivided ores, comprising a generally rectangular furnace chamber, means for heating the bath within the furnace chamber comprising elongated heating elements depending into the furnace chamber and being spaced from each other and being arranged in at least one row extending lengthwise of said chamber, at least one tube for charging into said chamber finely-divided ore to be treated, means for discharging from the chamber reduced metal, means for injecting reactants into said chamber comprising at least one set of at least two nozzles each directed generally tangentially to an imaginary horizontal circle within said chamber and adapted to inject a gas at high velocity for developing at least one upright freestanding gas vortex not supported by the walls of the furnace chamber, the set of nozzles for forming the upright gas vortex and the tube for charging the ore being arranged between the heating element locations and said tube being arranged to charge the ore into the vortex established by said set of nozzles.

2. A reactor as set forth in claim 1 wherein each set of nozzles includes four nozzles directed in mutually intersecting paths.

3. A reactor as set forth in claim 1 wherein a plurality of said charge tubes are provided each arranged to charge in front of one of said nozzles.

4. A reactor as set forth in claim 1 wherein a set of said nozzles is provided between each said heating ele- 8 ment to develop a free-standing vortex therebetween and one of said charge tubes is provided to charge ore into each of the vortices.

5. A reactor as set forth in claim 1 wherein the heating elements comprise electrodes which extend beneath the anticipated slag surface.

6. A reactor as set forth in claim 1 wherein the heating elements comprise fuel-fired burners extending toward the bath within the furnace chamber and said burners developing flames directed towards the anticipated slag surface.

7. A reactor as set forth in claim 6 wherein each burner extends through the furnace roof and depends generally vertically with its discharge orifice directed and in proximity with the surface of the slag.

8. A method for the production of metals from finelydivided oxidic or sulphidic ores in a generally rectangular furnace chamber which is heated by a plurality of spaced heating elements aligned in the longitudinal direction of the chamber, said heat being sutficient to effect the reactions and the deposit of the reaction products as a melt on the bottom of the furnace, the method comprising developing between each pair of heating elements one freestanding vortex, unsupported by the walls of the furnace, by injecting reactants at high velocity generally tangntially to an imaginary horizontal circle, and charging finelydivided ore into the vortices and at the same time heating the slag bath.

9. The method of claim 8 further including heating the slag bath by electrically heating the heating elements.

10. The method of claim 8 further comprising heating the slag bath by fuel firing the heating elements with fuel selected from the group consisting of solid, liquid or gaseous fuel together with a gas selected from the group consisting of air, oxygen-enriched air and oxygen.

11. The method of claim 8 wherein the step of charging includes charging with lead sulphide concentrate.

12. The method of claim 11 wherein the vortices are developed by injecting gas selected from the group c011- sisting of air, oxygen-enriched air and oxygen.

13. The method of claim 8 wherein the reaction temperature is maintained at such a level that metallic lead is recovered direct without passing through oxi-sulphidic intermediate products.

14. The method of claim 8 wherein said step of charging includes charging with oxidic ore and that the vortices are developed by injecting gases containing reducing agents selected from the group consisting of hydrogen and carbon monoxide containing gases or solid and fluid carbonaceous material.

References Cited UNITED STATES PATENTS 3,365,185 1/1968 Elvander et al. -23X ALLEN B. CURTIS, Primary Examiner U.S. Cl. X.R. 7523; 266-33

Images