US1680861A - Method of roasting and reducing ores - Google Patents

Description

METHOD OF ROASTING AND REDUCING ORES Filed larch 29, 1926 czgcrrq IL ll #1 ll 00 OCT (5,

GOOD

Patented Aug. 14, 1928.

PATENT OFFICE.

BROR CHBiISTIANSEN, OF SMEDJ'EBACKEN, SWEDEN.

METHOD OF BOASTING AND REDUCING ORES.

Application filed March 29, 1928, Serial No. 98,347, and in Sweden April 7, 1925.

This invention relates to an improved method of roasting and reducing ores in a channel furnace through which the ore charged on carriages or the like is successively moved. The method is especially adapted for producing spongy iron of fine iron ores but it can also be used for the reduction of other iron ores as well as the ores of other metals. I

The chief object of the invention is to provide an improved reduction method of said kind by which the ore can be roasted and reduced in a single operation in a simple manner and at low cost.

The invention consists, chiefly, in first introducing'the ore in.a preheating and roasting zone of the channel furnace where combustion of gaseous fuel takes place by means of an excess of air so that the ore is preheated and roasted, then transferring the ore to a prereduction zone wherein it is acted upon by a reducing atmosphere containing carbon monoxide, and finally transferring the ore into a reduction zone separated from the prereduction zone through which gases consisting chiefly of carbon monoxide are circulated, said gases being outside the reduction furnace regenerated by means of an incandescent layer of carbon, the excess of gas formed inthe circulation system being wholly or partly utilized for the prereduction of the ore in the prereduction zone and finally combusted in the roast-ing zone.

In the accompanying drawmgs I have shown diagrammatically in Fig. 1 a longitudinal vertical section of channel furnace adapted for the producing of spongy iron according to this invention. Fig. 2 is a horizontal longitudinal section of the furnace.

Referring to the drawings, A is the introduction end of the channel furnace and B isthe discharge end. Nearest to the introduction end A is a preheating zone C and then a roasting zone D and a prereduction zone E follow.. Through the introduction end carriages b made of refractory material and loaded with the ore to be treated are successively introduced into the furnace. The ore loaded on the carriages is preferably in the form of pressed cakes or blocks. When a carriage is to be introduced a shutter a at the introduction end is opened and the loaded carriage pushed into the furnace while the whole'row of carriages is moved one step forwards, whereupon the shutter a is immediately closed. Combus tible gas is supplied through a pipe at 'I, said gas being obtained from the recarboniz ing furnaces described herebelow, and at F an excess of preferably preheated air is supplled by means of which the gas supplied at T is combusted in the zone D whereupon the combustion gases pass the zone C and escape through the chimney I. In the zone C a preheating of the ore takes place by the hot combustion gases and the temperature of the ore rises the nearer the carriages come to the inner end of the zone D. By this preheating the ore cakes are in wellknown manner converted into rather hard briquettes. As air is present in the zones D, C in excess the ore is simultaneously roasted, the sulphur in the ore being oxidized into sulphurous acid which escapes together with the combustion gases. If the ore consists of magnetite (Fe O it is also oxidized into Fe O which is profitable for the following reduction process. The temperature in the zone D should be kept as high as possible without the ore being smelted or sintered. WVhen treating ores which are not easily fusible the temperature inthe zone D can be raised up to 1400 to 1450 C.

The inner end of the combustion zone D is in direct communication with the prereduction zone E. When the desulphurized and oxidized incandescent briquettes have been introduced into the zone E they are subjected to the reducing action of a current of gas contaning as an essential constituent carbon monoxde, said gas being supplied at T at the inner end of the zone E from either of the recarbonizing furnaces P and P for the time being heated byasupply of air as will be further explained below. The gas may be preheated, if necessary, before it enters the zone E and its temperature may be about 1100 C. As the briquettes already before their entrance into-the zone E have a temperature sufiiciently high for the reduction this process takes place immediately, the carbon monoxide of the gas supplied being partly oxidized into carbon dioxide by the oxygen of the ore so that the latter is partly reduced.

By this prereduction the briquettes are re duced substantiallyinto ferrous oxide (FeO) whereby the carbon monoxide is utilized in the most economical manner and the carbon monoxide into carbon dioxide.

as when leaving the zone E will have a hi gh percentage of carbon dioxide. The prereduction zone E is by means of a shutter a se arated from the final reduction zone 0, sa1d shutter being momentarily opened when the carriages are moved forwards in the furnace.

In the final reduction zone 0 the briquettes are subjected to the reducing action of a current of carbon monoxide which is introduced at G and taken out at H and the tem-v perature of which at the entrance may be for instance 900 to 1000 C. As the briquettes still have a temperture suitable for the performance of the reduction such process is continued in the zone 0, the remaining oxygen of the ore being combined withsthcs a1 reaction continues until at the prevailing temperature a corresponding equilibrium is obtained between the carbon dioxide formed and the remaining carbon monoxide. By the continuous supply of carbon monoxide at G the effect is obtained that the briquettes are subjected to a as richer in carbon monoxide the nearer t ey come to the gas supply G whereby a complete reduction is secured. Such reduction is also facilitated by the porosity of the briquettes and the intermediate spaces between them. It is not necessary to supply the circulating carbon monoxide at G inasmuch as a satisfactory re ducing effect can be obtained also when the gas is circulated in the opposite direction,

i. e. when the gas is supplied at H and taken out at G.

The performance of the process depends on the temperature which is obtained in the final reduction zone and the ratio of the carbon dioxide and carbon monoxide obtained in said zone. As the temperature of the briquettes when they enter the zone 0 generally is about 1400 to 1450" C. but the reducing gas supplied to said zone has a lower temperature the temperature of the briquette is lowered as they are fed forwards through the zone 0 while the temperature of the gases flowing in the opposite direction is raised. The excess of heat of the briquettes helps thus to maintain the required temperature in the final reduction zone. If said excess of heat should not be sufficient to prevent a too eat fall of temperature in the final re uction zone the drawback would arise that the carbon monoxide would be partly decomposed into free carbon and carbon dioxide. Such draw back which may happen for instance when treating easily fusible ores which cannot be preheated to a sufiicientl high temperature, can be removed by heat eing sup lied from an external source of heat to the al reduction zone.v For such purpose electric heating resistances K may be provided in the walls of said zone as indicated in Fig. 2 but also other heatin means may be used, as for instance com ustion ases circulating through channels provided in said walls.

Thereducing as having passed through. the zone 0 is tal en out at H and supplied to the recarbonizing furnaces P and P, which are filled with a charge of incandescent coke or other solid fuel. Said furnaces are operated alternately in such manner that one is reheated while the other delivers its heat to the circulating gas for the endothermic reaction CO +C=2CO. A shiftable distribution valve L controls the quantities of gas supplied to either of the furnaces P and P By a shiftable valve Q, air can be supplied to either of the recarbonizing furnaces and by means of another shiftable valve R the escaping gases can be supplied to the final reduction zone or to the prereduction zone at will.

\Vhen the valves Q, R are in the positions shown in Fig. 1, a portion of the circulating gas is introduced at the lower part of the furnace P together with air. The su ply of air to said furnace is regulated m such manner that the carbon monoxide of the gas supplied to the furnace is only partly combusted. Also the solid fuel is to some extent combusted partly by direct combustion with the air supplied and partly by the carbon dioxide of the gas taking up carbon so as to be converted into carbon monoxide. In this manner the fuel charge in the furnace P is reheated to a high temperature. The carbon monoxide consumed for the reheating operation is partly covered by carbon monoxide formed from the fuel, so that the gas when escaping from the furnace P still has a rather high percentage of carbon monoxide. The said gas is introduced in the channel furnace at T and effects the prercduetion of the ore in the zone E, and is then combusted in the roasting zone D'as above described. The other portion of the gas taken out at H is introduced in the re carbonizing furnace P and is passed through its incandescent layer of fuel which has previously been reheated as above described with reference to the furnace P When the reduction gas is passed through the incandescent carbon layer in the furnace P its content of carbon dioxide is reduced into carbon monoxide so that the gas escaping from said recarbonizing furnace consists, chiefly, of carbon monoxide which through the valve R and a fan M or the like is returned to the channel furnace at G.

The additional heat which is necessary for the reaction is taken from the heat accumulated in the incandescent fuel. When the temperature of the fuel has decreased in such degree that the formation of carbon monoxide begins to cease the valves Q and R are reversed so that the furnace P is disconnected from the circulation system and is set roasting operation, and all combustible gas forreheating While the furnace P is con nected to the circulation system and delivers heat to the circulating gas. For preventing the temperature of the circulating gas from sinking too much a plurality of recarbonizing furnaces may be used in which case one always is connected to the circulation system While the others are reheated. If desired, heat can be supplied to the recarbonizing furnace by electrical heating or in other man ner. Preferably, the electric energy is in formed in the process is fully utilized.

The process can be regulated in several manners. The percentage of carbon monox: ide of the circulating gas can be regulated by regulating the speed of circulation and the quantity of circulating gas by means of the valve L. The percentage of carbon monoxide of the gas which is supplied to the roasting zone can be regulated by regulating the quantity of air supplied to the recarbonizing furnaces and the thickness of fuel in such case supplied to the recarbonizing furthe latter. The reduction time is regulated naces only during the reheating periods. Such supply of electric energy is suitable es pecially when an expensive fuel such as charcoal is used and the electric energy is cheap.

Before the recarbonized gas is introduced at G it can be conveyed through a heating apparatus S for raising its temperature in any desired degree.

As above mentioned it is not necessary to conduct the reducing gases through the final reduction zone G from G to H, i. e., in

counter-current to the movement of the loaded carriages inasmuch as the reducing effect will be practically the same if the reducing gases are conducted through the zone 0 from H to G, the piping from the valve B being then connected to H and the piping from G being connected to the lower portions of the recarbonizing furnaces P and P In this latter case the heatin apparatus S is, preferably, connected in the piping leading from G to the furnaces P P in order to reheat the gases escaping from the final reduction zone before they enter the recarbonizing furnaces.

From the final reduction zone 0 the car riages are passed into cooling chambers N which are separated from the zone 0 and from each other by shutters d. In the first of said chambers the cooling preferably takes place indirectly by means of air which is passed through pipings or the like 6, Fig. 2, and then is supplied to the roasting zone D and utilized for the combustion of the gas supplied to said zone and, if desired, also to the recarbonizing furnaces. For the further cooling of the material pipings f, Fig. 2, supplied With cooling Water is used so that the spongy iron when taken out from the last cooling chamber is sufiieiently cooled for preventing that any reoxidation thereof takes place. The cooling should, preferably, take place in an atmosphere free from air or oxidizing gases and for this purpose some indifferent gas or gas mixture may be supplied to the cooling chambers.

The process above described gives a good economy inasmuch as the reduction is carried out immediately after the roasting while the briquettes still have the high temperature which they have attained during the by the feeding of the carriages.

For facilitating the reduction the porosity of the briquettes can be increased by mixing the ore with saw-dust, pulverulent charcoal or the like, said addition being gasified in the preheating and roasting zones leaving corresponding holes in the briquettes. Said additional fuel can also to some extent by itself assist in effecting the reduction of the inner portions of the briquettes.

- The circulating gases can, of course, also contain hydrogen in a greater or less quantity. A gas containing hydrogen can for instance be obtained by supplying steam to the rccarbonizing furnaces during the reheating periods together With the circulating gas. The percentage of hydrogen is regulated by regulating the supply of steam in relation to the circulating gas supplied to the temporarily reheated furnace.

What I claim is 1. Method of reducing-ores, which comprises transporting the ore successively in a substantially horizontal direction through preheating, roasting, prereduction and final reduction zones of a channel furnace, subjecting the ore in the final reduction zone to the reducing action of circulating reducing gases, recarbonizing said gases outside the channel furnace in alternately operative recarbonizing furnaces, drawing off the exoess of circulating gases and partially combusting it in the momentarily inoperative recarbonizing furnace by a regulated supply of air for reheating said reca-rbonizing furnace, supplying the gases formed by said partial combustion to the prereduction zone of the channel furnace and finally combust ing them by an excess of air in the roasting zone.

2. Method of reducing ores, which comprises transporting the ore successively in a substantially horizontal direction through preheating, roasting, prereduction, final reduction and cooling zones of a channel furnace, subjecting the ore in the final reduction zone to the reducing action of circulating reducing gases, cooling the reduced ore indirectly by means of air,'reca-rbon1z1ng the circulating gases outside the channelfurnace in alternately operative recarbonizing furnaces, drawing off the excess of circulating zone of t ing gases and partially momentarily inoperative recarbomzmg furnaoe by a regulated suppllylof air for reheating said recarbonizing rnace, supply ng the gases formed by said partial com ust on to the prereduction zone of the channel flirnace, and finally combusting them in the roasting zone of the channel furnace b means of the hot air escaping from the coo ing zone.

3. Method of reducing ores, which comprises transporting the ore successively in a substantially horizontal direction through preheating, roasting, prereduction and final reduction zones of a channel furnace, subjecting the ore in the final reduction zone to the reducin action of circulatin reducing gases supp ied to said zone at t e inlet end for the ore, recarbonizing said gases outside the channel furnace in alternately operative recarbonizing furnaces, drawing off the excess of circulating gases and partially combustin' it in the momentarily inoperative recar nizing furnace by a regulated supply of air for reheating said recarbonizing furnace, supplying the gases formed by said partial combustion to the prereduction zone of the channel furnace, and finally combusting them b an excess of air in the roasthe channel furnace so as to combusting it in the stantially horizontal direction throu h rea heating, roasting, prereduction, and ma reduction zones 0 a channel furnace, subjecting the ore in the final reduction zone to the re ucing action of circulating reducing gases, recarbonizing said gases outside the channel furnace in alternately o erative recarbonizing furnaces, drawing 0 the excess of circulating gases and partially combusting it in the momentarily inoperative recarbonizing furnace by a regulated supply of air for reheating said recarbonizing furnace sup lying the gases formed by said partial com ustion to the 'prereduction zone of the channel furnace and finally oombusting them together with the fuel mixed with ore by an excess of air in theroasting zone of the channel furnace so as to roast the ore and heat it to a temperature above that necessary for the reduction.

In testimony whereof I have signed my name. 4

BROR CHRISTIAN SEN.

Images