SE190897C1

SE190897C1 -

Info

Publication number: SE190897C1
Authority: SE
Publication date: 1964-01-01

Description

Uppfinnare: R P Smith och D E Babcock Prioritet begard frdn den 30 jail 1956 (USA) Foreliggande uppfinning hanfOr sig till ett fOrbattrat satt att reducera maim. Narmare bestamt avses reduktion av exempelvis jam-maim vidyid forhajd temperatur, vid vilken det kannbara varmet i den reducerade produkten utnyttjas fOr forkolning av det kolhaltiga materialet, som innehaller flyktiga bestandsdelar. Inventors: R P Smith and D E Babcock Priority requested from 30 Jail 1956 (USA) The present invention aims to reduce the cost of maim. More specifically, it refers to the reduction of, for example, a very high temperature, at which the appreciable heat in the reduced product is used for charring the carbonaceous material, which contains volatile constituents.

Vid reduktion av maim till motsvarande metall, exempelvis vid reduktion av jarnmalm till metalliskt jam är det vanligt alt aavanda kolhaltiga reduktionsmedel av olika slag. Mr det kolhaltiga reduktionsmedlet som anvandes direkt i reduktionsprocessen, innekaller vdsentliga mangder flyktiga bestandsdelar, sasom fallet dr betrdffande stenkol, sagspan, tory, lignit och dylikt, har det visat sig vara svart att undvika, att icke eller endast partiellt forbranda flyktiga bestandsdelar avgâr frail reaktionszonen. En sadan avgang av icke forbranda eller endast delvis forbranda flyktiga bestandsdelar in.nebar en forlust i varmevarde och medlar ocksa. luftfaroreningar. Man bar .ocksa beakta, att flyktiga bestandsdelar kunna kondenseras i anldggningarna och ddr bilda tjarliknande aterstoder eller dylikt som kunna ha (benagenhet att bilda ytoverdrag pa apparatdelar eller tilltappa ledningar. When reducing maim to the corresponding metal, for example when reducing iron ore to metallic jam, it is common to use carbonaceous reducing agents of various kinds. Although the carbonaceous reducing agent used directly in the reduction process contains significant amounts of volatile constituents, as in the case of hard coal, sawdust, tory, lignite and the like, it has been found to be unavoidable that only or only partially combustible volatile constituents are removed. . Such disposal of non-combustible or only partially combustible volatile constituents entails a loss of heat value and also mediates. aviation pollution. It should also be borne in mind that volatile constituents can condense in the plants and thus form tar-like residues or the like which may have (tendency to form surface coatings on appliance parts or tap pipes.

Man ham av detta skill ansett det lampligast att i de fiesta fall anvanda kolhaltiga reduktionsmedel med lag halt flyktiga bestandsdelar, exempelvis koks, trakol och dylikt, for reduktionen. Sadana material aro emellertid icke tillgangliga i naturen, och det ãr darfar nodvandigt att framstalla dem av naturliga radmnen med hog halt flyktiga bestandsde- Dupl. kl. 18 a: 18/0 lar, exempelvis stenkol eller dylikt. Delta medfor n5dvdndigheten av torrdestillation i och far avlagsnande av flyktiga bestandsdelar, och den vdrmemangd som erfordras for denna behandling tillhandahdlles vanligen genom partiell forbranning av deft behandlade materialet Delta innebar naturligtvis ocksâ en vdsentlig forlust av materialets ursprungliga varmevarde. From this distinction, it was considered most appropriate to use, in most cases, carbonaceous reducing agents with legally volatile constituents, such as coke, trachol and the like, for the reduction. Such materials are, however, not available in nature, and it is necessary to produce them from natural raw materials with high volatile stock- Dupl. at 18 a: 18/0 lar, for example coal or the like. Delta entails the need for dry distillation and the removal of volatile constituents, and the heat required for this treatment is usually provided by partial combustion of the deftly treated material. Delta of course also entailed a significant loss of the original heat value of the material.

En ytterligare forlust av varmevardet asamkas av det vanligen tillampadc sittet att reducera maim vid forhojd temperatur och ddrefter snabbt avkyla produkten, exempelvis genom stOrtkylning i vatten, i andainal att forebygga ateroxidation av den heta metallen. A further loss of heat value is associated with the commonly used seat of reducing heat at elevated temperature and then rapidly cooling the product, for example by supercooling in water, in general to prevent atheroxidation of the hot metal.

Ovanndmnda svarigheter undvikas vid sattet enligt foreliggande uppfinning, vid vilket maim reduceras vid forhajd temperatur, sta att reduktionsprodukterna komma att innehalla en vdsentlig mangd kannbart varrne, och sattet kannetecknas av att namnda reduktionsprodukter bringas i varmevaxling med kolhaltigt rdmaterial, som innehaller avsevarda mangder flyktiga bestandsdelar, sa att det kolhaltiga materialet undergar torrdestination under bildning av en kterstod av fast kol samt en brannbar flyktig fraktion. The above-mentioned similarities are avoided in the set according to the present invention, in which the temperature is reduced at elevated temperature, provided that the reduction products will contain a significant amount of known products, and the set may be characterized in that said reduction products are brought into heat exchange with carbonaceous raw material containing significant amounts. said that the carbonaceous material undergoes dry destination to form a solid carbon residue and a combustible volatile fraction.

Vid en sarskilt lämplig utforingsform av foreliggande uppf inning anvandes derma fasta koldterstod och den brannbara flyktiga fraktionen for reduktion av ytterligare kvantiteter maim. In a particularly suitable embodiment of the present invention, this solid cold residue and the combustible volatile fraction were used to reduce further quantities of milk.

I foreliggande sammanhang avses med ut- trycket kolhaltigt ramaterialkolhaltigt material med hog halt brannbara, flyktiga bestandsdelar, exempelvis stenkol, och med 2— — uttrycket forkolat kol» avses den reaktiva aterstoden, som erhalles vid torrdestillation av det kolhaltiga ramaterialet, och vilken aterstod är relativt fattig pa flyktiga bestandsdelar. In the present context, the term carbonaceous raw material carbonaceous material having a high content of combustible volatile constituents, for example hard coal, and the term "carbonated carbon" means the reactive residue obtained by dry distillation of the carbonaceous raw material, and which residue is relatively poor in volatile constituents.

Enligt foreliggande uppfinning kan praktiskt taget alla malmer behandlas, savida deras metalliska bestandsdelar dro reducerbara med tillhjalp av kolhaltiga reduktionsmedel vid forhojd temperatur. Uppfilmingen avser emellertid i synnerhet jarnmalm och narmare bestamt jarnfattig maim av rtaconit»-typen. Pd liknande salt kan det kolhaltiga rdmaterialet vara vilket som heist kolhaltigt reduktionsmedel, som innehaller avsevarda mangder brannbara flyktiga material, som kunna avdrivas med hjalp av varme, sh att man erhaller en kolaterstod, men enligt uppfinningen foredrages ett lace koksande kol. Eombinationen av kolhaltiga ramaterial och maim bOr givetvis foljas sa, att det kolhaltiga ramaterialet kan forkolas vid den temperatur, som det fran reduktionsprocessen. utgaende materialet har. According to the present invention, practically all ores can be treated, provided that their metallic constituents are reducible by means of carbonaceous reducing agents at elevated temperature. The filming, however, relates in particular to iron ore and more specifically to iron-poor iron of the rtaconite type. On a similar salt, the carbonaceous red material may be any hot carbonaceous reducing agent, which contains considerable amounts of combustible volatile materials, which can be evaporated by means of heat, to obtain a carbonate residue, but according to the invention, a lace of coking carbon is preferred. The combination of carbonaceous feedstock and milk should of course be followed so that the carbonaceous feedstock can be charred at the temperature required from the reduction process. outgoing material has.

Reduktionen av jarnmalm enligt foreliggande uppfinning kan utgora en partiell reduktion, exenapelvis Iran hematit till magnetit eller andra lagre jarnoxider eller ocksd kan det utgOra en fullstandig reduktion till metalliskt jam. Det kan till och med vara en fullstandig reduktion till metalliskt jam innefattande smaltning och stelning av det bildade jarnet, men detta medfor nodvandigheten att anvanda komplicerade oak dyrbara anlaggningar for varmevaxlingen Iran reduktionsprodukterna till det kolhaltiga mamaterialet i och for forflyktigande av de flyktiga bestandsdelarna i sistnamnda material och man foredrager darfor vanligen att tilllampa processen endast i samband med par- hellav jarnmalm eller vid reduk- tion till metalliskt jam under sad.ana beiingelser, att smaltning och stelning icke in-trader. Det ovan namnda varmevaxlingsforhallandet kan utgaras av direkt koutakt och detta foredrages vanligen, fOrutsatt att lampliga atgarder latt kunna foretagas for att efterat skilja de forkolade resterna av det kolhaltiga ramaterialet frail reduktionsprodukterna pa satt som har nedan beskrives. The reduction of iron ore according to the present invention may constitute a partial reduction, for example Iran hematite to magnetite or other lower iron oxides or it may also constitute a complete reduction to metallic jam. There may even be a complete reduction to metallic yarn including melting and solidification of the formed iron, but this entails the necessity of using complicated and inexpensive plants for heat exchange Iran the reduction products to the carbonaceous feedstock in and for volatilization of the volatile constituents in the latter material and it is therefore usually preferred to apply the process only in connection with par-wholemeal iron ore or in the case of reduction to metallic jam under such conditions that melting and solidification do not occur. The above-mentioned heat exchange ratio can be effected by direct co-actuation and this is usually preferred, provided that suitable steps can be taken to subsequently separate the charred residues of the carbonaceous raw material from the reduction products in the manner described below.

Vid direkt varmevaxling är det nodvandigt att vidtaga sadana atgarder, att sammansintring (solidifikation) av blandningen fran reduktionsugnen och det kolhaltiga ramaterialet eller det forkolade materialet intrader, enar det foreligger en benagenhet fOr tjaror och liknande produkter, vilka ocksa frigoras frail det kolhaltiga materialet under forkolningen, att blanda sig med materialpartiklar Iran. reduktionsugnen oak det forkolade materialet, varigenom dessa material sammansmalta till en sammanhangande massa, vil_ket icke dr lampligt. Detta kan undvikas om man anvander ett icke forkoksande ramate rial och om man genomfor forfarandet i ett karl utrustat med raka, eller annat omroringsorgan eller ocksi genom att genomfora f5rfarandet i fluidiserad bald under anyandning av en. inert gas, naturgas eller dylikt eller oeksa luft som fluidismingsmedel. In the case of direct heat exchange, it is necessary to take such steps that sintering (solidification) of the mixture from the reduction furnace and the carbonaceous raw material or the charred material enters, otherwise there is a tendency for tar and similar products, which are also released from the carbonaceous material during carbonization. , to interfere with material particles Iran. the reduction furnace and the charred material, whereby these materials are fused together into a coherent mass, which is not suitable. This can be avoided by using a non-coking raw material and by carrying out the process in a vessel equipped with a straight or other stirring means or also by carrying out the process in a fluidized bale while inhaling one. inert gas, natural gas or the like or exhale air as a fluidizing agent.

Varmevaxlingen kan emellertid ocksa utforas indirekt, exempelvis genom att infOra den heta reducerade jarnmalmsprodukten i det yttre rummet i en dubbelvaggig behallare och det kolhaltiga ramaterialet, som skall forkolas i det inre rummet eller vice versa. However, the heat exchange can also be performed indirectly, for example by introducing the hot reduced iron ore product into the outer space of a double-walled container and the carbonaceous raw material to be charred into the inner space or vice versa.

Vid en sarskilt lamplig utforingsform avses reduktion av relativt stora stycken jarnmalm med relativt finfOrdelat kol vid forhojd temperatur i och for framstallning ax en het reduktionsprodukt besttiende av en blandning av relativt stora stycken reducerad jarnmalm och relativt finfordelat overskottskol, blandning av namnda heta reduktiansprodukt och kolhaltigt ramaterial innehallande avsevarda mangder flyktiga brannbara material, avdrivning av de flyktiga materialen fran namnda kolhaltiga ramaterial och uppsamling av namnda flyktiga material och utnyttjande av dem som bransle, medan de fortfarande aro varma, om sa onskas for att uppratthalla den hoga temperaturen vid reduktion av ytterligare mangder jammalm, separation av de relativt stora styckena reducerad jarnmalm fran namnda overskottskol och fran den tillsatta, forkolade produkten och anvandning av Overskottskolet och det forkolade materialet for reduktion av ytterligare mangder jarnmalm, Med uttrycket »relativt stora stycken» avses en avsevart storre kornstorlek an. med »relativt finfordelat» kol eller andra material, varvid skillnaden i kornstorlek ãr sddan, att en. separation grundad pa skillnaden i kornstorlek, exempelvis siktning, underlattas. Vid praktisk tillampning har det visat sig lampligt att anvanda jarnmalmen i form av stycken med 13-25 mm diameter och kol och kolhaltiga ramaterial med ungefar 2-3 mm diameter. Saval jarnmalmen som det overskottskol, som medfoljer den reducerade jarnmalmsprodukten efter reduktionen, har befunnits vasentligen bihehalla sin ursprungliga partikelstorlek genom reduktionsprocessen, forutsatt att lampliga forsiktighetsatgarder vidtagits for att farebygga agglomerering. In a particularly suitable embodiment, this means reduction of relatively large pieces of iron ore with relatively finely divided carbon at elevated temperature in order to produce a hot reduction product consisting of a mixture of relatively large pieces of reduced iron ore and relatively finely divided excess coal, mixing of said hot carbon reduction material containing significant amounts of volatile combustible materials, stripping the volatile materials from said carbonaceous feedstock and collecting said volatile materials and utilizing them as fuel while still hot, if desired to maintain the high temperature by reducing additional amounts of jammalm , separation of the relatively large pieces of reduced iron ore from the said surplus coal and from the added, charred product and use of the surplus coal and the charred material for reduction of further quantities of iron ore, With the expression «relatively large pieces» es a considerably larger grain size. with «relatively finely divided» coal or other materials, the difference in grain size being sddan, that a. separation based on the difference in grain size, for example sieving, is omitted. In practical application, it has proved appropriate to use the iron ore in the form of pieces with a diameter of 13-25 mm and carbon and carbonaceous raw materials with a diameter of approximately 2-3 mm. Saval iron ore, as the excess coal which accompanies the reduced iron ore product after the reduction, has been found to substantially retain its original particle size through the reduction process, provided that appropriate precautionary measures are taken to prevent agglomeration.

Vid en. altemativ utforingsform av ovan beskrivna process kan de reducerade jarnmalmsstyckena separeras frail overskottskelet i produkten och endast kolet inblandas i det kolhaltiga ramaterialet, som skall fOrkolas. Separationen skall givetvis genomforas inedan reduktionsprodukterna fortfarande aro heta. Det heta Overskottskolet levererar det nodvandiga varmet for att avdriva de flyktiga materialen fran det tillsatta kolhaltiga ramaterialet. De flyktiga bestandsdelarna uppsamlas och anvandas som bra.nsle for bibehallande av den hoga temperaturen i oak for reduktion av — —3 ytterligare maim. Den kolmangd, som omfattar det ursprungliga overskottskolet on det nybildade kolet kan darefter aterforas till reduktionsprocessen. By a. In an alternative embodiment of the process described above, the reduced pieces of iron ore can be separated from the excess skeleton in the product and only the carbon can be mixed into the carbonaceous raw material to be charred. The separation must of course be carried out before the reduction products are still hot. The hot Surplus School delivers the necessary heat to drive the volatile materials away from the added carbonaceous raw material. The volatile constituents are collected and used as a good source for maintaining the high temperature in oak for the reduction of - —3 additional mimes. The amount of carbon comprising the original excess carbon on the newly formed carbon can then be returned to the reduction process.

For att aterga till Ira gan om varmevaxlingen kan namnas, att, sasom ovan papekats, det ãr la'mpligast med direkt kontakt. Bland de fordelar, som detta arbetssatt medfor, kan namnas den starre mojligheten att variera det stalle, vid vilket det kolhaltiga ramaterialet infores i det fran reduktionszonen kommande materialet. Det kan exempelvis inblandas det ur en roationsugn utmatade materialet, I vilken rotationsugn reduktionen genomfores, .och tillatas sta i kontakt clamed under en lamplig tid, innan separationen genomfores. Kontakten genomfores i vilken som heist lamplig anordning, exempelvis ett schakt, en transportor, en trumma eller dylikt. In order to return to Iran about the heat exchange, it can be mentioned that, as stated above, direct contact is most appropriate. Among the advantages which this working method entails is the rigid possibility of varying the stable at which the carbonaceous raw material is introduced into the material coming from the reduction zone. For example, the material discharged from a rotary kiln can be mixed in, in which rotary kiln the reduction is carried out, and allowed to remain in contact with the clamed for a suitable time before the separation is carried out. The contact is made in any suitable device, for example a shaft, a conveyor, a drum or the like.

ExeTnp el. 1. En jarnmalm med faljande analys: Total halt Fe 34,9 % Si02 26,8 % A13 5,1 % CaO 9,2 % MgO 0,2 % resten oxidsyre och tillfalliga fororeningar, inmatades i en rotatioasugn tillsammans med kol. Kolet hade en genomsnittlig partikelstorlek av cirka 2-3 rum on malmen hade krossats och klasserats till stycken av 13-38 mm diameter. Inmatningshastigheterna fOr maim och kol installdes sa till varandra, att ungefar 0,65 kg kol infordes i ugnen per kg dari inford maim. Ugnen upphettades medelst en oljebrannare anordnad i ugnens undre ande, d. v. S. i uttomningsanden, och denna install-des sa, att temperaturen h011s mellan 1027 och 1049°C i ugnens undre tredjedel, van i reduktionen forsiggick. Luft- och oljeintagen installdes sa, att en reducerande atmosfar uppratth011s Over badden. Ugnens rotationshastighet installdes sh, att den genomsnittliga uppehallstiden for malmen uppgick till 2,5 timmar i den heta delen av ugnen. En blandning av reducerad maim och restkol utmatades ur ugnen med en temperatur om 1038°C. En analys av detta material visade, att ungefar 0,12 delar kol hade forbrukats per del maim under den tid chargen uppehollit sig i ugnen. ExeTnp el. 1. An iron ore with the following analysis: Total content Fe 34.9% SiO 2 26.8% A13 5.1% CaO 9.2% MgO 0.2% residual oxide oxygen and incidental impurities, fed into a rotary kiln together with coal. The coal had an average particle size of about 2-3 chambers on which the ore had been crushed and classified into pieces of 13-38 mm diameter. The feed rates for maim and coal were set so that approximately 0.65 kg of coal was introduced into the furnace per kg from maim. The furnace was heated by means of an oil burner arranged in the lower spirit of the furnace, i.e. in the exhaust spirit, and this was installed so that the temperature was kept between 1027 and 1049 ° C in the lower third of the furnace, accustomed to the reduction. The air and oil intakes were installed so that a reducing atmosphere was maintained over the bath. The rotational speed of the furnace was set so that the average residence time of the ore was 2.5 hours in the hot part of the furnace. A mixture of reduced milk and residual carbon was discharged from the oven at a temperature of 1038 ° C. An analysis of this material showed that approximately 0.12 parts of coal had been consumed per part of maim during the time the charge remained in the furnace.

Detta heta (cirka 1038°C) utmatade material inmatades direkt i en annan rullugn tillsammans med stenkol, som vid ett tidigare Virg& visat sig lamna 0,8 delar forkolningsprodukt per del stenkol. Hastigheten varmed det ur brannugnen kommande materialet inmatades injusterades till den hastighet, varmed stenkolet inmatades i den andra ugnen sa, att 0,42 delar stenkol infordes per del jam i det Iran brannugnen kommande materialet. Denna mangd stenkol motsvarade 0,33 delar fOr- kolat material per del jam eller 0,12 delar fOr- kolat material per del ursprungligen inmatad maim, dvs. den mangd som forbrukats i det f5regende reduktionssteget. I ugnen var anordnat ett gasuttag, och den bildade gasen leddes direkt tillbaka till utloppsanden av den f5rsta ugnen, dar den forbrandes i den dar befintliga gasbrannaren. P0 grund av den ytterligare varmemangd, som pa detta satt tillfOrdes ugnen, visade det sig vara nadvandigt att forminska oljematningen till oljebrannaren med cirka 3/4 av dess ursprungliga varde i on for uppratthallande av temperaturbetingelserna. This hot (about 1038 ° C) discharged material was fed directly into another kiln together with coal, which in a previous Virg & was found to leave 0.8 parts of carbonization product per part of coal. The rate at which the material coming out of the furnace was fed was adjusted to the rate at which the coal was fed into the other furnace, so that 0.42 parts of coal were introduced per part of jam into the material coming from the furnace. This amount of coal corresponded to 0.33 parts of charred material per part of jam or 0.12 parts of charred material per part of originally fed maim, ie. the amount consumed in the subsequent reduction step. A gas outlet was arranged in the furnace, and the gas formed was led directly back to the exhaust sand of the first furnace, where it was combusted in the gas burner there. Due to the additional amount of heat added to the furnace, it was found necessary to reduce the oil supply to the oil burner by about 3/4 of its original value in order to maintain the temperature conditions.

Den Iran den andra ugnen utmatade produkten var efter en genomsnittlig uppehallstid dari uppgaende till 30 minuter en blandning av reducerad jarnmalm och forkolat material, varav en del utgjordes av det i ugnen inforda Overskottskolet och resten var nybildat kol, som erhallits genom inverkan av det lean ugnen utmatade heta materialet pa stenkolet. Det ur den andra ugnen utmatade materialets temperatur lag vid cirka 871°C. Det avkyldes och siktades i och for avlagsnande av de stora styckena reducerad jarnmahn, vilka underkastades ytterligare behandling till metallisld jam. Det nybildade kolet och overskottskolet avskildes darefter pA magnetisk vag fran sma partiklar reducerat jam, som bildats genom nOtning i ugnen. Denna finfordelade jarnmalm sammansintrades (consolidated) med den aterstaende jammalmen och bearbetades med denna till metalliskt jarn. Den forkolade produkten aterfordes darefter till brannugnen tillsammans med ytterligare jarnmalm och forfarandet upprepades. The product produced by Iran in the second furnace was, after an average residence time of up to 30 minutes, a mixture of reduced iron ore and charred material, part of which consisted of the surplus coal introduced into the furnace and the rest was freshly formed coal obtained by the influence of the lean furnace. discharged the hot material onto the coal. The temperature of the material discharged from the second furnace was about 871 ° C. It was cooled and sieved in order to remove the large pieces of reduced iron manhole, which were subjected to further treatment into metallic iron. The newly formed coal and the excess coal were then separated on a magnetic wave from small particles of reduced jam formed by wetting in the furnace. This finely divided iron ore was consolidated with the remaining iron ore and processed with it into metallic iron. The charred product was then returned to the kiln together with additional iron ore and the process was repeated.

Enligt en sarskilt foredragen utforingsform av foreliggande uppfinning aterfores, sasom ovan papekats, de brannbara flyktiga produkterna, som Midas vid fnrkolningen till forbranningssystemet i reduktionsugnen. Det bor emellertid papekas, att dessa flyktiga bestandsdelar kunna utg8ra en mellanprodukt for framstallning av vardefulla kemikalier och darfor om sO onskas kan uppsamlas och vidarebearbetas pa kant satt i och for utvinning av dessa kemikalier. According to a particularly preferred embodiment of the present invention, as mentioned above, the flammable volatile products which are present in the charcoal are returned to the combustion system in the reduction furnace. It should be noted, however, that these volatile constituents may constitute an intermediate product for the production of valuable chemicals and therefore, if desired, can be collected and further processed by edge in the process of extraction of these chemicals.

Foremalet for foreliggande uppfinning begransas icke av de har ovan givna speciella utforingsformerna utan endast av foljande pantentansprak. The subject matter of the present invention is not limited by the particular embodiments set forth above but only by the following claims.

Claims

Patent claim:

1. sat in the reduction of iron ore at elevated temperature using the intrinsic heat of the reduction product for evaporation of volatile constituents, which are not in a carbonaceous material, may be characterized by the fact that the reduction product contains an excess charred material and that the reduction product or doss material in directly contalded with the crude carbonaceous material, with further charred material and a. combustible fractions are formed, which are used in the industry to maintain an elevated temperature for the reduction of additional amounts of iron ore, whereby the additional amount of / eh / or the excess charred material is recovered and re-used to reduce additional amounts of maim and is in relatively finely divided form, while the iron mahri consists of relatively large pieces, so that despite direct contact between the furnace batches a transfer to cohesive masses (agglomerates) of & Maria furnace baffles is prevented.

2. A claim according to claim 1, characterized in that the hot reduction product is mixed with the carbonaceous material before the use of the excess charred material and the formed charred material for the reduction of further quantities of maim, the relatively large pieces of reduced iron ore being separated from the excess charred material and the charred material formed.

3. Set according to patent claim 2, characterized in that the separation is carried out by sieving the hot reduction product. Request publications: Patents from Sweden 47,047; Great Britain 269 179, 744742; Germany 294707, 488615, 513110.