US1447071A - Process of agglomerating mixtures of fine ore and fuel in shaft furnaces - Google Patents

Description

Feb. 27, 1923. 1,447,071.

C. GIESECKE. PR cEss 0F AGGLOMERATING MIXTURES or FINE one AND FUEL m sum FURNACES.

I FILED SEN-25, I922.

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CARL GIESEGKE, or BAD HARZBURG, GERMANY.

PROCESS OF AGGLOMERATING MIXTURES OF FINE ORE AND FUEL IN FURNACES.

SHAFT Application filed September 26, 1922. Serial No. 590,679.

To all whom it may concern:

Be it known that I, CARL GIESEOKE, engineer, a citizen of Germany, residing at Bad Harzburg, Germany, have invented a certain new and useful Improvements in Processes of Agglomerating Mixtures of Fine Ore and Fuel in Shaft Furnaces (for which I have filed "application in Germany, February 18, 1920), of which the following is a specification.

My invention relates to a process of agglomerating mixtures of fine ore and fuel in shaft furnaces.

The process of agglomerating blocks of line iron ore by means of small coke within shaft furnaces in some cases yields a prod uct which, in addition to a high degree of rigidity, shows a very high degree of porosity, as compared to the product ordinarily resulting from the sintering process. The sintering is always accompanied by a certain glazing by reason of a partial melting of the mass. In view of these facts I have made researches to ascertain under what conditions products having said desirable properties may be obtained, my object being to carry out the process in such a way as to obtain the desirable properties at will. In blast furnaces those agglomerates have the highest value which, where the solidarity of the products is the same, are the least glazed.

I have found that very porous agglomerates are obtained where the furnace is operated according to certain principles, the essential feature being that the piece or block which is not glazed in the sintering zone is thereafter brought intocontact with very hot air, from transform the protoxid or oxid-protoxid into oxid. By thus taking up oxygen the block is transformed in a manner similar to crystallization, which transformation-is effected uniformly throughout the block and results in a cementing of the individual particles to the skeleton and a corresponding increase of the volume of the particles. However, the amount of oxygen taken up by the mass is small, so that the size of the pores is not materially reduced, while the increase in rigidity caused by the oxygen is material.

The object of this invention is to operate the furnace in such a way that the process is which it takes up oxygen toregularly carried out and agglomerates are obtained which have the valuable properties hereinbefore referred to. With this object in view, my invention consists in charging the shaft furnace with blocks having a small quantity of fine carbon uniformly distributed therein, rapidly heating a comparatively low layer thereof above the combustion zone while slightly sintering the same, in order to cause reduction of the iron o-xid to the oxydul, and heating by means of gaseous fuel, such as flue gas, generator gas, mixed gas, or the like, plied to the combustion zone and assisted in burning. by means of ascending air.

In a modification of the process the agglomerates are subjected to a higher reducing heat by having a larger amount of carbon admixed therein, regulating the supply of gas above the combustion zone and within In the accompanying diagrammatic vertical sectional view of a shaft furnace suitable for carrying out my process, 1 represents the furnace, of which the shaft preferably flares slightly downwardly and outwardly. The furnace is charged (preferably continuously as by a conveyor 2) with blocks 3 which are formed of a mixture of fine ore and a small amount of fine coke. Near the surface of the column of blocks in the furnace, ordinarily from three to six feet below said surface, gas under pressure is supplied to the furnace through nozzles 4. The amount of gas supplied through the nozzles 4 may be controlled as by a valve 5. The products of combustion are drawn off at the top of the furnace by any suitable means, as by a suction fan 6, so that air, which may be supplied by nozzles 7 or other suit said gas being supcontinues as by means of a conveyor 8.

The advantages of my new process, as compared to the old method wherein the ore is heated by means of solid fuel, are best illustrated by the following example: Where the ore is heated by means of solid fuel carbon is burnt, but where it is heated by means of gas mainly carbon oxid is burnt,

the product of the combustion being in both cases carbon dioxid. When burning carbon to produce carbon dioxid one kilogram of oxygen is developed.

808O- =3O3O calories.

But when burning carbon oxid to produce carbon dioxid one kilogram of oxygen is developed.

(8080 2473) 4210 calories.

Therefore, in order to develop the same amount of heat by burning carbon dioxid, only 72 per cent of the volume of air is necessary, as compared to the volume of air required for burning carbon. The reduc-- tion in the volume of air required makes it possible to preheat the air to a higher temperature when ascending within the furnace and coming into contact with the sintered blocks; and, when thus heated to higher temperature, the air causes a more intense re-oxidation below the combustion zone, so much the more because, by reason of its diminished volume, it consumes less heat in raising its own temperature. Therefore, very hot air will cause the reoxidation with such a rise of temperature that the .air reaches its maximum temperature below the combustion zone, thus causing the sintering to take place below the combustion zone. However,

such sintering is limited to the desirable degree, because it depends on the amount of oxygen passing into the ore under treatment, and the oxygen ceases'to permeate the ore as the density increases.

. As a matter of fact, with carbon oxid and carbon, the diiference of the temperatures of the preheated air is higher so far as the result is concerned, than may be assumed from the above example, as will appear from the following calculation. It may be assumed that in one case the amount of small coke used in the process amounts to 8 per cent of the final sintered product, that 1 kilogram of small coke consumes 10 cubic meters of air (having regard to the necessary excess of air), that the specific heat of the sintered product is on an average 0.18,

T 1250-O.l8

For burning carbon oxid only 72 per cent of the volumeof air is required, which air is therefore heated when entering into the combustion zone to T :126O C.

So far it has been assumed that the heat is transmitted without any loss, which is practically impossible. The heat radiated from that part of the furnace which is below the combustion zone reduces the efi'ect of the preheating of the air, so that actually the above temperatures are not attained, the

temperature being in case of solid fuel about 750 (1., if the furnace is rapidly operated.

, Similarly the temperature of the air in case of gaseous fuel is less than 1260 C., and it is about from 1000 to 1050 0. Of course the temperature of 1260 C. can not be attained, because it can in no case be more than the sintering temperature, which is about 1250 C. However, there is a sufficiently intense reoxidation only where the temperature is as high as just stated, whereas at the lower temperature of the air, where the firing is done by coke, reoxidation does not take place at all, such reoxidation being observed only where the old process is practiced in connection with some products and where there has been accidental and irregular operation of the furnace.

High preheating of the air is particularly important, if it is desired, by reoxidation below the combustion zone, to raise the temperature of the sintered product for the purpose of partly solidifying the same. By 0x1- dation of 1 kilogram of iron in the compound of Fef) to produce Fe O 571 calories are set free. If it is assumed that in 1 kilogram of ore only 0.2 kilogram of Fe have before been reduced to FeO and thereafter are reoxidized to Fe O 114.2 calories are set free. This heat raises the temperature of the air and of the piece of ore the specific heat of which may be set at 0.20 at the said temperature, by

If, before the beginning of the reaction the temperature of the air was already as high as 1000 (3., this slight increase is sufficient to raise the ore to sintering temperature, which is not more than 1250 (1., while the temperature can be raised to 1302. Notwithstanding this there is no melting, because the oxidation and the generation of tinguished from the known heat cease as soon as the structure of the ore has been brought to a certain density. Therefore, the furnace can be operated in a very simple manner.

Furthermore, the method has the advantage that, even a gas of low heating capacity can be used, because it is not desired to raise the temperature in the combustionzone and above the latter sufliciently to sinter the blocks. The amount of heat set free by! reoridation is considerably increased wlfen reducing iron oxid to metal, even if such reduction is effected with only a very small part of the ore. What is most important is that reoxidation in the same manner as reduction takes place within the agglomerates, where also the heat is developed. Thereby high solidity is imparted to the individual agglomerates, and they have less tendency to being welded together into large size blocks, as is the case where the heat required for sintering is developed by burning solid or gaseous fuel between the agglomerates.

I am aware that it is known in the art to utilize for the purpose of sintering, the heat set free by reoxidation of the ore which had previously been reduced. My process is disprocesse first, in that I obtain a product of high porosity, instead of slag, and large blocks instead of small ones, second, in that I heat by means of completely burnt gas, and third, in that I reduce by a small amount of carbon finely divided in the ore.

I claim:

1. The herein described process of agglomerating fine ore, which consists in mixing the ore with finely divided carbon, heating the same in a shaft furnace bymeans of reducing gas admitted at a point near the surface of the material and below the same at a temperature insufiicient to materiallysinter the material and reoxidizing the ore after it has passed the combustion zone by means of hot air rising in opposition to the ore.

2. The herein described process of agglomerating fine ore, which consists in mixing the ore with finely divided carbon, heating the same in a shaft furnace by means of reducing gas admitted at a point near the surface of the material and below the same at a temperature substantially not higher than is necessary for reducing the ore to protoxid or metal and insufficient to materially sinter the material, and thereafter reoxidizing and sintering the ore after it has passed the combustion zone by means of hot air rising in opposition to the ore.

In testimony whereof I have affixed my signature in presence of two witnesses.

CARL GIESECKE. Witnesses:

WILHELM LEHRKE, WILLI FAHN.

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