US1400963A - Operation of blast-furnaces - Google Patents

Description

UNITED STATES PATENT OFFICE.-

VASILI LIZOUNOFF, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO MARTIN A. ROSANOFF, OF PITTSBURGH, PENNSYLVANIA.

OPERATION OF BLAST-FURNACES.

No Drawing.

To all whom it may concern Be it known that I, VAsILI LIzoUNorF, residing at Pittsburgh, in the county of Allegheny and State of Pennsylvania, a subject of the Russian Empire, have invented or discovered certain new and useful Improvements in the Operation of Blast-Furnaces, of which improvements the following is a specification.

I necessarily conditioned on nor consequent upon a prior normal use .of the furnace through several years, but such is the usual and economically desirable practice.

Iron with a silicon content of 1 to 3.25% has wide use in the industries, 'and it isa matter of value and importance to produce it as cheaply as possible. The attempt so to regulate the blast-furnace operation as to attain a product of precisely regulated composition is attended with considerable difficulty, so that the blast furnace cannot be looked to as the unaided and immediate source of iron silicon alloy for industrial use. There is need of a supplementary operation, in which the uncertain proportions of the component metals may be brought certainly to the desired values. This supplementary operation is ordinarily performed in the cupola furnace of the foundry. Under present-day practice the foundryman who proposes to produce iron silicon alloy of the quality called for in the industries, buys pigiron having a smaller silicon content than is required, and on the other hand he buys a ferro-silicon, and he compounds the two in his cupola furnace, proportioning his charge to afford him the desired composition'of product. The foundrymans demand for a ferro-siliconofhigh silicon content is therefore apparent.

Specification of Letters Patent.

Patented Dec. 20-, 1921.

Application filed April 27, 1920. Serial No. 377,105.

In addition, ferro-silicon of high silicon content is required by steel mills, for producing steel castings for special purposes; and, finally, such high-silicon alloy is called for by operators of Bessemer converters. Silicon has a high heat of combustion, and the Bessemer operator finds it a valuable ingredient, on occasion, of his converter charge; for, in being consumed under the air blast, it becomes a most effective heating agent, and in consequence of its use the time of the run of a converter may be reduced.

At the present time the'ferro-silicon of high silicon content so required by foundry man, steel maker, operator of Bessemer converters, and others is produced in part in the blast furnace, in part in the electric furnace. Production in the electric furnace is relatively expensive, but in the electric-- furnace operation there is no limitation on,

tainable, whereas in the blast furnace under present-day conditions ferro-silicon produc tion is limited to a product in which the silicon ingredient is scarcely greater than 12%. The richer the ferro-silicon be in its silicon content the greater the price it can command.

By following my present invention, it becomes possible to produce in the blast furnace ferro-silicon in which the proportion of the silicon ingredient may be increased to as much as 25%.

In the operation now commonly pursued in making ferro-silicon in the blast furnace the charge is made up of the following ingredients having the characteristics noted 1-.

The ore used is highly reducibl (that is, to say iron is present in the form of Fe O rather than in the form of Fe O,) further more, the ore chosen is lean, high. lin aluminum content, and also contains a certain amount of silica.

The limestone used is of a' grade low in magnesium and rich in calcium," and this for the reason that the magnesium present tends to increase the fluidity of the slag and torprevent in corresponding degree the formati'on of an iron alloy rich in silicon. The limestone component of the charge-is rela tively small.

The coke used is low in sulfur. This particularity is consequent upon the fact that but little limestone is used, and therefore less sulfur can be carried off in the slag.

' In addition to these, the major components of the charge, the following items should benoted: Quartz is generally added, for the purpose of increasing the silicon content of the burden; broken brick may be added, to increase both the silicon and the aluminum -rrn-ents; for the same pur clay may be added; and, finally, and again for the same purpose, various slags, waste products of iron and steel manufacture, are sometimes thrown in as auxiliary materials.

The total silicon content of the furnace charge is about four or five times that which remains in the product.

In operation, the temperature of the air blast is kept high and the furnace is driven slowly. In consequence, the output per unit of time is about one third of the output of the normal blast-furnace operation, when making cast iron.

I have so minutely described the practice hitherto of making ferro-silicon in the blast furnace, in order to bring into comparison .with it my own practice and to emphasize the features of novelty.

My improved procedure also is preferably (not necessarily, ofcourse) carried out in a'blast furnace which is approaching the end of its term of life.

According to my invention, the furnace charge is far different from that hitherto employedto produce ferro-silicon. I pref-- erably use no ore, any limestone, place of ore, I

nor do I ordinarily use or quartz, brick, or clay. In preferably use heating-furnace cinder and rely on it primarily as the source of iron (and of silicon as well). This heating-furnace cinder is a familiar byproduct of heating-furnaces used in steel mills and wherever steel is fabricated, and usually has approximately. the following composition, given here as typical: iron, 44.20%; manganese, 1.30%; phosphorus 06%; sulfur, 4%; silica, 34.10%; alumina, 5.40%; calcium oxid, 4.20%; magnesium oxid, 2.40%.

In place of limestone, I use blast-furnace slag, and this in especially large quantities. he normal, usual slag contains, essentially, silica, 32% alumina, 13%; and calcium oxid and magnesium oxid together, about 38%.

I use coke low in sulfur, as in the operation now commonly practised and characterized above, and I use somewhat more coke than that operation requires. The normal blast furnace operation for making ordinary cast iron requires about .80 to 1.20 units of coke for every unit of iron produced; the old operation of producing ferro-silicon in the blast furnace characterized above rewhich of course quires at least 1.70 units of coke per unit of product; my improved operation which I now am describing, requires 1.75 to 2 units of coke to each unit of product. It must not, however, be supposed that my operation is therefore more costly than the old opera tion; to the contrary, considering the economies realized in other respects in the composition of the furnace charge, the advantage is emphatically in my favor.

These ingredients are so compounded that the slag produced in my operation shall have this approximate percentage of the essential ingredients: silica, 38%; alumina, 19%; and calcium oxid and .magnesium oxid together, 38%.

Some further notes on the ingredients of my furnace charge may be made: First, chemically, it is advantageous to derive the needed calcium from slag rather-than from limestone-advantageous because the slag substituted for limestone itself brings into the furnace charge excess measures of silicon,

are present during the operation, to manifest advantage in the chemical formation of the desired product. Another advantage lies in this, that blast-furnace slag is practically free from phosphorus, as limestone often is not. Of the blast-furnace slag, it is to be remarked that it is now an almost valueless substance, and is indeed an encumbrance upon ordinary blast-furnace operations.

It may finally be asked, whether the absence of limestone would not result in the introduction of excessive amounts of sulfur into the ferro-silicon product. All my ex perience shows that this is not the case; about half of the sulfur is expelled at the high temperature of my operation, through volatilization, and half is carried off by the excess of slag produced. The high temperature of operation here alluded to arises from the comparatively large amounts of fuel used, from the high heat of the blast which I employ, from the slow rate at which the furnace is driven, and from the high melting point of the resulting slag.

The advantages of using heating-furnace cinder, rather than iron ore, are, first, that it costs relatively little; and second, that the silicon present in large quantities in this cinder, combined chemically as it is with FeO in the form of silicates of iron, now appears (and this is my discovery) to be in excellent condition, chemically, to make new union, under the reducing conditions obtaining in the blast-furnace operation, with the iron alone, and so to form the desired ferro-silicon. The mere presence of both iron and silicon in the furnace charge, each in combined state, and each in a separate combination, affords no assurance that in the operation of the furnace the silicon of the furnace.

will be released to unite with the iron. And, so far as concerns heating-furnace cinder, the belief has been that, inasmuch as it contains iron in the form of silicate, it is quite generally inappropriate as an iron-affording component of the blast-furnace charge, on account of the difficulty of reducing iron from silicates. My experience has led to the discovery that under the special conditions of ferro-silicon production, these ferro-silicates are reduced very readily; and in that they contain iron and silicon already chemically combined, they constitute the very best material from which to derive ferro-silicon. As for the blast-furnace slag in the charge, it should, as has been said, be introduced in large quantities. If too little slag were used, the bottom ofthe furnace would soon rise; that is to say, a layer of congealed ferrosilicon would rapidly grow upon the bottom An excess of molten slag keeps the bottom of the furnace washed clean of any such accumulation. There follows this further benefit: the furnace may always be tapped through the iron notch, whereas, in ordinary practice it sometimes happens that, because of bottom incrusta tion, the molten ferro-silicon must be tapped through the cinder notch.

Still another advantage consequent upon the use of a large excess of blast-furnace slag lies in this: After the ferro-silicon is already formed, there is danger that some of the silicon may be burned out (this is a surface action, of course) by the gases present in the furnace. The great excess of slag affords a surface cover, and mechanically protects the new-formed molten ferro-silicon. Having now described the furnace charge", I have still to explain the method by which the operation is brought into practice. The operation of my invention i brought into effect gradually. The furnace should have been in blast. for several days before the modifications in operation are begun which, when completed, will constitute the ferrosilicon producing operation of my invention.

Let it be supposed, then, that a furnace is in blast, and is carrying the usual burden. When now the ferro-silicon process is to be introduced, the addition to the furnace charge are modified. As the burden goes down, the operator begins filling with a mixture of coke and blast furnace slag. When a layer of this mixture has been spread, the ensuing .addition consists of the same mixture, but with a relatively small addition of heating-fufii'ace cinder (about 40% of the ultimate and normal ratio). ratio of cinder will be gradually increased, until at last it comes to normal.

,VVhile such adaptation is being made the As further additions are made the to acquire an increasing silicon content. The

melt will from time to time be tested,;and'

the charging will be governed according to the results of such test. The increase of the ratio of heating-furnace cinder is so timed that the normal ratio is reached at a time when the silicon content in the product has reached a value of 18 to 20%.

From this point, the operation is straightforward It is advisable, as is'common practice in blast-furnace operation, to prevent loss in the form of outblown dust by wetting the furnace charge at the top.

According to the old ferro-silicon process practised in the blast furnace and characterized above, a product is obtained in which the silicon content scarcely exceeds 12%. In the practice of my invention now described I double that figure and produce ferro-silicon with-a silicon content of as much as 25%. For reasons stated, this is a far more valuable product.

The ferro-silicon operation is preferably practised upon a furnace which is approaching the end of its term of life. The old process of making ferro-silicon brings the life of the furnace to an end after about three to four months; in'the practice of my invention the furnace will last four to five months-a gain of 30%.

In the ensuing claims I define the essence of my present invention. The features of operation, over and above what is so defined, and described above, are described in an exemplary way merely, and are not to be understood as limitations upon the invention. The invention will be practised if the features defined in the claims he prescinder.

2. The method herein described of producing ferro-silicon in a'blast furnace which consists in conducting the blast-furnace operation upon a furnace charge including heating-furnace cinder and a heat-affording substance.

3. The method herein described of producing ferro-silicon in a blast furnace which consists in modifying the charge of a continuously. operating blast furnace and introducing a mixture of blast-furnace slag and coke with an increasing ingredient of iron in chemical combination.

4. The method herein described of producing ferro-silicon in. a blast furnace which consists in modifying the charge of a continuously operating blast furnace and introducing a mixture of blast-furnace slag and coke, with an increasing ingredient of heating-furnace cinder.

5. The method herein described of producing ferro-silicon from an iron-silicate which consists in subjecting a body of ironsilicate in the presence of a heating agent and fluxing material not having avidity for 10 silicon to the reducing action of a blast furnace.

In testimony whereof I have hereunto set my hand.

VASILI LIZOUN OFF. Witnesses:

' BAYARD H. CHRISTIE;

MARTIN. A. RosANoFF.