US1917968A - Blast furnace - Google Patents

Description

F. C. GREENE Jul 11, 1933.

BLAST FURNACE Filed June 27, 1931 I N VEN TOR. f ran/(17. Free/1E flmbv y ATTORNEXJ:

, blast furnace Patented July 11, 1933 UNITED STATES FRANK'C. GREENE, on on caso, ILLINOIS BLAST FunuAcE Application filed June 2'7,

This invention relates to an improved blast furnace and, more particularly, to blast furnaces of reduced height and improved operating characteristics.

A heretofore. usual blast furnace for smelting iron is a stack-like structure having a height in'the neighborhood of from S0 to 90 feet, although this height may be varied according to the daily output desired. A charge consisting essentially of iron ore, fuel, and limestone is fed into the top of this stack, the limestone and the fuel, usually coke, being in fairly large pieces. A blast of air is forced upwardly through this charge and the ingredients react with one another and with the air'to produce, finally, at the bottom of the furnace, molten iron.

Complex reactions take place in the interior of the blast furnace involving the production of carbon dioxide and carbon monoxide gases, the latter being an important medium in the reduction of the iron oxide ore to the metallic condition. The size and height of the blast furnace make it a costly apparatus to construct,but the prevailing height has been found necessary to give time for the complex reactions, involved in the reduction of the ore, to take place. The coke used as fuel is also more expensive than coal, but bituminous coal has not been generally used due to the necessity of providing a fuel with a strong physical structure which *lll not crush and compact in the furnace to prevent the free passage and distribution of the air blast throughthe charge. Also, the air blast is usually supplied to the furnace at a pressure of 30 to pounds and this would have to be materially increased if a fuel which decrepit-ates and packs in the furnace were used. If the height of the could be reduced without re ducing the capacity of the furnace, great economics of operation and costofinstallation would result. Large savings could also be effected if coke could be replaced by the less expensive bituminous can, i 7 It has now been discoveredthat a blast furnace may be constructed of reduced height and in which bituminous coalmay be used as a fuel. It is, accordingly, an

1931. Serial No. 547,385.

object of the invention to provide a blast furnace of reduced height for the same output capacity. Another object of the invention is to provide a blast furnace employing coal as fuel. Still another object of the invention is to provide'a blast furnace in which the reaction time of the charge is lessened andin which the air blast pressure is reduced: A further object of the invention is to provide a blast furnace in which an improved porosity ofithe charge may be maintained. an additional object of the invention is to provide a -method of reducing ore to metal in an improved and efficient manner. To the accomplishment of the then, consists of the means hereinafter fully described and 'PZLliJlCllliLIlY pointed out in the claims. a V

The annexed drawlng and the following foregoing and related ends, said invention,

description set forth in detail certain mechablast furnace; Fig. 2 is a'horizontal section taken alongthe line 22 of Fig.1; Fig. 3 is an enlarged detail View of a portion of the blast furnace; and Fig. 4: is a fragmentary sectional view taken along the line 4ll of Fig. 1. l

Referring to Fig. 1, it will be noted that n the structure there shown has many of the features of the lower part of a standard blast furnace, but that, in place of an open top closed by a bell, the top of the present structure is closed with acrown o. The structure may be viewed as a standard blast furnace which has been cut off and" crowned at a point corresponding to the temperatures prevailing in a blast furnace from 500 to 800 C., although it will be understood that the height of my blast furnace Will be determined by the factors met with in each installation. The body of the stack part of the furnace comprises an outer cylindrical wall 4 supported by numerous buck stays 5, and resting on a frame 6, wiich. is suitably sealed against the escape of gases. Below .the wall f the furnace narrows to form a bosh 7 as in the standard blast furnace. A hearth 8 rests on foundations 9. 10 supplies a blast of air to the tuyeres 11 through which the air passes into the furnace. .lVithin the body of the furnace above the bosh is provided a cylindrical casing 12 concentrically spaced from the inner surface 13 of the furnace wall 4. Between this ing and the inner surface of the wall isalso concentrically spaced a cylindrical muffle 14;

which is curved inwardly at its upper extremity 15 toward the interior of the furnace. This muffie is adapted to be rotated by means described below. Inside the rotatable mufiie is a stationary screw or stator 16 having upon its exterior a number of flights 17 which may he integrally cast or otherwise attached to the exterior of the stator. The number of flights may be varied but sixhas been found to be a'convenient number. p

The charge consisting of iron'ore, limestone, and coal, which have been ground together, is fed to the blast furnace at a point somewhat above the bosh instead of through the top as in standard practlce. 'as mixed, may be stored in a bin 18 from which it is fed into a hopper 19 where a conveyor 21 picks it up and transports it to the blast furnace. Any well Known. type of conveyor suitable for the purpose may be used, such as a screw conveyor.

The charge is poured into a rotatable feed pan 22 which surrounds the inner casing 12, rotation of caused to travel upwardly on the: flights 17 of the stator 16 due to the friction between the rotating muflie and the charge. It will be noted that, in the drawing, the space hetween the muffle 14c and the stator 16 in-:

for convenience of assembly and other means of constructing these elements may be used as found to be feasible. A. slight clearance will be left between the mu'lile and the stator to allow for expansion. r

A bustle inside the mufiie 14 by the vanes The charge,

Between the muffle 141 and the inner sur face 13 of the furnace" wall is a passage 26 communicating with the interior of the furnace and having an outlet 27 communicating with stoves or with a stack or with other installations according to the disposition which ,itfis desired tomake of exit gases from tne blast furnace. I

The operation of the new blast furnace is as follows. "A mixed charge of iron ore,

slack coal and limestone which has been finely divided, say to pass a hundred mesh screen, is conveyed from the hopper 19 through the conveyor 21 into the rotating feed pan 22- where it is taken up and forced The intimately mixed charge is caused to rise on the flights 17, ofthe stator 16 by frictional contact with the inner surface of the rotating muffle 14:, which surface may be left rough as to. the top of thefurnace under the crown '3 where the inwardly curved extremity of the muffle forces it into, the interior of the furnace. wardly between the casing 12 and the muilie 14, blast furnace gases leaving the charge within the furnace pass downwardly .through thepassage 26 between the muffle and the furnace wall 4 where they heat the incoming charge, the gases finally passing out through the gas off-take 27 Heat will. also be imparted to the fresh charge from the contents of the furnace throughthe casing 12. The charge thus receives progressive temperature iniprcssments up to at least 600 C. The turbulent flow of the charge resulting from the frictional contact of the muffle 14 with the material on the flights l7, promotes rapid heat absorption.

mainin after wet rindin of these is driv- .en off by the heat and may be prevented from passing upward through the mass by adjusting the speed of propulsion so that the charge lags and fills the spaces between the stator and the mufilcr so as to seal these spaces. The free moisture will. consequently pass downward as superheated steam and give up its total heat to the cold incoming L mass. lifter the mass coal therein starts melting at about 350 C., thus becoming plastic and tending to bind the minute neighboring particles of ground limestone and iron ore. contact between the fuel and the other in gredientsof the charge thus results. By the time t-lre'charge has been heated to 450 C. by the'lica from the interior of the furnace and the heat from the exit gases, the fuel has set to a form which is many times as reactive as metallurgi *al coke, i. e., it has many times the ability of metallurgical coke to reduce carbon dioxide to carbon monoxide. The reactivity of the fuel increases formed, and rises gradually l'Vhile the charge is moving up- Free moist-ure picked up by the materials or rehas been dried, the

A very intimate untila maximum is reach atabout 600? O. and, in the preferred method of ope 'ating the blast furnace, this is the temperature at which the charge is passed into the interior of the shaft or stack of the furnace.

It will be seen that the charge'has been raised during its passage between the muflle and the casing 12, to a temperature which approaches that prevailing in a standard blast furnace at alike distance above the hearth. N 0 air has reached the fuel up to this point and, consequently, any reduction of the ore which may have taken place will be due primarily to the reaction of coal carbon or hydro-carbons with the iron oxide. However, the fuelin the charge has swelled and imparted great porosity to the charge, the coal having bound itself during the plastic stage in intimate contact with the fine particles of iron ore andlimestone present. When this highly reactive charge drops into the interior of the furnace, the carbon dioxide there present will be quickly reduced to carbon monoxide by the highly active fuel and, since the fuel is in'intimate contact with the particles of ore, the production ofcarbon monoxide, which is the most important agent in the reduction of the ore, will take place in close proximity to'the ore particles. The reduction of the ore will stack which has been omittedis to heat the charge to a reacting temperature and to subject the iron oxide ore to the reducing effect of carbon monoxide and carbon. Complex reactions take place in the stack involving the production and distribution of both carbon monoxide and carbon dioxide accompanied by partial or complete reduction of portions of the charge. The methodof operating the present construction must supply an effect upon the charge approximately equivalent to the effect produced in the upper part of the stack of the ordinary blast furnace. The heating effect is achieved in part or in whole by the temperature increments which the fresh charge receives in its passage between the inner casing and the muffle. In addition, by making useof coal instead of coke in the charge and by finely dividing and intimately mixing the constitu- V ents of the charge, it is possible to bring the mixture to the highly reactive condition defined above as the ability to reduce carbon may take place.

. dioxide to carbon monoxide. In this highly porous mass. permeable to gas, it is thought that carbon monoxide reaching the charge as it is passed into the, interior of the furnace, may be catalyzed by the iron oxide of the ore to produce. finely divided carbon which deposits adjacent the particles of ore distributed throughout the mass. Carbon dioxide is also produced as the other product of its reaction, but it is the finelydivided carbon which is of present interest. This finely divided carbon, distributed adjacent or in contact with the particles of ore, isextremely reactive and promotes'the work of reduction by additional carbonmonoxide until th'elast remnants of iron oxide are reduced rapidly and completely. This application of the known reaction 2C0 C+ CO offers an explanationof the manner in which a blast furnace charge, finely divided and intimately. mixed, is brought by the present method to a condition where it quickly approximates the reduced condition obtained in standard blast furnace practice only by passage through a long stack.

'Bv use ofthe' present method and appa-.

ratus for reducing ore, low sulphur slack coal may -be'made to take the'place of the more expensive coke. Installation and operating costs may be reduced due to the employmentof a smaller structure. for the same output of pig iron. In addition, it may be possible to use less blast air and the blast pressure canbe materially reduced sincethe air must be forced through a smaller'column of charge and the increased porosity of the charge imparted by the preheating treatment results in increased permeability of the charge to the blast. v

1 IVhile a dry charge may be used, it is also possible to employ wet grinding, for mixing the materials for thepurpose of reducing dustlosses and reducing grinding costs.

Excess watermay be removed by means of a filter press, but a certain amount of water in'the charge is advantageous since, when driven ofl during-the reactivating treatment, it increases the porosity of themass. Porosity of the mass during the preheating treatment is also increased by the drivingoi'l of volatiles and oxygen all of which result in an increased surface upon which reaction A further advantage of the present method over those now in use is that the porous charge containing its constituent-s in finely divided form permits carbon monoxide toreach every particle of iron oxide, whereas in the customary practice,

reduction of the lump charge requires a high stack and even then reduction is not wholly efficient.

The present method and apparatus, while involving a radical departure in operating technique, achieves ultimate conformation tothe chemicalreactions of the standard blast 'furnace and, consequently, a product of similar characteristics.

. While the main product of my blast furnace is naturally pig iron, another product is a fuel gas of higher calorific value than that nowobtained from standard blast furnaces. Bywithdrawing gases from a furnace having a depth of charge approximately equal to that described above, a gas is obtained having a high carbon monoxide content undiluted by increasing amounts of carbon dioxide such as are acquired in the upper-region of the standardblast furnace.

In effect, removal of the gas takes place at a point corresponding to the so-called F ranchot oflf-take in the standard blast furnace where it is known a richer gas may be obtained.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being made-as regards the mechanism herein disclosed, provided the means stated by any of the following claims or the equivalent of suclr stated means be employed.

I therefore particularly point out and distinctly claim as my invention.

1. A blast furnace comprising a furnace body, a casing concentrically spaced from the inner wall of said furnace body, means for feeding a charge into the lower end of v the space defined by said wall and said'casing, and means for discharging saidcharge from the upper end of said space into the interior of the furnace.

2. A blast furnace comprising a. furnace body, a casing concentrically spaced from the inner Wall of said furnace body, a muflie concentrically spaced between said casing and said inner wall, means forpassing a. char e upwardly between said casing and said muffle into the interior of said furnace and means for passing furnace gasesdown wardly between said muflle and said inner wall. I

a 3. A blast furnace comprising a furnace body having the characteristics of a standard blastfurnace for smelting iron, cut off and crowned in the temperature Zone from 500 7 800 C., a casing concentrically spaced from the inside wall of said furnace body, means for passing a charge between said casing 7 and said inner wall, and means for discharg- :ing the same into the interior of said furnace. 4. A blast furnace comprising a'furnace body having the characteristics of a standard blast furnace for smelting iron, cut off and crowned in the temperaturezone' from 500 to800 C., a casing concentrlcally spaced from-the innerwa'll of said furnace body, a muffle concentrically spaced between said casing and said wall, meansfor passing a blast furnace charge between said'casing andsaid muflle into the interior of's'aid fur- .nace and means for passing the furnace furnace.

gases between said "muffle and saidwall in heat transfer relation to said charge.

5. A blast furnace comprising a furnace body having the characteristics of a standard blast furnace for smelting iron, out off and crowned in; the temperature zone from 500 to 800 C, a casing concentrically spaced from the inner wall of said furnace body, a muiile concentrically spaced between said casing and said inner wall, means for passing a finely divided blast furnace charge and said casing.

7. A blast furnace comprising a furnace body, a casing concentrically spaced from the inner wall of said furnace body, a rotatablemu'flie concentrically spaced between saidcasing and said inner wall, a stationary screwinounted between saidinufile and said casing, means for feeding a blast furnace charge to said screw and meansfor discharging the same into the interior of said 8. A blast furnace comprising a furnace body, a casing concentrically spaced from the inner wall of said furnace body, a rotatable muffle concentrically spaced between said casing and said inner wall, a stationary screw mounted between said muffle and said casing, means for feeding ablast furnace "charge to said screw, meansfor rotating said -mufile to lift said'charge, and means for "discharging the same into the interior of said furnace. i

9. A 'blast furnace comprising-a furnace body, a casingconcentrically spaced from the inner all of said furnacebody, a 1'0- tatable muffle concentrically spaced between said casing and said inner wall, a stationary screw lnounted'betwcen' said muffle and said casing, means for feeding a blast furnace charge to said screw, means for rotating said muffle to lift said charge, and said muflle having an inwardly curved top to direct said,

charge into the interior of said. furnace.

10. A blast furnace comprising a furnace body having the characteristics of a standard blast furnace for smelting iron, out off and crownedin the'temperature Zone from 500 to 800 CL, a casing.concentrically spaced from the inner wall of said furnace body, a rotatable muliie concentrically spaced between said casing and said wall, a station- 'aryscrew mounted between said lnuilie and 7 said casing, meansfor feeding a blast "furnace charge to said screw and means for rtating said muflle to lift said charge and to discharge the same into the interior of said furnace.

11. A blast furnace comprising a furnace body having the characteristics of a standard blast furnace for smelting iron, cut off and crowned in the temperature zone from 500 to 800 C., a casing concentrically spaced from the inner wall of said furnace body and a rotatable mufile spaced between said casing and said wall.

12. A blast furnace comprising a furnace body, a casing concentrically spaced from the inner wall of said furnace body, a 1'0- tatable muffle concentrically spaced between said casing and said wall, a screw mounted between said casing and said muffle, means for feeding a blast furnace charge to said screw, means for rotating said muffle to raise said charge along said screw and into the interior of said furnace, means for passing blast furnace gases counter-currently to said charge and in heat transfer relation therewith, and means for passing said gases out of said furnace.

13. A blast furnace comprising a furnace ard blast furnace for smelting iron, out off and crowned 1n the temperature zone between 500 to 800 C.,vmeans for continuously passing a blast furnace charge containing coal, counter-currently to hot gases for heating a blast furnace charge containing coal, so that, upon being discharged into the top of the furnace, it assumes a condition equivalent to a standard charge in a standard blast furnace at the same distance above the hearth. V

15. A blast furnace comprising a furnace body having the characteristics of' a standard blast furnace for smeltingiron, out off and crowned in the temperature zone between 500 and 800 0., and associated means for heating a blast furnace charge containing coal so that, upon being discharged into the top of the furnac'e,.the iron in said charge isreduced to molten metal during its passage through the body of said body having the characteristics of a standfurnace.

Signed by me this 19th day of J une,-1931.

FRANK O. GREENE.

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