US2476628A - Method for operating blast furnaces - Google Patents

Description

Patented July 19, 1949 METHGBJ'FDRE0PERATING}BLAST3 EUBNACES Henry T? Rudolf, Stenblenvilf; Ohio ApplicafionrJmuaryzeB, 19433; ,,Ser iaLNo,a4-72-,204s

ITCIaifiL; (Cl. 75 -41) This invention. relatestto .improyementssinblash furnaces-and. method. of .operating;the,=same.. The; iron blast furnace. is-

apparatus of: considerablee antiquity. It istusedqfonthepurposerof reducing. iron ore, which isrusua11y;- in -zth e form.:.otthe$oxr. ides E6203 0r Ee3Oi4 tO iron, by; causing the oxygen of the ore. to; combine with carbonlmonoxide. (CO) formed by. the combustion of carbon-cone tainingfueLlusualhncoke.

As. the demands, for" pig iron. haveincreasedj; the efiort' of those skilledlin the .artlhasflbeen. to devise blast furnacesof greater productive capacity Generally, speaking, thishas beentdoner by increasing the size. of. the furnace: andefparticularly by enlarging the hearth area; As;a,-,v result of these efiorts, blast furnaces have been. built 'in'thisrco-untry havingzh'earths of T26ifet"in cliameter.and;1 asv is well knowmzto build suc11" furnaces involvestremendous expense. so farvasi I" know, increasing the hearth area. isytlieonly' practicable method heretoforesuggested landjffil-E. lowed "for the purpose of "increasing the, produo; tion' of pig iron.-

I propose to increasethe production of "'Dig'iiron" in existing furnaces. or" to providejnewfurnaces of greatly;increased-capacity withoutlnrreasing the heartn'area': ln'connectiorrwithisuclrstruc tural changes as I propose, I have developedanew method; of 0peratin'gblast"furnaces-S0 asto increase greatly their DIGdIlCtiCIF'Of*p1gfilO1Tif1"- a*un'it of time:

My invention involves the applicationmf anew thought to the operation of blast furnaces whichi stated-broadly; is the-speeding up of' th'e rate ofi fuel combustion without increasing the volumeof gas that passes upwardly througlr the volds in the burden; in the stack:

According to: my invention, more oxygen supplied for combustion: by increasing 'theair blast volume; thereby generating: an increased the stack is accelerated .while-the volumerofEgas 50-- passing upwardly through: the stack zis'i'zlimiteda to-.;-substantia11y the; same ivolume -3S;.Wh6l1i?: the. furnaceis normally operating atvmaximum leaspacityi.

ASdS-rxWGllfkI-IOWII :tozthose skilled-drrz-the 11", a; 65 afiiilowsas la -but how to obtain; suclr-;a1qrat;ioyhas;i'

2"; blast furnace .is blown-on .v acwindgivolume" whichi is,.-. generally speaking, determined: experimen'etally. Such :factors ,are takeniinto, consideration; as ,the character; of the fiiel'j and the" natlne of l thetburden with respectfto the sizejor, the partr ales andthe ovoid far-east Thewind volumeis 'fixe'd at that ,point," where the gas will pass free'IitHIf-f Wardly through; the. b'urdmwittfout such resists ance aswilfcreate a b'ack pressure sufficient to:

impedethe'descentof the burden or causeittb hang in thestack,v There are, of course, other fa ctorswhicl'f are taken'in'to' consideration*in--determiningtlrewind volinnebut-so farasmy-prociess'is'con'cernegi theyneednot be consideredmerei Q'mtrfewin'gl volume so; determined; the produce tionof pigiironina unit"oftime'wlll-be*the-maxi:- nrum? f or a particular-furnace; alli other factors remainingiconstant.

Ifit be-attempted to 'increase the-wind volunre beyond the point so experimentally determined? theoperation of th'e fiirnaee will be ser-iouslyyimpaired. The gas volume will either notpass freely" througtf the -burdn,-* th us creating a baek pressure which will impede its descent, or thefbiast will b'e so strong" as -to=--bl0w mucli of the-#- ore out 'of the furnacein the-form of dustj there-t by upsetting-the carefully calculated= proportiorri of fuel to orey-causing th'e iurrrace to ibecome too hot 'as *wvel-l as 1 reducingthe"pig 'ironproduotihm By my improvement;- a given bla'st'ifurnace can? be operateds on a wind volnme in excess; by so muoh as may -be desired, o fathe volumeawhrch been: experimentally-1 determined i fori'maximum' plg'siren productionz.intithatifurnaceewithnut inn 3 terferingnm ithithermovement:ofifitheeburdemandt withoutz'inereasingqthesdustilosss. Thislitzaccomplish by I wlthdrawingcthe sexcess rgas vOlum'e-mree ated' by theoincreasedoblastisosthatisubstantiallw theesamezvolumeeot gas passesxthroughagthesburs' clenzas .whenrthelfurnacedsnormallyoperatingiat its maximunriproduotions.

v Fonmanrs/ears t a b l e d that-a las e u e nace; WQUldEODfiIfl B; mu f cie ly. when h CO/QQz IatiOsOf f the top; gas As -2 2-1): However;

45 this belief is no .lo l cl itenaloler Ratiosga'swlowtas;

lei zlilyhavevbeenr obtained; andritvis now believed on-,-good authority;that :the-ratio-mamloe ,rreducedq touasiilom; as; 1'21; Gen-erallyyspeaking argblasby furnaceels? mosttefiicient' thermally :andacls ermlecallyz when} thelwGQz 35in!) theetop; gas- 1s:v highest But it:rr-lustloe :borne inmindethatc eigherhe.-; (3,02 content of the gasithe lower rw l-lbedtsicalos rific value. Pig iromrnay beg-produ ed f ioally whezr the QQ/GOa ratiQs oft-the top; 8% is not heretofore been known. By my process such a ratio may be obtained, as well as any other desired ratio within practical limits, and this without affecting the calorific value of the gas.

As is well known, the blast furnace gas is used to heat the air blast for the furnace, to operate the blowing engines and, in an integrated plant, for many other purposes. Generally, the apparatus used has been designed to be operated on fuel of fairly definite heat value and it is important not to greatly reduce that value. By my process the production of pig iron in a. unit of time may be greatly increased without sacrificing any of the heat value of the gas.

As heretofore stated, I propose to increase the wind volume to accelerate fuel combustion and thereby produce an increased gas volume, but the increase in gas, or substantially all the increased gas volume, is withdrawn from the furnace so that approximately the same volume of gas passes upwardly through the burden. The CO/COa ratio of the top gas in my process is thereby reduced and hence its calorific value is decreased. However, I may mix with the top gas the withdrawn excess gas volume, or any desired part of it, which has a high calorific value, thereby producing a gas mixture of substantially the same heat value as that of the top gas which is produced in the normal operation of the furnace.

But instead of mixing the two gas volumes as just described, I may use each volume separately. The top gas may be used for low temperature combustion whereas the withdrawn gas may be used for higher temperature combustion. The choice will be made with reference to the nature of the apparatus at a particular plant and the desire of the operator in respect to the heat value of the gas.

My invention may best be explained and more readily understood by reference to an ordinary blast furnace operated to produce the maximum quantity of pig iron in a given time. For example, a blast furnace operating on a Wind volume of 60,000 C. F. M. (cubic feet per minute) of air at normal temperature and pressure will produce a top gas volume of about 84,000 C. F. M. at normal temperature and pressure and will produce a certain number of tons of pig iron in a unit of time. This top gas contains, roughly, about 40% carbon gases and about 60% nitrogen. There will also be a small percentage of hydrogen due to moisture in the air and the burden, but this may be disregarded for my purposes.

The carbon gases in the top gas comprise, on the average, about 26.6% C and about 13.3% CO2, so that the CO/COa ratio is about 2:1. The volumes, in my example, are substantially 22,400 C. F. M. of CO and 11,200 C. F. M. of C02. The bosh gas contains roughly about 40% CO, or a volume of 33,600 C. F. M. Hence, it is plain that only about one-third of the available CO is used in the reduction process and becomes CO2 by union with the oxygen of the ore.

The 11,200 C. F. M. of C0 thus used will reduce a certain quantity of ore in a given time. If we can lower the CO/COz ratio to 1:1, thus utilizing an additional 5600 C. F. M. of C0. or a total of 1.5 times as much CO, we should be able to reduce an additional percentage of ore in the same time by the same proportion, provided we can make the burden travel 1.5 times as fast.

The rate of the down travel of the burden can be increased by removing the bulk of the coke more rapidly, so that the ore can settle faster, whereby more oxygen of the ore is available for union with the CO to produce CO2 in increased quantity. In the example given, I propose to speed up the rate of coke combustion 1.5 times. It is known that combustion proceeds roughly as the rate of application of the oxygen of the air to the carbon of the coke. Generally speaking, it takes about '75 cubic feet of air at 62 F. and 30 inches of mercury to burn one pound of carbon. But this air volume is subject to variation on account of changes in the temperature and humidity of the air and in barometric pressure. The air volume will also vary in accordance with the carbon content of the fuel. In my process it is desired to increase the rate of down travel of the burden 1.5 times and this can be accomplished by speeding up the combustion of the fuel to 1.5 times the normal rate. This means that 1.5 times as much oxygen will be supplied in the same time period which, in turn, means that the wind volume must be increased .5 times. Thus, in my example of a furnace operating on a blast of 60,000 C. F. M., the blast must be increased to 90,000 C. F. M. in order to increase the combustion rate 1.5 times. Thus, the bulk of the coke is more rapidly removed and it follows that the burden will descend more rapidly in the stack, providing that it is not prevented from so doing by the increase in gas volume which is produced by the increased air blast.

Such an increase in blast volume would be unthinkable if it were not for the improvements I propose in the construction and operation of the furnace. If, in my example furnace, in which, when operating at capacity, 84,000 C. F. M. of gas passes upwardly through the burden, the gas volume is increased to 126,000 C. F. M., it will readily be understood that the back pressure created will be so great as to cause the burden to hang in the stack. However, I provide means for removing this increased part of the gas volume from the furnace before it can enter the stack, thus maintaining the volume of gas that passes upwardly substantially constant. This I accomplish by the means and method now to be described.

To make my explanation clear, I have appended hereto a drawing showing a blast furnace with my improvements applied. This drawing is only illustrative and is entirely diagrammatic, no attempt being made to show any particular proportion of parts or precise location of elements.

I The single figure of the drawing is a vertical section of a blast furnace comprising th conventional elements, hearth I, bosh 2 and stack 3. At the top I show only the large bell 4. From the top, the gas passes through the downcomer 5 into any form of cleaning apparatus 6. The usual bustle pipe is marked 1 and from this the air blast passes through the tuyeres 8, which are of the usual or desired number and of typical construction. Thus far, the parts of the furnace described may be of any well known construction, size and shape.

My improvement, structurally, resides in the provision of gas escape openings or exhaust ports 9, of which a plurality are provided, and which are located at or about the bosh line. The exhaust ports 9 all communicate with a collector pipe or manifold 10 which may surround the furnace in the same manner as the bustle pipe 1. An exhaust pipe H leads from the collector 5 nine-.- lkto hecleanine apparatusgfiz hisg a ter featurev will; bee incornorated 5 wh never; t. s 1. sit s; to. mix; the; withdrawn.- e ess. volume easswiththei qp easemanatins r m he fu nac nthe; usual. manner.- H wever, where i s desiredto use; theses. volumesseparate y. the xmust-p pe. ILmav. 1ead-: o-anv.- th r form of cleanin and: p cessing apparatus. so that; the. excesseas of. high, calorific. value may e usedseparatelv. from the ord nary. pas.

At anyv convenientzplase in thapipe Izplaeea valve V which may be either automatically or. manually-controlled so as, to.regulate. the escape fegas. .from..the h hthrough heports 9; The mechanism. for. operating the. valve, may be any of; theknown ratio control devices, or the valve. maybe: of; the. pressure; responsive. type. which. will-open. only .whenethegas. pressure in the.. bosh. reachesa predeterminedspoint. Thus, thevalve. V is. used for the purposeof. controlling andv regulating the-quantity of gas in. the bosh which will; be. permitted, to escape. andthus preventing it fromipassingupwardly.throughthestach By this arrangement. the. volume of gaspassing upwardly. through the. burden. may. be. maintained substantially the same as the gas. volume that Passes throughthestackin the normal operation-of the. furnace. In theexample heretofore giyen of afurnace. normally operating on a wind of. 60,000 C. F; M. andthe blast is increased to 90Q00- C. F. M., the. gas volume is increased from: about; 84,000 C. F.- M. to 126,000 C. F. M. This increaseof approximately llOOtl C. F. M. in, the .gas. volume may substantially.v all be with drawn through the. exhaust ports 9; and this result-will be accomplishedsby a proper regulationof the valve V.

It will,. of course, be understoodthat once. a blast. furnaceis equipped with. my improvements it- .nee.d notbecontinuously operated in accordance with my process. That is to say, it'may be desirable at times to. operate the furnace in h normal man r so. asto rodu ly h tollrthseof: pig iron corresponding toits rated capacity. Atsuchtimes. the,- valve V may be permanently closed.- and thus nonev ofthe gas volume withdrawn prior to its. entry intothe. 1 39 5,. In such cases, of course, the-wind-volmneis ;reduced=toits normakfieure.

I have shown and describedtheexhaustports or outlets. 9;;aslocated. at or about the bosh line. This is the preferred location oi said ports because at this point-the.gaspressureis lowest per unit cross sectional area of the. furnace. Moreover, at this point dust and finepa'rticles have completed melting or have aggljcjin erated so that there is little' 'o r no danger thatthe increase in gas pressure will cause; any increase. at all;

theidust loss.

Eroin the foregoing description of the construction of ablast furnace embodying my improvements and of operation thereof, I believe that my invention will be clear to those skilled ln,the.art. Ob.V10.I1ly,- my structural; improve-.. ments and new method may be appliedt and used-in connection with, existing. furnaces. It islikewise clear that new. furnaces maybe built embodying my improvements from the start and that such. furnaces.. maybe madeverymuch smallerand-yet have. the same capacity as the large furnagesmow in use.- Thus, there results. a considerable saving in building and maintenance expense.

Because of the fact that in my furnace operated in accordance with my method the rate of respondingly reate burde o umes. He e,

more. o h GQ the I gas wi n te-i with; he oxygen or: the or n sul inam-ereaten reduction in;th eiventime-per od:. ne mi thtasah ehe percentagecf-zthaCol s thusmn erte nt 0G2, t follows t at; the 01/. Qa ati f? he:- top gas ismormsnonfinelr: reduc whi h. ofy ourse s. ccompanie by. a. eduelenl nthe heat: va ue- 0.1; that gas; E r exampl iwhenethe fur ac s, op ating normally and he; CQZQQa atio. is on he avera eapsroximate v he. alor fi value (iii-the. easis subst nti l y- 87 B t:,-u-; p r. cubiceot. When; the. ratio. is edu ed to: 11 he lerific. value. of theas; falls o approx mate y: 65:41:13.1 t; 11.- p r cubidioot. may-be a.seri-. ils-loss. i:heat-..va1ue.in. v. ve.niplant;.Wh r the toves. for. he. irv wa ta dthe ow ng; n nes. anda xiliary equipment. aredesien d to, ope ate; on. ga havin a. high r, heating value...

However. bymy process. thereneedrbe. no ,re.-.,. sulting, loss in heating; value 0.f.3th e stars. Thisis because. the .ewithdrawn e.X6.8.5.8. gas. volume; taken from the bosh-may be .mixe.dj=,with; the. top gas, as. heretofore described. Thegas volumethus with drawnv contains nearly..40%.CO and; therefore, has a calorific; value. of; approximately 130.05; B. t. u. per cubic foot-.- Thus,. in theexample. furnace. operation heretofore described; the; normal. gas volume;..is..8.4 000.0; M'.: Under my. process whereby. the CO/COz .ratio .has: been reduced to 1:1, the heating.' value-30f that volume ofz-gasis; 65.4.3. ti u. pert cubicv foot. The in-. creased'gas volume of"42;000 611M. withdrawn from. the bush has aheating. value of 130.05- B; t. u. per cubic vfoot. lfswemix thesetwo volumes weshallthenget a total of 126;!)00 C. F. M. of gas having a calorificvalue of approximately 875. t. u. pei cubic foot, Wh'iChdS-the same heating value of the top -gastheiurnace hetd: when it was operating" normally. and when the CO/CO2- ratiois 2:1. 7

Thus in accordance with-the-foregoing, it will be seen that by my process'the production of pig iron in a given unit of time may be very greatly re s w thout any. orres en ms l e e i n e hee n va ii eii e as 'wi be understcod; however, that I; do not contemplate that alwaysand in eyery casev the entire. excess volume of gas withdrawn from the bosh. shall-be migedwith the topgas. There may be. cases where the reduction in, .he ating value of the. top gas is onor sufiicient consequence to require. the ,mixing ,.ot the. two 2 gas volumes and Where the. separate use of the- .bos'h.igas may.-be. initselfof considerable value In. he. xam le s fl i' l I; .3."? m e less arbitrarily elected totreduce; the.- (IO/CO2 ratio from 2-::1.to 151.; This -,of; course, is not always. necessary nor may it be desirable. always 3 to make such a great'reductionanq the ratio and; such a correspondingly great increase -in--,the. air blast volume. Wha .I, propqseto-do in any casev is to determine. the :QQKGOz; ratio ,of, the top gas when the, ;furna ce ;is.-operating atrits rated maxi mum-capacity. and then to;..red.uce,.that ratio to any desirable pointlimitlngmyseltperhaps to the ratio of li; 1. .whichgismow onigood :authority .believed to be attainable in an economic ore reduction process. However, it will be seen that if we start off with a normal ratio of 2:1, it may be desired to reduce this only to, say, 1.5:1. In such a case, instead of using only 33 of the available CO in the reduction process, we shall use approximately 40% of the CO. This means an increase of 20% and, hence, in that case the air blast volume would be increased by 20%.

An important result of the use of my improved blast furnace and method of operation is that the temperature gradient of the furnace will be very much steeper. In the ordinary blast furnace in normal operation, the temperature gradient is estimated to be from about 3300 F. to about 400 F. whereas in my process the gradient will be from a higher point, say, 3600 F. down to 100 F. This means that more of the heat of the gas volume is given up in the exchange in the reduction process with the result that the various sections of the burden will reach the different zones of the furnace at more nearly the proper temperature. It is also possible that because in my process the gas emerges at the top at a so much lower temperature and pressure, more gas may pass upwardly through the stack than in the normal operation of the furnace.

I am aware of the fact that it has heretofore been proposed to speed up the rate of coke combustion in a blast furnace by oxygen enrichment of the blast, that is to say, by adding pure oxygen to the air blast. Doubtlessly, this will have the effect of speeding up combustion which, as heretofore stated, proceeds roughly as the rate of application of oxygen to the carbon in the fuel. However, such oxygen enrichment of the blast is not practicable, for the reason that there results a serious unbalance of the components of the gas generated. It will be quite apparent that the percentage of nitrogen in the gas generated by such an oxygen enriched air blast will be very much reduced and this will seriously impair the operation of the furnace. It is well known that the function of nitrogen in the gas is that of a heat-transferring agent and, obviously, where the nitrogen content is seriously reduced, the heat exchange in the furnace is impaired and the ratio of direct and indirect reduction will be altered so as to cause a much higher percentage of direct reduction. This, of course, will radically and adversely affect the efficiency of the furnace.

I am also aware of the fact that blast furnaces have at times been operated on what is called slack wind. That is to say, whenever it has been desired to operate a furnace at less than its maximum capacity, the wind volume has been reduced. After such reduction, and when it was desired to restore the operation to normal maximum capacity, the wind volume has been increased. My process is, of course, readily distinguished from this slack wind operation because I increase the air blast volume above that which is normally used when the furnace is operating at its maximum capacity.

Whenever throughout this specification, and in the appended claims, I use the expression increasing the production of pig'iron or increasing the capacity of the furnace, it is to be understood that I mean an increase over and above the rated maximum capacity of the furance. For example, if the capacity of a blast furnace to produce its maximum tonnage of pig iron is defined as that condition under which the furnace burns 60 pounds of coke per 24 hours per cubic foot of volume of the furnace measured from the center line of the tuyeres to the stock line, then it is that capacity which I increase. In the example given, a furnace operated in accordance with my process would burn pounds of coke per 24 hours per cubic foot of volume of the furnace measured as above stated. By my process a blast furnace which, when operating at its capacity, produces approximately 1000 tons of pig iron per 24 hours may be operated so as to have a capacity of approximately 1500 tons per 24 hours.

It will be understood that the figures given throughout this specification for ratios, volumes and percentages are not intended to be exactl but are fair approximations of average figures. Nor are these figures constant because, as is well known to the blast furnace engineer, they vary from furnace to furnace and even in the same furnace from time to time. There are, of course, many other factors that affect the operation of a blast furnace and its production of pig iron but these I have not thought it necessary to mention herein because they will affect a blast furnace operated by my process in the same way and proportionately.

On more recently built blast furnaces, there usually is a good deal more wind volume available than is normally used and in such cases sufllcient excess capacity may be found so that the blowers can be used in my process Without change. On older furnaces it may be necessary to incorporate new blowers having sufiicient capacity for my purposes. So far as the tuyeres are concernecl, it will probably be necessary to increase their cross-sectional area to meet the higher wind volume while maintaining the pressure substantially constant. These things can readily be taken care of by the skilled blast furnace operator who desires to use the new process herein described.

I claim as my invention:

The method of operating a blast furnace to increase the production of pig iron which comprises increasing the air blast volume to speed up the rate of fuel combustion and thereby increase the rate of down travel of the burden, and controlling the gas volume entering the burden to maintain the rate of up travel of the gas substantially constant.

HENRY T. RUDOLF.

REFERENCES CITED The following referenices are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 117,246 Bessemer July 25, 1871 1,357,781 Koppers Nov. 2, 1920 OTHER REFERENCES Blast Furnace Practice, 1st ed, page 161, by Sweetser; published in 1938 by McGraw-Hill Book Co., New York.

Blast Furnace Practice, vol. 2, page 260; by Clements; published in 1929 by Ernest Benn Limited, London.

Transactions of the American Mining and Metallurgical Engineers, vol. 120, page 72; published by the A. I. M. E., New York.

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