US1756349A - Iron smelting - Google Patents

Description

and it comprises a process of smelting iron Patented Apr. 29, 1930 I RICHARD rnancno'r, or WASHINGTON, msrnrcror COLUMBIA, Assranor. TO rnnno CHEMICALS, INC. OF DELAWARE No Drawing.

This invention relates to iron smelting;

ores with solid carbonaceous fuels and preheated air in a blast furnace provided with hot gas outlets for the diversion of gas and saline vapors wherein the temperature of the air blast in much lower than in current practice, theburden of ore is nevertheless substantiallylarger, the slag is less basic or more siliceous, while thegas passing out-the.

furnace top is substantially spent; all as more fully hereinafter set forth and as claimed.

Exactly one blast was patented by ain- The use of blast heatlefiects a saving in the coke required to smelt iron amounting to as much as 7 5 percent of that needed with cold blast. It also materially increases furnace capacity. The development of later day practice has been toward the use of higher and higher blast temperatures until 1600 F. or higher is not uncommon. Other things being equal, the greater the blastheat the better is the fuel economy, that is to say,

hundred years ago 'thehot :the ratio of ore to coke may be increased with increase of. blast temperature.

However,- much irregularity is found in the rate of eflicien'cyincrease with increase of blast heat, the returns in fuel saving with-the higher blast temperatures being substantially di= minished. The functonal variationas not linear. The use of great blast heats is often attended with operating sometimes no economy in the highest blast temperatures.

In prior patents, notably 1366,64A of Aug. 28, 1928and 1,555,784: of Sept. 29, 1925, are described methods and means of improving the fuel economy of the blast furnace process wherein. the furnace is provided with outlets for hot gases carrying out of the hot zone alkali cyanid and other saline matter in vapor form, thereby preventing or limiting the accumulation in the furnace of such volatile matter, and wherein the rate of driving and the burden of ore charged with the coke are sub stantially increased over rates of driving and without hot gas and saline burden ratios used vapor diversion, theblast heat being varied 1n Neilson in Great Brit-' cyanid vapor around 900 troubles; there being .is usually suited to a .pulsion of alkali vapor from the slag,

IRON sMEmING Application filed March 15, 1928. Serial No. 262,047.

inverse proportion with the rate of hot gas diversion, and the use of the highest possible blasttemperatures being recommended. In the practice of these inventions the benefit of high blast temperatures is more'marked ticable. In other words, there has been lessdiminishment of return from blast tempera tures ranging up to above 1600 F. In these inventions the chemical activity of the air nitrogen is controlled by limiting alkali accumulation in the furnace with its consequent formation and associated heat absorption in the hearth or combustion zone.

I have discovered that, with a diversion from the furnace of hot gases and saline vapors in amounts and at temperatures sufficient to prevent undue accumulation of alkalies in the furnace and thus to hold a relatively low concentration of alkali (cyanid) vapor in the hearth gases, it is possible to run with a moderate blast temperature and at the same time to charge with the coke a burden of ore larger than has even been done wlth the greatest blast heats. I find that a blast temperature I results in greatly improved fuel economy and makes possible a fast rate of driving without necessitating anundue diversion ofgas for heating the blast. lVith blast temperatures of 900 F. and below, vaporization of slag is relatively small. A blast temperature between 700 and-900 F.

zone of between 20. and 25 per cent of the gases formed in the hearth. temperature may version in order to provide fuel for heating the blast. .With adequate alkali or cyanid vapor outlet, a limitation of the blast heat furtherlimits the chemical activity ofthe air p by lowering the combusnitrogen not only 7 tion temperature but also by limiting the exthe latter limitation itself increasing the availability of the combustion heat for, maintaining high hearth temperatures; A further effect of the lower blast heat is that of limitdiversion from the hot \VASHINGTGN, DISTRICT or COLUMBIA, A CORPORATION or higher blast require a greater rateof di 2200 F. works well ulation the blast heat .still be kept below .However diversion of the equivalent of ing slagvaporization with its attendant heat absorption. And when, in turn, the burden of ore is adjusted to the increase of available heat, then, as I have found, the furnace works smoothly and much more uniformly than heretofore. Even with quite low blast temperatures it is possible to make the burden great enough to cause substantially complete utilization of the latent energy of the gas put through the shaft, as evidenced by a top gas composition'showing CO ratios closely approaching 100 per cent, that is, with practically all GO converted to CO In the present invention fuel economy ,is improved over prior practice by decreasing the blast heat while increasing the ore burden. The blast heat should be in direct relation with the rate of hot gas diversion the blast temperature being raised or lowered as the proportion of gas diverted is made greater or smaller; With a diversion rate about the equivalent of 25 per cent of the gases formed by the air blast the blast temperature may 900 F. If desired, the temperature of the blast may be that of the atmosphere, it being practicable to work with cold blast when a relatively-large diversion of fuel gas is desired for the sake of the gas. it is better practice to divert a smaller amount of gas and to work with a moderate blast heat, proportioning the blast heat in direct ratio with the amount ofgas diverted. The amount of gas to be diverted depends somewhat upon thealkali content (K 0 and Na -O) of the material smelte'd; ore and coke of relatively higher alkali content requiring a greater diversion of than others in order to prevent undue accumulation of alkali in the furnace. Ordinarily, for example, Southern ores, by reason of their higher potash content, require a gr'caterproportion of the gas to be diverted than do the Lake ores; this difference,however, being 'modified in some instances by the greater amounts of gan 'ue in the Southern ores, requiring more heat for fluxing. In general, a about 25 per cent of the air gasat a ten'iperature around with a blast temperature from 800 to 900 F. In adjusting these two factors in correlation for purposes of regs is lowered or raised as thediversion of hot-gas is decreased or increased. In some cases good fuel eoonomy'is obtainable with blast temperatures around 500 to 600 F. but'in general abetter balance is secured with a heat of 800 to 900 F. The blast temperature is conveniently regulated by mixing unheated air by well known means with air heated to temperatures above the one desire While the blast temperature is thus limited the burden is made relatively large.

Even with moderate blast heats and with a.

20 to 25 per cent hot gas diversion, the ore -burden,the ratio of ore to coke, is made great- (3) lessening the slag heats and lillfitll burdens, the metal .roduced ertnan has ever been found practicable with the greatest blast heat without hot gas diversion, greater indeed than has hitherto been generally considered theoretically possible. The burden should be at least great enough to prevent solution loss, that is, the gasiiication of coke carbon otherwise than by air. The amount of ore charged with the coke ma be thatsufficient to convert to CO all the CO formed by the air oxygen less the amount of CO diverted in hot gas;this CO formation being effected through direct oxidation b the oxids of the charge aided by the break ing up of 2C0 into C and CO the latter-action being promoted by the extension of the zone of temperature suitable thereto which results from the diversion of hot gas and the adjustment of the ore burden. In addition, a third positive beneficial step is possible,

namely that of putting into the charge an amount of basic flux, limestone or dolomite, sul'istantially-less, relative to the silica and alumina contained in the ore and coke than is usually charged, this step havingthe effect of making the slag less basic or more siliceous than heretofore. This is made permissible by the greater production of iron'and slag per unit of coke and thus by the greater slag volume per unit of sulfur input, the latter being usually for the most part fur in the coke. To adequately eliminate sulfur from the iron the proportion by weight of lime and magnesia. together to silica and alumina together may be, with, coke sulfur well over 1' per cent, substantially less than the usual 1 tol.

This proportion of bases may average less than 0.8 to land it may be considerably lower. The step of lowering the ratio of lime and magnesia to silica and alumina is in itself beneficial by way of oecreaslngthe expulsioirof alkali vapor potash and soda) from the slag, thereby lessening alkali accumulation and vaporization with cyanid formation, hence by way of making more heat available to the hearth for strictly. smelting.

The three steps l) lowering the blast temperature, (2) increasing the ore burden, and

basi i a e cumulac tlvely and 'interdependently beneficial. Im provement upon prior inventions is secured by Way of reducing the requirement of gas to be diverted; less fuel and smaller plant capacity being now needed for heating the blast. There is a further advanta e in bein abl b b always to have a substantial reserve of blast heat. Furthermore as a result of lessened nitrogen activity associated with smaller blast contains less nitrogen and is of superior quality. The process controls the re ection of unutlhzedenergy from the furnace and atthe a matter of the 5111-- hematite ore having i volume taking 43,000 to ore, 4,070 lbs. limestone and 2710 lbs.

' panylng form of a hot rich gas which is more efficient as afuel than the blast furnace gas ordinarily produced. 1

As an example embodying the principles of this invention may be taken the smelting of a natural content of 52 per cent iron and 11 percent silica and alumina-with coke containing as charged 85 per cent fixed carbon, 1.1 percent sulfur and12 per cent ash consisting mainly of silica and alumina; the flux used being a 40 mixture of limestone and dolomite containing'as available bases 44 per cent lime and 9 per cent magnesia. To make foundry iron of such materials in a furnace of 24,000 cubic feet working 47,000 cubic feet of air per minute (60 F. and one atmosphere pressure), the furnace being provided near the top of the bosh with four gas outletsabout 4 feet in-diameter throttled down to maintain adequate furnace pressure and delivering into a valve controlled gas conduit, the'amount of of free gas per minute (atmospheric tempera- ;ture and pressure) having as'lt leaves the furnace a temperature of 2200 F., the blast temperature is best kept between 7 00 and 800 F. and the ore burden charged vith the coke can then be in aratio of 2.9 to 1. with stone mixture added to the extent of 18 per cent of the weight of ore. The rounds charged may be the'equivalent of 13,000 lbs. coke, 37,700 lbs. dolomite. Vith the described rate of blowing, hot gas diversion, blast heat and burden ratio the furnace'can produce daily over 7 tons of foundry iron 'averaging'25 percent silicon and f 0.025 per cent sulfur about 1400 lbs. coke per ton, a pig lron yield of with a consumption of (were?) per cent on the ore and a'slag volume of about 41 per cent of the weight of pig or 320'tons per day, using 760 lbs. stone per ton of iron; the slag analyzing 56 per cent silica and alumina to 43 per cent lime and magnesia and 1.4 per cent sulfur (the diverted hotgas carrying considerable sulfur outof the furnace) the gas diverted being some 24,000 cubic feet per ton of iron and "having a' calorific value between 120' and 130 B. t. u. per cubic foot, with upwards of 40 B. t. u. of sensible heat in addition. 0

" The above exemplified production is at a rate of about 2 pounds iron with its accomslag and gas per pound of'carbon burning with air. It may be noted that the oxygen removed from the ore in reduction of 2 I lb'sbf this iron is the amount used in oxidizing 'by theair blown, the burden of ore gives up to an amount of oxygensuflicient to CO 64 per cent out of the 7 5 per the gases convert to the airoxygen'plus the as diverted should be about 13,000 cubic feet 4 heat generation being cent of'the CO formed by the air which is caused to flow up through the shaft','or some per cent of the undiverted CO. It is also to be notedthat the blasttemperature, 750 F., makes the heat generated in CO formation by blast heat 5420 B. t. 11. per pound carbon, of which some30 per cent (about 800 B. t. u. per pound pig) is available in the hearth at 2700' F. A 25 per cent loss in water cooling and radiation, 1350 B. t. u. per pound carbon, leaves 4,000 B. t. u. effective. Of this, 950 B. t. u. being taken out assensible heat of the gas diverted at 2200 F.,the rem'aining heat; 3050 B. t. u., is'sufficient to supplV the 2560 B. t. u. absorbedin heating the metal and slag and decarbonating the stone (oxidation of CO to CO by the oxidslof the ore being exothermic). The unusued heat as generated by the air .(490 B. t.'u.), together with the latent heat of carbon depositionin 12 per cent of the CO formed by air oxygen and unused in reduction (350 B.'t. uI), con.- stitute a surplus of 840 B. t. u. per pound carbon burning with air. This surplus is available for drying the charge and heating the top gases to a moderate temperature, 200 to 250 F. Any temporary deficiency of heat can be supplied by increasing theblast volume more coke, the rate of thus increased both by increasing the combustion of carbon in the hearth andby increasing the deposition of carbon in the shaft. The carbon deposited (equal to about 6 per cent of that burning with air) may be nearly or quite sufiicient to supply that dissolved in the metal, in fact, it is possible to have the air burn more carbon than is charged as coke. In the described process substantially all the CO passed up the shaft may be converted.- to CO partly in direct'reduction of'iron oxid, partly in carbon without burning any deposition. The top gas is thus completely spent. The hot gas diverted from the bosh contains in sensible heat and combustible components (CO and H somewhat more than20 per cent of the calorific energy of the coke fed to the furnace; the blast heat being about 8 per centofthe coke energy. In eflicient recuperators and power plants the diverted hot gas sufficesfor heating and blowing the air blast.- A p art of whatever alkali that may be contained in the ore and coke is recoverable as cyanid from the diverted gas, using-the air as a cooling agent. Normally a recovery of at least a ton of potassium cyanid per day is possible.

' The chief benefit to present invention-1s that of improved economy in' iron smelting. Compared with current practice without ;hot gas diversion s but with. blast temperatures above 1200 F., it is now possible with blast temperatures 'be- ,low'900 F. to increase furnace production by 20 to 30 per .centfwithout increase'of blast volume and with a substantial decrease of be derived from the.

I dailyv coke consumption. Using coke the meta'llurgy of the furnace maybe made more =efiicient than the'best charcoal practice has been; the quality of the produced iron being for many purposes improved.

In further contrast to prior practice using very hot air, with or without diversion of hot gas, the present invention lends itself to ready control of the gasproducing function of the blast'furnace. The new process may confine the rejection of latent energy by the furnace to the rich gas diverted near the bot tom and when an increased production of fuel gas is desired, all that is necessary is to decrease the amount of ore charged with the coke andto increase the'diversion of gas. 7 'fI'claim: 1.- In 1 smelting iron ores with solid carbonaceous fuels and preheated air in a blast furnace to produce 'iron alloys, fuel gas and slag, the process which comprises divertinga limited-amount of hot gases and -saline vapors from the hot zone of the furnace and introducing the air blast at a temperature below 900 F.

2.1In smelting iron ores with solid carbonaceous fuels and preheated air in a V blast furnace to produce iron alloys, fuel gas and slag, the process which comprises divertmg a limitedamount of hot gases and saline .vapors from'the hotzone of the furnace, introducing the air "blast at a temperature be- .low900 F and chargingwith the fuel an amount of ore and'fluxisuflioient to convert ;-to'CO substantially. all the CO'in" the un- 'divertedgases. v

3. In smelting: iron ores with solid carbonaceous fuels and preheated air in a blast furnace to produce iron alloys, fuel gas and slag; the process which comprises diverting a limited amount of hot gases and saline vapors from the hot zone of the furnace, introducing the air blast at a temperature below 900 F., charging with the fuel an amount of ore and flux sufficient to convert to'CO substantially all the CO in the undiverted gases, and maintaining in the slagza proportionby weight of less than'eightparts of lime and magnesia taken together to ten parts of silica and alumina taken together.

4. In smelting iron ores with solid carbonaceous fuels and preheated air in a blast furnace to' produce'iron alloys, fuel gas and slag, the process which comprises diverting alimited amountofhot'gases and saline vapors from the hot zone of the furnace, introducing the air blast at a. temperature below 900 F., and maintaining in the slag a proportion by weight of'less than eight parts of eelime and magnesia taken together to ten parts of silica and alumina taken together.

. 5. 'Theprocess of improving fuel economy insinelting alkaliferous iron ores with coke and preheated air in a blastfurnace to pro- 6 duce ironalloys, slag-and fuel gas which com- I )IOUOllJlOH with the amount prises diverting hot gas and. alkali'vapors from the hotzone ofthe furnace, lowering 'the blast temperature and increasing the ratio of ore burden to coke.

6. The process of improving fuel economy in smelting alkaliferous iron ores with coke and preheated air in a blast furnace to produce iron alloys, slag and fuel gas which comprises diverting hot gas andalkali vapors lowering I the blast temperature, increasing the ratio of from the hot zone of the furnace,

and lessening the slag of hot gases from the hot zone of the furnace and adjustng the blast temperature in direct of gases so diverted, the blast temperature being raised as the rate of hot gas diversion is increased and lowered as the diversion rate is decreased.

8. In smelting iron ores with carbonaceous fuels and preheated air in a blast furnace, the

process which comprises diverting a limited amount of gas from the furnace-at a temperature around2200 F., transferring heat from the diverted gas to the air blast and lowering or raising the temperature of the blast respectively by'decreasing or increasing the rate of diversion of hot gas from the furnace, thus compensating the increase or decrease of diverted energy by increase or decrease of blast heat.

9. In the smelting of iron ores with coke and preheated air in a blastfurnace with diversion of hot fuel gas from the hot 'zone of the furnace, the method of regulating the furnace operation which comprises adjusting the amount of fuel gas diverted in direct relation with the blast temperature, said diversion being increased with rise of blast temperature or decreased with drop in said temperature.

10. In operating a blast furnace for smelting iron ores'with coke 'andpreheated air while withholding from the shaft some of the hot gases produced in the hearth, the process which'comprises keeping the blast temperature below 900 F. and adjusting the amount of ore charged with the coke to the amount of gas put through the shaft, charging'sufhcient ore toutilize substantially all the energy of the gas put through the shaft,

and thus causing the gas leaving the top of thefurnace to be nearly spent, that is to possess substantially no latent calorific energy.

In testimony whereof, I have hereunto af- 1 fixed my signature.

RICHARD 'FRANCHOT.

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