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84 Proceedings of Electric Furnace Conference, 1962

4. Low phosphorus, sulphur, and silicon contents easc slag-control problcms and reduce heat times.

5. Low residual elements ensure meeting the specifications for all grades of steel \vherc certain elelncnts are restricted. When used in combination \oith scrap i t acts as a cliluent for thc t ramp elements in the scrap.

6. Using a high percentage in the charge, tests have sho\vn a marked improvement in cleanliness and physical properties. The improvement in forgeability was par- ticu1:trly significant.

Electric Furnace Iron Smelting at

Chimbote, Peru, S. A.

WHEN the President of Peru, Dr. hllanuel Prado, co~inectcd the electric power to the two Tysland-Hole furnaces in Chimbote, on April 21, 19.58, hc inaugurated not only the first pig-iron making facilities in Peru but also thc first electrical furnace plant in the Western Hemisphere tha t \vas designed for the production of pig iron.

General Description of Facilities

The reduction facilities in Chimbotc consist of two 13,200-kva Tysl:tnd-Hole furn:tccs, built by the firm of Elektrokemisk A.S. of Oslo, Norway. Fig 1 sho~vs the general arrange- nlent of the furnaces and thc building. The building is designed for earthquakc conditions and because of cconornic considerations was constructed of reinforced concrete. Various insulating materials, firebrick and thrce types of ramming pastes arc uscd for lining thc furnaces. Thc pastes are ran~lned bchind steel forms, which are riot removed before the original burdening of the furnacc.

The furnace electrodes are the Soderberg type. As thcy are consumed, sheet-steel shells are wclded onto the top of the electroclc casing. The elcctrode is then lcngthencd by filling the steel shell with electrode pastc-a mixture of calcined anthracite and coal- t a r pitch. The clectrodes are suspended by hcavy chains, which also serve as the media for electrode rcgulation and counterbalance. Electrical contact to the electrodes is maintained by spring-tensioned water-cooled electrode clamps. T h e electrodes are periodically lowered or slipped as the ends arc consumed. Po\vcr input is maintained during the slipping operation.

Internal water cooling, in addition to tha t a t the electrode clamps, is providcd in the roof supporting structure, which is made of cast-steel beams tha t havc bccn cored during manufacture to allow the internal circulation of water. There is no internal cooling within the furnace shell but the lower part of the shell is cooled by a n external \\rater spray.

* President, Ramseyer and hLiller, Inc., New York, N.Y.

Sources of Iron for Electric Steelmaking 85

The roof of thc furnace is provided with a gas exhaust hood. The gas is collected under the furnace roof, withdrawn, washed in a Buffalo scrubber and then fed into the general plant distribution system which is quite sinlilar t o the systems used for handling blast furnace gas. The gas system is arranged so tha t the recovery section can be bypassed and the gas wasted by flaring a t the top of chimneys abovc the furnacc building. The electrodes arc surrounded by a hood \vhich collects urly furnacc gas tha t escapes between the electrode and the electrode roof ring and thc gases forr~zcd by the volatiliza- tion of the electrodc materials. These gases are vented over the top of thc building.

Fig 1-Cross section of furnace and building.

The electrical line diagram for the furnacc installations is given in Fig 2. The electrical systcm is quite complete, allowi~ing continuous automatic and/or manual control of the rcspective electrode positions and the electrode currents. Each furnacc has a n individual illstrumentation and control center. The operator's desk for each furnace has a separate panel for each clectrode. The panels indicate the electrical condition of each electrode and have the necessary facilities for resetting the autonlatic electrode regulation together with the equipment for manual control of thc electrode.

The furnacc instrumentation indicates voltage and current for each electrode. The phase balance between the three electrodes and the phase power consumptions are indicated, the total power consumption is both indicatcd and recorded.

The voltage tap changers shown in the schematic diagram are operable under load. The busbar configuration has been designed to minimize the high inductive reactance associated with an electrical current of over 40,000 amp. The busbars are arranged so


13.2 K V .

DISCONNECT

TRANSFORKR TO ELECTRODE PRIMARY CURRENT REGULATOR

A- Y MANUAL OR AUTO. SWITCH

ON LOAD TAP

FURNACE TRANSFORME CHANGER FOR MANUAL VOLTAGE REGULATION

13.2 KV / 2 2 0 - 63V.

A E A 8 A B A B A 8 A 8

TYPICAL SECTION OF INTERLACED BUS

(TWELVE I/Z- 1 1>1/2' CU. BARS WITH I /B-SPACES) ,

ELECTRIC PIG IRON REDUCTION FURNACE

Fig 2-Electrical line diagram.


that each pair of the three-phase conductors are interleaved (interlaced) from the transformer poles to points equidistant between the two electrodes that are fed by the two bus conductors. This arrangement keeps a parallel configuration for each set of busbars t o the last possible point, where they must divide in order to be connected to their respective electrodes. The combination of delta-delta or delta-wye connections and the transformer taps in the primary circuit allow secondary phase voltage selections in about 40 steps from 63 volts to 220 volts. The basic transformer design was based on a secondary current of 34,750 amp per phase. This might be compared to present operations that are using 46,000 to 50,000 amp per phase.

Raw Materials

The materials used in the smelting furnace are generally the same as those used in the blast furnace-iron ore, coke, and limestone. The iron ore and coke are received by ship

Fig 3-Rear view of pig-iron plant showing coke and stone conveyor belt, side-dump cor for filling bins, ore

pile, and skip hoist.

in the Chimbote harbor, which is about one mile from the plant. The ships are unloaded with dock cranes that are equipped with clamshell buckets. These buckets are emptied into 60-ton surge hoppers, which are supported by a gantry structure that can be moved on steel rails. The surge hopper discharges into large trucks that carry these two materials to the pig-iron plant (Fig 3). High grade limestone is purchased from local vendors who deliver +2-in. run-of-mine stone, which is crushed and screened a t an installation within the plant.

htarcona Mining Co., which has mining concessions a t San Juan in southern Peru, supplies the plant with hematitic iron ore. When the ore is trucked from the dock i t is dumped in a 4000 sq m ore-storage yard. The ore is reclaimed from this yard by a crawler crane and placed into reinforced concrete raw-material bins.

Minus 2-in. metallurgical coke, presently being purchased in Europe, is used as the reducing medium. The coke is purchased in two sizes: >/4 to $/, in. and 3/4 to 2 in. Experi- ence has shown that a ratio of one part of the larger to 2% to 3 parts of the smaller size gives a relatively smooth furnace operation. Typical chemical analyses of the ore, coke, and limestone are given later in a burden calculation sheet.


At one time, anthracite mines that have railroad connections with the steel plant were worked in the Santa River Valley. iJThen this coal was available, about 20 pct of the imported coke was replaced by domestic anthracite. During this period it was found that a mixture of anthracite slate, which contained about 40 pct ash and cleaned anthracite gave a smoother furnace operation than was possible with cleaned anthracite alone. The Peruvian anthracite is very dense, extremely low-volatile, and thus does not have the chemical reactivity that is desired of a Tysland-Hole reductant. Many operators of Tysland-Hole furnaces have found that gas or other low-temperature cokes are the most desirable reductants. At one time the Chimbote plant purchased its coke rcquirements as gas and/or special low-temperature cokes from the British Isles. Such low-temperature cokes command a price premium over the coke fines from blast furnace operations. The operating personnel a t Chimbote have found it more economical to use the lower

Fig 4-Scderberg electrodes, suspension chains, raw-material Telfer car, and charging holes.

cost metallurgical coke in their smelting operation as they have developed practices to maintain equivalent operations with either type of coke.

The coke and the sized limestone are trucked to a ground level hopper which uses a vibrating feeder to discharge onto a belt conveyor. The belt conveyor feeds into side- dumping transfer cars (Fig 3) which move on tracks locatcd over thc top of the raw- material bins. A total of 12 raw material-bins give storage capacity for about six days of operation. Each of the bills has 12 manually operated quadrant gates. The furnace charge is made up by running a scale car under the desired bins, discharging the desired weights of the raw materials, then transporting the weighed charge to the skip pit. The skip cars are pulled up an inclined bridge and durnped into a receiving hopper two floors above the working floor of the furnace. A self-propelled monorail Telfer car (Fig 4) is used to take the material from the receiving hopper and deliver it into charging chutes over and around the periphery of the furnace. The chutes go directly to boxlike openings in the roof of the furnace. These box openings and their chutes are choke-fed to minimize both the escape of furnace gas and the infiltration of air. Thc furnace also has closable plug openings in the furnace roof. These openings permit the immediate addition of corrective materials if a quick change of metal analysis or an adjustment to the furnace

Sources of lron for Electric Steelmaking 89

operation is required. A stecl bar can be inserted through these holes to explore the top of the burden or to break any incrustatiolls t h a t may form around the electrode.

Operation of Furnaces

The furnace, which is tappccl a t 4 t o 6-hour intervals, does not t a p in the sanlc manner as a blast furnacc. Thc slag and the metal arc tapped from a conlnlon taphole and then scparatccl by a slag skimmcr. Thc scparated slag drops into a water flume t h a t pulverizes the slag as i t is l~ydraulically culsrictl to a slag collection pit (Fig 5). The

Fig 5-Base of furnace showing water spray on lower shell and slag flume.

tapping and separating operation is similar t o conventional front slagging cupola practice. Thcre is no assurance, howcvcr, t h a t the Tyslnnd-Hole will, like the cupola, t a p iron first, then iron and slag, and finally almost all slag. I t is quite common t o have a mixture of iron and slag for the cntirc tapping. This ~nixturc probably results from the violent stirring caused by the electric currents in the molten materials. The power input need not be reduced while tapping. \\'hen the initial flow is iron and not a mixture of slag and iron, the slag-mctnl separation probably has been caused by a temporary incrustation ovcr the taphole, n snlall or restricted taphole, or possibly a combination of the two. Thc taphole is opened by either a n electric arc using a shunt circuit to one of the electrodes and a steel bar, a n oxygen lance, or a combination. A blast furnace mud gun is used for closing the tapllolc. A niixture of adobe and sand, materials t h a t are native t o this area, is usccl for filling tlic taphole a i ~ d the patching of runners.

Toble 1-Range of Analysis of lron Taps

Carbon. . . . . . . . . . . . . . . Silicon.. . . . . . . . . . . . . . Manganese. . . . . . . . . .

. . . . . . . . . . . . . Sulphur. Pllosl,horus. . . . . . . . . . .

Aloximn~n Pct

?vlinimum Pet

Average Pet

4 .20 0 .80 1 .oo 0.034 0.125


The operatiilg statistics prcscnted rcprcsent unit consumptiolls and production da ta taken over a recent 30-day period. During this period, in which only basic iron was produced, the average production was 93 metric tons per day per furnace with an avcrage powcr consumption of 2417 kw-hr pcr ton. During this period thc analysis of thc iron taps varicd within thc rango shown in Tahlc 1.

The average values arc uscd latcr in developing the theoretical burden calculations. During this 30-day period the electrode voltages were regulated as follo\vs:

Voltage 1 E-1 E-2 ( E-3

Maximum.. . LOO 94 95 Miuimum. .. 84 75 A v e r a g e I 93 I 1 83

These voltages were measured t o ground. I n order to convert them t o phase voltages, it is necessary t o add the two legs of the wye. The phase voltages between electrodes, therefore, approximate 1.732 times the voltages t o ground tha t are listed. Other average data during the 30-day period were:

High tension, vol ts . . . . . . . . . . . . . . . . . . . 12,800, all phases Low tension, volts. . . . . . . . . . . . . . . . . . . . 160, all phases High-tension current, amp. . . . . . . . . . . . 590, all phases Cosine 4 (calculatcd). . . . . . . . . . . . . . . . . 0.76

The average mcasured recovery of furnace gas during this period was 606 cu m (21,400 cu ft) per metric ton. A typical Orsat analysis of the gas is: COz, 19.3 pct; CO, 70.2; 02, 0.2.

The gas analysis indicates tha t 10.3 pct of the gas volume is unreported. Tysland-Hole furnace gas usually contains about 2 pct t o 4 pct hydrocarbons and 2 pct t o 8 pct hydrogen. Since Chimbote is in desert country, wherc it may rain a n inch in 20 years, the charged materials will contain relatively minor amounts of moisture. Additionally, the Marcona ore contains less than 1 pct of natural and combined water and a high-temperature coke is being uscd as a reductant. It is therefore reasonable t o assume tha t the volume of gases containing hydrogen will be a t a minimum. If 4 pct of hydrogen-containing gases are added t o the Orsat analysis, thc gas fractions total 93.7 pct. The balance of 6.3 pct is assumed to be Nz. Although such an Nz concentration is about three times tha t normally expected, the assumption in regard t o Nz is believed t o be reasonable, as Chimbote has steady, strong off-ocean winds, which undoubtedly cause above normal air infiltration around the top of the furnace. On the basis of these data and assumptions (70 pct carbon monoxide, 2 pct hydrogen and 2 pct methane), the gas would have a calorific value of about 240 Btu per cubic foot or about 5,136,000 Btu per metric ton of iron. A small part of the furnace gas is used a t the pig-iron plant for runner drying and ladle heating \vhile the majority is used a t the rolling-mill furnaces.

The burden sheet shows that there are two primary sources of furnace gas-limestone and the carbonaceous materials. The analysis shows 19.3 pct of the total of 606 measured cubic meters of recovered furnace gas consists of CO-equivalent t o 117 cubic meters per metric ton of pig iron. The 180 kgs of limestone per ton of iron would produce approximately 40 cubic meters of Con. If the limestone source of COz were removed, assuming burnt lime were charged, the corrected gas volume would drop t o 566 cubic


meters of furnace gas. If the gas analysis were corrected for burnt lime charging the new gas analysis would approximate only 13.6 pct C 0 2 with 75.0 pct CO. As the above C 0 2 content would represent thc C 0 2 derived from both the indirect reduction of iron ore by CO and from the decomposition of high concentrations of CO it is obvious that ncithcr of these possible rcactioiis liavc occurred to any substantial degree.

The furnace gas analysis sho\\~s 19.3 pct COz with 70.2 pct CO, which \\rould reprcscnt an equilibrium mixture, with an cxcess of carbon, of about 1350°F. I t therefore appears that high CO concentrations arc obtained in the hotter parts of the furnace but that little of this CO is uscd for thc indirect reduction of iron. In all probability the time a t reaction temperatures is far too short to allow any appreciable degree of (1) indirect iron-ore reduction by CO, (2) decomposition of high CO concentrations into C and C02, and (3) convcrsio~i of CO2 from the limestolie into CO as it contacts cokc a t calcination temperature.

Fig &Working floor showing gos toke-off, electrode clomp, fettling hole, roof structure, and charging bins.

Each ton, of iron co~isunied 348 kg of fixed carbon and 18 kg of electrodes, or about 14 kg of carbon. Cokc handling and gas dust losses \\ill amount to about 1 pct, so that the gross consumption of carbon will approximate 359 kg. Forty-two kilos of carbon enter into the iron, leaving 317 kg to enter into gas-forming reactions which would produce 592 cu m of carbon oxide gases. Adding the 40 cu m of C 0 2 from thc limestone makes a total of 632 cu m of gases containing one molecule of carbon that should be produced from the consumed materials. If the actual gas analysis is corrected for thc assumed 2 pct mctliane, thc carbon-bearing fractions account for 91.5 pct of the total gas. The produccd volumc of gas calculated from analysis and the charged carbon would thus nl)])roxirnate 632/91.5, or 690 cu m, which includes the infiltrated air. The gas losses in the system therefore al~l~roximate 84 cu In (690 less 606) I)cr ton, or about 12 pct of the total gas volunle. Some of these losses, for instance the gases from volatili- zation and burning of clectrodc pitch above the furnace roof, are unavoidable. The anliular opening between thc electrode and its roof ring, which has bee11 redesigned since the Chimbote furnaces were manufactured, is probably the greatest source of gas loss and minor losses occur through the roof and its charging ports (Fig 6).


A calculation of the gross energy requirement would show t h a t Chinibotc uses 408 kilos of carbonaceous material made up of 390 kilos of coke and 18 kilos of electrodes per metric ton of iron. If a reasonable 13,000 Btu per pound is applied t o this consumption, energ). amounting to 11,700,000 Btu is supplied as carbonaceous niatcrial. Forty- two kilos of carbon reside in the liquid iron and are tapped, so that thc consunletl carbon supplies approximately 10,500,000 B t u per nletric ton of pig iron. The conversion of the electrical cnergy to Btu increases the gross energy input to approximately 18,600,000 Btu per metric ton. As already nlcntioned, more than 5,100,000 Btu is rccovcrable from the furnace gases, and if credit is allowed for this energy, the gross Rtu consumption per metric ton will al~proximate 13,500,000.

Thc burden shect givcs tlic analysis of the ran7 materials uscd ant1 the analysis of the slag ancl iron produced cluriilg the period \\.hen the operating d a t a were accumulated. The coke contailis a0out 1.4 pet volatile matter and 89.4 pct fixcd carbon. It also contains slightly over 9 1)ct ash, and this percentage, together with the analysis of the ash, has bee11 usccl to rlcvclop thc anlounts of slag-forming materials tha t are contained in the coke charge. 'l'hc material analysis da ta was used to make a burden calculation on a basis consistent with 1,ast experience with Tysland-Hole smelting, assuming tha t 0.80 pct silicon nlctal would bc produced. In gencral the calculated rcsults are fairly consistent with thc results obtained from the operation.

The calculated limc and silica contents of the slag vary from the actual results slightly more than one would normally expect. A logical and probable cause of this differencc lies with thc slag from thc clectric furnace steel shop, a portion of which is charged back into the Tysland-H01c furnaces for the maintenancc of slag volunle and thc rccovcry of free manganese and iron units plus lime calcine.

Obviously each heat of melt-shop slag is not analyzed separately or kept segregated within thc Chimbote plant. The electric furnace steel plant a t Chinlbote makcs carbon steel in the range from 0.08 pct to 0.35 pet carbon. The charge for thc furnaces may vary from as high as 75 pet molten and/or cold pig iron to heats made from 100 pct stecl scrap. Thus thc stecl furnace slag analysis would be cxpected to vary considerably bc- tween these two extremes of practice, although i t is believed tha t tlic slag analysis used in the burden shcct rel~rcsents reasonably average values. Another probable causc is possible variations in the analysis of the limestonc, which is purchased from thrce rcla- tively small operators. It is also known that the silica, and sulphur in various i\iIarcona ore shipments can vary more than 10 pct from the values for these elcmcnts shown in the burden. . One might note tha t the sulphur content in the slag shows considerable difference between the calculated and expected. This is probably caused by the higllcr than antici- pated iron content in the slag. The average actual analysis of FeO in the slag was 0.80 pct (0.62 pct Fe) and this iron oxide content undoubtedly is responsible for the actual sulphur distribution ratio being a t 29 with the relatively high slag basicity ratio of 1.57 pct. Although the dcsulphurization ability, as shown in the opcrating data , is below the average desulphurizing power tha t can be associated with Tysland-Hole smelting, this type of smelting generally cannot maintain the sulphur distribution ratios for a n y given slag basicity tha t are associated with blast furnace smelting.

The burden shect (Table 2) shows a calculated slag volume of al~proximately 345 kilos (760 lb) per metric ton of metal. This relatively low figure, \\.hen compared with average blast furnace ol~erations, is the result of a relatively high-grade burden and the low unit co~lsunlption of coke, since coke is not supplied for thermal but only for chemi-

Table 2-Burden Calculation

~Marcona ore. . . . . . . 1.460 Coke . . . . . . . . . . . . . 390 Limestone . . . . . . . . . 180

. . . . Elec. fur. slag. . 193 Total charge.. . . . . . Loss. . . . . . . . . . . . . .

T o metal. . . . . . . . . . . T o s lag . . 345

1 . 8 3 . 2 0 . 5 1 1 6 . 0 3 1 . 0 2 . 0

131.8

(Si) 0 . 8 0 1 7 . 2

3 3 . 1 114.6 7 . 1

Actual Analysis -

Arrrnge analysis slag. PCI . 1 0 . 6 2 1 : 1 7 . 6 4 6 . 2 Average analysis metnl, p c t . . . .

. . . . . . . % CaO + MgO - Calculated. 1 .73 Slag basicity.. . . . . . . . . . . . . . Actual.. . . . . . . . . . . 1.57

% SiOz % S' Calculated.. . . . . . . 3 3 . 5

Sulphur distribution. . . . . . . . - . . . . . . . . . . % S" .4ctunl.. 29


cal requirements. Actually 345 kilos is not a low slag volume, as slag volumes of less than 300 kilos have been obtained in commercial Tysland-Hole smelting operation. I t is obvious that substituting lime for the steel furnace slag would make a substantial reduction in slag volume.

Mechanics of Ore Reduction

A great deal has been written conccrning the theory, degrees of cquilibrium, chemical reactions and operating techniques of the conventional blast furnace. Although many of the fine points, such as possible intermediate reactions or the reversal of reactions, remain the subject of debatc and discussion as well as further research, the concept and princil~les of blast furnacc smelting are understood in a general manner by many operating people, chemists and metallurgists. The same is not felt to be true of Tysland- Hole furnace operations. In fact, metallurgical books have a tendency to completely omit the mention of electric iron smelting furnaces and those that do make mention touch on electric iron-ore smelting in a very superficial manner.

Thc discussion which follows gives one conception of the Tysland-Hole furnacc smelting a t Chimbote, l'cru. This discussion may introduce some concepts of Tysland- Hole smelting that are in disagrecment with the thoughts of others. However, the general concepts of smelting that follow should be considered of some value, since thc majority of people in the iron and steel industry in this hemisphere have little conception of the Tysland-Hole operation.

Fig 7 shows the important dimensions of the Chimbote Tysland-Hole furnaces. If the relative physical dimensions established between the furnace walls, the furnace bottom and the electrodes arc develol~ed in accordance with the desired operation, the furnace lining becomes almost nonwearing, since the lining tends to become stabilized a t most working lines by being built up with charged materials. This is especially true with the side-wall linings in a zone horizontal to the lower ends of the electrodes. The side-wall lining above this zone is subject to some abrasive wear and below this zone to the relatively moderate attack of molten pig iron.

With the furnace design considered most desirable, a zone on the same horizon as the ends of the electrodes and the top of the crucible of the furnace will actually bc built up slightly by the furnace burden. The bottom of the furnace is subject to attack by the liquid metal. Experience has shown that this attack becomes self-stabilizing. If the ends of the electrode are too near the bottom, a high bottom temperature develol,~ and the bottom is eroded. If the distance from thc bottom to the electrode end is in- creased, the bottom will becomc encrusted with pig iron, which then forms the working hottom of the furnace. Thus i t is possible, with a correctly dcsigned furnace, to have an almost indefinite refractory life where the lining undcr othcr conditions might be subjcct t o liquid attack.

This "perfect" design of furnace parameters has one drawback. If the working furnace is operated with a power input above the theoretical design input, some of thc refractory (perhaps too much) will be eroded before the lining contours stabilize. If the furnacc is operated below its dcsign power input, the working lining contours grow inward until it is possiblc to have operating troublcs bccausc zone IV of thc furnace becomes too large and causcs low-temperature, high-sulphur metal.

Fig 7 divides the furnace into four zones. Thc first zonc around the bottom of the electrodes is where nearly all of the electrical energy that is used for reduction and melting is converted into heat. During normal operation, a nest of coke will build up

Sources o f Iron for Electric Steelmaking 95

underneath and around the bottom sections of the electrodes. The coke has accumulated here since all of the rest of the burden moving down the center of the furnace has been converted to liquid and has trickled down through the coke and then collectcd as slag and metal in the crucible. The electrical energy is transformed to heat in this area by

Fig 7-Cross section of typical Tysland-Hole furnace.

both arcing and the electrical resistance of the coke betnreen the electrodes. Two electrical paths are available. The first is horizontal betlveen thc clectrodes using the cokc as a conductor. The second is tlo\vn\\-ard from the electrode to the bath, across thc bath, then upward to the other electrotles. Thc division of the electrical currcnt through thcsc


two possible paths (assuming constant coke path conductance) can be controlled by the electrode height above the bath.

Zone 11, immediately above the coke nest and shapecl as an inverted conical frustum, hits been divided into two strata, the top section where there is a l i t t l c~ndi rec t reduction b u t substantial preheating, and the lower section where calcination, partial direct and indircct reduction and fusion take place. The prcl,ondcrant amount of burden movcs

, lnce down through zone I 1 into the hottest zone of the furnacc, zone I, the coko ncst. '3' zones I and I1 are the real working zones of the furnace, their workings should be ex- amined in greater detail. 'l'hc burden enters the tol, of the furnacc and tends to follo\v :t direction leading t o the center of the furnacc a t thc bottom of the electrodes. The arrows showing the direction of charge movement in Fig 7 have their lengths in propor- tion t o the expected volume or rate of charge movement a t the respective positions within the furnace.

As the burden moves downward in the u1)per section of zone 11, i t absorbs the heat from the rlsing gases and is preheated. The transfer of heat from gases t o solids is quite efficient. Because of the limited gas veloclty and the lack of channels, the gas tenll>ei-a- ture a t the top of the charge will apl~roximate 200°F. Somc partial indircct rcduction with CO tha t was produced in the lo\vcr parts of the furnace occurs In the upper section of zone I1 but the amount of reduction is not felt t o be substantial. As the burdcn moves nearer the coke nest into lower zone 11, the limestone is calcined, further indirect reduction and some direct reduction are obtained, and finally the reduced and unrcduced ore and the slag-forming constituents are fused. As the partially reduccd ore is fuscd, i t passes ou t of lo\\er zone I1 into the cokc nest, where reduction is practically com- pleted, as the reducing po\\-er of coke a t arc temperatures is \rcrjr high. The ore reduction in the coke nest and in lower zone I1 produce the CO for the indircct reduction t h a t takes place in their respective superior zones. Although the same secjuence of reactions takes place in the peripheral edges of zone 11, i t is obvious tha t the amount of material tha t passes through the outer edges of this zone is relatively small.

I t is generally agreed t h a t the iron ore is almost totally rcduced 111 the blast furnacc before i t reaches the fusion zonc. The samc is not fclt to be true In 'l'ysland-Hole smelting. Similarly, the fusion zone in a blast furnacc is considered as a near horizontal linc. In the furnace under discussion, the fusion linc is a t the metal 11nc a t the sidc \vall, runs horizontal until near the cokc nest, and then rises as it estends tonard the center of the furnace, foIlo\\~ing a linc over the to]) of the coke ncst. I t 1s log~cal to assume t h a t the nearer the center of the furnace, the higher the fusion zone \\ill bc above the cokc ncst.

Zone 111, comprising the volunle bct\veen zone I 1 and the furnace sidc lining, has a very slow vertical rate of movement. The material t h a t movcs do\vn\vard through this zone is not subject to the temperatures or the gases tha t are prevalent in zone IT. 111

the concept of smelting tha t is being developed, i t is fclt tha t practically all of the chemical reactions entered into by the mate r~a l moving do\\n\\ard through zonc I11 take place in zone IV. Probably the greatest amount of chemical reaction other than calcining occurring in zone IV takes place a t the slag-metal interface under rclativcly tvcak reducing conditions.

It has been shown tha t the reduc~ng conditions of this furnace vary from being in- tense (probably stronger than those in a blast furnace) a t the furnace center t o only mildly reducing a t the outer edges. Fortunately, the major~tjr of the burden is smelted in the center of the furnace, where the reduction potential 1s high, so tha t the metal tapped, which represents the average of the metal reduced, is not unduly influenced by


thc chargc passing through zone IV and outer zonc [IT tha t \\,as not smelted under highly reducing conditions. The metal processed in thesc zoncs, however, has some in- fluence, for i t is the ore t h a t descends in zone IV and through the outer areas of zones I and I1 ~ i t h o u t substantial reduction tha t causcs thc higher iron oxide of Tysland- Hole slags \\.hen they are compared \+ith blast furnace slags of similar chemistry. This ore carries oxygcn down to the slag and thus crcates a sul~l11-y of available oxygen in the liquid slag. It is felt t h a t this available oxygen, couplccl with lower slag temperatures in zone IV, causes the lower sulphur distribution ratios between slag and metal tha t are found mhcn comparing the sulphur distribution of l'ysland-Hole and blast furnace operations a t the samc basicity of slag.

As thc rcduction of iron ore and the supply of the heats of fusion a t the slag-metal interface in zone IV require heat t h a t can be supplied only from molten phases, the materials going through zone IV probably contribute to the slightly lower average tapping temperatures tha t are found when comparing Tysland-Hole and blast furnaec metal of relatively the same silicon analysis. The rcduction of iron ore a t the slag-metal interface also appears to be a partial cause of the lower carbon contents of Tysland-Hole metal, which seldonl forms much graphite kish on cooling. \\'ith the same silicon contents, Tysland-Hole metal can be expected to have 0.25 pct to 0.40 pct less carbon than blast furnace metal. Other factors tha t would be expected to contribute to the lower carbons arc lower average bath temperatures and a limited amount of excess carbon in contact n i th thc liquid iron.

The general conception of silicon reduction in blast furnace smelting is t h a t silica is reduced, forming iron silicide, a t the slag-metal interface. Although this slag-metal reaction undoubtcdly takes place to some extent in thc Tysland-Hole furnace, i t appears probable t h a t the majority of the silicon originates in the central par t of the coke nest, where tempcratures evist tha t are far above those encountered anywhere within a blast furnace. Therc are two methods of controlling the silicon content of Tysland-Hole metal and they are usually uscd in combination. Thc first method is to decrease the basicity of the slag. The second is t o run a higher temperature in the cokc nest by decreasing the distance between the ends of the electrodes and thc bath. The latter method tvould increase the amount of electrical energy being consumed in electrical arcs betneen the electrodcs and the bath and decreases the amount of electrical energy t h a t is dissipated by the rcsistancc of the coke between the electrodcs. Expcricnce has sholvn t h a t each I pct increase in silicon content of the metal mill rcqr~irc an additional 110 to 125 k~v-hr per metric ton of iron.

Comparison of Tysland-Hole Smelting With Blast Furnace Operation

I n general, the Tysland-Hole furnace should be considered a production tool tha t is as metallurgically versatile as a blast furnace. However, the inherent advantages and disadvantages of cach must be recognized. The opcmtional results from both reduction units are highly depcndent on chemical and physical characteristics of the raw materials tha t are used in the burden as well as the acumen of the o]~erators. TTThile i t might be conceded tha t the blast furnace is a more efficient process for eliminating sulphur, many raw materia.1~ do not require the sulphur removal efficiency associated n i th the blast furnace operation. Furthermore, the poorer sulphur elimination in electric smelting, in some'cases, can be offset by the fact t h a t less sulphur nccds to be eliminated by Tysland- Hole smelting, since electric smelting uses less sulphur-bearing carbonaceous material per ton of production. The previous burden sheet sho~vs about 15 pct of the total sul-


phur as a "10~s.'~ Experience has sho\\n that all of the charged sulphur cannot be ac- counted for in the metal and slag. The "lostJ' sulphur has been removed with the furnace gases and there is a t least some indication that the sulphur was removed as sublimed sulphides.

The Tysland-Hole is able to smelt titaniferous ores with much more facility than a blast furnace. While one school of operators considers a 1.5 pct Ti02 slag content as the undesirable maximum in blast furnace smelting, the Tysland-Hole can handle 10 pct Ti02 slags without undue furnace operating difficulty.

Operating people especially, would probably be interested in any operating problems associated with Tysland-Hole smelting. The Tysland-Hole operators make reference to the same term as their counterparts operating blast furnaces-"a smooth running furnace." This term covers practically every phase of the operation and to the writer means a furnace that is running on a stabilized basis within the speaker's concept of how the furnace is desired to operate. Actually the smooth running Tysland-Hole furnace, like the blast furnace, is developed on the basis of general operating and technical principles coupled with minor trial and error changes in operating procedures until the furnace becomes stabilized n its operation. Once the Tysland-Hole operation has been stabilized, the procedures established are maintained until something goes wrong, a t which time minor corrections are made to get back to the desired operation. The oiler- sting diligence required for the maintenance of stabilization of the Chimbote furnaces is probably less than the diligence required to maintain a smooth running blast furnace. Basically i t is felt that this develops because Tysland-Hole smelting is a relatively simple process, since i t does not have the extensive blast furnace auxiliaries, such as blowers, stoves, and top-bell systems which magnify and/or add to the complexities of operating the real reduction unit, which is the furnace shaft.

Under normal operation, the Tysland-Hole will deliver metal, from tap to tap, with only a little greater variation than would be expected from a smooth running blast furnace. The principal cause for this greater variation is believed to be the smaller taps that are made under Tysland-Hole practice, which prohibit the mixing or blending of reduced metal to the same extent developed in blast furnace practice.

In general, the mechanical troubles associated with the Tysland-Hole can be considered to be less than that expected of a blast furnace. Practically all electrode break- age can be associated with gross operating negligence, so tha t electrode trouble is normally nonexistent.

The Tysland-Hole furnace has two operating faults in common with the blast furnace-channeling and hanging. They are caused by the same reasons and avoided by the same means as in the blast furnace practice. As there is no air blast introduced in the Tysland-Hole furnace, i t is never necessary to incorporate operating procedures to allow the furnace to "slip." On the other hand, the lack of air pressure a t the bottom of the Tysland-Hole stack requires a slightly more open burden to allow the unrestricted upward movement of the gases generated within the furnace. The lack of large air volumes in the Tysland-Hole reduces the amount of dust fines that are carried off in the furnace gas.

I n both furnaces the maximum rate of production, as well as the smoothness of furnace operation, is highly dependent upon the physical and chemical characteristics of the burden materials. The electrical resistivity of the carbonaceous material can be an important factor in Tysland-Hole smelting. The carbonaceous material should have a higher chemical reactivity than would Ile required for blast furnace operation. If the


reactivity of the reductant is low, the furnace will take a larger portion of its carbon requirements from the electrodes. On the other hand, the Tgsland-Hole, with a burden height of about 12 ft, does not require the coke strength that is needed to support the high blast furnace burden column, and thus can use many carbonaceous materials not suitable for a large blast furnace operation. Althougl~ tests,for the reactivity and electrical rcsistancc of coke have been devised, they have not proved to be infallible and the best test is to use the coke in actual operations and to see if it is possible to stabilize the furnace a t an acceptable standard of operation. Because of the lower stack height (shorter dwell time in the furnace), the physical sizes of the materials in the Elektro- kemish furnace burden should be smaller than those used in the average blast furnace operation.

Adjustments can be made to a Tysland-Hole smelting operation much more quickly and more easily than is possible in a blast furnace. By adding additional coke, fluorspar, silica, or other material in the hand addition holes or the raw-material boxes on the Tysland-Hole furnace roof, it is possible to move ahead of all the burden materials that are between the scale car beneath the raw-material bins and the material that is about to enter the furnace. The hand addition holes also allow the operator to explore into thc charge of the upper part of the furnace for possible incrustations, bridges, or voids.

Thus it is possible for an experienced operator to make corrective additions to his furnace and have the additions cause effect within a few hours, whenever he senses that the furnace is departing from the desired operation, or whenever it is desired to modify the analysis of the tapped metal. The blast furnace can make some regulation of its daily output by reducing wind, or if a greater diminution of production is required, by adopting "fanning practice." The Tysland-Hole can reduce the unit rate of electrical input or periodically interrupt the current to the electrodes.

There is one point of operation that is practiced in Chimbote which it is believed is not generally practiced elsewhere a t this time by other Tysland-Hole operators. The normal procedure for making up the Soderberg electrode is to preheat the electrode paste until it is plastic and then ram it into the steel shell extension that was welded to the top of the electrode. Since early this year, Chimbote has merely addcd the cold electrode paste into the new casing extension and has found no difficulties as a result of the change from the old procedure of paste preheating and packing, which had been established for many years.

Acknowledgments

The cooperation of SOGESA, the operators of the Chimbote steel plant, and the assistance and guidance of Mr. Francisco Alvarez Calderon, their Technical Director, Mr. Antonio Haaker their Works Manager, and Mr. Roberto Lind their Chief Chemist in the preparation of this paper is gratefully acknowledged.

(For discussion, see page 376.)

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