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IS 12668 (1989): Melting characterstics of spongeiron/direct reduced iron (DRI) [MTD 30: Sponge Iron andSmelting Reduction]

IS 12668:1989

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Indian Standard

MELTING CHARACTERISTICS OF SPONGEIRON/DIRECT REDUCED IRON ( DRI )

UDC 669’162’263’25 : 69’141.17

@ BIS 1990

B U R E A U O F I N D I A N S T A N D A R D S *MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

March 1990 Price Group 3

Sponge Iron Sectional Committee, SMDC 36

FOREWORD

This Indian Standard was adopted by the Bureau of Indian Standards on 20 April 1989, after thedraft finalized by the Sponge Iron Sectional Committee had been approved by the MetallurgicalEngineering Division Council.

During the past few years the use of sponge iron has become increasingly important, in the electricarc and other steel making furnaces mainly due to irregularity in price and the poor quality ofscrap available. Also, due to its inherent plus points like virgin nature, low sulphur and phosphorouscontent and consistency of composition, more and more iron and steel foundries are using directreduced iron ( DRI ) for the production of quality castings.

The technology of melting sponge iron is presently in an evaluationary state as the characteristics ofDRI differ appreciably from iron and steel scrap as well as pig iron. Because of the vary nature ofthe product, the melting characteristics depend on the type of furnace in which it is used.Accordingly, this standard on melting characteristics has been divided into four sections:

Section I Melting characteristics of DRI in electric arc furnace ( EAF )

Section 2 Melting characteristics of DRI in basic oxygen furnace ( BOF )

Section 3 Melting characteristics of DRI in ( cupola furnace ) foundry

Section 3A Melting characteristics of DRI in ( induction furnace ) foundry

For the purpose of deciding whether a particular requirement of this standard is complied with, thefinal value, observed or calculated, expressing the result of a test or analysis, shall be rounded off inaccordance with IS 2 : 1960. ‘Rules for rounding off numerical values ( revised )‘. The number ofsignificant places retained in the rounded off value should be the same as that of the specified valuein this standard.

.

AMENDMENT NO. 1 JUNE 2010 TO

IS 12668 : 1989 MELTING CHARACTERISTICS OF SPONGE IRON/DIRECT REDUCED IRON (DRI)

(Page 1, clause 1.2) — Substitute ‘IS 15774 : 2007’ for ‘IS 10812 :

1984’.

(Page 1, clause 2.1) — Substitute ‘IS 15774 : 2007 Sponge iron/direct reduced (DRI), hot briquetted iron (HBI) and cold briquetted iron (CBI) for steel making‘ for ‘IS 10812 : 1984 Classification of sponge iron/direct reduced iron (DRI) for steel making in electric arc furnaces’.

(Page 1, clause 2.1) — Substitute ‘IS 11348 : 1989 Iron ore pellets – Apparent specific gravity, true specific gravity and apparent porosity – Methods for determination (first revision)’ for ‘IS 11348 : 1985 Method for measuring the apparent specific gravity and the porosity of iron pellets’.

(Page 1, clause 4.1.1, line 3) — Delete ‘optimum’.

(Page 1, clause 4.1.1, line 4) — Substitute ‘as per IS 15774’ for ’90 ± 2’.

(Page 3, clause 6.4, Title) — Substitute ‘Flux Consumption’ for ‘Lime Consumption’.

(Page 3, clause 6.4, first sentence) — Substitute ‘Flux’ for ‘Lime’.

(Page 3, clause 6.5) — Add the following sentence at the beginning of the text: ‘The refractory consumption is mainly influenced by residual iron oxide content and other impurities in DRI.’

(Page 6, clause 14.2) — Substitute ‘IS 11348 : 1989’ for ‘IS 11348 : 1985’.

(Page 6, clause 14.3, line 2) — Delete ‘(–5 mm size fraction)’.

(Page 6, clause 15.2.2, line 1) — Substitute ‘principle gangue content (SiO2 + Al2O3)’ for ‘total (SiO2 + Al2O3) gangue content’. (MTD 30)

Reprography Unit, BIS, New Delhi, India

IS 12668 : 19s9

Indian Standard

MELTINGCHARACTERISTICSOFSPONGEIRON/DIRECTREDUCED IRON(DR1)

1 SCOPE

1.1 This standard prescribes the melting charac-teristics of sponge iron/direct reduced iron( DRI 1 in electric arc furnace, in basic oxygenfurnace when used as coolant, in cupola furnaceand in induction furnace.1.2 This standard should be read in conjunctionwith IS 10812 : 1984.

2 REFERENCES

2.1 The following Indian Standards are necessaryadjuncts to this standard:

IS 5842 : 1986

IS 10812 : 1984

IS 11348 : 1985

IS 11896 : 1986

Method for measuring bulkdensity of iron oxides; lumpores, sinters and pellets (firstrevision )Classification of sponge iron/direct reduced iron ( DRI ) forsteel making in electric arcfurnacesMethod for measuring theapparent specific gravity andthe porosity of iron ore pelletsMethod for determination ofapparent specific gravity, truespecific gravity and apparentporosity of iron ore lumps andsinters

SECTION 1 MELTING CHARACTERISTICSOF DRI IN EAF

3 GENERAL3.1 This section of the standard prescribes themelting characteristics of DRI in electric arcfurnaces.

4 EFFECT OF CHEMICAL CONSTITUENTS/OTHER PARAMETERS

4.1 Effect of MetallizationIn freshly prepared DRT, un-reduced iron oxidesare primarily wustite ( Fe0 >. The furnace shouldbe operated in such a way that the Fe is recoveredby adding extra carbon to reduce Fe0 even at theexpense of some additional energy consumption.

4.1.1 For DRI produced from coal based rotarykiln processes with a carbon content of around0’ 1 percent, the optimum degree of metallizationis 90 & 2 percent and while melting, extra carbonin the form of petroleum coke, broken graphiteelectrodes, etc, should be charged at the furnacebottom to achieve maximum reduction of FeO.

DRI produced from gas based processes have anedge, in this regard, as its carbon content is muchhigher, over its coal based counterpart. Lowerdegree of metallization results in increased powerconsumption and longer heat time. Conversely,at very high metallization levels, there is insuffi-cient oxygen in DRI to maintain a continuousboil and under these conditions, an increasedproportion of the arc radiation is lost to therefractories with a consequent reduction inmelting efficiency and increased overall powerconsumption.

4.1.2 Indian arc furnaces are generally lowpowered ( 100 - 200 kVA/t ) and only some aremedium powered ( 200 - 400 kVA/t ) and theircapacity ranges between 10 - 25 tonnes. This aut-omatically imposes limitations on the proportionof scrap that can be substituted by DRI. Highpower ( 400 - 700 kVA/t ) and ultra high power( above 700 kVA/t ) furnaces can consume evenup to 100 percent DRI whereas in case of theformer the optimum ranges between 40 - 50percent. It has been established that for a 50 tUHP electric arc furnace using 100 percent DRT,for 1 percent decrease in the degrees of metalli-sation, power consumption increases by 10 kWh/tof steel tapped and the same is likely to be higherfor smaller furnaces. When partial charge ofDRI is used, the sensitivity of power consump-tion with degree of metallization is smaller as atlower degree of metallization, more vigorouscarbon boil is expected.

4.2 Effect of Carbon Boil

Unreduced iron oxides present in DRI can beused to advantage by the steel maker by reactingwith appropriate amount of carbon to maintain a‘carbon boil’ at the slag-metal interface. Thevolume of gas evolved from this reaction isappreciable, and it lies in the range of 4 - 10 m”/min/m* of bath area. This increases the slagdepth while decreasing the slag density markedly.A 10 cm thick slag can be foamed to over a 50 cmdepth while the slag density goes down below1 gm/cm3. Further, due to this vigorous carbonboil, both hydrogen and nitrogen contents aredecreased to very low levels, refractory is protect-ed and refining reactions become faster.

4.3 Effect of Gangue

The presence of gangue in DRI influences thesteel making operation through its effect on slagweight and slag composition. The magclitude ofthis effect depends on the amount and nature of

IS 12668 : 1989

the gangue in the DRI as well as the quantity ofDRI being added to the charge. Typically, anincrease of slag weight of 50 kg/t of steel tappedmay result in an increase in melting energy consu-mption of about 50 kWh/t of steel. This slope isdependent on cofnpositions and nature ofboth the slag makmg materials and the result-ing slag and thus can vary between 35 kWh/t to35 kWh/t of steel/50 kg slag.

5 EFFECT OF PLANT PRACTICE

5.1 Batch Charging

For DRI produced from coal based processes, theoptimum percentage in the charge is in the rangeof 10 - 20 percent whereas for DRI from gasbased processes, the same is in the range of 20-30percent.

Batch-wise charging is suitable in cases whereDRI is used in limited quantities or sporadicallyso that the additional cost of installing continuouscharging facilities is not justified. Batch chargingis also the only recommended process for 5t arcfurnaces.

5.2 Continuous Charging

As mentioned in 4.1.2, in the case of continuouscharging in furances of 10 t or more capacity, theoptimum DRI percentage is 40-50 percent.

5.2.1 Continuous charging of DRI is mostbeneficial when melting takes place at the slag/metal interface - this necessitates the DRIquickly penetrating the slag layer. For typicalDRI pellets/lumps with a size range of 6-25 mma vertical velocity at impact with the slag in therange of 7-9 m/s has been found adequate forgood slag penetration. Further, foaming slag isalso required for overcoming penetration problem.In general, DRI feed rates are maintained in therange of 27 to 35 kg/min/MW of applied power.

5.2.2 Normally, first a molten pool of scrap isformed in the centrc of the furnace and when thebath temperature reaches around 151 O”C, conti-nuous feeding of DRI should start at one third toone half the normal rage at full power. AfterIO-15 minutes a good boil and foaming slag areestablished, the feed rate is increased at full powerto maintain the bath temperature at 1570°C. Useof gaseous oxygen helps in the faster melting andas such the overall heat time can be decreased.The refining operations are controlled in such away that the furnace is tapped soon after com-pleting the continuous feeding of DRI charge.

5.2.3 While using 100 percent DRI in the charge,the ‘hot heel’ practice, in which 10 percent or moreof the metal from the prior heat, plus some slagare retained in the furnace after tapping, shouldbe adopted. The DRI is then continuously fedunder full power to this molten pool, and a good

foaming slag is formed which protects the refrac-tories from arc radiation. The foaming slagpractice also allows for use of a lower arc thatimproves electrical efficiency with no detrimentaleffect to wall and roofs.

5.2.4 Continuous charging of DRI in EAF resultsin significant benefits, such as less power ‘off’ time,lower heat losses, higher power input, improvedbath heat transfer and faster metallurgicalreactions, overlapping of melting and refiningoperations, etc. These effects continue to increasefurnace productivity and reduce both electrodeand power consumption relative to batch charg-ing. With larger proportions of DRI in thecharge, beyond the optimum value, the adverseeffects of gangue and incomplete metallisationtend to decrease the benefits of continuouscharging.

5.3 Continuous Charging of Hot DRI

Hot DRI ( from gas based processes > at a tempe-rature of around 700-SOO”C, can be continuouslycharged into an electric arc furnace. With a highDRI charge, this can result in 20 percent reduc-tion in electrode consumption, up to 35 percentincrease in the feed rate and around 30 percentincrease in productivity compared to cold DRIcharging practice.

6 EFFECT OF DRI ON EAF PERFORMANCE

6.1 Productivity

During batch charging of DRI, the chargingpractice is adjusted in such a way so as to elimi-nate one or more back charges. This results inincreased furnace productivity relative to all scrappractice with the optimum occurring at about15 percent for coal based DRl, or 20 percent forgas based DRI.

6.1.1 For continuous charging of DRI, in mostcases, the increase in productivity occurs. Thebest results are obtained with 45-50 percent DRIin the charge when productivity can go up by20 percent.

6.2 Power Consumption

In general, batch charging of DRI leads toincreased power consumption, the magnitude ofwhich is directly proportional to the amount ofDRI charged, the gangue content and the amountof unreduced iron oxides in it.

6.2.1 For continuously charged DRI heats ( with45-50 percent DRL in the charge >, power con-sumption can go up by about 10 percent ascompared to all scrap heats.

6.3 Electrode Consumption

In batch charged heats with a maximum of 15-20percent DRI in the charge, and where the usage

2

.of such DRI eliminates at’least’one b;ack charge,electrode consumpti,on is not likely to increase.

,6.3.1 However, in the continuously charged DRIheats, with 45-50 percent DRI in the charge, the,electrode consumption is likely to decrease by5-10 percent, as compared to all scrap practice,mainly due to the less number of electrode break-ages while using DRI.

6.4 Lime Consumption

Lime consumption definitely goes up while usingDRI depending on the gangue and phosphorousin DRI present and the levels of sulphur andphosphorous required in the steel. As a result,the usage of DRI leads to increased slag volumein an EAF.

6.4.1 All EAF shops planning to use DRI, there-fore, must make arrangements to handle thisincreased slag volume for smooth plant operations.Water cooled rakes and bigger slag boxes canhelp in coping up with this problem.

6.5 Refractory Consumption

When 15-20 percent DRI is batch charged, it hasvery little effect on the overall refractory consum-ption relative to all scrap practice.

6.5.1 During continuously charged DRI heats,from the end of scrap melting to tapping ofmetal, the electric arcs operate under open bathconditions and the furnace lining is exposed toheavy radiation attack. However, by suppressionof the arc radiation by creating a foamy slagduring continuous charging of DRI, it is possibleto keep the refractory consumption at more orless the same level as in conventional scrappractice. Foamy slag also protects the slag linerefractory from excessive attack.

6.5.2 The introduction of water cooled panelshas led to the development of improved refrac-tories, characterised by high thermal conductivityand high resistance to thermal shock for use inclose contact with the panels. DRI alwayscontains some unreduced iron oxide mainly inthe form of, Fe0 and can have a harmful effecton the furnace bottom and side walls but withbetter quality refractories now available, thisaspect also is taken care of.

6.6 Lowering in Levels of Residual Elements

Use of DRI in the charge results in a decrease inthe level of residuals in steel. This is a straight-line relationship, higher the proportion of DRI,lower would be the level of these elements insteel. This ultimately leads to improved coldworkability of steel especially pertaining to coldrolling and deep drawing operations.

IS i28bs.I 1989

SECTION 2 MELTING CHARACTERISTICSOF DRI IN BASIC OXYGEN FURNACES

(BOF)

7 GENERAL

This section of the standard prescribes the chara-cteristics of DRI when used as a coolant in basicoxygen furnace.

8 EFFECT OF DRI QUALITY

8.1 Metallization and Metallic Content

Sponge iron addition as coolant increases the ironoxide content of the final slag. For 15-30 percentreplacement, the increase in Fe0 over the normalheat is about 1’0 percent. Thus, in order tomaintain the Fe0 level in the slag within satis-factory limits, the sponge iron must be of highermetallization. The yield, which depends on theslag volume, is found to increase marginally atvalues of metallization about 90 percent where atlower values, the yield is expected to decrease.On an average, for every tonne of DR! an excessof 0’15 percent hot metal is required to keep theyield at the same level at metallization valuesbelow 90 percent. Replacement ratios of 1’2:1with scrap has been achieved at higher metalliza-tion values without affecting the blowing charac-teristics.

8.2 Gangue Content

The addition of gangue through DRI additionhas a two fold effect:

a) The slag volume increases, and

b) The lime consumption increases due toexcess silica input in the sponge iron.

The increase in slag volume depends on the silicacontent in the DRI and may need an increase inthe number of times deslagging is done.

8.2.1 The increase in lime consumption has beenfound to be of the order of 10 kg/t of steel for anincrease in DRI of 20 kg/t of steel. This againvaries with different percentages of silica in theDRI and the basicity of the bath desired.

8.3 Density and Bulk Density

The density/bulk density of sponge iron beinglow, will effect its storing, charging and dissolu-tion when charged into the converter. In relationto its dissolution behaviour two cases may beassumed:

a) Specific gravity of DRI < Specific gravityof liquid slag, and

b) Specific gravity of DRI > Specific gravityof liquid slag.

8.3.1 In case ( a ) the melting of DRI particleswould be hampered due to poor heat transfer to

3

IS I2668 : 1989

DRI particles from the molten slag/slag-metal-slagemulsion. It has been seen that increasing thedensity has a pronounced effect till values above3 gin/cm” are reached. Coarser particles ofdensity between 3 and 7 gm/cm3 tend to passrelatively fast, down to slag metal interface wherefaster melting is achieved. Melting of denser DRIpellets/briquettes ( 7 gm/cma ) has been found tocause prob!ems.

8.4 DRI Particle Size

It is found that -4 or -3 mm sizes are notsuitable for charging in converters as they giverise to flaming, if charged after the hot metal orduring the blow. Further, lower sizes lead toformation of ‘ice bergs’ and create problems inmelting.

9 EFFECT OF DRI ON OPERATINGPARAMETERS

The effectiveness of a material as a coolantdepends on its thermal properties and varies overa wide range. Iron ore, for example, is about 4’5times as effective as ferrous scrap as a coolant.

9.1 Coqling Power

The cooling power of sponge iron depends on thedegree of metallization and to a lesser extent ofgangue content. For 15-30 percent replacement,the cooling factor has been found to be about1’4 corresponding to a metallization level ofabout 85 percent. For higher replacements,.thecooling power of about 1’5 has been found withthe same DRI.

9.2 Basicity

The excess silica input from sponge iron must beconsidered particularly for its impact on the pathof slag formation and its consequent effect on theslag basicity. The average final basicity of thebath at 31-40 percent replacement and 41-60percent replacement ( DRI of 88 percent metal-lization and 3’4 percent silica ) have been foundto be 3’4 and 3’1 respectively. Increase in basicityat lower replacement level may be attributed tobetter lime dissolution due to higher Fe0 in slag.

9.3 Desulphurization

It is observed that the degree of desulphurizationis lower when DRl is used as a coolant. This ison account of the relatively lower basicity of theslag due to lower lime consumption and lowerbath temperature with increasing levels of DRI.But since most DRI contain very low levels ofsulphur and help in diluting the sulphur inputthrough hot metal, the above drawback is morethan offset.

9.4 Dephosphorization

It is seen that unlike the degree of desulphuriza-tion, the degree of dephosphorization is greater

4

when DRI is used. This is attributed to lowerbath temperature and high Fe0 content of theslag. The extent of dephosphorization is foundto increase up to about 60 percent DRI additionand decrease later on up to 100 percent replace-ment. This is due to higher bath temperaturesat higher DRI percentages.

9.5 Slag Volume

As too large a slag volume leads to slopping, theuse of sponge iron as a replacement to scrap intotal or in portion has to be examined in termsof chemical composition of the same. It isobserved that the number of times the deslaggingis done when DRI is used is almost twice thenumber when only scrap is used. This is due tothe extra gangue input with sponge iron in thecharge.

9.6 Blowing Time

It is noted that increased use of sponge ironrequires additional Fe0 units to take care of theadditional slag quantity due to increased ganguecontent in the sponge. The oxygen input fromsponge iron, approximately compensates theoxygen requirement for slag formation. Therefore,observed blow duration is only marginallydifferent in all the instances.

9.7 Hot-Metal Consumption

The consumption of hot-metal in BOF process.using sponge iron is very much affected byquantity of sponge iron in the charge. Thespecitic consumption of hot metal increases atthe rate of about 40 kg/t for an increase in DRIto 10 kg/t at 15-30 percent DRI level, 15 kg/t foran increase in DRI of 10 kg/t at higher DRLlevels.

This is a combined effect of metallization level,quantity of sponge iron, silicon in hot metal andamount of mixer slag carryover with the hotmetal.

10 OPERATING PRACTICES WITH DRICOOLANTS

10.1 Because of its sizing and chemical composi-.tion, DRl melts more rapidly in hot metal thaneither iron ore or scrap. Although, this situationmay permit decreased blowing time, care must betaken to avoid excessive amounts of DRI in theinitial charge since this can lead to excessiveinitial cooling of the hot metal and consequent‘cold starts’ and prolonged blowing times.

10.2 When DRI is used as the primary coolant,only a portion of the DRI should be charged intothe bottom of the vessel, with the remainderadded continuously after ignition has been raisedto about 1 450°C. The DRI charged during theblow should be at least of + 4 mm size, sincefiner material will be lost to the fume qollection

system. The - 4 mm material should be chargedinto the bottom of the furnace prior to the hotmetal. Bath temperatures can be maintainedessentially constant during the blow with DRIfeed rates of 6 to 7 kg/ma of oxygen with theexception of briquettes. DRI should not be fedat the end of the blow, since the DRI may floaton the slag or become coated with slag and failto melt into the bath. Similarly, if DRI is usedto cool a superheated bath, the heat usually mustbe re-blown in order to mix the DRl with thebath, quickly.

10.3 The method of addition of DRI to the BOFhas an effect on performance. The continuousfeeding of appreciable quantities of DRI tends tocool and stiffen the slag, especially late in theblow. The effect is significantly more pronouncedfor the low-density, finer sized pellets and lumpmaterials than for briquettes.

10.4 In certain cases, this chilling effect has ledto lower slag metal partitioning co-efficients formanganese, phosphorous, sulphur. Charging ofDRl into the BOF prior to hot-metal additionhas shown no effect on the partitioning co-effici-ents up to 100 kg/t of steel.

10.5 Non-briquetted DRI can absorb considerableamounts of moisture. The DRI intended forcharging into the bottom of the BOF prior to hotmetal addition should be kept free from moistureto avoid explosions in the vessel or gas collectionsystem. Damp DRI is to be charged on top ofhot metal with caution.

10.6 When large amounts of DRI are to be added,low carbon material is advantageous in avoidingexcessive quantities of waste gas. The high bulkdensity of DRI plus its case of handling relativeto that of scrap offers advantages for automatedBOF charging systems.

SECTION 3 MELTING CHARACTERISTICSOF DRI IN ( CUPOLA FURNACES )

FOUNDRY

II GENERAL

11.1 This section of the standard prescribes themelting characteristics of DRl in cupola furnace.

I2 DRI MELTING IN CUPOLA

12.1 DRI can replace a part of steel scrap and/orpig iron charged to cupola furnace. It is well knownthat one of the major disadvantages of Indianpig iron is that it contains titanium in the rangeof 0.095 to 0’200 percent because there is an ap-preciable amount of titanium oxide in the ore andcoke used in the blast furnace in India. On. theother hand DRI does not contain any titanlum.Although the effect of titanium can be neutralisedby the addition of misch metal or cerium, thisinvolves an extra cost. It has been estimated thatadditional requirement of innoculants for 0’1

IS I2668 : 1989

percent titanium will be approximately l/2 to.I kg/t. Savings of innoculants will be still moresince DRI contains lower levels of sulphur.

DRI can be used advantageously to bring downthe carbon content of certain cast iron gradeswhich would otherwise have an unfavourablecarbon to silicon ratio.

12.2 Up to 25 percent DRI can be used in acupola charge ( to replace pig iron ) withoutcausing any significant operational difficulties.With higher percentages of DRI in the charge,however, the permeability of the charge decreasesand as a result, the gas flow experiences greaterresistance. This causes increased air pressure inthe wind box and decreased air flow.

12.3 DRI should not be included in the first 6 to8 charges if added in the earlier charges, it maycause difficulty in tapping out the liquid iron.This also ensures that when DRI reaches meltingarea, its temperature is sufficiently high.

12.4 For use in cupola, briquetted or lump DRIshould be charged. Small DRJ pellets can causeoperating problems because they trickle downthrough voids and melt ahead of the materiallayer with which they were charged, causing thatlayer to be depleted of DRI pellets. The slagvolume of the cupola furnace increases withincreasing amounts of DRI in the charge. With25 percent DRI, the slag volume can go up bylo-15 percent, consequently the smelting capacityof the cupola is expected to go down, dependingupon its gangue content.

12.5 Carbon and silicon contents of the cast ironalso go down with the usage of DRl, but the rateof decrease in case of the later is more rapid.Therefore, extra ferro-silicon additions will haveto be made to make up the same.

SECTION 3A MELTING CHARACTER-ISTICS OF DRI IN INDUCTION

FURNACE

I3 GENERAL

13.1 This section of the standard prescribes themelting characteristics of DRI for melting ininduction furnace.

13.2 With the development of solid state powersupply, and inverters for supplying maximumpower and maintaining throughout, during theentire melting time, the efficiency of moderninduction furnaces has gone up beyond 95 percentcompared to SO-85 percent ten years ago. Theenergy consumption in large main frequencyinduction furnace employing liquid heel meltingis below 600 kWh/t in modern furnaces.

13.3 Induction melting of DRl imposes someguidelines for successful and trouble free melting.

*5

18 12668 : 19#39

Firstly, unlike scrap 100 percent DRI meltingneeds a heel of melt occupying at least about30 percent of the furnace capacity. Secondly,unlike other furnaces, induction furnace does notprovide the adequate environment for reductionof the un-reduced Fe0 in the DRI. Thirdly, thegangue of the DRI with un-reduced Fe0 formsslag cover over the melt, and thus occupies auseful fraction of the furnace volume. Fourthly,DRI addition to the molten pool should becontinuous and balanced with the rate of energyinput to the furnaces. The fast melting of DRIrequires that DRI added should dip immediatelyin the slag cover and melts at the slag-metalinterface. For smooth, fast and efficient meltingof DRI in induction furnace, some particularphysico.chemical charscteristics arc required.These characteristics are discussed in 14 and 15.

14 PHY SICO-CHEMICAL CHARACTER-ISTICS OF DRI

15 CHEMICAL CHARACTERISTICS14.1 Apparent Specific Gravity

The melting of DRI particles should take placedipped in the slag at the slag-metal boundary line.

15.1 Equivalent M&diieation

Therefore, the apparent specific gravity of the Equivalent metallization rather than metallizationz;rstli;F should be higher than the specific gravity should be considered to include the effect of

i* carboncontent of the DRI ( see IS 10812 : 1984 ).

14.2 True Specific Gravity and Porosity 15.2 Metallic Content

Apparent specific gravity, porosiiy, and truespecific gravity may be determined in accordancewith the method8 given in IS 11348 : 1985 and,IS 11896 : 1986.

14.3 Aggregate of DRI

DRI for induction melting should be of goodquality, evenly sized, having low dust ( -5 mmsize fraction,), good strength and high metalliccontent.

14.4 Size Distribution

Close size range with minimum of dust should beused. The upper permissible limit may be negoti--able between buyer and seller.

14.5 Bulk Density

Higher bulk density is desirable. Bulk densitymay be determined in accordance with IS 5842 :1986.

The true specific gravity provides a good insightabout the metallic iron content of the DRI andthe gangue alongwith the un-reduced Fe0 content.Combined with the apparent specific gravity, itcan also provide insight about porosity accordingto the formula :

Porosity, “/oTrue sp gr= - Apparent sp gr

True sp grX IO3

15.2.1 It is important to have a DRI with highmetallic iron content and low gangue content.

15.2.2 The total ( SiOZ $ AlsOs > gangue contentof the DRI forms slag. As very little fluxingagent or addition is practiced in induction melting,the proportion of these two oxides shouldmatching, as far as possible, A1303/Si02 Q 1 is.recommended. The total A1,O1 + SiOo should be:below 5 percent.

9

6

I_-__ -..___ _~_ ._ ~.

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Dot : No. SMDC 36 ( 3408 1

Amendments Issued Since Publication

Amend No. Date of Issue Text Affected

BUREAU OF 1NDlAN STANDARDS

Headquarters:

Manak Bhavan, 9 Bahadur Shah Zafar Marg, New Delhi 110002Telephones : 331 01 31, 331 13 75

Regional Ofhces:Central : Manak Bhavan, 9 Bahadur Shah Zafar Marg

NEW DELHI 110002

Eastern : l/14 C. 1. T. Scheme VII M, V. 1. P. Road, ManiktolaCALCUTTA 700054

Northern : SC0 445-446, Sector 35-C. CHANDlGAKH_160036

Southern : C. I. T. Campus, IV Cross Road, MADRAS 600113

Western : Manakalaya, E9 MIDC, Marol, Andheri (East)BOMBAY 400093

Telegrams : Manaksanstha(Common to all Offices)

Telephone

331 01 31331 13 75

36 24 99

t 2 3 1641 1843

(41 24 42

6 32 92 95

Branches : AHMADABAD. BANGALORE. BHOPAL. BHUBANESWAR.GUWAHATI. HYDERABAD. JAIPUR. KANPUR. PATNA.TRIVANDRUM. \

Printed at Saini Priqters, Delhi, India

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