AUTHORS: Abdul Malek Omar, Thandayithabani a/lAppasamy and Francesco Memoli Perwaja Engineering Sdn Bhd, Perwaja Steel Sdn Bhdand Techint SpA

Perwaja Steel Sdn Bhd is one of the major Malaysiansteel companies for the production of wire rods and

bars. The plant currently operates two 75t DC EAFs, andone was revamped with the Techint KT Injection Systemin 2003, designed to increase the proportion of DRImelted and reduce consumables.

An average DRI feeding rate of 40kg/min/MW hasbeen achieved, a value considered high for this size offurnace, which is now able to charge up to 100% DRI.The multipoint oxygen lancing and combined carbonpowder injection have also improved the foamy slagpractice, increased the efficiency of energy transferred tothe steel bath, resulting in electrical energy savings ofmore than 10% and increased productivity by 5%.

PERWAJA STEEL PLANTConceived as the country’s first national steel plant in1982, Perwaja’s first aim was to ensure self-sufficiencyand relieve the country of the vagaries of world supplyand demand for steel. The site at Kemaman, located onthe east coast, fulfilled many important criteria. First,there is an abundance of natural gas from Terengganu’soffshore gas fields. Second, it is very close to an electricalsupply, and finally, the site is situated next to the coastwhich could be developed into a deep water port forunloading large quantities of iron ore. The Kemamancomplex started operation in 1985, and in 1990 thedirect reduction plant was upgraded. The HYL III processadopted has doubled the annual capacity to 1.2Mt/yr ofcooled and screened DRI.

MELTSHOP AND EAFThe meltshop houses three AC EAFs, which are currentlybeing revamped, and two DC EAFs, numbers 4 and 5. TheKT Injection System was installed on furnace 4 to reduceenergy consumption and improve productivity. Scrap is

The installation of multipoint carbon and oxygen injectors, coupled with new melting practices toimprove slag foaming has increased DRI charge capability to 100%, increased productivity andreduced electrical energy and refractory consumption.

Increased DRI feeding rate for a DC EAF

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charged by scrap bucket and DRI is continuously fedthrough the furnace roof by a conveyor belt system. Thefurnace is equipped with a 60MW DC transformer, a700mm diameter electrode, one upper shell of 5,380mmdiameter, with two lines of water cooled panels in theupper shell (12 panels on the upper line and 18 panels onthe lower line), and one bottom shell, 5,800mm diameterequipped with an eccentric bottom tapping (EBT) system.

PROBLEMS TO BE SOLVEDBefore the installation of the KT system, the furnace wasequipped with a standard consumable lance manipulatorinserted through the door, with two oxygen lances andone powder carbon lance. One of the problems with thisfurnace was the impossibility of raising the DRI feedingrate as high as desired because of the formation of DRI‘icebergs’, which impeded melting, and lowered the bathtemperature, causing big delays during tapping. Thecause of the icebergs was the location of the DRI feedingpoint, which was placed on the EBT-side of the furnace, atapproximately 2 o’clock.

For a conventional AC furnace using DRI pellets addedfrom the roof, the aim is to direct the pellet flow towardsthe centre of the three electrodes where there is themaximum power input. However, with DC EAFs theelectrode occupies the centre of the furnace so the DRIfeeding point must be positioned between the electrodeand the furnace wall, thus creating a cold spot. The DRIfeeding rate is measured in kg DRI charged per minuteand per MW of active power. The maximum feeding ratefor this furnace before the KT revamp was30kg/min/MW, thus in 46 minutes the furnace was onlyable to charge 65t of DRI with an average active power of49MW. Above 30kg/min/MW, the formation of icebergsbecame critical, causing operational problems.

THE SOLUTION: THE KT INJECTION SYSTEMThe main objective in installing the system was to increaseDRI consumption, and after only six months of operationthe furnace was achieving a monthly average DRI feedingrate of 38.8kg/min/MW (74.2t of DRI charged in 33

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minutes with an average active power of 57.9MW).This result has been achieved by installing:

` Four KT oxygen lances` Two KT carbon injectors` A new oxygen and gas valve stand (see Figure 1)` A revamped powder carbon dispenser(see Figure 2)` New hardware and software for KT Injection System

automation

There are three main reasons for this improvement: oneKT oxygen lance is directed on the DRI feeding point toprovide additional energy input and better bath stirringso preventing the formation of icebergs (see Figure 3);energy input in the furnace is more balanced as there aremultiple oxygen injection points around the shell directedinto the liquid bath (see Figure 4); and average activepower is raised thanks to the better foamy slag formedwith the carbon injectors.

BENEFITS OBTAINEDDRI percentage charged Overall this has beenincreased by more than 10% and the number of heatsusing 100% DRI has also been increased. This isparticularly beneficial as the DRI price is lower than thescrap price in Malaysia.

Electrical energy This has decreased by more than100kWh/t (22%). By increasing the amount of oxygeninjected into the bath a conversion from electrical tochemical energy was expected at a rate of about 3 to 4equivalent kWh/Nm3 of oxygen, so the maximum benefitexpected was about 60kWh/t. An additional 40kWh/tarose from the furnace efficiency increases (reduction ofpower-on time plus increase in furnace tapping weight)which have resulted in an increase in productivity. Seealso Figure 5 showing pre and post KT total energyconsumption.

rFig.1 Oxygen valve stand

rFig.5 Total energy consumption

rFig.2 Pneumatic carbon injection system

rFig.3 KT oxygen lances in pilot flame mode

rFig.4 Lance installed at slag line

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Electrode consumption A reduction of 20% hasoccurred which is related mainly to the improvementmade to the foamy slag operation. The depth of foamyslag during DRI melting can rise to 1,500mm whichprovides an ideal covering of the electrode tip, sopreventing graphite oxidation. Here, too, theproductivity increase achieved is very significant,because the active power increase and oxygen injectionincrease are normally factors which increase electrodeconsumption.

Consumable lances Consumable lances are no longerrequired.

Heat size This has been increased by four tonnes (6%),thanks to the increased power input. Unfortunately itcannot be increased further because of crane andbuilding restrictions.

Power-on time A decrease in power-on time of 25% isa direct consequence of the increase in furnace powerinput achieved through a combination of the additionalchemical energy and the increase of active power ofabout 10MW, thanks to the foamy slag protection to thewall bricks and panels.

Refractory consumption This has reduced by 56%thanks to reduced radiation resulting from the betterfoamy slag practice, despite the active power increasing

by more than 20%. The furnace campaigns in terms ofheats produced have doubled and there has been adecrease in plant interruptions for gunning. Also, specialbricks are no longer required for the refractory liningand special care of the furnace conductive bottom is nolonger a critical item for the operation of the furnace.

Table 1 gives a resume of the consumption figures andother furnace data from start-up in January 2003 untilJune 2003, and compared to the previous data in 2002.

THE NEW MELTING PROCESS With such a high DRI % and high rate of oxygeninjection, it might be expected that slag FeO wouldsignificantly increase. This is not the case. The slagcomposition (wt%) at Perwaja No. 4 is typically, FeO =29.6, CaO = 33.6, SiO2 = 15.8, MgO = 7.6 and MnO =0.85. This composition is indicating a fairly low binarybasicity index (CaO/SiO2) of about 2.1. (Note there is noDololime addition and lime charged per heat is about40kg/t).

The amount of slag generated per heat is about 120kg/t,considering normal components like the normal refractorywear and DRI of a composition shown in Table 2.

For a typical tapping temperature of 1,610°C and tapcarbon contents between 0.04–0.07%C, the FeO addedto the slag with the DRI is around 2,500kg and the FeOcontained in the slag is around 2,650kg. This means thatthere is a minimal production of FeO generated by

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Parameter Units Dec 2002 Feb 2003 Apr 2003 Jun 2003 Difference Dec to JuneDRI in the charge % 77 82.0 87.5 87.65 +10.65Electrical energy EAF kWh/tls 597 510 504 463 -134Active power MW 49.0 53.8 56.4 57.9 +8.9Oxygen Nm3/tls 30.5 47.0 44.0 45.6 +15.1Natural gas Nm3/tls 0 6.0 5.0 5.4 +5.4Electrode consumption Kg/tls 1.30 1.2 1.14 1.05 -0.25Powder carbon Kg/tls 31.0 36.0 32.8 27.8 -3.2Anthracite Kg/tls 6 6 5.6 8.5 +2.5Heat size tls 71.0 73.0 74.7 75.15 +4.15Power-on time mins 52.0 41.5 40.0 36.0 -16.0DRI feeding time mins 46.0 40.0 38.0 33.0 -13.0Gunning material Kg/t 6.5 5.0 4.3 3.5 -3.0Refractory bricks Kg/t 1.22 1.12 0.98 0.53 -0.69DRI metallisation % 95.4 — — 96.33 + 0.93DRI carbon content % 2.04 — — 2.18 + 0.14

DRI charge 74.2 t/heat Carbon 2.18% SiO2 1.43% MgO 0.63%Metallisation 96.33% FeO 3.34% Al2O3 0.15% S 0.005%Total Iron 90.87% Gangue 4.32% CaO 2.09% P 0.035%

rTable 1 Furnace operating data

rTable 2 DRI useage and composition

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oxidation of the liquid bath of about 2kg/t. This isinsignificant considering the very important productivityincreases.

Figures 6 and 7 show the melting pattern andoxygen/carbon consumption for typical heats.

The explanation relates to the very efficient carboninjection process and is shown in the 10 steps below.

PLANT BENCHMARKING To understand the improvement at Perwaja it isinteresting to compare these results with some otherEAFs using a high percentage of DRI in the charge (seeTable 3). Ten furnaces considered for this comparisonare located in seven different countries, produce at least400,000t/yr per furnace [total production is 7Mt], andcharge at least 50% DRI continuously from the roof.The plants have officially approved all the datareproduced here and some of them are considered asreference plants worldwide for DRI melting.

It is always difficult to compare data from differentplants, mainly because of differences in steel grades,type of production, furnace sizes, operating practicesand so on, however, some general comparisons can bemade.

Perwaja has the lowest electrical consumption, thehighest % DRI charged and the highest feeding rate.For an even better comparison this table can be re-calculated to equalise the tapping temperature to1,645°C and the percentage of DRI in charge to 71% bygiving standard values to the ratios kWh/°C andkWh/% DRI of 0.35 and 1.69 respectively (see Table 4).These standard values are the average of the valuesconsidered in each one of the ten plants for suchconditions of DRI in charge.

It is possible then to calculate the total energy inputby giving a standard value to O2 of 3.2kWh/Nm3, theaverage of values considered in each one of the plants,and net productivity on power-on time (see Table 5).

Perwaja is the plant consuming less energy and withthe second highest net productivity, the plant justbehind for consumption is plant D, which has a totalenergy consumption still below 600kWh/tls. Plant Hhas higher net productivity, but with a very high energyconsumption. Plants D and H have a lower specificpower per tonne charged, which is explained by a lowerbath surface: steel volume ratio.

CONCLUSIONSThis benchmark study confirms that by using the KTInjection System to improve oxygen injection efficiencyand produce a foamy slag practice on furnaces withhigh DRI charge, it is possible to reach high levels ofproductivity without compromising the FeO in the slagand yield and with big benefits in terms of variable costreduction. MS

ACKNOWLEDGEMENTSExcellent results are always achieved thanks to the hardwork of the people involved. Thanks to all of them fortheir support and for all their excellent ideas which havecontributed to the success of this installation.

Increase of production requires DRI feeding rate up to 157t/h = 40kg/min/MW

]Problem of DRI iceberg formation during melting process

]This needs oxygen injection for additional chemical power and bath stirring

]Oxygen is injected deeply in the steel bath with KT oxygen lances

]Powder carbon injection is used to control and reduce FeO in the slag

]Carbon is injected at the steel/slag interface with KT carbon injectors

]High reduction of FeO and production of CO from iron oxide reduction

]Improvement of foamy slag operation with a slag depth up to 1,500mm

]Increase in active power thanks to good arc and wall covering with slag

]Significant increase in DRI feeding rate due to a higher total power input

rFig.6 Energy and DRI rates during a heat

rFig.7 Oxygen, natural gas and powder carbon consumptions

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Abdul Malek Omar is Operations Manager, PerwajaEngineering and Thandayithabani a/l Appasamy isSteel Plant Manager, Perwaja Steel Sdn Bhd, Malaysia.Francesco Memoli is Technology Service Manager,Techint SpA, Italy)

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PlantParameter Units Perwaja A B D E F G H ITotal Charge t 84.7 87 87 116 137 173 190 230 220DRI % 87.7 72 58 65 75 46 75 79 82Heat size tls 75.2 79.7 79.4 105 117 150 160 190 190Yield % 88.8 91.6 91.3 90.5 85.4 86.7 84.2 82.6 86.4Power-on time min 36 45 36 47 70 87 87 84.1 106Av. active power MW 57.9 62.7 68.8 69.7 55.5 69.3 71.7 88 66.1Electricityconsumption kWh/tls 462.9 590 520 520 553 670 650 649 615Oxygenconsumption Nm3/tls 45.6 20 30 19 25.6 27 20 26.3 18Carbonconsumption kg/tls 27.8 6 6 14 12 24 25 12.8 12FeO slag content % 29.6 31 32 29 33 23 32 35 28Tapping temp °C 1,610 1,650 1,650 1,662 1,640 1,650 1,660 1,643 1,640DRI metallisation % 96.3 94.4 94.4 95 92.3 91.7 93 93 92Total iron in DRI % 90.9 91.5 91.5 93 91.4 90.6 90.8 91 89.11DRI carbon content % 2.18 2.1 2.1 2.1 2.8 0.14 2.1 2.1 1.8DRI feed rate kg/min/MW 38.8 27 27.2 30.9 29.4 15 25.1 26.5 24.8DRI charging time min 33 37 27 35 63 77 79 78 110

PlantParameter Units Perwaja A B D E F G H I

Power-on time min 33.9 44.9 37.4 47.9 69.1 91.6 86.0 82.2 106.0Av. active power MW 57.9 62.7 68.8 69.7 55.5 69.3 71.7 88.0 66.1Electricity consumption kWh/tls 435.1 588.2 540.7 529.5 545.9 705.4 642.8 634.5 615.0Oxygen consumption Nm3/tls 45.6 20.0 30.0 19.0 25.6 27.0 20.0 26.3 18.0Carbonconsumption kg/tls 27.8 6.0 6.0 14.0 12.0 24.0 25.0 12.8 12.0FeO slag content % 29.6 31.0 32.0 29.0 33.0 23.0 32.0 35.0 28.0DRI feeding rate kg/min/MW 38.8 27.0 27.2 30.9 29.4 16.2 25.1 26.5 24.8

Net productivity t/h 133.1 106.5 127.3 131.6 101.6 98.3 111.6 138.7 107.5Total consumption kWh/t 581 652 637 590 628 792 707 719 673Specific power MW/t 0.68 0.72 0.79 0.60 0.40 0.40 0.38 0.38 0.30

rTable 3 Benchmark study of high DRI consumption EAFs

rTable 4 Data standardised to 1,645°C and 71% DRI

rTable 5 Data standardised to 3.2kWh/Nm3 O2

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