optimization of steel making process

THE MANUFACTURE OF STEEL
Steel refers to any iron-carbon alloy, although steels usually contain other elements as well. In New Zealand steel is made by BHP NZ at Glenbrook, where about 90% of New Zealand’s annual steel requirements are produced.Iron occurs mainly as oxide ores, though it is also found in smaller quantities as its sulfideand carbonate. These other ores are usually first roasted to convert them into the oxide.On a world scale the most important ore is haematite (Fe2O3), but in New Zealand thestarting materials are magnetite (Fe3O4) and titanomagnetite (Fe2TiO4). The oxides are reduced with carbon from coal, through the intermediate production of carbon monoxide.The carbon initially burns in air to give carbon dioxide and the heat, which is necessary forthe process. The carbon dioxide then undergoes an endothermic reaction with morecarbon to yield carbon monoxide: C + O2 CO2 H = -393 kJ mol-1

C + CO2 2CO H = +171 kJ mol-1 The oxide ores are then principally reduced by the carbon monoxide produced in thisreaction, the reactions involving very small enthalpy changes: Fe2O3 + 3CO Fe3O4 + 4CO 2Fe + 3CO2 3Fe + 4CO2 H = -22 kJ mol-1 H = -10 kJ mol-1

In conventional ironmaking this reduction occurs in a blast furnace, whereas in New Zealand a rotary kiln is employed for direct reduction, followed by indirect reduction in an electric melter. This technology is used because the titanium dioxide present in the ore produces a slag which blocks conventional blast furnaces as it has a high melting point. The iron produced in this way always contains high levels of impurities making it very brittle. Steel making is mainly concerned with the removal of these impurities. This is done by oxidising the elements concerned by blowing pure oxygen through a lance inserted into the molten alloy. The KOBM (Klockner Oxygen Blown Maxhutte) used for this in New Zealand is unusual because oxygen is also blown through holes in the base of the converter. The oxides produced are either evolved as gases, or combine with limestone to form an immiscible slag which floats on the surface of the liquid metal and so is easily separated. INTRODUCTION Steel is a term given to alloys containing a high proportion of iron with some carbon. Other alloying elements may also be present in varying proportions. The properties of steel are highly dependent on the proportions of alloying elements, so that their levels are closely controlled during its manufacture. The properties of steel also depend on the heat treatment of the metal. Steel is by far the most important metal, in tonnage terms, in the modern world, with the annual global production of over 700 million tonnes dwarfing the approximately 17 million tonnes of the next most prolific, aluminium. The low price and high strength of steel means that it is used structurally in many buildings and as sheet steel it is the major component of
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motor vehicles and domestic appliances. The major disadvantage of steel is that it will oxidise under moist conditions to form rust. A typical steel would have a density of about 7.7

The New Zealand production of about 650 000 tonnes per year at Glenbrook, 40 km southwest of Auckland, is minimal on a world scale, being less than 1% the output of the major producing countries. However, the two main stages in the production of steel in New Zealand are both unusual, making the overall process almost unique.

THE MANUFACTURING PROCESS Iron ore is converted to steel via two main steps. The first involves the production of molten iron and the second is that of actual steel manufacture. The details of these steps are outlined below. Step 1 - The production of molten iron The Primary Concentrate is mixed with limestone and coal and heated. The iron oxides are reduced in the solid state to metallic iron, which then melts, and the impurities are removed either as slag or gas. The production of molten iron The multi-hearth furnaces There are four multi-hearth furnaces, each of which feeds a rotary kiln. The furnaces preheat the materials fed into the rotary kiln and reduce the amount of volatile matter present in the coal from about 44% to about 9%. This is important because the large volumes of gas produced during the emission of the volatile matter would otherwise interfere with the processes in the rotary kiln. There are 12 hearths in each furnace and the feedstock passes down through these. In the first three hearths, hot gases from the lower stages preheat the material in the absence of air to about 450oC. Air is introduced in hearths 4 to 9 to allow combustion of the volatile
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material, so as to increase the temperature to about 650oC. The supply of air is adjusted to control the percentage of residual volatiles and coal char in the product. In the final hearths (10 - 12) the char and the primary concentrate equilibrate and the final temperature is adjusted to 620oC. The total residence time in the multi-hearth furnace is 30 - 40 minutes. The multi-hearth furnaces also have natural gas burners at various levels. These are used to restart the furnace after shutdown and to maintain the temperature if the supply of materials is interrupted. The waste gas from the multi-hearth furnace contains water vapour and other volatileompounds from the coal (e.g. carbon dioxide, carbon monoxide and other combustion products) as well as suspended coal and primary concentrate dust particles. These solids are removed and returned to the furnace. This gas along with gas from the melter (mainly carbon monoxide) is mixed with air and burnt. The heat so produced is used to raise steam for the production of electricity. As well as providing a valuable source of energy, this combustion of the waste gases is necessary to meet emission controls. The rotary kilns There are four rotary kilns. Here about 80% of the iron of the primary concentrate is reduced to metallic iron over a 12 hour period. The kilns are 65 m long and have a diameter of 4.6 m, closely resembling those used for cement production. The pre-heated coal char and primary concentrate from the furnaces is mixed with limestone and fed into the kiln. In the first third of the kiln, known as the pre-heating zone, the feed from the multi-hearth furnace is further heated to 900 - 1000oC. This increase in temperature is partly a result of the passage of hot gases from further along the kiln and partly a result of the combustion of the remaining volatile matter in the coal. The last two-thirds of the kiln is known as the reduction zone, and

is where the solid iron oxides are reduced to metallic iron. In this region the air reacts with the carbon from the coal to produce carbon dioxide and heat: C + O2 CO2 H = -393 kJ mol-1 The carbon dioxide then reacts with more carbon to produce carbon monoxide, the principal reductant, in an exothermic reaction: C + CO2 2CO H = +171 kJ mol-1 Some of the carbon monoxide burns with the oxygen to produce heat, whilst the remainder reduces the magnetite1 to iron in a reaction that is almost thermochemically neutral. 2CO + O2 Fe3O4 + 4CO 2CO2 H = -564 kJ mol-1 H = -10 kJ mol-1

3Fe + 4CO2

1Magnetite can be regarded as 1:1 combination of wustite (FeO) and haematite (Fe2O3). The separate reduction processes from these two components are:

FeO + CO Fe2O3 + 3CO

Fe + CO2 ?H = -10 kJ mol-1 2Fe + 3CO2 ?H = -22kJ mol-1

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In a similar manner the titanomagnetite is reduced to iron and titanium dioxide. The product from the kiln is known as Reduced Primary Concentrate and Char (RPCC) and is nearly 70% metallic iron. Unchanged ore, unburnt char, titanium oxide and coal ash accout for the rest of the mixture. This hot (950oC) mixture is then discharged to the melters. In this latter part of the kiln the temperatures can reach 1100oC. Higher temperatures would lead to an increase in the percentage reduction of the concentrate, but unfortunately they also produce accretions of solids on the walls of the kiln which reduce its efficiency and damage the refractory lining. Air is injected into the kiln at nine evenly spaced points along its length. In the kiln the limestone is converted to lime (calcium oxide) which then acts as a flux in the melters. The waste gases from the kiln are scrubbed to remove solids and burnt to remove any flammable compounds before being vented to the air. There are currently plans to use the energy from this process for the co-generation of electricity. The melters The hot reduced primary concentrate from the kilns is fed into two melters. These are about 27 m by 12 m and hold a total charge of 1000 tonnes of iron and 900 tonnes of slag. Lime and primary concentrate may also be added to control the composition of liquid iron in the melter. The lime reacts predominantly with sulfur from the coal. Power is supplied by three continuously renewed carbon electrode pairs, which pass a large three-phase a.c. current through the contents of the melter. The potential difference across an electrode pair is 300 V and current is typically 60 kA. The temperature in the melters rises to 1500oC, and this causes the reduced primary concentrate to melt and form two layers. The lower layer is of molten iron with some elements, especially carbon, dissoved in it. The upper layer is liquid oxide slag and this supports the solid feed. During the melting process reduction of the remaining iron ontaining compounds occurs. The electrodes are immersed in the molten slag and, because ts electrical resistance is much greater than that of iron, most of the heat is generated in this layer. One problem affecting the melters is that the refractory lining is subject to attack by the molten slag. In order to combat this, the solid feed in introduced around the perimeter of the melter to provide a protective barrier. The gas produced in the melter is mainly carbon monoxide and this presents both toxic and explosion hazards. It is recovered and burnt for

co-generation of electricity. Molten iron and slag are both tapped periodically by drilling a hole through the refractory sidewalls at special tapping points, higher up for the slag and lower down on the opposite side for the molten iron. The slag from the melter is approximately 40% TiO2, 20% Al2O3, 15% MgO, 10% CaO and 10% SiO2 with smaller amounts of sulfides and oxides of iron, manganese and vanadium. Step 2 - Steel making Vanadium recovery Before conversion into steel, vanadium is recovered from the molten iron. This is done irstly because of the value of the vanadium rich slag produced (15% vanadium as V2O5) and econdly because a high vanadium content can make the steel too hard. n the vanadium recovery unit a ladle containing 75 tonnes of molten iron has oxygen blown ver the surface, where it oxidises silicon, titanium, manganese and vanadium to form a slag hat floats on the surface. At the same time argon is blown through the molten metal to stir it. hen the composition of the molten metal has reached the required vanadium specification, he slag is scraped off, cooled and crushed. Additional advantages of this pre-treatment are that it causes the molten metal to reheat, so permitting temperature control, and, if required, the procedure can be modified by the addition of lime to reduce sulfur levels. The Klockner Oxygen Blown Maxhutte process The KOBM steel making process, like most modern processes involves oxidising dissolved impurities by blowing oxygen through the molten metal. The KOBM is unusual in that it blows oxygen through the bottom of the furnace as well as through a lance inserted from the top. This type of furnace was selected for Glenbrook becasue of its capacity to cope with high levels of titanium and vanadium coupled with its very fast turn round time. The disadvantage of this type of furnace is that it is technically rather more complex than those that are blown only by a lance. The KOBM is initially charged with about 6 tonnes of scrap steel. 70 tonnes of molten metal from the vanadium recovery unit is then added. Oxygen is then blown through six holes in the base of the furnace, at a total rate of about 1500 litres per second. Oxygen is also blown through a lance inserted from the top of the furnace at a rate of over 2500 litres per second.
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The oxygen oxidises the elements other than iron (including any free carbon) to their oxides. In this way contaminants are removed as the oxides form a slag which floats on the surface of he molten metal. Powdered lime is blown in to help with slag formation and this particularly educes the levels of sulfur and phosphorous by combining with their acidic oxides. Due to ts low melting point, iron(II) sulfide (FeS) is particularly harmful to the high temperature roperties of steel. So sulfur level must be reduced before further processing. Typical levels f the major elements in the metal fed into the furnace and in a typical steel are shown in he molten iron is analysed just before being added to the furnace and the temperature taken. This determines the length of the oxygen blow and it also to a certain extent affects the amount and composition of the scrap added. The length of the oxygen blow required is also judged by moitoring the CO:CO2 ration in the gases from the furnace. Blow times vary, but 15 minutes would be typical. During the oxygen blow the temperature would typically rise from 1500oC to 1700oC owing to the exothermic reactions that are occuring. he slag is firstly tipped off and, after cooling, it is broken up so that the iron trapped in it an be recovered

magnetically. The slag, which contains sulfur and phosphorous and has a igh lime content, is then sold for agricultural use. Aluminium, which removes excess issolved oxygen, and alloying materials, such as ferro-silicon and ferro-manganese (which ncrease the hardness of the steel) are added at this point so that they are well mixed as the olten metal is tipped into a ladle. The whole cycle in the KOBM takes about 30 minutes. he Glenbrook site also has an electric arc furnace for steel making, the feed for this being mainly scrap steel. Ladle treatment The final stage of steel making is the ladle treatment. This is when fine adjustments are made o bring the composition of the molten steel, from either furnace, into line with the required omposition. The bulk of the alloying elements are added in the furnace and, after blowing rgon hrough the molten metal to ensure homogeneity, the temperature is measured and a ample removed for analysis after stirring. The analysis by optical emission spectrometry, hich measures the levels of 15 elements, takes about five minutes. Alloying materials are dded to adjust the composition. If the metal requires cooling, scrap steel is added. If the emperature is too low, aluminium is added and oxygen blown through. When complete argon is blown through once again to ensure mixing and the ladle to the continuous casting machine. Here it is cast into slabs of 210 mm thickness and a width of between 800 and 1550 mm. This slab is cut into lengths of from 4.5 m to 10 m and sent for further processing. Most of the production is converted to steel coil.
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ANCILLARY PROCESSES The major ancillary processes carried out by the plant involve the supply of raw materials, the processing of waste and the production of electricity. Even though waste heat is used to co-generate electricity on site, this only amounts to about 12½% of total consumption, so large amounts of electricity are purchased. Natural gas is also used as a minor energy source and this is brought to the site from Taranaki through a pipeline. Iron primary concentrate mining This is obtained from the ironsand mine at Waikato North Head and is a mixture of magnetite (Fe3O4) and titanomagnetite (Fe2TiO4), and is thought to originate from the volcanic eruptions of Mt. Taranaki. It is mined by standard open cast methods and suspended as an aqueous slurry. The ironsand is a low grade ore, with sand and clay being the major impurities. The concentrated material typically contains 58% iron (i.e. 80% Fe3O4), 8% TiO, 4% Al2O3, 3½% SiO 2 and 3% MgO by mass with smaller quantites of calcium, phosphorous and sulfur. Initial separation is effected by magnetic separators which rely on the magnetic properties of magnetite and tintanomagnetite. Further concentration is then achieved by gravity separators because these minerals are denser than most impurities. The slurry is then pumped though a 21 km long, 200 mm diameter pipeline to Glenbrook at a rate of 300 tonnes per hour. Here it is dewatered to a moisture level of ca. 5% and discharged onto a stockpile. Annual production of this material, known as Primary Concentrate (PC), is about 1.2 million tonnes. Coal preparation This is sub-bituminous B and C grade mined by both open cast and underground methods at Huntly. The annual consumption of 750 000 tonnes per year is delivered by rail to Glenbrook. Here it is stored on a stockpile and then blended with primary concentrate as the feedstock for the multihearth furnaces. The aim of the blending is to achieve a consistent carbon-iron ratio.

Scrap steel recycling Much of the scrap steel used is waste from the production process. Steel is also purchased from scrap metal dealers, though it must be free from copper which is difficult to remove from molten steel and adversely affects its properties. The scrap steel is sorted into different grades according to alloy content.

Limestone mining This is mined near Otorohanga. Limestone chip is blended with the coal and primary concentrate to help form a slag in the reduction of the iron oxide. Some is also supplied in the form of lime (calcium oxide) for use in steel making. Oxygen production This is manufactured by the fractional distillation of liquid air, which also produces nitrogen and argon. About 4000 m3 of oxygen is consumed for each 75 tonne load of steel, giving an annual consumption of about 75 000 tonnes. Some of the nitrogen and argon is used in steelmaking. The excess liquid nitrogen is sold for freeze drying foods and the excess argon is mainly sold for use as a gas shield for welding processes.
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Electricity The total annual consumption of electricity is 1000 GWh, the typical power demand being 130 MW. This is purchased from Electrocorp and brought to the site through overhead power lines operating at 110 kV. The waste gases from various processes, particularly the multi-hearth furnaces and the melter are burnt to raise steam in four boilers. The steam is used to power two turbines each rated at 18 MW, which produce 12½ % of the electricity needed by the plant. In the near future the on site generation of electrical power is to be considerably expanded and greater use made of waste gases from the rotary kilns. This will enable the plant to produce over half the total electrical power consumed. THE ROLE OF THE LABORATORY In general the laboratory is responsible for quality control of the various stages of production and of the end product. The laboratory uses optical emission spectroscopy2 to determine the sample composition of the molten metal in the melter, vanadium recovery unit, K.O.B.M. unit and casting machine and during the ladle treatment stage. The levels of carbon, silicon, manganese, tin, vanadium, sulfur, phosphorus, aluminium and nitrogen are closely monitored. The test only takes four minutes, enabling operators to adjust process parameters on the basis of test reports before problems become serious. The nitrogen content in steel can also be found by heating the steel in a helium flushed electric furnace. As the temperature increases any nitrogen in the sample comes off and mixes with the helium carrier gas. The gas mixture is analysed by a thermal conductivity cell at the gas outlet. Samples of ironsand and slag are analysed with X-ray fluorescence spectroscopy. The slag samples are fused with boron before testing. The laboratory is also involved in daily testing of effluent water to ensure that all water released into the environment is safe.

ENVIRONMENTAL IMPLICATIONS Due to the nature of the steel making process, large amounts of solid, liquid and gaseous wastes are generated in the steel plant. Careful planning is necessary to ensure that these do not have a negative impact on the environment.

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The steel mill requires 1.2 to 1.4 million tonnes of ironsand each year, which means that up to 10 million tonnes of pure sand must be mined. The non-magnetic sand is returned to the

area from which it was mined, and marram grass and radiata pines planted to stabilise the deposits. Wet scrubbers and baghouses are the principal means of controlling air pollution. The wet scrubbers (see oil refining article) wash the dust out of the hot process waste gases which result from iron and steel making while the cloth bags inside a baghouse filter dust out of the gas. The dust collection system is shared by the steel production and steel processing sections, and collects a total of between five and ten tonnes of dust every hour. Extensive water recycling is used in the plant to minimise the quantity of waste water.

ElectricArcFurnaceSteelmaking FURNACE OPERATIONS The electric arc furnace operates as a batch melting process producing batches of molten steel known "heats". The electric arc furnace operating cycle is called the tap-to-tap cycle and is made up of the following operations:
• Furnace • Melting • Refining

charging

De-slagging
• Tapping • Furnace

turn-around

Modern operations aim for a tap-to-tap time of less than 60 minutes. Some twin shell furnace operations are achieving tap-to-tap times of 35 to 40 minutes. Furnace Charging The first step in the production of any heat is to select the grade of steel to be made. Usually a schedule is developed prior to each production shift. Thus the melter will know in advance the schedule for his shift. The scrap yard operator will prepare buckets of scrap according to the needs of the melter. Preparation of the charge bucket is an important operation, not only to ensure proper melt-in chemistry but also to ensure good melting conditions. The scrap must be layered .

The first step in any tap-to-tap cycle is "charging" into the scrap. The roof and electrodes are raised and are swung to the side of the furnace to allow the scrap charging crane to move a full bucket of scrap into place over the furnace. The bucket bottom is usually a clam shell design - i.e. the bucket opens up by retracting two segments on the bottom of the bucket. The scrap falls into the furnace and the scrap crane removes the scrap bucket. The roof and electrodes swing back into place over the furnace. The roof is lowered and then the electrodes are lowered to strike an arc on the scrap. This commences the melting portion of the cycle. The number of charge buckets of scrap required to produce a heat of steel is dependent primarily on the volume of the furnace and the scrap density. Most modern furnaces are designed to operate with a minimum of back-charges. This is advantageous because charging is a deadtime where the furnace does not have power on and therefore is not melting.

Minimizing these dead-times helps to maximize the productivity of the furnace. In addition, energy is lost every time the furnace roof is opened. This can amount to 10 - 20 kWh/ton for each occurrence. Most operations aim for 2 to 3 buckets of scrap per heat and will attempt to blend their scrap to meet this requirement. Some operations achieve a single bucket charge. Continuous charging operations such as CONSTEEL and the Fuchs Shaft Furnace eliminate the charging cycle.

Melting

The melting period is the heart of EAF operations. The EAF has evolved into a highly efficient melting apparatus and modern designs are focused on maximizing the melting capacity of the EAF. Melting is accomplished by supplying energy to the furnace interior. This energy can be electrical or chemical. Electrical energy is supplied via the graphite electrodes and is usually the largest contributor in melting operations. Initially, an intermediate voltage tap is selected until the electrodes bore into the scrap. Usually, light scrap is placed on top of the charge to accelerate bore-in. Approximately 15 % of the scrap is melted during the initial bore-in period. After a few minutes, the electrodes will have penetrated the scrap sufficiently so that a long arc (high voltage) tap can be used without fear of radiation damage to the roof. The long arc maximizes the transfer of power to the scrap and a liquid pool of metal will form in the furnace hearth At the start of melting the arc is erratic and unstable. Wide swings in current are observed accompanied by rapid movement of the electrodes. As the furnace atmosphere heats up the arc stabilizes and once the molten pool is formed, the arc becomes quite stable and the average power input increases.

Chemical energy is be supplied via several sources including oxy-fuel burners and oxygen lances. Oxy-fuel burners burn natural gas using oxygen or a blend of oxygen and air. Heat is transferred to the scrap by flame radiation and convection by the hot products of combustion. Heat is transferred within the scrap by conduction. Large pieces of scrap take longer to melt into the bath than smaller pieces. In some operations, oxygen is injected via a consumable pipe lance to "cut" the scrap. The oxygen reacts with the hot scrap and burns iron to produce intense heat for cutting the scrap. Once a molten pool of steel is generated in the furnace, oxygen can be lanced directly into the bath. This oxygen will react with several components in the bath including, aluminum, silicon, manganese, phosphorus, carbon and iron. All of these reactions are exothermic (i.e. they generate heat) and supply additional energy to aid in the melting of the scrap. The metallic oxides that are formed will end up in the slag. The reaction of oxygen with carbon in the bath produces carbon monoxide, which either burns in the furnace if there is sufficient oxygen, and/or is exhausted through the direct evacuation system where it is burned and conveyed to the pollution control system. Auxiliary fuel operations are discussed in more detail in the section on EAF operations. Once enough scrap has been melted to accommodate the second charge, the charging process is repeated. Once the final scrap charge is melted, the furnace sidewalls are exposed to intense radiation from the arc. As a result, the voltage must be reduced. Alternatively, creation of a foamy slag will allow the arc to be buried and will protect the furnace shell. In addition, a greater amount of energy will be retained in the slag and is transferred to the bath resulting in greater energy efficiency.

HOW A BLAST FURNACE WORKS The purpose of a blast furnace is to chemically reduce and physically convert iron oxides into liquid iron called "hot metal". The blast furnace is a huge, steel stack lined with refractory brick, where iron ore, coke and limestone are dumped into the top, and preheated air is blown into the bottom. The raw materials require 6 to 8 hours to descend to the bottom of the furnace where they become the final product of liquid slag and liquid iron. These liquid products are drained from the furnace at regular intervals. The hot air that was blown into the bottom of the furnace ascends to the top in 6 to 8 seconds after going through numerous chemical reactions. Once a blast furnace is started it will continuously run for four to ten years with only short stops to perform planned maintenance. The Process Iron oxides can come to the blast furnace plant in the form of raw ore, pellets or sinter. The raw ore is removed from the earth and sized into pieces that range from 0.5 to 1.5 inches. This ore is either Hematite (Fe2O3) or Magnetite (Fe3O4) and the iron content ranges from 50% to 70%. This iron rich ore can be charged directly into a blast furnace without any further processing. Iron ore that contains a lower iron content must be processed or beneficiated to increase its iron content. Pellets are produced from this lower iron content ore. This ore is crushed and ground into a powder so the waste material called gangue can be removed. The remaining iron-rich powder is rolled into balls and fired in a furnace to produce strong, marble-sized pellets that contain 60% to 65% iron. Sinter is produced from fine raw ore, small coke, sand-sized limestone and numerous other steel plant waste materials that contain some iron. These fine materials are proportioned to obtain a desired product chemistry then mixed together. This raw material mix is then placed on a sintering strand, which is similar to a steel conveyor belt, where it is ignited by gas fired furnace and fused by the heat from the coke fines into larger size pieces that are from 0.5 to 2.0 inches. The iron ore, pellets and sinter then become the liquid iron produced in the blast furnace with any of their remaining impurities going to the liquid slag.

The coke is produced from a mixture of coals. The coal is crushed and ground into a powder and then charged into an oven. As the oven is heated the coal is cooked so most of the volatile matter such as oil and tar are removed. The cooked coal, called coke, is removed from the oven after 18 to 24 hours of reaction time. The coke is cooled and screened into pieces ranging from one inch to four inches. The coke contains 90 to 93% carbon, some ash and sulfur but compared to raw coal is very strong. The strong pieces of coke with a high energy value provide permeability, heat and gases which are required to reduce and melt the iron ore, pellets and sinter. The final raw material in the ironmaking process in limestone. The limestone is removed from the earth by blasting with explosives. It is then crushed and screened to a size that ranges from 0.5 inch to 1.5 inch to become blast furnace flux . This flux can be pure high calcium limestone, dolomitic limestone containing magnesia or a blend of the two types of limestone. Since the limestone is melted to become the slag which removes sulfur and other impurities, the blast furnace operator may blend the different stones to produce the desired slag chemistry and create optimum slag properties such as a low melting point and a high fluidity. All of the raw materials are stored in an ore field and transferred to the stockhouse before charging. Once these materials are charged into the furnace top, they go through numerous chemical and physical reactions while descending to the bottom of the furnace. The iron ore, pellets and sinter are reduced which simply means the oxygen in the iron oxides is removed by a series of chemical reactions. These reactions occur as follows: 1) 3 Fe2O3 + CO = CO2 + 2 Fe3O4 Begins at 850° F 2) Fe3O4 + CO = CO2 + 3 FeO Begins at 1100° F 3) FeO + CO = CO2 + Fe Or

FeO + C = CO + Fe Begins at 1300° F At the same time the iron oxides are going through these purifying reactions, they are also beginning to soften then melt and finally trickle as liquid iron through the coke to the bottom of the furnace. The coke descends to the bottom of the furnace to the level where the preheated air or hot blast enters the blast furnace. The coke is ignited by this hot blast and immediately reacts to generate heat as follows: C + O2 = CO2 + Heat Since the reaction takes place in the presence of excess carbon at a high temperature the carbon dioxide is reduced to carbon monoxide as follows: CO2+ C = 2CO The product of this reaction, carbon monoxide, is necessary to reduce the iron ore as seen in the previous iron oxide reactions. The limestone descends in the blast furnace and remains a solid while going through its first reaction as follows: CaCO3 = CaO + CO2 This reaction requires energy and starts at about 1600° F. The CaO formed from this reaction is used to remove sulfur from the iron which is necessary before the hot metal becomes steel. This sulfur removing reaction is: FeS + CaO + C = CaS + FeO + CO The CaS becomes part of the slag. The slag is also formed from any remaining Silica (SiO2), Alumina (Al2O3), Magnesia (MgO) or Calcia (CaO) that entered with the iron ore, pellets, sinter or coke. The liquid slag then trickles through the coke bed to the bottom of the furnace where it floats on top of the liquid iron since it is less dense. Another product of the ironmaking process, in addition to molten iron and slag, is hot dirty gases. These gases exit the top of the blast furnace and proceed through gas cleaning equipment where particulate matter is removed from the gas and the gas is cooled. This gas has a considerable energy value so it is burned as a fuel in the "hot blast stoves" which are used to preheat the air entering the blast furnace to become "hot blast". Any of the gas not burned in the stoves is sent to the boiler house and is used to generate steam which turns a turbo blower that generates the compressed air known as "cold blast" that comes to the stoves. In summary, the blast furnace is a counter-current realtor where solids descend and gases ascend. In this reactor there are numerous chemical and physical reactions that produce the desired final product which is hot metal. A typical hot metal chemistry follows: Iron (Fe) = 93.5 - 95.0% Silicon (Si) = 0.30 - 0.90% Sulfur (S) = 0.025 - 0.050% Manganese (Mn) = 0.55 - 0.75% Phosphorus (P) = 0.03 - 0.09% Titanium (Ti) = 0.02 - 0.06% Carbon (C) = 4.1 - 4.4%

Now that we have completed a description of the ironmaking process, let s review the physical equipment comprising the blast furnace plant. There is an ore storage yard that can also be an ore dock where boats and barges are unloaded. The raw materials stored in the ore yard are raw ore, several types of pellets, sinter, limestone or flux blend and possibly coke. These materials are transferred to the "stockhouse/hiline" (17) complex by ore bridges equipped with grab buckets or by conveyor belts. Materials can also be brought to the stockhouse/hiline in rail hoppers or transferred from ore bridges to selfpropelled rail cars called "ore transfer cars". Each type of ore, pellet, sinter, coke and limestone is dumped into separate "storage bins" (18). The various raw materials are weighed according to a certain recipe designed to yield the desired hot metal and slag chemistry. This material weighing is done under the storage bins by a rail mounted scale car or computer controlled weigh hoppers that feed a conveyor belt. The weighed materials are then dumped into a "skip" car which rides on rails up the "inclined skip bridge" to the "receiving hopper" (6) at the top of the furnace. The cables lifting the skip cars are powered from large winches located in the "hoist" house (20). Some modern blast furnace accomplish the same job with an automated conveyor stretching from the stockhouse to the furnace top. At the top of the furnace the materials are held until a "charge" usually consisting of some type of metallic (ore, pellets or sinter), coke and flux (limestone) have accumulated. The precise filling order is developed by the blast furnace operators to carefully control gas flow and chemical reactions inside the furnace. The materials are charged into the blast furnace through two stages of conical "bells" (5) which seal in the gases and distribute the raw materials evenly around the circumference of the furnace "throat". Some modern furnaces do not have bells but instead have 2 or 3 airlock type hoppers that discharge raw materials onto a rotating chute which can change angles allowing more flexibility in precise material placement inside the furnace. Also at the top of the blast furnace are four "uptakes" (10) where the hot, dirty gas exits the furnace

dome. The gas flows up to where two uptakes merge into an "offtake" (9). The two offtakes then merge into the "downcomer" (7). At the extreme top of the uptakes there are "bleeder valves" (8) which may release gas and protect the top of the furnace from sudden gas pressure surges. The gas descends in the downcomer to the "dustcatcher", where coarse particles settle out, accumulate and are dumped into a railroad car or truck for disposal. The gas then flows through a "Venturi Scrubber" (4) which removes the finer particles and finally into a "gas cooler" (2) where water sprays reduce the temperature of the hot but clean gas. Some modern furnaces are equipped with a combined scrubber and cooling unit. The cleaned and cooled gas is now ready for burning. The clean gas pipeline is directed to the hot blast "stove" (12). There are usually 3 or 4 cylindrical shaped stoves in a line adjacent to the blast furnace. The gas is burned in the bottom of a stove and the heat rises and transfers to refractory rick inside the stove. The products of combustion flow through passages in these bricks, out of the stove into a high "stack" (11) which is shared by all of the stoves. Large volumes of air, from 80,000 ft3/min to 230,000 ft3/min, are generated from a turbo blower and flow through the "cold blast main" (14) up to the stoves. This cold blast then enters the stove that has been previously heated and the heat stored in the refractory brick inside the stove is transferred to the "cold blast" to form "hot blast". The hot blast temperature can be from 1600° F to 2300° F depending on the stove design and condition. This heated air then exits the stove into the "hot blast main" (13) which runs up to the furnace. There is a "mixer line" (15) connecting the cold blast main to the hot blast main that is equipped with a valve used to control the blast temperature and keep it constant. The hot blast main enters into a doughnut shaped pipe that encircles the furnace, called the "bustle pipe" (13). From the bustle pipe, the hot blast is directed into the furnace through nozzles called "tuyeres" (30) (pronounced "tweers"). These tuyeres are equally spaced around the circumference of the furnace. There may be fourteen tuyeres on a small blast furnace and forty tuyeres on a large blast furnace. These tuyeres are made of copper and are water cooled since the temperature directly in front of the them may be 3600° F to 4200° F. Oil, tar, natural gas, powdered c oal and oxygen can also be injected into the furnace at tuyere level to combine with the coke to release additional energy which is necessary to increase productivity. The molten iron and slag drip past the tuyeres on the way to the furnace hearth which starts immediately below tuyere level. Around the bottom half of the blast furnace the "casthouse" (1) encloses the bustle pipe, tuyeres and the equipment for "casting" the liquid iron and slag. The opening in the furnace hearth for casting or draining the furnace is called the "iron notch" (22). A large drill mounted on a pivoting base called the "taphole drill" (23) swings up to the iron notch and drills a hole through the refractory clay plug into the liquid iron. Another opening on the furnace called the "cinder notch" (21) is used to draw off slag or iron in emergency situations. Once the taphole is drilled open, liquid iron and slag flow down a deep trench called a "trough" (28). Set across and into the trough is a block of refractory, called a "skimmer", which has a small opening underneath it. The hot metal flows through this skimmer opening, over the "iron dam" and down the "iron runners" (27). Since the slag is less dense than iron, it floats on top of the iron, down the trough, hits the skimmer and is diverted into the "slag runners" (24). The liquid slag flows into "slag pots" (25) or into slag pits (not shown) and the liquid iron flows into refractory lined "ladles" (26) known as torpedo cars or sub cars due to their shape. When the liquids in the furnace are drained down to taphole level, some of the blast from the tuyeres causes the taphole to spit. This signals the end of the cast, so the "mudgun" (29) is swung into the iron notch. The mudgun cylinder, which was previously filled with a refractory clay, is actuated and the cylinder ram pushes clay into the iron notch stopping the flow of liquids. When the cast is complete, the iron ladles are taken to the steel shops for processing into steel and the slag is taken to the slag dump where it is processed into roadfill or railroad ballast. The casthouse is then cleaned and readied for the next cast which may occur in 45 minutes to 2 hours. Modern, larger blast furnaces may have as many as four tapholes and two casthouses. It is important to cast the

furnace at the same rate that raw materials are charged and iron/slag produced so liquid levels can be maintained in the hearth and below the tuyeres. Liquid levels above the tuyeres can burn the copper casting and damage the furnace lining. CONCLUSION The blast furnace is the first step in producing steel from iron oxides. The first blast furnaces appeared in the 14th Century and produced one ton per day. Blast furnace equipment is in continuous evolution and modern, giant furnaces produce 13,000 tons per day. Even though equipment is improved and higher production rates can be achieved, the processes inside the blast furnace remain the same. Blast furnaces will survive into the next millenium because the larger, efficient furnaces can produce hot metal at costs competitive with other iron making technologies.

COKE PRODUCTION FOR BLAST FURNACE IRONMAKING INTRODUCTION A world class blast furnace operation demands the highest quality of raw materials, operation, and operators. Coke is the most important raw material fed into the blast furnace in terms of its effect on blast furnace operation and hot metal quality. A high quality coke should be able to support a smooth descent of the blast furnace burden with as little degradation as possible while providing the lowest amount of impurities, highest thermal energy, highest metal reduction, and optimum permeability for the flow of gaseous and molten products. Introduction of high quality coke to a blast furnace will result in lower coke rate, higher productivity and lower hot metal cost. COKE PRODUCTION The cokemaking process involves carbonization of coal to high temperatures (1100°C) in an oxygen deficient atmosphere in order to concentrate the carbon. The commercial cokemaking process can be broken down into two categories: a) Byproduct Cokemaking and b) Non-Recovery/Heat Recovery Cokemaking. A brief description of each coking process is presented here. The majority of coke produced in the United States comes from wet-charge, byproduct coke oven batteries (Figure 1). The entire cokemaking operation is comprised of the following steps: Before carbonization, the selected coals from specific mines are blended, pulverized, and oiled for proper bulk density control. The blended coal is charged into a number of slot type ovens wherein each oven shares a common heating flue with the adjacent oven. Coal is carbonized in a reducing atmosphere and the off-gas is collected and sent to the by-product plant where various by-products are recovered. Hence, this process is called byproduct cokemaking.

The coal-to-coke transformation takes place as follows: The heat is transferred from the heated brick walls into the coal charge. From about 375°C to 475°C, the coal decomposes to form plastic layers near each wall.

At about 475°C to 600°C, there is a marked evolution of tar, and aromatic hydrocarbon compounds, followed by resolidification of the plastic mass into semi-coke. At 600°C to 1100°C, the coke stabilization phase begins. This is characterized by contraction of coke mass, structural development of coke and final hydrogen evolution. During the plastic stage, the plastic layers move from each wall towards the center of the oven trapping the liberated gas and creating in gas pressure build up which is transferred to the heating wall. Once, the plastic layers have met at the center of the oven, the entire mass has been carbonized (Figure 2).

Figure 1: "Coke Side" of a By-Product Coke Oven Battery. The oven has just been "pushed" and railroad car is full of incandescent coke that will now be taken to the "quench station".

Figure 2: Incandescent coke in the oven waiting to be "pushed".

Non-Recovery/Heat Recovery Coke Production:

In Non-Recovery coke plants, originally referred to as beehive ovens, the coal is carbonized in large oven chambers (Figure 3). The carbonization process takes place from the top by radiant heat transfer and from the bottom by conduction of heat through the sole floor. Primary air for combustion is introduced into the oven chamber through several ports located above the charge level in both pusher and coke side doors of the oven. Partially combusted gases exit the top chamber through "down comer" passages in the oven wall and enter the sole flue, thereby heating the sole of the oven. Combusted gases collect in a common tunnel and exit via a stack which creates a natural draft in the oven. Since the by-products are not recovered, the process is called Non-Recovery cokemaking. In one case, the waste gas exits into a waste heat recovery boiler (Figure 3) which converts the excess heat into steam for power generation; hence, the process is called Heat Recovery cokemaking.

Figure 3: Heat Recovery Coke Plant.

COKE PROPERTIES High quality coke is characterized by a definite set of physical and chemical properties that can vary within narrow limits. The coke properties can be grouped into following two groups: a) Physical properties and b) Chemical properties. a) Physical Properties: Measurement of physical properties aid in determining coke behavior both inside and outside the blast furnace (Figure 4). In terms of coke strength, the coke stability and Coke Strength After Reaction with CO2 (CSR) are the most important parameters. The stability measures the ability of coke to withstand breakage at room temperature and reflects coke behavior outside the blast furnace and in the upper part of the blast furnace. CSR measures the potential of the coke to break into smaller size under a high temperature CO/CO2 environment that exists throughout the lower two-thirds of the blast furnace. A large mean size with narrow size variations helps maintain a stable void fraction in the blast furnace permitting the upward flow of gases and downward of molten iron and slag thus improving blast furnace productivity. Blast Furnace Operating Zones and Coke Behavior.

Table I. Coke Quality Specifications: Physical: (measured at the blast furnace) Mean Range Average Coke Size (mm) 52 45-60

Plus 4" (% by weight) 1 4 max Minus 1"(% by weight) 8 11 max Stability 60 58 min CSR 65 61 min Physical: (% by weight) Ash 8.0 9.0 max Moisture 2.5 5.0 max Sulfur 0.65 0.82 max Volatile Matter 0.5 1.5 max Alkali (K2O+Na2O) 0.25 0.40 max Phosphorus 0.02 0.33 max FACTORS AFFECTING COKE QUALITY A good quality coke is generally made from carbonization of good quality coking coals. Coking coals are defined as those coals that on carbonization pass through softening, swelling, and resolidification to coke. One important consideration in selecting a coal blend is that it should not exert a high coke oven wall pressure and should contract sufficiently to allow the coke to be pushed from the oven. The properties of coke and coke oven pushing performance are influenced by following coal quality and battery operating variables: rank of coal, petrographic, chemical and rheologic characteristics of coal, particle size, moisture content, bulk density, weathering of coal, coking temperature and coking rate, soaking time, quenching practice, and coke handling. Coke quality variability is low if all these factors are controlled. Coke producers use widely differing coals and employ many procedures to enhance the quality of the coke and to enhance the coke oven productivity and battery life.

Chemical Properties: The most important chemical properties are moisture, fixed carbon, ash, sulfur, phosphorus, and alkalies. Fixed carbon is nthe fuel portion of the coke; the higher the fixed carbon, the higher the thermal value of coke. The other components such as moisture, ash, sulfur, phosphorus, and alkalies are undesirable as they have adverse effects on energy requirements, blast furnace operation, hot metal quality, and/or refractory lining. Coke quality specifications for one large blast furnace in North America are shown in Table I. Table I. Coke Quality Specifications: Physical: (measured at the blast furnace) Mean Range Average Coke Size 20 Minus 1"(% by 21 Stability 60 58 min CSR 65 61 min Physical: (% by weight) Ash 8.0 9.0 max Moisture 2.5 5.0 max Sulfur 0.65 0.82 max Volatile Matter 0.5 1.5 max Alkali (K2O+Na2O) 0.25 0.40 max Phosphorus 0.02 0.33 max FACTORS AFFECTING COKE QUALITY A good quality coke is generally made from carbonization of good quality coking coals. Coking coals are defined as those coals that on carbonization pass through softening, swelling, and resolidification to coke. One important consideration in selecting a coal blend is that it should not exert a high coke oven wall pressure and should contract sufficiently to allow the coke to be pushed from the oven. The properties of coke and coke oven pushing performance are influenced by following coal quality and battery operating variables: rank of coal, petrographic, chemical and rheologic characteristics of coal, particle size, moisture content, bulk density, weathering of coal, coking temperature and coking rate, soaking time, quenching practice, and coke handling. Coke quality variability is low if all these factors are controlled. Coke producers use widely differing coals and employ many procedures to enhance the quality of the coke and to enhance the coke oven productivity and battery life. Background Raw Materials used Stockhouse: screening and weighing of burden materials Bell less top: proper distribution of burden materials in the furnace Gas cleaning: cleaning of bf-topgas in two steps: 1. dry dust catcher for coarse particl 2. Wet scrubber for final cleaning Gasholder: big vessel to buffer flow and pressure fluctuations Hot blast stoves: regenerative heat exchanger for heating of hot blast Hot Metal: liquid hot iron Slag: liquid byproducts (CaO, SiO2, Al2O3, MgO) Blower: generates compressed air (mm) weight) 8 52 11 45-60 max

Blast Furnace’s have been the preferred route of making pig iron for thousands of years. Over this time many improvements have been made to their productivity through innovative new design of equipment. The materials charged into a Blast Furnace have remained relatively unchanged though and consist of Coke produced in a Coke Oven, Iron or Lump Ore, Iron pellets – formed Iron ore and Sinter – a mixture of coke and ore fines from a Sinter plant. In addition to these key ingredients, fluxes are added in small quantities to ensure correct composition of Hot metal and Slag Background Types of Furnace Charging Burden probes: temperature and gas probes to control the distribution of the burden materials Throat armour: high resistant metal plates to protect the refractories from dropping burden materials Bustle main: ring pipe for hot blast

Before the material can be charged into the furnace, it must first reach the top of the blast furnace where the material charging system is located. These pictures show three methods of delivering the burden material from the stockhouse where the batches are weighed out to the furnace top. The first shows a skip bridge allowing two skips to supply the charging system with material. The middle picture shows a bucket conveyor, allowing the material batch to be brought up continuously in several stages. This type of furnace charging is now rarely used as it means the stockhouse is located very close to the blast furnace and often raw material will have further to travel to reach the stockhouse. The most common type, shown on the last picture involves an angled belt conveyor between the stockhouse and the blast furnace. This allows the stockhouse to be located away from the Blast furnace.

Background Furnace Top Hoppers 1. 2. 3. 4. 5. Hopper filled with material Upper Seal valve closes Hopper pressurised above furnace operating pressure Lower Seal valve and Material Flow gate opens Lower Seal valve and Material Flow gate closes

-

Moving or Rocking Chute Material Hopper

Upper Seal Valve

Material Flow Control Gate

Lower Seal Valve

Once material has been transported to the top of the Blast Furnace it is held in material hoppers until it is required to fill the furnace. There are several different arrangements of hoppers possible, I shown here is the most common for larger furnaces – two parallel hoppers. On smaller furnaces two hoppers can be positioned in series, or even one hopper. Either way the basic procedure for filling and emptying the hoppers will be the same. Since the introduction of more advanced charging systems, better burden distribution has become possible. This has lead not only to a decrease in ab-normal operation through burden slips and material hanging in the furnace but also to better productivity. The first widely used mechanical systems were developed in the 1960’s and contained a cone or bell inside the furnace throat to distribute the material to the outside of the blast furnace. Despite continuous improvement in these designs with double bells developed to vary the falling trajectory of the material. Both the Yawata and the IHI tops were developed by and for use on the Japanese blast furnaces at this time, while The Davy universal, McKee distributor and CRM were developed in the USA and Europe. Despite the lack of control these charging systems give the operator over the placement of material inside the furnace, they are still common across the world – mostly on smaller furnaces. This is due to the fact that while productivity and therefore profitability could be increased by installing a newer top, the price for a new top is generally much higher for the more complicated equipment. Steel Alloy Selection v Steel q Major material in heavy equipment q Iron for steel is used 20 times as much as all other metals combined v Alloying and heat treating of steel q Extends product life through microstructural change q Uses energy and resources

q v q q

Produces wastes and emissions The challenges Weighing product life against potential environmental impacts Predicting potential environmental impacts from manufacturing

Iron and Steel HIGHLIGHTS PROCESSES AND TECHNOLOGY STATUS – The basic materials for iron production are iron ore, coal and coke (also used as energy input to the process) or alternative reducing agents, limestone and dolomite. Steel production requires iron, steel scrap and lime (burnt limestone). The iron ore is smelted to produce an impure metal called "hot metal" when in liquid phase or "pig iron" when in solid phase. In smelting, a reducing agent - usually coke - and heat are used to remove oxygen from the metal ore. Carbon dioxide (CO2) and carbon monoxide (CO) are produced during the reduction process. Limestone is used to remove impurities such as slag. Blast Furnace, Midrex Direct Reduction Iron (DRI), Corex Smelting Reduction Iron (SRI) and Hylsa are currently commercial processes. Hismelt Smelting Reduction Iron and Hi-Oxy coal plants (with a high rate of coal powder injection) are new processes currently available at the pilot plant level. Iron and steel production processes with CO2 emissions capture and storage (CCS) are still under development and testing. COST – The main components of the iron and steel production cost are capital investment and raw materials. Investment costs for the traditional production processes are approximately $211 for Blast Furnaces (BF) with a capacity of one ton of pig iron per year (US $/(t/a)) and $100 for a Basic Oxygen Furnace (BOF) with a unit capacity (US $/(t/a). Investment costs for the alternative production technologies range from $220/t-yr for Direct Reduced Iron (DRI) and Electric Arc Furnace (EAF) combinations to $320/t-yr for the Smelting Reduction (SRI) technology. Other main cost drivers are scrap and electricity. Total costs amount to $92/t for BF and BOF combinations (including energy inputs), $214/t for DRI and EAF combinations and $198/t for SRI.

POTENTIAL & BARRIERS – The iron and steel production sector is the second-largest industrial consumer of energy after the chemical sector. It accounts for about 20% of industrial energy consumption and is the largest industrial emitter of CO2, including all the process emissions from coke ovens, blast furnaces, etc.

PROCESS OVERVIEW Pure iron is not readily available since it easily oxidises in the presence of air and moisture. The iron industry reduces iron oxides to obtain pure iron, i.e. metallic iron. Steel is an alloy based on iron and carbon, with carbon concentration ranging from 0.2% to 2.14% in weight. High carbon content results in higher hardness, tensile strength, and lower ductility. The resulting steel is also more brittle. Steel alloys can be enriched with other materials to tune the final material properties that also depend on production techniques and on the quality of the basic materials.

Iron Ore classification – The basic material for iron and steel production is iron ore or ferrous scrap. Iron ores are classified based on shape and volume. Iron fines have a majority of particles with a diameter of < 4.75 mm; iron lump ore has a majority of particles with a diameter of > 4.75 mm; iron pellets are a fine-grained concentrate rolled into balls (with a binder) and indurated in a furnace. Their diameter ranges from 9.5 to 16.0 mm. Iron and Steel production – The iron and steel production process can be subdivided into 3 sub-processes: iron-making, steel-making and steel manufacturing. All processes can be summarized as in Figure 1 [2]. A more detailed scheme and material flow can be found in Figure 9. Conventional steel production takes place in integrated steel mills that often include facilities for coking and sintering. In the basic process, the input materials - a combination of sinter, iron pellets, limestone and cokes - enter a blast furnace (BF) to be converted into molten pig iron. The pig iron is then loaded into an oxygen furnace to produce steel slabs. Alternative processes are direct reduction iron (DRI) and smelting reduction iron (SRI). Ferrous scrap can also be processed in an electric arc furnace (EAF) to obtain steel. Today most used steel-making processes consist of a combination of a blast furnace and basic oxygen furnace. IRON PRODUCTION Blast Furnace (pig iron) – Blast furnace (Figure 2) is a process for producing liquid raw iron by smelting pellets or sinter in a reducing environment. The end products are usually molten metal, slag and blast furnace gas. In the reduction process, oxygen (O2) is taken out of the pellets or sinter. Coke is often used as a reducing agent, as well as fuel. Fuel (coke) and pellets or sinter are supplied continuously through the top of the furnace and O2- enriched air is blown out the bottom by electrical air ventilators. The chemical reactions take place while the materials move downward. Coke also serves as a carrier to move the bulk material column downward in the blast furnace [5]. Various alternative reducing agents are available, such as hydrocarbons, coke, coal, oil, natural gas (nowadays in some cases, also plastics). In the past, a widely used reducing agent was charcoal, in particular charcoal from eucalyptus trees. Whatever the fuel and coke oven sintering pelletisation Blast furnace Basic oxygen furnace Smelting reduction Direct reduction Scrap melting Electric arc furnace Casting (different methods) Rolling / Galvan reducing agent, the content of the furnace needs to have optimum permeability to the flow of gaseous and molten products. Blast furnace gas contains CO (20-28%), H2 (1– 5%), inert compounds such as N2 (50-55%) and CO2, (17-25%), some sulphur and cyanide compounds, and large amounts of dust from impurities of coal and iron ore.The lower heating value of blast furnace gas ranges from approximately 2.7 to 4.0 MJ/Nm3. The

production of blast furnace gas is approximately 1200 to 2000 Nm3/t pig iron [5]. Much effort is devoted to increasing efficiency and reducing emissions of the blast furnaces [1]. Coking – Coking or coal pyrolysis is the way coke is produced by heating coal in an oxidation free atmosphere. Flue gases at temperatures between 1150° C and 1350° C heat up coal indirectly to 1000-1100° C for 14-24 hours. At the e nd of the grate, coke is fully carbonised and it is quenched mostly by water, or by inert gas. Air cannot be used for this purpose, as the oxygen would cause the hot cokes to ignite spontaneously. Some 1000 kg of coal usually yields 750-800kg of coke and approximately 325 m³ COG (Coke Oven Gas) Sintering and Pelletisation – Sinter and pellets are produced by mixing together raw or recycled materials, which undergo a physical and metallurgic agglomeration process. The high permeability and the reducibility of sinter and pellets enhance the BF performance. In the sintering process, ores, additives, recycled sinter and coke breeze are blended in a mixing drum. This mixture is then loaded onto a moving grate and ignited. As the mixture proceeds along with the grate, air is drawn downwards through the sintering bed by powerful fans causing the combustion front to move downwards through the mixture. The sinter is cooled in a separate cooler, after which it is crushed. Pelletisation is a process to convert iron ore into small balls (9–16 mm) while upgrading its iron content. While sintering is mostly used in integrated steelworks, pelletisation is mostly used at mining sites. The process of forming pellets can be divided into four steps: Grinding and Drying; Green ball preparation; Induration; and Screening and Handling. In the first step, wet or dry ores are ground (grated) and the resulting slurry is mixed with additives to prepare the green balls. Induration involves green balls drying, heating and final cooling. During this process, almost all magnetite is transformed into hematite. This explains the large amount of heat needed for the process (magnetite ore has a low iron content and must be upgraded to make it suitable for steelmaking). In the last screening/handling step, undersized or broken pellets are recycled. Direct Reduction (direct reduced iron, DRI) – Direct reduction is the name of a broad group of processes based on different feedstocks, furnaces, reducing agents, etc. The common principle is the removal of oxygen (reduction) from iron ores in the solid state. Natural gas (and in some cases coal) is used as a reducing agent to enable this process. In 2000, some 92.6% of DRI was based on natural gas processed in shaft furnaces, retorts and fluidized bed reactors. The metallization rate of the end product ranges from 85% to 95 % (often even higher). DRI is prone to combustion and is therefore sometimes called hot briquetted iron (HBI). The concept Fig. 2 - Simplified scheme of a blast furnace [10] of direct reduction dates from the 1950s, with the first plant operated in 1952 [2]. As shown in Figure 3, DRI production has been steadily growing since 1970, with a fallback in 2008 and 2009 due to the ongoing financial crisis [8]. In 2008, the global DRI production amounted to 68.5 Mt and was based primarily on MIDREX technology (58.2%), on HYL/Energiron (14.5%), and on other gasbased (1.6%) and coal-based (25.7%) technologies. Gojic and Kozuh [3, 4, 5] have identified 30 different DRI processes of which MIDREX (Figure 4) is the world’s leading technology. The MIDREX process often consists of four stages: 1) Reduction gas; 2) Reforming; 3) Heat recovery; and 4) Briquette making. A mixture of pellets or lump ore, possibly including up to 10% of fine ore, enters the furnace shaft. As ore descends, oxygen is removed by counter-flowing reduction gas, which is enriched in hydrogen and carbon monoxide. Further information on different DRI processes can be found in [3] and [6]. In total, some 166 DRI facilities were in operation in 2008. Based on Figure 5, the concentration of DRI plants is higher in emerging countries that do not have a significant number of blast furnaces. Some 25% of DRI facilities are in Asia and Oceania, 18% in the Middle East and North Africa, 18% in Latin America, 4.6% in the former Soviet

Union and Eastern Europe, 1.2% in Sub-Saharan Africa, and 1.4% in North America and West Europe [8]. Fig. 3 – Global DRI production over time (mill. tonnes) Smelting Reduction (smelting reduced iron, SRI) – Smelting reduction iron is a recent alternative to DRI and to the BFs. The final product obtained is liquid pig iron or, in some cases, liquid steel. SRI (Figure 6) is a common name for a number of processes, some of which have been commercially proven while others are still under demonstration. The basic principle is akin to that of a blast furnace, but using coal instead of cokes. Iron ore first undergoes a solid-state reduction in the prereduction unit. The resulting product – very similar to DRI - is then smelted and further reduced in the smelting reduction vessel where coal is gasified, thus delivering heat and CO-rich hot gas. Coal gasification takes place due to the reaction with oxygen and iron ore in liquid state. The heat is used to smelt iron and the hot gas is transported to the pre-reduction unit to reduce the iron oxides that enter the process. Reduced iron-oxides (now similar to DRI) are in turn transported to the smelting reduction vessel for final reduction and smelting. The CO rich gas generated in the smelting reduction vessel can be further oxidized to generate additional heat in order to smelt the iron. This process is called post-combustion and thus leads to a trade-off in the utilization of the gas between increased pre-reduction potential or increased heat delivery for smelting [2, 4]. 30 the post-combustion degree, the pre-reduction degree and the heat transfer efficiency. The post-combustion degree is the degree to which the CO formed in the smelting reduction vessel by coal gasification is converted into CO2. A too high degree of postcombustion results in a gas too lean for pre-reduction and off-gas that is too hot. A too low degree of postcombustion results in a gas too rich and increased coal consumption. The pre-reduction degree is the degree to which the iron oxides are reduced in the pre-reduction shaft. The heat transfer efficiency is the ratio of the heat transferred from hot gases to the bath of molten iron, ore and slag to the heat generated by post-combustion. Low heat transfer results in off-gases that are too hot. Based on these parameters, smelting reduction is subdivided into first- and second-generation processes. First generation is characterized by high pre-reduction rates (up to 90%) and second generation by high postcombustion rates, with reduction in the molten bath of iron and pre-reduced iron. [4] Commercial utilization of smelting reduction is still dominated by first generation processes, notably the COREX process (Figure 7), developed in Germany and Austria. Further information on these technologies is available in [3, 6]. The first SRI plant started operation in 1989 based on the COREX process [5]. The use of SRI technology is still limited. STEEL PRODUCTION Basic Oxygen Furnace – [11] The basic oxygen furnace (also called LD converter, from the Linz-Donawitz process, 1956) is based on an oxygen injection into the melt of the hot metal. The oxygen burns out the carbon as carbon monoxide CO and carbon dioxide CO2 gas Fig. 4 - MIDREX Process: 1) natural gas; 2) iron ore; 3) compressor; 4) scrubber; 5) off-gas; 6) air blower; 7) gas reformer; 8) reducing gas; 9) heat recovery; 10) reformer gas; 11) combustion air; 12) reduction zone; 13) shaft furnace; 14) cooling zone; [3] Fig. 5 - 2008 DRI production by region (mill. tons) [8] Fig. 6 - Smelting reduction technology [2] which is collected in the chimney stack and dust-cleaned. As the oxidation reactions are highly exothermic, the process needs cooling in order to control the temperature of the melt. This cooling is done by charging scrap (recycled and mill scrap) and by adding iron ore during the blowing process. Scrap and lime are charged into the converter to also remove phosphorus, silicon and manganese. The converter is lined with dolomite or magnesite refractory which best resist erosion by slag and heat during oxygen blowing. The life of a converter lining is about 800 to 1400 cycles. The process provides a high productivity of steel with low levels of impurities. Inert gas (e.g. argon) is injected into the bottom of the

converter to stir melt and slag. This increases productivity and metallurgical efficiency by lowering iron losses and phosphorus content. The amount of O2 consumed depends on the hot metal composition (C, Si, P, etc.). Electric Arc Furnace (EAF) – EAFs were first used to convert ferrous scrap into steel. Scrap is first pre-heated by EAF offgases (energy recovery) and then charged into the EAF together with lime or dolomitic lime. Lime is used as a flux for the slag formation (dolomitic lime contains calcium and magnesium whereas normal lime contains more calcium). Charging the EAF is a gradual process. At about 50%–60% load, the electrodes are lowered to the scrap and an arc is struck. This melts the first load before further loading. When fully loaded, the entire content of the EAF is melted. To achieve this result, oxygen lances and/or oxy-fuel burners can be used in the initial stages of melting. The ferrous scrap used in the EAF includes scrap from steelworks and steel manufacturers and consumer scrap. DRI is increasingly used as a feedstock in the EAF as it contains a small amount of gangue. [5] INVESTMENT AND PRODUCTION COSTS All costs are given in US dollars (US$2000). Blast Furnace – The overnight investment cost of a blast furnace ranges between $148 and $275 per ton of hot metal per year ($/t-yr) [6]. The variable operation and maintenance (O&M) cost is around $90/t-yr of hot metal Direct Reduction (DRI) – The investment costs of Midrex and Hylsa direct reduction technologies are about $142145/t-yr. The economical lifetime is estimated at 20 years. The O&M cost for both technologies is around $13/t-yr of DRI. Not included in this cost are pellets, fuel (natural gas) and electricity. [6] Smelting Reduction (SRI) – The investment costs for the Tecnored smelting reduction process (with/out cogeneration) are $122/t-yr and $98/t-yr ($ per ton of hot metal per year), respectively. The investment cost of the Hismelt smelting reduction process is $320/t-yr. For both processes, variable O&M costs range between $13/t-yr and $19/t-yr. For the Tecnored technology this excludes coke, pellets, lime, natural gas and electricity consumption. For Hismelt, this excludes iron ore fines, coal fines, oxygen gas, flux (lime), natural gas and electricity. Electric Arc Furnace – The EAF investment cost is about $80/t of steel per year. The O&M costs are about $32/t-yr and do not include steel scrap, lime, O2 gas, natural gas (auxiliary fuel) and electrical power. [6] IMPROVING EFFICIENCY AND REDUCING EMISSIONS IN IRON AND STEEL PRODUCTION Blast Furnace (pig iron) – According to conservative estimates, scrap pre-heating in the BF process could increase the yield from today’s rate of about 20% up to about 30%. Also, recirculating basic oxygen slag to the BF would result in a reduced demand for limestone and Fig. 7 - COREX process: 1)

non-coking coal; 2) ore; 3) reduction shaft; 4) reduction gas; 5) melter gasifier; 6) dust; 7) scrubber; 8) export gas; 9) hot gas cyclone; 10) cooling gas; 11) settling pond. thereby reduced CO2 emissions. An alternative option could be the use of the slag for other applications, e.g. cement production. Oxygen Blast Furnace (pig iron) – The efficiency of a blast furnace can also be increased by using pure oxygen instead of oxygen-enriched air, and by recycling part of the blast furnace gas (i.e. Top Gas Recycling) [1]. Top gas recycling minimises the need for reducing agents (e.g. coke) and therefore enables emissions reduction. In combination with the CO2 capture and storage (see below), this technology can minimise the carbon emissions from blast furnaces. Plasma Blast Furnaces (pig iron) – Plasma-heated blast furnaces require neither hot blast nor oxygen and additional auxiliary reductants [14]. In this process, part ofthe top gas flow is fed to a plasma burner and heated to a temperature of about 3400° C. The CO2 content o f the top gas is transformed into CO by an endothermic reaction with carbon from coke. This results in a calculated flame temperature of 2150° C. Another portion of the top g as undergoes CO2 removal in a scrubber, as in the case of the nitrogen-free blast furnace, before being externally heated at about 900° C and injected into the lower part of th e blast furnace shaft via a second tuyere row. Electric Arc Furnace (steel) – The CO2 emissions from the EAF process are 0.058 tons per ton of EAF iron. Dust emissions are 1-780 g/ton of EAF iron. The SO2 emissions ranges from 24 to 130 g/ton of EAF iron depending on basic input materials and conditions. The NOx emissions range from 120 to 240 g/ton of EAF iron [5, 6] Direct Reduction – The CO2 emissions from DRI Midrex and Hylsa processes are 0.65 and 0.53 tons CO2 per ton DRI [6]. The use of DRI is appropriate if the availability of good quality scrap is not sufficient enough to get good quality steel, if the regional demand is insufficient to run a blast furnace, or if the BF hot metal output needs to be increased [5]. When using the DRI Blast Furnace Sinter Production Powder Coal Coal Cokes Pellets/ Sinter Iron Ore Pellets/ Iron Ore DRI Sponge iron Crude Steel Grinding Pellet Production

Coking Smelting Reduction Direct Reduction Scrap Basic Oxygen Furnace Electric Arc Furnace Direct Reduction (Reformed) 34 Nat Gas Hot metal Pig Iron Export Powder Slag GAS Wood process, the quality of the end product depends highly on the quality of the input ores since pollutants cannot be removed in solid state. [2] Smelting Reduction (pig iron or steel) – The CO2 emissions for the Tecnored and Hismelt processes are 1.79 and 1.57 tons CO2 per ton of hot metal [6]. Smelting reduction has advantages and disadvantages. Some SR processes cannot use fine iron ore. On the other hand,SR processes are more flexible as far as the quality of used coal is concerned, and no coking is necessary. Power consumption in SR is nominally higher than in the BFs but off-gas can be used as an energy source. Hence, specific process and operation can have a significant impact on the overall efficiency. Future developments will probably improve energy efficiency by 5% to 30% in comparison with BFs [2, 5]. SR processes are also expected to reduce pollutants emissions. By avoiding coking, dust and VOC emissions are reduced. If sintering is omitted, the emission of metallic and non-metallic dust and gaseous pollutants is also reduced. However, first of a kind SR processes do not yet report these reduced emissions and the potential for future reductions is a matter of debate [2] Carbon Capture and Storage (CCS) in Iron and Steel Production – Two main options exist for capturing CO2 from the blast furnaces. The first consists of using a shift reaction and the physical absorption capture. Blast furnace gas is upgraded to a reducing feedstock (CO) tobe used in the blast furnace itself. This reduces coal and coke consumption, and the emissions as well, while physical absorption is used to capture the remaining CO2. The second option (see Figure 8) is based on the use of an oxy-fuelled blast furnace where pure oxygen is used as a feedstock [13], re-cycling blast furnace gas and capturing emissions from the top gas. The recycling stream can be split into two different flows - a cold stream, injected into the bottom of the BF and a hot stream to be injected higher. It improves the process at the reaction level. CCS processes are also under consideration for direct reduction and smelting reduction processes. By combining it with oxygen injection, CCS could result in a 85% to 95% reduction in CO2.

Manufacturing Processes

• Manufacturing started during 5000 – 4000 BC Wood work,ceramics,stone and metal work • Steel Production 600-800 AD • Industrial Revolution 1750 AD: Machine tools run by invention of steam engine. • Mass Production and Interchangeable Parts • Computer Controlled Machines 1965 • CNC,FMS systems

Period Egypt ~3100 B.C. to ~ 300 B.C Greece ~1100 B.C. to ~146 B.C Roman Empire ~500 B.C. to 476 A.D Middle Ages 476 to 1492 Renaissance 14th to 16th centuries Before B.C 4000

Metals and Casting Gold,copper iron and meteoritic

Forming Process Hammering Stamping Jewelry

4000-3000 B.C. 3000-2000 B.C. 2000-1000 B.C. 1000-1 B.C. 1A.D – 1000 A.D 1000-1500 A.D.

Copper casting,stone and metal molds,lost wax process,silver,lead,tin,bronze Bronze casting Wrought iron,brass Cast iron, cast steel Zinc steel Blast furnace, type metals,casting of bells,pewter

Wire by cutting and drawing, gold leaf

Stamping of coins Armor,coinage,forging steel swords Wire drawing,gold silver smith work

Historical development of materials - The Industrial Revolution
Industrial Revolution 1750-1850 1500-1600 A.D. Cast iron cannon, tinplate Water power for metal working,rolling mill for coinage Rolling(lead,gold,silver ) Shape rolling(lead)

1600-1700 A.D.

Permanent mold casting,brass from copper and metallic zinc

1700-1800 A.D.

Malleable cast iron,crucible steel Extrusion (lead pipe), deep drawing, rolling(iron bars and rods) Centrifugal casting,Bessemer process,electrolytic aluminum,nickel steels,Babbitt, galvanized steel, powder metallurgy, tungsten steel, open hearth steel Steam hammer, steel rolling,seamless tube piercing,steel rail rolling, continuous rolling , electroplating

1800-1900 A.D.

Steps in Modern Manufacturing
Definition of product need, marketing information

Conceptual design and evaluation Feasibility study

Design analysis;codes/standards review; physical and analytical models

CAM and CAPP Production

Prototype production testing and evaluation Inspection and quality assurance CAD Production drawings; Instruction manuals Packaging; marketing and sales literature

Material Specification; process and equipment selection; safety review

Product

Pilot Production

Manufacturing of a Paper Clip
• • • • What is the function How long does it last How critical is the part Material

• Dimension • Method of manufacturing • Function based design

• Style

Metallic - what type Non metallic – plastic Diameter of clip Shape of clip Manual Automated Stress, Strain Life of clip Stiffness Appearance,Color,Finish Plating,painting

Two methods of forming a dish shaped part from sheet metal Left: conventional hydraulic/mechanical press using male and female dies Right: explosive forming using only one die.
pressure

Upper die

Explosive

water

work piece

Lower Die

Three methods of casting turbine blades A: conventional casting with ceramic mold B: directional solidification C: Method to produce single crystal blade
SCOOP - Steel COst OPtimization – is a tactical and strategic decision aid tool. It is developed by n-Side for top decision makers to optimize globally their raw material purchases and main process setups, such as build-up and intermediate EAF steel composition. Its purpose is to enhance decision making process of steel managers by providing them an easily and rapidly accessible decision-making tool which relies on state-of-the-art business analytics and mathematical modeling techniques. SCOOP considers both technical and economical models. It takes into account chemical equilibriums, process thermodynamics, includes all the costs occurring during steelmaking process, and also performs various cost analysis. It diff erentiates from existing models in the industry by completely integrating all the processes from the raw material purchasing to the fi nal steel casting. Its global integration in one single model enables important optimization levers. SCOOP provides recommendations to maximize the absolute margin of a given plant under certain set of market and technical conditions and constraints. More precisely, SCOOP is mainly used for: optimization tion of real value in use of a raw material for the steelmaking process that guides negotiation efforts to be focused on the most attractive raw materials processes (e.g. EAF vs. AOD) SCOOP can also be used at a more operational level, especially for electrical steel production where prices and availabilities of scraps and ferroalloys change rapidly. In case of interlinked multiple sites, it calculates the optimal allocation of the raw material availability to the sites, based on respective orderbook. Specifi c versions of SCOOP are available:

SCOOP Stainless Steel & Special Steel covering Carbon Steel for Integrated Steel Works covering coke plant, sinter plant, blast furnace, steelmaking shop, and power plant. SCOOP Corporate, module adding optimization capabilities over multiple sites and multiple periods. The combination of the diff erent versions of SCOOP is alsopossible, e.g. using hot metal to partially charge in the EAF. STAINLESS & SPECIAL STEEL SCOOP (Steel COst Optimization for Stainless Steel and Special Steel) is one of the solutions which have quickest returns on investment (a few weeks). SCOOP mainly targets the raw material costs, which in some steel, like for the austenitic and other special steel grades with high content of expensive elements. It optimizes the raw material mix according to the production process. It enables Stainless and Special Steel makers to achieve savings lates into millions of dollars per year. Therefore it is certainly a strategic asset for any steel producer.

EXAMPLES OF MAIN LEVERS: 1. Trade-off between Ferro-Alloys and Scraps, depending on their respective market price and availability: As prices for raw materials change quickly, steel-makers must be ready to change the raw material mix with more or less usage of Ferro-alloys. The following graph is a simulation showing a sensitivity burden as its price increases, all other prices being constant. The graph on the right shows in more details how the diff erent nickel sources (ferro-nickel, nickel oxide, nickel cathode, …) are introduced in the mix as the total ferro-nickel usage increases. The order in which ferro-nickels are introduced in of their price, their availability and technical considerations (composition, thermal impact). PRICE OF STAINLESS SCAP 2. Selection of the Ferro-Alloys depending on contract type, market price, chemical analysis and currency rates: It is the same value. The reasons are diff erent market prices, contractual agreements and of course the chemical characteristics of the Ferro-Alloys. SCOOP optimizes the choice of sible cheapest grade by taking into account all quality and pricing constraints. 3. Process build-up (Intermediate Steel Composition): The process build-up is defi ned by the increase of mass from the fi rst stage of the process (EAF) to the second stage (AOD). It is related to the quantity of materials added to the converter (AOD or VOD). There is usually a technical degree of freedom about where to add material between the electrical furnace and the converter. The steel composition (carbon and silicon content) at the output of the electrical furnace can be adjusted within a limited margin to enable for more material addition in the converter. The production cost impact is important here, since the quantity of raw materials is infl uenced by the diff erent oxidation and reduction processes taking place at both process steps. There is high benefi ts by giving more fl exibility to the build-up. of steel by optimizong the intermediate steel between the EAF and converter processes. Note that process integration benefi ts will be higher for more complex production processes - involving blast furnaces or even coke plant and sinter plant, 4. Limit Marginal Price feature accelerates evaluation of the value of raw materials: In order to evaluate the value of a raw material, the Limit Marginal Price feature of SCOOP shows the price value of the next tons of a certain raw material. This value indicates whether or not adding that raw material to the raw material mix at a certain price will increase or

decrease the total production cost. This can be used during raw material purchasing negotiations to obtain a price that will minimize the cost impact to the current raw material mix. It also allows comparing the attractiveness between diff erent raw materials to choose the one with the highest value. This evaluation is a by-product of the optimization, it takes into account all technical impacts of the raw material on the process, like the impact on the slag quantity, thermal balance and productivity. 5. Improves communication between Process Managers The objectives of the process managers and the procurement people are not always compatible. Process people are mainly concerned about obtaining the required product quality and a high productivity whereas the objective of procurement people usually is to purchase raw materials at the best prices. Using a tool like SCOOP allows sharing objective information so best compromises can be made. 6. Productivity Optimization: Productivity plays an important role in SCOOP objective function of profi t maximization. In the case of high market demand, the productivity can be an important decision factor. By increasing the productivity, there can be high production and more revenues. Furthermore, min/max values for production level of each grade can be set (especially in the events of make to stock or uncertain demand). That will bring additional revenues by maximizing the production of the most profi table grades. Usually the most profi table grades are also often the most complex (and time taking) to produce therefore there will be a trade off to be found for the optimum production level of each grade family. www.scoop4steel.com 7. Optimal assignment of raw materials to each grade: SCOOP Stainless assigns optimally the usage of raw materials to different grades because each raw material doesn’t have the same value in use for each steel quality. 8. Multi-sites: optimal assignment of raw materials to each site: For bigger companies producing stainless or special steel on multiple sites and being partially supplied in raw materials from the same network, SCOOP Stainless can assign optimally the raw materials to each site in order to take the best value of each raw material. This value is infl uenced by the grades to be produced on the sites, the logistic costs to bring raw materials to each site and the process diff erences between the sites. 9. Downstream processes: The profi t maximization of selling the fi nal products can be limited by the capacity of an equipment in the downstream process. SCOOP also optimizes the usage of each downstream equipment considering a metallic loss and both economical and productivity aspects in order to produce the more profi table products. SCOOP brings the benefi ts of the integration and genericity compared to existing process and logistics models in market. It can be customized and calibrated for the specifi c needs of a given plant. Through its integrated nature, it brings together experts from diff erent departments of a steelmaking plant in order to align on common global objectives. THE SOLUTION SCOOP USE CASES Material Budget Yearly User group Pricing model, math. opt. model

negotiation eff ort Yearly Buyer Pricing model, LMP, scenario comparison tool Support IT/ spot contract negotiation Quarterly, Monthly Buyer Pricing model, LMP, scenario comparison tool Material Budget Quarterly, Monthly Math. opt. model, scenario comparison tool Optimize build up EAF and AOV/VOD Quarterly, Monthly Process experts Math. opt. model, scenario comparison tool Support process re-design Quarterly, Monthly Process experts Math. opt. model, scenario comparison tool Knowledge aggregation Cont. All Technical documentation SCENARIO COMPARISON _ JUST ONE CLICK Scenario optimization with SCOOP is extremely fast. It has been designed to give the results of a calculation in just one click. This allows the user to simulate multiple scenarios with diff erent assumptions in a minimum of time. This feature will emphasize the diff erences between multiple simulations, therefore facilitating the interpretation of the results. LIMIT MARGINAL PRICE CALCULATION TOOL SCOOP facilitates price negotiation based on the Limit Marginal Price calculation feature. This price indicates when a given raw material becomes attractive in terms of quality and price, and how the production cost is aff ected to any price variation. SENSITIVITY ANALYSIS KEY FEATURES Sensitivity analysis on the build-up showing the nickel mass balance at EAF and AOD It is often extremely important and interesting to uncover the trends within process, and relationships between various parameters and the fi nal result. The Sensitivity Analysis permits the variation of one or multiple parameters between predefi ned boundaries. It also allows launching multiple simultaneous optimizations for all the values of selected parameters between those boundaries. Any result of SCOOP (production volume, chemical analysis, cost calculation, etc.) can be exported to an Excel spreadsheet so that trend graphs can be drawn to visualize the impact of the considered parameters. either from the literature or from the site experience (sometimes accumulated over many years) are documented in SCOOP using hypertext. It can easily be seen, where and how a parameter is used in a particular formula and what are the impacts of other parameters on that formula. Hyperlink documentation includes many kinds of documents and graphics. The document platform in SCOOP is the ideal tool for plant knowledge aggregation and transfer. Technical models are based on publicly available scientific information. All models are nevertheless open for detailed review by expert users, moreover several customizations can be introduced to incorporate each site’s specifi c knowledge, especially regarding to empirical relationships.

SCOOP is both a tactical and strategic tool. It should not be seen as software for real-time process control. Built with a high degree of parameterization, SCOOP can easily be confi gured Saving One Barrel of Oil per Ton [SOBOT] A New Roadmap for Transformation of Steelmaking Processes Introduction Currently, energy represents about 20% of the total cost of producing steel and is rising. The increasing cost of energy and even its current and future availability have led to the need to refocus attention on energy intensity in steel production. To address this issue long-term, American Iron and Steel Institute (AISI) members are proposing the “Saving One Barrel of Oil per Ton”, or SOBOT, Research Program. Using today’s process routes and technology, the steel industry [integrated and EAF steelmakers] uses 12.6 million BTU per ton shipped, or 2.07 barrels of oil per ton shipped [2003 data].

Table 1: Steel Industry 19.55 MMBTU Energy Use [2003 Data] Integrated Steelmakers Electric Steelmakers 5.25 MMBTU Total Industry [49% 12.6 MMBTU EAF]

3.22 Barrels of Oil/t

.86 Barrels of Oil/t 2.07 Barrels of Oil/t

Approaches towards lowest energy steel production (low-carbon ironmaking and steelmaking) could involve: • Developing new processes having lower energy intensity, or new technologies that enable improved energy performance for existing processes. This includes technologies that can take advantage of the energy currently lost in existing processes. Alternative approaches may include: o avoiding a heating/cooling step o reducing the temperatures required

o recovering and applying heat at high temperatures • Coupling ironmaking and steelmaking processes to energy generation and thereby making maximum use of the chemical energy and thermal energy by-products of iron and steelmaking (the perspective of “the energy plant that produces a steel byproduct”). • Developing processes having lower carbon intensity or that use renewable forms of carbon. The steel industry can also develop technologies to transform the industry so it generates its own fuels or uses alternative fuels as they are developed by others. Such strategies can greatly reduce the use of natural gas an important national and industry goal. This requires making better use of the hydrocarbon fuels that are already in use, weaning itself away from its dependence on hydrocarbon fuels, and finding ways to sequester the greenhouse gases produced. In all likelihood, there will be no single technology that will accomplish all that is needed, but a combination of technologies Alternative fuels that could be substituted into the steelmaking process: The Paired Straight Hearth Furnace is an example of a high-productivity, low energy intensity ironmaking process. It uses no natural gas and the flow sheet below shows the relationship of the Hearth Furnace and Oxygen Melter working in synchronization energywise, i.e., the off-gas from the Oxygen Melter is used to fire the Hearth Furnace. This technology exemplifies the type of transformational project envisioned in the SOBOT Program. Chapter 1 - ENERGY SAVINGS This portion of the Saving One Barrel of Oil per Ton roadmap addresses the energy savings aspect of the program. The steelmaking process has undergone continuous optimization and re-invention over the past decades. Reasonable and obtainable energy efficiency improvements in the steel plant are on the order of 0.7 % per year. AISI recently reported that the United States steel industry has achieved a new milestone in energy efficiency by reducing its energy intensity per ton of steel shipped by approximately seven percent in 2003 compared to 2002 [Figure 1], thus extending its drop in energy intensity to 23 percent since 1990. Because of the close relationship between energy use and greenhouse gas emissions, the industry's aggregate carbon dioxide (CO2) emissions per ton of steel shipped were reduced by a comparable amount during the same period. AISI 2005 Chairman John P. Surma, president and CEO of United States Steel Corporation, said. "As part of our industry's Climate VISION agreement with the Department of Energy, we set a goal to improve energy intensity per ton of steel shipped by 10 percent by 2012 compared to the 1998 baseline. The 2003 data show we are making solid headway toward achieving that target." Figure 5 The goal of this program is to far surpass the energy savings conceived under CLimateVISION. This section provides a roadmap for maximizing energy savings in steel production operations by drawing upon the findings compiled in the document “Steel Industry Marginal Opportunity Study” (SIMOS) prepared by Energetics, Inc.

The term “energy savings” is considered equivalent to a reduction in energy consumption and accordingly would include energy recovery methods where potential energy losses are ultimately recovered and reused directly in the steel production process, e.g., scrap preheating by hot off-gases and post combustion. This chapter follows the general layout of the SIMOS document by considering energy saving opportunities through the sequential phases of the steel production process. Likewise, the scope of this chapter has been restricted to considering only steel production in North America. While this chapter includes a qualitative discussion regarding related reductions in the consumption of consumable items employed in steel production (e.g., refractories, electrodes, ferroalloys), the energy employed in the production of these consumables is not quantitatively considered. When one looks beyond the steel plant into the entire value chain, a compelling rationale for energy and environment-focused projects is often found. For example, the development of advanced high strength steels (AHSS), now being adopted by automakers, is resulting in tremendous energy and environmental benefits as a result of dramatic improvements in fuel savings. The following benefits are based on a market penetration of only 7% of AHSS- type vehicles, a low hurdle given the rapid adoption

Another way to look at this example is a lightweight steel vehicle of the type designed under AISI’s Ultra Light Steel Auto Body – Advanced Vehicle Concepts [ULSAB-AVC] Program saves 21.2 MMBTU per year over a vehicle operating at today’s mileage standard of 27.8 mpg and driving 10000 miles per year. Even when applied to only 1 million vehicles per year, about 6% of the new
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vehicles built and entering service each year, the energy savings is 2.12 X 10 BTU/Yr. Savings throughout the steel value chain should not be ignored and may impact heavy equipment, trucks, cars, machinery and buildings. Steelmaking Processes Since the majority of energy consumption in the production steel occurs during the respective ironmaking and steelmaking (including melting, refining and casting) processes, consideration of these process steps should provide the most significant opportunities for energy savings. Many of these energy savings opportunities are generally applicable to both ore-based and scrap-based steelmaking processes. Some of these are listed below along with possible relevant technologies included in parentheses. - improved energy management (sensors, post-combustion) - increased yields (near-net shape casting) - reduced refractory consumption (improved refractory, slag splashing) - reduced flux consumption Integrated Steelmaking The integrated steelmaking process, as defined in SIMOS, is the ore-based manufacture of steel and combines hot metal production and BOF steelmaking. The document goes on to identify a possible energy saving of just over 30%. Since the vast majority of the total integrated steelmaking energy expenditure (about 98%) occurs in the production of hot metal, the majority of readily accessible energy savings (about 65% of the gap) is directly attributable to the ironmaking process. Most of the remaining energy savings are categorized as general, (e.g., preventive maintenance, improved variable speed drives for pumps and fans, etc.) Today’s modern blast furnace is the product of decades of technological improvements. Energy consumption in blast furnace ironmaking has decreased by more than 50% since 1950. Still, the blast furnace accounts for nearly 40% of the overall energy use in the steel industry and significant
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energy opportunities remain. However, a review of the SIMOS document reveals that about ½ of the bandwidth falls outside the realm of energy savings (captureable predominately as latent energy recovery/co-generation . While modest improvements in blast furnace efficiency still continue to be found (through optimized injection technologies and better sensors/process control), any major gains may have to be achieved via alternative ironmaking technologies. However, it should be recognized that environmental concerns (primarily associated with the production of coke and sinter for the blast furnace process) have been the primary drivers for the development of these new processes, not reduced energy consumption. Thus R & D efforts directed to decrease/optimize overall energy consumption in new alternative ironmaking processes are an appropriate focus for this program. The BOF process itself is not a major energy consumer. It is the inherent energy of the charge materials that impact the overall energy intensity of this steelmaking path. Given the high energy cost in the production of hot metal, any technologies that allow an increased scrap/hot metal ratio in the BOF charge would provide a clear benefit and accordingly deserve some consideration. EAF Based Steelmaking Data in the SIMOS report indicates that transitioning from the integrated ore-based steelmaking to scrap-based EAF steelmaking provides the single most effective means of lowering energy requirements for steel production. Driven by this and other associated benefits (e.g., lower capital cost, reduced CO2 generation, increased flexibility) the percentage of EAF produced steel has gradually increased over the past 50 years. The introduction of low cost EAF/Continuous Casting based technology in the 1970’s quickly displaced integrated producers in the long products market. The rate of increase in EAFproduced steel has risen dramatically in the 1990’s with the introduction/proliferation of thin slab casting and the corresponding penetration into the flat products market. The growth of EAF based steel tonnage is expected to continue. However, a number of factors will start to have an impact on this trend, the most prominent being future limitations on scrap availability. Developing a means to overcome some of these barriers (e.g. improved processes for low-grade scrap recovery) could represent research opportunities. Within the EAF steelmaking process, the SIMOS document indicates an energy gap comprising over 45% of the industry average. This is split 2/3 from implementation of “best practices” opportunities and 1/3 from current and future R&D opportunities. Most of the “best practice” opportunities are related to energy savings, primarily achieved through improvements in furnace design, process control, scrap preheating/charging practices and post combustion. Home scrap availability will decrease as further gains in yield are made. Furthermore, based on 1997 data, 89% of discarded automobiles, 80% of discarded appliances, and 60% of discarded steel cans were already being recycled.
Some of the process control improvement efforts include striving for increased electrical energy transfer efficiencies (e.g. current carrying conducting electrode arms), reduced tap-to-tap times, and increased percentage of power-on time. R&D opportunities could include sensible heat recovery from slags, fumes and off-gases. Casting The major energy savings obtained in the casting processes have been achieved as a result of the transition from ingot casting to continuous casting product, the elimination of soaking pit cycles for ingot reheating, and from the significant additional yield improvements in the continuous
† †

casting process. The transition from ingot to continuous casting is virtually completed for flat products. However, some ingot making capacity still exists in the production of long products. The primary barrier to the complete conversion to continuous cast long products is perceived differences in quality, especially steel cleanliness. A concerted effort has been underway to eliminate this particular barrier. Near-net shape casting provides the opportunity for energy reduction in the subsequent rolling process by reducing the number of forming steps required to produce a final product. Thin slab casting is probably the most significant form (in terms of tonnage) of near-net shape casting. Strip casting is still in the early stages of commercialization and needs to overcome some quality and productivity concerns before it can achieve widespread acceptance and provide any significant impact on steel industry energy savings objectives. Beam blank casting is a growing near-net shape process in the long products category. Rolling and Finishing The primary means of energy savings in rolling operations is the elimination/minimization of reheating steps. This may be achieved to a certain extent through new casting and rolling technologies including near-net shape casting (discussed above) and direct rolling. Fruehan et al. has estimated that direct charging decreases energy consumption of the rolling process by about 80%. (The actual energy savings would depend on the charging temperature of the slab/bloom.) Most of the perceived barriers to direct rolling are based on either logistical or quality issues. Logistical barriers include plant layout and product mix/order size impact on scheduling. The quality barriers are predominately tied to the multi-stage inspection and conditioning requirements currently necessary to meet increasing customer expectations on surface quality. Energy is also consumed in the deformation of the steel during rolling/forming processes (i.e. energy for mill motors and drives). This amount of energy consumed
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ENERGY SUBSTITUTION Worldwide economic and population growth have caused the demand for energy to increase dramatically. During the period 1990 to 2001, global energy usage increased by approximately 15%. Inevitably, this has been a significant factor in causing energy prices in North America to rise during that period by over 75%. Furthermore, energy prices have always been very volatile. These trends are expected to continue and even worsen in future years. Additionally, many fear that the increasing concentration of greenhouse gases in the atmosphere from human activities is contributing to global climate change. These trends create pressure and opportunities in the steel industry to seek new technologies for the generation, conservation, and substitution of fuels, and ultimately the development of new steelmaking processes. Energy substitution has near, medium and long-term aspects. In the short term, the steel industry has the opportunity to avail itself of or maximize its use of alternative fuel technologies already extant. Near Term In the near term, the steel industry must continue to implement the latest energy saving technologies. This implies the need for worldwide benchmarking of best practices. We must also look to expand the use of known energy saving and fuel substitution strategies. For example, blast furnace coal injection avoids the losses inherent in the cokemaking operation and facilitates tends to be small in comparison to the energy consumed for reheating. Still there are opportunities for reducing the energy consumption, perhaps through appropriately applied casting of near-net shape forms requiring less deformation and less energy.
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The issue of mechanical vs. thermal processing needs to be studied. Such a study will discover opportunities to replace thermal processing with less energy intensive mechanical processing.

Table 5: Barriers & Opportunities to Achieving Barriers Energy Savings in Steelmaking Opportunities Steelmaking Improved energy Return–on-Investment as a management (sensors, post- rationale for Capital combustion) Investment - Increased yields (near-net shape casting) Reduced refractory consumption (improved refractory, slag splashing) - Reduced flux consumption Integrated possible energy savings (bandwidth) of just over 30%. Transition BOF to EAF steelmaking BOF Steelmaking Increased scrap/hot metal ratio in charge EAF Steelmaking Electrical energy transfer efficiency Casting Net shape casting Development and maintenance cost Rolling Net shape casting Development and maintenance

Inputs to the process include raw materials such as iron ore, limestone, scrap and alloys, and energy such as coal, coke, natural gas, and electricity. Outputs include both the finished steel product (the “product”), as well as by-products in the form of gases, liquids, solids, and heat (“by-products). In a 100% efficient process, all of the inputs, both raw materials and energy, would be converted to finished product at ambient temperature (the basis of the theoretical minimum energy requirement calculations); but obviously, this level of efficiency is unattainable. Even in the most ideal case, the process of making steel requires heating the raw materials to a temperature above the liquidus of the final steel composition, processing it, and returning it to ambient temperature. For cold rolled products, processing requires yet another temperature excursion to the annealing/heat treating temperature and again, cooling to ambient. Even if the raw materials and energy conversion were 100% efficient, there would still be a substantial loss of heat to the environment, heat which contains potentially usable energy. Since iron ore sources are less than 100% pure iron, there will inherently be by-products representing the

grid. In this example, the by-product outputs (volatile coal off-gases) are converted into electrical energy, which offsets electricity that would otherwise be generated elsewhere. The research community is thus challenged to examine all of the by-product outputs of both conventional and emerging steelmaking processes for other opportunities to recover and redistribute energy. Several other potential by-product energy sources will be discussed subsequently to start the thought process in this regard.

Cokemaking Process Energy Recovery Opportunities Traditional cokemaking processes include coal as the major raw material input and use coke oven gas and electricity as the primary energy inputs. Outputs include: solid coke, which is charged to the blast furnace; off-gases from the coking reaction; and heat, much of which is converted to steam during the coke quenching operation. The off-gases include a mixture of H2 and CO, and a mixture of hydrocarbons and other volatile compounds released from the coal during heating. Minor amounts of CO2 are also produced due to infiltrated air. Potential energy recoveries from the cokemaking process include: combusting the offgases to produce electricity in a steam turbine (as illustrated in the non-recovery coke making process example cited earlier); extracting the hydrogen from the coke oven gas for use in hydrogen-powered vehicles or equipment; recovering the heat in the steam from the quenching process for lower temperature heating or power generation processes; or as is currently done, using these off-gases in blast furnace stove heating and in the blast furnace itself via tuyere injection. Technologies that can allow the recovery of sensible heat of the coke oven gas prior to ammonia liquor quenching should be investigated. The steam from the quenching process or produced by utilizing the latent heat in the off-gases could be captured and filtered for use in steel plant processes that require steam, such as heating process baths (pickle tanks, strip cleaning tanks) and steam equipment (steam ejector based vacuum degassers). Improvement to current dry quenching technology must also be investigated. Blast Furnace Ironmaking Process Energy Recovery Opportunities Major blast furnace process inputs include: iron ore; fluxes, such as limestone to extract the gangue oxides from the ore and to absorb impurities; coke; natural gas, fuel oils, and directly injected coal to add carbon units; electricity; and combustion air and natural gas or coke oven gas to fire the hot blast heating stoves. Major outputs include: liquid pig iron; molten slag containing the impurities in the input ore; furnace off-gases consisting primarily of CO and CO2 from the combustion of coke and the reduction of iron oxide; and stove off-gases consisting of CO2 and water from the combustion of natural gas, blast furnace gas and coke oven gas. The furnace off- gases also contain a quantity of fines from the furnace. Major sources of waste-heat include that released

from the molten slag while cooling to ambient, combustion gases from the stove, and heat losses through the furnace shell. Opportunities for energy recovery include: combusting the blast furnace off-gases in the hot blast stoves; the cokemaking process , or hot mill reheating furnaces (as is common practice currently); extracting hydrogen from the furnace gases for use in hydrogen powered vehicles or equipment; CO2 removal from the top gas to possibly enhance its calorific value; and recovering the latent heat from the molten slag, stove off-gases, or steam captured in slag granulation systems. Modern high top pressure furnaces have energy recovery turbines. Higher turbine conversion efficiencies and more economical designs for medium top pressure furnaces could be investigated. Pelletizing and sintering are two ways by which iron bearing materials are engineered 3 for superior performance in modern-day blast furnaces. In a pelletizing plant, iron ore feed is ground, impurities are partially removed, and the purified ore is converted into balls which are then heated at high temperatures. The pelletizing operation has recirculating combustion gas streams that allow for recovery of sensible heat. Improved heat exchanger designs would allow for increased energy recovery, primarily from the off-gases in the first preheating zone. Direct-reduced Ironmaking Process Energy Recovery Opportunities Modern direct-reduced ironmaking (DRI) processes convert iron oxide directly to solid sponge iron. The reactions occur at elevated temperatures, requiring heat input to and heat liberation from the process. Reductions are driven either by CO–CO2 reactions, starting from coal, or H2/CO - H2/CO2 reactions using natural gas. Any DRI process generates waste heat that could be subsequently recovered and redistributed. The processes also either generate CO/CO2 off gases, which could be further combusted to generate electricity or other power/heat; or H2/CO/CO2, from which hydrogen could be extracted for use in hydrogen-powered vehicles or equipment. Steelmaking/Casting Process Energy Recovery Opportunities The steelmaking/casting process stage includes several individual processes that are used in multiple combinations – electric arc furnace (EAF) melting or BOF steelmaking, ladle or AOD refining, desulphurization, argon stirring, vacuum degassing, and continuous casting. Major raw material inputs include: molten pig iron (from the blast furnace), solid scrap at ambient temperature, ferroalloys, oxygen, slag fluxes, and equipment cooling water. Major energy inputs include chemical energy (contained within the molten pig iron) and electricity. Major by-product outputs include: molten slag, hot iron fines and oxides, CO/CO2 resulting from decarburization processes
2 2

The viability of this needs to be further investigated due to the very non-luminous flame. While their may be opportunities for heat recovery from sintering operations, the low use of sintering in North America limits such opportunities

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(including both the BOF, AOD, VOD and vacuum degasser), spent cooling water, nonrecovered heat from the cooling water, heat lost to the ambient environment, and heat o in the slabs which exit the caster at temperatures around 1100 C. Perhaps the most significant energy recovery opportunity in the steelmaking/casting process is the off-gases from the BOF process in integrated plants. Both sensible heat and chemical energy of the contained gases must be considered. While technologies currently exist for this purpose, they have not been economically viable for implementation in North America. Technology that can prove to be viable in the North American market would be of tremendous importance. The heat remaining in the slabs as they exit the caster is another potential area for heat recovery. Some of the heat generated in the ironmaking and steelmaking process must be extracted to cool the steel to a solid form that is amenable to subsequent hot rolling processes. Typically, the steel is cooled to a temperature of approximately 1100 C prior to exiting the caster. The heat lost during cooling from temperatures above the liquidus to an 1100 C exit temperature is typically dumped directly into the environment and lost. Currently, some steelmaking shops are configured to hot charge the cast slabs to the reheating furnaces at the hot mill, thereby reducing the energy that would otherwise ultimately be required to heat the slabs to the hot rolling temperature. Unfortunately, not all shops are favorably configured, and steelmaking shop/hot mill scheduling often prevents scheduling slabs for hot rolling immediately as they exit the caster. It would be of great value to develop technologies that better facilitate hot charging, or otherwise recapture and recover the latent heat energy contained in the slabs as they cool before reheating for hot rolling. Hot Rolling Process Energy Recovery Opportunities Major raw material inputs at the hot rolling process include slabs from the caster and equipment/process cooling water. Major energy inputs include: latent heat in slabs that can be hot charged; natural gas, coke oven gas, and/or blast furnace gas for the reheat furnaces; and electricity. Major by-product outputs include heat lost by the steel slab/strip during cooling from the reheating temperature to ambient, reheat furnace off-gases, spent equipment and process cooling water, and a small amount of iron oxide generated by oxidation in the reheat furnaces and during hot rolling.
4 o o

4

Given the exit water temperature either from mold or spray cooling, the temperature difference may be too low for meaningful exploitation. Any significant opportunity to recover heat energy from this application would need to consider a different solidification methodology.

The energy potential of input gases at the reheat furnaces is generally completely consumed by the combustion process. Generally, the greatest energy recovery opportunity in the hot rolling process is from the heat remaining in the strip after exiting the finishing stand and again after exiting the cooling table. Upon exiting the reheating furnace and through the final finish rolling stand, heat is continuously lost from the slab/strip to the environment. This heat is generally unrecoverable, although technical developments are targeting methods to keep as much heat in the strip as possible as it proceeds through the rough and finish rolling processes (e.g. transfer table covers, coil boxes, etc.). Thermal energy could potentially be recovered after finish rolling at two stages – during cooling from the finishing temperature to the coiling temperature on the run-out table, and subsequently during cooling of the finished coils from the coiling temperature to ambient temperature in preparation for subsequent cold processing. Such thermal energy recovery techniques would need to take into account the need to maintain controlled cooling rates consistent with those necessary to achieve the appropriate metallurgical properties of the specific product. Finishing Process Energy Recovery Opportunities There are considerably fewer opportunities for recovering and redistributing energy from the by-product outputs of processes subsequent to the hot rolling step. The one possible exception is the annealing process. In this step, cold rolled steel is heated to temperatures up to around 820 C to anneal the cold rolled structure, and subsequently to provide controlled cooling to impart desired structure and metallurgical properties. Annealing processes include batch and continuous annealing for cold rolled strips, and continuous annealing as part of the continuous hot dip galvanizing process. Potential energy recovery opportunities in this process include energy contained in offgases from heating processes using combustion, and from the heat liberated from the steel strip during controlled cooling from the annealing temperature to ambient. In addition, many annealing processes use protective atmospheres containing from 5 to 100% hydrogen; these off-gases are not normally recovered and represent a potential source for hydrogen recovery and redistribution. The research community is encouraged to examine other by-product outputs in the finishing stage for other energy recovery opportunities not recognized here.
STEEL RECYCLING One aspect of the steel industry’s contribution to the sustainable use of natural resources within an integrated product policy. STEEL SCRAP MARKET The steel industry has been operating steel scrap recycling systems on a large scale for more than 150 years, and operates via a well-established market that has developed without any public incentive. Furthermore, recycling has grown in parallel with increased steel consumption. Recycling of steel scrap has economic as well as environmental advantages for the steel industry by saving resources and energy. The steel recycling system is very efficient and all the steel in collected end-of-life products is recycled, irrespective of the percentage of steel in the products. Products that are easy to disassemble, with easily separated steel parts, have a greater potential to be recycled. The magnetic properties of steel make it very easy and economic to separate from other. Steel scrap, including new scrap from the steel making process, scrap from the manufacturing industry and post-consumer scrap, e.g. end of life products, represents an important and much desired raw material for the steel industry. However, with steel
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consumption continuing to grow in conjunction with the long service life of an average steel product, current demand for steel scrap cannot be satisfied. Figure 5: There has always been a strong economic incentive to recycle steel scrap There is already an economic incentive to recycle steel, due to the inherent value of scrap. The European steel industry is working to maximise the efficiency of scrap collection from all waste streams. This brochure is for information only. EUROFER assumes no responsibility or liability for any errors or inaccuracies that may appear. No part of this brochure may be reproduced in any form without the prior written permission of EUROFER. All rights reserved. Steel can be recycled over and over again without loss of properties. Steel’s 100% recyclability is demonstrated by the existing high recycling rates, without the need to specify minimum recycled content levels. Steelmaking Technologies Contributing to Steel Industries 1. Introduction NKK has continued to develop new steelmaking technologies in its never-ending pursuit of the ideal of meeting the needs of society. The unique, world-leading steelmaking technologies developed and put into practice by NKK are represented by the dramatic reduction in the amount of slag generation due to efficient dephosphorization in the hot metal pre-treatment process; high-speed and extremely effective quality control in the continuous casting process; and the development of useful products made from steelmaking slag. These technologies constitute an important foundation for the newly formed JFE Steel Corporation to continue responding to social needs into the 21st century. This paper summarizes major steelmaking technologies that NKK has developed in recent years, noting their significance. Refining technologies Hot metal pre-treatment technology The hot metal pre-treatment method, where hot metal is dephosphorized prior to refining in a converter, was actively put into practice in the 1980’s by the major steelmakers of Japan in order to meet customers’ requirements for lower phosphorous content in steel products, while reducing slag generation and increasing the iron yield. However, dephosphorization by this method is still insufficient, and a more effective process was desired. A thorough investigation by NKK on the dephosphorization mechanism revealed that lowering the silicon content in the hot metal to an ultimate level leads to a dramatic improvement in the efficiency of lime for dephosphorization. Based on this finding, a firstinthe- world, open-ladle-type desiliconization station was installed at Fukuyama Works in March 1998. The silicon content of the hot metal was minimized before dephosphorization, improving the efficiency of lime for dephosphorization. Moreover, slag generation through the entire steelmaking process was successfully lowered to an ultimate level. The phosphorous content of the steel was lowered to the level of the final product specification while still in the hot metal stage, and slag generation during dephosphorization in the converter was nearly eliminated. Therefore, this technology was named the ZSP (Zero Slag Process) and deployed at Keihin Works as well in May of the same year, expanding the application of this process company-wide1). the process flow at the Fukuyama Works. Hot metal is transferred through the desiliconization station, a mechanical-stirringtype desulfurization process called KR, a ladle type dephosphorization station called the NRP (New Refining Process), or an LD-converter-type dephosphorization process called LD-NRP, before finally being charged into a converter. Each technology for the ZSP is described below. Technology for mass-production ultra-low silicon hot metal

The silicon content of hot metal tapped from the blast furnace is already lowered to a level of 0.2% by the low silicon operation of the blast furnace. This is achieved by methods such as low temperature operation, wherein the temperature is measured continuously. The low silicon hot metal is then sent to the desiliconization station, where itbecomes ultra-low silicon hot metal with a silicon content of less than 0.10%. At the desiliconization station, oxygen gas is used along with sintered iron ore (iron oxide) as the oxidizer for deoxidation. Steelmaking Technologies Contributing to Steel Industries siliconization. The reaction vessel is a ladle type, and the hot metal is vigorously stirred by injecting lime through a submerged lance. This method dramatically improved the oxygen efficiency for desiliconization over the conventional method of desiliconization, which is performed in hot metal runners on the cast-floor, and provides a highly efficient and stable supply of ultra-low silicon hot metal. Hot metal dephosphorization technology Experiments confirmed that reducing the silicon content of hot metal in turn lowers the amount of CaO that reacts with silica to form calcium silicate (2CaO-SiO2) in the early stage of desiliconization. Instead, calcium phosphate (3CaO-P2O5) is formed directly. Also, a practical technology was established for performing the dephosphorization of the ultra-low silicon hot metal by controlling the oxygen flow rate and temperature. The reduced silicon content increased the efficiency of lime for dephosphorization, significantly lowering the lime consumption and stabilizing the phosphorous content in the hot metal after treatment. At the Fukuyama No.2 steelmaking shop where the ladle- type dephosphorization process (NRP) is employed, the reduced slag generation retards the slag foaming phenomenon and other process-hindering factors. Hence, the extent of dephosphorization in the NRP was markedly increased by elimination of freeboard limitation in the hot metal transfer ladle. On contrary, the LD-converter-type dephosphorization process (LD-NRP) has been in operation at the Fukuyama No.3 steelmaking shop since 1995. The LD converters in this shop are used as a decarburization furnace in the first half of their vessel life and then as a dephosphorization furnace in the latter half. Using ultra-low silicon hot metal, the dephosphorization furnace performs high-speed dephosphorization operation on all the hot metal that goes through this shop. This dephosphorization operation is synchronized with the tap-to-tap time of the decarburization furnace, to which the hot metal is then sent. The efficient high-speed dephosphorization achieved by these technological developments allowed an increase in the ratio of hot metal for which the dephosphorization operation can be applied. At Fukuyama Works, it is now possible to apply the ZSP to 100% of hot metal, even at the high production amount of 10 million tons per year. The average phosphorous content of hot metal after treatment is consistently less than 0.012%, allowing the decarburization furnace to be operated without the need of performing dephosphorization. Hence, flux consumption at the decarburization furnace was lowered to the minimum level required to protect the furnace refractories. Fig.2 shows slag generation before and after the desiliconization station was installed. The slag, which was previously generated at a rate of more than 100 kg per ton of steel, was decreased by half. The slag generated in the converter dropped to less 59 than 10 kg/t. Effect of ZSP on slag generation The lowered generation of slag brought about various additional benefits. The first is that the direct reduction of manganese ore in the converter became possible. Thus, NRP de[Si] BF de[P] de de[C] KR

LD-NRP De [Si] –ST Before ZSP ZSP (Present) 150 0 50 100 de[P] de[Si] ferromanganese consumption was markedly reduced. The second is that the life of the refractory lining of the converters was extended from 3000 charges to 8500 to 9000 charges. In addition, the ZSP had a large effect on improving the quality of the steel produced, such as a significant reduction in the generation of alumina, as described later. Further, the compositions of the slags were simplified, which expanded their effective uses. As also described later, slag from desiliconization is now used effectively as potassium silicate fertilizer, while slag from dephosphorization is formed into large blocks by carbonation for constructing artificial fishing reefs. These slag products have been commercialized by NKK as environmentally friendly products that open the way to the nextgeneration steelmaking process. 2.2 New converter technologies 2.2.1 High-speed blowing technology In the 1980’s, a top-bottom-combined blowing technology (NK-CB) was developed by NKK for steelmaking converters2). Next, the development of the ZSP described above turned a converter into a decarburization furnace that can effectively perform direct reduction of manganese ore3). Major problems associated with this operation were iron spitting during oxygen blowing due to the minimized slag volume, decreased iron yield due to the increased dust generation rate, and unstable furnace operation. These problems hindered the realization of high-speed blowing for increasing productivity. NKK achieved high-yield, high-speed blowing by developing new technologies, as listed below, and shortened the blowing time by about 25%. As a result, the steel-producing capacity of one furnace (in the Fukuyama No.3 steelmaking shop) was increased to more than 480000 tons per month, contributing greatly to the increase in productivity. (1) On-line dust measurement system Dust generation from a converter has complicated relationships with various factors, such as the speed of oxygen gas blown through the oxygen lance and the lance nozzle shape. These make it difficult to quantitatively predict the dust generation behavior, and no effective method had been available for directly evaluating the dust generation volume or rate. Hence, an on-line dust measurement system was developed4). This system continuously measures the converter dust generation volume by continuously sampling the dustcollecting water discharged from a wet-type dust catcher and measuring the dust concentration optically. The on-line dust measurement system adopted at the Fukuyama No.3 steelmaking shop is schematically shown in Fig.3. With this system, the dust generation during converter blowing operation is measured on-line, allowing optimization of the oxygen blowing pattern and other operational parameters. Those data resulted in the rapid development of a new lance nozzle.

Schematic view of on-line dust measurement system (2) Dynamic pressure control of top-blown oxygen Iron spitting and dust generation rates in a converter are correlated with the dynamic pressure of the top-blown oxygen jet on the molten metal surface. This correlation was used to develop a new technology for controlling dust generation by using the dynamic pressure calculated from the nozzle shape and other blowing conditions5). When applying this technology to actual operation, the on-line dust measurement system was used to rapidly optimize the nozzle shape and other blowing conditions. These technologies reduced the amount of dust generation from the converter and stabilized the operation .



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