process of iron making

iron processing | britannica

iron processing | britannica

iron processing, use of a smelting process to turn the ore into a form from which products can be fashioned. Included in this article also is a discussion of the mining of iron and of its preparation for smelting.

Iron (Fe) is a relatively dense metal with a silvery white appearance and distinctive magnetic properties. It constitutes 5 percent by weight of the Earths crust, and it is the fourth most abundant element after oxygen, silicon, and aluminum. It melts at a temperature of 1,538 C (2,800 F).

Iron is allotropicthat is, it exists in different forms. Its crystal structure is either body-centred cubic (bcc) or face-centred cubic (fcc), depending on the temperature. In both crystallographic modifications, the basic configuration is a cube with iron atoms located at the corners. There is an extra atom in the centre of each cube in the bcc modification and in the centre of each face in the fcc. At room temperature, pure iron has a bcc structure referred to as alpha-ferrite; this persists until the temperature is raised to 912 C (1,674 F), when it transforms into an fcc arrangement known as austenite. With further heating, austenite remains until the temperature reaches 1,394 C (2,541 F), at which point the bcc structure reappears. This form of iron, called delta-ferrite, remains until the melting point is reached.

The pure metal is malleable and can be easily shaped by hammering, but apart from specialized electrical applications it is rarely used without adding other elements to improve its properties. Mostly it appears in iron-carbon alloys such as steels, which contain between 0.003 and about 2 percent carbon (the majority lying in the range of 0.01 to 1.2 percent), and cast irons with 2 to 4 percent carbon. At the carbon contents typical of steels, iron carbide (Fe3C), also known as cementite, is formed; this leads to the formation of pearlite, which in a microscope can be seen to consist of alternate laths of alpha-ferrite and cementite. Cementite is harder and stronger than ferrite but is much less malleable, so that vastly differing mechanical properties are obtained by varying the amount of carbon. At the higher carbon contents typical of cast irons, carbon may separate out as either cementite or graphite, depending on the manufacturing conditions. Again, a wide range of properties is obtained. This versatility of iron-carbon alloys leads to their widespread use in engineering and explains why iron is by far the most important of all the industrial metals.

There is evidence that meteorites were used as a source of iron before 3000 bc, but extraction of the metal from ores dates from about 2000 bc. Production seems to have started in the copper-producing regions of Anatolia and Persia, where the use of iron compounds as fluxes to assist in melting may have accidentally caused metallic iron to accumulate on the bottoms of copper smelting furnaces. When iron making was properly established, two types of furnace came into use. Bowl furnaces were constructed by digging a small hole in the ground and arranging for air from a bellows to be introduced through a pipe or tuyere. Stone-built shaft furnaces, on the other hand, relied on natural draft, although they too sometimes used tuyeres. In both cases, smelting involved creating a bed of red-hot charcoal to which iron ore mixed with more charcoal was added. Chemical reduction of the ore then occurred, but, since primitive furnaces were incapable of reaching temperatures higher than 1,150 C (2,100 F), the normal product was a solid lump of metal known as a bloom. This may have weighed up to 5 kilograms (11 pounds) and consisted of almost pure iron with some entrapped slag and pieces of charcoal. The manufacture of iron artifacts then required a shaping operation, which involved heating blooms in a fire and hammering the red-hot metal to produce the desired objects. Iron made in this way is known as wrought iron. Sometimes too much charcoal seems to have been used, and iron-carbon alloys, which have lower melting points and can be cast into simple shapes, were made unintentionally. The applications of this cast iron were limited because of its brittleness, and in the early Iron Age only the Chinese seem to have exploited it. Elsewhere, wrought iron was the preferred material.

Although the Romans built furnaces with a pit into which slag could be run off, little change in iron-making methods occurred until medieval times. By the 15th century, many bloomeries used low shaft furnaces with water power to drive the bellows, and the bloom, which might weigh over 100 kilograms, was extracted through the top of the shaft. The final version of this kind of bloomery hearth was the Catalan forge, which survived in Spain until the 19th century. Another design, the high bloomery furnace, had a taller shaft and evolved into the 3-metre- (10-foot-) high Stckofen, which produced blooms so large they had to be removed through a front opening in the furnace.

The blast furnace appeared in Europe in the 15th century when it was realized that cast iron could be used to make one-piece guns with good pressure-retaining properties, but whether its introduction was due to Chinese influence or was an independent development is unknown. At first, the differences between a blast furnace and a Stckofen were slight. Both had square cross sections, and the main changes required for blast-furnace operation were an increase in the ratio of charcoal to ore in the charge and a taphole for the removal of liquid iron. The product of the blast furnace became known as pig iron from the method of casting, which involved running the liquid into a main channel connected at right angles to a number of shorter channels. The whole arrangement resembled a sow suckling her litter, and so the lengths of solid iron from the shorter channels were known as pigs.

Despite the military demand for cast iron, most civil applications required malleable iron, which until then had been made directly in a bloomery. The arrival of blast furnaces, however, opened up an alternative manufacturing route; this involved converting cast iron to wrought iron by a process known as fining. Pieces of cast iron were placed on a finery hearth, on which charcoal was being burned with a plentiful supply of air, so that carbon in the iron was removed by oxidation, leaving semisolid malleable iron behind. From the 15th century on, this two-stage process gradually replaced direct iron making, which nevertheless survived into the 19th century.

By the middle of the 16th century, blast furnaces were being operated more or less continuously in southeastern England. Increased iron production led to a scarcity of wood for charcoal and to its subsequent replacement by coal in the form of cokea discovery that is usually credited to Abraham Darby in 1709. Because the higher strength of coke enabled it to support a bigger charge, much larger furnaces became possible, and weekly outputs of 5 to 10 tons of pig iron were achieved.

Next, the advent of the steam engine to drive blowing cylinders meant that the blast furnace could be provided with more air. This created the potential problem that pig iron production would far exceed the capacity of the finery process. Accelerating the conversion of pig iron to malleable iron was attempted by a number of inventors, but the most successful was the Englishman Henry Cort, who patented his puddling furnace in 1784. Cort used a coal-fired reverberatory furnace to melt a charge of pig iron to which iron oxide was added to make a slag. Agitating the resultant puddle of metal caused carbon to be removed by oxidation (together with silicon, phosphorus, and manganese). As a result, the melting point of the metal rose so that it became semisolid, although the slag remained quite fluid. The metal was then formed into balls and freed from as much slag as possible before being removed from the furnace and squeezed in a hammer. For a short time, puddling furnaces were able to provide enough iron to meet the demands for machinery, but once again blast-furnace capacity raced ahead as a result of the Scotsman James Beaumont Nielsens invention in 1828 of the hot-blast stove for preheating blast air and the realization that a round furnace performed better than a square one.

The eventual decline in the use of wrought iron was brought about by a series of inventions that allowed furnaces to operate at temperatures high enough to melt iron. It was then possible to produce steel, which is a superior material. First, in 1856, Henry Bessemer patented his converter process for blowing air through molten pig iron, and in 1861 William Siemens took out a patent for his regenerative open-hearth furnace. In 1879 Sidney Gilchrist Thomas and Percy Gilchrist adapted the Bessemer converter for use with phosphoric pig iron; as a result, the basic Bessemer, or Thomas, process was widely adopted on the continent of Europe, where high-phosphorus iron ores were abundant. For about 100 years, the open-hearth and Bessemer-based processes were jointly responsible for most of the steel that was made, before they were replaced by the basic oxygen and electric-arc furnaces.

Apart from the injection of part of the fuel through tuyeres, the blast furnace has employed the same operating principles since the early 19th century. Furnace size has increased markedly, however, and one large modern furnace can supply a steelmaking plant with up to 10,000 tons of liquid iron per day.

Throughout the 20th century, many new iron-making processes were proposed, but it was not until the 1950s that potential substitutes for the blast furnace emerged. Direct reduction, in which iron ores are reduced at temperatures below the metals melting point, had its origin in such experiments as the Wiberg-Soderfors process introduced in Sweden in 1952 and the HyL process introduced in Mexico in 1957. Few of these techniques survived, and those that did were extensively modified. Another alternative iron-making method, smelting reduction, had its forerunners in the electric furnaces used to make liquid iron in Sweden and Norway in the 1920s. The technique grew to include methods based on oxygen steelmaking converters using coal as a source of additional energy, and in the 1980s it became the focus of extensive research and development activity in Europe, Japan, and the United States.

sunflag steel | 5 steps of steel manufacturing

sunflag steel | 5 steps of steel manufacturing

Steel is easily one of the most popular construction and production alloys in the world. It is a versatile product that blends durability with cost effectiveness and flexibility to work with. India happens to be one of the top five producers of steel in the world. But while steel is a highly preferred production material, have you ever wondered how steel itself is produced?

The first step to making steel is to make the iron from which it will be made. This is usually done with the help of coal. Raw bits of iron ore, coke, and lime are put into something called a blast furnace. Here, they result in molten iron (which is also called hot metal

The primary steelmaking process either involves a BOS method (basic oxygen steelmaking) or EAF method (electric arc furnace). In BOS, recycled scrap steel is added into the molten iron. At a really high temperature, oxygen is blown into this mixture to reduce the overall carbon content. In EAF, however, the recycled steel scrap is put through high-power electric arcs (of temperatures as high as 1650 C) in order to fully melt it and convert it to high quality steel.

Secondary steelmaking puts together both these processes. This is mainly done to fine-tune the composition of the steel being produced. Elements are added in specific temperature and environmental controls to create the perfect composition. These controls can include stirring, ladle-furnace, ladle injections, degassing, and CAS-OB (Composition Adjustment by Sealed Argon Bubbling with Oxygen Blowing).

The molten iron is now put into a cooling mold, which sets the shape to a certain degree. It also causes the formation of a thin, hard shell. This shell is separated by the use of guided rolls. The strands of the shell are malleable, and can be worked into the desired shape, length depending on what they will be used for. Examples include flat sheets, beams, wires, or thin strips.

This is the final shaping process, where hot rollers are used to fine tune the cast. The defects of casting are removed, and the steel is molded into the exact desired shape and surface finish. This is the stage at which the rough shape of the steel transforms into definitive ones like, pipes, wire rods, bars, rails, and more.

In todays world, steelmaking is trying to produce alternate and more sustainable methods that allow for this process to continue with minimal damage to natural resources. While steel remains a powerful and durable alloy, its production is massively carbon based. Steel companies in India are trying to find alternate routes to this.

For instance, a process calledPulverized Coal Injection is sometimes used in the primary steelmaking process. In this case, coal is directly injected into the furnace instead of coke. The coal used can be of low carbon content, which also reduces the cost of production.

Another fact is that steel is completely, 100% recyclable. The BOF process uses 30% of recycled steel, while EAF uses up to 90-100%. This is a far more sustainable option instead of mining more iron ore as a fresh ingredient in the steelmaking process.

There is also an alternate steelmaking process called HIsarna ironmaking. In HIsarna, iron ore is processed immediately into hot metal. The blast furnace used is a cyclone converter furnace, which skips the making of iron pellets. This skipped step makes the entire process far more energy-efficient and lowers the carbon footprint of steel production.

Steelmaking remains crucial in the industrialized world, an unavoidable process from massive scale infrastructure to the smallest kitchen utensils. It is simply a matter of finding a process that can be sustainable in the future, and cause minimal environmental damage while doing so.

ironmaking process - an overview | sciencedirect topics

ironmaking process - an overview | sciencedirect topics

The ironmaking process in the blast furnace is a heat and mass transfer process, and the furnace can be divided into different zones according to physical and chemical state of the feed and temperature. Figure 1.1.5 illustrates various zones of the blast furnace and feed distribution and materials flow [13]. Corresponding to each temperature interval, typical reactions will take place. The descending burden is dried and preheated during its descent by the ascending gas. The preheated blast is blown into the furnace through the tuyeres in the lower part of the furnace. Oxygen in the blast reacts with coke carbon to produce carbon monoxide and blast humidity reacts with carbon to produce carbon monoxide and hydrogen:

The role of nitrogen in the blast is to act as a heat carrier together with CO, CO2, and H2. The combustion space in front of the tuyeres is called the raceway. The adiabatic flame temperature in the raceway is about 21002300C. The ascending hot gas heats up the dripping iron and slag, which are collected in the hearth below the tuyere level and tapped at certain intervals. The ascending gas flows through the cohesive zone, also called softeningmelting zone. Here iron and slag become soft, and they separate and melt down. The slag phase contains some unreduced iron oxide FeO. The reduction of this iron by solid carbon is called direct reduction:

These reactions diminish when gas temperature falls below 900C. Reduction reactions, increasing in CO2 content and cooling of the gas continue along with its ascending. The remaining heat content of the gas is used to dry and preheat the burden before the gas leaves the furnace top at 100300C. The top gas is still a valuable fuel having a lower heating value of 34MJ/Nm3.

After the relatively rapid heating to about 900C, the burden reaches the chemical reserve zone where the temperature difference between gas and solid is about 50C. At about 10001100C (depending on the chemical composition of the ferrous burden and the reduction degree), the burden comes to the cohesive zone. Iron oxides are mainly reduced to metallic Fe. The burden starts to soften. Iron and slag separate. The FeO content in slag phase can vary inside a large range, e.g., 525%. Metallic iron is carbonized by carbon in the coke and CO gas and melts at 12001300C. Molten iron and slag drip down through the coke layer to the hearth where they reach their final temperature and composition.

The BF ironmaking process is currently the dominant process for providing steelmaking raw materials worldwide. However, the BF process relies heavily on metallurgical coke and involves cokemaking and sintering operations, which often attract serious environmental concerns. Therefore, DR and SR technologies using noncoking coal or other gases as reducing agents to replace metallurgical coke are expected to emerge as future alternative routes for iron production. Due to the vast difference in operating conditions between these processes, different quality parameters are imposed by their operators on ferrous burden to ensure the efficiency and economics of the process. To quantify these quality parameters, a variety of standard and nonstandard physical tests have therefore been developed. The standardized tests are simple but generally are conducted at fixed conditions, which often represent the extreme situations encountered by ferrous materials. However, while nonstandardized physical testing methods are very sophisticated, they simulate the working conditions that the ferrous materials encounter more closely. Therefore, nonstandard physical tests are recommended in addition to standard physical tests when unfamiliar burden materials are used. Finally, because different ferrous materials have distinct characteristics, a comprehensive burden evaluation program allows the plant operator to maximize productivity at the lowest cost by optimizing the burden composition.

Regardless of the ironmaking process, sulfur and phosphorus are generally undesirable elements in any raw material, since they can make the final steel product brittle and weak. Often limestone (CaCO3) or dolomite (CaMg(CO3)2) is added with the feed to an RK and mixed with iron ore concentrate to act as a desulfurizing agent. The specification for sulfur in RK-grade coal in India is a maximum of 1% [38]. The maximum moisture content allowed in the same coals is 7%.

One disadvantage of the coal-based technologies is that they often bring significant levels of impurities with them, as part of the coal ashfor the low-grade Indian coals, ash can be as high as 27.5% of the coal [38]. This ash is typically made up of common slag-forming components such as SiO2, Al2O3, CaO, MgO, and FeO, though other oxides and sulfides are often present. The exact mix of components in a particular coal ash can be criticalfor example, ash containing more than 70% silica can react with ferrous oxide (FeO) to form a low-melting point compound (fayalite, Fe2SiO4) that interferes with the reduction process [39].

A schematic diagram of the flash ironmaking process is given in Figure 4.5.30. Natural gas or hydrogen will be partially combusted with industrial oxygen through a burner on top of the flash reactor to generate a reducing gas stream at 16001900K. Iron ore concentrate will be injected in the vicinity of the burner and will undergo reduction reaction as it flows down. Although this figure displays the version of the process wherein the reduced iron is collected as a molten bath for the possibility of direct steelmaking in a single unit, the reduced product may also be collected as solid particles and briquetted to be charged in separate steelmaking furnaces.

In the new process, the concentrate will be reduced to a high degree of metallization in suspension in a hot reducing gas generated by the partial combustion of natural gas, heavy oil, hydrogen, or a combination thereof.

The flash ironmaking process is initially expected to be operated using natural gas as a fuel and reducing agent. Natural gas is an abundant readily available resource in the United States. According to the 2011 Annual Energy Outlook [64], the estimations on the United States production rate of natural gas predict a steady increase. Further, there is a big push to increase natural gas production in the United States from its considerable reserves. The recently discovered reserves in Marcellus Shale [65] represent a good example of this trend. For an annual production of 20million tons of iron, which would represent about 40% of the current United States production rate, the flash ironmaking process would require 0.33TCF/year (trillion cubic feet per year) of natural gas. This represents less than 1.5% of the total United States consumption rate (22.7TCF/year) [64]. As a comparison, this is similar to the 1.5% of the total United States energy consumption used by the United States steel industry. When natural gas is used as a reducing agent, the proposed process will produce iron with varying carbon contents such as the iron produced by HYLs ZR self-reforming process [66]. In the latter process, carbon levels can be up to 5.5%.

Hydrogen would be the cleanest reductant and/or fuel from the viewpoint of environmental concerns and reduction kinetics. There is much expectation for the development of hydrogen economy and thus the availability of inexpensive hydrogen, for which much effort and resources are being devoted [67,68].

The proposed technology is to be applied either as an ironmaking step, with the product to be fed directly to the secondary steelmaking units such as an EAF, bypassing the converting step like BOF, or as an integral part of a continuous direct steelmaking process from the concentrate [52]. A silicon-free, lower carbon iron, as will be produced by the proposed process, is used in the LD-ORP (LD converter-optimized refining process) of NSC (Nippon Steel Corp.) or in NSCs converter-based all scrap melting process with coal. Alternatively, carbon could be added in the briquetting step, or the EAF could be modified by adding a lance for gas injection to promote optimum slag foaming, rather than relying on CO produced from dissolved carbon, to enhance the refining and steelmaking reactions.

Although the new technology under development at the University of Utah is aimed at eventually replacing the BF, it could be used, on a moderate scale, to increase output in a conventional integrated steel plant by utilizing COG as a hydrogen source not only by extracting its hydrogen content but also by reforming the methane present therein.

The flash ironmaking process will remove many of the limitations associated with other alternative processes. Specifically, (a) direct use of iron oxide concentrates without the need for pelletization or sintering; (b) no cokemaking required (if coal is used to generate the hot reducing gas, pulverized coal of wide variety can be used); (c) high temperature can be used because there will be no particle sticking or fusion problems; (d) possibility to produce either solid or molten iron; and (e) low refractory problems, ease of feeding the raw materials, and the possibility of direct steelmaking in a single unit, as shown in Figure 4.5.30.

An important condition for the proposed process is whether iron oxide concentrate can be reduced to a high metallization degree within the few seconds of residence time available in a typical flash furnace. This issue will be addressed below together with others that need to be resolved before the new process becomes ready for commercialization. Suffice it to note here that the rate is sufficiently fast for the reduction of iron ore concentrate in a flash reaction process above 1450K [60,69].

Ironmaking and steelmaking slags are inevitably generated as a by-product from ironmaking and steelmaking processes. Main components of the slags are CaO, SiO2, Al2O3, MgO, and iron oxides, and the compositions of slags depend on the process. In the case of Japan, three types of slags, namely BF slag, BOF slag, and EAF slag are mainly produced, which amount is shown in Figure 4.4.11 [79] and the typical compositions of each slag are summarized in Table 4.4.2 [80]. Main component of BF slag is SiO2 and Al2O3, coming from iron ore as gangue minerals, and CaO added as a flux during sintering process. On the other hand, BOF slag mainly contains CaO added as a refining agent, and SiO2 and iron oxides produced by oxidation refining process. The EAF slag is classified into two types, oxidation slag and reduction slag, which are produced during steel refining and reduction of iron oxide to metallic iron, respectively.

Slag compositions of constituents entrained from gangue components depend on the compositions of raw materials, while those of other constituents added as a flux for refining processes are designed to maximize its refining performance, and thus there is a wide variety of components and compositions of slags. Approximately 300kg/ton-pig iron and 100kg/ton-steel of BF slag and steelmaking slag (BOF or EAF slag) are generated. Totally 24, 11, and 2.9 million ton of BF, BOF, and EAF slags (FY2011) are produced in Japan [79].

Common slag treatment process in Japan is shown in Figure 4.4.12 [81]. About 80% [79] of BF slag is quenched by water spray and the quenched BF slag sand produced is used mainly for cement, concrete and civil engineering resources. The rest is cooled by field air cooling and the slow cooled slag is used as a resource for road construction, concrete coarse aggregate, and so on. On the contrary, since steelmaking slag contains iron droplets at several percents in weight the slag cannot be quenched by water splashing. Therefore, slag is treated by field air cooling and then crushed and screened. Iron droplets are recovered by magnetic separation and remained slag is sold for various purposes such as civil engineering, cement or concrete resource. BF slag is completely recycled, while small fraction of steelmaking slag cannot be utilized due to the elution of hazardous elements such as heavy metals or fluorine. Development of new technologies to use such slag is an important solution to reduce the amount of slag landfilled without any utilization.

Regarding the measure to decrease the environmental load by slags generated from ironmaking and steelmaking processes, following two methods are considered. The first is the reduction of generated slag amount by development of highly efficient processes. Metallurgical slags have been mainly designed to increase the refining capability as a function of slags so far. Recent process and slag designs are based not only on the improvement of the refining capability but also on the reduction of environmental load such as the decrease of slag amount, discontinuation of the use of hazardous elements, or the development of the process which generates recyclable by-products (slags). The second measure is the development of the new utilization method of slag as a resource. Utilization method of the ironmaking and steelmaking slags as an abundant resource should be developed by creating new functions and additional values.

The carbonization of coal has its historical roots in the iron and steel industries. The ironmaking process developed around the Mediterranean Sea spreading northward through Europe (Attig and Duzy, 1969). Historians state that the Phoenicians, Celts, and Romans all helped spread ironmaking technology, with one of the ironmaking techniques spread by the Romans as far north as Great Britain. Originally, charcoal produced from wood was the fuel used to melt the iron ore. A tremendous amount of wood was needed for this industry. For example, one type of furnace, the Stuckofen, used in fourteenth century Germany could produce 4000 pounds of iron per day with a fuel rate of 250 pounds of charcoal per 100 pounds of iron produced (Wakelin, 1999). This was an early version of the charcoal blast furnace and these furnaces that developed in continental Europe soon spread to Great Britain.

By 1615, 800 furnaces, forges, or ion mills existed in Great Britain, with 300 of them blast furnaces. The rate of growth in the number of these furnaces was so great and their consumption of wood so high that during the 1600s parliament passed laws to protect the remaining forests. Consequently, many blast furnaces were shut down, alternative fuels were looked for, and England encouraged the production of iron in its North American colonies, which had abundant supplies of wood and iron ore. The first successful charcoal blast furnace in the New World was constructed outside of Boston at Saugus, Massachusetts, in 1645.

As a result of the depletion of virgin forests in Great Britain to sustain the charcoal iron, the iron masters were forced to look at alternative fuel sources. The alternative fuels included bituminous coal, anthracite, coke, and even peat (Wakelin, 1999). The development of coke and anthracite ironmaking paralleled each other and coexisted with charcoal production during the 1700s and 1800s, while the use of bituminous coal and peat never became a major ironmaking fuel. The wide use of coke in place of charcoal came about in the early 1700s when Abraham Darby and his son demonstrated in 1708/1709 that coke burned more cleanly and with a hotter flame than coal (Berkowitz, 1979). Up until 1750, the only ironworks using coke on a regular basis were two furnaces operated by the Darby family (Wakelin, 1999). However, during the period 17501771, the use of coke spread with a total of 27 coke furnaces in production. The use of coke increased iron production because it was stronger than charcoal and could support the weight of more raw materials, and thus furnace size was increased.

The use of coke then spread to Continental Europe: Creussot, France in 1785; Gewitz, Silesia in 1796; Seraing, Belgium in 1826; Mulhiem, Germany in 1849; Donete, Russia in 1871; and Bilbao, Spain in 1880 (Wakelin, 1999). In North America, the first attempt to use coke as 100% fuel was in the Mary Ann furnace in Huntington, Pennsylvania, although coke was mixed with other fuels as early as 1797 in United States blast furnaces.

The efficient use of coke and anthracite in producing iron was accelerated by the use of steam-driven equipment, the invention of equipment to preheat air entering the blast furnace and the design of the tuyeres and the tuyere composition (Wakelin, 1999). The evolution of both coke and anthracite ironmaking paralleled each other in the United States during the 1800s, and by 1856 there were 121 anthracite furnaces in operation. With coke being the strongest and most available fuel, the evolution of 100% coke furnaces continued with major steps being made in the Pittsburgh, Pennsylvania area between 1872 and 1913. The Carnegie Steel Company and its predecessor firms developed technological process improvements at its Monongahela Valley ironmaking furnaces that ultimately made it possible for the United States to take over worldwide leadership in iron production. This is not true today, however, as much of the steel production has shifted overseas beginning in the 1960s and early 1970s.

Cokeless technologies can be divided into two principle groups: carbon-based (directuse of coal and biomass products) and hydrogen- or electricity-based ones.The first group, which includes SR processes (with some restrictions, see Section13.5.1) and coal-based direct reduction processes, may diminish but not solve the problem of CO2 emissions. By the second group of methods, the crucial point is themass hydrogen or carbon-free electricity production at a reasonable price. Atransition period from carbon- to hydrogen-based iron and steel production is unavoidable.

Carbon serves until now as a main chemical reactant to convert iron-bearing materials to iron and steel, and CO2 is an unavoidable by-product of this reaction. The amount of carbon required is dictated by laws of chemistry, physics, and thermodynamics. Since many decades, CO2 emissions in the steel industry reflect the primary energy consumption (Fig.13.17, left side). This dependence makes it hardly possible to mitigate further carbon dioxide emission in the most energy-intensive ironmaking sector. The best performing BFs operate with energy consumption close to the thermodynamic limit while using the high-quality raw materials.

The following ways can be considered as short and midterm measures to break the direct dependence of CO2 emissions on primary energy consumption (Fig.13.17, right side) and to counteract the lowering quality of raw materials by using the BF process as well as DR and SR ironmaking processes (Babich etal., 2016; Babich and Senk, 2017):

In the process of stack gas injection some hydrocarbon fuel is reformed to a mixture of H2 and CO and this gaseous reducer is injected into the lower stack of the blast furnace. This process was investigated by several authors and steel plants and is thought to be a proper candidate for lowering CO2 in the ironmaking process. The results of these experimental investigations have been reviewed in the state-of-art paper of Rhee [4] and are summarized in fig.3. The data are from the experimental and real blast furnace tests of the different institutions like CRM, NKK, Nippon Steel and U. S. Bureau of Mines already done during 1960s and 70s. The effectiveness index of the stack gas injection in lowering coke consumption in the blast furnace can be expressed in the sense of effective (CO+H2) volume per ton hot metal which is calculated from the content of partial pressures of CO, H2, CO2, and H2O in the injected gas stream. Fig.3 shows that the coke consumption can be lowered proportionally to the effective (CO+H2) volume.

Fine and ultra-fine ferrous ores must first be agglomerated to produce sinter or pellets respectively. Lump ore may be charged directly to a blast furnace but only after it has been suitably sized and screened to remove overand undersize material. Lump ore, however, usually comprises a minor portion of the total ferrous feed. Coal cannot be directly charged via the furnace top, it must first be transformed to coke.

Raw materials are charged to the furnace in alternating layers of coke and ore. This alternating layer structure inside the furnace has a profound impact on the operation of the furnace and on the required quality of coke. This in turn has an influence on the VIU of the parent coals used to make that coke.

For many ironmaking plants coke is an expensive raw material and/or is in short supply. Pulverised coal (PCI) may be injected through the tuyeres as a substitute for coke. However, PCI has some fundamental impacts on blast furnace operation, which will be discussed later. Because of these impacts only ~40% of coke requirements may be replaced by coal injection.

Internally the blast furnace is considered to consist of five discrete zones, see Fig.17.2, through which all furnace gases and/or liquids must pass. The location, shape and extent of each zone is influenced by the properties of the material layers (relative thickness, etc.) and by the properties of the materials themselves. These factors interact to determine the flow and distribution of gases within the furnace. It is the distribution of gas flow within the furnace which largely determines the four most important aspects of ironmaking profitability:

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