The use of direct reduced iron (DRI) and DRI products is constantly on the rise and will be for the foreseeable future. DRI production in 2013 hit 75.22 million tons compared to only 23.65 million tons twenty years prior in 1993 and only 49.5 million tons in 2003. Accordingly there are very few individuals even remotely associated with the iron and steel industry that do not know of DRI and its forms as Hot DRI (HDRI), Cold DRI (CDRI) and Hot Briquetted Iron (HBI). But DRI like other metallics can vary in its makeup. There are numerous product properties but only a few that have an immediate, direct and significant effect on the overall iron/steel production process, especially in the electric arc furnace (EAF). Optimizing these variables relative to one another is critical to reducing the total operating cost of iron and steel production. The question often asked is, What are the properties of the best DRI? Although some would have us to believe there is one utopian answer, the truth is remarkably different. The better question to ask may be how can DRI best help our operations. At AM Montreal, our objective is to maximize liquid steel output while reducing the utility costs to an optimum level. The past four decades of operations has led us to determine that metallic content and physical quality are paramount.
To set the stage, ArcelorMittal not only has the largest capacity for DRI production in the world, the company also has the complete suite of DRI process technologies, operating both MIDREX Process and HyL Process shaft furnace/reactor plants as well as rotary kiln plants. Further, our history of DRI production is extensive. Our MIDREX Module 1 at Arcelor Mittal Montreal has been in operation since 1973. The reason we operate these direct reduction plants is very simple; we need high quality low residual metallics for production of steel via the most cost effective route possible.
The use of DRI for ArcelorMittal in general, and more specifically at ArcelorMittal Montreal, is dependent on several factors including; costs versus that of comparable scrap, utility price of natural gas and electrical power, specification for the steel being produced and environmental impact. As with any issue, there are both positive and negative aspects of using DRI. Figure 1indicates the relative movement of the price for DRI versus Busheling. One can easily see that there is in most cases a raw cost advantage with charging DRI versus scrap and at this time the total operating cost of steel production with DRI is $50 per ton less than that using Busheling.
The advantages of DRI include: predictable chemistry, low tramp material content, carbon and foamy slag formation, lower capital and operating costs, relatively uninterrupted continuous iron making, EAF feed adjustment via blending with lower quality feed material (usually scrap), and less back charging. Figure 2 indicates EAF yield variation when charging DRI compared to scrap loading. It is quite obvious that charging DRI is advantageous to hot metal quality.
Notwithstanding these advantages there are disadvantages as well. These include: additional energy to melt gangue material, increased slag handling, potential for DRI chute blockage, increased baghouse dust and fines, higher refractory costs, lower yield and, and in the case of CDRI versus HBI, there are additional procedures that must be taken for storage, handling and transportation.
With all of this being said, the advantages of DRI in regards to its value to steelmaking operations far outweigh the disadvantages. Being in a position of supplying DRI primarily for internal use we frequently monitor and test the quality of our DRI to assure we are meeting the needs and expectations of our customer which in this case are our own meltshops.
Of course DRI is not 100% Fe. It inherently contains some portion of non-reduced iron oxide, carbon and any other components contained within the feed material. Whatever the case, the primary reason for feeding DRI is its iron content. Normally DRI produced from an EAF grade iron oxide material, formally referred to as DRI grade, will contain 91% to 93% total iron depending on the initial feed material properties. Direct reduction, as the name implies, reduces these pellets into metallic iron by removing oxygen from FeO to produce a product that is typically 92% to 96% metallized (Fe). Metallization is the percentage of metallic Fe out of the total iron content.
The rate of metallization depends on the DRI process and how it is operated, typically the higher the metallization rate, the lower the production rate and higher the specific consumptions rates for natural gas and electrical power. Further, in addition to gangue materials, the DRI will contain some quantity of carbon. In the EAF, this carbon can be used to first complete the reduction of the final fraction of the 4% to 8% iron oxide not reduced after which carbon in the product, can be useful for the formation of CO to produce foamy slag above the EAFs melt line. Carbon is also of course needed to meet the required carbon content in the final steel produced, and it also, can be used to add chemical energy to the EAF to lower the electrical consumption of the EAF. Figure 3 indicates the composition of typical DRI produced at AM Montreal.
One must look at the requirements of the meltshop and the economics of the DRI plant operation to determine what chemistry is optimum for his/her overall operation. Specifically the total iron content, degree of metallization and carbon content must be controlled to optimize the overall cost and throughput of the total cycle. Minimizing gangue content and reducing fines, (<5%) are beneficial regardless of the balance of the chemistry. Accordingly, for all practical purposes, the DRI quality can be defined based on two types of characteristics: those that are created by the DRI process such as degree of metallization, carbon content, and those that reside independent of the process such as the gangue content in the raw materials and fines concentration. See Figure 4*.
Ultimately the purpose of using DRI is to provide metallic iron to the meltshop, thus DRI is of better value to us if we can get more Fe to the meltshop. Metallization, fines, gangue and carbon all represent potential limitations to this goal.
When addressing these properties, metallization, carbon and fines may be effected by the process. Whatever gangue, predominantly silica, is fed to the DRI plant is discharged as part of the product as the reduction process only removes oxygen from the product, not gangue materials. In any case, less is better when considering the total gangue in the DRI feed material. For reference see Figure 6indicating the cost of increasing gangue content by one percent.
It should also be noted that fines can be created in the DRI process itself, but in this case we are referring more to the generation cause in normal handling of the raw materials and finished product. In any case, the more fines generated can be viewed as a loss of iron that could otherwise be utilized in the steelmaking process.
To minimize electricity consumption and increase efficiency, the goal is to have as much metallic iron as possible, meaning having a high rate of metallization (%Fe out of FeO). For every additional percent of metallized iron charged to an EAF there will be improvements in EAF yield, EAF productivity, EAF power consumption, refractory degradation and electrode degradation. Based on our experience at AM Montreal these relative effects are indicated in Figure 7.
As just stated, the real reason one uses or buys DRI is for its metallized iron content. Addition of any other component such as gangue materials and even carbon decreases the total iron in a charge. With that said, carbon is necessary in the EAF. The primary reasons are: reduction of the remaining non-metallized iron oxide in the DRI, formation of foamy slag, to meet the carbon specification in the steel being produced, and as additional chemical energy to the EAF thus reducing the electric power requirement. Figure 8 indicates the benefit of adding one full percent carbon to the EAF based on our experience at AM Montreal.
The value of the DRI is based on at least four major qualities, none of which are uniform, but all affect every operation. Our objective is to maximize liquid steel output from the EAF while reducing the utility costs to an optimum level. Over decades of operations we have determined that metallic content and physical quality are paramount. In any case we wish to start with the best raw materials (iron oxide feed materials) possible in order to have the least possible gangue and minimize fines generation. After that we need to maximize our Fe content even further through making DRI with high metallization. Based on our current utility, ore and scrap prices along with the production and quality demands of our onsite customer we are producing DRI at 94% to 95% metallization and 2.0% to 2.2% carbon. Ideally the EAF melt shop would prefer 95% to 96% metallization, but our DRI plants must do a continuous balancing act to assure optimum operations. Other AM DRI plants run at similar metallization rates with carbon levels ranging between 2.2% to 2.7% so even within our own company the optimum rates differ, yet the primary focus is still the Fe first. Please also note that in our scenario at AM Montreal we are looking at CDRI only, as that is reflective of our operations. HBI & HDRI share similar favorable qualities as CDRI, however, in the case of HDRI, temperature of the product is a major factor to increased EAF efficiency, without sacrificing metallic content.
In a DR process, iron ore pellets and/or lump iron ores are reduced by a reducing gas to produce DRI or hot briquetted iron (HBI). Depending on the generation of the reducing gas, two different DR processes are commercially available: gas-based and coal/oil-based. In the gas-based DR process, the reducing gas is produced by chemically reforming a mixture of natural gas and off-gas from the reducing furnace to produce a gas that is rich in hydrogen and carbon monoxide. Typical examples of the gas-based DR process include MIDREX and HYL, which are often the preferred technology in countries where natural gas is abundant. However in the coal/oil-based DR process, the reducing gas is generated from hydrocarbons (primarily coal, but sometimes oil and natural gas) in the reduction zone of the furnace, which is typically a rotary kiln. Typical examples of the coal-based process include the SL/RN and ACCAR processes. The coal-based DR process is more popular in India and China. Different types of reactors, such as shaft furnaces, fluidized beds, rotary kilns, and rotary hearth furnaces, have been used in different variations of the processe to achieve the metallization required.
Based on statistics (Anon 3, 2014), India is the world leader in DRI production producing about 17.8Mt of DRI in 2013, approximately one-forth of world DRI production. The gas-based DR processes are producing almost 80% of the world's DRI. MIDREX is the key variant of the gas-based DR processes accounting for about 63.2% of world DRI production in 2013, followed by HYL (15.4%). Therefore, the following discussion focuses mainly on the MIDREX process.
Direct reduction (DR) processes have been in existence for several decades. The evolution of direct reduction technology to its present status has included more than 100 different DR process concepts, many of which have only been operated experimentally. Most were found to be economically or technically unfavorable and abandoned. However, several were successful and subsequently improved to develop into full-scale commercial operations. In some instances, the best features from different processes were combined to develop improved processes to eventually supplant the older ones.
Direct reduction processes may be classified, according to the type of the reducing agent used, to gas-based and coal-based processes. In 2000, DRI produced from the gas-based processes accounted for 93%, while the coal-based processes produced 7%. Gas-based processes have shaft furnaces for reducing. These furnaces can be either a moving bed or a fluidized bed. The two most dominant gas-based processes are MIDREX and HYL III, which combined to produce approximately 91% of the worlds DRI production. Fluid-bed processes, by contrast, have recently received attention, because of its ability to process fine iron ores. These processes are based either on natural gas or coal. A list of the processes together with their relevant characteristics is given in Table 1.2 (MIDREX, 2001).
The gaseous (or carbothermic) reduction of nickel oxide, obtained by dead roasting of nickel sulfide matte or concentrate, is an important intermediate step for nickel production. In the Mond process, crude nickel is obtained this way before undergoing refining by carbonylation. Crude nickel has sometimes been cast into anodes and electrolytically refined. Nickel laterite ores are reduced by carbon monoxide before an ammoniacal leach. Nickel oxide reduction reactions are simple one-step reactions, as follows:
Both reactions have negative Gibbs free energy values. For hydrogen reduction it is 7.2 and 10.3kcal/mol, respectively, at 600K and 1000K. For reduction by CO, the free energy values are 11.1kcal/mol at both 600K and 1000K. The thermodynamic data used here as well as below were obtained from Pankratz et al. (1984). The corresponding equilibrium ratio pH2/pH2O is 2.4103 and 5.6103, respectively, at 600K and 1000K, and the equilibrium ratio pCO2/pCO is 9.5105 and 3.7103, respectively, at the same temperatures. Therefore, the reactant gases are essentially completely consumed at equilibrium in both cases. These reduction reactions are mildly exothermic, the standard enthalpy of reaction (Hro) being 2 to 3kcal/mol for hydrogen reduction and 11.2 to 11.4kcal/mol for reduction by carbon monoxide.
Zinc occurs in nature predominantly as sphalerite (ZnS). The ZnS concentrate is typically roasted to zinc oxide (ZnO), before the latter is reduced to produce zinc metal by the following reactions (Hong et al., 2003):
The overall reaction is essentially irreversible (G=12.2kcal/mol at 1400K) and highly endothermic (H=+84.2kcal/mol at 1400K) and the gaseous product contains a very small amount of CO2 at temperatures above 1200K (Hong et al., 2003). It is also noted that this reaction is carried out above the boiling point of zinc (1180K), and thus zinc is produced as a vapor mixed with CO and the small amount of CO2 from the reaction. Zinc is recovered by condensation. Zinc vapor is readily oxidized by CO2 or H2O (produced when coal is used as the reducing agent) at lower temperatures. Thus, zinc condensation should be done as rapidly as possible, and the CO/CO2 ratio in the product gas must be kept as high as possible by the use of excess carbon in the reactor.
The final process in tungsten production is the hydrogen reduction of the intermediate tungsten oxide (WO3 or W4O11) obtained through the various processes for treating tungsten ores. Because of the substantial volatility of the higher oxide, its reduction is carried out at a low temperature to obtain nonvolatile WO2. WO2 is then reduced to tungsten metal at a higher temperature (Habashi, 1986), as indicated below:
The reduction reaction is carried out at about 2200C and thus magnesium is produced as a vapor (B.P. = 1090C). Much like zinc vapor mentioned earlier, magnesium vapor is susceptible to oxidation and requires similar measures for its condensation and collection.
For other aspects of gaseous reduction of metal oxides, including reduction by carbon involving gaseous intermediates, the reader is referred to the literature (Alcock, 1976; Evans and Koo, 1979; Habashi, 1986).
Gas-based direct reduction processes are particularly suitable for installation in those areas where natural gas is available in abundance and at economical prices. The MIDREX process is a shaft-type direct reduction process where iron ore pellets, lump iron ore or a combination are reduced in a Vertical Shaft (reduction furnace) to metallic iron by means of a reduction gas (see Figure 1.1.39) .
The reducing gas is produced from a mixture of natural gas (usually methane) and recycled gas from the reduction furnace. The mixture flows through catalyst tubes where it is chemically converted into a gas containing hydrogen and carbon monoxide. The desired reducing-gas temperature is typically in the range of 900C. The gas ascends through the reduction shaft in the counter-current direction and removes oxygen from the iron carriers. The product, DRI, typically has the total iron content in the range of 9094% Fe. After the DRI exits from the bottom of the shaft, it can be compressed in the hot condition to HBI for safe storage and transportation. DRI or HBI are virgin iron sources free from tramp elements and are increasingly being used in EAF to dilute the contaminants present in the scrap.
The first commercial-scale MIDREX Direct Reduction Plant began operation in 1969 at Oregon Steel Mills in Portland, Oregon. There are now over 60 MIDREX Modules operating, under construction, or under contract in 20 countries. The scale of MIDREX plants continues to grow and today MIDREX has built the largest single module DR Plant in the world at Hadeed in Saudi Arabia, with a rated capacity of 1.76 milliontons/year. A more detailed description of direct reduction processes can be found in Chapter 1.2.
Natural gas-based DR processes account for about 92% of worldwide production of DRI. Natural gas consists primarily of methane (CH4), together with small amounts of other hydrocarbons, nitrogen, and carbon dioxide. Natural gas cannot be used directly in the reduction of iron ore because it decomposes to form soot at a temperature below that which iron oxide can be reduced. Natural gas is used in three main ways: first, as a feedstock for producing the reducing gas, second as a fuel for supplying the necessary heat in the furnace and gas reformer, and third as a coolant and carburizing agent for freshly-prepared DRI. A major constraint on the specification for natural gas is its sulfur content; if above 10ppm, it can deactivate some types of reformer catalyst. Techniques are available to remove sulfur if necessary.
The essence of any DR process is to reduce iron oxide to metallic iron to the greatest extent economically viable. By the nature of the chemistry involved (and customer needs), there is carbon pickup as well. The first step in determining the ratio of pellets to DRI is calculating the chemical changes due to loss of oxygen and gain of carbon. This is a straightforward calculation, requiring values for the iron content of the feed, metallization of the DRI, and DRI carbon content .
One example of these calculations can be seen in Figure 1.2.32. Here the desired ratio is plotted as a function of metallization and carbon content for a specific iron content (in this case, 67%, which is fairly common in the industry in 2012). The trends are as expected. The higher the metallization, the lower the weight of the product, which increases the relative weight of the feed. Adding carbon to the product increases its weight, thus reducing the relative amount of feed. Since this plot covers the typical range of DRI metallization and carbon content, it indicates that the pellet-to-DRI ratio is between 1.32 and 1.38. However, this is only the theoretical minimum, assuming feed pellets of exactly the right size distribution with no fines generation during shipping and handling. Unfortunately, this never occurs, and the amount of pellets purchased must always be greater than theoretical to overcome these yield losses.
Midrex is the most successful gas-based DR process; it is a continuous process. It is basically a countercurrent process where a hot and highly reducing gas (95vol.% of this gas mixture being hydrogen and carbon monoxide with a ratio of H2:CO varying from 1.5 to 1.6) reduces lump iron ore or pellets to metallic iron as the metallic charge descends through the top portion of the vessel. At the bottom third portion of the vessel, the metallic iron is cooled by an inert gas to a temperature below 50C before it is discharged from the furnace. The DRI product is unstable in air due to its higher surface area, thus it must be briquetted to decrease its surface area and make it more stable.
In order to carry out investigations of one of the most advantageous direct reduction processes, the fluidized bed reactors, computational tools need to be utilized. One such tool is the Computational Fluid Dynamics - Discrete Element Method (CFD-DEM) method. In this work, two of the most common types of models that represent the reactions between solid particles and fluids are implemented into the CFD-DEM library. Levenspiel (1999) describes these models as the Shrinking Particle Model (SPM), where the solid particle reacts with the fluid and changes its size, and the Unreacted Shrinking Core Model (USCM), where after reacting a product layer is formed around the layer that impedes the reaction rate. The SPM is used to verify communication between the CFD and DEM sides, whereas the USCM is used to represent the reduction of iron-ore.
The USCM is validated with a case that considers only a single iron-ore particle that reacts with a gas mixture of CO and N2. The results are then compared with available experimental data that uses the ISO 4695 conditions at 950 C and 50 Nl/min. We investigate possible parameters that influence the reduction process such as the particle porosity and pore diameter. Also, the reaction parameters such as the frequency factor, activation energy and the equilibrium constants are investigated by comparing the fractional reduction rates of simulations with experiments. These outcomes give us insight about the total reduction process.
In the co-production of iron and syngas (for conversion to methanol) according to Table 1, the total annual fuel requirement for producing 0.50 million tons iron and 0.408 million tons methanol would be 19.5 million GJ. The separate production of Fe in efficient modern plants by the direct reduction process (DRI, operated below the melting point of iron) requires 12.8 GJ per ton of iron . In this case, the production of 0.50 million tons Fe would require 6.4 million GJ. The total fuel consumption of methanol synthesis by conventional steam-methane reforming is 44.5 GJ/ton methanol [10a], For the production of 0.408 million ton methanol, the total fuel requirement would be 18.16 million GJ. Thus, the separate conventional production of the above amounts of Fe and methanol would require 24.6 million GJ. The fuel saving by the proposed co-production vs. the separate production is therefore 20.6 %.
An oxygen BF with top gas recycling using the CCS technology (carbon capture and storage), which is one of the options for reducing gas injection presented in Figure 17.24, is being developing. This technology includes, along with reducing gas, coinjection of PC (Figure 17.30); the calculated coke/HRG replacement ratio, which is the ratio of the amount of coke saved to the amount of injected reducing gas, kr0.200.25kg/m3, for HRG with low content of oxidizing components CO2+H2O; and its achieved value at the experimental BF kr0.17kg/m3 (Hirsch et al., 2012).
Smelting and direct reduction technologies are being typically indicated as alternatives to the BF; in the future, these processes might be complementary. For example, a process scheme for HRG injection based on the coupling of Corex and BF was suggested (Figure 17.31). In this technology, the Corex export gas after the removing of CO2 is heated up and then injected into the BF (Wiesinger et al., 2001).
Looking at direct reduction processes, not only off-gases but also sponge iron in form of DRI or LRI might be used in the BF. Figure 17.32 shows a proposed and tested laboratory-scale operation modus of the Circofer process (a coal-based direct reduction process using a CFBcirculating fluidized bed reactor), in which products DRI/LRI and char are used in the BF, for example, by means of injection via tuyeres (Born et al., 2012).
Further developments should target at a hydrogen-rich BF, where minimum coke amount will only be required as the burden supporter and perhaps carburizer. The crucial point thereby is the mass hydrogen production at a reasonable price. Therefore, aside from hydrogen generation using electrolysis, water steam reforming, partial oxidation of hydrocarbons, fermentation or photosynthesis, and available sources like NG or COG should be considered (Babich and Senk, 2013b).
The existing BF design makes an operation without coke impossible. Chernov suggested in 1940s to separate in the BF zone of solid-phase reduction and zone of melting without excess of solid carbon and developed a coke-less BF design (Chernov, 1950). Further iron-making development took the other way of alternative to the BF direct and smelting reduction processes. Later on, Tovarovsky developed further the Chernov's coke-less BF considering already the Corex experience (Tovarovsky, 1994). In this BF, said the shaft-hearth aggregate, the iron oxides are reduced in solid phase up to metallization degree of 7585% in shaft and bosh by reducing gas, introduced in shaft at t<900C (Figure 17.33). Hot reducing gas from the tuyere zones 5 is mixed with cold reducing gas injected via tuyeres in shaft 6 to get the temperature of about 900C.
Figure 17.33. Expected material distribution and motion in the shaft-hearth aggregate (the upper part, which is not shown here, is the same as that the conventional BF): 1shaft, 2bosh, 3hearth, 4arch, 5, 6tuyeres (Tovarovsky and Ljaljuk, 2001).
Steel is commonly used in modern society and is probably the most important construction material of today (Fig.12.1). This chapter deals with coal use and ways for increasing its efficiency in ironmaking, steelmaking, secondary or ladle metallurgy and continuous casting by different steel production routes.
More attention is paid to ironmaking as the most energy consuming segment of the process chain. For example, blast furnace ironmaking including sintering and coking plants consumes about 65-75% of the entire energy at an integrated steelworks (ca. 1112 GJ/t hot metal) (Babich, 2009). Both direct and indirect coal use, e.g. in the form of coke, is presented. Use of coal and coke breeze for sintering is out of the scope of this contribution.
Furthermore, alternatives to coal materials and energy sources such as biomass or waste plastics are discussed, which are of great importance in the course of efforts to recycle secondary sources and to mitigate carbon dioxide emissions due to the global climate change challenge.
There are four main steel production routes in modern ferrous metallurgy: blast furnace-basic oxygen converter (BF-BOF), smelting reduction converter (SR-BOF), direct reduction-electric arc furnace (DR-EAF), and scrap-electric arc furnace (Fig.12.2) (Steel Institute VDEh, 2008). In the first route, hot metal is produced in the BF which is then refined in the BOF to produce liquid crude steel. In the second route, liquid metal is produced in the melter-gasifier without cokemaking and sintering, which is also refined in the converter to produce liquid crude steel. In the third route, sponge iron instead of hot metal is produced and then this directly reduced iron is melted in the EAF. In the fourth route, only scrap is used as solid metallic input to produce liquid crude steel in the EAF.
The BF has existed for over 700 years and remains the main aggregate for reduction of iron ores. It has demonstrated flexibility and adaptability to changing conditions and today produces up to 10 00013 000 tons of hot metal a day. Besides coke and auxiliary fossil reducing agents such as coal, oil and natural gas, further renewable and secondary sources can be used to perform both chemical reduction work and necessary heat generation. The liquid products hot metal and slag can be effectively separated from each other. Pre-treatment of the hot metal enables reduction of the levels of tramp elements prior to the refining process (Steel Institute VDEh, 2008).
The direct reduction processes in combination with the melting of directly reduced iron to produce steel in the EAF offer an alternative to the BF-BOF route. The basis of the direct reduction process is that solid sponge iron is produced by removing oxygen from the ore in a shaft furnace, rotary kiln furnace or fluidised bed. Sponge iron can be produced in the form of Direct Reduced Iron (DRI), Hot Briquetted Iron (HBI) and Cold Briquetted Iron (CBI); also Low Reduced Iron (LRI), which is pre-reduced iron ore with a reduction and metallisation degree lower than that for common DRI, can be produced. The direct reduction processes can be divided into gas reduction and coal reduction processes depending on the type of reducing agent used (see Section12.5). DRI and HBI are predominantly processed in the EAF, and predominantly for the production of steel grades of long products. Compared to scrap, the advantage of DRI/HBI is low content of trace elements; however, the disadvantage is higher cost (Steel Institute VDEh, 2008). Furthermore, DRI/LRI can also be applied as pre-reduced material for the BF.
The smelting reduction processes are characterised by the production of hot metal from iron ores without an agglomeration step and almost without coke. Classification and examples of SR processes are given in Section12.7. The advantages of this technology are low demand on coke and increased energy utilisation efficiency as a result of post-combustion of CO (Steel Institute VDEh, 2008).
In the year 2011, 1490.1 million ton (Mt) of crude steel, 1082.7 Mt of blast furnace hot metal and 63.5 Mt of DRI were produced worldwide (World steel association, 2011). The ratios of oxygen steel and electric steel were 69.6% and 29.2%, respectively; the worldwide metallic charge was 1690 Mt, and the major part of it was hot metal from blast furnace (64.7%), the rest was mainly steel scrap (30.6%); the share of DRI/HBI and hot metal from smelting reduction (Corex/Finex) was 4.3% and 0.4%, respectively (Peters and Schmoele, 2012). According to the analysis, an increase in world steel production is expected until 20202025 (Harada and Tanaka, 2011).
Carbon is a major reducing agent and heat source to convert iron ores to iron and steel. The required amount of carbon is determined by thermodynamics and chemical kinetics. Carbon in the steel industry is used mainly in the form of coal and the product of its thermal treatment coke but can also be used in the forms of biomass, hydrocarbons (natural gas) and C-H compounds like oil or plastics.
Contrary to the almost pure iron of meteoric origin, manufactured iron (pig iron or hot metal) and steel are ferrous alloys of iron with carbon and further impurities (Fig.12.3). Carbon lowers the melting point of iron from 1538C in pure iron to 1147C in the eutectic with 4.3% C. Carbon content in steel is up to 2.14% that corresponds to maximum dissolubility of carbon in -iron (usually C-content in steel does not exceed 1.5%). Carbon content in hot metal makes up more than 2.5% (typically 45%); ferromanganese may contain up to 6.06.5% C. Alloys with carbon content from 2% to 2.5% have no technical application. The properties of pig iron and steel depend significantly on their carbon content.
Reducing CO2 emissions is the biggest challenge facing the steel industry. The CO2 emission from the BF-BOF route is approximately 2 tons per ton of crude steel (Riley et al., 2010); for the DR-EAF route this value is 33% lower (using the Midrex-EAF process (Ameling et al., 2011). Noncarbon metallurgy based on hydrogen, plasma or electricity is still far away from industrial application. In the short and medium terms, CO2 emissions should be mitigated by significant increase in carbon efficiency, using renewable energy sources like biomass or products of their processing charcoals, semi-charcoals or torrefied materials, and development and introduction of CCS technologies for blast furnace ironmaking, direct and smelting reduction processes as well as processing of CO2 into chemical products.
The wide range of Rotary Kiln Coal-based DRI Plant offered by Globus is manufactured through advanced technology and quality tested components in strict compliance with set industry standards. Globus is reputed for being a global manufacturer and supplier of high quality Rotary Kiln a pyroprocessing device used for calcination employed in a systemic process.
Direct Reduction, also known as Sponge Iron is formed when iron ore is turned to its metallic form through a reduction process which occurs below the melting temperature of both metallic iron and its oxidised form.
Even though this process is carried out at lower temperature than melting point, a greater amount of material is eliminated during reduction reaction. Oxygen removal form iron ore creates lots of microscopic pores. This microscopic pores give the iron a sponge-like texture and appearance. This is why it is known as Sponge Iron.
Production of Sponge Iron is now rising because it is richer than pig iron, its uniform composition, size, and high bulk density, possibility of sensible heat recovery from waste gases, its capability of forming protective layer of foamy slag in the bath, and its high purity makes it an excellent feedstock for EAFs used by mini mills. It enables the mills to produce higher grades of steel.Get in Touch with Mechanic