Ironmaking And Steelmaking Theory And Practice By Ghosh Chatterjee PdfBy Michael D. In and pdf 12.05.2021 at 19:02 4 min read
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- The magic of ironmaking
- The magic of ironmaking
- The magic of ironmaking
An ironworks or iron works is an industrial plant where iron is smelted and where heavy iron and steel products are made. The term is both singular and plural, i. Ironworks succeed bloomeries when blast furnaces replaced former methods.
Iron is an essential ingredient in the manufacture of steel, which, in turn is a critical component in the production of engineering goods. However, the making of quality iron has been a challenge down the ages. For India, what is crucial is the indigenisation of ironmaking processes based on local raw materials and conditions, together with use of appropriate technology.
Gour Gopal Roy takes us on a magical journey through these processes in the making of superior iron and steel. L ET me start with an illustration that represents the major products of a steel plant and various routes to achieve those products from iron ore in a novel composition temperature diagram. Various products like direct reduced iron DRI , hot metal HM and liquid crude steel CS are also shown in the temperature composition diagram.
Now, how do we approach these products, starting from pure hematite? We produce DRI or sponge iron by solid state reduction process like coal-based rotary kiln, or gas-based shaft furnace processes like midrex, HYL etc. In contrast, gasbased direct reduction DR processes are carried out at comparatively lower temperatures o C , using reformed natural gas. In case of blast furnace, we can see that majority of oxygen is removed by o C at solid state in the upper dry zone of the furnace.
In the lower part of the furnace only melting and carburisation takes place. Hot metal of similar quality to that of blast furnace can also be produced by smelting reduction SR process using non-coking coal.
Here, the reactor is different. Blast furnace BF is a complex reactor maintaining dry zone and wet zone interfaced by a cohesive zone in a single reactor. Although BF is a very efficient reactor, it imposes very stringent raw material requirement to maintain such complex internal structure suitable for efficient counter current gas-liquid-solid heat and mass exchange. For example, BF prefers agglomerated burden like sinter and pellets with better strength over lumpy run of mines ore to minimise fines generation during their decent in BF and maintain proper bed permeability for counter current gas-solid reaction.
Since these two reactors are decoupled and independent and connected by solid and gas stream externally, the quality of raw material is not important. This is a two-stage SR process, inspired by energy-efficient BF process.
However, single-stage process is also available but with higher coal rate. In general, carbon rate of SR process is much higher than BF process. So, in the diagram, we can see majority of oxygen in SR process is removed under liquid state at high temperature.
Now, hot metal can be refined using oxygen to remove the carbon and get the liquid steel. Finally, can we have a direct steelmaking process at o C to produce liquid steel from iron ore?
Not yet; but it remains a potential route of steelmaking. The scenario of input material landscape for steelmaking is changing rapidly. Initially, in an integrated steel plant hot metal was the major input material for steelmaking and it was supplemented by plant generated scrap. Today, with the advent of technology like continuous casting, internal scrap generation has decreased but end-of-life scrap is increasing with increasing usage of steel.
Besides, DRI, or sponge iron production using non-coking coal and synthetic gas is on the rise. Since, sponge can be produced independently using cheaper raw material, various integrated steel plants are keeping captive DRI units or outsourcing from market at cheaper price.
So, the cold charge scrap, DRI is increasing progressively in the proportion of input material for steelmaking. Since BF has limitations in melting cold charge, EAF emerges as a better alternative to refine raw materials containing different proportion of cold and hot charges.
Besides, use of scrap in EAF is also considered carbon neutral as scrap is already pure iron and does not require any reduction. However, electricity that is used in EAF should be from renewable source to make it truly carbon neutral and may be termed as green technology.
It has remained up-to-date and competitive with new technologies. Major developments in blast furnace have taken place by Figure2. It started with iron ore beneficiation and use of overseas rich ore; idea was to reduce the gangue and the wet zone in blast furnace where the major pressure drop takes place. It followed with the use of iron ore pellets, agglomerated iron ore burden with higher strength and regular spherical shape, which provides better bed permeability in the dry zone enhancing indirect reduction and consequently yielding lower coke rate and higher productivity.
Subsequently, the auxiliary injection through tuyere in the form of oil injection was introduced, which partially supplemented the function of coke like heating and reduction, reducing coke rate.
Since oil is hydrocarbon, it also produced H2 along with CO, and it improved the indirect reduction. As a result, oil injection replaced coke more efficiently with a replacement ratio kg of coke saved per kg of oil used greater than 1. It is to be mentioned that indirect reduction takes place in the upper part of the furnace utilising the CO generated in the lower part of the furnace. Direct reduction, where carbon directly participates in the reaction through in-situ CO generation by carbon gasification reaction [Eq.
Direct reduction is not a problem in blast furnace due to large availability of carbon; while in direct reduction in the upper part of the furnace is limited by the uniform distribution of CO gas in large cross-section of BF for iron ore reduction. Therefore, indirect reduction can be ensured by good permeability of the bed, which in turn can be ensured by good quality burden. Indirect reduction can also be ensured by availability of hydrogen because it is a better reductant than CO, both thermodynamically and kinetically.
Next development in blast furnace was the introduction of preheated air blast. With the advent of blast furnace stoves, air blast could be preheated to o C. Supply of large amount of sensible heat through preheated air blast, supplements the heating by carbon oxidation and reduces the coke rate.
It is to be noted that nitrogen also plays a crucial role in heat exchange through the long shaft in the blast furnace. It increases the heat capacity of the gas and supply the sensible heat to meet up the heat demand of the entire solid bed in the long shaft for preheating. But, heat capacity of BF gas in the upper part of the furnace should not exceed much beyond the heat required by the solid, such that gas leaves the furnace at around o C.
Thereafter realisation came to decrease the amount of nitrogen in air through oxygen enrichment to reduce the volume of air blast, blast furnace gas, and its heat capacity. Oxygen enrichment also increases the flame temperature. Therefore, it is usually accompanied with most of the auxiliary injection that increases heat capacity of gas and reduces flame temperature, like fuel and steam injection.
Steam injection introduces H2 in the BF gas through endothermic carbon gasification [Eq. Since steam injection introduces H2 as reductant, it is good for indirect reduction and lowering coke rate; but as it causes endothermic reaction in the lower part of the furnace, it is usually accompanied by oxygen enrichment. The oil crisis in the s forced the steel producers to shift to pulverised coal injection PCI as an alternative to oil injection in blast furnace.
This has happened with improved refractory and mainly with improved cooling arrangement of refractory using copper staves. These are water cooled rectangular copper plates that cools the refractory from being overheated and develop weakness. Comparatively recent research has introduced the concept of nut coke a product of coke oven , which is usually smaller in size mm than normal coke mm. Nut coke has been found to improve the bed permeability significantly in the dry zone as well as cohesive of the blast furnace when it is optimally used.
However, excessive replacement of regular coke by PCI and nut coke reduces the coke layer thickness, which increases the gas flow resistance and pressure drop significantly. Blast furnace is a counter current gas solid reactor that in fact helps in gas utilisation in the furnace.
Let us take a brief look at iron oxide reduction. Reduction of hematite takes place in three sequential stages: hematite Fe2 O3 to magnetite Fe3 O4 ; magnetite to wustite wustite represents non-stoichiometric lowest order iron oxide, FexO where x is typically 0. It means that for conversion of one mole wustite to iron, CO requirement is 3. It is to be mentioned here that o C is an important temperature in blast furnace because a large middle portion of the furnace remains at this temperature, called the isothermal zone, which allows the heat exchange between gas and blast furnace burden to complete separately, both at the lower and the upper part of the furnace.
All indirect reduction of wustite takes place in isothermal zone and wustite-iron equilibrium is also attained in the upper part of the isothermal zone, called the chemical reserve zone. This allows the blast furnace to be treated as two-stage reactor5 see Figure3 , where heat and materials balance could be made independently in the lower part of the furnace to develop a complete predictive model to define minimum coke rate, called the RIST diagram or, operating line in blast furnace.
Since blast furnace is a counter current gas solid reaction, hematite and magnetite reduce in the locations up in the blast furnace as CO requirements are low and their oxygen dissociation pressures are also high. Wustite having higher requirement of CO are reduced lower part in the furnace and it undergoes both direct and indirect reduction at high temperature.
Considering the utilisation factors for various iron oxides at o C, indirect reduction of iron oxides may be given by Eqs.
So, it is obvious that direct reduction is economic in carbon while indirect reductions are expensive. The fuel economy may further be enhanced if ore oxygen is optimally partitioned between direct and indirect reduction such that CO evolved from direct reduction is just sufficient to support rest of indirect reduction. Stoichiometrically, it can be shown that kg of ore oxygen is required to be removed to produce one ton of iron, out of which kg of oxygen is associated with wustite only.
Therefore, CO utilisation in blast furnace can be maximised if the wustite oxygen is optimally partitioned between direct and indirect reduction. It is to be noted here that CO utilisation for indirect reduction of wustite further decreases with increase in temperature and vice versa see Figure4. Therefore, if the wustite reduction could be carried out at comparatively lower temperatures, the overall CO utilisation efficiency could further be improved, reducing the coke rate and emission.
The minimum coke rate in blast furnace for a given burden material with fixed heat demand, can be calculated by heat and material balance in lower part of the furnace independently, which yields a fixed straight line, the slope of which provides the coke rate known as RIST diagram. The line called the optimum operating line is pined by two points; one arising out of heat balance called the thermal pinch point H and the other by the equilibrium point for wustite reduction W.
Since the hydrogen utilisation efficiency at higher temperature is greater than CO, the Fe-C-O phase diagram is shown here, as it controls the reduction efficiency. Now it can be seen that as the temperature of reduction decreases, the wustite equilibrium point on operating line shifts to the right W to? This is referred as low temperature and low emission technology for blast furnace.
However, lowering the wustite reduction temperature is not easy because to sustain the wustite indirect reduction at lower temperature, CO supply by direct reduction of wustite has also to be ensured at lower temperature. This is challenging as direct reduction is highly endothermic that requires higher temperatures. It has been shown by researchers that temperature of direct reduction, or carbon gasification reaction that controls the direct reduction, can be lowered by: i increasing the reactivity of coke; ii presence of impurity in coke that catalyses carbon gasification reaction; and iii use of iron ore-coal composite pellets that brings in intimacy of carbon and iron ore particles.
Today CO2 emission is an important parameter to judge the sustainability of ironmaking process. In spite of all above advancement for more efficient and productive blast furnace, CO2 emission is still at an average of 2 ton of CO2 per ton of hot metal produced.
There are some potential techniques that can reduce the CO2 emission significantly. In this version of BF, oxygen at room temperature is charged in place of preheated air blast and top gas is recycled back after scrubbing CO2. On counts of demerit: Since heat capacity of gas decreases significantly in absence of nitrogen , to maintain upper part heat balance, heat capacity of the solid has to be decreased either by improving burden quality or decreasing the shaft height.
THE reductant carbon in blast furnace is used in the form of coke, a strong, consolidated product of coal produced by heating coking coal a special variety of coal used for coke making in absence of air in coke oven. The coking coal reserve in India is very limited, that too with high ash content. Therefore, India mostly depends on the imported coking coal, primarily from Australia.
On the contrary, India has a large reserve for non-coking coal, which has very limited use in steelmaking, except its use as pulverised coal injection PCI in BF.
India has also large waste dumps in the form of off-grade iron ore fines, iron bearing waste dust, sludge from plants, which otherwise pollutes the atmosphere. So, it is aimed to utilise iron bearing solid waste, and non-coking coal through alternative routes of ironmaking. Coke ovens and sinter plant ore agglomeration plant also pollutes atmosphere.
Therefore, alternative routes are evolving for directly utilising off-grade iron ore fines, iron bearing solid waste, non-coking coal, synthetic gas and producing value added sponge iron direct reduction processes , which can subsequently be melted in electric furnace; or directly producing liquid iron using non-coking coal smelting reduction processes.
The magic of ironmaking
Ironmaking And Steelmaking: Theory And Practice by Ahindra Ghosh And Amit Chatterjee is a complete reference text material on metallurgy, the process of making iron and steel, primarily intended for undergraduate and postgraduate students of engineering. Ironmaking And Steelmaking: Theory And Practice is a book for the benefit of engineering graduates and postgraduates. It records all the procedures of making iron and steel that serves the researchers interested in this subject. Students will find this book highly useful as it traces the historical events in the making of steel and iron. Ironmaking And Steelmaking: Theory And Practice comprises 6 sections with further sub-sections of 24 chapters. The initial chapter explains the historical information and general concepts of iron and steel.
This authoritative account covers the entire spectrum from iron ore to finished steel. It begins by tracing the history of iron and steel production, right from the earlier days to todays world of oxygen steelmaking, electric steelmaking, secondary steelmaking and continuous casting. The physicochemical fundamental concepts of chemical equilibrium, activity-composition relationships, and structure-properties of molten metals are introduced before going into details of transport phenomena, i. Particular emphasis is laid on the understanding of the fundamental principles of the processes and their application to the optimisation of actual processes. Modern developments in blast furnaces, including modelling and process control are discussed along with an introduction to the alternative methods of ironmaking. In the area of steelmaking, BOF plant practice including pre-treatment of hot metal, metallurgical features of oxygen steelmaking processes, and their control form part of the book. It also covers basic open hearth, electric arc furnace and stainless steelmaking, before discussing the area of casting of liquid steelingot casting, continuous casting and near net shape casting.
Buy Ironmaking And Steelmaking: Theory And Practice by GHOSH, AHINDRA, CHATTERJEE, AMIT PDF Online. Download Free Sample from PHI Learning.
The magic of ironmaking
Iron is an essential ingredient in the manufacture of steel, which, in turn is a critical component in the production of engineering goods. However, the making of quality iron has been a challenge down the ages. For India, what is crucial is the indigenisation of ironmaking processes based on local raw materials and conditions, together with use of appropriate technology. Gour Gopal Roy takes us on a magical journey through these processes in the making of superior iron and steel. L ET me start with an illustration that represents the major products of a steel plant and various routes to achieve those products from iron ore in a novel composition temperature diagram.
Balst Furnace Iron Making - a. Vaish, P. Biswas, s.
Save extra with 2 Offers. It begins by tracing the history of iron and steel production, right from the earlier days to todays world of oxygen steelmaking, electric steelmaking, secondary steelmaking and continuous casting.
The magic of ironmaking
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Navigationsleiste aufklappen. Sehr geehrter ZLibrary-Benutzer! Wir haben Sie an die spezielle Domain de1lib. This authoritative account covers the entire spectrum from iron ore to finished steel. The physicochemical fundamental concepts of chemical equilibrium, activity-composition relationships, and structure-properties of molten metals are introduced before going into details of transport phenomena, i.
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