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2010 | Buch

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Innovation in Electric Arc Furnaces

Scientific Basis for Selection

verfasst von: Yuri N. Toulouevski, Ilyaz Yunusovich Zinurov

Verlag: Springer Berlin Heidelberg

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik"

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Über dieses Buch

Electric Arc Furnaces are being greatly improved at a fast pace. This book equips a reader with knowledge necessary for critical analysis of these innovations and helps to select the most effective ones and for their successful implementation.

The book also covers general issues related to history of development, current state and prospects of steelmaking in Electric Arc Furnaces. Therefore, it can be useful for everybody who studies metallurgy, including students of colleges and universities.

The modern concepts of mechanisms of Arc Furnace processes are presented by numerous journal articles and conference proceedings. These materials are difficult of access for a practicing engineer or metallurgist. The knowledge of general simplified yet correct in principle concepts is sufficient for decision-making. These concepts are discussed in the book at the level sufficient to solve practical problems: To help readers lacking knowledge required in the field of heat transfer as well as hydro-gas dynamics, it contains several chapters which provide the required minimum of information in these fields of science. In order to better assess different innovations, the book describes experience of the application of similar innovations in open-hearth furnaces and oxygen converters. Some promising ideas on key issues regarding intensification of the heat, which are of interest for developers of new processes and equipment for Electric Arc Furnaces, are also the concern of the book

It should be noted, that carrying out the simplified calculations as distinct from using "off the shelf" programs greatly promotes comprehensive understanding of physical basics of processes and effects produced by various factors. This book gives numerous examples of such calculations performed by means of simplified methods and formulas.

Getting familiar with material in this book will allow the reader to perform required calculations on his / her own without any difficulties.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Modern Steelmaking in Electric Arc Furnaces: History and Prospects for Development

Abstract

Process, ecological, economic, health and safety requirements to steelmaking units. The change in these requirements with developing of current steel production. A negative effect of existing contradictory practice of the forming in prices for scrap, iron, electrical energy, and natural gas on general technological progress in steelmaking.

Increasing productivity is considered as the most important direction in EAF development. Due to numerous innovations implemented during the last decades, furnace productivity increased more than 4 times, electrical energy consumption was approximately halved, and electrode consumption reduced by 4 - 5 times. Basic innovations are as follows: increasing power of EAF transformers up to 1.0 - 1.5 MVA /ton; implementing the secondary ladle metallurgy and changing furnace functions for semi-product production; intensive oxygen and carbon injection into a bath; slag foaming; furnace operation with “hot hill”; using hot metal, etc. All these innovations are analyzed in details.

Electrical circuit specifics of modern furnaces, optimum electrical mode of the heat, and problems of electrical energy supply are discussed as well. Prospects for development of steelmaking in EAFs are analyzed.

Yuri N. Toulouevski, Ilyaz Y. Zinurov

Chapter 2. Electric Arc Furnace as Thermoenergetical Unit

Abstract

The main task of electric arc furnaces under today’s conditions is to melt down solid charge and to heat liquid bath up to the tapping temperature with decarburization of the melt. Thermo-technical nature of this task. Transformation of an EAF to a thermo-energetical unit. Analysis of basic furnace processes from the unified thermo-energetical viewpoint.

Both external, regarding the charge melted down and the liquid bath, and internal heat energy sources. The former are electric arcs burning over the bath and oxy-fuel burners; the latter are electric arcs submerged into slag and chemical reactions of oxidation of carbon, iron, and other elements inside the bath. Useful heat of different energy sources as an amount of heat transferred to the charge materials or the bath. Enthalpy of metal at the tapping temperature as a useful heat of the entire heat.

Two groups of factors limiting the power of external energy sources, namely, the factors inherently connected with the physical–chemical processes of the heat and the external (random) factors. A key role of heat transfer processes as the main factor limiting the power of external sources. The need to increase the intensity of the heat transfer processes.

Yuri N. Toulouevski, Ilyaz Y. Zinurov

Chapter 3. The Fundamental Laws and Calculating Formulae of Heat Transfer Processes

Abstract

The aim of this chapter is to provide a useful guide to quick mustering minimum knowledge required for the analysis of innovations with the aid of thermal calculations for the readers slightly familiar with this field of physics.Elementary level of presentation without compromising scientific strictness.

Heat transfer processes; three ways of heat transfer. Stationary and non-stationary processes. Heat conduction of simple-shaped and complex-shaped bodies. The thermal conductivity coefficient.

Convective heat exchange. Free (natural) convection and forced one. Laminar and turbulent motion of fluxes. Boundary layer. Formulae and tables for determination of the heat transfer coefficients between a wall and liquid (gas). Heat transfer between two fluid flows through a dividing wall. Thermal resistances and intensifying heat transfer processes.

Heat radiation. The coefficient of black body radiation. Emissivity of bodies. Radiation of solids, liquids, and gases. Radiant heat exchange between bodies.

Simplified formulaes for calculations of thermal processes in some furnace elements with the accuracy required in practice. Concept of numerical methods of calculating stationary and non-stationary heat conduction for complex-shaped bodies.

Yuri N. Toulouevski, Ilyaz Y. Zinurov

Chapter 4. Energy (Heat) Balances of Furnace

Abstract

Equations of heat (energy) balances: for the entire furnace and its different zones (the freeboard, the bath, electro-technical zone, gas evacuation system); for different time intervals (the entire heat, separate process stages), for a given moment of time (instantaneous balance). Analysis of equations. The heat balance for a modern 130-ton EAF. Input and output items of the balance. Errors in composing of balance equations.

The so-called “energy equivalent” of oxygen - the value which does not have any clear physical meaning. Oxygen itself introduces no energy into a furnace. Amount of chemical energy released per 1 m3 of oxygen varies over a wide range depending on steel grade, charge composition, and a design of blowing devices. Inexpediency of using of the “equivalent” discussed for heat balance equations.

The method of total enthalpies for calculation of thermal effects of chemical reactions in the heat processes with different temperatures of reagents and products. Tables required for using the method. Advantages of the method - versatility and simplicity. Impermissibility of using in EAF balance equations so-called standard thermal effects at \(25{-}\ ^{\rm o}{\rm C},^{-} (-\varDelta {\rm H} _{298}^{0})\).

Yuri N. Toulouevski, Ilyaz Y. Zinurov

Chapter 5. Energy Efficiency Criteria of EAFs

Abstract

Methods for evaluating energy efficiency of innovations for EAFs. Difficulties associated with the quantitative determination of EAFs’ energy efficiency in connection with the joint utilization of different energy sources. Non-promising attempts to estimate this value by a certain common single coefficient.

Specific coefficients for the energy efficiency of various sources η: electrical energy (in arcs and other furnace zones); oxy-fuel burners; coke (both charged with scrap and injected into a bath); chemical heat of exothermic reactions of oxidation of iron, carbon, and other elements.

Determination of the EAF energy efficiency with the aid of a balance equation of useful energies using the specific energy efficiency coefficients η for different sources.

Determining methods for specific coefficients: active experiments with varying parameters of furnace operation modes in the course of heat; reverse heat balances. Determining the coefficients η as the main task of heat engineering studies of EAFs.

Yuri N. Toulouevski, Ilyaz Y. Zinurov

Chapter 6. Preheating of Scrap by Burners and Off-Gases

Abstract

Calculated estimation of scrap preheating efficiency for EAF. Three-fourths of all the useful heat introduced into a furnace are used for heating of scrap to the melting point. Scrap preheating up to 1200°C reduces electrical energy consumption about 4 times and tap-to-tap time by half.

Analysis of scrap heating methods with off-gases and gas burners in the last few decades. High-temperature heating of scrap in rotary tube-type heating furnaces; heating in charging baskets and in special buckets; in horizontal and vertical conveyor-type devices; in shaft and twin-shell furnaces. Pros and cons of various methods.

The reasons for abandonment of the use of off-gases for the scrap heating. Loading gases with toxic compounds (dioxins) when heating the furnace scrap contaminated with oil, plastics, and other flammable components. Increasingly strict requirements to the environment protection. The need for decomposition of dioxins by heating of gases after they pass through the scrap preheaters. Additional fuel consumption for heating of gases denudes the use of the heated scrap of its energetical advantages. Realization of the scrap preheating idea requires new engineering solutions.

Yuri N. Toulouevski, Ilyaz Y. Zinurov

Chapter 7. Replacement of Electric Arcs with Burners

Abstract

Analysis of attempts to develop steelmelting units operating with scrap without utilizing electric arcs. Reasons of failures.

Limited possibilities of low-power sidewall oxy-gas burners. The constant flame direction as a basic factor hindering the increase in burner power. High-power rotary (HPR) burners. Moving the flame of HPR-burners from those already heated to the relatively cold zones of scrap pile during the heat allows to increase their power up to 20–30 MW and the energy efficiency coefficient η up to 0.7.

HPR-burner design variants: roof, oriel (balcony), and sidewall. They open new possibilities for replacing electrical energy with fuel. Two-stage process of the heat: at the first stage the scrap is only heated by the burners, and at the second one the scrap is heated with both the burners and arcs or with the arcs only.

Results of trials of both HPR-burners and two-stage process in 6-ton, 100-ton, 200-ton furnaces prove the reality of developing a 120-ton fuel arc furnace (FAF) operating on scrap with basic performances as follows: tap-to-tap time − 35 min; consumptions are electrical energy − 140 kWh/ton; natural gas − 25 m³/ton; oxygen − 80 m³/ton. Maximal power of transformer − 85 MW, that of 5 HPR-burners − 137 MW.

Yuri N. Toulouevski, Ilyaz Y. Zinurov

Chapter 8. Basic Physical–Chemical Processes in Liquid Bath: Process Mechanisms

Abstract

Today’s general ideas of processes in the bath required when evaluating of innovations.

Hydrodynamics of oxygen blowing as a factor, which defines the running of processes. Oxygen jets as practically the only source of oxygen under current conditions. Reaction zones. Mechanisms of oxygen spreading from the reaction zones throughout the volume of the bath

Two-stage scheme of carbon oxidation to CO in the bath: at first, oxidation of iron; then, oxidation of carbon by the ferrous oxides spreading throughout the bath.

Three stages of melting scrap lumps in the melt: freezing of the melt; diffusive melting due to enriching the surface layer of scrap lumps with carbon; and intensive melting at the bath temperature significantly exceeding the scrap melting point. In modern EAFs the two first stages are slightly expressed. To shorten the melting duration it is necessary to intensify the heating of the bath.

Both non-uniformity of distribution over the surface of the bath and extremely high density of heat flux from the arcs. The key role of the stirring intensiveness in processes of uniform bath heating, its decarburization, and melting of scrap lumps submerged into liquid metal.

Yuri N. Toulouevski, Ilyaz Y. Zinurov

Chapter 9. Bath Stirring and Splashing During Oxygen Blowing

Abstract

Methods of quantitative definition of the bath stirring intensity. The method of radioactive tracers in experiments at the furnaces, and the cold physical modeling of processes.

Mechanisms of stirring. Circulation stirring of the melt macro-volumes by oxygen jets and CO bubbles. Pulsation stirring of the bath micro-volumes due to turbulent pulsations. Stirring intensity as a factor limiting intensiveness of the bath oxygen blowing. The over-oxidation of liquid metal and injecting the carbon into the melt.

Bath splashing by oxygen jets and effect splashing on the furnace operation. The methods of studies; results of the cold physical modeling. Quantity and composition of splashes and fine-dispersed dust. The effect both of design parameters of oxygen tuyeres and their positioning relative to the bath on splashing intensity. Two maximums of splashing intensity: when approaching the tuyere tip to the slag surface and to the slag–metal boundary. Minimum of splashing (close to zero) when positioning the tip in slag.

Aimed changing of design and mode parameters of oxygen blowing as a key to control the physical–chemical processes and stirring in the bath.

Yuri N. Toulouevski, Ilyaz Y. Zinurov

Chapter 10. Jet Streams: Fundamental Laws and Calculation Formulae

Abstract

The aim of this chapter is to familiarize the readers with elementary ideas of basic laws for jet streams of incompressible and compressible gas.

Flooded free turbulent gas jets. Formation mechanism; the turbulent mass exchange between the jet and surrounding gaseous medium. Jet core and boundary layer. The initial and main regions of the jet; a conditional jet boundary. Constancy of the momentum (the amount of motion) along the jet.

The speed of sound. Simple cylindrical and tapered nozzles. Subsonic jets. Equality of the maximal (critical) velocity of gas projecting from simple nozzles to the speed of sound.

Supersonic jets and nozzles. De Laval nozzle and so-called coherent nozzles providing the minimum flow turbulence. The operating of supersonic nozzles in the design mode; with under-expansion and over-expansion of gas.

Simplified formulae for calculations of parameters both of nozzles and jets: in the field of low-velocity incompressible jets and in the field of compressible high-velocity and supersonic jets.

Yuri N. Toulouevski, Ilyaz Y. Zinurov

Chapter 11. Devices for Blowing of Oxygen and Carbon into the Bath

Abstract

Competing methods and devices for blowing (injection) of oxygen and carbon into the bath by means of consumable steel pipes via a furnace slag door; mobile water-cooled tuyeres introduced through openings at a furnace roof and walls; using jet multifunctional modules placed in protective boxes; tuyeres installed in the bottom lining.

Analysis of shortcomings, advantages, and prospects of various methods with taking into consideration of a curtain experience collected in open-hearth furnaces and converters. The reasons for replacing other blowing devices with jet modules. Efficiency of the use of oxygen, carbon, and natural gas in jet modules.

Radical increase in blowing efficiency when submerging tuyeres into the bath to the slag–metal boundary and even lower into metal. The durability and explosion-safety problem of water-cooled tuyeres for a deep blowing installed in the bottom lining. A system providing for the complete tuyere explosion-safety due to the circulation of cooling water in a closed circuit.

Yuri N. Toulouevski, Ilyaz Y. Zinurov

Chapter 12. Water-Cooled Furnace Elements

Abstract

Elements whose durability significantly affects productivity and cost effectiveness of the furnaces’ operation and even the selection of directions of the heat intensification are reviewed. General laws of thermal performance of elements; processes defining their durability. Reasons for wearing. The necessity of avoiding the cooling in the mode of water local boiling.

Experimental data on maximal densities of heat fluxes perceived by elements at the EAF freeboard. An idea of the critical element zone. Calculation formulae for determination of minimal required water flow rate, temperatures of external surface and that flown around by water, and hydraulic resistance of water channels. General diagram of new element calculation.

Calculations of thermal performance for both a mobile oxygen tuyere and an element with pipes cast into copper or with channels for water passing. Jet cooling of stationary tuyere for a deep oxygen blowing of the bath providing for the removal of heat fluxes with the density up to 10 MW/m² without water local boiling due to the increase in the convective heat transfer coefficient α up to 150 kW/m² × °С.

Yuri N. Toulouevski, Ilyaz Y. Zinurov

Chapter 13. Principles of Automation of Heat Control

Abstract

Automated and automatic control systems. Providing with information (data on the heat processes) as a key factor determining potentialities of systems. Disadvantages of static systems based on accumulated information. Advantages of dynamic systems using on-line information.

Direct and indirect on-line information. An unsuitability of indirect information to control over heating and decarburization of the bath. Problems of direct information sensors.

Control with the aid of mathematical models. Factors hindering strictly cause-and-effect mathematical description of the heat processes without using statistical data. Disadvantages of statistic models using accumulated information. Automated systems utilizing statistic models and operating in the mode of operator’s advisor. The lack of fundamental difference between such systems and those of control according to instructional manuals.

Two approaches for estimating operator’s participation in the heat control. Operator’s role depending on providing information level for systems. Factors determining expedience and necessity of automatic control by the separate processes as well as by the entire heat. Rational degree of automation

Yuri N. Toulouevski, Ilyaz Y. Zinurov

Chapter 14. Off-gas Evacuation and Environmental Protection

Abstract

Primary and secondary gas-duct emissions characteristics: composition, amount, temperature, physical, and chemical heat content (enthalpy). Systems for both capturing and preliminary preparing of emissions to their cleaning in bag filters. The reasons resulting in the fact that an amount of gases cleaned in bag filters exceeds 70 and even more times that of primary dust-loaded gases generated in EAF’s freeboard. Some ways of reducing unjustified high electrical energy consumption related to gas evacuation. The problems of high toxic emissions: CO, dioxins, etc.

Simplified techniques for calculations of gas parameters of the direct evacuation system: carrying capacity of the system, hydraulic resistance of its elements; examples of calculations.

Air curtains for eliminating air infiltration into a furnace slag door: theoretical grounds, calculation methods, design features.

Yuri N. Toulouevski, Ilyaz Y. Zinurov

Backmatter

Titel: Innovation in Electric Arc Furnaces
verfasst von: Yuri N. Toulouevski
Ilyaz Yunusovich Zinurov
Verlag: Springer Berlin Heidelberg
Electronic ISBN: 978-3-642-03802-0
Print ISBN: 978-3-642-03800-6
DOI: https://doi.org/10.1007/978-3-642-03802-0

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