Without a doubt, there is a consensus around the international community which suggests that our current way of life is unsustainable for a healthy planet, society and economy. One focal point that should be taken deeply into consideration is the steel industry as, globally, it accounts for 8% of global emissions. Thus, there is a dire need to incorporate drastic measures, if one wishes to reach net-zero emissions by 2050, in accordance with the Paris Agreement of 2015. Electric Arc Furnaces are seeing a rapid implementation in the steel industry. However, at 0.5 tonnes of CO2 emitted per tonne of liquid steel produced, this emissions rating is still significant considering the amount of steel being produced annually. Additionally, these furnaces emit off-gases which must be treated from the dust. This leaves operators with a conundrum as the dust content compromises the use of waste heat recovery boilers for energy recovery, due to constant breakdowns. Therefore, this study aims to analyse the feasibility of using bioenergy and carbon capture and utilisation (CCU) concepts to capitalise on the high off-gas energy and emissions content to remedy the dust issue, whilst producing higher value products. The proposed concept evaluates the effectiveness of using the off-gas as the energy carrier and feed-stock for a biogasificaiton unit. Three different cases based on different EAF off-gas compositions have been investigated. Case 1 suggested that the off-gas composition is very CO2-heavy, whichled to investigating the option of adopting a CO2 biogasification concept to directly use the CO2. Case 1 performed the best in terms of CO2 utilisation efficiency; being 0.293. The system energy utilisation also noted that 49.3% of the inlet streams energy was transferred to the desired product. On a broader picture, this means that around 11% of the total energy coming out of the EAF would be utilised in producing a value-added product in the form of syngas. This contrasts with allowing around 33% of the energy in the EAF either being completely dissipated to the environment or converting it into electricity via waste heat recovery. The following two cases, Case 2 and 3, indicate EAF off-gas composition containing 72% and 40% nitrogen respectively. For Cases 2 and 3, a steam biogasification process was integrated which did not yield positive results for CO2 utilisation, since is a more promising gasifying agent. In addition, significant energy from EAF off-gas is used in raising the temperature of steam to the design temperature of the gasifier. However, although the CO2 was not directly used in this part of the process, it allows for other opportunities of process integration, for example the reverse water-gas shift step.

Thesis (MScEng) --University of Stellenbosch, 2010. / ENGLISH ABSTRACT: This thesis deals with the development of a new process for the production of Direct Reduced Iron (DRI), intended for use specifically by small scale Electric Arc Furnace (EAF) based steel mills, who require small volumes of DRI. The term development as used here is taken to include such aspects as conceptual design, theoretical verification and initial practical testing. The rise of EAF steelmaking brought about the metamorphosis of steel scrap from a waste product into a valuable raw material. Scrap prices rose steeply during the period 1995 to 2009 compelling EAF steelmakers, wishing to have more control over the cost of their input material, to seek for scrap supplements or alternatives. DRI has become an accepted and sought after supplement, or even complete alternative, to steel scrap. Adding DRI to an EAF charge has a range of advantages, including the dilution of tramp elements and possible cost benefits, but it does have negative effects. These include the lowering of the scrap to liquid metal yield and an increase in power consumed. The effect of charging DRI to a small EAF is quantified. The maximum DRI that may be added to the burden whilst still maintaining the present steelmaking volume, is shown to be as high as 50% if charged continuously, and the maximum price payable for DRI, is shown to be approximately 80% of base grade scrap price. Finally other requirements unique to small scale EAF operators are considered in order to prepare a schedule of requirements for a DRI plant specifically for small scale EAF steel mills. A review of published information on existing DRI production technology, processes and plants is undertaken is establish the fit of existing processes to the requirements set. Initially the thermodynamics and kinetics of iron ore reduction and coal gasification, specifically downdraft gasification are reviewed. Thereafter existing processes are reviewed. Shaft based processes and rotary kiln based processes are identified as possible suitors to the requirements. Limitations of these processes, specifically heat transfer in rotary kilns and the pressure drop over a reduction shafts are investigated. Finally a typical process in each of the main process classes is adjudicated against the set requirements. None is found to match the set requirements. A new process is proposed that is claimed to better suit to small scale operation. The uniqueness of the process is embodied in the combination of existing technologies of downdraft gasification and iron ore reduction in a shaft, in a single reactor. The process consists of two shafts, one placed above the other. Iron ore is charged into the top shaft, called the pre-heat shaft, where it is pre-heated and lightly reduced to wustite with gas from the bottom shaft, called the reduction shaft. The pre-heated ore is then charged together with coal into the reduction shaft. Gasification air is drawn into the top of the reduction shaft where the coal is gasified in a downdraft gasifier, generating reduction gas which reduces the ore as the gas moves concurrently with the iron ore. The exit gas is cleaned and pumped to the pre-heat shaft where it combusted with air to pre-heat the iron ore in the pre-heat shaft. The concept is analysed thermodynamically using amongst others, FactSage, and is shown to be thermodynamically viable. To test the concept process concept practically, an extremely small pilot plant with a production rate of 2kg DRI/h, consisting of only a gasifier/reduction shaft, was designed and constructed using reduction rate data obtained from literature supplemented with data obtained from thermogravimetric analysis of CO reduction of lump Sishen hematite. Pilot Plant trials were performed using various reductant sources. The degree of metallizaion was analysed using visual inspection of cut and polished samples compared to calibrated standards. Analysis of the results indicate that coal rate and production rate influence the degree of reduction positively and negatively. The conclusions arrived at include the fact that the process is thermodynamically viable, that it was possible to reduce iron ore in a simplified pilot plant, and that the process was found to be stable and controllable. It is recommended that a larger scale pilot plant, embodying the full proposed flow sheet be erected to test the process more completely. / AFRIKAANSE OPSOMMING: Die tesis handel oor die the ontwikkeling van ‘n nuwe proses vir die vervaardiging van sponsyster. Die proses is beoog spesifiek vir gebruik deur kleinskaalse Elektriese Boogoond (EBO) gebaseerde staal aanlegte, wat kleiner hoeveelhede sponsyster benodig. Die term ontwikkeling soos hier gebruik word aanvaar om aspekte soos konseptuele ontwerp, teoretiese verifikasie en aanvanklike toetsing te behels. Die vinnige groei van EBO staalvervaardiging het skroot getransformeer van weggooiproduk tot waardevolle grondstof. Die prys van skroot het skerp gestyg gedurende die periode 1995 to 2009. EBO gebaseerde staal produsente, in ‘n poging om meer beheer te hê oor die koste van hul insetmateriaal, het hul in ‘n toenemende mate tot skrootalternatiewe gewend. Sponsyster het ‘n aanvaarde en gewaardeerde byvoeging, en selfs alternatief tot staalskroot geword. Die byvoeging van sponsyster by die lading van ‘n tipiese EBO het besliste voordele, maar het dit ook nadelige effekte. Die voordele sluit die verdunning van reselemente en moontlike kostevoordele in, terwyl van die nadele die verlaging van die skroot tot vloeistaal opbrengs, en ‘n verhoging in kragverbruik, is. Die effek van die byvoeging van sponsyster tot ‘n EBO lading word gekwantifiseer. Daar word getoon dat die maksimum hoeveelheid sponsyster wat by ‘n EBO lading gevoeg kan word terwyl die hoeveelheid staal geproduseer konstant gehou word, ongeveer 50% is indien die sponsyster kontinue gelaai word, en die maksimum prys wat vir die sponsyster betaal kan word, word bereken op ongeveer 80% van die prys van basisgraad skroot. Ander vereistes uniek aan kleinskaal EBO bedrywers word oorweeg ten einde ‘n lys van vereistes vir ‘n sponsysteraanleg, uniek aan kleinskaal EBO bedrywers, te kan bepaal. ‘n Oorsig van gepubliseerde inligting oor sponsysterproduksietegnologie word onderneem ten einde die passing van bestaande prosesse met die gestelde vereistes te kan bepaal. Nadat die termodinamika en kinetika van ysterertsreduksie en steenkoolvergassing be-oordeel is, word bestaande sponsysterprosesse beskou. Skag- en Roterende oond gebaseerde prosesse word as moontlik gepaste prosesse identifiseer. Hitte-oordrag en die drukval oor gepakte beddens, synde tipiese beperkings eie aan die twee prosesse, woord beskou. Tipiese prosesse in elk van die hoofklasse van prosesse word ten laaste be-oordeel aan die gestelde kriteria. Daar word bevind dat geeneen van die bestaande prosesse aan die vereistes voldoen nie. ‘n Nuwe proses, wat skynbaar die behoefte van kleinskaalse EBO gebaseerde staalprodusente beter bevredig, word voorgestel. Bestaande tegnolgie word in ‘n unieke opstelling geïntegreer. Reduksie word in ‘n reduksiekag gedoen as gevolg van die ooglopende massa- en hitte-oordragvoordele van ‘n skag. Reduksiegas word verkry van steenkoolvergassing in ‘n afstroomvergasser ten einde teerverwydering in ‘n naverwerkingsstap oorbodig te maak. Die uniekheid van die proses is beliggaam in die kombinasie van ‘n steenkoolvergasser en reduksieskag in ‘n enkele reaktor. Die proses bestaan uit twee skagte, een bo die ander. Ystererts word in die boonste skag, wat die voorverhitskag genoem word, gelaai. Hier word die erts voorverhit en moontlik lig gereduseer tot wustiet met gas van die onderste skag, wat die reduksieskag genoem word. Die voorverhitte erts word saam met steenkool in die reduksieskag gelaai. Vergassingslug, word in die reduksieskag gesuig waar die steenkool in ‘n afstroomvergasser vergas word. Hierdeur word reduksiegas gegenereer wat die erts verder reduseer soos dit saamstromend met die erts af beweeg. Die uitlaatgas word gesuiwer en na die voorverhitskag gepomp waar dit verbrand word om die erts te voorverhit. Die konsep is termodinamies analiseer met gebruikmaking van onder andere FactSage, en werkbaar bevind. ‘n Baie klein, vereenvoudigde proefaanleg, met ‘n produksievermoë van 2kg DRY/uur, bestaande uit slegs ‘n reduksiekag, is ontwerp en gebou met gebruikmaking van kinetika inligting uit die literatuur aangevul met inligting uit termogravimetriese analise van die CO reduksie van Sishen hematiet. Proefaanleglopies is uitgevoer met ‘n reeks reduktantbronne. Die metallisasiegraad is bepaal deur visuele inspeksie van gesnyde, gepoleerde monsters wat vergelyk is met gekalibreerde standaarde. Analise van die resultate toon dat die steenkoolkoers ‘n positiewe verband, en die produksiekoers ‘n negatiewe verband met die metallisasiegraad het. Die slotsom waartoe gekom is, is dat die proses termodinamies werkbaar is, dat reduksie van ystererts in ‘n vereenvoudigde proefaanleg bewerk kon word, en dat die prose stabiel en beheerbaar voorgekom het. Die aanbeveling word gemaak dat ‘n groter proefaanleg wat die volledige voorgestelde vloeiskema verteenwoordig, opgerig behoort te word, ten einde die proses meer volledig te kan toets.

Le laitier EAF inox et le laitier AOD sont les deux principaux laitiers issus de l'élaboration des aciers inoxydables. Aujourd'hui ces laitiers ne sont valorisés qu'en construction routière. Cette utilisation ne permet pas d'assurer une valorisation complète et pérenne de ces laitiers dont une large part reste stockée. Compte tenu des propriétés physiques des laitiers EAF inox et AOD solidifié par stabilisation, leur utilisation comme granulats dans le béton peut être intéressante. L'objectif de cette thèse est d'étudier la faisabilité de cette voie de valorisation. Ces travaux sont réalisés en deux parties.Premièrement les propriétés physico-chimiques et mécaniques des granulats de laitiers EAF inox et AOD stabilisé sont déterminées. La composition minéralogique complète de ces granulats de laitiers issus de l'élaboration d'aciers inoxydables est aussi analysée afin de rechercher la présence éventuelle de minéraux instables et incompatibles à leur utilisation dans le béton. Compte tenue de la fluorescence sous rayons ultra-violet (UV) des laitiers, une nouvelle approche qui associe les UV et les analyses minéralogiques courantes (DRX, MEB, EDS) est développée dans cette étude. Cette étape de caractérisation des granulats des laitiers étudiés fait de ce mémoire de thèse le premier rapport sur la caractérisation physique, chimique et minéralogique des granulats de laitier AOD stabilisé. La deuxième étape de cette étude consiste à réaliser des bétons en substituant, dans des proportions variées, des granulats naturels silico-calcaires d'un béton de référence par des granulats de laitiers EAF inox et AOD stabilisé. Les propriétés physiques et mécaniques de ces bétons à matrice ordinaires et à hautes performances sont évaluées. Une étude de durabilité de ces bétons est aussi effectuée à travers le suivi des propriétés mécaniques des bétons sur 365 jours, l'analyse d'indicateurs de durabilité et la réalisation d'essais de gonflement. Enfin des observations MEB sont faites sont faites les échantillons de béton âgés de 365 jours pour observer et analyser le réseau de fissures à l'interface granulat – matrice cimentaire. Les résultats montrent des propriétés adaptées à une utilisation structurelle, avec une légère amélioration des caractéristiques mécaniques et des propriétés de durabilité acceptables pour les bétons de granulats de laitiers EAF inox et AOD stabilisé. / Electric Arc Furnace (EAF) slag and Argon Oxygen Decarburization (AOD) slag are the two principal slags resulted from stainless steel manufacture. Unlike blast furnace slag, a significant part of these steel slags is not valued and has to be treated as waste. Stainless steel slags are nowadays only used as aggregates in road construction and their future valorisation in concrete for building could be interesting. To our knowledge, that possibility has not yet been studied in the literature. The objective of this work is to study the possibility of using slags from stainless steel process as aggregates in concrete. Moreover, this is the first report on mineral composition and physical properties of stabilized AOD slags from stainless steel process.In this study, physicochemical and mechanical properties of EAF slag and stabilised AOD slag aggregates are firstly determined. Mineralogical composition of these stainless steel slag aggregates is also analysed to verify if they contain mineral phases likely to show expansion reactions. An original method using short and long UV lights was developed for studying the mineralogical composition of slag. Secondly, the natural aggregates of reference concretes are substituted, in different proportions, by stainless steel slag aggregates and several physical and mechanical properties are measured on concrete samples. The evolution of concrete mechanical properties has been followed over the time up to 365 days. Similarly, durability tests and swelling tests are made on concrete samples to assess the impact of EAF and AOD slag aggregates. SEM observations of crack network at the paste-aggregate interface and in concrete samples were carried out. The results show adequate structural properties, with a slight improvement of the mechanical properties for concretes made of stainless steel slag aggregates. The durability and expansion characteristics of these concretes are sufficient for construction use.

Na fabricação de aço pelo processo de aciaria elétrica há geração de vários tipos de resíduos, dentre estes, as poeiras de aciaria. Este resíduo possui como principais constituintes os elementos Fe, O e Zn, sendo considerado perigoso na maioria dos países. Além destes elementos, a presença do cloro provoca interferência deletéria na maioria dos processos de reciclagem ou incorporação do PAE em outros materiais. Por este motivo, o cloro representa um obstáculo à ampliação das possibilidades de destinação ou reciclagem destas poeiras. Este trabalho propõe uma nova tecnologia hidrometalúrgica para a redução do teor de cloro solúvel das poeiras para teores menores que 0,3% (b.s). Esta técnica..., de modo a possibilitar a aplicação de um processo especialmente desenvolvido de lixiviação aquosa, que evita a necessidade de agitação e equipamentos especiais. O principal objetivo foi reduzir o teor de cloretos das poeiras utilizando uma baixa relação sólido:líquido, em um processo de maior sustentabilidade e menor utilização de energia e recursos hídricos. Nos ensaios foram utilizadas poeiras previamente caracterizadas em seus principais elementos e provenientes de três usinas semi-integradas, cada uma com um perfil produtivo diferente e com teores de cloro médio variando de 2,01 a 5,26% (b.s). Foram testadas duas variantes principais desta nova tecnologia, em temperatura ambiente e a 60°C. Os resultados alcançados demonstraram a possibilidade de redução do teor de cloro solúvel das poeiras acima de 90%, com uma relação sólido:líquido de até 1:0,43. Também foi possível a geração de soluções concentradas de sais que atingiram até 20% em massa de concentração, em temperatura ambiente, sem necessidade de evaporação. A fácil obtenção destas soluções concentradas potencializa a aplicação e o desenvolvimento futuro de novas tecnologias para recuperação dos sais de poeiras de aciaria elétrica, principalmente sais de potássio. O material residual, com teor de cloro reduzido, possui melhor qualidade e aptidão para ser utilizado como matéria-prima em novos ou tradicionais processos de reciclagem e incorporação em outros materiais. / The Electric steelmaking generates several types of wastes, among them the electric arc furnace dust – EAFD. This residue has as main constituents the elements Fe, O and Zn, being considered dangerous in most countries. In addition to these elements, the presence of chlorine causes deleterious interference in most of recycling processes or incorporation in other materials. For this reason, chlorine represents an obstacle to increase the possibilities for disposal or recycling these dusts. This work proposes a new hydrometallurgical technology to reduce the soluble chlorine content of these dusts to lower levels than 0.3 wt% (dry basis). This technique is based on … to enable the application of a specially designed aqueous leaching process, that avoids the need for special equipment and stirring. The main objective is to reduce the chloride content of dusts using a low solid:liquid ratio in a process of greater sustainability and lower use of energy and water resources. In the tests, dusts previously characterized in main elements were used. These dusts come from three semi-integrated plants, each one with a different production profile and average chlorine content ranging from 2.01 to 5.26 wt% (dry basis). Two main variants of this new technology were tested at room temperature and 60°C. The results showed the possibility of reducing soluble chlorine content of dusts at levels above 90%, with solid:liquid ratio up to 1: 0,43. It was also possible to generate concentrated salt solutions, reaching up to 20 wt% concentration of salts, at room temperature, without evaporation. These concentrate solutions are easily obtained and potentialize the application and future development of new technologies for recovery of electric arc furnace dust salts, especially potassium salts. The residual material with low chlorine content, has better quality and suitability for use as raw material in new or traditional recycling processes and incorporation in other materials.

This thesis centers around an electric arc furnace (EAF) at a steel mini-mill in Wilton, IA. First, the thesis replicates previous optimization attempts. Next, the modeling is greatly altered to produce a much improved steel-melting model. Then, a new optimal control system is created and used to reduce energy and fuel costs over the melting process. Finally, results are presented. This thesis shows that when the new optimal control is simulated, the system shows significant energy and fuel savings.

This work investigates the interactions of carbonaceous materials (metallurgical coke, natural graphite and HDPE/coke blends) with three EAF slags [FeO: 24% to 32%]. Experiments were conducted using the sessile drop technique (1500??C-1600??C) with off-gases (CO, CO2) measured using an IR analyzer; the wetting behaviour was determined from contact angle measurements. Estimation of slag foaming behaviour was determined from the droplet volume changes calculated using specialized software. At 1550??C, all slags were non-wetting with coke due to increased surface tension due to sulphur. At 1550??C, slag 1 was initially non-wetting on natural graphite due to gas entrapment in the slag droplet; the wetting improved after that. Other slags showed comparatively better wetting. At 1600??C, all slags were non-wetting with coke. Slags showed a shift from non-wetting to wetting behaviour with natural graphite. Slag/coke reactions produced high off-gases levels causing extensive FeO reduction; gas entrapment in the slag was poor (small volume droplets). Slag/natural graphite interactions revealed both slow gas generation rates and FeO reduction, and excellent gas entrapment (higher droplet volumes) with minor changes in slag properties due to low ash levels. The iron oxide reduction rates were determined to be 1.54x10-5 and 4.2x10-6 mol.cm-2/sec (Slag 1, 1550??C) for metallurgical coke and natural graphite respectively. Slag interactions with coke/HDPE blends showed increasing off-gas levels with increasing HDPE levels. Blend#3 produced the highest off-gas levels, extensive FeO reduction and displayed significantly higher slag foaming and better wetting compared to coke. Our line on trends compared well for slag/carbon interactions and resulted in deceased specific energy consumption and carbon usage and increased productivity. These findings have enhanced the possibility of utilizing polymeric wastes in blends with coke in EAF steelmaking for slag/carbon interactions.

The objective of the present thesis is to optimize the electric arc furnace (EAF) practice from an environmental view point. Two aspects that meet the requirements of the secondary steelmaking industries today, viz. Mo alloying with maximum retainment of the alloying element in molten steel and optimization of foaming by carbonate addition with a view to optimize the energy need of the process. Both these aspects would also have a significant impact on the process economy. Iron molybdate (Fe2MoO4) has been synthesized from commercial grade materials and proposed as a new potential precursor for steel alloying with Mo. The thermal stabilities of different molybdates, viz. Fe2MoO4, CaMoO4 and MgMoO4, were studied using thermogravimetry analysis (TGA). It was found that Fe2MoO4 is the most stable one and doesn’t evaporate in Ar atmosphere when heating up to 1573 K. The synthesis of Fe2MoO4 requires high temperature (1373 K) and long holding time (up to 16 hours). In a view of this, the possibilities for in-situ formation of Fe2MoO4 and CaMoO4 from their precursor mixtures were studied with the aid of high-temperature X-ray diffraction (XRD) and TGA analysis. Laboratory and industrial trials on steel alloying with Mo were conducted using precursor mixtures as sources of Mo. It was found that the mixture, which contains FeOx, MoO3 and C (Fe2MoO4 precursor), can provide the Mo yield up to 98 % at both the laboratory as well as industrial trials. The Mo yields even in the case of C+MoO3 and C+MoO3+CaO mixtures were around 93 % in these trials. The higher yield for the MoO3+C+FeOx mixture was attributed to the stabilization of Mo in the precursor (marked by the decrease in the Gibbs energy of Mo) and the readiness to dissolve in the steel bath. The heat effect of the slag foaming with carbonates addition was studied at 1623 and 1673 K with the aid of thermal analysis technique with a new crucible design. Experiments were conducted by adding limestone and dolomite pieces of defined shapes (together with iron sinkers) in molten slag and monitoring the temperature changes accompanying the decomposition of carbonates. It was found that the decomposition energies for dolomite and limestone for the studied slag composition are in the range 56-79 % of theoretical values, which is linked to the energy saving effect of slag foaming. No influence of sample shape on decomposition energy was found both for limestone and dolomite. The kinetics of slag foaming by limestone particles was studied at 1773 K with the aid of X-ray imaging system. A model was proposed to describe the decrease in foam height with time on the basis of CaO shell formation during decomposition reaction. The energy impact of limestone and raw dolomite addition was examined in a 100-ton EAF. It was found that, in the case of addition of carbonates after the scrap is completely molten; the endothermic heat effects for limestone and dolomite (2255 and 2264 kJ/kg respectively) were only 70 % from theoretical values. This is indicative of the resistance to heat transfer due to increased foaming. / QC 20100914

This work investigates the interactions of carbonaceous materials (metallurgical coke, natural graphite and HDPE/coke blends) with three EAF slags [FeO: 24% to 32%]. Experiments were conducted using the sessile drop technique (1500??C-1600??C) with off-gases (CO, CO2) measured using an IR analyzer; the wetting behaviour was determined from contact angle measurements. Estimation of slag foaming behaviour was determined from the droplet volume changes calculated using specialized software. At 1550??C, all slags were non-wetting with coke due to increased surface tension due to sulphur. At 1550??C, slag 1 was initially non-wetting on natural graphite due to gas entrapment in the slag droplet; the wetting improved after that. Other slags showed comparatively better wetting. At 1600??C, all slags were non-wetting with coke. Slags showed a shift from non-wetting to wetting behaviour with natural graphite. Slag/coke reactions produced high off-gases levels causing extensive FeO reduction; gas entrapment in the slag was poor (small volume droplets). Slag/natural graphite interactions revealed both slow gas generation rates and FeO reduction, and excellent gas entrapment (higher droplet volumes) with minor changes in slag properties due to low ash levels. The iron oxide reduction rates were determined to be 1.54x10-5 and 4.2x10-6 mol.cm-2/sec (Slag 1, 1550??C) for metallurgical coke and natural graphite respectively. Slag interactions with coke/HDPE blends showed increasing off-gas levels with increasing HDPE levels. Blend#3 produced the highest off-gas levels, extensive FeO reduction and displayed significantly higher slag foaming and better wetting compared to coke. Our line on trends compared well for slag/carbon interactions and resulted in deceased specific energy consumption and carbon usage and increased productivity. These findings have enhanced the possibility of utilizing polymeric wastes in blends with coke in EAF steelmaking for slag/carbon interactions.

Na fabricação de aço pelo processo de aciaria elétrica há geração de vários tipos de resíduos, dentre estes, as poeiras de aciaria. Este resíduo possui como principais constituintes os elementos Fe, O e Zn, sendo considerado perigoso na maioria dos países. Além destes elementos, a presença do cloro provoca interferência deletéria na maioria dos processos de reciclagem ou incorporação do PAE em outros materiais. Por este motivo, o cloro representa um obstáculo à ampliação das possibilidades de destinação ou reciclagem destas poeiras. Este trabalho propõe uma nova tecnologia hidrometalúrgica para a redução do teor de cloro solúvel das poeiras para teores menores que 0,3% (b.s). Esta técnica..., de modo a possibilitar a aplicação de um processo especialmente desenvolvido de lixiviação aquosa, que evita a necessidade de agitação e equipamentos especiais. O principal objetivo foi reduzir o teor de cloretos das poeiras utilizando uma baixa relação sólido:líquido, em um processo de maior sustentabilidade e menor utilização de energia e recursos hídricos. Nos ensaios foram utilizadas poeiras previamente caracterizadas em seus principais elementos e provenientes de três usinas semi-integradas, cada uma com um perfil produtivo diferente e com teores de cloro médio variando de 2,01 a 5,26% (b.s). Foram testadas duas variantes principais desta nova tecnologia, em temperatura ambiente e a 60°C. Os resultados alcançados demonstraram a possibilidade de redução do teor de cloro solúvel das poeiras acima de 90%, com uma relação sólido:líquido de até 1:0,43. Também foi possível a geração de soluções concentradas de sais que atingiram até 20% em massa de concentração, em temperatura ambiente, sem necessidade de evaporação. A fácil obtenção destas soluções concentradas potencializa a aplicação e o desenvolvimento futuro de novas tecnologias para recuperação dos sais de poeiras de aciaria elétrica, principalmente sais de potássio. O material residual, com teor de cloro reduzido, possui melhor qualidade e aptidão para ser utilizado como matéria-prima em novos ou tradicionais processos de reciclagem e incorporação em outros materiais. / The Electric steelmaking generates several types of wastes, among them the electric arc furnace dust – EAFD. This residue has as main constituents the elements Fe, O and Zn, being considered dangerous in most countries. In addition to these elements, the presence of chlorine causes deleterious interference in most of recycling processes or incorporation in other materials. For this reason, chlorine represents an obstacle to increase the possibilities for disposal or recycling these dusts. This work proposes a new hydrometallurgical technology to reduce the soluble chlorine content of these dusts to lower levels than 0.3 wt% (dry basis). This technique is based on … to enable the application of a specially designed aqueous leaching process, that avoids the need for special equipment and stirring. The main objective is to reduce the chloride content of dusts using a low solid:liquid ratio in a process of greater sustainability and lower use of energy and water resources. In the tests, dusts previously characterized in main elements were used. These dusts come from three semi-integrated plants, each one with a different production profile and average chlorine content ranging from 2.01 to 5.26 wt% (dry basis). Two main variants of this new technology were tested at room temperature and 60°C. The results showed the possibility of reducing soluble chlorine content of dusts at levels above 90%, with solid:liquid ratio up to 1: 0,43. It was also possible to generate concentrated salt solutions, reaching up to 20 wt% concentration of salts, at room temperature, without evaporation. These concentrate solutions are easily obtained and potentialize the application and future development of new technologies for recovery of electric arc furnace dust salts, especially potassium salts. The residual material with low chlorine content, has better quality and suitability for use as raw material in new or traditional recycling processes and incorporation in other materials.

Independentemente do nível de verticalização ou da sua escala de produção, a redução de custos e o aumento de produtividade têm sido os principais focos internos das empresas da indústria do aço. Dois fatores controlam fundamentalmente o custo de produção do aço: o preço e o consumo dos insumos e matérias-primas. O primeiro depende fortemente do poder de barganha da empresa e das condições de mercado e, muitas vezes, não é possível exercer grande controle sobre ele. Sendo assim, é através da diminuição do consumo específico dos insumos e matérias-primas que a empresa pode obter sucesso na sua missão, internamente, de maximizar seu lucro. Em aciarias elétricas, o consumo dos insumos tem impacto importante na composição do custo final do aço, dos quais se destaca o consumo de energéticos utilizados no forno elétrico a arco, que pode representar até 30% do custo operacional desse tipo de aciaria. Para quantificar o aporte desses diferentes tipos de energia no forno, normalmente é utilizado o indicador de consumo de energia total, que utiliza o poder calorífico de cada tipo de energético na transformação para a unidade de kWh/t. O objetivo desse trabalho foi avaliar o impacto na eficiência energética do forno, medida através do consumo de energia total, da redução da vazão de gás natural nos modos lança e da modificação da proporção entre oxigênio e gás natural (O2/GN) em um dos modos queimador do sistema de injeção de um forno elétrico a arco. Para tanto, foi realizado um teste estatístico dividido em quatro cenários no formato de projeto de experimentos (DOE). O cenário em que as modificações no modo queimador e nos modos lança foram aplicadas conjuntamente apresentou a maior redução no consumo de energia total (2,50%), impulsionada principalmente pelas reduções no consumo de gás natural (16,94%) e no consumo de energia elétrica de forno e forno-panela (-1,90%). Através da análise do carbono de vazamento de todas as corridas não foi possível afirmar que os ganhos em consumo de energia elétrica foram provenientes de uma maior oxidação de ferro da carga nas corridas. / Companies have been extensively focusing on cost reduction and productivity optimization in the last few years, independently of their levels of production or verticalization. The cost of production is basically controlled by two factors: the price and the consumption of raw and input materials. The price depends on the current conditions of the market and the capacity of the company to deal with its suppliers about the price to be paid. Due to that, it is very difficult to control this factor and for this reason, through the reduction in raw material and inputs consumption that companies can achieve their mission of becoming more profitable. In electric steelmaking, consumption of inputs plays an important role on the final billet cost, with particular emphasis to the energy consumption in the electric arc furnace, which can represent up to 30% of the operational cost in a melt shop. To quantify the contribution of different types of energy in the furnace, it is used the performance indicator of total energy consumption, which associates the heat of combustion of each type of energetic in order to use the unit kWh/t. The aim of this study was to evaluate the impact on the energy efficiency of the furnace, measured by the total energy consumption, reducing the flow of natural gas in lance modes and modifying the ratio between oxygen and natural gas (O2/NG) in one of the burner modes of the injection system in an electric arc furnace. Thus, a statistical test divided into four scenarios in the format of design of experiments (DOE) was conducted. The scenario in which the burner mode and lance mode modifications were applied together resulted in the greatest reduction in total energy (2,50%), driven especially by reductions in natural gas consumption (16,94%) and electrical energy consumption of furnace and ladle furnace (1,90%). Through the analysis of tapping carbon of all heats it was not possible to assert that gains in electrical energy were due to a higher oxidation of iron contained in the blend charged.