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Steel is the mother of industry, and is also an energy consumption intensive industry. Since the energy crisis, the various countries iron and steel plants positively take each energy frugal measure in order to reduce the fuel and the electric power consumption. In the iron and steel plant comparatively consumes the energy the system regulation equipment is the reheating furnace, so to save energy in a reheating furnace and reduce the energy consumption become one of important topics. The reduction consumes energy the countermeasure aspect may by analyze the heat transfer model and the change reheating furnace characteristic begins. In this thesis, we will build a simulation system of reheating furnace to analysis the temperature change of slab in a reheating furnace and discussion energy consumption factor. And then we use the thermal balance model to analysis the situation of fuel consumption. According to different conditions, we want to discuss the relationships energy consumption and increasing temperature of slab inside furnace.

Nowadays, many industries are searching new and effective substitutes for traditional energy resources. Heavy industries are not excluded. In order to use the most of the limited resources, they look for new techniques and new energy management systems which are efficient in energy consumption. Studying in saving energy for reheating furnace and in approving operation conditions may help heavy industries to reduce costs and to enhance quality of products. ¡@¡@Inevitably, the inner compositions of alloy ingots are not uniform during continuous casting. To solve this problem, we usually do heat treatment on alloy ingots before casting. Besides, to ensure the quality and stability of alloy ingots in heat treatment, we need an effective tool to monitor the temperature distribution on ally ingots. Moreover, the precise control over energy consumption can improve the efficiency of reheating furnace and can reduce costs. ¡@¡@This study focuses on alloy ingots. We simulate heat transfer by numerical methods and construct the integrated software to simulate the characteristics of reheating furnace in batch type operation. Analyses in the temperature distribution and energy consumption of alloy ingots in reheating process are also included. Besides, we choose some parameters, which might affect the energy consumption and try to find the best level parameter composition in reheating furnace analysis by Taguchi method. Some results are shown below: ¡]1¡^When temperature rising process starts, our model provides ¡@ ¡@reasonable and exact prediction in one or two hours. ¡]2¡^Reheating furnace treatment ability is the most important ¡@ ¡@control factor (out of eight) in this study. ¡]3¡^We can reduce around 3% of the consumption with the ¡@ ¡@parameters obtained by Taguchi method. ¡]4¡^The soaking degrees are all below 0.01¢J after heat treatment ¡@ ¡@on alloy ingots. ¡]5¡^We change the temperature rising rate to simulate the situation ¡@ ¡@of heated alloy ingots. We find that the higher temperature ¡@ ¡@rising rate is, the more significant temperature difference ¡@ ¡@inside alloy ingots is. On the other hand, the lower rate would ¡@ ¡@increase the soaking degree.

Abstract Steel is the mother of industry, and is also an energy consumption intensive industry. Especially for the rolling mill, the energy consumption in a reheating furnace take a half, so to save energy in a reheating furnace and reduce the energy consumption become the major issue in the future. The reheating furnace used in general process of steel producing can divided into two types-Continuous type and Batch type- through its ability of steel rolling¡Napproach and its demand. In this thesis, our research target is the batch type reheating furnace, we based on theory of heat transfer in a reheating furnace to build a simulation system of reheating furnace and calculate the temperature-time curve of slab and its heat flux. And then we use the thermal balance model to analysis the situation of fuel consumption. According to different operated conditions, we want to discuss the relationships between energy consumption and increasing temperature of slab inside furnace¡Nsoaking degree¡C From analysis result, we can find that fixed the total time in furnace, the longer of heating time is, the lower of average temperature of slab and the higher of temperature difference of discharge slab are. But in the process of increasing temperature, the max temperature difference of slab is lower. Using the exhaust gas to preheat air through the heat exchanger, we can find that when the temperature of preheated air is increasing, the heat loss of exhaust gas and fuel consumption will be lower. When air-fuel ratio is getting higher, the temperature difference in the process of increasing temperature will be getting lower, and it will be higher as the slab soaks. When air-fuel ratio is increasing, the quantity of fuel consumption will increase too. In respect of refractory material, heat loss of furnace and accumulation of heat in refractory material caused by using the refractory cottons is less than using the refractory bricks. Besides that, the different fuel will only affect the quantity of fuel consumption, not increasing temperature of slab and soaking degree.

Reheating furnace is a furnace that using fuel combustion energy to heat steel products before hot rolling. Materials need to reach the temperature around 1400K uniformly after heating in reheating furnaces. Steel oxidizes during the reheating process. Oxidize scale layer on the surface will changed the heat transfer properties of surface and increase the inner stress of material, reducing the quality of the steel. In this study, a model of scale formation under reheating furnace working condition is developed. The model can be coupled into computational fluid dynamics (CFD). The commercial software, ANSYS FLUENT®, was utilized to give a prediction of furnace atmosphere and calculate the formed scale. A calculator is also developed to predict the scale formation of a single point during the reheating process using measurable flow field data. Furthermore, a series of parametric studies has been investigated to study the influence of operating conditions.

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Os defeitos superficiais são os maiores problemas de qualidade em barras laminadas a quente, representando inúmeros transtornos durante o processo produtivo, pois dependendo de suas características geram elevada rejeição durante o processo de inspeção. Elevada rejeição significa retrabalho e possível sucateamento. Dentre as diversas causas para a ocorrência de defeitos superficiais, estão os defeitos nos tarugos, a temperatura de laminação, conseqüência da temperatura de reaquecimento e ritmo de laminação e a remoção de carepa após o reaquecimento. Definiu-se o aço SAE 1043 para o desenvolvimento deste trabalho devido aos níveis de rejeição superficial e elevados volumes de produção, o que gera grande impacto na produção das linhas de inspeção. Os resultados obtidos a partir dos testes realizados demonstram que a temperatura de laminação até determinado limite não tem influência na rejeição superficial, mas que abaixo deste gera elevado índice de rejeição. O uso do descarepador tem grande influencia nos níveis de defeitos superficiais, e o controle de seus parâmetros principais é fundamental. O condicionamento superficial dos tarugos é o parâmetro que mais apresentou influência positiva sobre a rejeição superficial, demonstrando que defeitos pré-existentes na matéria-prima têm grande impacto no produto final da laminação. / Surface defects are major quality problems in hot rolled bars, representing numerous disturbances during the production process, as depending on their characteristics generate high rejection during the inspection process. High rejection means rework and scrap. Among the various causes for the occurrence of surface defects are defects in the billets, rolling temperature, a consequence of the reheating temperature and rate of roll and removal of scale after reheating. The steel SAE 1043 used in this work was selected due to its level of surface defects and high production volumes, which generates large impact on production inspection process. The results show that the rolling temperature of up to a certain limit does not influence the surface defects, but below this generates a high rate of rejection. The use of descaling has a large influence on the levels of surface defects, and control of its main parameters is essential. The surface conditioning of billets is the parameter that showed a positive influence on the reduction of surface defects, demonstrating that pre-existing defects in materials has large impact on the final rolled product.

Os defeitos superficiais são os maiores problemas de qualidade em barras laminadas a quente, representando inúmeros transtornos durante o processo produtivo, pois dependendo de suas características geram elevada rejeição durante o processo de inspeção. Elevada rejeição significa retrabalho e possível sucateamento. Dentre as diversas causas para a ocorrência de defeitos superficiais, estão os defeitos nos tarugos, a temperatura de laminação, conseqüência da temperatura de reaquecimento e ritmo de laminação e a remoção de carepa após o reaquecimento. Definiu-se o aço SAE 1043 para o desenvolvimento deste trabalho devido aos níveis de rejeição superficial e elevados volumes de produção, o que gera grande impacto na produção das linhas de inspeção. Os resultados obtidos a partir dos testes realizados demonstram que a temperatura de laminação até determinado limite não tem influência na rejeição superficial, mas que abaixo deste gera elevado índice de rejeição. O uso do descarepador tem grande influencia nos níveis de defeitos superficiais, e o controle de seus parâmetros principais é fundamental. O condicionamento superficial dos tarugos é o parâmetro que mais apresentou influência positiva sobre a rejeição superficial, demonstrando que defeitos pré-existentes na matéria-prima têm grande impacto no produto final da laminação. / Surface defects are major quality problems in hot rolled bars, representing numerous disturbances during the production process, as depending on their characteristics generate high rejection during the inspection process. High rejection means rework and scrap. Among the various causes for the occurrence of surface defects are defects in the billets, rolling temperature, a consequence of the reheating temperature and rate of roll and removal of scale after reheating. The steel SAE 1043 used in this work was selected due to its level of surface defects and high production volumes, which generates large impact on production inspection process. The results show that the rolling temperature of up to a certain limit does not influence the surface defects, but below this generates a high rate of rejection. The use of descaling has a large influence on the levels of surface defects, and control of its main parameters is essential. The surface conditioning of billets is the parameter that showed a positive influence on the reduction of surface defects, demonstrating that pre-existing defects in materials has large impact on the final rolled product.

Os defeitos superficiais são os maiores problemas de qualidade em barras laminadas a quente, representando inúmeros transtornos durante o processo produtivo, pois dependendo de suas características geram elevada rejeição durante o processo de inspeção. Elevada rejeição significa retrabalho e possível sucateamento. Dentre as diversas causas para a ocorrência de defeitos superficiais, estão os defeitos nos tarugos, a temperatura de laminação, conseqüência da temperatura de reaquecimento e ritmo de laminação e a remoção de carepa após o reaquecimento. Definiu-se o aço SAE 1043 para o desenvolvimento deste trabalho devido aos níveis de rejeição superficial e elevados volumes de produção, o que gera grande impacto na produção das linhas de inspeção. Os resultados obtidos a partir dos testes realizados demonstram que a temperatura de laminação até determinado limite não tem influência na rejeição superficial, mas que abaixo deste gera elevado índice de rejeição. O uso do descarepador tem grande influencia nos níveis de defeitos superficiais, e o controle de seus parâmetros principais é fundamental. O condicionamento superficial dos tarugos é o parâmetro que mais apresentou influência positiva sobre a rejeição superficial, demonstrando que defeitos pré-existentes na matéria-prima têm grande impacto no produto final da laminação. / Surface defects are major quality problems in hot rolled bars, representing numerous disturbances during the production process, as depending on their characteristics generate high rejection during the inspection process. High rejection means rework and scrap. Among the various causes for the occurrence of surface defects are defects in the billets, rolling temperature, a consequence of the reheating temperature and rate of roll and removal of scale after reheating. The steel SAE 1043 used in this work was selected due to its level of surface defects and high production volumes, which generates large impact on production inspection process. The results show that the rolling temperature of up to a certain limit does not influence the surface defects, but below this generates a high rate of rejection. The use of descaling has a large influence on the levels of surface defects, and control of its main parameters is essential. The surface conditioning of billets is the parameter that showed a positive influence on the reduction of surface defects, demonstrating that pre-existing defects in materials has large impact on the final rolled product.

<p>Steel heating and melting processes consume the majority of the energy used in advanced short-process steelmaking practices. Economic and environmental pressures from energy consumption drive the research to improve the furnace operation efficiency and energy efficiency. The goal of this research is to utilize computational fluid dynamics (CFD) modeling to provide useful tools and recommendations on the steel heating and melting practices in the steelmaking process. The steel slab reheating process, the steel scrap preheating process and the steel scrap melting process are studied.</p> <p> </p> <p>A transient three-dimensional (3-D) CFD model was developed to simulate the flow characteristics, combustion process and multi-scale, multi-mode heat transfer inside the reheating furnace. The actual geometry of an operating industrial furnace was used and typical operating conditions were simulated. Specific walking speeds of slabs in production were modeled using a dynamic mesh model which is controlled by a user-defined function (UDF) solved using ANSYS Fluent. Fuel variations at different zones with respect to time were also considered. The model was validated with instrumented slab trials conducted at the SSAB Mobile (Alabama) mill. The temperature field in the furnace and the temperature evolution of a slab predicted by the CFD model are in good agreement with those obtained from the instrumented slab trials. Based on the simulation results, the slab reheating process and the temperature uniformity of a slab at discharge were able to be properly evaluated. In addition, a comprehensive two-dimensional (2-D) numerical heat transfer model for slab reheating in a walking beam furnace was developed using the finite difference method. An in-house code was developed. The model is capable of predicting slab temperature evolution during a reheating process based on real time furnace conditions and steel physical properties. The model was validated by using mill instrumented slab trials and production data. The results show that the temperature evolution predicted by the model is in good agreement with that measured by the thermocouples embedded in the instrumented slab. Compared with 3-D CFD simulation of a reheating process, this 2-D heat transfer model used for predicting slab temperature evolution requires less computing power and can provide results in a few seconds. A graphical user interface was also developed to facilitate the input and output process. This is a very convenient and user-friendly tool which can be used easily by mill metallurgists in troubleshooting and process optimization.</p> <p> </p> <p>CFD models for steel scrap preheating and melting processes by the combined effects of the heat source from both oxy-fuel combustion and electric arc were also developed. The oxy-fuel burners firing natural gas (NG) are widely used in EAF operation during the scrap preheating and melting stages. In order to understand the role of oxy-fuel combustion and potentially increase the energy input from NG while decreasing the electricity consumption, numerical simulation of scrap preheating by oxy-fuel combustion in an EAF was firstly conducted. A 3-D CFD model was developed with detailed consideration of gas flow, oxy-fuel combustion, heat transfer between gas and solid scrap and scrap oxidation. The model was validated by a small-scale experimental study and applied onto a real-scale EAF.</p> <p> </p> <p>Scrap melting in bath is comprehensively studied with a CFD model developed to simulate the melting in bath process under given operating conditions. Two sub-models were developed for model integration: steel melting model and coherent jet model. The multiphase volume of fluid (VOF) model and the enthalpy-porosity technique are applied to describe the steel melting process. The coherent jet model calculates the gas jet momentum and is integrated into the flow model to calculate its effect on the fluid flow in the bath. The electric arc was treated as a heat flux to represent the heat transfer from the electric arc during the melting process. Model validations were conducted for each sub-model to ensure their accuracy. Parametric studies were also carried out to obtain useful information for real practice. </p><p>Overall, the CFD models developed in this research work have demonstrated value in improving energy efficiency in the energy-intensive steelmaking processes. The developed CFD models also provide insights for better understanding of the multi-physics processes.<br></p> <p> </p>