The increase of the reduction temperature in direct reduction furnaces has been a recurring tool due to the benefits that it provides to the process. However, its increase cannot be performed without taking into account some considerations, since the sticking phenomenon is directly correlated with it and could lead to permeability problems and reactor performance. An analysis of the formation of pellets clusters at different temperatures was carried out with focus on morphological characterization of reduced materials to better understand the causes and effects of these actions. The results showed a correlation between the morphology of the metallic iron present in the samples and the clustering index. At low reduction temperatures, 1123 K (850°C), the iron formed is eroded and deformed and the cluster hardly remains after tumbling. When forming iron with fibrous structure, 1223 K (950°C), the clustering index increases because of anchor points which make the material to stick together. Finally, under the effect of high temperature and long time, it generates fresh precipitated iron, enhancing the resistance of the clusters so that they cannot be separated.

ResumoO fenômeno de colagem é a formação de aglomerados de pelotas, denominados clusters, devido à sinterização do ferro gerado durante o processo de redução. O resultado disto é a elevação da perda de carga nos reatores de redução direta. Tal fenômeno vem sendo estudado por vários pesquisadores, pois as práticas operacionais dos reatores têm priorizado o uso de temperaturas de bustle gas (BG) cada vez maiores, o que potencializa o aparecimento dos clusters. Uma alternativa para controlar a colagem é por meio de utilização de agentes de coating (AC's). Em relação às matérias primas utilizadas como AC´s, as questões que surgem agora são as seguintes: Como se comportam os AC's em temperaturas muito elevadas de BG? Qual seria a maior temperatura possível de BG? A fim de começar a entender a melhor maneira de responder a estas questões foram realizados alguns testes de caráter exploratório e não convencionais para avaliar o comportamento de alguns materiais de coating a elevadas temperaturas de redução. Os resultados destes testes mostraram a possibilidade dos AC's funcionarem a temperaturas maiores que a de inicio do amolecimento da carga e que, nestas temperaturas, a sua granulometria pode ser parâmetro determinante para seu desempenho. O aprimoramento dos ensaios de simulação do processo de redução em reatores de redução direta é fundamental para responder as questões que se apresentam em relação ao tema. Palavras-chave: Pelota; Redução direta; Colagem; Coating. STUDY OF ALTERNATIVE COATING TO HIGH TEMPERATURES OF BUSTLE GAS AbstractThe clustering phenomenon consists of the sintered iron generated during the reduction process. The result of sintering could lead to the formation of strong clusters which disturb the gas flow inside the reactor. This phenomenon has been studied by many researchers because of client's movement in order to enhance the temperature of bustle gas to reach larger productivity. An alternative to control clustering is using coating agents (AC's). Above raw materials, the following questions arise now: What is the biggest possible temperature of BG? How behave the AC's in extreme temperatures? Some exploratory and unconventional tests were conducted to evaluate the behavior of some coating materials for high temperature reduction in order to begin to understand the best way to answer these questions. The results of these tests show that the AC's are able to work in higher temperatures than the charge's softening temperature and, at these temperatures, their particle size could be an extremely important characteristic. The intention is to enhance the evaluation tests and use them to definitively answer the questions that arose in relation to the problem.

The objectives of this work were to verify the moisture content influence on the maximum compression force values, to determine the Proportional Modulus of Deformation, the Maximum Tangent and Secant for acerola seeds under compression on its natural repose position and for fixed deformations. Acerola seeds with moisture content varying from 0.12 to 0.46 (d.b.) compressed uniaxially between two parallel rigid plates. It can be concluded that the compression needed for deforming the acerola seeds decreases as its moisture content increases when the deformation values were within 19.2 and 548.8 N. The Proportional Modulus of Deformation increases with the reduction of the moisture content, where values found were within 5.2 to 72.1 × 10 7 Pa. The sigmoidal model represented resistance to the compression of the acerola seeds adequately for different moisture content.

Climate change is often subject of discussions around the world that implies in several initiatives that support the reduction of greenhouse gases (GHG). Currently, countries that signed the Paris Agreement in 2015 have plans to restrict GHG emissions based on the NDC (Nationally Determined Contributions) established. These reductions are expected to come also from industries, including the steel one. Some countries and regions are highlighted for having more developed policies than the rest of the world, such as Europe, which since 2005 has been implementing an Emission Trading Scheme (ETS). In this context, the European steel industry has been facing challenges which impose a need for disruptive technology innovation. This work presents four different European steel mills from different countries. A variety of finished products were analyzed, and it was found that in all four cases there is a deficit between the verified GHG emissions and the licenses granted for emission. The specific emissions per ton of steel and energy efficiency of each plant play an important role in justifying these differences in CO 2 balance among the plants. Therefore, there are multiple initiatives in progress involving steel producers in Europe that encourage the use of new technologies and modified routes to reduce and mitigate the volume of emissions in the steel production chain. The success of these initiatives from a technical and an economic point of view is the path to sustainability, competitiveness and value generation for the future industry.

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Publicado pela ABM. Este é um artigo publicado em acesso aberto (Open Access) sob a licença Creative Commons Attribution, que permite uso, distribuição e reprodução em qualquer meio, sem restrições desde que o trabalho original seja corretamente citado. a ResumoA cadeia produtiva da mineração de minério de ferro é extensa e flexível, inicia-se na lavra e tem como fim o momento de estocagem em pátios e expedições através de navios, trens ou caminhões. Independente da rota, um ponto chave comum é que o minério precisa ter uma boa escoabilidade ao longo do processo. Dependendo do nível de umidade, características intrínsecas do minério, circunstâncias de operação e dimensionamento dos equipamentos esse comportamento de escoabilidade se altera e traz consequências importantes para a eficiência técnica e econômica do empreendimento. Testes de bancada são relevantes nesse contexto, uma vez que contribuem para um melhor entendimento e previsibilidade de desempenho. No estudo em questão dois minérios de características diferentes: um de hematita granular e lamelar compacto e outro de hematita microcristalina porosa; foram submetidos a um teste experimental de Sticking em níveis de umidade distintos. Os resultados mostraram que: quanto maior a umidade, maior o grau de agarramento do material; para uma mesma umidade, o minério de hematita microcristalina apresenta maior tendência ao agarramento; o teste de bancada correspondeu e teve boa sensibilidade para avaliar os diferentes cenários.

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The Direct Reduction (DR) process has been growing worldwide, and there are strong context suggestions that it will grow even more. One of these factors is the environmental pressure that occurs worldwide, and there are already projects to migrate Blast Furnace route steel plants to the Direct Reduction (DR) route, due to its smaller carbon footprint. Considering the importance of this process and the challenges of carrying out experimental tests on a pilot scale, an adequate way to evaluate the process and its impacts is through numerical simulations. There are different techniques applied to models that describe the counter-current reactor in the DR process, but none of them account for the clustering phenomenon. Clustering occurs because of the sintering of the metallic iron on the surface of the pellets in such a way that they attach to each other, forming clusters that hinder the gas flow through the shaft. The present study attempted to adapt a numerical model of a DR process to account for the effect of the cluster formation. Some clustering index equations from literature and some developed as part of this study were used and tested in the model, as a function of temperature, by varying the solid volume fraction in the control unit. The equation that resulted in the adjusted output closest to the current empirical value was implemented in the model and proved to be successful.