In recent years, the consequences of global warming have increased the discussion about the climate impact caused by humans and the fossil emissions. Sweden has decided to reduce the negative climate impact with a zero vision for the fossil carbon dioxide emissions in year 2045. In order to achieve this, great efforts and changes are needed both in the inhabitants' way of living but primarily in the base industry. The major cause is the use of fossil coal, which generates fossil carbon dioxide in the steel industry in particular. The fossil coal is added to the blast furnace in the steel process in forms of coke and coal, which reduces the iron and emits heat. The quality of the coke is important as it functions reducing agent, provides a mechanical support to the bed and enables the gas flow up through the blast furnace and enables dissolution of carbon in hot metal. Also, coke supplies energy from exothermic reactions between carbon and carbon dioxide that takes part in the blast furnace and the energy are further used for the heating and melting of the cold iron pellets. Due to these factors, the blast furnace process is dependent on coke for its function, which means that the entire process must be replaced if the steel production should work without fossil coal. However, there are many studies that have been done on how to replace some of the fossil coal with bio-coal, which is produced from biomass. If some of the fossil coal could be replaced by some bio-coal, this would mean that fossil carbon dioxide emissions would decrease and lead to a reduced climate impact. The process would still generate carbon dioxide, but on the other hand, a cycle would be formed because when biomass is grown, carbon dioxide is taken up, e.g. by the trees grown for this purpose. However, bio-coal does not have the same properties as fossil coal, which in turn affects the quality of the coke. Bio-coke is more reactive and more porous than fossil coke. In order to be able to replace fossil coke with bio-coke, it is likely necessary to pre-treat the biocoal before it replaces part of the fossil coal in the coke production. Bio-coal contains ash that acts as an internal catalyst. One theory is that if it is possible to produce a bio-coal with ash-free carbon structure, it can be used in the production of coke without having such a great effect on the coke quality. In this project, the ash's impact on the properties of bio-coal in coke was studied. Previous studies have shown that leaching is an effective method for removing ash from bio-coal. It can be leached in three different ways, either with water, weak acid or acid. However, it has been found that acid leaching has a certain impact on the carbon structure itself. For this reason, two types of bio-coal, torrefied Grot (forest residue) and torrefied sawdust were selected, which were leached both with water but also with weak acid in order to achieve an ash-reduced carbon structure. The acid selected was acetic acid, as it has been tested for similar purposes in previous studies. The leaching efficiency was evaluated by analysing the leachate with ICP-OES after leaching. According to the result, a significant part of the ash had been leached out, but the leaching with weak acid was much more effective than water leaching. To ensure that the carbon structure was not altered, light-optical microscopy was made which showed that the structure was intact. However, it was not possible to determine whether the pore sizes were changed after leaching and it is therefore relevant to investigate this further. Moreover, the leached II bio-coal replaced 5% of the fossil coal in the coal mixture for coke making. In addition to this, coke was also made with only the ash from the two bio-coals to see what effect the ash has on the coke quality. The result that was obtained from the TGA showed that the ash had a low impact on the reactivity of the coke. However, the coal structure of the coke had a great impact on the reactivity behaviour. Keywords: Bio-coke, bio-coal, leaching, ash, coke quality, carbon structures, torrefied sawdust

A utilização de briquetes de misturas de carvão fóssil e biomassa em substituição ao coque como agente redutor pode contribuir para a diminuição das emissões de CO2 à atmosfera no processo de redução de minério de ferro. O fenômeno do amolecimento e fluidificação do carvão fóssil durante o aquecimento permite que o mesmo absorva certa quantidade de materiais inertes à coqueificação durante o tratamento térmico. O objetivo deste trabalho é correlacionar o efeito das principais variáveis de processo de fabricação (temperatura e tempo de tratamento térmico, tamanho de partícula dos componentes, porosidade e proporção de carvão vegetal e carvão fóssil) sobre as propriedades obtidas (resistência mecânica e reatividade ao CO2) de briquetes compostos de misturas de carvão fóssil e carvão vegetal, para uso na indústria siderúrgica. Briquetes de dois formatos diferentes foram preparados em matriz cilíndrica e em maquina briquetadeira e tratados termicamente em forno vertical aquecido com resistência elétrica sob atmosfera de nitrogênio. A resistência à compressão dos briquetes foi analisada em função das seguintes variáveis: proporção de carvão fóssil e carvão vegetal, taxa de aquecimento do tratamento térmico e tamanho de partícula dos carvões. A reatividade ao CO2 dos briquetes tratados termicamente foi analisada em função das seguintes variáveis: temperatura de ensaio e vazão de CO2. Foram comparados os resultados obtidos de ambos os formatos de briquetes. Com o aumento da proporção de carvão vegetal nos briquetes cilíndricos de biocoque, a densidade aparente e a resistência à compressão após tratamento térmico aumentaram para as misturas contendo 5, 10 e 15% de carvão vegetal. A partir dessa composição (15% de carvão vegetal) tanto a densidade final quanto a resistência à compressão apresentaram diminuição. Encontrou-se que tanto os briquetes cilíndricos a verde quanto os briquetes tratados termicamente apresentam perda de resistência mecânica com o aumento do tamanho de partícula do carvão fóssil. Os melhores valores de resistência à compressão foram obtidos em briquetes feitos com carvão fóssil em mistura de 15% em peso de carvão vegetal, tamanho de partícula abaixo de 0,044 mm, tratados termicamente a 1100°C durante 8 horas. Com o aumento na adição de carvão vegetal nos briquetes compostos de carvão fóssil e carvão vegetal, observou-se um aumento da reatividade do biocoque ao CO2. As micrografias dos briquetes tratados termicamente mostraram que a textura dos briquetes tende a ser mais homogênea com aumento de carvão vegetal de madeira na mistura. Os briquetes de biocoque fabricados em briquetadeira permitiram a ampliação do processo de fabricação de briquetes a uma escala laboratorial maior e mostraram a viabilidade industrial na fabricação do biocoque. Encontrou-se que a adição de carvão vegetal de madeira na mistura influencia diretamente na resistência a compressão e a reatividade ao CO2, devido a diferentes fatores como a composição das cinzas da madeira, a diminuição da fluidez devido à ação do inerte na mistura a carbonizar, a formação de uma estrutura porosa dentro da matriz carbonosa. Não encontrou-se correlação entre o índice de alcalinidade dos briquetes e sua reatividade ao CO2. / The substitution of metallurgical coke by briquetted mixtures of coal and biomass as a reducing agent can lower the emissions of greenhouse gases (CO2) in the iron and steelmaking industry. The thermal plasticity of the coking coal can be used to absorb an amount of inert materials during heat treatment. The objective of this study is to correlate the effect of the main processes variables (heat treatment temperature and duration, particle size of the materials, porosity and coal and charcoal ratio) on the properties (compressive strength and CO2 reactivity) of briquetted mixtures of coal and charcoal. Two types of briquettes were produced, one in a cylindrical die and another in a laboratory briquetting machine. The briquettes were heat treated in a vertical electrical furnace under nitrogen atmosphere. The compressive strength of the briquettes was analyzed as a function of the following variables: coal and charcoal ratio, heating rate and particle size. The CO2 reactivity of the heat treated briquettes was analyzed as a function of the following variables: temperature and CO2 flow. For the cylindrical briquettes, the increase of charcoal (5, 10, 15 wt%) in the coal-charcoal mixtures caused an increase on the bulk density and on the compressive strength of the heat treated briquettes. Above 15 wt% of charcoal in the mixtures, the bulk density and the compressive strength decreased. It was found out that both green and heat treated briquettes had a decrease in compressive strength with the increase of the coal particle size. Optimum results of compressive strength were obtained in the briquettes with 15 wt% of charcoal, particle size <0.044 mm, heat treatment temperature of 1100°C for 8 hours. The increase in charcoal proportion caused an increase in the CO2 reactivity of the briquettes. The SEM micrographs of the heat treated briquettes showed that the texture of the briquettes tend to be more homogeneous with the increase of charcoal in the mixture. The properties of the briquettes produced in the laboratorial briquetting machine showed that a large scale production could be viable. Also, it was found out that the addition of wood charcoal in the mixture directly affects the compressive strength and the CO2 reactivity of the briquettes due to factors such as: the ashes composition, the decrease in fluidity because of the inert material in the mixture, the formation of a porous structure inside the carbon matrix. It was not found a relation between the alkalinity index and the CO2 reactivity in the briquettes.

A utilização de briquetes de misturas de carvão fóssil e biomassa em substituição ao coque como agente redutor pode contribuir para a diminuição das emissões de CO2 à atmosfera no processo de redução de minério de ferro. O fenômeno do amolecimento e fluidificação do carvão fóssil durante o aquecimento permite que o mesmo absorva certa quantidade de materiais inertes à coqueificação durante o tratamento térmico. O objetivo deste trabalho é correlacionar o efeito das principais variáveis de processo de fabricação (temperatura e tempo de tratamento térmico, tamanho de partícula dos componentes, porosidade e proporção de carvão vegetal e carvão fóssil) sobre as propriedades obtidas (resistência mecânica e reatividade ao CO2) de briquetes compostos de misturas de carvão fóssil e carvão vegetal, para uso na indústria siderúrgica. Briquetes de dois formatos diferentes foram preparados em matriz cilíndrica e em maquina briquetadeira e tratados termicamente em forno vertical aquecido com resistência elétrica sob atmosfera de nitrogênio. A resistência à compressão dos briquetes foi analisada em função das seguintes variáveis: proporção de carvão fóssil e carvão vegetal, taxa de aquecimento do tratamento térmico e tamanho de partícula dos carvões. A reatividade ao CO2 dos briquetes tratados termicamente foi analisada em função das seguintes variáveis: temperatura de ensaio e vazão de CO2. Foram comparados os resultados obtidos de ambos os formatos de briquetes. Com o aumento da proporção de carvão vegetal nos briquetes cilíndricos de biocoque, a densidade aparente e a resistência à compressão após tratamento térmico aumentaram para as misturas contendo 5, 10 e 15% de carvão vegetal. A partir dessa composição (15% de carvão vegetal) tanto a densidade final quanto a resistência à compressão apresentaram diminuição. Encontrou-se que tanto os briquetes cilíndricos a verde quanto os briquetes tratados termicamente apresentam perda de resistência mecânica com o aumento do tamanho de partícula do carvão fóssil. Os melhores valores de resistência à compressão foram obtidos em briquetes feitos com carvão fóssil em mistura de 15% em peso de carvão vegetal, tamanho de partícula abaixo de 0,044 mm, tratados termicamente a 1100°C durante 8 horas. Com o aumento na adição de carvão vegetal nos briquetes compostos de carvão fóssil e carvão vegetal, observou-se um aumento da reatividade do biocoque ao CO2. As micrografias dos briquetes tratados termicamente mostraram que a textura dos briquetes tende a ser mais homogênea com aumento de carvão vegetal de madeira na mistura. Os briquetes de biocoque fabricados em briquetadeira permitiram a ampliação do processo de fabricação de briquetes a uma escala laboratorial maior e mostraram a viabilidade industrial na fabricação do biocoque. Encontrou-se que a adição de carvão vegetal de madeira na mistura influencia diretamente na resistência a compressão e a reatividade ao CO2, devido a diferentes fatores como a composição das cinzas da madeira, a diminuição da fluidez devido à ação do inerte na mistura a carbonizar, a formação de uma estrutura porosa dentro da matriz carbonosa. Não encontrou-se correlação entre o índice de alcalinidade dos briquetes e sua reatividade ao CO2. / The substitution of metallurgical coke by briquetted mixtures of coal and biomass as a reducing agent can lower the emissions of greenhouse gases (CO2) in the iron and steelmaking industry. The thermal plasticity of the coking coal can be used to absorb an amount of inert materials during heat treatment. The objective of this study is to correlate the effect of the main processes variables (heat treatment temperature and duration, particle size of the materials, porosity and coal and charcoal ratio) on the properties (compressive strength and CO2 reactivity) of briquetted mixtures of coal and charcoal. Two types of briquettes were produced, one in a cylindrical die and another in a laboratory briquetting machine. The briquettes were heat treated in a vertical electrical furnace under nitrogen atmosphere. The compressive strength of the briquettes was analyzed as a function of the following variables: coal and charcoal ratio, heating rate and particle size. The CO2 reactivity of the heat treated briquettes was analyzed as a function of the following variables: temperature and CO2 flow. For the cylindrical briquettes, the increase of charcoal (5, 10, 15 wt%) in the coal-charcoal mixtures caused an increase on the bulk density and on the compressive strength of the heat treated briquettes. Above 15 wt% of charcoal in the mixtures, the bulk density and the compressive strength decreased. It was found out that both green and heat treated briquettes had a decrease in compressive strength with the increase of the coal particle size. Optimum results of compressive strength were obtained in the briquettes with 15 wt% of charcoal, particle size <0.044 mm, heat treatment temperature of 1100°C for 8 hours. The increase in charcoal proportion caused an increase in the CO2 reactivity of the briquettes. The SEM micrographs of the heat treated briquettes showed that the texture of the briquettes tend to be more homogeneous with the increase of charcoal in the mixture. The properties of the briquettes produced in the laboratorial briquetting machine showed that a large scale production could be viable. Also, it was found out that the addition of wood charcoal in the mixture directly affects the compressive strength and the CO2 reactivity of the briquettes due to factors such as: the ashes composition, the decrease in fluidity because of the inert material in the mixture, the formation of a porous structure inside the carbon matrix. It was not found a relation between the alkalinity index and the CO2 reactivity in the briquettes.