Application of Wastes from Pulp and Paper Industries for Steelmaking Processes
Time: Fri 2021-10-01 09.00
Subject area: Materials Science and Engineering
Doctoral student: Tova Jarnerud , Materialvetenskap
Opponent: Prof. Em. Carl-Erik Grip,
Supervisor: Docent Andrey Karasev, ; Professor Pär Jönsson, Processer
Over the past several years, considerable efforts have been made to develop a more circular economy. The ambition to reuse, remanufacture and recycle materials is of great significance for the establishment of a sustainable society. An extended longevity of materials helps to decrease the amount of wastes in landfills, as well as to reduce the mining of natural assets. Pulp and paper industries and steel industries are two of the largest basic industries and export industrial sectors in Sweden. The pulp and paper industries generate large amounts of organic and inorganic wastes. A significant part of these wastes ends up in landfills. The deposit of wastes in landfills is becoming more costly and more challenging to employ, due to stronger regulations and demands with respect to the environment. During Electric Arc Furnace (EAF) and Argon Oxygen Decarburization (AOD) stainless steelmaking operations, burnt lime (primary lime) is charged together with other slag forming components in the furnace or converter to obtain a specific basicity of the slag and to attain purification from undesired elements by chemical reactions between the steel and slag. In blast furnace (BF) operations, fossil carbon is charged in the form of coke and injected as powder to provide heat to melt the iron ore and to reduce the iron oxides by separating iron from oxygen. The use of this primary lime and fossil carbon does not comply with the closing the loop idea that is being prioritized in modern society. This thesis presents results from preliminary experiments for examining the replacement of primary lime with recovered lime from pulp and paper production waste as slag formers in EAF and AOD converters and as neutralizing agents for acidic wastewaters, as well as hydrochar from organic sludges as a carbon source in BF. The gained results showed a possibility of partly replacing primary lime with recovered lime in the EAF without negative effects on the process. In the AOD process, the use of recovered lime didn´t show any negative effects on the decarburization process nor on the reduction process. Moreover, the desulphurization function was similar when using recovered lime compared to when using the primary lime. However, the P content in the metal increased slightly. Thus, the replacement ratio of the recovered lime will be limited by the acceptable P level in the final steel due to higher P content in the recovered lime materials from pulp and paper mills compared to that in primary lime. Furthermore, the obtained results of laboratory-scale trials using recovered lime materials as neutralizers showed that they can be successfully used instead of primary lime to significantly raise the pH level of the wastewaters as well as to decrease the concentrations of Cr, Fe, Ni, Mo and Zn. Also, the results from the industrial-scale experimental trials using hydrochar derived from mixed organic biosludge and from green waste showed that the production rate of hot metal, amount of dust, fuel rate and amount of injected coal, amount of slag, contents of FeO in slag and %C and %P in the hot metal of the BF process were very similar compared to the reference periods. Thus, it was proven that hydrochar derived from various types of organic residues could be used for metallurgical applications. However, the replacement ratio was very low and longer trial campaigns are needed to obtain more certain results. Moreover, it was revealed during this study that slags from AOD converters can be used as binding agents for briquetting of these recovered lime materials. In summary, these results show that waste materials/by-products from two of the most important Swedish base industries can unite two major industrial sectors in a circular symbiosis towards obtaining a more sustainable future.