TY - BOOK

T1 - Recycling of electric arc furnace dust with hydrogen

AU - Brandner, Ulrich

N1 - embargoed until 16-09-2027

PY - 2022

Y1 - 2022

N2 - Greenhouse gas emission reduction targets force the industry to transform its processes under the consideration of sustainability and recycling processes operating with the lowest possible emissions of greenhouse gases are necessary. The present thesis focuses on the recycling of electric arc furnace dust (EAFD). The state-of-the-art technology for the processing of EAFD is based on the carbothermal reduction of metal oxides causing direct carbon dioxide emissions. Steel production via the electric arc furnace route is predicted to rise, resulting in an increase in the amount of EAFD generated and additional carbon dioxide emissions. The substitution of carbon as a reducing agent by hydrogen allows for the avoidance of direct carbon dioxide emission during the processing of EAFD. In the present thesis, the reduction behavior of EAFD with hydrogen is explored. A comprehensive literature and patent survey gained the already available efforts to develop hydrogen-based reduction technologies for the processing of EAFD. Thermodynamic calculations allowed for the fundamental classification of the already available recycling concepts and the deduction of a novel recycling conceptualization implementing the recovery of hydrogen. After the simultaneous reduction of iron and zinc oxide and the subsequent separation, the process presented theoretically allows for the lowest consumption of hydrogen via the oxidation of reduced iron and zinc with water vapor. The basic conceptualization of the recycling of EAFD with hydrogen raises questions concerning the fundamental feasibility of the described reactions and the reduction and behavior of the oxides present in EAFD with hydrogen. The fulfillment of this task is ideally conducted via thermogravimetric analysis (TGA) as it is predestined for the investigation of the kinetics of solid-gas reactions. In the present thesis, an adapted lab-scale TGA setup was developed to investigate the reduction of oxides present in EAFD and the oxidation of prereduced iron. The comparison of the reduction kinetics of pure iron oxide, zinc ferrite and zinc oxide with hydrogen and carbon monoxide confirmed and quantified the kinetic advantage of hydrogen against carbon monoxide. The kinetic advantage decreases from factor 2 for iron oxide and zinc ferrite to the factor of 1.5 for zinc oxide at 800 °C. TGA trials with EAFD resulted in a kinetic advantage of a factor of 2.5 at 900 °C and additionally allowed for the determination of the rate-limiting factors. Additionally to the temperature and reduction degree dependency, the influence of the gas flow rate and composition, the specimen size and the specific surface area were found to be significantly rate-limiting. The oxidation of prereduced iron oxide and EAFD proved the thermodynamically suggested capability to oxidize iron to Fe3O4. The oxidation rate gets increased by a higher temperature and maximum oxidation capacity is limited by the enrichment of hydrogen of more than 30 %. In addition to the investigation of the reduction and oxidation behavior in lab scale, the present thesis covers the upscaling of the reduction behavior into extended lab scale. A self-developed hydrogen retort was applied to compare the reduction behavior of pelletized EAFD with hydrogen when upscaled by a factor of 100. The upscaling to the extended lab scale reduces the rate to 60 % of the reduction rate in the TGA, despite the same specific gas flow rate and temperature being applied. Thus, the necessity to further focus on upscaling effects is postulated.

AB - Greenhouse gas emission reduction targets force the industry to transform its processes under the consideration of sustainability and recycling processes operating with the lowest possible emissions of greenhouse gases are necessary. The present thesis focuses on the recycling of electric arc furnace dust (EAFD). The state-of-the-art technology for the processing of EAFD is based on the carbothermal reduction of metal oxides causing direct carbon dioxide emissions. Steel production via the electric arc furnace route is predicted to rise, resulting in an increase in the amount of EAFD generated and additional carbon dioxide emissions. The substitution of carbon as a reducing agent by hydrogen allows for the avoidance of direct carbon dioxide emission during the processing of EAFD. In the present thesis, the reduction behavior of EAFD with hydrogen is explored. A comprehensive literature and patent survey gained the already available efforts to develop hydrogen-based reduction technologies for the processing of EAFD. Thermodynamic calculations allowed for the fundamental classification of the already available recycling concepts and the deduction of a novel recycling conceptualization implementing the recovery of hydrogen. After the simultaneous reduction of iron and zinc oxide and the subsequent separation, the process presented theoretically allows for the lowest consumption of hydrogen via the oxidation of reduced iron and zinc with water vapor. The basic conceptualization of the recycling of EAFD with hydrogen raises questions concerning the fundamental feasibility of the described reactions and the reduction and behavior of the oxides present in EAFD with hydrogen. The fulfillment of this task is ideally conducted via thermogravimetric analysis (TGA) as it is predestined for the investigation of the kinetics of solid-gas reactions. In the present thesis, an adapted lab-scale TGA setup was developed to investigate the reduction of oxides present in EAFD and the oxidation of prereduced iron. The comparison of the reduction kinetics of pure iron oxide, zinc ferrite and zinc oxide with hydrogen and carbon monoxide confirmed and quantified the kinetic advantage of hydrogen against carbon monoxide. The kinetic advantage decreases from factor 2 for iron oxide and zinc ferrite to the factor of 1.5 for zinc oxide at 800 °C. TGA trials with EAFD resulted in a kinetic advantage of a factor of 2.5 at 900 °C and additionally allowed for the determination of the rate-limiting factors. Additionally to the temperature and reduction degree dependency, the influence of the gas flow rate and composition, the specimen size and the specific surface area were found to be significantly rate-limiting. The oxidation of prereduced iron oxide and EAFD proved the thermodynamically suggested capability to oxidize iron to Fe3O4. The oxidation rate gets increased by a higher temperature and maximum oxidation capacity is limited by the enrichment of hydrogen of more than 30 %. In addition to the investigation of the reduction and oxidation behavior in lab scale, the present thesis covers the upscaling of the reduction behavior into extended lab scale. A self-developed hydrogen retort was applied to compare the reduction behavior of pelletized EAFD with hydrogen when upscaled by a factor of 100. The upscaling to the extended lab scale reduces the rate to 60 % of the reduction rate in the TGA, despite the same specific gas flow rate and temperature being applied. Thus, the necessity to further focus on upscaling effects is postulated.

KW - Recycling

KW - CO2 Reduction

KW - Kinetics

KW - Electric Arc Furnace Dust

KW - Thermogravimetric Analysis

KW - Hydrogen

KW - Reduction

KW - Oxidation

KW - Recycling

KW - CO2 Reduktion

KW - Kinetik

KW - Elektrolichtbogenofenstaub

KW - Thermogravimetrische Untersuchungen

KW - Wasserstoff

KW - Reduktion

KW - Oxidation

M3 - Doctoral Thesis

ER -