Impact of Hydrogen in a Reheat Furnace in the Steel Industry: a Computational Fluid Dynamics Study

Abstract

The steel industry accounts for around 2.8 gigatonnes of CO2 emissions per year. Reheat Furnaces are used in integrated steel mills prior to hot rolling and are a significant source of emissions. The focus of this thesis is on the decarbonization of reheat furnaces in the medium term and has an objective of evaluating the use of hydrogen-methane mixtures as fuel in reheat furnaces using computational fluid dynamics simulations. To do this, first, the numerical models and other settings used are tested on simple single burner cases, and a NOx post-processor was developed. Then, due to the periodically transient nature of the furnace, an iterative procedure was implemented to solve for the furnace load. A Test Furnace was used to validate this methodology by comparison to published simulation results obtained using an alternate methodology. Finally, a reheat furnace based on information provided by Stelco is modeled as a baseline and the use of various fuel mixtures is evaluated. The baseline case yielded an exiting slab average temperature of 1520K, compared to the 1530-1540K expected based on the validation data. A basis of constant heat input to the furnace was used to calculate fuel inputs for a range of cases using hydrogen-methane fuel mixtures. Hydrogen addition was found to lead to an increase in the average slab temperature by up to 55 K and in NOx emissions. It was also found to cause a decrease in the temperature difference across the slab and in CO2 emissions. The change in fuel did not heavily impact the temperature profile of the slab. The impact of hydrogen on the slabs is expected to be easily mitigated by slightly reducing slab residence time or reducing fuel input Further analysis and research on the practical considerations of hydrogen substitution, such as the impact of increased volumetric flow rates and burner material requirements would be essential to determine the extent of work required to retrofit existing furnaces to be able to use hydrogen as a fuel. Additional NOx reduction may be desired as well, with several methods available for consideration. As hydrogen pricing is a major obstacle in the implementation of the fuel substitution considered, a cost analysis is recommended for future work. In the present study, scale formation was neglected, but further modeling of this phenomenon may also be beneficial.