Optimised Integrated Steel Plant Operation Dependent on Seasonal Combined Heat and Power Plant Energy Demand

Abstract

The steel industry is energy intensive with large corresponding contributions of fossil CO2 emissions, which accounts to around 7 % of the global emissions. This presents great challenges, and continuous work is therefore done to reduce energy consumption and CO2 emissions. This work evaluates ways of decreasing the total energy demand and CO2 emissions in a system containing integrated steel plant connected to a combined heat and power plant (CHP), through optimised production operation with respect to seasonal-dependent energy demands.The studied system, which includes SSAB EMEA Lulea (integrated steel plant) and LuleKraft (CHP), is located in the municipality of Lulea in northern Sweden. The CHP produces the base demand of district heat (DH) for the community, with process gases from the integrated steel plant as its main fuel. Oil is used as an extra energy source when the amounts of process gases are insufficient to meet the DH demand, which happens mainly in the cold winter periods. Therefore, this study aims to find production guidelines to minimise the additional energy consumption of oil through matching cold winter periods with high production of process gases. Optimisation of the system is performed with a mixed integer linear programming (MILP) model based on process data for a normal year. The year is divided into periods based on varying DH demand, to give the model possibility to choose how the integrated steel plant is best operated in each period. The main variables in the integrated steel plant for the study are coke production and usage of recirculated materials, which are bound by yearly demand and availability. Optimisation of this setting is then evaluated in comparison to an optimisation where the integrated steel plant is operated in a constant manner the whole year. Results show that an optimised use of recirculated materials and coke production decreases yearly oil consumption with up to 8 GWh and increases yearly electricity production with up to 8 GWh.