Investigating Sustainable Steel Manufacturing Processes

Abstract

A considerable portion of the energy consumed in the steel industry is rejected as waste heat from the electric arc furnace (EAF). In contrast, most of the CO2 emissions are produced from the direct reduction (DR) process. Capturing this energy impacts the efficiency of production significantly by reducing operating costs and increasing the plant's productivity. Alternative fuel such as hydrogen also presents excellent opportunities to improve the industry's competitiveness and sustainable operation through a significant reduction in emissions. This work presents an assessment of steel manufacturing in the United Arab Emirates (UAE). It demonstrates the potentials of thermal energy storage systems (TES) in recovering heat from the high-temperature exhaust fumes of the electric arc furnace and integrating renewable energy into an introduced hydrogen direct reduction (HDR) process configuration. The investigation entails mapping the material and energy requirements of the current steel production method, i.e. natural gas reforming for syngas production, direct reduction of the iron ore, and secondary refining to obtain the steel in the EAF. Analysis of an obtained EAF off-gas temperature and flow rate profiles are then used as a basis in the development of a waste heat recovery (WHR) model. Simulation results from the model reveal that in a period of 4 days, an output power of 2108 kW per tap-to-tap (TTT) cycle can be achieved from a continuous charge EAF. This can be harnessed and used either internally or externally in the steel manufacturing process. On the other hand, an optimization model is developed based on the energy requirements of the direct reduction process in order to switch to HDR and realize the optimal configuration for integrating renewable energy into it. Hence, a water electrolyser is used as means of hydrogen production, and Solar PV is modelled to power this electrolyser. Optimization results disclose that installed PV, and electrolyser capacities of 11.75 GW and 1.06 GW respectively would achieve cost competitiveness with the current process while emitting 98.6% less CO2.

Date of Award	Nov 2021
Original language	American English