Colloquia

Summary

Thermochemical heat storage stores surplus electricity as a combination of thermochemical and sensible heat in a porous redox-active oxide structure. During discharge, airflow through the material triggers an exothermic oxidation reaction, releasing high-temperature air suitable for industrial processes. This compact storage system offers high energy density, the ability to accommodate fluctuating renewable energy sources, and reduces reliance on fossil fuels. The integration of high-temperature thermochemical heat storage, referred to as HERCULES, with a renewable electricity generator and a steel manufacturing plant was comprehensively investigated in this study. The reactive core material of HERCULES module used is a composite of Cobalt oxide/cordierite, while the hot blast stoves, as operated in Tata Steel IJmuiden's plant, were employed as the case study. Two integration concepts were assessed: concept one with HERCULES functions as an active air preheater, and concept two with HERCULES as a passive preheater. The dynamic models were developed in MATLAB Simulink, incorporating detailed physical behaviour as well as economic parameters to capture realistic system responses. Validation against published experimental data of similar material has confirmed the model's accuracy, and extensive sensitivity analyses were performed by varying wind turbine capacity and HERCULES module mass to evaluate their impact on the system’s dynamics, gas savings, and economic performance.

Both HERCULES integration concepts are technically feasible and capable of reducing gas consumption. In both cases, increasing the number of wind turbines consistently results in greater gas savings, while increasing the HERCULES module mass has a negligible impact on gas reduction. However, financial analysis shows that higher gas reduction does not always translate into improved economic performance. For both concepts, increasing the turbine count raises both capital expenditure (CAPEX) and operating expenditure (OPEX). Increasing module mass also raises CAPEX but reduces the frequency of operation cycles, thereby lowering material replacement cost, a component of OPEX. This indicates that the economic impact of these parameters is non-linear.

Concept 2 with 14 wind turbines and a HERCULES module mass of 100 tons is identified as the most optimal configuration, which could reduce 16,815 tons of gas annually or 24% of total usage.