The Techno-Economics of Electrification of Heat and Power Plants with Thermochemical Energy Storage - a Swedish Case Study

Achieving high penetration levels of renewable electricity is crucial in order to decarbonize the energy system. However, a large share of renewable electricity will be in the form of variable renewable electricity (VRE) technologies, i.e., foremost wind and solar power, which rely on efficient strategies to include flexibility in the energy system, such as the introduction of energy storage in order to maintain the value of VRE. Thermochemical energy storage (TCES) systems offer a possibility for long-term storage at ambient conditions and with energy densities of the same order of magnitude as currently used carbon-based-fuels.

This work proposes and assesses the use of heat and electricity generation with incorporation of a TCES using high temperature redox reactions in large-scale fluidized bed reactors. Sweden is used as a case study and therefore- considering the presence of iron-ore mining industry and the development of hydrogen-based steel production - iron oxide is chosen as the investigated system. The possibility for retrofitting existing biomass-fueled fluidized bed combustion (FBC) plants is assumed, since Sweden has a relatively large fleet of FBC plants in operation that will need to provide more flexibility due to increased share of VRE and surge in biomass prices. The reduction step utilizes hydrogen produced via electrolysis during periods of competitive electricity prices and the oxidation reactor (retrofitted boiler) dispatches heat and electricity to meet the demand. The work includes i) the computation of energy and mass balances of the process, ii) the construction of a plant investment cost function and iii) a cost-optimal sizing of the process for three different scenarios of the development of the Swedish electricity system. The results of the work indicate the ability of the proposed scheme to generate heat and electricity at a preliminary cost (including CAPEX and OPEX) of 20-70 eur/MWh_heat after the retrofit.