Electrified District Heating Plants using Thermochemical Energy Storage
Examensarbete för masterexamen
Cortés Romea, Javier
Carbon emissions, particularly from electricity and heat generation, remain a major cause of global warming, accounting for 40 % of global CO2 emissions in 2021. To decarbonize the electricity sector, the use of variable renewable energy (VRE) sources is being encouraged. At the same time, variation management strategies are required to maximize the value of VRE as its share increases and to reduce curtailing. Meanwhile, the heating sector is called to transit into an electrified scheme, which should also reduce the use of biomass, as it is becoming a limited resource. Thermochemical energy storage (TCES) systems, particularly high-temperature solid cycles, such as metal redox-looping, provide a solution for both the electricity and heating sectors. TCES systems have the potential to use non-dispatchable renewable electricity to reduce a metal oxide, which can be stored for long periods of time at ambient conditions and subsequently oxidized to release the stored energy in the form of high-temperature heat (700-1100 °C). This thesis presents an economic assessment of the retrofitting of biomass-firing DH plants by incorporating a TCES scheme based on metal-oxide redox cycles. The viability of the proposed system is analyzed through a case study. Sweden was selected for the study case owing to the existence of a metal extraction and processing infrastructure and the availability of DH plants based on fluidized bed (FB) boilers. The cost of the retrofit was estimated and used as an input in a linear cost optimization model to investigate the impact of the electricity price variability on the cost-optimal size and operation of an electrified DH plant. Today’s typical capacity of biomass-firing DH plants was selected as a reference. The results of the study indicate that as a consequence of including storage the operation of the plant can be adapted to respond to electricity price variations. The proposed process can cover the heat demand at a cost of 55-70 €/MWh. The proposed main scheme proved profitable for the investigated scenarios of electricity price variation, while the economic viability of using solid oxide electrolyzer cells (SOEC) instead of alkaline ones or adding hydrogen storage depends on the potential cost reductions in these technologies in the future.
variable renewable energy (VRE) , thermochemical energy storage (TCES) , iron looping , district heating (DH) , electricity system , Sweden , decarbonization , electrification