Biomass power plant integrated with a thermochemical heat storage system using a fluidized bed reactor worked by variable renewable energy: Dynamic simulation, energetic and economic analyses

This study focused on a biomass power plant (Organic Rankine Cycle: ORC, 1 MWe) integrated with a ther-mochemical heat storage (TCS) system as a Carnot battery. In the TCS, a fluidized bed reactor using CaO/Ca (OH)2/alumina particles was used, and steam was used as a fluidizing and reacting gas. The surplus electricity from variable renewable energy (VRE) is converted to heat and stored during daytime, and the stored energy is utilized to generate power in the evening. In this study, there were three objectives. First, process performances were compared when R245fa or R1233zd was used as a working fluid of ORC, and influences of ORC parameters such as the turbine inlet temperature, superheat temperature, and the scale of the power generation, were evaluated. In addition, effects of the fluidized bed volume and the reduction of biomass fuel combustion were also investigated. Second, a potential of the proposed process that can absorb the VRE fluctuation was evaluated by the dynamic calculation. Third, the economics of the TCS system was evaluated. Results show that the round-trip efficiency of the process using R1233zd was 8.77 %, which was slightly lower than that of the process using R245fa (8.84 %). The increases of a turbine inlet temperature led to the increase of heat recovery from the outlet steam of the TCS reactor, meanwhile, the round-trip efficiency decreased. The efficiencies of the cases changing the superheat temperature (5 -> 15 degrees C) were slightly changed (<0.5 %). To achieve high energy efficiencies, a large-scale biomass power plant and a small-fluidized bed volume was effective. It was found that the VRE fluctuation was mostly absorbed by the TCS with a fluidized bed and ORC process. In the economic evaluations, the levelized cost of storage regarding only the TCS system was 0.92-2.37 USD/kWhe when the charging elec-tricity cost is 0.05 USD/kWhe. LCOS also decreases to 0.50-1.14 USD/kWhe if the electricity cost is free during daytime in the future and power output is two times in a day.

Automated summary

This study investigated a biomass power plant integrated with a thermochemical heat storage system. The performance of the system was evaluated by comparing different working fluids, ORC parameters, and biomass fuel combustion. The results showed that the proposed process can effectively absorb the fluctuation of variable renewable energy and has economic potential.