Energy and exergy assessment of a combined supercritical Brayton cycle-orc hybrid system using solar radiation and coconut shell biomass as energy source

Abstract

The present investigation presents a novel hybrid solar-biomass system for electric power generation in remote areas. The proposed system integrates a Supercritical Brayton Cycle (SBC) to an Organic Rankine Cycle (ORC) as a bottoming cycle, driven by a Concentrated Solar Tower (CST) system and biomass furnace (coconut shell). The thermal energy generation potential of the biomass was determined from the fiber content, lignin, density, calorific value, and ash content, and the level of pollutant emissions at different combustion rates. Energy and exergy analyses were carried out considering three scenarios: hybrid solar-biomass SBC-ORC, SBC-ORC/solar, and SBC-ORC/biomass. The results revealed that coconut shells feature a low content of inorganic matter with a calorific value of 25.29 MJ/kg, and the best combustion efficiency (CO2/CO) was given at a speed of 0.0895 °C·min−1 (43.16%). The hybrid solar-biomass SBC-ORC system showed an exergetic efficiency of 26.60%, an increase of 17.28% with respect to the SBC-ORC/solar system in its base condition. The turbine inlet temperature was the variable with the greatest influence on the exergetic efficiency of the SBC-ORC/solar system, which reached a maximum of 23.8% at 700 °C. In conclusion, the integration of coconut shell biomass as an alternative and supplementary thermal source is a promising solution for the intermittence of solar-driven systems. This study demonstrated that the novel hybrid system ensures stability, good combustion efficiency, and enhanced performance compare to the standalone solar operation.