Extensive techno-economic assessment of combined inverted Brayton – Organic Rankine cycle for high-temperature waste heat recovery

This work is a techno-economic study of the combination of inverted Brayton cycle, and organic Rankine cycle (combined IBC-ORC) applied for high-temperature waste heat recovery (WHR) of the engine exhaust energy. In IBC, exhaust gases expand to subatmospheric pressure in the turbine, transmit heat residuals to ORC, and restore pressure to 1 atm in the compressor. The system is analysed in the Aspen Hysys software in design conditions at the case study of 1.4 MW gas-fueled internal combustion engine as a high-temperature waste heat source (470–570 °C). Firstly, the paper shows the performance of the system optimised for different ambient temperatures. The role of water condensation contained in flue gas is emphasised for these bounds. Then, the paper presents a multi-objective optimisation illustrated by Pareto fronts for the objective functions of system electric efficiency and levelized cost of energy (LCOE) in the mentioned range of exhaust temperatures. TOPSIS-based Pareto-front analysis results in recommendations of the best sets of cycle parameters in this trade-off. For exhaust temperatures 470 °C, 520 °C, and 570 °C, optimal configurations identified via TOPSIS methodology demonstrate 10.8%, 12.1%, 13.3% efficiencies with LCOE equal to 185.5 $/MWh, 162.4 $/MWh and 146.1 $/MWh correspondingly.