Advanced exergy and exergoeconomic analyses of a novel low-temperature industrial waste driven combined power and hydrogen system

Efficient and low-cost waste heat recovery is critical for alleviating energy crisis and environmental challenges. This study proposes a combined power and hydrogen system comprising a reversed Brayton cycle, methanol decomposition-based thermochemical recuperation reaction unit, reheating SCO₂ cycle and two organic Rankine cycles. By coupling reversed Brayton cycle and thermochemical recuperation unit to upgrade the low-grade waste heat to high-grade chemical energy via methanol decomposition: the separated hydrogen is delivered for multiple end uses, and the upgraded high-temperature flue gas generated by CO combustion is subsequently supplied to drive the downstream power cycles. To overcome the lack of in-depth analysis of avoidable exergy destruction and exergy-based avoidable costs in energy systems, both conventional and advanced exergetic techniques are used to reveal the potential for techno-economic performance improvement. The results indicate that the exergy efficiency is 60.26 % under real condition and could be increased to 62.19 % under unavoidable condition. Conventional analysis results the combustion chamber yields the highest exergy destruction rate of 313.51 kW and total cost rate of 42.33 $/h. While the advanced exergetic analysis indicates that the combustion chamber has the highest endogenous avoidable exergy destruction rate of 27.89 kW and the high-temperature ORC condenser has the highest endogenous avoidable total cost rate of 3.99 $/h. Furthermore, the endogenous part of both exergy destruction rate and exergy cost rate are higher than the exogenous part of them for all the components in the system, which indicates that the intrinsic exergy destruction rate of each component dominates the thermo-economic performance of the system. Overall, the avoidable exergy destruction/cost/investment cost of the system accounts for 5.62 %, 12.41 % and 15.02 % of the total, respectively, thereby indicating the substantial potential for system optimization.