Frontiers in Energy Research (Apr 2021)
Process Systems Engineering Evaluation of Prospective Working Fluids for Organic Rankine Cycles Facilitated by Biogas Combustion Flue Gases
Abstract
The organic Rankine cycle (ORC) has recently emerged as a practical approach for generating electricity from low-to-high-temperature waste industrial streams. Several ORC-based waste heat utilization plants are already operational; however, improving plant cost-effectiveness and competitiveness is challenging. The use of thermally efficient and cost-competitive working fluids (WFs) improves the overall efficiency and economics of ORC systems. This study evaluates ORC systems, facilitated by biogas combustion flue gases, using n-butanol, i-butanol, and methylcyclohexane, as WFs technically and economically, from a process system engineering perspective. Furthermore, the performance of the aforementioned WFs is compared with that of toluene, a well-known WF, and it is concluded that i-butanol and n-butanol are the most competitive alternatives in terms of work output, exergy efficiency, thermal efficiency, total annual cost, and annual profit. Moreover, the i-butanol and n-butanol-based ORC systems yielded 24.4 and 23.4% more power, respectively, than the toluene-based ORC system; in addition, they exhibited competitive thermal (18.4 and 18.3%, respectively) and exergy efficiencies (38 and 37.7%, respectively). Moreover, economically, i-butanol and n-butanol showed the potential of generating 48.7 and 46% more profit than that of toluene. Therefore, this study concludes that i-butanol and n-butanol are promising WFs for high-temperature ORC systems, and their technical and economic performance compares with that of toluene. The findings of this study will lead to energy efficient ORC systems for generating power.
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