Exergy analysis for alternative Orangic Rankine Cycle (ORC) based combined systems for recovering moderate-to-low temperature waste heat of flue gas

Articles in Press

Document Type : Research Article

Authors

1 1- Department of Mechanical Engineering, Islamic Azad University, Shahrood branch, Shahrood, Iran

2 Department of Mechanical Engineering, Islamic Azad University, Shahrood branch, Shahrood, Iran

Abstract

Utilization of waste heat in processes of coal-fired plant has been taken into account as the most promising technology to improve thermodynamic performance. This paper proposes and investigates alternative Orangic Rankine Cycle (ORC) based combined systems for recovering moderate-to-low temperature waste heat of flue gas based on energy and exergy analysis. Advanced exergy analysis, splitting the exergy destruction into endogenous/exogenous and avoidable/unadvoidable parts, is applied to reveal more detailed information about components inefficiency on each other and real potential of optimized system for improvement. The results show that the optimal compression ratio for Simple Supercritical Carbone Dioxide ORC (S-sCO2-ORC) and Regeneration Simple Supercritical Carbone Dioxide ORC (RS-sCO2-ORC) systems is respectively 1.8 and 2.2. Compared with ORC-based sCO2 systems, ORC-ORC system considering heptane/R601a as working fluids yields the highest thermal and exergy efficiencies of 16.37% and 45.54%, respectively. Based on the advanced exergy analysis, the endogenous exergy rate is higher than exogenous exergy in all the system components. The exogenous exergy rate of Condenser 1 pertains to the same magnitude order as that of high-temperature heat exchanger, far more than other components in the system. Due to the high value of endogenous-avoidable part in Turbine 1 and Condenser 1, technical modifications of these two components could improve efficiency of the ORC-ORC system. In this current work, 25.65% of the overall exergy destruction can be avoided.

Keywords

Iranian Journal of Chemistry and Chemical Engineering

Articles in Press, Accepted Manuscript
Available Online from 08 January 2024

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