Emergy-based exergoeconomic and exergoenvironmental evaluation of a combined power and cooling system based on ORC-VCR

Abstract

Ensuring efficient operation of energy conversion systems in terms of economics and ecology is a prime objective that should be addressed within the design, optimization, and development stages of such systems. Adopting appropriate measures for accurate assessment and comprehensive evaluation of thermodynamic systems is a sheer necessity for accomplishing this purpose. In this study, the newly developed emergy-based exergoeconomic (i.e., emergoeconomic) and emergy-based exergoenvironmental (i.e., emergoenvironmental) analyses have been employed to assess a combined power and cooling system, including a gas turbine cycle, a steam Rankine cycle, and an integrated organic Rankine cycle-vapor compression refrigeration (ORC-VCR) subsystem serving as a waste heat recovery unit. The merit of emergy-based methods is that they can evaluate and express results by an identical unit of measurement (i.e., sej) which enables us to undertake a fair and accurate comparison between the methods in question. The results showed that the combustion chamber, with the total economic emergy rate of 6.83E13 (sej h−1) and the total ecological emergy rate of 6.05E14 (sej h−1), was the most critical component in the entire system from both the economic and ecological viewpoints. Moreover, a parametric study was carried out on the entire system, as well as the ORC-VCR unit, to examine the effect of design parameters on the emergy-based monetary and ecological performances. Increasing the air compressor pressure ratio from 6 to 11 enhanced the entire system’s both emergy-based performances by almost 8%, followed by improvements made by the gas turbine isentropic efficiency and combustor inlet temperature, with 6.5% and 5.5%, respectively. However, other design parameters exerted limited impact. Regarding the ORC-VCR, raising the ORC turbine inlet temperature and the isentropic efficiencies associated with the ORC turbine and VCR compressor improved the emergy-based performances, while the reverse was observed for the ORC condenser and evaporator temperature rise.