Comparative Thermo‐Economic Evaluation of Basic Versus Regenerative ORC Configurations for Gas Turbine Waste Heat Recovery With Next‐Generation Working Fluids

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ABSTRACT Waste heat rejected from gas turbine exhaust represents a substantial and largely unexploited energy resource, and the organic Rankine cycle (ORC) is the established means of recovering it. The selection of a working fluid for this duty is, however, increasingly constrained by environmental regulations, and the introduction of an internal heat exchanger (IHX) alters the thermodynamic and economic balance of the cycle in ways that have not been assessed consistently for conventional and next‐generation fluids under a common set of conditions. The present study addresses this gap. Its objectives are threefold: to quantify the thermodynamic and thermo‐economic penalty associated with substituting low global warming potential (GWP) fluids for conventional hydrocarbons; to determine the extent to which internal recuperation offsets that penalty; and to establish whether the resulting fluid ranking is governed by thermodynamic or by economic criteria. Eight working fluids—toluene, cyclohexane, cyclopentane, isopentane, n‐pentane, R1233zd(E), R245fa, and Novec 649—are compared in basic and regenerative configurations using a model implemented in Python with CoolProp, validated against published gas turbine and ORC data to within 1.5% and 2.1%, respectively. The analysis combines first‐ and second‐law performance, component‐level exergy destruction, capital cost estimation, and uncertainty propagation, with the ORC evaporation temperature coupled to the exhaust‐gas exit temperature through the pinch‐point constraint. Regeneration raises the thermal efficiency by 41.7%–53.2%, with the largest relative gains accruing to the low‐GWP fluids, which narrows the performance spread between fluid families from a factor of 2.01 to 1.86; total exergy destruction falls by 44.5% for toluene at unchanged net work output. Toluene attains the highest thermal efficiency (26.44% basic, 37.46% regenerative) and the lowest specific investment cost ($374/kW), while Novec 649 is the least favorable on both counts ($1471/kW). The economic ranking is shown to follow specific work rather than thermal efficiency, and the heat exchangers are found to dominate both the irreversibility and the capital cost. All configurations remain economically viable, with levelized costs of ¢0.59–2.31/kWh against an assumed selling price of ¢8/kWh.

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