Performance optimization of thermal integrated-Carnot battery for waste heat utilization in industrial integrated energy systems

Abstract

Thermally integrated Carnot battery (TI-CB) systems offer unique advantages for industrial waste heat recovery, but their performance under fluctuating, off-design conditions remains poorly understood. To address this gap, this study proposes a quasi-dynamic mathematical model with solution methodologies applicable to both design and off-design operating conditions. A dynamic evaluation framework is also developed to account for the temporal mismatch between energy storage and release processes. A multi-operating-condition set constructed via multivariable sampling is used to enable systematic analysis of key design parameters under both design and off-design conditions. The results reveal that heat source utilization parameters and heat pump temperature rise are dominant factors affecting TI-CB performance, while off-design analysis shows that ORC mass flow rate variations have a more significant impact on system performance than heat pump fluctuations. Due to irreversible heat losses, an increase in the heat source temperature difference leads to a decrease in round-trip efficiency (η_rt) from 62.6% to 45.8%, while η_orc and η_ex also exhibit downward trends. A higher temperature lift in the heat pump results a decrease in the mean COP from 7.6 to 4.8, whereas η_orc increases from 7.0% to 10.2%. Among working fluids evaluated, R1336mzz(Z) demonstrates superior performance but exhibits nonlinear behavior, while R1233zd(E) provides optimal stability across operating ranges, making it suitable for practical engineering applications.

Graphical abstract

Keywords

Carnot battery / thermodynamic performance / integrated energy systems / modeling / waste heat recovery

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