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Thermodynamic and Economic Comparison of Low Grade Heat Recovery Systems

Rémy H. Poirier1, Mikhail Sorin1 and Nicolas Galanis1 and Simon Gaboury2

1. Département de Génie Mécanique, Université de Sherbrooke, Sherbrooke J1K 2R1, Canada

2. Rio Tinto Alcan, Alma G8B 5W2, Canada


Abstract: This paper compares two waste heat recovery systems (WHRS), finding their own advantages and disadvantages. The first system consists of two heat exchangers, one being at the heat source site, and the other being at the heat load site, and of an intermediate underground closed loop in which circulates a heat transport fluid. The second system is composed of an organic Rankine cycle (ORC), which produces electricity, and of a heat pump (HP), which consumes electricity and generates heat. The heat source corresponds to a typical large aluminum plant gas treatment center. Both systems are designed to supply the same heat power to the load. The two systems are evaluated in terms of three indicators: energy efficiency, exergy efficiency and economic desirability. Results indicate that the system composed of two heat exchangers and an intermediate loop offers the best energetic and exergetic efficiencies. The economic desirability of the systems is sensible to various assumptions related to environmental and societal factors, such as the topography of the surrounding land or the costs for rights-of-way across privately owned properties. The conditions for which the two systems are equivalent from the economic perspective are analysed.

Key words: Waste heat recovery, ORC, HP, economic analysis.
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