Entropy 2015, 17(11), 7530-7566; https://doi.org/10.3390/e17117530
Entropy Generation of Desalination Powered by Variable Temperature Waste Heat
Rohsenow Kendall Heat Transfer Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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Academic Editor: Kevin H. Knuth
Received: 26 June 2015 / Revised: 22 October 2015 / Accepted: 22 October 2015 / Published: 30 October 2015
(This article belongs to the Section Thermodynamics)
Abstract
Powering desalination by waste heat is often proposed to mitigate energy consumption and environmental impact; however, thorough technology comparisons are lacking in the literature. This work numerically models the efficiency of six representative desalination technologies powered by waste heat at 50, 70, 90, and 120 °C, where applicable. Entropy generation and Second Law efficiency analysis are applied for the systems and their components. The technologies considered are thermal desalination by multistage flash (MSF), multiple effect distillation (MED), multistage vacuum membrane distillation (MSVMD), humidification-dehumidification (HDH), and organic Rankine cycles (ORCs) paired with mechanical technologies of reverse osmosis (RO) and mechanical vapor compression (MVC). The most efficient technology was RO, followed by MED. Performances among MSF, MSVMD, and MVC were similar but the relative performance varied with waste heat temperature or system size. Entropy generation in thermal technologies increases at lower waste heat temperatures largely in the feed or brine portions of the various heat exchangers used. This occurs largely because lower temperatures reduce recovery, increasing the relative flow rates of feed and brine. However, HDH (without extractions) had the reverse trend, only being competitive at lower temperatures. For the mechanical technologies, the energy efficiency only varies with temperature because of the significant losses from the ORC. View Full-Text
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Warsinger, D.M.; Mistry, K.H.; Nayar, K.G.; Chung, H.W.; Lienhard V, J.H. Entropy Generation of Desalination Powered by Variable Temperature Waste Heat. Entropy 2015, 17, 7530-7566.